Geneva, Switzerland, 13 July 2010 - Allosteric modulation company Addex Pharmaceuticals Ltd. (SIX:ADXN) announced today that its preclinical drug candidate ADX71943 was effective in a model of osteoarthritis pain. ADX71943 is a potent and selective positive allosteric modulator of gamma-aminobutyric acid subtype B (GABA-B) receptors. GABA-B receptors mediate the slow, prolonged physiological effects of the inhibitory neurotransmitter GABA and are implicated in pain processing.  Phase I clinical testing is scheduled to start by the end of 2010.

“We believe the allosteric mechanism of ADX71943 is the key factor in the differentiated tolerability and lack of tolerance development observed in these preclinical studies.  We look forward to testing this compound in humans, where we hypothesize that this product could provide not only a novel treatment for osteoarthritis pain, but also an important opioid-sparing therapy for other chronic pain indications,” Addex CEO Vincent Mutel said.

The effects of ADX71943 on mechanical hyperalgesia (increased pain sensitivity) and mechanical allodynia (pain produced by a normally innocuous stimulus) were assessed in the monosodium iodoacetate (MIA) model of osteoarthritis, a model of chronic nociceptive pain. ADX71943 significantly reduced mechanical hyperalgesia and showed a trend toward reducing mechanical allodynia after both acute and sub-chronic (8 days) dosing. Statistically significant antihyperalgesic activity was observed on the first day and was maintained on day 8, despite increased pain severity.

A maximal effect of ADX71943 was already achieved with the lowest dose tested (1 mg/kg). The efficacious plasma concentration (corresponding to 1 mg/kg) was approximately 30-50 ng/mL. Importantly, no development of tolerance was observed during the eight day treatment period.

Addex reported previously that ADX71943 is orally efficacious in rodent models of inflammatory pain (formalin test and Complete Freund's Adjuvant-induced hypersensitivity) and visceral pain (acetic acid-induced writhing). ADX71943 also displays an improved tolerability profile with reduced side effects compared to baclofen.

Baclofen, a marketed generic orthosteric GABA-B receptor agonist, has shown analgesic effects in animal models of inflammatory and neuropathic pain. There also is some evidence of analgesic activity of baclofen in patients with neuropathic and cancer pain, although its use in patients is limited by CNS side effects.

Addex Pharmaceuticals (www.addexpharma.com) discovers and develops allosteric modulators for human health and is focused on validated therapeutic targets for diseases of the central nervous system, metabolic disorders and inflammation. Subject to the completion of Phase I testing and regulatory approvals, Phase II clinical trials are expected to start in 2010 in four indications for two lead products: ADX48621, an mGluR5 negative allosteric modulator (NAM), in dystonia and Parkinson’s disease levodopa-induced dyskinesia (PD-LID); and ADX71149, an mGluR2 positive allosteric modulator (PAM), in schizophrenia and anxiety. ADX71149 is licensed to Ortho-McNeil-Janssen Pharmaceuticals Inc. In addition, Merck & Co., Inc. has licensed rights to two preclinical products: mGluR4 PAM for Parkinson's disease and mGluR5 PAM for schizophrenia. Additional preclinical discovery stage programs include: mGluR2 NAM, GLP1R PAM, IL1R1 NAM and TNFR1 NAM. Roche Venture Fund and SR-One, corporate venture arm of GlaxoSmithKline, are investors in Addex.

Chris Maggos
Investor Relations & Communications
Addex Pharmaceuticals
+41 22 884 15 11
chris.maggos(at)addexpharma.com

Disclaimer: The foregoing release may contain forward-looking statements that can be identified by terminology such as "not approvable", "continue", "believes", "believe", "will", "remained open to exploring", "would", "could", or similar expressions, or by express or implied discussions regarding Addex Pharmaceuticals Ltd, its business, the potential approval of its products by regulatory authorities, or regarding potential future revenues from such products. Such forward-looking statements reflect the current views of Addex Pharmaceuticals Ltd regarding future events, future economic performance or prospects, and, by their very nature, involve inherent risks and uncertainties, both general and specific, whether known or unknown, and/or any other factor that may materially differ from the plans, objectives, expectations, estimates and intentions expressed or implied in such forward-looking statements. Such may in particular cause actual results with allosteric modulators of mGluR2, mGluR4, mGluR5, mGluR7 or other therapeutic targets to be materially different from any future results, performance or achievements expressed or implied by such statements. There can be no guarantee that allosteric modulators of mGluR2, mGluR4, mGluR5, mGluR7 will be approved for sale in any market or by any regulatory authority. Nor can there be any guarantee that allosteric modulators of mGluR2, mGluR4, mGluR5, mGluR7 or other therapeutic targets will achieve any particular levels of revenue (if any) in the future. In particular, management's expectations regarding  allosteric modulators of mGluR2, mGluR4, mGluR5, mGluR7 or other therapeutic targets could be affected by, among other things, unexpected actions by our partners, unexpected regulatory actions or delays or government regulation generally; unexpected clinical trial results, including unexpected new clinical data and unexpected additional analysis of existing clinical data; competition in general; government, industry and general public pricing pressures; the company's ability to obtain or maintain patent or other proprietary intellectual property protection. Should one or more of these risks or uncertainties materialize, or should underlying assumptions prove incorrect, actual results may vary materially from those anticipated, believed, estimated or expected. Addex Pharmaceuticals Ltd is providing the information in this press release as of this date and does not undertake any obligation to update any forward-looking statements contained in this press release as a result of new information, future events or otherwise, except as may be required by applicable laws.