key: cord-0005055-xsi3hbzs authors: Nikonov, O. S.; Chernykh, E. S.; Garber, M. B.; Nikonova, E. Yu. title: Enteroviruses: Classification, diseases they cause, and approaches to development of antiviral drugs date: 2018-01-03 journal: Biochemistry (Mosc) DOI: 10.1134/s0006297917130041 sha: 503f44cc78f151fae7c1914c912e21bb5b2bf12e doc_id: 5055 cord_uid: xsi3hbzs The genus Enterovirus combines a portion of small (+)ssRNA-containing viruses and is divided into 10 species of true enteroviruses and three species of rhinoviruses. These viruses are causative agents of the widest spectrum of severe and deadly epidemic diseases of higher vertebrates, including humans. Their ubiquitous distribution and high pathogenici- ty motivate active search to counteract enterovirus infections. There are no sufficiently effective drugs targeted against enteroviral diseases, thus treatment is reduced to supportive and symptomatic measures. This makes it extremely urgent to develop drugs that directly affect enteroviruses and hinder their development and spread in infected organisms. In this review, we cover the classification of enteroviruses, mention the most common enterovirus infections and their clinical man- ifestations, and consider the current state of development of anti-enteroviral drugs. One of the most promising targets for such antiviral drugs is the viral Internal Ribosome Entry Site (IRES). The classification of these elements of the viral mRNA translation system is also examined. After virus penetration into a cell, the RNA mole cule released from the capsid triggers a cascade of events that result in formation of mature viral progeny and even tually cell death. These events begin with synthesis of viral proteins, i.e. with the translation of viral RNA by the cellular translation system. Expression of viral genes is often regulated at the level of initiation of mRNA trans lation. At this step, the 40S ribosomal subunit binds to an mRNA and scans it in the 5′ 3′ direction until it reaches the start codon, where the 80S ribosome is to be assem bled. Various host proteins and cis acting RNA molecules participate in this process. A cap structure is present at the 5′ terminus of most eukaryotic mRNAs, which par ticipates in capturing 40S ribosomal subunits. The scan ning mechanism implies that the ribosome initiates translation at the first AUG codon. This is the case for most mRNAs. However, the first AUG codon may be ignored if it is in a non optimal sequence context. In this case, translation is initiated at the next AUG codon. This initiation mechanism is referred to as leaky scanning. It is BIOCHEMISTRY (Moscow) Vol. 82 No. 13 2017 realized in many viruses, which allows saving coding sequence length. Picornavirus mRNAs ((+)ssRNA viruses) lack the cap structure. In 1988, it was demonstrated that initiation of translation of such uncapped mRNAs is implemented via a structural feature in mRNA molecule, which allows assembly of the translation apparatus near a start codon. These stable secondary structure elements were called internal ribosomal entry sites (IRESs) [1, 2] . Since then, such cap independent translation initiation pathway has been extensively studied [3] . This discovery overturned a major dogma in translation initiation stating that the eukaryotic ribosome can bind mRNA exclusively at the 5′ terminus. IRESs are usually situated in the 5′ untrans lated region and frequently have a complex secondary and tertiary structure. Since these elements were discovered in picornaviruses, they have also been found in several other viral mRNAs. The mechanism of IRES dependent trans lation is presumably exploited by some cellular mRNAs. Translation of these mRNAs continues when cap dependent translation is repressed, which may happen during endoplasmic reticulum stress, hypoxia, starving for nutrients, mitosis, and cell differentiation [4, 5] . In addition to the above mentioned picornaviruses, initia tion of translation at internal sites is utilized in represen tatives of Flaviviridae [6] , Retroviridae, Dicistroviridae [7] , Herpesviridae [8] , some insect viruses [9] , and plants viruses [10] , and also retrotransposons in insects and rodents [11] . However, it appeared that, unlike cap dependent translation initiation (scanning), there is no common mechanism for functioning of all IRESs. Furthermore, the IRESs are very different: no structural element has been found that is shared by all IRESs. Their sequences also lack significant homology [3, 12] . However, it was shown that the majority of viral IRESs have stable sec ondary and tertiary structure that facilitates their efficient binding to the 40S subunit. Such binding can be either direct or require participation of additional canonical translation initiation factors along with some other host proteins referred to as ITAF (IRES trans acting factors). It is possible that some ITAF directly participate in spe cific interaction of mRNA with the 40S subunit, whereas others stabilize specific functionally active IRES confor mations [13 15] . Unlike viral mRNAs, existence of IRES dependent translation of cellular mRNAs is cur rently being vigorously discussed [4, 5, 16] . Since the discovery of viral IRESs, difficulties in their classification have arisen due to their dissimilarity. However, extensive studies on viruses, their mRNA, and mechanisms of its translation revealed several common features that may be used to clearly distinguish between the IRES types. The viral IRESs that are now classified according to their sequence and secondary structure are divided into separate families: 1 -intergenic IRESs of dicistroviruses of invertebrates (Dicistroviridae family; for instance, the cricket paralysis virus); 2 -IRES of hepati tis C (HCV) and related viruses of animals (Flaviviridae family), and 3 -IRESs of picornaviruses that are in turn divided into five classes (I V) . Besides, there are poly purine A rich IRESs (PARS) [17] . An IRES of this type was first discovered in tobamovirus СrTMV [18] . However, we return to reviewing picornavirus IRESs. Picornavirus type I IRESs include IRESs of all represen tatives of the genus Enterovirus and a single representative of the genus Harkavirus [19] . Length of such IRES is approximately 450 nucleotides (nt). It comprises domains two to six (Fig. 1) ; it contains Yn Xm AUG at the 3′ ter minus, where Yn -pyrimidine sequence (n = 8 10 nt), X -a linker between Yn and the AUG triplet (m = 18 20 nt) [20 22 ]. This motif is considered to be a region of ribosome binding at the 5′ UTR [23] . It is separated from the start codon with a non conserved region whose length ranges from <30 nt in rhinoviruses to >150 nt in poliovirus. Conserved functionally important nucleotides are situated at the base of the second domain, in the cru ciform fourth domain, and in the fifth domain [12, 19, 24] . Specific binding of the fifth domain to eIF4G and RNA helicase eIF4A promotes binding of the 43S com plex to the IRES [12] . Translation initiation on all the studied type I IRESs depends on the presence of ITAF, whose complete list is not yet determined (Fig. 2) [19] . Initiation of translation on type II IRES requires specific binding of factors eIF4G and eIF4A with domains J K [25, 26] . At the same time, such IRESs can function without eIF4E and factors par ticipating in ribosome scanning (eIF1 and eIF1A). Hence, type II IRES differs from type I IRES by the lack of ITAF requirement (with one exception: it has been demonstrat ed that in certain cases, cellular RNA binding protein PTB (pyrimidine binding protein) is required) [25, 26] (Fig. 2) . The type III IRES is only found in hepatitis A virus. It is around 410 nt long [27] . IRESs of this type signifi cantly differ from the first two types both by sequence and structural elements. Efficiency of the translation initia tion on this IRES is considerably lower compared to the first two IRES types. The hepatitis A IRES requires the host cap binding protein eIF4E for functioning, though the exact reason for that is not clear [28] (Fig. 2) . The type IV IRES is found in representatives of gen era Kobuvirus (Aichivirus C (porcine kobuvirus)), 29 31] (Fig. 2) . Recently, the type V IRES was discovered. It was found in representatives of genera Oscivirus, Kobuvirus (Aichivirus A, Aichivirus B), and Salivirus. This type of IRES is a "hybrid": its central domain is homologous to the fourth domain of the type I IRESs, whereas the next domain that binds to eIF4G is homologous to domain J of the type II IRESs [32, 33] . The start codon of the viral polyprotein is a part of the Yn Xm AUG motif and is situated in the stable hairpin of domain L. Translation initiation on these IRESs requires participation of an ATP dependent RNA helicase DHX29, PTB, and a set of canonical factors (Fig. 2) . The simplest mechanism of translation initiation is a hallmark of an intergenic 180 nt long IRES of represen tatives of dicistroviruses (for instance, the intergenic IRES of the cricket paralysis virus). Like the hepatitis C IRES, it forms a complex tRNA like structure, binds directly to the ribosome (P site), and triggers initiation without involving eukaryotic translation initiation factors [25, 34] (Fig. 2) . The modern classification of enteroviruses was accepted in 2012 and published as an update to the 9th issue of virus taxonomy from the International Committee on Taxonomy of Viruses. Since then, correc tions to this classification have been issued [35 39] . At present, genus Enterovirus belonging to family Picornaviridae includes nine enterovirus species (namely, Enterovirus A, B, C, D, E, F, G, H, and J) and three rhi novirus species (Rhinovirus A, B, and C). A new enterovirus was discovered in camels in 2015, which is apparently the first representative of a new species, Enterovirus I (Fig. 3) . The species Enterovirus A includes 25 (sero)types: coxsackievirus A2 (CV A2), CV A3, CV A4, CV A5, CV A6, CV A7, CV A8, CV A10, CV A12, CV A14, CV A16, enterovirus A71 (EV A71), EV A76, EV A89, EV A90, EV A91, EV A92, EV A114, EV A119, EV A120, EV A121, simian enteroviruses SV19, SV43, SV46, and baboon enterovirus A13 (BA13). The species Enterovirus B is one of the most numer ous. It consists of 63 (sero)types: coxsackievirus B1, CV B2 -B6, CV A9, echovirus 1 (E 1), E 2 -E 7, E 9, E 11 -E 21, E 24 -E 27, E 29 -E 33, enterovirus B69 (EV B69), EV B73 -EV B75, EV B77 -EV B88, EV B93, EV B97, EV B98, EV B100, EV B101, EV B106, EV B107, EV B110 (from chimpanzee), EV B111, EV B112 (from chimpanzee), EV B113 (from mandrill), and simian enterovirus SA5. The species Enterovirus C includes 23 (sero)types: poliovirus (PV) 1, PV 2, PV 3, coxsackievirus A1 (CV A1), CV A11, CV A13, CV A17, CV A19, CV A20, CV A21, CV A22, CV A24, EV C95, EV C96, EV C99, EV C102, EV C104, EV C105, EV C109, EV C113, EV C116, EV C117, and EV C118. The species Enterovirus D is relatively uncommon; it includes five (sero)types: EV D68, EV D70, EV D94, EV D111 (from human and chimpanzee), and EV D120 (from gorilla). The species Enterovirus E includes bovine enterovirus group A: from EV E1 to EV E4. The species Enterovirus F includes bovine enterovirus group B (at present, six types are described): from EV F1 to EV F6. The species Enterovirus G consists of 16 (sero)types: from EV G1 to EV G16. The species Enterovirus H includes three monkey viruses isolated in 1950 (SV4, SV28, and SA4) and A 2 plaque virus. However, these four viruses were joined into a single (sero)type enterovirus H1 (EV H1) due to their strong similarity at the molecular level. The species Enterovirus J contains six simian enterovirus species: SV6, EV J103, EV J108, EV J112, EV J115, and EV J121. The species Rhinovirus A is the most numerous; it contains 80 (sero)types: rhinovirus (RV) A1, A2, A7 A13, A15, A16, A18, A19 A25, A28 A36, A38 A41, A43, A45 (RV) B3 B6, B14, B17, B26, B27, B35, B37, B42, B48, B52, B69, B70, B72, B79, B83, B84, B86, B91 B93, B97, and B99 B106. As to viruses belonging to the species Rhinovirus C, despite its difference from Rhinovirus A and Rhinovirus B, until recently there were difficulties and misunderstanding in its classification and discriminating the individual types within the species. Some authors on the basis of numerous tests considered these viruses closely related to Rhinovirus A and called all of them HRV A2 [40, 41] . Others pre ferred to refer to these viruses as HRV C [42 45] or HRV X [46] . Since 2010, based on significant phylogenetic clus tering of the considered enterovirus species, reasonable suggestions appeared for creating a genetics based system that would allow discriminating its types similarly to (sero)types of other enterovirus species [47, 48] . By now, this species consists of 55 (sero)types (C1 C55). In addition, the genus includes several yet unclassi fied enteroviruses: one monkey enterovirus (SV 47) (it was not assigned to a certain species as its genome is not sequenced) and EV 122 and EV 123, which do not match any of the existing species. Thus, the genus Enterovirus includes many viruses including those highly dangerous for humans. At the same time, these viruses are widespread and highly resist ant to the action of physicochemical factors. At the beginning, enteroviral infections in humans were classified as acute respiratory diseases caused by intestinal viruses. It was generally accepted to discrimi nate infections caused by polioviruses (certain (sero)types of Enterovirus C) to a separate group called poliomyelitis. We have reviewed polioviruses and their current position in the viral taxonomy. The disease they cause was known already in ancient Egypt [49, 50] . In 1840, the German orthopedist Jacob von Heine discriminated poliomyelitis as a separate disease. In 1890, the Swedish pediatrician O. Medin suggested infectious nature of this disease based on its epidemic dissemination pattern. Poliomyelitis mainly affects children under 5 years old. Unfortunately, there is no antiviral drug for poliomyelitis treatment, only prevention is possible. This disease has several clinical forms. The abortive form proceeds with no symptoms of nervous system damage. This form of poliomyelitis is called a minor illness as it passes relatively gently, lasts around one week, and ends by recovery [51] . The nonparalytic form is serous meningitis caused by poliovirus. The disease proceeds significantly more severely than the abortive form with a complete set of meningeal symptoms. However, it also passes favorably and patients make a full recovery [51] . The paralytic form of poliomyelitis is the most dan gerous [52] . The above mentioned forms may convert into the paralytic form upon adverse development of the disease. However, it should be mentioned that this form develops in only 1% of patients. The disease may proceed rapidly, and general paralysis may occur within hours due to damage to the central nervous system. The recovery period may last up to 2 years. It is followed by the after math stage with stable paralyses, contractures, and defor mations. Irreversible paralysis (usually in legs) occurs in one out of 200 patients. Mortality in this group of patients reaches 10% due to further development of paralysis and its expansion to the respiratory muscles. In turn, the paralytic form is also divided into sever al kinds or forms [53] . The spinal form of paralytic poliomyelitis is the most common. It is characterized by lesion of predominantly the lumbar section of the spinal cord. Cervical and other sections are damaged less often. However, lesion of cervi cal and thoracic sections of the spinal cord is the most severe as it may cause paralysis of the respiratory muscles and thus disturb respiration. The most dangerous in this respect is diaphragmatic paralysis. The pontine form occurs upon lesion of the bridge of Varolius [54] . It can be isolated or be accompanied by damage to the spinal cord (pontospinal form) or medulla (pontobulbar form). It is characterized by facial muscle paralysis [55] . Most patients make a full recovery, which begins at 10 14 days of the disease. The bulbar form occurs in 10 15% cases of paralytic poliomyelitis. In this case, bulbar and glossopharyngeal nerves are affected [56] . The disease proceeds rapidly and is characterized by very serious general condition. Fast development of paralysis of corresponding muscle groups is typical. Pharyngeal paralysis (lesion of the palate and the larynx) may develop, leading to disturbance of respira tion and upper airway obstruction with saliva, mucus, and sputum. Earlier, this pharyngeal form of poliomyelitis was characterized by high mortality. At present, however, the pharyngeal paralysis may have a good prognosis and with recovery without consequences if it is treated in due time and correctly. In some patients, pharyngeal paralysis is combined with other disorders (spinal, oblongata). Development of collateral laryngeal paralysis (lesion of the larynx and ligaments) is possible. The acute form of this paralysis can cause sudden asphyxiation and cyanosis. The respiratory center may be affected in bulbar poliomyelitis, which results in disturbance in breathing rhythm and frequency and appearance of other breathing pathologies. Breathing disorders are accompanied with vasomotor and vegetative disorders. Early lesion of the vasomotor center may cause death due to sudden decrease in arterial pressure and cardiac arrest. In approximately half of lethal cases evoked by this form of poliomyelitis, an acute interstitial myocarditis is registered. A rare encephalitic form of poliomyelitis with high mortality has also been described. This form proceeds rapidly, mental confusion developing very fast and trans forming into stupor and coma [53] . Poliomyelitis in pregnant patients is considered sep arately [57] . During the first half of pregnancy, the disease may cause miscarriage, or preterm birth if infection occurred later. However, most women infected with poliomyelitis during pregnancy give birth in due time without obstetric surgery. Typically, the fetus is affected by intoxication and hypoxia rather than by direct transmis sion of the infection. Respiratory disorders pose an ele vated threat, which remains even after the acute phase of the disease is passed, for pregnant woman as well. Poliomyelitis outbreaks were widespread from the end of the 19th century. At the middle of the 20th centu ry, anti poliomyelitis vaccines appeared and were widely used. In 1988, the World Health Organization set the task of elimination of poliomyelitis worldwide by the 2000 [58] . Active prevention measures with wide use of vac cines decreased the incidence level by 99% (as of 1988) [59] . Currently, high risk of poliomyelitis outbreaks remains only in Afghanistan and Pakistan. In 2013, a new strategic plan for elimination of poliomyelitis by 2018 was presented at the global vaccine summit in Abu Dhabi (United Arab Emirates). The first reliable mention of the disease caused by non polio enteroviral infection occurred in 1856. Exactly in this year, there was an outbreak of pleurodynia in Iceland, which was described later in 1874. The first pub lication devoted to this illness is dated to 1872, when a Norwegian medical journal first published a communica tion of Dr. A. Daae to Dr. C. Homann titled "Epidemics of acute muscular rheumatism transmitted through the air in Drangedal". The Norwegian name for this illness is "Bamble disease" after the place it first appeared [60] . Later, it was referred to as Bornholm disease after the Danish island Bornholm, whereas it is now known as epi demic myalgia. Normally, the disease is caused by cox sackievirus B infection. More rarely it may be caused by coxsackieviruses A and certain (sero)types of echovirus [61] . It evokes myositis of the upper abdominal muscles and pectoral muscles, fever, and headache. Typically, the prognosis is positive -the patient recovers in 7 8 days. However, there are possible severe complications (includ ing, though rarely, aseptic meningitis) up to lethal out come. Viral myopericarditis is a combination of myocardi tis and pericarditis, which involves inflammation of both the cardiac muscle and the serous layer of pericardium. In infants, typically, myocarditis is developed, whereas peri carditis is more common in children and adults. Incorrect or late treatment may result in death. The frequent cause of myopericarditis is coxsackievirus B [62, 63] infection or coinfection with coxsackieviruses A and B [64] . Echoviruses may also evoke this disorder [65, 66] . The disease may proceed without symptoms or be accompa nied with chest pains, vertigo, general weakness, arrhyth mia, heart failure, fever, diarrhea, and sore throat. Swelling in the hands and legs may also occur. Sometimes, myopericarditis causes sudden loss of con sciousness, which may be associated with abnormal heart rhythms. Breathing difficulties may occur in children. Viral myopericarditis may convert into acute myocardial infarction [67] . Acute hemorrhagic conjunctivitis or enteroviral hemorrhagic conjunctivitis is a highly contagious oph thalmic infection that first appeared in 1969 1970 [68, 69] . It proceeds with visible hyperemia, chemosis, eye irritation, photophobia, eye discharge, and subconjuncti val hemorrhage. These symptoms appear along with gen eral symptoms (preauricular adenopathy, headache, increased body temperature, tracheobronchitis, etc.) [70] . Recovery occurs in 7 10 days. Causative agents for acute hemorrhagic conjunctivitis are enterovirus 70 and coxsackievirus A24 [71] . The most frequent manifestation of enteroviral infections is a nonspecific febrile illness. Usually, these infections are well tolerated and pass within a week. The disease may proceed in two phases [72] . Acute respirato ry viral infections (ARVI) are also ascribed to low hazard enteroviral infections caused by rhinoviruses and known as nasopharyngitis, rhinopharyngitis, rhinovirus infec tion, rhinonasopharyngitis, epipharyngitis, and the com mon cold [73] . However, some respiratory enteroviral infections (for instance, those caused by enterovirus 68) may lead to serious consequences resulting in severe com plications such as pneumonia [74] . Aseptic meningitis is a viral infectious disease that affects humans of all ages. However, individuals under 30 years old are more susceptible. The most common cause for this disease is non polio enteroviruses [75] , namely coxsackieviruses A and B, echoviruses, and enteroviruses 69 and 73 [76, 77] . During infection, the meninges are affected. Patients suffer from headache, fever, muscle aches, stomach aches, and stiff neck. Other possible symptoms are light sensitivity, rush, nausea, diarrhea, sore throat, and cough. As a rule, this illness has good prognosis and passes without consequences in 7 10 days. However, especially in newborns, the infection may develop to symptoms of encephalitis with focal neurolog ic signs and cramps. In this case, prognosis may be very poor up to lethal outcome caused by heart failure or liver damage [78] . Such infectious damage of the central nerv ous system in children may be associated also with enterovirus A71. In this case, the disease proceeds in more severe form and may evoke paresis and brainstem encephalitis [79] . Herpangina is an acute infectious disease caused mainly by coxsackieviruses A, which affects 3 10 years BIOCHEMISTRY (Moscow) Vol. 82 No. 13 2017 old children. This disease may be caused also by enterovirus A71 [80 82] . Distinctive symptom of her pangina is appearance of vesicles with serous contents on the soft palate, tonsils, and back of throat. They are small and resemble herpetic damage. Usually, vesicles open rapidly, dry up with a crust formation, and then heal. Upon bacterial coinfection, they may suppurate or ulcer ate. The disease proceeds with general symptoms such as fever, headache, rhinitis, hypersalivation, severe sore throat, hyperemia, and pain during palpation of regional lymph nodes. The disease usually passes in a few days. Enteroviral vesicular stomatitis (hand, foot, and mouth disease, HFMD) is an acute disease caused by coxsackieviruses A, B, and enterovirus A71. It predomi nantly occurs in children under 10 years old. However, it may also affect adults [83, 84] . Incubation period lasts approximately 3 6 days. During the prodromal period (12 to 36 h), patients expe rience such symptoms as cough, sore throat, general ill ness, and loss of appetite. After that, vesicular rash appears on hands, legs, and oral cavity. If the disease goes on auspiciously, it ends in 5 7 days. However, sometimes (especially if infection is caused by enterovirus A71) it may lead to severe neurological complications such as encephalitis, meningitis, and paralyses like those caused by poliovirus. This form is highly severe and features high mortality. From 2008 to 2012, over seven million cases were registered in China. It was fatal in 2457 cases [85] . Enteroviral encephalitis amounts to approximately 5% of cases of enteroviral infections [86] . The main cause of this severe neurological disease is coxsackieviruses A and B, echoviruses [87] , and enterovirus A71 [86] . The disease involves inflammation of the brain. It is accompa nied by fever, vomiting, headache, and weakness. Disorders of consciousness, cramps, behavior disorder, and paresis may occur. Severe disease may result in coma. Acute cerebellar ataxia, drop attacks, and hemichorea may occur in children. Several clinical types of enterovi ral encephalitis are discriminated according to localiza tion of inflammation: brainstem, cerebellar, hemispheric. The cerebellar form is the most auspicious, which ends with full recovery [88] . However, enteroviral encephalitis is a deadly disease [89] . Encephalitis caused by enterovirus A71 infection usually has brainstem clinical features and high mortality [86, 90] . Polio like illnesses, acute flaccid paralysis and acute paralytic poliomyelitis of non polio etiology, are diseases having symptoms similar to those of poliomyelitis but caused by other viruses, namely enteroviruses 68 71, cox sackieviruses, and echoviruses [91, 92] . These diseases affect predominantly children. The most severe forms are commonly caused by enterovirus A71 [93, 94] . Lesion of the central nervous system occurring during development of severe forms of the diseases, similarly to poliomyelitis, may evoke very serious consequences including fatal out come [95] . Enteroviral infections are dangerous not only for humans. Many animal species are susceptible to these viruses, especially higher mammals. Enteroviral infec tions of animals may worsen life of pets and even cause significant damage to entire branches of agriculture asso ciated with livestock farming. Cases of severe gastroen teritis caused by enteroviral infections leading to 50% mortality in young stock were registered in poultry farm birds [96] . Livestock farming suffers from outbreaks of enteroviral infections causing high mortality in farm ani mals (for instance, pigs) [97] . In addition, entire popula tions of rare or endangered species become victims of these infectious diseases. Even dolphins are susceptible to these infections [98] . Thus, counteraction to spread of these diseases is of great importance. Early diagnosis of enteroviral infection followed by antiviral therapy may prevent occurrence of severe com plications in patients. However, now there are no highly efficient and widely used anti enteroviral preparations. Therefore, treatment of enteroviral infections is limited to a complex of procedures for relieving the general con dition of patients, counteracting concomitant bacterial infections, and minimizing possible complications. Viral infection as such must be dealt with by the immune sys tem of the patient. Therefore, there is a great need for development of highly efficient antiviral agents for treat ment of enteroviral infections. The life cycle of enteroviruses includes virus adsorp tion, release of genetic material from the envelope, RNA translation, maturation of viral proteins, replication of viral RNA, and virus assembly. Any of these stages can be a target for antiviral agents. The enterovirus envelope consists of four viral pro teins (VP1 VP4). VP1 is one of the most frequently used targets in counteracting enteroviral infections. A great number of chemical compounds have antiviral proper ties in vitro through interaction with VP1 and prevention of virus adsorption or release of viral RNA from the envelope. One of the most successful experiences in designing antiviral preparation that interacted with the viral envelope was pleconaril [99] . It inhibited replica tion of several enteroviral (sero)types by 50% (though it did not affect EV A71) [100] . It was demonstrated that intake of this drug alleviated disease passage [101] . Although the preparation has numerous negative side effects and it did not pass clinical trials yet, it served as a basis for developing other more efficient and less toxic antiviral drugs [102] . Preparations based on other drugs that interact with viral capsid, but have not passed clini cal trials due to side effects, are also being developed [103] . BIOCHEMISTRY (Moscow) Vol. 82 No. 13 2017 Viral proteases are also targets in drug design. Proteins 2A and 3C are proteases of picornaviruses that play an important role in the processing of the viral polyprotein. In addition, they affect host cap dependent protein synthesis by cleaving elongation factor eIF4GI/II [104] , disturb nuclear transport [105] , and impair cellular splicing and transcription [106] . Successful propagation of many viruses depends on correct processing of the viral polyprotein. For instance, polyprotein EV A71 is cleaved by viral proteases, giving rise to four structural envelope proteins (VP1 VP4) and seven nonstructural proteins (2Apro, 2B, 2C, 3A, 3B, 3Cpro, and 3Dpol), which are required for virus replication [107] . During translation, 2A protease cleaves its own N terminus from C terminus of VP1, thus separating capsid protein precursor from precursor of replicative proteins. However, 3C protease in considered the main viral protease, as it is responsible for cleaving the other linkers joining proteins in the viral polyprotein [108, 109] . It was shown that alkylating agents (iodoacetamide and N ethylmaleimide) reduce activity of 2A protease [110] . Caspase inhibitors also may block 2A protease of rhinoviruses and coxsackievirus 2A both in vitro and in vivo [111] . Some antiviral agents affecting 3C protease were obtained based on the substrate of this protease. Many of them are peptides comprising 3 5 amino acid residues (a.a.), aldehyde groups of which are used as elec trophilic anchors [112] . Some peptide inhibitors of the 3C protease were modified so that they could form irre versible covalent bonds with the protease [113] . Such agents possess high antiviral activity toward rhinoviruses CV A21, CV B3, and EV A70, and echovirus 11. It is known that some alkaloids have antiviral prop erties. So, lycorine (an alkaloid of the family Amaryllidaceae) having a broad spectrum of biological activities inhibits development of polioviruses and EV A71 by affecting, in particular, 2A protease [114] . Rupintrivir was initially designed as an inhibitor of rhinoviral 3C protease. Later it demonstrated antiviral activity toward other representatives of the family Picornaviridae. Derivatives of this preparation were also able to inhibit enteroviruses EV A71 and CV A16 [115] . The following group includes antiviral drugs affect ing viral proteins involved in replication of viral RNA, or cell systems that are used by viruses for RNA replication. Replication of viral RNA occurs with the participation of replicative complex comprising various viral proteins: 2B, 2C, 2BC, 3A, 3B, 3AB, 3CD, and 3D. Some of these were tested as targets for antiviral agents. The prepara tions obtained featured a narrow activity spectrum and also had side effects [116] . For example, 5 (3,4 dichlorophenyl)methylhydantoin (a hydantoin deriva tive) inhibits replication of EV A71 RNA. The exact mechanism of this effect is to be studied, but, apparently, the process of viral RNA replication is disturbed due to interaction of the preparation with the capsid protein VP3, thus blocking activity of 2C protein, which also directly interacts with VP3 [117] . Compound BPR 3P012 (6 bromo 2 [1 (2,5 dimethylphenyl) 5 methyl 1H pyrazol 4 yl]quinoline 4 carboxylic acid) interacts with viral RNA dependent RNA polymerase (3D) and inhibits translation of EV A71 RNA [118] . Already known drugs frequently possess antiviral activity by affecting replication of viral RNA. For instance, isoflavone formononetin, which is commonly obtained from red clover [119] , or antifungal broad spectrum preparation itraconazole [120] . Besides, experiments are carried out for discovery of antiviral preparations based on noncoding regulatory microRNAs, which are also used for vaccine preparation [121] . A promising target for antiviral drugs is the internal ribosome entry site (IRES) on viral mRNA. A region of the 5′ UTR of viral mRNA, on which the preinitiation complex assembles, plays a pivotal role in regulation of its translation [122] . Viral IRESs differ from cellular IRESs by the presence of highly ordered secondary structures, a set of factors used for the translation initiation, and requirement for IRES trans acting factors (ITAF). Therefore, the process of translation initiation of viral mRNA is a promising target for pharmacological action. Besides, it was demonstrated that mutations in IRES affecting interaction of ITAF with viral mRNA also affect viral tissue tropism [123, 124] . IRESs of some viruses may act as chaperones influencing development of viral infec tion not only during the initiation of translation of viral mRNA [125] . As soon as viral IRESs were discovered, attempts were made to use them for therapy [126 129 ]. The main efforts were focused on developing a compound that would be able to modify IRES structure to make it ineligible for initiation of protein synthesis, or disturbing its interaction with the ribosome, translation initiation factors, and ITAF [126 128, 130 133] . Approaches associated with designing or searching for antiviral agents whose action is directed against IRESs are being extensively developed. The following com pounds are considered as such preparations or a basis for their development: complementary oligonucleotides [131] , peptide nucleic acids [130] , locked nucleic acids [130] , morpholines [134, 135] , short RNA hairpins [133, 136, 137] , small interfering RNAs [133, 136, 137] , RNA aptamers, ribozymes [138, 139] , DNAzymes [140, 141] , peptides [142, 143] , and low molecular weight inhibitors [141 148] . Historically, the first agents directed against IRESs were complementary oligonucleotides. The majority of early attempts were made to prevent hepatitis C virus gene expression [149 151 ]. BIOCHEMISTRY (Moscow) Vol. 82 No. 13 2017 Two approaches were applied in these works. One approach used complementary DNA oligonucleotides as a target for RNase H cleavage. The second approach con sisted in designing DNA oligonucleotides that would block interaction between IRES and the ribosome. Unfortunately, the latter approach has several typical dis advantages associated with efficiency of transport of DNA oligonucleotides, their intracellular stability, and in certain cases negative side effects. To improve stability and affinity of complementary DNA oligonucleotides, their modified analogs were developed, which consisted of peptide nucleic acids and locked nucleic acids [151 153 ]. However, it did not solve the problem of delivery, intracellular transport, and toxicity of these compounds. During development of this approach, attention of researchers was drawn to morpholines (single stranded DNA like cell penetrating complementary agents able to decrease levels of gene expression by blocking comple mentary RNA sequences). They represent a third genera tion of complementary oligonucleotides and feature acceptable toxicity and resistance to nucleases [154] . Morpholino-RNA duplexes are significantly more stable than similar DNA-RNA duplexes. Morpholines sterical ly block target RNA. They are widely used for modulating expression of genes of certain organisms (such as frogs and zebrafish) [154] . A set of peptide conjugated phos phorodiamidate morpholino oligomers (PPMO) was designed that were complementary to conserved type I IRES regions of RNA viruses (rhinovirus B14, coxsack ievirus B2, and poliovirus type 2) [155] . These com pounds are soluble in water and resistant to the action of nucleases. They efficiently penetrate cells and inhibit virus replication through forming a duplex with comple mentary viral mRNA. In cell culture, they reduce virus titer by several orders of magnitude. Application of PPMO increases survivability in mice infected by poliovirus, coxsackievirus B3, Ebola virus, and influenza virus [155, 156] . Octa guanidine conjugated to morpholines (Vivo morpholinos, vPMOs) are also single stranded DNA like complementary agents. It was shown that these com pounds reduced RNA replication and expression of a capsid protein of EV A71 virus. Besides, these com pounds inhibited development of poliovirus and coxsack ievirus A16 [157] . Single stranded mRNA regions potentially available for binding are preferable targets when designing a com plementary antiviral agent using the above mentioned technologies. These regions are usually located within apical loops of various hairpins, in bulges, and in other elements of RNA secondary structures [151, 152, 158] . Another kind of antiviral drugs is RNA hairpins or small interfering RNAs (siRNAs) [159] . Upon transfec tion of poliovirus infected murine fibroblasts with siRNAs, strong inhibition of poliovirus replication occurs [160] . Though siRNAs might be used as a basis for devel opment of medications, they suffer the same cell trans port problems as the above mentioned drugs. Furthermore, these RNA agents carry net negative charge and they are less stable, which impedes their delivery into the cell. To overcome these problems, liposomes and polymeric nanoparticles are used as drug delivery vehicles [161] . Besides, siRNAs suffer a significant disadvantage: they can activate protein kinase K, which inhibits transla tion of cellular proteins due to phosphorylation of the α subunit of translation initiation factor 2 [13, 162] . Therefore, approaches based on use of DNA oligonu cleotide agents are currently considered more promising as these agents feature higher intracellular stability and increased affinity toward target viral RNA. The next kind of antiviral drugs are ribozymes, DNAzymes, or ribozyme conjugated RNA aptamers. DNAzymes are catalytic DNAs that can cleave the phos phodiester bond in an RNA molecule [163] . They can be obtained more easily than synthetic ribozymes, and they are more stable. Unlike siRNAs, DNAzymes do not acti vate protein kinase K [164] . As ribozymes and DNAzymes can specifically inhibit viral IRESs, they rep resent a reasonable basis for developing therapeutic preparations directed against viruses that use IRES dependent translation initiation [164 167] . Peptide inhibitors and small molecules are extensive ly used in medicine [168, 169] . These peptides usually consist of 5 40 a.a. They mimic functionally active regions of intact proteins that serve as the basis for their design. Due to their small size, they can specifically bind target RNA, disrupting functional complexes that were formed already [168, 170] . Several such peptides were designed to block an IRES of hepatitis C virus [133, 142, 144] . They are based on an RNA recognition motif of La autoantigen and prevent binding of La to the IRES of hepatitis C virus [142] . However, La is also an ITAF for numerous viral and cellular IRESs [4, 5, 171, 172] . Therefore, such peptides are not specific to hepatitis C virus. To solve the problem of intracellular peptide resist ance against proteolysis, unnatural amino acids are intro duced into them (the corresponding compounds are referred to as peptidomimetics). Liposomes and polymer ic nanoparticles are used for delivery of these peptides to cells. Also, a peptide can be linked to a protein domain that assists its transmembrane transport. Alternatively, they may be synthesized in cells upon transduction with viral vectors during gene therapy [168] . Currently, small molecules are preferred drugs [169] . There are new approaches directed toward generation of libraries of small molecules with desired properties [169] . Using combinatorial chemistry, large libraries are gener ated of closely related structural analogs that are further tested in biological screening. Numerous attempts are made to of small molecules able to deactivate viral IRESs [ 173 176] . As a result, some potential low molecular weight antiviral agents were obtained [173, 176] . For BIOCHEMISTRY (Moscow) Vol. 82 No. 13 2017 instance, it was shown that the 9 aminoacridine deriva tive quinacrine inhibits translation of poliovirus in a cell free system and in infected HeLa cells, which makes it prospective for further studies [174] . Only a few mole cules become subject to clinical trials. However, despite these failures, such approach is still considered one of the most prospective ones Summarizing the above said, it should be noted that despite several promising direct action antiviral prepara tions including the ones already approved for medical application [177] , there is no worldwide certified and commonly recognized antiviral drug for treatment of dis eases caused by enteroviruses. Physicians are forced to counteract consequences of disease rather than its cause. Thus, valuable time is lost, which increases risks of irre versible damage in patients. Currently, the only very effi cient remedy against enteroviral infections is prevention. Joint global efforts in this direction may provide great outcome like that reached in fighting poliomyelitis [59] . For this reason, vaccines against other dangerous repre sentatives of the genus Enterovirus are being developed extensively [85] . Nevertheless, despite 99% reduction in infection cases because of global efforts toward elimina tion of poliomyelitis, this disease persists. At the same time, one should clearly recognize that if there is still a single poliovirus infected individual, unvaccinated peo ple worldwide are at risk of infection. It should be mentioned that development of antiviral drugs is associated with significant difficulties, not only scientific ones, but also organizational and financial dif ficulties on a global scale. To be efficient, prevention must be ubiquitous and constant, which is still a problem. Besides, vaccine usually is highly specific, whereas enteroviruses are very diverse. Furthermore, under cer tain conditions vaccination may lead to negative events, such as vaccine borne virus infection as occurs during overall successful fighting against poliomyelitis. A main point is that prevention does not help those who are already infected. They may only rely on their own immune system and symptomatic treatment. Therefore, the urgent need for designing drugs that directly affect enteroviruses causing numerous dangerous diseases is clear. Drugs with wide spectrum of specificity are espe cially required, which would allow suppressing enterovirus epidemics at the beginning, before they spread. Development of such preparations is being car ried out worldwide. Internal initiation of translation of eukaryotic mRNA directed by a sequence derived from poliovirus RNA A segment of the 5′ nontranslated region of encephalomyocarditis virus RNA directs internal entry of ribosomes during in vitro translation Internal translation initiation: diversity of mechanisms and possible role in cell life Internal ribosome entry sites in cellular mRNAs: mystery of their existence Cellular IRES mediated translation: the war of ITAFs in pathophysiologi cal states Internal translation initiation of picornaviruses and hepatitis C virus Structural and functional diversity of viral IRESes Identification of an intercistronic internal ribosome entry site in a Marek's disease virus immediate early gene Naturally occurring dicistronic cricket paralysis virus RNA is regulated by two internal ribosome entry sites Identification of plant virus IRES Characterization of two distinct RNA domains that regulate translation of the Drosophila gypsy retroelement Direct functional interaction of initiation factor eIF4G with type 1 internal ribosomal entry sites The mechanism of eukaryotic translation initiation and princi ples of its regulation IRES induced conformational changes in the ribosome and the mechanism of translation initiation by internal ribosomal entry Translation initiation by factor independent binding of eukaryotic ribosomes to internal ribosomal entry sites Cap and IRES independent scanning mech anism of translation initiation as an alternative to the con cept of cellular IRESs Polypurine (A) rich sequences pro mote cross kingdom conservation of internal ribosome entry Complete nucleotide sequence and genome organization of a tobamovirus infect ing Cruciferae plants Translation initi ation on picornavirus RNA Cap independent translation of picornavirus RNAs: structure and function of the internal ribosomal entry site Structural features of the Seneca Valley virus internal ribosome entry site element; a picor navirus with a pestivirus like IRES Translation of poliovirus RNA: role of an essential cis act ing oligopyrimidine element within the 5′ nontranslated region and involvement of a cellular 57 kilodalton protein A conserved AUG triplet in the 5′ nontranslated region of poliovirus can function as an initiation codon in vitro and in vivo Structure of the 5′ nontranslated region of the coxsackievirus b3 genome: chemical modification and comparative sequence analysis Canonical eukaryotic initiation factors determine initiation of translation by internal ribosomal entry A cell cycle dependent protein serves as a template specific translation initiation factor In vitro characterization of an internal ribosomal entry site (IRES) present within the 5′ nontranslated region of hepa titis A virus RNA: comparison with the IRES of encephalomyocarditis virus Activity of the hepatitis A virus IRES requires association between the cap binding translation initiation factor (eIF4E) and eIF4G Factor requirements for translation initiation on the simian picornavirus internal ribosomal entry site Eukaryotic ribosomes require 872 initiation factors 1 and 1A to locate initiation codons dependent and eIF2 independent modes of initiation on the CSFV IRES: a common 875 role of domain II Polypyrimidine tract binding protein stimulates the poliovirus IRES by modulating eIF4G binding Internal initiation of mRNA translation in eukary ote Initiation of protein synthesis from the A site of the ribosome Virus Taxonomy: Classification and Nomenclature of Viruses: Ninth Report of the International Committee on Taxonomy of Viruses Ratification vote on taxonomic proposals to the International Committee on Taxonomy of Viruses Ratification vote on taxonomic pro posals to the International Committee on Taxonomy of Viruses Ratification vote on taxo nomic proposals to the International Committee on Taxonomy of Viruses Frequent detection of human rhinoviruses, paramyxoviruses, coronaviruses, and bocavirus during acute respiratory tract infections Characterization of a newly identified human rhinovirus, HRV QPM, discovered in infants with bronchiolitis MassTag polymerase chain reaction detection of respiratory pathogens, including a new rhinovirus geno type, that caused influenza like illness in New York State during Clinical features and complete genome characterization of a distinct human rhinovirus genetic cluster, probably repre senting a previously undetected HRV species, HRV C, associated with acute respiratory illness in children A diverse group of previously unrecog nized human rhinoviruses are common causes of respirato ry illnesses in infants Distinguishing molecular features and clinical characteristics of a putative new rhinovirus species, Human rhinovirus C (HRV C) Pan viral screening of respiratory tract infections in adults with and without asthma reveals unexpected human coronavirus and human rhinovirus diversity Proposals for the classification of human rhinovirus species A, B and C into genotypically assigned types Proposals for the classification of human rhinovirus species C into genotypically assigned types Poliomyelitis in Ancient Egypt? The poliomyelitis story: a scientific hegira Epidemics to eradication: the mod ern history of poliomyelitis Paralytic poliomyelitis A pontine form of poliomyelitis and isolated facial neuritis Poliomyelitis. The bulbar type Poliomyelitis in preg nancy Global Polio Eradication Initiative. Wild Poliovirus Weekly Update The occurrence of Bamble disease (epidemic pleurodynia) Pleurodynia caused by an echovirus 1 brought back from the tropics Coxsackievirus B detection in cases of myocarditis, myopericarditis, pericarditis and dilated cardiomyopathy in hospitalized patients Myocarditis caused by coxsackie B viruses in adults Acute viral myoperi carditis presenting as a transient effusive constrictive peri carditis caused by coinfection with coxsackieviruses A4 and B3 Isolation of ECHO virus type 22 from a child with acute myopericarditis -a case report Myopericarditis associated with ECHO virus type 3 infec tion -a case report Acute myocardial infarction spurred by myopericarditis in a young female patient: coxsackie B2 to blame Unusual type of epidemic conjunctivitis in Ghana An epidemic of conjunctivitis in Singapore in 1970 Acute hemorrhagic conjunctivitis Acute hemorrhagic conjunctivitis: anti coxsackievirus A24 variant secretory immunoglobulin A in acute and convales cent tear The virus watch pro gram: a continuing surveillance of viral infections in metro politan New York families. VII. Observations on viral excretion, seroimmunity, intrafamilial spread and illness association in coxsackie and echovirus infections Treatment of the common cold Outbreak of lower respiratory tract illness associated with human enterovirus 68 among American Indian children Enteroviral infections of the central nervous system Aseptic meningitis An outbreak of aseptic menin gitis caused by coxsackievirus A9 in Gansu, the People's Republic of China Aseptic meningitis and viral myelitis Neurologic complications in children with enterovirus 71 infection Enterovirus/picor navirus infections Risk factors of enterovirus 71 infection and associat ed hand, foot, and mouth disease/herpangina in children during an epidemic in Taiwan A typical hand, foot and mouth disease in adults associated with cox sackievirus A6: a clinicopathologic study Coxsackievirus associated hand, foot and mouth disease in an adult Enterovirus 71 infection and neurological complications Enterovirus associated encephalitis in the California encephalitis project Novel and predominant pathogen responsible for the enterovirus associated encephalitis in eastern China Fatal case of echovirus type 9 encephalitis Enterovirus 71: epi demiology, pathogenesis and management Acute flaccid paralyses in children under modern conditions Molecular epidemiology and recombination of human enteroviruses from AFP surveillance in Yunnan Understanding enterovirus 71 neuropathogenesis and its impact on other neurotropic enteroviruses Outbreak of neurologic enterovirus type 71 disease: a diagnostic challenge Fatal enterovirus type 71 infection: rapid detection and diagnostic pitfalls Poultry gastrointestinal diseases of viral etiology Studies on pathogenic porcine enteroviruses: 1. Preliminary investigations, Can Short communica tion: New recognition of enterovirus infections in bot tlenose dolphins (Tursiops truncatus) Controlled trial of pleconaril for the treatment of neonates with enterovirus sepsis. National institute of allergy and infectious diseases collaborative antiviral study group Activity of pleconaril against enteroviruses Efficacy and safety of oral pleconaril for treatment of colds due to picornaviruses in adults: results of 2 double blind, ran domized Design, synthesis, and struc ture activity relationship of pyridyl imidazolidinones: a novel class of potent and selective human enterovirus 71 inhibitors Study of the biological activity of novel synthetic compounds with antiviral properties against human rhinoviruses Proteolysis of human eukaryotic translation initia tion factor eIF4GII, but not eIF4GI, coincides with the shutoff of host protein synthesis after poliovirus infection Differential targeting of nuclear pore complex pro teins in poliovirus infected cells Inhibition of U snRNP assembly by a virus encoded proteinase Structural perspective on the formation of ribonucleoprotein com plex in negative sense single stranded RNA viruses 3C pro tease of enterovirus 68: structure based design of Michael acceptor inhibitors and their broad spectrum antiviral effects against picornaviruses Picornaviridae: The Viruses and Their Replication Purification and partial characterization of poliovirus protease 2A by means of a functional assay An antiviral peptide inhibitor that is active against picornavirus 2A proteinases but not cellular cas pases Selective inhibitors of picornavirus replication Structure based design, synthesis, and biological evaluation of irreversible human rhinovirus 3C protease inhibitors. 1. Michael acceptor structure activity studies A conserved inhibitory mechanism of a lycorine derivative against enterovirus and hepatitis C virus Enterovirus 71 and coxsackievirus A16 3C proteases: bind ing to rupintrivir and their substrates and anti hand, foot, and mouth disease virus drug design Development of antiviral agents for enteroviruses Hydantoin: the mechanism of its in vitro anti enterovirus activity revisited BPR 3P0128 inhibits RNA dependent RNA polymerase elongation and VPg uridylylation activities of enterovirus 71 Formononetin inhibits enterovirus 71 replication by regulating COX 2/PGE 2 expression Itraconazole inhibits enterovirus replication by tar geting the oxysterol binding protein Development of novel miRNA based vaccines and antivirals against enterovirus 71 Regulation mechanisms of viral IRES driven translation Cell specific proteins regulate viral RNA translation and virus induced disease Molecular mechanisms of attenuation of the Sabin strain of poliovirus type 3 The chaperone like activity of the hep atitis C virus IRES and CRE elements regulates genome dimerization Specific inhibition of hepatitis C virus expression by antisense oligodeoxynu cleotides. In vitro model for selection of target sequence Antisense oligonucleotide inhibi tion of hepatitis C virus gene expression in transformed hepatocytes In vitro mutational and inhibitory analysis of the cis acting translational elements within the 5′ untranslated region of coxsackievirus B3: potential targets for antiviral action of antisense oligomers Cytotoxic and immunogenic mechanisms of recombinant oncolytic poliovirus Intracellular inhibition of hepatitis C virus (HCV) internal ribosomal entry site (IRES) dependent translation by peptide nucleic acids (PNAs) and locked nucleic acids (LNAs) Oligonucleotide based strategies to inhibit human hepati tis C virus Targeting internal ribosome entry site (IRES) mediated translation to block hepatitis C and other RNA viruses Hepatitis C virus translation inhibitors targeting the internal ribosomal entry site A potent and specific morpholino antisense inhibitor of hepatitis C translation in mice A morpholino oligomer targeting highly conserved internal ribosome entry site sequence is able to inhibit multiple species of picornavirus Small interfering RNA targeted to hepatitis C virus 5′ nontrans lated region exerts potent antiviral effect Formulated minimal length synthetic small hairpin RNAs are potent inhibitors of hepatitis C virus in mice with humanized livers Inhibition of hepatitis C virus by an M1GS ribozyme derived from the catalytic RNA subunit of Escherichia coli RNase P Investigating a new generation of ribozymes in order to target HCV HIV 1 RT dependent DNAzyme expression inhibits HIV 1 replication without the emer gence of escape viruses Catalytic DNA: scocpe, applica tions, and biochemistry of deoxyribozymes A peptide derived from RNA recognition motif 2 of human La pro tein binds to hepatitis C virus internal ribosome entry site, prevents ribosomal assembly, and inhibits internal initia tion of translation A cell permeable peptide inhibits hepatitis C virus replica tion by sequestering IRES transacting factors Approved antiviral drugs over the past 50 years Inhibitors of protein synthesis identified by a high throughput multiplexed translation screen Design, synthesis, and biological evaluation of antiviral agents targeting flavivirus envelope proteins Quinacrine impairs enterovirus 71 RNA replication by preventing binding of polypyrimidine tract binding protein with internal ribosome entry sites New developments in small molecular compounds for anti hepatitis C virus (HCV) therapy Specific inhibition of hepatitis C virus expression by antisense oligodeoxynu cleotides. In vitro model for selection of target sequence Antisense oligonucleotide inhibi tion of hepatitis C virus gene expression in transformed hepatocytes Oligonucleotide based strategies to inhibit human hepati tis C virus Intracellular inhibition of hepatitis C virus (HCV) internal ribosomal entry site (IRES) dependent translation by peptide nucleic acids (PNAs) and locked nucleic acids (LNAs) RNA interference guided targeting of hepatitis C virus replication with anti sense locked nucleic acid based oligonucleotides con taining 8 oxo dG modifications Promising nucleic acid analogs and mimics: characteristic features and appli cations of PNA, LNA, and morpholino A morpholino oligomer targeting highly conserved internal ribosome entry site sequence is able to inhibit multiple species of picornavirus Inhibition of RNA virus infections with peptide conjugated morpholino oligomers Inhibition of enterovirus 71 infection by antisense octaguanidinium dendrimer conjugated morpholino oligomers Targeting internal ribosome entry site (IRES) mediated translation to block hepatitis C and other RNA viruses RNA mediated epi genetic regulation of gene expression Short interfering RNA confers intracellular antiviral immunity in human cells Solid lipid nanoparticles as non viral vector for the treatment of chronic hepatitis C by RNA interference Activation of the interferon sys tem by short interfering RNAs Use of deoxyri bozymes in RNA research Sequence specific cleavage of hepatitis C virus RNA by DNAzymes: inhibi tion of viral RNA translation and replication Inhibition of hepatitis C virus (HCV) RNA dependent translation and replication of a chimeric HCV poliovirus using synthetic stabilized ribozymes 2017 that efficiently interferes with hepatitis C virus translation and replication Site specific cleavage of HCV genomic RNA and its cloned core and NS5B genes by DNAzyme Inhibition of coxsackievirus B3 in cell cultures and in mice by peptide conjugated morpholino oligomers targeting the internal ribosome entry site Biased and unbiased strategies to identify biologically active small molecules Peptides as drugs: from screening to application La autoantigen is necessary for optimal function of the poliovirus and hepatitis C virus internal ribosome entry site in vivo and in vitro RNA binding proteins, multifaceted translational regulators in cancer Inhibitors of protein synthesis identified by a high throughput multiplexed translation screen Inhibition of encephalomyocarditis virus and poliovirus replication by quinacrine: implications for the design and discovery of novel antiviral drugs Quinacrine impairs enterovirus 71 RNA replication by preventing binding of polypyrimidine tract binding protein with internal ribosome entry sites Aminobenzoxazole ligands of the hepatitis C virus internal ribosome entry site Direct effect antiviral preparations registered with WHO We express our gratitude to A. P. Korepanov for care ful reading and valuable critical remarks. This work was supported by the Russian Science Foundation (project No. 15 14 00028).