ANX-201 Demonstrates a Unique Resistance Profile in Preclinical Tests

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
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You are cautioned not to place undue reliance on these forward-looking
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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.
SOURCE ADVENTRX Pharmaceuticals, Inc.

Investors, Ioana C. Hone of ADVENTRX Pharmaceuticals, +1-858-552-0866