Tanox, Inc. Reports 48-Week Results From TNX-355 Phase 2 Clinical Trial

HOUSTON, May 2 /PRNewswire-FirstCall/ -- Tanox, Inc. today reported 48-week results of its Phase 2 clinical trial of HIV drug candidate, TNX-355. Following previously reported 24-week data, the new results show that HIV-infected patients who received either study dose of TNX-355, in combination with an optimized background regimen (OBR), maintained a considerably 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 a statistically significant increase in CD4+ cells compared to those who received placebo plus OBR.

At 48 weeks, treatment with a 10 milligram-per-kilogram (mg/kg) dose of TNX-355 resulted in a mean viral-load reduction of 0.96 log10, compared with a 0.14 log10 reduction in the placebo group, representing a 0.82 log10 greater reduction (p<0.001) in viral load. Patients who received a 15 mg/kg dose of TNX-355 had a mean viral-load reduction of 0.71 log10, compared with a 0.14 log10 reduction in the placebo group, representing a 0.57 log10 greater reduction (p<0.010) in viral load. These results are from the modified intend to treat study population, using the last observation carried forward method of analysis.

In addition to experiencing sustained viral-load suppression, patients receiving the 10 mg/kg dose of TNX-355 had a greater increase in CD4+ cells than patients who received placebo, with mean CD4+ cell increases of 48 cells/mm3 and 1 cell/ mm3, respectively (p=0.031). Patients who received the 15 mg/kg dose of TNX-355 also experienced a greater increase in CD4+ cells than patients in the placebo group, with mean CD4+ cell increases of 51 cells/mm3 and 1 cell/ mm3, respectively (p=0.016).

Both doses of TNX-355 were well tolerated, with no severe adverse events related to the drug as assessed by investigators. No infusion-site reactions were reported.

"The 48-week results demonstrate the ability of TNX-355 to produce durable viral-load suppression, while also providing a clinically meaningful immunologic response," said Danong Chen, Tanox president and chief executive officer. "These data suggest that TNX-355 has the potential to be a first-in- class therapy to advance HIV care for treatment-experienced patients."

Tanox intends to submit additional 48-week data for presentation at the XVI International AIDS Conference Aug. 13-18, 2006 in Toronto.

"Results from this trial highlight the difficulty physicians face when attempting to construct an effective regimen for treatment-experienced patients," said Dr. Stanley Lewis, Tanox medical director for TNX-355. "The inability of the standard-of-care regimen (placebo plus OBR) to produce a marked viral-load reduction or immunologic response, underscores the need for more effective therapies for the increasing number of patients who have exhausted their treatment options. We're pleased to see that TNX-355, when combined with OBR, produced a significantly greater viral-load reduction and immunologic response in this patient population than did OBR alone."

Study Design

Eighty-two triple-class treatment-experienced HIV-1-positive patients who had viral loads of at least 10,000 copies/mL, CD4+ cell counts of at least 50 cells/mm3, and were failing or had recently failed highly active antiretroviral therapy (HAART) were enrolled in the Phase 2 study. The 48- week clinical trial was designed to compare two doses of TNX-355 -- 10 mg/kg and 15 mg/kg -- to that of placebo. Patients were randomized 1:1:1 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 study patients received an investigator-selected, resistance-test-guided OBR (standard-of- care regimen).

TNX-355

TNX-355 is a humanized monoclonal antibody and part of an emerging class of HIV therapies known as viral-entry inhibitors. TNX-355, which is administered intravenously, is distinct from other entry inhibitors in that it binds to CD4 receptors, the primary target of HIV infection. Since TNX-355 blocks HIV entry at a step prior to the co-receptor interaction, the drug candidate is "co-receptor tropism independent," with the ability to block both CCR5- and CXCR4-tropic viruses. The blockade presented by TNX-355 also does not depend on targeting a mutation-prone viral protein.

Continued Development

The Phase 2 clinical trial has been extended to 144 weeks, with all study patients given the opportunity to receive TNX-355.

An end-of-Phase 2 meeting with the Food and Drug Administration (FDA) is scheduled to take place by the end of the second quarter of this year.

"Given the unique mechanism-of-action of TNX-355 in targeting the CD4+ cell, we made the decision to seek the meeting with the agency once we had the benefit of 48-week data," said Chen. "We're very encouraged by the immunologic response we saw in both treatment arms at 48 weeks."

Meanwhile, Tanox is continuing to evaluate options for further development of TNX-355.

Conference Call

Tanox management will discuss the 48-week data during its quarterly results conference call today at 10 a.m., EDT. The conference call can be accessed at 1-800-591-6923 (domestic) or 1-671-614-4907 (international). The pass code is 7480-2827. Live audio of the call will be webcast on the Internet. The webcast can be accessed from the Tanox Web site at http://www.tanox.com in the Investor Relations section. An audio replay of the webcast will be available beginning at noon, EDT, May 2, 2006 through 11 a.m., EDT, June 2, 2006. Access phone numbers for the replay are: 1-888-286-8010 (domestic) and 1-617-801-6888 (international); conference pass code 7399-0184.

About Tanox, Inc.

Tanox is a biotechnology company specializing in the discovery and development of monoclonal antibodies. The company develops innovative biotherapeutics for the treatment of immune-mediated diseases, inflammation, infectious disease and cancer. Tanox's lead investigational therapy, TNX-355, is a viral-entry inhibitor antibody to treat HIV/AIDS. TNX-355 has shown significant antiviral activity in Phase 2 clinical testing. Tanox's first- approved drug, Xolair(R) (omalizumab), is the first antibody approved to treat moderate-to-severe confirmed, allergic asthma. Xolair was developed in collaboration with Genentech, Inc. and Novartis Pharma AG and is approved for marketing in the United States, Canada and major European countries. Tanox is based in Houston and has a manufacturing facility in San Diego. Additional corporate information is available at http://www.tanox.com .

This news release contains forward-looking statements regarding the potential for TNX-355 as a treatment for HIV-1-infected patients. These statements are based on Tanox's current beliefs and expectations, and are subject to risks and uncertainties that could cause actual results to differ materially. The absence of safety concerns after 48 weeks of treatment in 82 patients does not ensure that safety issues will not be identified in larger- scale clinical trials. The therapeutic potential of TNX-355 as a treatment for HIV-1-infected patients is subject to the risks inherent in drug development. The timing of future trials can depend on various business issues, including regulatory review and manufacturing sufficient quantities of clinical-trial material. Success in early stage clinical trials does not ensure that later-stage or larger-scale clinical trials will be successful, and the results achieved in later-stage trials may not be sufficient to meet applicable regulatory standards. Problems or delays may arise during clinical trials or in the course of developing, testing or manufacturing drugs. For more detailed information on the risks and uncertainties associated with Tanox's drug development and other activities, see Tanox's periodic reports filed with the Securities and Exchange Commission.

Photo: NewsCom: http://www.newscom.com/cgi-bin/prnh/20050207/TNOXLOGOPRN Photo Desk,photodesk@prnewswire.comTanox, Inc.

CONTACT: Steve Sievert of Tanox, Inc., +1-713-578-4211, orssievert@tanox.com

Web site: http://www.tanox.com/