Entry Inhibitor TNX-355: New Phase 2 Study Data

By Tim Horn, Senior Writer & Editor, AIDSmeds.com

Tanox, Inc. has reported 48-week results from its Phase 2 clinical trial of TNX-355, an HIV-entry inhibitor. The new data, which come directly from the company and have not yet been presented at a scientific meeting or published in a peer-reviewed medical journal, indicate that HIV-positive patients who received either study dose of TNX-355, in combination with an optimized background regimen (OBR), maintained a greater reduction in viral load than did patients given placebo in combination with OBR. The 48-week results also showed that patients who received TNX-355 with OBR experienced an increase in T-cells compared to those who received placebo plus OBR.

TNX-355 is a humanized monoclonal antibody and part of an emerging class of HIV therapies known as entry inhibitors. TNX-355, which is administered intravenously, is different from other entry inhibitors (such as vicriviroc and maraviroc) in that it binds to CD4 receptors, the primary target of HIV infection.

The Phase II study conducted by Tanox involved 82 treatment-experienced HIV-positive patients who had viral loads of at least 10,000, T-cell counts of at least 50, and were failing (or had recently failed) their most recent drug regimen. The clinical trial was designed to compare two doses of TNX-355 – 10 mg per kilogram of body weight (mg/kg) and 15 mg/kg – to that of placebo. Patients were randomized to receive 10 mg/kg every week for eight weeks followed by every two weeks thereafter, 15 mg/kg every two weeks, or placebo every two weeks. All of the patients enrolled in the study received OBR, involving any combination of approved anti-HIV drugs, based on the results of drug-resistance testing.

After 48 weeks, treatment with the 10 mg/kg dose of TNX-355 resulted in a mean viral load reduction of 0.96 log, compared with a 0.14 log reduction in the placebo group, representing a 0.82 log greater reduction in viral load. Patients who received the 15 mg/kg dose of TNX-355 had a mean viral load reduction of 0.71 log, compared with a 0.14 log reduction in the placebo group, representing a 0.57 log greater reduction in viral load.

Patients in both TNX-355 treatment groups experienced greater T-cell increases compared to those in the placebo group (an average increase of 48 T-cells in the 10 mg/kg group, an average increase of 51 T-cells in the 15 mg group, and an average increase of 1 T-cell in the placebo group).

According to Tanox, both doses of TNX-355 were well tolerated, with no severe adverse events related to the drug. No infusion-site reactions were reported.

The 48-week data have not yet been reviewed by the scientific community. However, the study investigators intend to submit the 48-week data for presentation at the XVI International AIDS Conference, scheduled to take place in Toronto in August.

Source:

Tanox, Inc.