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Pharmaceutical developer sees potential for fighting difficult-to-treat cancers

[caption id="attachment_19296" align="alignright" width="209" caption="Dr. Christopher Starr is CEO and co-founder of Raptor Pharmaceutical."][/caption]

NOVATO -- A peptide acquired by Raptor Pharmaceutical Corp. as a possible delivery system for drug therapies has shown itself to be a direct inhibitor of the protein necessary for the growth of a particularly hard-to-treat form of breast cancer.

A peptide is an organic or synthetic compound composed of a series of linked amino acids. Peptides are the building blocks of proteins.

Developed by Dr. Guojun Bu of the University of Washington, the proprietary peptide can bind to and suppress LRP6, a receptor protein that signals over activation of some tumors of the type known as triple-negative breast cancer, meaning it does not respond to the three most widely used and effective cancer therapies.

According to Raptor Chief Scientific Officer Todd Zankel, some cancer proteins have already been targeted by antibodies developed to bind to and inhibit them. But the subset of tumors dependent on LRP6 do not respond to existing antibodies.

"We at Raptor are really interested in the triple-negative tumors, which represent about 15 percent of all tumors," he said, adding that the peptide developed by Dr. Bu addresses a certain percentage of triple-negative tumor types.

LRP6 is a signaling receptor, so the first step in developing a therapy was to identify a protein-signaling pathway required by the targeted subgroup of breast tumors and to demonstrate dependency on that pathway. The next was to develop a molecule to bind to a component of the signaling pathway, in this case LRP6, and turn off the signal.

"When that happens, the cancer stops growing and the tumors shrink," said Dr. Zankel.

The peptide's efficacy has been shown in animal testing, he said.

"A big advantage of using a peptide rather than an antibody is avoiding the toxicity associated with completely shutting off the activity of LRP6, which negatively affects other fast-growing cells such as hair follicles and digestive cells. The peptide acts by moderating the activity of LRP6 without completely turning it off."

Once the peptide goes into human testing, the toxicity is expected to be much less as a result of the moderating effect, he said.

According to Raptor CEO and co-founder Chris Starr, it will be up to his company to generate enough data to show the peptide's potential to treat disease. Then Raptor will either seek a development partner or license the peptide to a developer.

"We have a pretty full late-stage portfolio right now. Our Cysteamine product candidate (for the more effective, less toxic treatment of cystinosis in children) is nearing stage three clinical trials. So we'll probably go out and see if we can get a pharmaceutical interested in the LRP6-targeting peptide," said Dr. Starr.

He doesn't think it will be difficult to find a partner, given the promise of Dr. Bu's research.

Raptor Pharmaceutical recently hired its 10th and 11th full-time employees, after doing a reverse IPO by merging with TorreyPines, giving it a listing on Nasdaq and bringing in $7.5 million in direct stock sales.

"We're definitely on an up cycle with a good team and steady growth," said Dr. Starr.