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Source: Pain Therapeutics, Inc.

Pain Therapeutics Announces Publication of New Data Demonstrating Better Opioid TherapyThursday July 21, 7:30 am ET

Five Publications to Appear in Peer-Reviewed Journals

SOUTH SAN FRANCISCO, Calif., July 21 /PRNewswire-FirstCall/ -- Pain Therapeutics, Inc. (Nasdaq: PTIE - News), a biopharmaceutical company, today announced the forthcoming publication of comprehensive new data that further demonstrate how ultra-low-dose opioid antagonists suppress undesirable effects of opioid therapy. Results of these studies are in press in four peer-reviewed journals and an academic review book. Data from these studies show that ultra-low-dose opioid antagonists can enhance analgesia; suppress certain ill effects of opioid therapy, such as tolerance or physical dependence; and reduce the euphoric/rewarding or addictive properties of opioid drugs. A new study also demonstrates a molecular mechanism of action for these effects at the level of opioid receptors. "These publications recognize exciting discoveries resulting from the tremendous efforts of academic collaborators, research clinicians and staff scientists," said Remi Barbier, president and chief executive officer. "The essential feature of these studies is simple to communicate: we believe they all support the use of painkillers containing ultra-low-dose opioid antagonists, such as Oxytrex. We also believe Oxytrex can address the large, growing clinical need for new ways to treat severe chronic pain, which makes this Phase III drug candidate all the more interesting." Pain Therapeutics' fundamental approach to developing new painkillers such as Oxytrex is to block the undesirable effects of opioid drugs by combining an ultra-low-dose opioid antagonist, such as naltrexone, with an opioid agonist, such as oxycodone. Oxytrex is a novel painkiller designed to deliver enhanced pain relief while minimizing certain ill effects of opioid therapy. For practical and ethical reasons, the Company does not conduct addiction studies in humans. About The New Publications The new publications expand on earlier scientific papers published in peer-reviewed journals, such as Brain Research (Crain & Shen, 2001) or Proceedings of the National Academy of Sciences USA (Crain & Shen, 1995). Collectively, these publications present a unified body of evidence that signaling changes by opioid receptors underlie tolerance and physical dependence and, potentially, the addictive effects of opioid drugs, since suppressing excitatory signaling with ultra-low-dose opioid antagonists suppresses these effects. The following publications are in press or published and will be linked to our web site (www.paintrials.com) upon publication. 1. Adding ultra-low-dose naltrexone to oxycodone enhances and prolongs

analgesia: A randomized, controlled trial of Oxytrex. (2005)

Chindalore VL, Craven RA, Yu KP, Butera PG*, Burns LH*, Friedmann N*.

Journal of Pain 6(6): 392-399.

2. Ultra-low-dose naltrexone suppresses rewarding effects of opiates and

aversive effects of opiate withdrawal in rats. (2005) Olmstead MC,

Burns LH*. Psychopharmacology, in press.

3. Ultra-low-dose naltrexone reduces rewarding potency of oxycodone and

relapse vulnerability in rats. (2005) Leri F, Burns LH*. Pharmacology,

Biochemistry and Behavior, in press.

4. Ultra-low-dose naloxone suppresses opioid tolerance, dependence and

associated changes in Mu opioid receptor -- G protein coupling and G..

signaling. (2005) Wang HY, Friedman E, Olmstead MC, Burns LH*.

Neuroscience, in press.

5. Ultra-low-dose opioid antagonists enhance opioid analgesia while

reducing tolerance, dependence and addictive properties. (2005) Burns

LH*. In: Recent Developments in Pain Research (Research Signpost, ed:

Capasso) pp. 115-136.

* Indicates author is on the scientific or clinical staff of Pain Therapeutics, Inc. The first paper describes a previously announced Phase II study designed to evaluate the safety and efficacy of Oxytrex relative to oxycodone and placebo. Over 350 patients suffering from moderate to severe chronic pain due to advanced osteoarthritis were enrolled. In this study, Oxytrex reduced pain scores by about 40% (p<0.001 vs. placebo and p=0.006 vs. oxycodone) over a 21-day treatment period with no overall increase in side-effects. By comparison, an equivalent daily dose of oxycodone reduced patients' pain scores by just 24%. The next two papers show a reduced addictive potential of Oxytrex. The first study was conducted in the laboratory of Assistant Professor C. Olmstead, Queen's University, Kingston, Ontario, and shows that the acute rewarding or euphoric effects of analgesic doses of Oxytrex are either absent or not sufficient to produce an environmental conditioning effect in rats. In contrast, oxycodone produces a strong rewarding effect. Additionally, prolonged treatment with Oxytrex followed by withdrawal did not produce a negative or aversive conditioning effect, in contrast to withdrawal from prolonged oxycodone treatment. Another study conducted in the laboratory of Assistant Professor Francesco Leri, University of Guelph, Ontario, directly examined self-administration of Oxytrex vs. oxycodone and subsequent drug-seeking behavior in rats. Results suggest that Oxytrex is significantly less rewarding and that drug craving should be reduced. The fourth paper speaks to the mechanism of action of ultra-low-dose opioid antagonists at the level of the opioid receptor. The data demonstrate that ultra-low-dose opioid antagonists prevent signaling changes of opioid receptors that underlie opioid tolerance and dependence. The laboratory of Associate Professor Hoau-Yan Wang of CUNY Medical School showed that chronic opioid treatment produces a switch in G protein coupling by the mu opioid receptor and that this switch is largely prevented by co-treatment with an ultra-low-dose opioid antagonist. In addition, the efficiency of coupling to the original G proteins is enhanced in the spinal cord even compared to opioid-naive rats, offering a possible explanation for enhanced analgesia of acute administration. The fifth publication is a book chapter that summarizes pre-clinical and clinical data regarding ultra-low-dose opioid antagonists combined with opioid agonists, including enhanced and prolonged analgesia, reduced tolerance, dependence and addictive properties. The chapter also provides an overview of the molecular mechanism of action. About Pain Therapeutics, Inc. We are a biopharmaceutical company that develops novel drugs. Our drug candidates target severe chronic pain, such as low-back pain or pain due to osteoarthritis or irritable bowel syndrome. We have three unique drug candidates in clinical development: Oxytrex, Remoxy and PTI-901, all of which are in Phase III clinical trials. We believe the target market for our three drug candidates exceeds $3 billion per year. We own commercial rights to our drug candidates. For more information please visit our website at www.paintrials.com. Note Regarding Forward-Looking Statements: This press release contains forward-looking statements for purposes of the Private Securities Litigation Reform Act of 1995 (the "Act"). PTI disclaims any intent or obligation to update these forward-looking statements, and claims the protection of the Safe Harbor for forward-looking statements contained in the Act. Examples of such statements include, but are not limited to, any statements relating to the timing, scope or expected outcome of the Company's clinical development, the potential benefits the Company's drug candidates and the size of the potential clinical opportunity or market for any of the Company's products. Such statements are based on management's current expectations, but actual results may differ materially due to various factors. Such statements involve risks and uncertainties, including, but not limited to, those risks and uncertainties relating to difficulties or delays in development, testing, regulatory approval, production and marketing of the Company's drug candidates, unexpected adverse side effects or inadequate therapeutic efficacy of the Company's drug candidates that could slow or prevent product approval or market acceptance (including the risk that current and past results of clinical trials are not necessarily indicative of future results of clinical trials), the uncertainty of patent protection for the Company's intellectual property or trade secrets, the Company's ability to obtain additional financing if necessary and unanticipated research and development and other costs. For further information regarding these and other risks related to the Company's business, investors should consult the Company's filings with the Securities and Exchange Commission.

Source: Pain Therapeutics, Inc.