SAN DIEGO and WOODCLIFF LAKE, N.J., Aug. 2, 2011 /PRNewswire/ —
Arena Pharmaceuticals, Inc. (NASDAQ:
ARNA) and Eisai Inc. announced today the completion of a
clinical study that measured lorcaserin concentrations in human
cerebrospinal fluid (CSF) and plasma and related data analyses. The
study was conducted to provide additional data that may be
informative for determining the human relevance of the observation
of brain astrocytoma in male rats. Using the results of this study
and other preclinical and clinical studies, Arena estimates that
the mean exposure of the human brain to lorcaserin at the
clinically tested dose (10 mg dosed twice daily (BID)) is
approximately 1.7 times the exposure in the human plasma. In
contrast, the measured exposure of the male rat brain to lorcaserin
at the dose at which no brain astrocytoma was observed (10
mg/kg/day) is approximately 24 times the exposure in the rat
plasma.

“We estimate that humans concentrate lorcaserin in the brain to
a much lower extent than do rats,” said William R. Shanahan, M.D.,
Arena’s Senior Vice President and Chief Medical Officer. “We
believe these results may be helpful in assessing the human
relevance of the observation of brain astrocytoma in the rat
carcinogenicity study.”

This study is one of the activities intended to address the
observation of brain astrocytoma in male rats as part of the
overall plan to submit a response to the lorcaserin Complete
Response Letter (CRL). Activities intended to address the
observation of mammary adenocarcinoma in female rats and other
issues identified by the US Food and Drug Administration (FDA) are
ongoing.

Study Rationale, Design and Related AnalysesBrain astrocytoma
was observed in male rats given certain doses of lorcaserin during
a two-year carcinogenicity study. One approach to estimating a
safety margin for this finding would be to use plasm

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