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OSI Pharmaceuticals, Inc. (Nasdaq: OSIP) provided an informational
update on data from its two preclinical development compounds, PSN821
and PSN602. This information was presented at the annual meeting of
the American Diabetes Association in San Francisco, CA. Preclinical
data on PSN821, a novel, orally available agonist of the G-protein
coupled receptor GPR119, being developed for the treatment of type 2
diabetes and obesity, were presented in an oral presentation. Also
presented were preclinical data on PSN602, an oral dual serotonin and
norepinephrine reuptake inhibitor and 5-HT1A agonist, being developed
for the treatment of obesity. Both compounds are due to enter Phase I
clinical trials in 2008.

“With diabetes and obesity rapidly emerging as a global health
care problem that threatens to reach pandemic levels we recognize the
need for novel, next-generation drugs and are encouraged by our
research from both of these programs,” said Anker Lundemose, M.D.,
Ph.D., President of (OSI) Prosidion. “PSN821 has the potential to be
the first orally available molecule which delivers both glucose
control and substantial weight loss, while PSN602 is designed to give
greater weight loss efficacy without causing the cardiovascular side
effects seen with some anti-obesity agents.”

Following are summaries of the two presentations:

PSN821: A Novel Oral GPR119 Agonist for the Treatment of Type 2
Diabetes Producing Substantial Glucose Lowering and Weight Loss in
Rats (Matthew Fyfe et al., Abstract # 297-OR)

In this presentation, OSI researchers presented preclinical data
suggesting that PSN821 has the potential to achieve, as an oral agent,
both substantial glucose lowering and meaningful body weight loss in
patients with type 2 diabetes. PSN821, which stimulated the release of
both insulin and Glucagon-like peptide-1 (GLP-1), demonstrated
pronounced glucose lowering in rodent models of type 2 diabetes with
no loss of efficacy on repeated administration, and substantial
reductions of body weight in a rodent model of obesity.

Data from the studies showed, in male diabetic ZDF rats, that both
acute and chronic administration of PSN821, given orally,
significantly and dose-dependently reduced glucose excursions in an
oral glucose tolerance test. Further, in prediabetic male ZDF rats
daily oral dosing of PSN821 for 8 weeks significantly lowered
non-fasting blood glucose concentrations and HbA1c levels compared to
vehicle. Data also showed that in weight-stable, dietary-induced obese
(DIO) female Wistar rats, daily oral dosing of PSN821 for 4 weeks
reduced body weight substantially and significantly by 8.8%, comparing
favorably with the 10.6% weight loss induced by a high dose of the
prescribed anti-obesity agent, sibutramine.

PSN602: A Novel Monoamine Reuptake Inhibitor with 5-HT1A Agonism
That, in Rats, Exhibits Equivalent Weight Loss to Sibutramine with a
Superior Cardiovascular Profile (Gerard H Thomas et al., Abstract #
1744-P)

Sibutramine is a dual serotonin (5-HT) / norepinephrine (NE)
reuptake inhibitor approved for the treatment of obesity. It is
associated with elevations in blood pressure and heart rate in some
patients, raising safety concerns and limiting the ability to dose
titrate upwards to achieve greater efficacy. It was hypothesized that
the addition of 5-HT1A agonism to monoamine reuptake inhibition would
reduce the risk of unwanted cardiovascular activity. OSI researchers
presented preclinical data demonstrating that PSN602 was as effective
as a high dose of sibutramine at reducing body weight in a rodent
model of obesity, but exhibited a more favorable cardiovascular
profile after single doses.

Data from the study showed that PSN602, in vitro, is a potent
inhibitor of both NE and 5-HT reuptake and a full agonist at the
5-HT1A receptor. In weight-stable, dietary-induced obese (DIO) female
Wistar rats, daily oral dosing of PSN602 for 4 weeks significantly
reduced body weight by 9-17% compared with controls, matching the
weight loss (14%) induced by a high dose of sibutramine. In
telemetered rats, single oral doses of PSN602 (up to 3 x ED50 to
inhibit food intake over 24h), in contrast to sibutramine (2 x ED50 to
inhibit food intake over 24h), caused no significant rise in mean 2-8h
blood pressure or mean 2-8h heart rate. Translation of these effects
to man would potentially allow dose-escalation of PSN602 to achieve
greater weight loss than that seen with sibutramine.

About OSI Pharmaceuticals

OSI Pharmaceuticals is committed to “shaping medicine and changing
lives” by discovering, developing and commercializing high-quality and
novel pharmaceutical products designed to extend life and/or improve
the quality of life for patients with cancer and diabetes/obesity. The
Company’s oncology programs are focused on developing molecular
targeted therapies designed to change the paradigm of cancer care.
OSI’s diabetes/obesity efforts are committed to the generation of
novel, targeted therapies for the treatment of type 2 diabetes and
obesity. OSI’s flagship product, Tarceva(R) (erlotinib), is the first
drug discovered and developed by OSI to obtain FDA approval and the
only EGFR inhibitor to have demonstrated the ability to improve
survival in both non-small cell lung cancer and pancreatic cancer
patients in certain settings. OSI markets Tarceva through partnerships
with Genentech, Inc. in the United States and with Roche throughout
the rest of the world. For additional information about OSI, please
visit http://www.osip.com.

This news release contains forward-looking statements. These
statements are subject to known and unknown risks and uncertainties
that may cause actual future experience and results to differ
materially from the statements made. Factors that might cause such a
difference include, among others, the completion of clinical trials,
the FDA review process and other governmental regulation, OSI’s and
its collaborators’ abilities to successfully develop and commercialize
drug candidates, competition from other pharmaceutical companies, the
ability to effectively market products, and other factors described in
OSI Pharmaceuticals’ filings with the Securities and Exchange
Commission.