CytomX Snags $25M From Pfizer to Make Souped-Up Antibodies

Xconomy San Francisco — 

Pfizer was tripped up a couple years ago, when safety concerns emerged around the first drug ever approved that could combine the targeting ability of an antibody with a toxin to give it more tumor-killing kick. But the New York-based pharma giant still sees potential in the field of souped-up antibody drugs, and it’s seeking help from South San Francisco-based CytomX Therapeutics, a startup aiming to make potent, but safer, drugs of this kind.

CytomX is announcing today that it has formed a partnership with Pfizer (NYSE: PFE) to help the bigger company develop multiple antibody-drug conjugate products, against multiple molecular targets, to fight cancer. The little company is eligible to get up to $25 million through upfront payments, research payments, and for hitting certain near-term goals in animal testing. In a best-case scenario, CytomX could collect as much as $610 million if the fruits of the collaboration reach certain regulatory and sales goals, plus royalties on future product sales. Pfizer will pay the bills for clinical development and commercialization of any drugs that come from the partnership.

Pfizer is expressing growing interest in one of the hotter fields in biotech today, in which scientists are designing antibodies to be more potent than ever before against tumors. Pfizer inherited the first drug in this class, gemtuzumab ozogamicin (Mylotarg), through its 2009 acquisition of Wyeth, but scientists believe it failed to deliver on the concept because it didn’t have a stable enough linker to keep the antibody and drug intact long enough in the bloodstream so it could hit the tumor. The drug was pulled off the market in 2010, but since then, interest has only grown in the field. Seattle Genetics won FDA clearance for an empowered antibody against rare lymphomas, and Roche/Genentech more recently got cleared to sell trastuzumab emtansine (Kadcyla), a souped-up version of its original “naked” antibody marketed as Herceptin.

“Interest in the industry is intensifying if anything,” said CytomX CEO Sean McCarthy (pictured above). “The approval of Kadcyla is continuing to galvanize the industry to drive forward.” He adds: “We’re obviously thrilled with this deal, it’s a big step forward for the company.”

Pfizer has its own internal capabilities for making antibody drug conjugates, and it has a collaboration with Seattle Genetics, in which it is using that company’s antibody-drug linking technology against a single molecular target for treating cancer. The CytomX deal is broader than that, because it includes multiple drug candidates against multiple targets, although the number of targets, and the names of them, aren’t being disclosed.

The partnership with Pfizer is the first validation from a Big Pharma company for CytomX, which was founded in 2008 with technology from UC Santa Barbara. The company raised a $30 million Series B venture financing in September 2010 from Third Rock Ventures and Roche Venture Fund. The company added Canaan Partners to its list of Series B backers last July, and tacked on an additional $11 million in financing.

CytomX’s big idea is to combine a peptide with the antibody, so that the drug only gets activated in the presence of certain enzymes (proteases) in diseased cells. This way, the antibody will remain inactive while it circulates in the bloodstream, and then get activated when it comes into contact with these disease-related proteases. CytomX calls its molecules “Probody Drug Conjugates.”

The company, which has 28 full-time employees, still has the flexibility and capacity to do more partnerships against different cancer targets, and to make drug candidates against other diseases, McCarthy said. The company will continue to look for those deals to bring in cash to support operations, and get the most leverage out of its early venture investment, McCarthy said.

CytomX has said publicly that it is seeking to use its technology to make an antibody drug that could compete with Eli Lilly’s cetuximab (Erbitux) and Amgen’s panitumumab (Vectibix) against a target called EGFR. CytomX still retains full ownership of that drug program after striking the new collaboration with Pfizer, McCarthy said.