Shifting to Cancer Immunotherapy, CytomX Bags $70M In Crossover Cash

Xconomy San Francisco — 

[Corrected 6/17/15, 12:30pm. See below.] CytomX Therapeutics is crossing over in more ways than one.

With the help of investors who typically make bets on the public side of the market, the private biotech has reeled in a $70 million Series D financing. These so-called “crossover” investors are often a sign that a biotech is gearing up to go public.

South San Francisco, CA-based CytomX is also crossing over from a different product focus to ride the cancer immunotherapy wave. Sometime next year, if all goes well, CEO Sean McCarthy expects a move into the clinic for the company’s first anti-PDL1 checkpoint inhibitor—a type of immunotherapy that prevents tumors from suppressing a patient’s immune system.

[A previous version of this paragraph misstated CytomX’s funding history.] Two years ago nearly to the day, CytomX Therapeutics reeled in $25 million from Pfizer (NYSE: PFE) in a partnership to develop antibody-drug conjugates, or ADCs, which was CytomX’s main focus at the time. ADCs are a type of cancer treatment that attach a potent cell-killing drug to an antibody, which acts as a homing device to the tumor. There was no mention of cancer immunotherapy or checkpoint inhibitors. (CytomX announced a $20 million Series C round in January with Pfizer’s venture group in the lead.)

But CytomX has also been developing antibodies without the conjugation piece of the puzzle. As the cancer field has shifted to embrace immunotherapy the past couple years, CytomX is now rushing to take advantage of the momentum. The company wants to ask the FDA for a green light to test its own immunotherapy agent in humans next year, then quickly move it into combination studies with other cancer therapies, said McCarthy.

CytomX’s specialty is a type of antibody it calls a “Probody,” which is supposed to stay inactive in the patient until it gets to the specific area it’s meant to affect. In the case of cancer, that area is known as the tumor microenvironment. Once a Probody reaches its target microenvironment, enzymes specific to that location snip away the chemical “mask” that CytomX has constructed, and the drug becomes active.

The idea is to deliver powerful drugs to tumors without letting them go astray in the body and hit healthy tissues, causing bad side effects. Side effects have been a problem with the first wave of checkpoint inhibitors to be approved, starting with ipilumumab (Yervoy) from Bristol-Myers Squibb. Most notable is the severe rash and other immune-related problems with ipilumumab, as I described here.

McCarthy envisions his Probodies providing “local delivery of immunotherapy but with a systemic dosing,” giving doctors the possibility of more powerful doses delivered more precisely, with less fear of triggering side effects.

Do Probodies work? In humans, no one knows yet. No Probody has yet entered a clinical trial, either as part of a conjugate product or as a single agent. A Probody-drug conjugate wholly owned by CytomX could reach the clinic “in the 2017 timeframe,” McCarthy said. He declined to comment on the status of Probodies licensed to its pharma partners.

The Series D round was led by Fidelity and included Casdin Capital, Cormorant Asset Management, Deerfield Management, Perceptive Advisors, Redmile Group, Tekla Healthcare Investors and Tekla Life Sciences Investors, Venrock Healthcare Capital Partners, Wellington Management Company and additional undisclosed investors.