VX-680 is active against Gleevec Resistant BCR ABL and T315I mutant

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Good news!

Paper in Cancer Research Further Validates Ambit Biosciences'

KinomeScan Kinase Profiling Platform

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SAN DIEGO--(BUSINESS WIRE)--Jan. 16, 2006--Ambit Biosciences today

announced the publication in the January 15, 2006 issue of the

journal Cancer Research of a crystal structure that explains why the

Aurora kinase inhibitor VX-680 is active against Gleevec®

(imatinib)-resistant forms of the kinase BCR-ABL, including the T315I

mutant variant. The T315I mutation is the most common drug-resistant

mutation in chronic myelogenous leukemia (CML) and confers resistance

not only to Gleevec, but to all second generation BCR-ABL inhibitors

currently in clinical development. The interaction between VX-680 and

BCR-ABL variants was initially identified using Ambit's proprietary

KinomeScan kinase profiling platform.

The Cancer Research study was published in an article

entitled " Structure of the kinase domain of an imatinib-resistant Abl

mutant in complex with the Aurora kinase inhibitor VX-680 " (

A. Young, et al.) and is available online this week. The binding

profile of VX-680 across a large panel of kinases including ABL

(T315I), determined with KinomeScan technology, was published

previously by Ambit scientists in the August 2, 2005 issue of the

Proceedings of the National Academy of Sciences (PNAS) ( " Inhibition

of drug-resistant mutants of ABL, KIT, and EGF receptor kinases "

(Todd A. , et al.)).

" These data demonstrate that KinomeScan's profile of VX-680 was right

on target, " said Salka, Chief Executive Officer of Ambit. " This

study also highlights the versatility of KinomeScan, which rapidly

identifies, characterizes and quantifies kinase-small molecule

interactions. It can be utilized throughout the drug discovery and

development continuum, from specificity and lead optimization to the

identification of new indications for clinical compounds such as VX-

680. Additionally, Ambit has used KinomeScan to discover next-

generation kinase inhibitors, which we are currently evaluating in

preclinical studies, including a compound that specifically targets

the T315I mutation. "

The Cancer Research study was led by Young, Ph.D., and

Kuriyan, Ph.D., of the Medical Institute, University of

California, Berkeley, in collaboration with Neil Shah, M.D., Ph.D.,

and Sawyers, M.D., of the Medical Institute at

the University of California, Los Angeles, and Ambit Biosciences. The

study describes the crystal structure of VX-680 bound to the

catalytic domain of BCR-ABL containing a mutation that causes Gleevec

resistance but is inhibited by VX-680 in vitro. The paper also

demonstrates that VX-680 inhibits BCR-ABL activity in cells derived

from patients carrying the T315I mutation and that it retains

activity against T315I in vitro. VX-680 is currently being evaluated

in a Phase 1 clinical trial for cancer by Vertex Pharmaceuticals and

Merck.

About Ambit Biosciences

Ambit Biosciences is a privately-held biopharmaceutical company

engaged in the discovery and development of small molecule kinase

inhibitors for the treatment of cancer. Ambit plans to initiate

clinical trials for oncology in 2006. Ambit's proprietary kinase

screening technology, designed to expedite the drug discovery and

development process, has been validated through collaborations with

Roche, Bristol-Myers Squibb Company, GlaxoKline, Pfizer and

others. Ambit has raised a total of more than $50 million from

investors including Perseus-Soros Biopharmaceutical Fund, Forward

Ventures, Roche Venture Fund, Avalon Ventures, GIMV NV, MDS Capital

and Genechem.