Silverback Therapeutics, headquartered in Seattle, closed on an oversubscribed Series B financing round worth $78.5 million. It was led by U.S. Venture Partners with participation from new investors including Nextech Invest, Hunt Investment Group, Pontifax Venture Capital, Colt Ventures and NS Investment. Existing investors participating included OrbiMed Advisors, Bristol Myers Squibb and Alexandria Venture Investments.
The company plans to use the funds to support continuing development of SBT6050, its anti-HER2 antibody conjugate that attaches to a potent TLR8 agonist to treat HER2-expressing solid tumors. It also will advance its pipeline of ImmunoTAC programs. Silverback hopes to file an Investigational New Drug application (IND) and launch a clinical trial for SBT6050 this year.
“Our preclinical studies demonstrate that systemic delivery of our TLR8 agonist targeted to HER2-expressing tumors potently activates myeloid cells to kill cancer and reprograms the tumor microenvironment, resulting in durable, curative single-agent activity,” said Peter Thompson, co-founder, chairman and chief executive officer of Silverback. “We are pleased to attract a group of world-class investors who believe in our bold vision to develop potent immune-modulating agents that can be delivered systemically, but act locally at the site of disease. With these additional resources, we’re focused on advancing our lead program into the clinic this year and progressing our preclinical pipeline assets towards the clinic.”
Jonathan Root, general partner at USVP and Thilo Schroeder, partner at Nextech, will join Silverback’s board of directors.
The financing round brings the company’s total investments up to about $125 million.
HER2 is overexpressed most notably in a subtype of breast cancer, which is particularly aggressive and does not respond well to hormone therapy. But HER2 is also expressed in subsets of lung, stomach and colon cancers.
Valerie Odegard, Silverback’s chief scientific officer, told Xconomy, “We initiated this program with a desire to identify a very potent agonist for myeloid cells, which are readily abundant in human tumors, and when they are appropriately activated, unleash a number of immunological mechanisms that ultimately kill tumor cells. The challenge has been really being able to target the myeloid cells in the tumor because of associated toxicities in the past with systemically administered TLR or myeloid cell agonists.”
One of the most common types of side effects of these drugs, particularly immunotherapies, is cytokine release syndrome. This is a massive overreaction of the immune system that causes body-wide inflammation. Silverback believes their drug conjugates can minimize the side effects by delivering the toxic chemotherapeutic agents directly to specific cancer markers, such as HER2.
The company has about 40 staffers. Its ImmunoTAC technology is designed to create potent therapeutic molecules that can be administered systemically, but that are so targeted to the disease sites that they minimize side effects.
In December, the company presented preclinical data from SBT6050 at the San Antonio Breast Cancer Symposium (SABCS). The data showed that the therapy effectively activated human myeloid cells and drove multiple anti-tumor immune mechanisms in a HER2 dependent manner in vitro. A mouse surrogate also showed potent anti-tumor effects as a single agent and in combination with Genentech’s Herceptin (trastuzumab)