Vertex Pharmaceuticals Inc. released 24-week results from a 48-week Phase III trial showing that 73 percent of 166 HIV-positive patients taking the company's protease inhibitor, GW433908, achieved undetectable viral load, compared to 54 percent of 83 patients taking Pfizer Inc.'s nelfinavir, or Viracept.

The NEAT study is one of three Phase III studies of 908, as the drug is known in abbreviated form, which was co-discovered by GlaxoSmithKline plc, of London.

"We are very pleased with these results," said Vertex President Vicki Sato. "From a number of different perspectives, we believe this is a potent and well-tolerated protease inhibitor in this combination."

GSK plans to file a new drug application for 908 in December, Sato told BioWorld Today, and Vertex would get royalties and the right to co-promote. The drug candidate is the calcium phosphate ester prodrug of Vertex/Glaxo's Agenerase, or amprenavir.

Patients were randomized to receive either 1,400 mg of 908 (or two tablets) twice a day, or 1,250 mg of nelfinavir (or five tablets) twice a day. Each group took those medications in combination with 300 mg twice a day of abacavir (Glaxo's Ziagen) and 150 mg of lamuvidine, originally developed by Laval, Quebec-based BioChem Pharma Inc. Sato said there were no significant adverse events.

"In all patients across the board, we saw a significant reduction in viral load, [especially] in the patients with the highest viral load, who are the most challenging to treat," Sato said. "This was very important for us to see."

Of those patients with a high viral load, or one greater than 100,000 copies/mL, taking 908, 71 percent achieved a viral load of less than 400 copies/mL, and 42 percent achieved a viral load of less than 50 copies/mL, while comparable percentages of those taking nelfinavir were 35 percent and 11 percent, respectively.

The company has two other studies with 908, including the SOLO trial, which is an open-label trial that has enrolled more than 650 HIV-positive, treatment-na ve patients. Those participating have been randomized to receive either 1,400 mg of 908 plus 200 mg of ritonavir once a day or 1,250 mg of nelfinavir twice a day. They also receive abacavir and lamivudine (3TC), two nucleoside reverse transcriptase inhibitors.

A third Phase III trial called the Context study is an open-label trial in patients comparing 908 to ritonavir and lopinavir. That trial reached full enrollment with 50 patients. Results from the study are expected to be available in 2003, Vertex said.

Sato said the trials are designed to demonstrate not only how 908 performs in combination therapy, but also to generate comparative data to the market leaders for HIV treatment.

The studies also have another important dimension, she said, which is the fact that the patients are demographically diverse. Sato said the demographics of those with HIV are very different today than when the disease had its beginning, as today it is more widespread in the heterosexual and minority communities.

Sato said the studies "most accurately reflect the demographics of the disease with regard to gender and racial diversity," and therefore will speak to a broader segment of the population. Both Vertex and GSK have done this so that it can have the strongest data that will "support the strongest commercial positions," Sato said.

Vertex's stock (NASDAQ:VRTX) fell 65 cents Friday to close at $18.56.