SAN FRANCISCO -- Every six months, hepatitis C researchers from around the world gather to discuss new ways of combating the serious liver disease. In recent years, these biannual confabs have largely revolved around the development of a new, more potent class of drug that promises to bring cures to a larger percentage of hepatitis C patients than ever before.

Like previous meetings, the one that kicked off over the weekend here will have scientists (and the Wall Street investors and analysts who follow their work closely) talking a lot about

Vertex Pharmaceuticals'

(VRTX) - Get Report

drug telaprevir.

Data being presented will show once again telaprevir's impressive ability to directly interfere with and eliminate the virus that causes hepatitis C in patients who have failed previous treatments and in those who are being treated for the first time.

Competitors to Vertex are here, too.

Schering-Plough

( SGP) will present data on the ability of its experimental drug boceprevir to eliminate the hepatitis C virus in previously untreated patients. Companies with drugs in less advanced clinical trials, including

Pharmasset

(VRUS)

,

InterMune

(ITMN)

,

Boehringer Ingelheim

,

Johnson & Johnson

(JNJ) - Get Report

,

Merck

(MRK) - Get Report

and

Pfizer

(PFE) - Get Report

, also will be presenting new or updated data.

For many biotech investors, Vertex remains a central focus of these hepatitis C meetings because the company is in the midst of conducting two large phase III studies of telaprevir, with the first results expected in the first half of 2010.

Vertex intends telaprevir to become the first new hepatitis C drug approved in years, and one that will dramatically increase the cure rate for the disease, and do so in half the time of currently approved drugs. If the plan succeeds, Vertex will grab a large share of a multi-billion dollar commercial market opportunity.

There are no sure things in drug development, which is why the value of Vertex shares swing rather wildly, especially as new data is unveiled and questions -- new and old -- are raised at these gatherings of hepatitis C researchers.

Is telaprevir the best of this new crop of hepatitis C drugs? Will Schering-Plough catch up? Are second-generation drugs already in development more potent and more convenient than telaprevir? And if so, does that leave Vertex vulnerable?

Much of the most important data at this year's annual meeting of the American Association for the Study of Liver Disease will be presented Monday and Tuesday. However, the veil on some of this data has been lifted already. Here's a recap of what's available so far:

Vertex

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:

Telaprevir stands apart from other experimental hepatitis C drugs, including Schering-Plough's boceprevir, because it appears capable of curing the disease in large numbers of patients who have failed previous treatments.

A phase II study known as PROVE 3 showed that 52% of patients treated with telaprevir had undetectable levels of virus in their systems 12 weeks after treatment was stopped, according to interim data from the study being presented at the meeting. Vertex had previously announced some of these results last June.

Patients were enrolled in PROVE 3 if they had failed previous treatment with 48 weeks of pegylated interferon and ribavirin, the current standard hepatitis C therapy. These difficult-to-cure patients were then retreated with 12 weeks of telaprevir plus interferon and ribavirin, followed by another 12 weeks of interferon and ribavirin alone for a total of 24 weeks of therapy.

Breaking down the 52% overall result further, 73% of patients who had relapsed after receiving the standard treatment were able to drop their viral loads to undetectable levels, while 41% of patients who had not responded at all to previous treatment likewise achieved undetectable viral loads.

PROVE 3 also used as a control patients who were retreated a second time with the standard interferon and ribavirin. So far, just 30% of these patients have undetectable levels of virus after 36 of a planned 48 weeks of retreatment. Final data on these control patients is not ready, but far fewer are likely to reach undetectable viral loads in the observation period following treatment, based on historical data.

In a previous phase II study known as PROVE 2, which enrolled treatment-naive hepatitis C patients, telepravir helped 69% of patients reach undetectable viral loads 24 weeks after treatment. By comparison, 46% of patients treated with interferon and ribavirin alone saw the level of virus fall below undetectable levels.

The telaprevir regimen used in PROVE 2 was the same as that used in PROVE 3 -- 12 weeks of telaprevir plus interferon and ribavirin followed by another 12 weeks of interferon and ribavirin alone.

In all previous and ongoing clinical trials, patients take telaprevir every eight hours, or three times a day. For competitive reasons, Vertex would like twice-daily telaprevir. Interim data to be presented at the meeting suggests twice-daily telaprevir is possible and could be better than standard therapy. However, three-times-a day telaprevir still appears to be the most potent dosing schedule.

Schering-Plough

Schering's drug boceprevir is posting equivalent cure rates to that of telaprevir in treatment-naive patients, although the most effective treatment cycle is twice as long.

According to results from the phase II SPRINT-1 study released here, 74% of patients on a 48-week boceprevir regimen saw their viral loads fall below the level of detection 12 weeks following the cessation of treatment.

These patients began treatment with four weeks of interferon and ribavirin (a lead-in period) followed by 36 weeks of boceprevir in combination with interferon and ribavirin.

For patients without the four-week lead in, 66% saw their virus fall below detectable levels.

Using a shorter, 28-week boceprevir regimen, 55% and 56% of patients achieved undetectable viral loads with no lead in treatment, or a lead-in treatment, respectively.

Schering-Plough is currently conducting two phase III studies of boceprevir in treatment-naive and treatment-resistant patients.

Pharmasset

Pharmasset's drug R7128 hasn't been as broadly tested as those from Vertex and Schering-Plough, but the data generated so far has shown the drug to be very effective at tamping down the hepatitis C virus.

The biggest question mark hanging over the drug to date is toxicity. At an investor event Sunday, Pharmasset officials for the first time discussed in some detail the emergence of kidney toxicity seen in a safety study in monkeys.

According to Pharmasset, the monkey kidney toxicity is reversible and did not cause permanent damage. More importantly, no such problem has been observed in the short human studies of R7128 conducted to date.

Pharmasset is conducting a longer, six-month safety test of R7128 in monkeys, but at this point the company doesn't believe that the

Food and Drug Administration

will stop further human studies from starting in the first quarter of next year.

Still, judging by the volume of questions from investors at Sunday's meeting that began with the words, "I'd like to get back to those monkey studies ..." the issue isn't one that Wall Street is ready to put entirely to rest.

Pharmasset is developing R7128 with partner

Roche

, which just last week was forced to halt development of a rival hepatitis C drug derived from its own laboratories because of unacceptable safety problems.

This Roche setback upped the value of R7128. If the drug's safety can be verified, Pharmasset will be a hepatitis C company to watch.

At the time of publication, Feuerstein's Biotech Select model portfolio had no positions in any stocks mentioned.

Adam Feuerstein writes regularly for TheStreet.com. In keeping with TSC's editorial policy, he doesn't own or short individual stocks, although he owns stock in TheStreet.com. He also doesn't invest in hedge funds or other private investment partnerships. Feuerstein appreciates your feedback;

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