 |
|
|
| |
Report from International Workshop on HIV & Hepatitis Virus Drug Resistance 2nd Report, June 5-9 2012 Sitges, Spain
|
| |
| |
Written for NATAP by Mark A. Wainberg, PhD, McGill University AIDS Centre, Jewish General Hospital, Montreal, Canada
Clinical relevance of HIV drug resistance
In Abstract 24, KJ Metzner and colleagues asked the question as to whether minority drug resistant HIV variants might be sexually transmitted. In order to carry out this research, the team performed ultra-deep sequencing on plasma samples collected during primary infection from individuals who participated in the Zurich primary HIV infection cohort. They demonstrated that a number of mutations such as M184V, Y181C, K103N, and N155H were present in varying percentages of individuals ranging from 8.3% for M184V to 0.5% for N155H. Furthermore, they subjected the viruses that they had sequenced to phylogenetic analysis and were able to show that many of the individuals containing these mutations appeared to be members of transmission clusters based on commonality of sequences throughout the viral genome. They conclude that minority viral species can indeed be transmitted among individuals, although the full clinical relevance of this observation is not apparent in regard to subsequent responsiveness to therapy.
In Abstract 25, MA Papathanasopoulos and colleagues tried to determine whether or not the transmission of drug resistant minority variants might be associated with treatment failure in previously treatment naïve individuals. They performed sequencing of the reverse transcriptase and protease regions of HIV-1 and then followed patients who were found to possess minority drug resistant variants over times following treatment initiation. The results showed that minority viral variants were not associated with treatment outcome in the case of women who received antiretroviral drugs as part of strategies to prevent maternal to offspring transmission of HIV-1. In contrast, however, the presence of drug resistance minority variants in treated individuals was associated with virological failure in a significant proportion of cases. The mutations transmitted included K65R, K103N, and V106M, and, in this study, a total of 52 failures were observed among 528 baseline samples that included 350 drug naïve patients. This study thus documents treatment failure in a relatively high proportion of individuals who acquired viral variants containing drug resistance mutations as a majority infected species prior to initiation of antiretroviral drugs.
Abstract 26 by JZ Li and colleagues was on a similar theme that speaks to the controversy in regard to the significance of low level viremia and the chances of virologic failure in HIV infected individuals. In this study, low level viremia was defined as a viral load <1000 copies viral RNA/ml of plasma. The study showed that a significant proportion of individuals who had low level viremia on at least two occasions over a median period of 11 months were more likely to develop additional mutations associated with HIV drug resistance than people in whom low level viremia was not detected. Thus, the performance of resistance testing was found to be important in regard to ultimate treatment success in these individuals with low level viremia, since such genotyping was found to be important in regard to patient follow-up and the timely prescription of appropriate antiretroviral drugs. The authors concluded that strategies for early intervention in patients with low level viremia need to be further developed in order to deal with this matter.
In Abstract 27 V. Van Eygen and colleagues presented an analysis of baseline samples from patients who were treated with rilpivirine in the ECHO and THRIVE clinical trials. These authors performed ultrasensitive sequencing analysis and showed that there was no association between the presence of minority viral variants at baseline and ultimate virologic failure. The purpose of this study was to determine whether some of the patients who went on to develop the E138K and M184I mutations in reverse transcriptase might have possessed minority variants at baseline that were ultimately responsible for treatment failure. The results of this study suggest that this was not the case. These authors further found that among the drug resistance mutations responsible for failure in the ECHO and THRIVE trials that the 101E and E138K mutations were rarely found simultaneously on the same viral genome. In all likelihood, the simultaneous presence of these two mutations may severely compromise viral replication capacity. These investigators also demonstrated that the M184I mutation developed prior to the E138K mutation among subjects who ultimately went on to develop both of these substitutions in the context of virologic failures in the ECHO and THRIVE clinical trials.
In Abstract 28 by L. Rimsky and colleagues also analysed the potential reasons for virologic failure in the context of the ECHO and THRIVE clinical trials that led to the approval of rilpivirine as an antiretroviral drug. The purpose of this investigation was to assess whether connection domain mutations in reverse transcriptase might have been associated with virologic failure and/or phenotypic resistance. Accordingly, the connection domain was extensively sequenced and the results indicate that a number of viral variants did indeed possess some connection domain mutations. However, the distribution of such substitutions was comparable among patients undergoing virologic failure vs those who had excellent treatment responses. Thus, although the prevalence of connection domain mutations ranged between 0-23% of individuals analyzed, the presence of such mutations does not seem to influence ultimate treatment responsiveness.
In Abstract 29, P. Liegler and colleagues investigated the extent to which drug resistance might have occurred among HIV seroconverters in the FEM-PrEP study. This was a randomized trial in which the use of co-formulated FTC/TFV was used to attempt to protect against HIV infection. Unfortunately, the study was stopped short of its intended completion time because an interim analysis failed to document that the drug combination had succeeded in preventing new HIV infections. This finding was attributed to low levels of adherence among people who participated in the trial. At the same time, however, the investigative team was interested in determining whether or not the use of FTC/TFV in subjects who became infected while receiving these drugs might have led to drug resistance in view of the fact that these individuals had been receiving sub-optimal therapeutic combinations of drugs while infected. The results documented that levels of resistance associated with FTC were rare but did occur in certain cases, whereas no individual apparently developed the K65R mutation, associated with resistance against TFV, during the period of follow-up of over 52 weeks.
Abstract 30 by G. Hunt and colleagues was on the topic of drug resistance among children born to mother who received antiretroviral drugs for prevention of mother-to-child transmission in South Africa. A number of mutations, mostly associated with NNRTIs, were detected and these included Y181C, K103N, and G190A/F. In total, one-third of the children studied possessed drug resistance mutations in viruses sequenced from their plasma. This is a disconcerting finding in light of the widespread use of antiretroviral drugs in South Africa and the need to prevent new infections through strategies such as PMTCT.
Hepatitis B virus drug resistance
A plenary lecture was given by Professor M. Levrero on the topic of whether eradication of HBV might be possible in infected individuals. A major problem in this regard is the pool of cccDNA that persists over long periods regardless of the use of anti HBV chemotherapy. The issue is that cccDNA exists as a minichromosome within infected cells and that current knowledge does not permit the eradication of this DNA in most cases. Accordingly, drug resistance mutations can be archived and complete eradication of HBV remains problematic in spite of the availability of anti-HBV drugs and improved clinical success.
In Abstract 13, V. Svicher and colleagues tried to determine whether certain mutations within the HBV surface(S) antigen open reading frame might be involved in the development of hepatocellular carcinoma. Accordingly, sequencing of the S gene was carried out and a number of mutations identified. Although some of these mutations could be correlated with the later occurrence of hepatocellular carcinoma, it is still not understood whether any causative role may be attributed to their presence or whether such mutations may merely serve as markers of ultimate carcinogenesis.
Abstract 14 by N Warner et al was on the topic of whether anti-HBV drugs can select for variants that might possess increased pathogenicity. These investigators showed that some HBV variants selected during therapy seem to be more pathogenic than parental viruses and that they can directly contribute to apoptosis. More follow-up of the role of these mutations and possible promotion of more virulent variants of HBV are needed.
In Abstract 15, GM Foster and colleagues wished to understand the extent to which resistance against HBV drugs might be able to promote transmission of drug-resistant HBV variants. To date, most drug resistant samples evaluated have shown dimimished sensitivity to lamivudine. Although no evidence of transmission of drug resistant variants could be documented in this study, further follow-up is necessary, also because drug resistance against tenofovir (TFV) has yet to be documented in a general sense as well as in the case of the samples that were analysed. To this day, many physicians continue to prescribe tenofovir monotherapy for treatment of HBV disease. Although this might be counter-intuitive, and it might indeed be preferable to use combination FTC/TFV to treat HBV infected individuals, the fact remains that resistance against TFV in the aftermath of monotherapy with this drug for treatment of HBV is extremely rare.
Hepatitis C virus drug resistance
A plenary lecture was delivered by Professor C. Sarrazin on strategies to eradicate HCV infections. There are now a number of direct antiviral agents that have shown success in the clinic and there is hope that eradication of HCV might become a reality for most infected individuals within the next decade. Although only two anti-HCV drugs are currently approved for treatment, i.e. telepravir and bocepravir, it is likely that at least eight other drugs will gain approval from various regulatory agencies during the next several years. These new drugs will add to the armamentarium of compounds used in the treatment of HCV and will hopefully, when used in combination, lead to eradication in a high proportion of cases. This is possible because HCV does not become integrated into the host viral genome and hence does not exist in the form of reservoirs as is the case for HIV and HBV.
This notwithstanding, drug resistance has been documented against virtually all members of the protease inhibitor and polymerase inhibitor categories of anti-HCV drugs. Furthermore, cross resistance has been documented in a high proportion of cases among similar types of anti-HCV compounds that share the same target. A very interesting finding that has emerged from clinical trials is that the use of ribavirin helps to forestall treatment failure and the development of resistance against the directly anti-HCV drugs that are used in therapy. Accordingly, it is likely that ribavirin will continue to be used in treatment over a considerable period of time, although another drug that is currently in common use in treatment of HCV, i.e. pegylated interferon, may be more likely to disappear from use in combination therapy.
Considerable progress continues to be made in regard to development of novel anti-HCV compounds and Abstract 16 by M. Fourar and colleagues was on the topic of the NS5B RNA polymerase as a target of HCV drug development. The authors documented that a series of novel peptides can block HCV RNA dependent RNA polymerase activity. It is hoped that these peptides will be able to be developed for clinical use.
Abstract 18 by S. Franco et al was on the interesting topic of transmission of drug resistant variants of HBV. These investigators analyzed for the presence of a NS5B mutation at position S282T by allele-specific PCR. They have documented the sensitivity of this assay for specific detection of mutations at position S282T and have further shown that this mutation can be detected in 44% of patients but at extremely low levels. These findings document that S282T can be transmitted and sets the stage for a broader analysis of the presence of minority viral variants associated with HCV drug resistance that may be transmitted among individuals. It is unlikely that S282T pre-exists because of considerations of high genetic barrier for resistance, ie it is a G to C transversion, and lower fitness than wild-type virus.
In Abstract 19, RJ Barnard and colleagues studied the potential occurrence of HCV drug resistance against a novel HCV protease inhibitor termed MK-5172. They showed that no viral rebound was observed in treated individuals but that selection of resistance did occur in five patients. However, the viruses that contained mutations associated with drug resistance were not fit. Further studies will be necessary to further clarify the extent to which drug resistance is likely to develop against this novel and highly effective inhibitor of HCV protease activity.
O. Lenz and colleagues in Abstract 20 reported on resistance against TMC435 in the context of the PILLAR and ASPIRE phase IIB clinical trials. TMC435 is an investigational once daily NS3/4A protease inhibitor that has yielded sustainable virologic response in a high proportion of cases. The results show that the development of resistance against this agent was relatively rare but that patterns of drug resistance may differ between genotypes 1a and 1b. This study is important because the PILLAR trial was conducted among drug-naïve individuals whereas ASPIRE was performed among patients who had previously been treated with various anti-HCV drugs. The fact that similar results were obtained in both of these studies indicates that drug resistance against TMC435 is unlikely to be significantly different in the context of drug- experienced vs drug-naïve individuals.
In Abstract 23, R. Russell et al reported on a novel method to quantify genetic barriers for the development of drug resistance in HCV. They began work with a R251W virus that was mutated in the NS5B region and carried out sequence analyses on spontaneous revertants. The results showed that the generation of transitions took place more often than that of transversions in a system that minimizes the effects of viral fitness and levels of drug resistance. This work is important and may also have applicability to other viral systems.
|
| |
|
|
|
|
|
