New hepatitis C drugs pose many questions

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New hepatitis C drugs pose many questions

Hepatitis C treatment

Alcorn

Published: 08 April 2011

Even before new hepatitis C drugs come to market later this year, a vast array

of hepatitis C antivirals currently in clinical trials is opening up new

horizons for treatment of hepatitis C, in a situation strongly reminiscent of

the explosion of HIV drugs research in the mid-1990s.

At last week’s International Liver Congress (EASL) in Berlin, agents from four

new classes of drugs, as well as potential improvements to current therapy were

presented.

But the issue at the top of liver specialists’ agenda is how to use the new

hepatitis C protease inhibitors that will come to market in the United States

and Europe later this year – and who can afford to use them.

Telaprevir (being developed by Vertex and Tibotec, a & company)

and boceprevir (Victrelis, being developed by Merck) are due for review by the

US Food and Drug Administration in late April, with Europe to follow later in

the year. Both drugs have demonstrated improved rates of sustained virological

response (SVR) (an outcome that is considered a cure) in patients with hepatitis

C, when added to the current standard of care, pegylated interferon and

ribavirin.

Current SVR rates range from 15-40% and tend to be lower in African-Americans,

people with cirrhosis, transplant recipients and older people. People with HCV

genotype 1 have less favourable outcomes on current treatment, as do people with

HIV/HCV coinfection.

In comparison studies combining a protease inhibitor with standard of care have

shown SVR rates of 60-70% in previously untreated patients. A study of

telaprevir in coinfected patients indicates that the early response to treatment

is just as good as in monoinfected patients, but longer follow-up is needed to

confirm this.

Questions about how to use new drugs

However the headline outcomes of these trials conceal a number of caveats, notes

Swan of New York’s Treatment Action Group

In the Hepatitis C Treatment Pipeline Report published last month, she

highlighted a host of unanswered questions that should give clinicians pause for

thought when considering how to treat patients with hepatitis C using the new

drugs. These issues are likely to be just as relevant in HIV/HCV coinfected

people as in the much larger HCV-monoinfected population.

In particular she points to the lower rate of response in patients who failed to

respond to first-line treatment with pegylated interferon. These patients were

much less likely to achieve a sustained virological response in trials of

telaprevir and boceprevir, although the responses were still better than those

seen in the control groups receiving standard treatment.

In the case of the REALIZE study of telaprevir, for example, just 31|% of prior

null responders had a successful response to telaprevir, compared to 83% of

those who experienced a virological relapse after completing treatment

successfully. Among those null responders with cirrhosis – the people with a

more urgent need for successful treatment – the cure rate was just 14% in the

telaprevir group.

Cure rates were similarly lower among patients with cirrhosis who had a partial

response to prior therapy (defined as a reduction in HCV viral load of at least

2 log at week 12 without achieving undetectable viral load before therapy was

completed). 34% of this group achieved a sustained virological response compared

to 59% of non-responders in the study as a whole.

These findings suggest that patients with advanced liver disease will need to

weigh up carefully the risks and benefits of attempting another course of

pegylated interferon and ribavirin in combination with a new HCV protease

inhibitor. Would it be better to wait for further drugs, or is the severity of

liver disease such that a further attempt at a cure would be advisable now?

These issues may be more pressing for patients with HIV/HCV coinfection, where

liver disease may be more rapidly progressive, particularly if HIV is

uncontrolled by treatment.

There is also uncertainty about just how long patients need to take the new

drugs, a question that has a crucial bearing on the cost of new hepatitis C

treatments – and the convenience and tolerability of these drugs.

On the up side, trials of both protease inhibitors reinforced the concept of

`response-guided therapy` to hepatitis C treatment, by establishing a series of

time points at which protease inhibitor treatment or all treatment could be

stopped if HCV was undetectable.

In the case of telaprevir, there is evidence to suggest that the drug may be

withdrawn at week 4 or week 12 of treatment if HCV is undetectable. With

boceprevir, treatment should carry on until week 24, but hepatitis C treatment

can stop completely at this point if HCV RNA was undetectable at weeks 8 and 24.

However, a further complexity of boceprevir treatment is the four-week lead-in

phase of pegylated interferon and ribavirin, designed to reduce viral load and

so minimise the risk of resistance to boceprevir. What should happen if a

patient fails to show some signs of virological response after this four-week

lead-in phase? Is the patient fundamentally unresponsive to interferon, and thus

likely to fail treatment completely?

The REALIZE study of telaprevir in treatment-experienced patients showed that a

4-week lead-in phase did not improve response rates.

In a possible re-run of history from the HIV field, some experts are concerned

that premature use of new agents in patients with a poor chance of response

could leave them with resistance to new agents that may affect their response to

subsequent innovations in hepatitis C treatment.

Professor Heiner Wedemeyer, Secretary General of the European Association for

the Study of the Liver, told a press conference at last week’s Congress:

“Studies show that care must be taken in the prescription and use of the new

compounds. What we want to avoid is a rapid spread of HCV resistance within the

patient population, which could drastically lower the effectiveness of the new

drugs.”

Evidence from the SPRINT-2 study of boceprevir showed that patients in the

poor-responder category had a high risk of developing drug resistance. This in

turn could compromise their response to future experimental treatment. (See

Clinical Care Options summary of this study – registration required).

However there is also evidence that resistance mutations to telaprevir may fade

over time, possibly allowing that drug or other HCV protease inhibitors to be

used again. A lot more evidence will be needed on this question to convince

liver experts that re-use or sequencing of HCV protease inhibitors would be

possible in the case of treatment failure.

Other protease inhibitors are being developed. Tibotec presented preliminary

results from a phase IIb study of TMC-435, studied in combination with pegylated

interferon and ribavirin. Week 24 virological response data showed a much less

marked gap in response rates between relapsers, prior partial responders and

null responders. At week 24 92-96% of protease inhibitor recipients in the prior

relapser group had undetectable HCV RNA, as did 70-87% of null responders,

according to dosing and treatment schedule.

To make a meaningful comparison with boceprevir or telaprevir a further 24 weeks

of follow-up data will be needed in order to assess whether these patients

achieve a sustained virological response.

Abbott’s HCV protease inhibitor danoprevir also showed strong preliminary

results in a study of previous null responders, at least in patients infected

with HCV genotype 1b. Danoprevir is boosted with ritonavir in the same way as

HIV protease inhibitors, and administered alongside pegylated interferon and

ribavirin. By week 12 88% of those with genotype 1b receiving danoprevir had

achieved a rapid virologic response (undetectable HCV RNA by week 4). In

comparison a high rate of viral breakthrough occurred within weeks of viral

suppression in the genotype 1a group. (See Clinical Care options summary of this

study – registration required).

Moving towards interferon-free combination therapy

The news that caused the biggest stir at the Congress came from a study

conducted by Bristol-Myers Squibb which showed that, in a small number of

patients, it is possible to cure hepatitis C infection in 24 weeks without

pegylated interferon, using two new drugs – an HCV protease inhibitor and an HCV

NS5A inhibitor. Not only were these patients cured without interferon, but they

were patients who had previously failed to respond to interferon – the

hardest-to-treat group.

Furthermore, in those also treated with pegylated interferon and ribavirin the

cure rate was 90%.

These results come from a phase IIa study, which means that optimal dosing still

needs to be defined before large trials can take place to achieve licensing of

the drugs.

Similarly, two drugs developed by Pharmasset – a nucleotide analogue and an

inhibitor of HCV’s NS5A protein – produced undetectable HCV viral load after 14

days of treatment without pegylated interferon or ribavirin in 15 out of 16

previously untreated patients without cirrhosis.

These results also come from a phase Ib study and longer studies will be needed

to determine whether this very rapid response is sustained without interferon.

Better interferon?

Improving responses to interferon, or tolerability of interferon, was also an

important focus of research presented at the conference.

A study conducted in Romania showed that adding the cholesterol-lowering statin

fluvastatin to pegylated interferon and ribavirin resulted in a significantly

higher rate of sustained virological response (63% vs 49%) in monoinfected

patients treated for 48 weeks. These patients continued to receive fluvastatin

for a further 24 weeks.

Bristol Myers Squibb presented results from a phase IIb trial of pegylated

interferon lamda, a type of interferon which has interactions with fewer human

cell types. This means it should be better tolerated. The randomised study,

conducted in patients with all HCV genotypes, showed a higher rate of sustained

virological response in patients treated with pegylated interferon lamda,

coupled with fewer flu-like symptoms and less musculoskeletal pain. In HCV

genotypes 2 and 3 better responses were achieved only at higher doses of the new

product.