CytomX's antibody therapies target cancer, leave healthy tissue intact

Antibody technology holds promise for treating a wide array of diseases, and designing new antibodies is a hot area in biotech research right now. On the heels of Genentech's February FDA approval for its antibody-drug conjugate breast cancer therapy Kadcyla, one company is developing a new class of antibodies to combat cancer.

At the American Association for Cancer Research (AACR) annual meeting in Washington, D.C., April 6-10, CytomX Therapeutics presented promising preclinical research on its new probody platform and epidermal growth factor receptor (EGFR) probody drug conjugate.

In an interview at the AACR meeting, CytomX CEO Sean McCarthy explained to FierceBiotechResearch that a probody is an antibody that's engineered so that the antigen-binding site is masked and can't see the target. These masks are engineered so they can be removed from the antibody only by enzymes associated with the disease tissue.

The challenge with traditional antibodies, McCarthy said, is that the targets are often not only in disease tissue. So while an antibody might bind to a target in disease tissue, if that target is expressed or present in normal tissue, the antibody will bind in normal tissue, which has a harmful effect on normal tissue.

"We have been positioning probodies as a new generation of more highly tissue-targeted antibodies," McCarthy said.

In human cell models, mice and monkeys, the EGFR probody singled out and destroyed tumor tissues without harmful side effects. In monkeys, animals showed no signs of dermatological toxicity--skin rash--that is a hallmark of currently available treatments targeting EGFR.

McCarthy said the probody technology essentially provides the same benefits of antibody therapeutics without significant side effects, plus it expands the therapeutic window.

San Francisco-based CytomX has attracted attention--and funds--for its targeted antibody drugs and is backed by Canaan Partners, Third Rock Ventures and Roche Venture Fund.

- here's the CytomX press release