ACS Medicinal Chemistry Letters
LETTER
toxicity and no significant alterations in body weight were
observed at any dose for either 17 or 19.
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In summary, selective, orally bioavailable, and efficacious
inhibitors of B-RafV600E were developed. These inhibitors were
based on a novel 3-methoxy pyrazolopyridine hinge-binding
template, which evolved through structure-based design from a
simple pyridine lead (3). While the activity of 3 was micromolar
in both enzymatic and cellular assays, the introduction of a
hydrogen bond donor, utilization of a bicyclic hinge-binding
template, and addition of lipophilic contacts provided potent
pyrrolo- and pyrazolopyridine inhibitors of B-RafV600E. Optimi-
zation at the 3-position ultimately led to 3-methoxy pyrazolopyr-
idines 17 and 19, which demonstrated a 300-fold improvement
in potency over the lead pyridine 3. Compounds 17 and 19 were
highly potent against a broad panel of cancer cell lines driven by
B-RafV600E, particularly those derived from colon cancer, and
displayed significant antitumor activity in an in vivo colon cancer
model driven by B-RafV600E. Although 17 and 19 were well
tolerated in mice during the xenograft studies, RAF inhibitors
have been reported to activate the MAPK pathway in B-RafWT
cells.19,20,22,31-33 This paradoxical activation has been linked to
enhanced proliferation and stimulated tumor growth in vivo, and
hyperplasia of normal epithelial cells was observed in mice.34
Pyrazolopyridine Raf inhibitors likewise activate the MAPK
pathway, and the results from these studies will be presented
elsewhere.
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’ ASSOCIATED CONTENT
S
Supporting Information. Experimental procedures for
b
the synthesis of 3-5, 8-10, 13-19, kinase selectivity, and cell
viability data for 17 and 19 and details of in vitro and in vivo
assays. This material is available free of charge via the Internet at
’ AUTHOR INFORMATION
(14) Johnson, L. N. Protein kinase inhibitors: Contributions from
structure to clinical compounds. Q. Rev. Biophys. 2009, 42, 1–40.
(accessed Feb 22, 2011). A study to evaluate RAF265, an oral drug
administered to subjects with locally advanced or metastatic melanoma.
(16) Schwartz, G. L.; Robertson, S.; Shen, A.; Wang, E.; Pace, L.;
Dials, H.; Mendelson, D.; Shannon, P.; Gordon, M. A phase I study of
XL281, a selective oral RAF kinase inhibitor, in patients (Pts) with
advanced solid tumors. J. Clin. Oncol. 2009, 27, 15sAbstr. 3513.
(17) Kefford, R.; Arkenau, H.; Brown, M. P.; Millward, M.; Infante,
J. R.; Long, G. V.; Ouellet, D.; Curtis, M.; Lebowitz, P. F.; Falchook, G. S.
Phase I/II study of GSK2118436, a selective inhibitor of oncogenic
mutant BRAF kinase, in patients with metastatic melanoma and other
solid tumors. J. Clin Oncol. 2010, 28, 15sAbstr. 8503.
Corresponding Author
*Tel: 303-641-1076. E-mail: steve.wenglowsky@arraybiopharma.
com.
’ ACKNOWLEDGMENT
We thank Josh Ballard for HRMS data and Ben Colson for
solubility determinations. We also thank Jim Blake for helpful
discussions.
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dx.doi.org/10.1021/ml200025q |ACS Med. Chem. Lett. 2011, 2, 342–347