This diagram illustrates what happens during successful therapy with a protease inhibitor combined with peginterferon and ribavirin. At baseline, the majority of the virions are wild-type (w) at the PI-active site although there is still variation among the wild-type viruses at other sites (different colour wild-type viruses). A small number of resistant variants (r) pre-exist. When treatment is started, the PI and Peg/RBV suppress the wild-type virus and the Peg/RBV suppress the PI-resistant virus. Provided that Peg/RBV work adequately, the viral level falls below the limit of detection and eventually goes below the threshold for cure – presumably meaning no virus left in the body and hence an SVR is achieved.
If 10 12 virions are produced every day and an error occurs every 10 5 nucleotides copied, with a genome of 9600 nucleotides, there will be about 0.1 errors per replication cycle or about 10% of the time. This means that the virus will reproduce itself ‘accurately’ about 91% of the time. When errors occur, the majority will be a single error in a given genome. Of the 9% with errors, 8.7% will have just one error. Because of the huge production rate of viruses, there will be 8.7x10 10 viruses with a single mutation made every day. Since there are only about 10 4 places for errors to occur, this means that every possible single mutant will be made every single day. If you apply the math similarly to double mutants (ie virions with any 2 individual mutations), you see that all double mutants are also made every single day. Once you get down to triple mutants, the number of combinations is enormous (~10 12 ) and therefore even with the huge rates of viral production, only a small percentage of triple mutants will be produced every day. The consequence of these calculations is that every single and double mutant is made everyday meaning that any variants that lead to resistance with a single or double mutant will exist before starting therapy. This may mean that a combination of at least 3 DAAs will be required to eliminate interferon from HCV treatment. Notably, a lead-in phase will lower the viral level before starting the PI and theoretically lower the risk of selecting for PI-resistant virus. However, unless there is a very significant (>3 log) decline in HCV RNA during the lead-in phase, the numbers in the graph above do not change appreciably and all possibly single and double mutants will still pre-exist at the time the PI is introduced.
In these 4 patients treated with telaprevir monotherapy, all 4 started out with predominantly wild-type HCV (purple). Despite a very effective drop in viral load with telaprevir treatment, telalprevir-resistant variants started to emerge very quickly. By the end of the 2 week dosing period, the wild-type virus had been entirely replaced by various telaprevir-resistant variants. Fortunately, as shown in patient 1, the PI-resistant variants are still effectively suppressed by peginterferon and ribavirin.
As shown in the previous slides, the response to Peg/RBV is critical to controlling the emergence of resistance associated variants (RAVS). In patients treated in the SPRINT-2 trial, those with a poor response to Peg/RBV during the lead-in phase (<1 log decline in HCV RNA) had a much greater chance of developing resistance to boceprevir. This concept extends to the treatment-experiences population and explains the difference in rates of resistance and response seen in different groups of treatment-experienced patients: prior null responders (the worst Peg/RBV responders) have a lower response rate and a much higher rate of PI resistance than relapsers (the best Peg/RBV responders) when treated with a PI plus Peg/RBV.
In the absence of drug (left panel), the wild-type (wt) virus is more fit than the PI-resistant (PI-R) virus and will be the dominant virus in the population with only a few PI-R viruses present (circles at the top). When PI treatment starts, wt virus is suppressed and it has a major loss in fitness. At this point, PI-R virus does not gain fitness per se, it just gains a fitness advantage over wt virus. In fact, as shown here, PI-R virus may be slightly less fit in the presence of a PI than in the absence of a PI because drug resistance is not an all or none phenomenon. Most drug-resistant variants are still partially sensitive to the drug. However, the PI-R virus does gain a significant advantage over wt virus in the presence of a PI and hence it will emerge as the dominant virus in the population (circle at the top). If the PI is continued despite the presence of a majority PI-R viral population, the PI-R virus will start to gain fitness. Just like wt virus, the PI-R virus continues to mutate over time. Just by random chance, some of the mutations that occur with time will enhance the growth of the PI-R virus. Such beneficial mutations are called compensatory mutations because they compensate for the fitness loss of the initial resistance mutation. Over time, with multiple compensatory mutations (shown as x’s in genome below graph) the fitness of the PI-R virus will improve – it will remain the dominant viral species (circle at the top) and the viral load will likely increase to close to baseline levels. Whether this more fit resistant virus will be more difficult to treat in the future is unknown.
The genetic barrier to resistance refers to the ‘difficulty’ for a given a virus to develop resistance to an antiviral. Although there are other factors, the major issue driving genetic barrier is the number of mutations necessary for resistance to occur. For PIs, this is an important issue. With Peg/RBV treatment, genotype 1 subtyping is not very important. However when PIs are added, the risk of resistance varies significantly between genotype 1a and b. For genotype 1a, only 1 nucleotide substitution is necessary to confer resistance to PIs. For genotype 1b, (the ‘ B ’ etter subtype), 2 substitutions are necessary. As a result, baseline resistance to PIs is detected frequently in patients with genotype 1a infection whereas it is not described in patients with genotype 1b infection. As shown in the figure, in patients treated with boceprevir/Peg/RBV who do not achieve SVR, RAVS (resistance associated variants) are detected with much greater frequency in those with genotype 1a than genotype 1b infection.
With drug discontinuation (right panel), the fitness of the WT virus will markedly improve, returning to pre-treatment levels. However, PI-R virus with compensatory mutations may actually be quite fit. This ‘improved’ PI-R virus will almost certainly still have reduced fitness compared to WT but it will likely be more fit than PI-R virus in scenario 1, prior to any drug exposure. The balance of WT to PI-R virus (circle on the top) will depend on how fit the PI-R virus becomes and therefore how well it competes with WT virus. Over time, even a small advantage for WT virus will lead it to become the dominant species but if the fitness difference is small, return to a predominant WT viral population may take a long time. To prevent compensatory mutations, it is critical to stop the PI (or any DAA) in the setting of established drug resistance.
Of 56 people with documented telaprevir-resistant HCV at the end of unsuccessful therapy, only 11% (6/56) had resistant virus as the dominant viral species 2 years after stopping telaprevir. On the surface this would appear to support the concept that resistance is not archived in HCV and after stopping treatment, resistant virus will revert back to wild-type virus. Although it is theoretically possible that this is true, it is important to pay close attention to the methods used in this (and most) studies. On the next slide the sequencing methods will be compared. The real test of whether resistant virus has truly disappeared will be retreatment of patients who had documented PI resistance with another or the same PI. To date there are no such reported data.
Detection of resistant virus is only as good as the sequencing method used to detect it. In the figure above, the threshold of detection of resistant virus is shown for 3 methods of sequencing. Population sequencing determines the most common sequence among the quasispecies in a viral population. In general, population sequencing has a sensitivity down to about 20% meaning that any viral quasispecies that represent less than 20% of the total viral population will go undetected. As shown in this example, if 19% of the virions in a given patient harboured a PI resistance mutation, using this methodology, sequencing would report wild-type virus for this individual. Given the very high viral loads, even a very low percentage of resistant variants represents a lot of resistant virus. Clonal sequencing involves sequencing of individual viral clones (individual virions) from an individual. This method is effective but very labour intensive and relatively costly. In general, the sensitivity of clonal sequencing to detect resistant virus is about 5%. Deep sequencing uses modern so-called ‘Next Gen’ sequencing approaches. Although the technique is extremely powerful, the sensitivity of this method is limited by the need to convert the RNA into cDNA using reverse transcription, which has an intrinsic error rate. As a result, the sensitivity of this method is 0.5-1%. It is also extremely costly and generates a huge amount of data, which requires specialized expertise for analysis. If we now go back to the Extend data from the last slide, the results are less compelling. The data show that 11% of the patients had at least 20% resistant virus because resistance was detected using population sequencing. This is despite the fact that patients were off telaprevir for 2 years. In the other patients, although population sequencing showed them to be ‘wild-type’, they could have had up to 20% resistance virus with the methods used in the study. Ultimately we will only know whether resistance reverts to wild-type when we retreat patients. Unfortunately with population sequencing, the only practical way to sequencing on a large scale, we are just seeing the tip of the quasispecies iceberg.
Some measures can be taken to reduce the likelihood of emergence of resistance. Sub-optimal drug levels increase the risk of resistance. PIs must be taken every 8 hours (window of 7-9 hours), which is difficult, particularly given the need for twice daily ribavirin. Compliance will be a major issue for patients and must be stressed and monitored to reduce the risk of resistance. The pre-existing PI-resistant virus is suppressed by Peg/RBV. The probability of resistance is much higher in patients with poor Peg/RBV responses. Any strategies to improve Peg/RBV responsiveness will lower the chance of resistance. Such strategies include: weight loss, adequate dosing (especially ribavirin), compliance and possibly novel approaches such as vitamin D, coffee or SAMe supplementation. Because the Peg/RBV is a critical determinant of the risk of resistance, in patients with features predicting a poor Peg/RBV response, treatment with a PI should be carefully considered. Certainly patients with advanced liver disease need therapy, however patients with minimal or no fibrosis may not need therapy urgently. For such patients, it may be worthwhile to try to optimize factors associated with Peg/RBV responsiveness (eg. obesity, insulin resistance) or consider waiting for combination therapy. If patients develop resistance, it is very important to stop the PI promptly to avoid the development of compensatory mutations which will improve the fitness of PI-resistant virus, which will allow the resistant virus to persist even once the PI is stopped. The stopping rules outlined in the product monographs were developed to avoid continued exposure to the PI once resistance is likely present. The stopping rules should be followed.
Fortunately DAAs of different classes do not have overlapping resistance profiles meaning that resistance to one class (eg PIs) does not confer resistance to another class (eg polymerase inhibitors). However, within some classes, particularly PIs, there is intra-class cross resistance. Virus resistant to telaprevir will be resistant to boceprevir and vice versa. There is some overlap of resistance profiles between first and second generation PIs.
Palestra Novos Conceitos na Terapia com Inibidores de Protease - Dr. Jordan Feld
Protease Inhibitors for HCV: The devil is in the details Jordan J Feld MD MPH Assistant Professor of Medicine Toronto Western Hospital McLaughlin-Rotman Centre for Global Health
Disclosures – Dr. J. Feld <ul><li>Dr. Feld has the following financial disclosures relevant to this presentation: </li></ul><ul><ul><li>Abbott Laboratories – consulting </li></ul></ul><ul><ul><li>Merck (MSD) – consulting </li></ul></ul><ul><ul><li>Roche Pharmaceuticals – consulting </li></ul></ul><ul><ul><li>Vertex Pharmaceuticals – consulting </li></ul></ul><ul><li>Dr. Feld will be discussing the off-label use of boceprevir </li></ul>
Outline <ul><li>How will the drugs be used? </li></ul><ul><ul><li>Response-guided therapy </li></ul></ul><ul><ul><li>Lead-in vs no lead-in </li></ul></ul><ul><li>Resistance </li></ul><ul><ul><li>Does it matter? </li></ul></ul><ul><ul><li>Can it be prevented/minimized? </li></ul></ul><ul><li>IL28B </li></ul><ul><ul><li>Still important with DAAs? </li></ul></ul><ul><li>Adverse events </li></ul><ul><ul><li>Management strategies </li></ul></ul><ul><li>Drug-Drug Interactions </li></ul><ul><ul><li>Key drugs and where to find the rest… </li></ul></ul>
The Good News 0% 20% 40% 60% 80% 100% IFN IFN IFN/R IFN/R PegIFN PegIFN/R Sustained Response 16% 55% 6% 34% 42% 39% 6 mo 12 mo 6 mo 12 mo 12 mo 1991 1995 1998 2002 2001 Ribavirin Peginterferon Standard Interferon 12 mo 6-12 mo 75% 2010 DAA PegIFN/R/DAA
Advantages of RGT <ul><li>Allows shortening therapy </li></ul><ul><ul><li>44-65% of naïve pts </li></ul></ul><ul><ul><li>46% of trt-experienced pts (36 wks) </li></ul></ul><ul><li>Reduced exposure to PI </li></ul><ul><ul><li>Even those who do not have RVR8, stop BOC at wk 28 (continue only Peg/RBV to wk 48) </li></ul></ul>0 4 8 28 48 72 Wks Follow-up PR alone Peg2b/R + Boceprevir 800mg q8h PR lead-in BOC RGT
RGT Allows for Shortening of Therapy 59/ 82 155/ 161 156/ 162 55/ 73 Poordad et al NEJM 2011 44% RVR8 28 wk of trt No consequence to shorter BOC
RGT works in treatment- experienced as well SVR (%) 64 74 7 7 74 84 BOC RGT BOC/PR48 PR48 29 72 8 65 30 70 Bacon et al NEJM 2011
RGT Summary <ul><li>Generally useful paradigm </li></ul><ul><li>Allows for shortened therapy in naïve and experienced patients </li></ul><ul><li>Reduces exposure to PI </li></ul><ul><ul><li>Reduced toxicity & cost </li></ul></ul><ul><ul><li>Hb/WBC rebound when BOC is stopped </li></ul></ul><ul><li>Requires more frequent HCV RNA testing </li></ul><ul><li>May be less advisable in harder to treat pop’n </li></ul><ul><ul><li>Black patients </li></ul></ul><ul><ul><li>Advanced fibrosis </li></ul></ul>
SPRINT1: Benefit to lead-in 38 P/R Control 48 wks P/R 4 wks P/R/B 24 wks N=104 Lead-in Lead-in Kwo et al Lancet 2010 Appeared to modest efficacy advantage to lead-in % SVR 0 10 20 30 40 50 60 70 80 54 56 P/R/B 28 wks N=107 N=103 67 P/R/B 48 wks P/R 4 wks P/R/B 44 wks 75 N=103 N=103
The Theory w r w w w w w w w w w w w w w w w w w w w w w w w w w w w w w w w w r r r w w w w w w w w w w w w w LLD 0 virions per body Treatment Duration Start End w = wild-type virus r = PI resistant virus Peg/RBV/PI w w Peg/RBV Lower viral load before starting PI = less resistance
Let ’s do the math… Therefore… Average number of changes/genome = 0.096/replication cycle Conclusion: ALL single and ALL double mutants are produced everyday. Resistance associated variants (RAVS) all pre-exist. Unless 2-3 log drop in lead-in, no difference to resistance Rong et al Sci Transl Med 2010 # of nt changes Probability # of virions/d # of all possible mutants % of all possible mutants/d 0 0.91 9.1 x 10 11 1 0.087 8.7 x 10 10 2.9 x 10 4 100 2 0.0042 4.2 x 10 9 4.1 x 10 8 100 3 0.00013 1.3 x 10 8 1.0 x 10 12 3.4x10 -3
Other advantages of the lead-in <ul><li>Determination of tolerance and compliance with Peg/RBV </li></ul><ul><li>Allow Peg/RBV to reach steady-state – avoid PI mono/dual therapy </li></ul><ul><li>Identify source of adverse event (eg. anemia) </li></ul><ul><li>Prognostic information </li></ul><ul><ul><li>Very helpful in cases where treatment value is unclear </li></ul></ul><ul><li>Accurate assessment of IFN-responsiveness </li></ul><ul><ul><li>Strongest predictor of SVR </li></ul></ul><ul><ul><li>Important for treatment-experienced patients </li></ul></ul>
Real-Time Interferon response for trt-experienced Respond 2 26% null response despite at least partial historical response Esteban EASL 2011 % of Patients With Week 4 Response Historical Response Week 4 Response 10 10 56 140 84 140 46 253 207 253
Summary Lead-in <ul><li>Very useful prognostic information from lead-in, ie. IFN-response </li></ul><ul><ul><li>May even change your decision to treat </li></ul></ul><ul><ul><li>eg. Previous relapser with <1 log drop in lead-in and mild fibrosis…may wait for future therapy </li></ul></ul><ul><li>Useful to determine compliance/tolerance </li></ul><ul><li>Value to starting Peg/RBV separately </li></ul><ul><li>Probably little effect on risk of resistance </li></ul>
Resistance… Are we doomed? If PI resistant virus pre-exists, why do PIs work at all?
Resistance: A new issue in HCV Multi-pronged attack No IFN resistance Effective against PI-resistant HCV Potent but uniform attack Rapid DAA resistance IFN Receptor IFN ISGs Jak- STAT DAA
IFN response predicts resistance 0 100 50 25 75 4% 6% 52% 40% Boceprevir Resistance % RGT BOC48 RGT BOC48 >1 log decline during lead-in <1 log decline during lead-in SPRINT 2 Poordad et al NEJM 2011 Maximize Peg/RBV Response: - Obesity - Insulin resistance - Vit D - Coffee
Factors Limiting Growth of Resistant Mutants <ul><li>Fitness </li></ul><ul><li>Genetic barrier </li></ul><ul><li>Antiviral potency </li></ul><ul><li>Degree of resistance </li></ul>
Fitness is a moving target: Compensatory mutations Fitness No Drug PI Treatment Continued PI Treatment despite resistance WT PI-R WT PI-R WT PI-R x x x x x x x PI-resistant virus will become more fit over time if the PI is continued Therefore: Stop the PI as soon as resistance emerges Composition of viral pop’n
Genetic Barrier: Not all HCV Genotype 1 is created equal <ul><li>Genetic Barrier refers to the ‘difficulty’ for a given virus to develop resistance to an antiviral </li></ul><ul><ul><li>Number of mutations necessary for resistance </li></ul></ul><ul><li>For PIs – genetic barrier differs by subtype – 1a vs 1b </li></ul><ul><li> G1a R155K = 1 nt change AGG A A G </li></ul><ul><li> G1b R155K = 2 nt changes CGG AA G </li></ul>Brass EASL 2011 B for Bom
Does resistance disappear? <ul><li>Answer to this question determined by: </li></ul><ul><li>Archiving of resistance </li></ul><ul><ul><li>Persistence of resistant virus after drug discontinuation </li></ul></ul><ul><li>Fitness of resistant virus </li></ul>
HCV has no reservoir for archiving HCV Pol x x RT CD4+ x x x HIV x HBV RT x x x cccDNA x pgRNA
What happens if treatment stops? Fitness No Drug PI Treatment Continued PI Treatment despite resistance WT PI-R WT PI-R WT PI-R x x x x x x x PI-resistant virus may persist even after drug withdrawal if fitness has improved significantly with compensatory mutations during treatment Composition of viral pop’n WT PI-R x x x x x ? Drug discontinuation
What happens in patients? <ul><li> EXTEND trial </li></ul><ul><li>Long-term f/u of Telaprevir-treated pts </li></ul><ul><li>79 non-SVRs </li></ul><ul><ul><li>56 with TVR-resistant mutants at EoT </li></ul></ul><ul><ul><li>Median 25 mo f/u </li></ul></ul><ul><ul><li>NS3 by population sequencing (~20%) </li></ul></ul><ul><li>No longer detectable in 50/56 (89%) </li></ul>Does this really mean the resistance is gone? Probably NOT!!! Zeuzem et al AASLD 2010
Population sequencing: Tip of the iceberg Even if undetectable by population sequencing…may be lots of resistant virus 0 1 5 20 40 60 80 100 - - - - - - - Population Sequencing Clonal Sequencing Deep Sequencing % threshold for detecting resistant virus Wild-type virus Resistant virus
Prevention of Resistance <ul><li>Compliance, compliance, compliance – more important than with Peg/RBV </li></ul><ul><li>Maximize Peg/RBV response </li></ul><ul><li>Carefully consider need for treatment in patients with poor Peg/RBV response – especially if mild liver disease </li></ul><ul><ul><li>Prior null responders </li></ul></ul><ul><ul><li>Patients with poor prognostic features (non-CC, black race, obese etc.) </li></ul></ul><ul><li>Follow stopping rules and stop promptly if signs of resistance to prevent compensatory mutations </li></ul>
No Inter-Class Cross Resistance PI= ‘Intra’ Class Pol= no ‘Intra’ Class
Summary <ul><li>Resistance to PIs (and all DAAs) pre-exists in all </li></ul><ul><li>Risk factors for resistance : Poor IFN response, gt 1a </li></ul><ul><li>Resistant variants are less fit than wild-type but gain fitness with exposure to PI through compensatory mutations stop PI if resistance present </li></ul><ul><li>Resistance will persist for some time after stopping PI detection limited with population sequencing </li></ul><ul><li>Resistance can be overcome with combination therapy – either PI + Peg/RBV or DAA combinations </li></ul><ul><li>PI resistance may affect future therapy so consider need for therapy and optimize treatment to prevent resistance </li></ul>
IFN-Lambda Mania IL28b SNP associated with SVR & spontaneous clearance
Does IL28B help with PIs? SVR (%) Jacobson et al EASL 2011 IL28B tested in 454 (42%) of ADVANCE T12PR T8PR PR 48 CC CT TT TVR helps all IL28B genotypes ? T12 more important in non-CC 20/ 80 45/ 50 39/ 45 35/ 55 48/ 68 44/ 76 16/ 22 19/ 32 6/ 26
What about IL28B and BOC? SVR (%) Poordad et al EASL 2011 IL28B tested in 653 (62%) SPRINT-2 CC CT TT BOC helps only non-CCs…BUT 33/ 116 BOC/PR RGT BOC/PR 48 PR 48 63/ 77 44/ 55 50/ 64 67/ 103 82/ 115 23/ 42 26/ 44 10/ 37
SVR Among CC ’ s TVR vs BOC SVR (%) Comparison of CC only T12PR T8PR PR PR BOC PR48 BOC RGT <ul><li>PIs improve SVR in non-CC ’s </li></ul><ul><li>CC ’s less clear - ?shorten therapy </li></ul>TVR BOC 50/ 64 35/ 55
IL28B in Trt-Experienced SVR (%) Pol et al EASL 2011 IL28B tested in 527 (80%) of REALIZE CC CT TT Rel Partial Null Rel Partial Null T12PR48 PR48 Prior response trumps IL28B
Summary IL28B <ul><li>PIs still improve outcome in all IL28B genotypes </li></ul><ul><li>Benefit greatest in non-CCs </li></ul><ul><li>CCs do well without PI </li></ul><ul><ul><li>Consider shorter therapy for CCs with PI </li></ul></ul><ul><li>Response trumps IL28B </li></ul><ul><ul><li>Naïve – if RVR, do well if CC/non-CC + vice versa </li></ul></ul><ul><ul><li>Experienced – IL28B of limited utility </li></ul></ul><ul><ul><ul><ul><ul><li>- May combine with other factors to predict </li></ul></ul></ul></ul></ul>
Boceprevir Poordad et al NEJM 2011 <ul><li>Anemia </li></ul><ul><li>Dysgeusia </li></ul>
Anemia <ul><li>Anemia associated with SVR </li></ul><ul><li>Managed with EPO/RBV dose reductions </li></ul><ul><li>Cannot reduce BOC dose </li></ul>
Summary AEs <ul><li>More manageable with experience </li></ul><ul><li>Anemia – managed with EPO or RBV dose </li></ul><ul><ul><li>Rarely leads to discontinuation </li></ul></ul><ul><li>Dysgeusia – annoying but tolerable </li></ul>
Drug-Drug Interactions Put your pharmacist’s number on speed-dial! Farmacia 1 800 AJUDE-ME
PI Metabolism CYP3A4 PI Metabolites <ul><li>BOC & TVR are both substrates & inhibitors of CYP3A4 & P-gp </li></ul><ul><li>CYP3A4 – metabolizes many common drugs </li></ul><ul><li>P-gp – common pathway for drug elimination </li></ul>Drugs cleared by CYP3A4/P-gp Increased drug conc Drugs that induce CYP3A4/P-gp Decrease PI conc
A few important ones <ul><li>Seizure meds – contraindicated </li></ul><ul><li>Midazolam – 5x increase exposure to drug!! </li></ul><ul><li>Oral contraceptive – unreliable levels – need another method </li></ul><ul><li>HAART – variable but MANY interactions </li></ul><ul><li>CsA/Tacrolimus – marked increase exposure </li></ul><ul><li>Sildenafil – sorry gents…contraindicated! </li></ul><ul><li>Useful resources: </li></ul><ul><li>http://www.hep-druginteractions.org/ </li></ul><ul><li>http://medicine.iupui.edu/clinpharm/ddis/ </li></ul>
Final Summary <ul><li>RGT useful for most patients </li></ul><ul><ul><li>Consider longer therapy in Blacks, Advanced fibrosis </li></ul></ul><ul><li>Lead-in useful </li></ul><ul><ul><li>Compliance, tolerance of IFN/RBV, IFN response </li></ul></ul><ul><li>Resistance pre-exists </li></ul><ul><ul><li>More common 1a than 1b </li></ul></ul><ul><ul><li>Risk related to IFN responsiveness </li></ul></ul><ul><ul><li>Unknown if persists but stop PI once resistance present </li></ul></ul><ul><li>IL28B useful but response more useful </li></ul><ul><ul><li>May consider shortening therapy in CCs – stay tuned… </li></ul></ul><ul><li>Drug Interactions – a big issue, check all drugs!! </li></ul>