HCV drug resistance and DAA agents - Epidemiological Review

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RIWKH:URFáDZ0HGLFDO8QLYHUVLW\ ABSTRACT

New treatment options for HCV infection with Direct-Acting Antivirals (DAAs) increased SVR rate in treated SDWLHQWVEXWRQWKHRWKHUKDQGGUHZDWWHQWLRQWRWKHSUREOHPRI+&9GUXJUHVLVWDQFH'UXJUHVLVWDQW+&9PXWDQWV DUHSUHVHQWLQDOOLQIHFWHGSDWLHQWVHYHQEHIRUHWKHWUHDWPHQWLQLWLDWLRQDQGWKHLUQXPEHUJURZVVLJQLILFDQWO\RYHU the first few days of DAAs therapy. But HCV has no known genetic form of intra-cellular persistence (does not LQWHJUDWHZLWKKRVW¶VJHQRPHDQGFDQQRWSURGXFHHSLVRPDOIRUPVZKLFKHQDEOHVLWVWRWDOHUDGLFDWLRQ,WLVOLNHO\ WKDWWKHHIIHFWLYHLQWHUIHURQIUHHEDVHGRQDOORUDO'$$VGUXJFRPELQDWLRQZLOOEHDYDLODEOHZLWKLQWKHQH[W few years. This paper reviews HCV resistance mechanisms and their significance in treatment. I also presents results of recent DAAs trials.

.H\ZRUGV: HCV, drug resistance, nucleoside analogs INTRODUCTION

$SSUR[LPDWHO\PLOOLRQSHRSOHDUH+&9FDUULHUV worldwide (1). Until recently, pegylated interferon alpha LQFRPELQDWLRQZLWKULEDYLULQZDVWKHILUVWOLQHWKHUDS\ however, successful HCV eradication was achieved in only 50% of patients (therapy efficacy was lower in patients infected with HCV genotype 1 & 4 and higher LQLQGLYLGXDOVGLDJQRVHGZLWK+&9JHQRW\SHDQG 7KHUDSHXWLFIDLOXUHZLWKSHJ\ODWHGLQWHUIHURQDOSKD LQ FRPELQDWLRQ ZLWK ULEDYLULQ UHVXOWV IURP PXOWLSOH virus-, host-, and treatment-dependent factors. These IDFWRUVDUHOLVWHGLQ7DEOH

With the introduction of Direct-Acting Antivirals – '$$VWHODSUHYLUDQGERFHSUHYLUSURWHDVHLQKLELWRUV the likelihood of HCV eradication in patients infected with HCV genotype 1 has increased, however, HCV resistance to drugs raises some serious health concerns.

DRUG-RESISTANT HCV VARIANTS Drug-resistant HCV variants which typically have ORZHUUHSOLFDWLRQILWQHVVFDQQRWEHGHWHFWHGZLWKVWDQ-dard molecular methods, which is why they had not DWWUDFWHGPXFKDWWHQWLRQEHIRUHH[SHULPHQWVRQ'$$V 7DEOH )DFWRUVWKDWDIIHFWUHVSRQVHWRSHJ\ODWHGLQWHUIHURQ DOSKDDQGULEDYLULQLQWKHWUHDWPHQWRI+&9LQIHF-tions. 1. HCV-dependent (positive)  JHQRW\SHY  QXPEHURI+&9FRSLHVLQEORRGVHUXP0FRSLHV/9/ - fast kinetics of HCV clearance

 +RVWGHSHQGHQWQHJDWLYH

 SDVWDQGSUHVHQWKLVWRU\RIDOFRKRODEXVH - age > 40 years when infected

- male

- HBV and HCV co-infection  REHVLW\

 DEQRUPDOLWLHVLQOLSLGPHWDEROLVP

 DGYDQFHGKHSDWLFILEURVLVRUFLUUKRVLVRQLQLWLDWLRQRIWUHDWPHQW - racial affinities: African Americans: lower SVR rates, (Asians:

higher SVR rate)

- IVDU (intravenous drug users)

 ,QWHUOHXNLQESRO\PRUSKLVP,)1Ȝ695UDWHGHSHQGHQW RQJHQRW\SHSRO\PRUSKLVP&&&777 - poor treatment tolerance

- non-compliance 3. Therapy-dependent

 ,)1DOSKD LQ PRQRWKHUDS\  ,)1DOSKD5%9 FRPELQDWLRQ WKHUDS\3(*,)1DOSKD5%9FRPELQDWLRQWKHUDS\  WKHUDS\GXUDWLRQIRUJHQRW\SHPRQWKV IRUJHQRW\SHPRQWKV  5%9GRVHSHUEZ

 SHJLQWHUIHURQDOSKDE3(*,QWURQvs. peginterferon alpha-D3(*$6<6±,'($/VWXG\

Anna Szymanek, Krzysztof Simon 404 No 3 EHJDQ,GHQWLILHGLQWRRIFDUULHUVPXWDWLRQV UHVSRQVLEOHIRUUHVLVWDQFHWRSURWHDVHLQKLELWRUVWHOD-SUHYLU%,/1,7016&+DQGERFHSUHYLU 16%SRO\PHUDVHLQKLELWRU$*DQG16$DQ-WDJRQLVW$&+ZHUHFRQVLGHUHGWREHVSRUDGLFDQG clinically insignificant (3). Variants inducing resistance WRWHODSUHYLU5.90ZHUHIRXQGLQ RIQRQWUHDWHGFDUULHUVRIJHQRW\SHEDQGZHUHHLWKHU XQGHWHFWDEOHRUGHWHFWHGLQDYHU\VPDOOSHUFHQWDJH RISHRSOHIRU$6DQG90DQGIRU T54S) with genotype 1a. (4). Likewise, in patients with JHQRW\SHDPXWDWLRQVUHVLVWDQWWRERFHSUHYLU90 765.DQGE7$9$$6,9$ were very rare (5).

+RZHYHUZLWKWKHEHJLQQLQJRIFOLQLFDOVWXGLHVRQ SURWHDVHLQKLELWRUVLWZDVIRXQGWKDWGUXJUHVLVWDQWYDUL-DQWVFDQEHGHWHFWHGDVHDUO\DVRQWKHVHFRQGGD\DIWHU LQWURGXFWLRQRIWKHUDS\LQWRRILQGLYLGXDOV>@ There are several reasons that could explain such early mutations. Firstly, HCV replication is typically very dynamic. Within a single day, there are approximately 10QHZYLULRQVZLWKKRXUVRIHVWLPDWHGKDOIOLIH ZKLFKLVHYHQVKRUWHULQFDVHRILQWUDFHOOXODUIRUPV Also, RNA-dependent RNA HCV polymerase is very HUURUVHQVLWLYH  %DVHG RQ PDWKHPDWLFDO PRGHOV LWZDVFRQFOXGHGWKDWDOOSRVVLEOHVLQJOHGRXEOHDQG PRVWSUREDEO\DOVRWULSOH+&9PXWDWLRQVGHWHUPLQLQJ resistance to DAAs are present in carriers prior to the EHJLQQLQJRIWKHUDS\

(IILFLHQWDQWLYLUDOWKHUDS\EDVHGRQ'$$VHOLPLQDWHV drug-sensitive drugs, whereas drug resistant strains can SUROLIHUDWHIUHHO\,WLVDOVRSRVVLEOHWKDWVXEVHTXHQW compensatory mutations are selected in conditions of H[SRVXUHWRGUXJZKLFKPD\EHDEOHWRUHFRYHULQYLYR replication fitness of the mutated virus, i.e. replication ILWQHVVIURPEHIRUHWKHUDS\LVWKHUHE\UHVWRUHG,QYLYR replication fitness is the key condition for the mutated YLUXVWREHDEOHWRUHSOLFDWHVLQFHDQ\YLUXVRIORZ replication potential - even if it is highly resistant - is of lower clinical significance as compared to any other YLUXVRIORZUHVLVWDQFHDQGKLJKUHSOLFDWLRQILWQHVV HCV variants carrying a mutation at the locus 156 – ZKLFKH[KLELWWKHKLJKHVWUHVLVWDQFHWRWHODSUHYLUDQG ORZUHSOLFDWLRQSRWHQWLDO±ZHUHIRXQGWREHSUHVHQWDW DYHU\HDUO\VWDJHRIWKHUDS\DQGTXLFNO\UHSODFHGE\ viruses representing higher replication fitness (155, 36 and 155, 36 and 156) (10, 11). However, a wild-type YLUXVGRPLQDQFHFDQEHGHWHFWHGDVHDUO\DVLQGD\VRQ discontinuation of unsuccessful triple-drug therapy. But still, drug-resistant variants remain present, although are very few. As a result, even if any drug-resistant strains are isolated in these patients, it appears perfectly safe DQGFDQQRWEHFRQVLGHUHGDFRQWUDLQGLFDWLRQIRUUHSHDWHG WKHUDS\ZLWKILUVWJHQHUDWLRQSURWHDVHLQKLELWRUZLWK FURVVUHVLVWDQFHWRWHODSUHYLURUERFHSUHYLUDVORQJDV

these drugs are part of treatment regimen containing other drugs which successfully prevent replication of HCV without any signs of cross-resistance to protease LQKLELWRUV

7KXV+&9DELOLW\WRSURGXFHGUXJUHVLVWDQWPX-tations is not necessarily a serious health concern as in case of HIV and HBV. Unlike these viruses, HCV only replicates in cellular cytoplasm of the host, is not integrated with the host genome, and cannot produce any reservoirs of episomal forms (13). Therefore, anti-viral therapy creates some solid opportunities for HCV eradication (13).

Relying on mathematical models, the hypothesis is WKDWWKHUDS\ZLWK'$$VFRXOGEHDSSOLHGZLWKFRPEL-QDWLRQVRIGUXJVRIIHULQJDJHQHWLFEDUULHURIRUPRUH mutations (6).

According to the results of phase II and III studies on DAAs, triple-drug therapy failure in compliant per-VRQVFDQEHPDLQO\DWWULEXWHGWRWKHODFNRIUHVSRQVHWR LQWHUIHURQDQGULEDYLULQZKLFKUHVXOWVLQWKHVHOHFWLRQ RISUHH[LVWLQJPXWDWLRQVUHVLVWDQWWR'$$V

It is difficult to create an interferon-free treatment UHJLPHQEDVHGRQRUDO'$$DRIIHULQJRSWLPXPHIILFDF\ WRZDUGVDOO+&9JHQRW\SHVDORQJZLWKKLJKJHQHWLFEDU-rier, in order to guarantee high percentage of recoveries DWDUHDVRQDEOHWLPH

EXAMINING NEW TREATMENT REGIMENS 3URWHDVHLQKLELWRUVDSSHDUWRKDYHDVXSHULRUUH-sistance profile as compared to other drugs, such as RNA-dependent RNA HCV polymerase nucleoside / QXFOHRWLGHLQKLELWRUVZKLFKUHVXOWVLQWKHVHOHFWLRQRI viruses of lower replication potential, and cyclophilin LQKLELWRUVZKLFKWDUJHW+&9UHODWHGKRVWSURWHLQLQVWHDG of viral protein (14).

Some promising results were produced in studies on WKHHIILFDF\RIDVXQDSUHYLU16$SURWHDVHLQKLELWRU DQGRIGDFODWDVYLU±16$LQKLELWRULQFDUULHUVRI JHQRW\SHEZKRIDLOHGWRUHVSRQGWRSHJ\ODWHGLQWHU-IHURQDOSKDDQGULEDYLULQHOLPLQDWHGWKHYLUXVZLWKLQ ZHHNVRIWKHUDS\+LJKVXVWDLQHGYLURORJLFUHVSRQVH 695UDWHVZHUHUHSRUWHGLQDOOSDWLHQWV 36,QXFOHRWLGHDQDORJSRO\PHUDVHLQKLELWRU - is another promising drug which, in an add-on therapy with PRG/RBV, produced 90% SVR rate in patients infected with genotype 1 in the PROTON study (16).

,QDQRWKHUVWXG\695ZDVREVHUYHGLQRXWRI SUHYLRXVO\QRQWUHDWHGFDUULHUVRIJHQRW\SHRUDIWHU ZHHNVRQ36,LQFRPELQDWLRQZLWKLQWHUIHURQ IUHHULEDYLULQ)XUWKHULQWHUHVWLQJVWXGLHVRQWKLV molecule are in course, also in our center.

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HCV drug resistance and DAA agents ₄₀₅

No 3

'$$V7KH3,/27VWXG\HYDOXDWHGWKHHIILFDF\RID week interferon-free therapy - ABT-450 as an add-on to ULWRQDYLUDQG$%7LQFRPELQDWLRQZLWKULEDYLULQ ,QZHHNVDIWHUWKHWUHDWPHQWGLVFRQWLQXDWLRQ+&9 YLUHPLDZDVDEVHQWLQRISUHYLRXVO\QRQWUHDWHG SDWLHQWVLQIHFWHGZLWKJHQRW\SH,/%&&,Q WKH&23,/27VWXG\RQULEDYLULQDVDQDGGRQWR$%7 450 and ABT-333 ritonavir (non-nucleoside polymerase LQKLELWRUYLUHPLDZDVXQGHWHFWDEOHLQRYHUDQG  RI SUHYLRXVO\ QRQWUHDWHG DQG DQWLYLUDOWUHDWHG LQGLYLGXDOVUHVSHFWLYHO\LQZHHNVDIWHUWKHWKHUDS\ ZDV GLVFRQWLQXHG $OLVSRULYLU 'HELR  WKH KRVWV¶VF\FORSKLOLQLQKLELWRULVFXUUHQWO\WHVWHGLQSKDVH ,,,VWXGLHV5HVLVWDQFHWRDOLVSRULYLUFDQEHDWWULEXWHG to mutations in domain II of NS5A. Single mutations LQ16$FDQFDXVHRQO\QHJOLJLEOHUHVLVWDQFHRI+&9 to alisporivir, however, where multiple mutations are present in NS5A, significant resistance to all classes RIF\FORSKLOLQLQKLELWRUVFDQEHREVHUYHG2QWKHRWKHU hand, in consideration of the results of in vivo studies, DOLVLSURYLUFDQEHFRQVLGHUHGWRKDYHORZSRWHQWLDOWR LQGXFHYLUDOUHVLVWDQFH,QVKRUWWHUPVWXGLHV'HELR DVDQDGGRQWRULEDYLULQ16SURWHDVHLQKLELWRUV or nucleoside / non-nucleoside NS5B polymerase in- KLELWRUVZDVIRXQGWRKDYHDQDGGLWLYHHIIHFWLQLQKLELW-LQJ+&9UHSOLFDWLRQ'HELRDSSHDUVWREHDEOHWR GHOD\RUSUHYHQWUHVLVWDQFHWRSURWHDVHLQKLELWRUVDQGWR QXFOHRVLGHQRQQXFOHRVLGHSRO\PHUDVHLQKLELWRUV However, due to adverse effects and the development RIQHZF\FORSKLOLQLQKLELWRUVZRUNVRQWKLVGUXJZHUH discontinued.

CONCLUSIONS

HCV is present in multiple cellular compartments (apart from hepatocytes also in lymphocytes) , and WKHLVRODWHG+&9VWUDLQVH[KLELWVLJQLILFDQWGLIIHUHQFHV 7KHELRORJ\RI+&9GLIIHUVVLJQLILFDQWO\IURP WKDWRI+%9DQG+,9HVSHFLDOO\GXHWRWKHDEVHQFHRI reservoirs (HCV does not integrate with host’s genome and cannot produce episomal forms) which makes it SRVVLEOHWRHUDGLFDWHLWFRPSOHWHO\,WDSSHDUVWKDWVXF-FHVVIXOHUDGLFDWLRQFDQEHDFKLHYHGZLWKDFRPELQDWLRQ RIGUXJVWKDWHIIHFWLYHO\LQKLELWUHVLVWDQWPXWDQWVIRU several weeks or months. In consideration of the prog-ress in clinical studies on DAAs, an efficient treatment UHJLPHQZLOOEHKRSHIXOO\DYDLODEOHLQMXVWDIHZ\HDUV WLPH

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Anna Szymanek, Krzysztof Simon

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