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  HCV superstars spotlight viral load testing

 

CAP Today

 

 

 

June 2011
Feature Story

Anne Paxton

The Food and Drug Administration clears about 23 new drugs per year for use in the U.S., but few of those drugs have the dramatic therapeutic potential of Victrelis (boceprevir) and Incivek (telaprevir). These two protease inhibitors—developed, respectively, by Merck & Co. and Vertex Pharmaceuticals and approved by the FDA in May—are true game changers. They promise to transform the treatment of hepatitis C, the most common chronic bloodborne viral infection in the U.S., experts say.

In clinical studies, boceprevir and telaprevir, known as direct-acting antiviral therapies (DAAs), proved to be startlingly effective at curing many hepatitis C patients when used in combination with the current standard of care, a regimen of peginterferon and ribavirin. The DAAs work by blocking a key enzyme that the hepatitis C virus needs to replicate and spread. When the drugs start being used to treat some of America’s roughly 3.2 million chronic hepatitis C patients, “For the first time in 20 years, we’ll be able to cure more hepatitis C patients than we’re not curing,” says Mitchell L. Shiffman, MD, medical director of the Liver Institute of Virginia, Bon Secours Virginia Health System, Newport News.

The new DAAs could have a strong impact on clinical laboratories if they bring more intense usage of viral load testing and other molecular diagnostics. “You can almost double the response rate with these drugs,” says Rick L. Pesano, MD, PhD, medical director, infectious diseases at Quest Diagnostics. “That’s phenomenal, and it’s going to push diagnostics into making advances in understanding how to monitor the effectiveness of these drugs and why they’re sometimes not effective.” In addition, he points out, testing technologies may allow clinicians to decide whether some patients may be able to get away with less therapy with just as high a success rate, based on their biological response rates.

Shortly before the FDA’s announcement that it had approved the two new DAAs, the New England Journal of Medicine published two studies of boceprevir. One concluded that the “triple therapy” of boceprevir plus the standard therapy, peginterferon-ribavirin, significantly increased rates of sustained virologic response in previously untreated adults with chronic HCV genotype 1 infection (Poordad F, et al. N Engl J Med. 2011; 364:1195–1206). The second study drew a similar conclusion about previously treated patients (Bacon BR, et al., 1207–1217).

For hepatitis C patients who’ve never been treated, the studies showed that the triple therapy brought about a 30 percent increase in the number of cures, says David R. Hillyard, MD, medical director, Department of Molecular Pathology, ARUP Laboratories, Salt Lake City. “If you look at patients who failed therapy, it’s even more dramatic. Without protease inhibitors, re-treated patients are only cured 20 percent of the time. The new trials show success rates of 60 to 65 percent.” According to the FDA, telaprevir has also shown a high cure rate. In clinical studies, 79 percent of patients taking telaprevir experienced a sustained virologic response, with the infection no longer detectable 24 weeks after treatment is stopped.

“These drugs are remarkably effective. The clinical trials for both drugs were very impressive, and there’s no question they are going to revolutionize therapy,” says Angela Caliendo, MD, PhD, director of Emory Medical Laboratories, Emory University Hospital, Atlanta, and a member of the CAP Microbiology Resource Committee.

About 70 to 75 percent of people infected with HCV in the U.S. are infected with genotype 1, but that is the most difficult HCV genotype to treat, says D. Robert Dufour, MD, emeritus professor of pathology at George Washington University Medical Center and consultant, pathology and hepatology, Veterans Affairs Medical Center, Washington, DC. “So now you have a drug which is really sort of custom-designed; it hones in on this very, very large population of patients that are hard to treat to begin with.”

“In clinical trials, the response rate with interferon and ribavirin was about 40 to 45 percent. But in fact most people practicing get response rates around 30 percent.” The reason: Clinical trials are selective in whom they take. “In clinical practice you don’t have that luxury.”

Protease is an enzyme produced by hepatitis C, Dr. Dufour explains. “The problem is that’s a region of the virus that has a lot of mutations in it, so there’s some very limited evidence that these drugs may not work so well in genotypes 2 and 3. However, other therapies already do work—about 60 to 70 percent of the time for genotype 3 and about 75 percent for genotype 2.”

For a number of reasons, only about 10 or 15 percent of people with HCV have ever been treated, Dr. Dufour estimates. First, only a fraction of the people who are infected even know they have hepatitis C, though it can progress to cause cirrhosis or liver cancer. In addition, patients are often wary of the well-known side effects of treatment. The Veterans Affairs hospital, where he has worked most of his career, tends to have a lot more patients with hepatitis C than in the general population, probably because a higher percentage of veterans who seek care in the VA are people with histories of substance abuse and mental health issues. “I work one afternoon a week in a clinic seeing patients with liver disease, and a fair number of them have heard about side effects. Some people don’t want to have to deal with them, and they don’t feel bad, so they don’t see why they should need to do treatment.” As a result, “By the time we see them, most people with hepatitis C will have probably been infected for a number of years,” Dr. Dufour says.

In fact, the side effects of standard hepatitis C treatment—anemia, nausea, flu-like symptoms—can be so unpleasant that, as one recent study showed, dropouts are common. Says Dr. Hillyard: “It has been estimated that only about 60 percent of patients actually complete treatment due to side effects and other factors.”

One of interferon’s major side effects is a worsening of depression, so that’s one contraindication to treatment. Since it’s an immune stimulus drug, Dr. Dufour explains, it can trigger or worsen autoimmune diseases or hypothyroidism, and can lower white cell and platelet levels. “We have drugs to control that in many patients, and in some cases if you just reduce the treatment for a while, that can allow the patient’s bone marrow to recover enough to resume treatment.”

Ribavirin, for its part, is toxic to red blood cells and can cause severe anemia, which can necessitate stopping or reducing treatment. “That can help. But the more you reduce the treatment, the more likely the patient isn’t going to respond. It’s a trade-off that we have to deal with,” Dr. Dufour says.

Dr. Shiffman hopes that the much higher cure rate now possible with the DAAs will bring people who have known they had hepatitis C for many years off the sidelines and into treatment, despite the drugs’ side effects. “In the past the nonresponders were the majority,” Dr. Shiffman says. “That’s the minority of patients now.”

The history of hepatitis C therapy is relatively short. Only since the late 1990s has there been any treatment for the infection. Interferon monotherapy came first, and it had low response rates, about 10 to 15 percent. “Then it was realized if interferon was combined with a drug called ribavirin that the therapy was much more effective,” Dr. Hillyard says. The next stage was pegylating interferon (attaching the molecule polyethylene glycol) to create peginterferon, which allows a more steady concentration in the blood, less frequent dosages, and higher response rates. Peginterferon combined with ribavirin has been the standard therapy for the past five years; “it’s driven development of all the treatment algorithms and has been studied extensively in clinical trials.”

Alongside those studies, researchers have sought to understand how viral load testing can be used to evaluate patients on therapy. “Quantitation of the virus offers several insights into the patient’s clinical course. An important discovery was that patients who did not respond early in treatment were unlikely to have a sustained viral response,” Dr. Hillyard says. This led to the development of “stopping algorithms”—sparing patients unlikely to respond from an arduous course of therapy. “Conversely,” he says, “patients who responded most rapidly had the highest probability of therapeutic cure.” Analysis of the kinetics of response provided by viral load testing has been a cornerstone of all subsequent therapeutic trials, including the new protease inhibitor studies, Dr. Hillyard notes.

The author of the New England Journal of Medicine editorial that accompanied the two boceprevir studies in the March 31 issue suggests that as treatment algorithms evolve, hepatitis C therapy will become “more complex, not simpler.” But, says Dr. Caliendo, “I don’t see that as necessarily complicated. I grew up in the HIV world where regular monitoring of people is the standard of practice.” A definite advantage of more frequent monitoring is that it will spare more patients from drug regimens from which they are unlikely to benefit. “Some people are going to have a shorter duration of therapy,” she says.

Even in the early days of hepatitis C treatment, she says, “We came to appreciate one of the first great steps in monitoring. It was the realization that if there wasn’t at least a 2 log10 drop in viral load after 12 weeks of treatment with peginterferon and ribavirin, then the patient was not going to respond.”

This recognition set the stage for monitoring at time zero and checking viral load at 12 weeks, then discontinuing therapy if there was no progress. “The next step from a testing perspective was adding monitoring at four weeks to assess for a rapid virologic response, as well as 24 weeks and the end of therapy. Now, with the use of DAAs, it may be important to monitor at 16 weeks after initiating therapy; those patients who have a 2 log10 drop in viral load at 12 weeks, but whose RNA is still detectable at 16 weeks, may also have decreased response rates. We will need to wait for the updated practice guidelines to see what monitoring time points are recommended.”

Based on what she hears from colleagues, she predicts that laboratories will see further increases in hepatitis C viral load testing, along with demand for faster turnaround time. “I would say our testing has doubled in the last eight years. There is no need to offer viral load testing on a stat basis, but more and more clinicians are going to need it within days to a week. We were offering the test once a week and now, based on demand, we’re offering it a couple of times a week.”

The real-time assays that most laboratories perform need to be batched into 24 tests to be cost-effective, she points out. “Hospital-based laboratories may not have the volume to do that three days a week.” But because there could be a substantial increase in the volume of testing, she says, laboratories have to be prepared to offer the test or refer it out.

Dr. Caliendo’s laboratory uses the Roche AmpliPrep Cobas TaqMan HCV Test, an automated sample preparation, amplification, and quantitation test approved by the FDA in 2008. The other FDA-approved HCV assays are Siemens’ Versant HCV RNA assay, for use with the Versant 440 molecular system, and Abbott Diagnostics’ RealTime HCV assay, approved in May, which was developed for use on the Abbott m2000 molecular diagnostics system. As of yet, there are no FDA-cleared genotyping tests, and that’s a gap she would like to see filled.

There are several different methods in use to measure viral load, and most of them are FDA-cleared, but there’s been a marked shift toward real-time PCR measurements of viral load, says Frederick S. Nolte, PhD, D(ABMM), F(AAM), professor of pathology and laboratory medicine and director of clinical laboratories, Medical University of South Carolina, Charleston. “In the CAP proficiency testing Survey for 2010, the distribution of methods for HCV viral load testing showed 242 labs using real-time PCR, 15 using conventional PCR, and 55 using branched DNA. Among those, most of the labs doing real-time PCR are using some form of the Roche Cobas assay either as an IVD, ASR, or RUO.” According to Dr. Dufour, the majority of laboratories no longer offer qualitative testing for HCV.

The new hepatitis C treatments are likely to affect other testing as well. When a patient presents with hepatitis C, Quest’s Dr. Pesano notes, “You don’t only test for viral load. The diagnostic tests that Quest offers try to make HCV testing a composite, to include different factors like hepatic function—identifying individuals with abnormal liver function—as well as a hepatitis panel to determine what types of virus are involved, baseline viral load, and HCV genotyping.” If the patient’s disease stage is advanced, a liver fibrosis panel is also appropriate, “because that makes a difference in the context of all these other parameters, as to whether somebody has a better chance of responding to therapy.”

But the kinetics of viral load decline will continue to be important in deciding on the optimal therapy for individual cases, Dr. Nolte says. An evidence-based HCV treatment algorithm using rapid virologic response as an important milestone was described in a 2008 Clinical Infectious Diseases article (Poordad F, et al., 446: 78–84). Under this algorithm, for patients with a low baseline viral load (less than or equal to 600,000 IU/mL), he explains, testing in week four determines the presence or absence of detectable HCV RNA. “If it’s absent, that’s defined as a rapid virological response, and if you have genotype 1 infection, then you may only need 24 weeks of therapy.”

“If HCV RNA is detectable at week four, then you drop to week 12, do another measurement, and if HCV RNA is undetectable then, you get 48 weeks of therapy and there’s a really good chance you’re going to have a good response.

“If, at week 12, HCV is detectable but you’ve had a greater than 2 log drop in your viral load, you do another measurement at week 24. If virus is still detectable in your plasma then, therapy is discontinued because there is essentially zero chance of having a sustained virological response in that case.”

That’s a big advance, Dr. Nolte says, over the early phases of treatment, which was to treat everyone for 48 weeks. “You’ve spared that group of patients 24 weeks of expensive, toxic therapy.” If the virus is undetectable at week 24, the treatment is extended to 72 weeks—“which is actually a good thing because you have a good chance of having a sustained virological response,” Dr. Nolte says.

The algorithm has another arm for patients with genotype 1 infection and a high baseline viral load (greater than 600,000 IU/mL). “You’re still measuring at the same points, but at week 12 you start sorting patients out in different ‘bins.’ If the virus is undetectable at week 12, then those patients get 48 weeks of therapy. If it’s detectable but there’s been a greater than 2 log drop, then you measure again at week 24. And if HCV is detectable then, therapy is discontinued because they’re not going to respond. If it’s undetectable—just like the low baseline group—you extend them for another 24 weeks, for a total of 72 weeks.”

This evidence-based algorithm could change with the new triple therapy. “We may have additional time points on the triple therapy so that eight weeks may become important in assessing patients’ response,” Dr. Nolte says. Together with the expected intake of more new patients into treatment, that could add up to a major impact on the lab in terms of total volume of viral load testing, he believes.

Triple therapy for hepatitis C using boceprevir or telaprevir will add more pills on top of the four to six pills of the peginterferon-ribavirin regimen: four pills three times a day for boceprevir and two pills three times a day for telaprevir. “The sheer inconvenience and number of pills patients are confronted with” makes lack of compliance with the prescribed dosing more likely, Dr. Hillyard notes. There is no independent lab monitor of whether patients are skipping a dose, making lack of compliance difficult to detect.

But many patients who’ve tried traditional therapy are lining up for the new drugs. “The patients and their physicians are very savvy; they know these drugs are coming, and one of the approaches has been, especially for patients without signs of active serious liver disease, to wait for these new drugs to come out,” Dr. Hillyard says.

Unlike patients with hepatitis B and HIV, hepatitis C patients do have the chance to be cured for life. Hepatitis C does not integrate into human ge­nomes as HIV does, and it does not establish a stable, nuclear, covalently closed DNA copy the way hepatitis B does, Dr. Hillyard explains. “HIV and HBV patients may achieve very low viral copy numbers and very good control of their disease and symptoms, but it’s not accompanied with elimination of the virus from the body.”

The current HCV viral load assays are excellent, Dr Hillyard says. “It used to be that quantitative assays for testing HCV were less sensitive than the qualitative. But now the quantitative tests are exquisitely sensitive; in fact the only way to make them more sensitive would be to insist on a larger blood sample from the patient and to process a larger amount of plasma in the assay. So we’ve sort of reached a plateau in the quality of viral load testing.” Since HCV treatment for a single patient averages about $17,000 per year, given viral load testing’s cost compared with that of other tests, and considering its extreme importance in guiding therapy, the assays are very cost-effective, he adds.

Boceprevir and telaprevir were studied in conjunction with interferon and ribavirin, Dr. Pesano notes. Boceprevir was administered after a four-week lead-in period of just peginterferon and ribavirin, while telaprevir was started at the same time as the other two agents. The reason: to avoid resistance.

“The risk of using monotherapy with these direct-acting antivirals is the development of resistance. Boceprevir and telaprevir are both powerful drugs with a proposed dosage of 800 mg three times a day, and experts say if they are not taken according to prescription, the virus can rapidly develop resistance, in as little as one day,” Dr. Pesano says.

Like HIV, HCV is an RNA virus and it’s easy for it to generate mutations that lead to resistance, Dr. Nolte says. “So being able to keep ahead of that high mutation rate is really the name of the game.” When patients are treated with just an antiviral drug alone, Dr. Shiffman explains, “what happens is that the viral level comes down rapidly as you eradicate your ‘wild’ type dominant virus because it’s sensitive. Then you get down to very low and sometimes undetectable levels, and as you keep treating, the virus reappears. Now the resistant virus has started to grow, and it grows because it has lots of food around, because all the other viruses are gone.” The Darwinian bottom line: “The resistant species to the agent are already there; you’re just selecting them out.”

That’s the reason you need peginterferon and ribavirin when you treat patients with a direct protease inhibitor, Dr. Shiffman says. “The broad-based antiviral activity of peginterferon and ribavirin eradicates low levels of viruses. The lower the level of virus, the more effective peginterferon-ribavirin is. The amount of resistant species present is at much lower levels because they are crowded out by the wild type virus strain, which is much more plentiful.”

The question could become not only how to deal with the possibility of increased resistance, but also how to test for it, “and that’s technology that Quest is certainly working on,” Dr. Pesano says. Dr. Nolte, however, believes that there is no place yet for testing for drug-resistant variants of HCV “because there’s really nothing much you’re going to do with that information, and viral load testing will remain the way to assess response rapidly.” Until there are alternative drugs available with different targets, “then there’s probably not going to be much clinical need to determine resistance mutations.”

The medical community’s many decades of experience in treating HIV led to insights that have helped refine treatment for HCV. “It became obvious that HIV was not being treated by immune modulators like interferon and ribavirin, but in fact was working with drugs that directly affected the virus,” Dr. Pesano says. Once researchers understood more about the life cycle of HCV, then they had targets to go after and could develop drugs specific to those targets.

But there are critical differences between HCV and HIV infections. Says Dr. Nolte: “The consequences of untreated HIV are death. Hepatitis C, on the other hand, is a slowly progressive disease, and depending on when they got it and their specific risk factors, many people with chronic infections may die of something else before the liver fails.”

However, there is another class of antiviral drugs that target the hepatitis C virus’ polymerase, the non-nucleoside and nucleoside drugs. “These are in an earlier phase of study and are still a few years away from approval, but show tremendous potential as well, with high response rates, higher barriers to resistance, and lower side effects,” Dr. Hillyard says. Many patients who are not successfully treated by the existing therapies will be looking forward to the polymerase inhibitors. “I think everybody’s dream will be to put together a cocktail akin to the highly active antiretroviral therapy, and not including interferon, a formulation that’s been so successful for the treatment of HIV,” Dr. Hillyard says.

Another promising avenue for predicting HCV treatment response is human markers. In April, Quest Diagnostics announced availability of the AccuType IL28B test for identifying a certain polymorphism of the IL28B gene found in individuals infected with HCV genotype 1. “This polymorphism which encodes interferon lambda 3 is associated with approximately a twofold improved response to hepatitis C treatment,” says Dr. Pesano. A similar test has been offered for some time by Laboratory Corp. of America, Dr. Dufour reports, and just starting this year by ARUP Laboratories.

Patients from previous clinical trials have also been genotyped, so investigators have had access to a lot of outcome data under different treatment protocols, Dr. Hillyard explains. “They quickly discovered that there were favorable and unfavorable human genotypes. Compared to previous factors like age, fibrosis, weight, viral load, race, insulin resistance, and alcohol consumption—all of these factors were less predictive than IL28B.” Among other things, this explains why some racial groups like blacks are more difficult to treat; they have been found to have an increased frequency of the unfavorable SNP (single nucleotide polymorphism) or what is called the TT genotype. Asians, on the other hand, have been easier to treat because they have higher frequencies of the favorable CC genotype.

“So it provides a very powerful predictor of whether patients in the absence of therapy are going to recover from chronic hepatitis C by spontaneously losing the virus, and whether patients will respond to therapy,” Dr. Hillyard says. Going forward, he believes typical testing will include genotyping of the patient as well as virus genotyping and viral load testing. “It’s all useful information to predict the likelihood of a patient responding.” He notes that the new drugs, now known to be effective against HCV genotype 1, also have activity against genotype 2 (which is already easy to treat with peginterferon and ribavirin), but not against genotypes 3 and 4. “The data are not in on 5 and 6,” he says.

A 30 percent cure rate is nothing to be downplayed, Dr. Shiffman points out. “There are lots of people who have been cured in the past based on a 30 percent cure rate.” However, with a favorable CC genotype “you have an incredibly high chance of responding to just interferon and ribavirin therapy, without even engaging in the triple therapy of added boceprevir or telaprevir.” Whether that third drug will prove optional for some patients is an intriguing question. “It’s currently unclear and probably won’t be answered until we have additional retrospective studies as well as prospective studies to evaluate that,” Dr. Shiffman says.

So we’re in a period of learning about all the nuances of the new therapy, Dr. Hillyard says. “I think the conservative stance is to continue to gather as much information as possible so we can put together the most effective algorithms for providing therapy.”

The VA has had several conference calls on the subject of IL28B but so far no consensus, says Dr. Dufour, who is on the VA technical advisory committee on hepatitis C. “We’ve been wrestling with this. Some people are saying just go ahead and use all three drugs, while others say maybe we should do the test for IL28B first, and try interferon-ribavirin if the patient has a CC SNP.”

Is personalized medicine going to increasingly be a component of HCV therapy? Dr. Shiffman believes it will. “I like to think you can personalize treatment for many different diseases, including HCV, by tailoring your treatment and treatment durations to the specific genetic profile of the patient. And I think as we start to identify more genes that have significant impact, we’ll be able to tailor and personalize treatment, so that patients who have favorable genetics don’t require additional medications or have potential side effects—or, for example, can receive different medications that are much more effective.”

Dr. Nolte is less sure about the role of IL28B. “Basically the polymorphism predicts who’s better able to clear the virus either spontaneously or with therapy. For patients who have spontaneously cleared the virus, that’s kind of after-the-fact information. Currently, there’s nothing different you’re going to do in the way of treating the patient based on the IL28B genotype.” But he does see the IL28B test as potentially valuable in motivating patients to stick with the treatment plan. “Patients just giving up on therapy is not uncommon. So keeping them motivated through this rather lengthy, toxic treatment is of benefit, but kind of difficult. If I had HCV and I knew I had a favorable genotype, then I’d be more likely to stay the course of therapy.”

Patients without this favorable genotype can nonetheless respond, “and one powerful predictor of that is whether, once you put them on therapy, they experience a rapid virological response [RVR],” Dr. Hillyard says. “That’s what we look for and hope for the most with traditional therapies. And there’s an evolving concept of extended RVR; that is an RVR that persists for a defined period of time.”

One study in genotype 4 showed that patients who had a rapid virological response seem to do just about as well with half as long a treatment, Dr. Dufour says. “Also, if some patients had a partial response to treatment, we may try to re-treat them for a longer period of time—for example, 72 weeks instead of 48 weeks. That’s not the standard of care, but there’s some evidence it might work.”

Another example would be a patient who had a rapid virological response and some significant side effect, Dr. Dufour says. “We’re probably much more likely with that patient to see what we can do to manage the complications and maybe get them through at least 12 weeks of treatment, because they have a high likelihood of getting rid of the virus.” With someone who hasn’t had much response at four weeks and has significant side effects, “we’re not going to press them as hard to continue as somebody who’s having a rapid virological response.”

One of the questions researchers would like to answer is whether HCV is curable without interferon. “We won’t know that until we have several antiviral agents that can be tested simultaneously for hepatitis C,” Dr. Shiffman says. “There are at least 16 other drugs in the pipeline going through phase two clinical trials, and we will have lots of drugs to treat HCV. We’re already starting studies to see if we can cure HCV without interferon by just using a combination of two to three antiviral drugs.”

It’s unclear how soon the clinical community will formally revise treatment recommendations to incorporate the new DAAs. Although the current guidelines are for the most part accepted by hepatologists, Dr. Nolte says, not all clinicians are up to speed with them. “I just saw an e-mail from a colleague who said their hepatology group had just started to implement viral load measurements at week four, which seems kind of strange given that that evidence has been out for a while. But that’s what happens; the uptake by clinicians can be sporadic.”

Over the long run, however, the impact of the DAAs is likely to be profound in leading more patients into treatment and using increased virologic monitoring to guide that treatment. Says Dr. Nolte: “It’s a big shift in the paradigm and it’s come with big changes in clinical success. So it is a new era.”


Anne Paxton is a writer in Seattle.
 
 
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