ANX Mast Therapeutics, Inc.

ADVENTRX Presents Results at Keystone Symposia HIV Pathogenesis Conference SAN DIEGO, March 31 /PRNewswire-FirstCall/ -- ADVENTRX Pharmaceuticals, Inc. (AMEX:ANX) announced that it presented preclinical results for ANX-201, the Company's broad-spectrum antiviral product candidate at the Keystone Symposia HIV Pathogenesis Conference in Banff, Alberta on March 30, 2008. The preclinical results demonstrate a unique resistance profile for ANX-201 and suggest suppression of resistance to nucleoside reverse transcriptase inhibitors (NRTIs), a commonly used class of drugs to treat HIV. The HIV Pathogenesis Conference is part of the Keystone Symposia Global Health Series, which is supported by the Bill & Melinda Gates Foundation. The poster presentation entitled "The pyrophosphate analogue thiophosphonoformic acid confers a favorable HIV resistance profile," was presented by Shani Waninger, Ph.D., associate director for research and development at ADVENTRX. ANX-201 (thiophosphonoformic acid) is a pyrophosphate analog and member of a new class of reverse transcriptase inhibitor (RTI) that is being developed to provide benefits for treatment-resistant HIV-infected patients. Foscarnet, the main metabolite of ANX-201, is approved by the FDA for use in immunocompromised patients with CMV retinitis and mucocutaneous acyclovir-resistant HSV infections. However, clinical use of foscarnet is limited, in part due to its intravenous administration and low oral bioavailability. In contrast, in vivo tests have demonstrated increased oral bioavailability of ANX-201, relative to foscarnet, potentially enabling oral delivery. The preclinical data presented at the conference show that virus selected for resistance to ANX-201 develop genetic mutations, some previously described for foscarnet-resistant virus, as well as unique genetic mutations not previously linked to foscarnet or foscarnet derivatives. Regardless of the specific mutations, the preclinical studies show that ANX-201-resistant virus was sensitive, and in most cases hypersusceptible, to multiple NRTIs and non-nucleoside reverse transcriptase inhibitors (NNRTIs). The nature of the resistance mutations suggest that, if patients develop resistance to ANX-201, they may be resensitized and made hypersusceptible to NRTIs or NNRTIs. The preclinical studies also show that virus coresistant to ANX-201 and NRTI could not be generated, which supports the mutually exclusive resistance mechanism of these two drug classes. This suggests that patients treated with ANX-201 combined with NRTIs may be less likely to develop, or have a delay in development of, treatment-resistance. Activity of ANX-201 was also examined using the PhenoSense(R) assay against a panel of clinical isolates containing viruses that had developed varying degrees of resistance to NRTIs and/or NNRTIs. All clinical isolates tested were sensitive to ANX-201, the majority being hypersusceptible. This suggests that patients infected with viruses that are NRTI- or NNRTI-resistant may be hypersusceptible to ANX-201. Clinical studies have shown that hypersusceptibility to HIV drugs is a significant predictor of the magnitude of HIV reduction and increase in CD4 T cells in patients who have failed one or more previous antiretroviral regimens. About ANX-201 ANX-201 (thiophosphonoformic acid) is a pyrophosphate analog and member of a new class of reverse transcriptase inhibitor (RTI) that is being developed to provide benefits for treatment-resistant HIV-infected patients. The resistance profile of ANX-201 is unique among approved RTIs and has been shown to resensitize NRTI-resistant viruses. In preclinical studies, ANX-201 has shown activity against treatment-resistant clinical isolates and demonstrated synergistic activity with NRTIs, suggesting potential clinical benefits of combination therapy. In other preclinical studies, ANX-201 has shown broad-spectrum antiviral activity against HIV-1, HIV-2, human and avian influenza viruses, and herpes simplex viruses 1 and 2 (HSV-1 and HSV-2). About ADVENTRX Pharmaceuticals ADVENTRX Pharmaceuticals is a biopharmaceutical company focused on in-licensing, developing and commercializing proprietary product candidates primarily for the treatment of cancer and infectious disease. The Company seeks to improve the performance and commercial potential of existing treatments by addressing limitations associated with these treatment regimens. More information can be found on ADVENTRX's web site at http://www.adventrx.com/. Forward Looking Statement ADVENTRX cautions you that statements included in this press release that are not a description of historical facts are forward-looking statements that involve risks and assumptions that, if they materialize or do not prove to be accurate, could cause ADVENTRX's results to differ materially from historical results or those expressed or implied by such forward-looking statements. These risks and uncertainties include, but are not limited to: the validity of research results; the risk that preclinical results are not indicative of the success of subsequent clinical trials and that products will not perform as preclinical data suggests or as otherwise anticipated; unexpected adverse side effects or inadequate therapeutic efficacy of ADVENTRX's product candidates and other uncertainties inherent in the drug development process; the timing and success of clinical trials; difficulties or delays in developing, testing, manufacturing, and obtaining regulatory approval for ADVENTRX's product candidates; the risk that ADVENTRX will be unable to raise sufficient capital to fund the projects necessary to meet its anticipated or stated goals and milestones; and other risks and uncertainties more fully described in ADVENTRX's press releases and public filings with the Securities and Exchange Commission. ADVENTRX's public filings with the Securities and Exchange Commission are available at http://www.sec.gov/. You are cautioned not to place undue reliance on these forward-looking statements, which speak only as of the date when made. ADVENTRX does not intend to update any forward-looking statement set forth in this press release to reflect events or circumstances arising after the date on which it was made. DATASOURCE: ADVENTRX Pharmaceuticals, Inc. CONTACT: Investors, Ioana C. Hone of ADVENTRX Pharmaceuticals, +1-858-552-0866 Web site: http://www.adventrx.com/

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