Bitterroot Bio nabs $145M Series A with a plan to tackle challenging cancer target for heart medicines

The founders of cancer biotech Forty Seven had initially envisioned that the company would also work on developing heart drugs that cut down inflammation. Before it could really get started on that front, however, the company was bought by Gilead for $4.9 billion.

But Forty Seven’s founders, including Stanford professor of cardiovascular medicine Nick Leeper and stem cell pioneer Irv Weissman, kept working on that science, publishing an article in the New England Journal of Medicine in 2021 demonstrating how Forty Seven’s lymphoma drug candidate magrolimab also tamped down on blood vessel inflammation.

Now, that initial vision is coming into fruition — independent of Gilead and Forty Seven (but with foundational IP from them). The Stanford duo launched Bitterroot Bio in 2021 after the publication of that paper, and the biotech announced Wednesday morning it closed a $145 million Series A from some deep-pocketed investors: ARCH Venture Partners, Deerfield Management, Google’s venture arm GV, Koch Disruptive Technologies and Alexandria Venture Investments.

ARCH’s Steve Gillis chairs Bitterroot’s board, and Pavan Cheruvu, formerly head of Sio Gene Therapies (which was previously Axovant), joined as CEO. Craig Basson, who worked on Novartis’ canakinumab — an inflammation drug the pharma company was testing in heart disease before the program imploded, and who later became CMO of Boston Pharma — is Bitterroot’s CMO. The biotech, based out of both Palo Alto and Boston, currently has 15 employees, along with a network of consultants.

“Don’t eat me”

The name Bitterroot is derived from the Bitterroot Valley in Montana, where both Weissman and Leeper grew up. Weissman has a ranch by the Bitterroot River where he holds lab retreats, and he and Leeper would go fly fishing and take long afternoon walks by the river, which Leeper says is “perhaps one of the most beautiful rivers in the world.”

It was on one of those afternoon walks where the early ideas for the biotech were born.

Bitterroot Bio’s first program, an antibody known as BRB-002, targets CD47, the same “don’t eat me” signal as Forty Seven and Gilead’s magrolimab. CD47 is a protein found on the surfaces of healthy cells to tell white blood cells not to destroy them — but cancer cells use the signal to protect themselves from the immune system.

By targeting CD47 in cancer, the goal is to block that signal from cancer cells so that white blood cells consume them. However, research out of Leeper’s lab suggests that blocking the signal can also cut inflammation, which may play a key role in heart disease.

Craig Basson

Basson told Endpoints News that the biotech hopes BRB-002 will be in the clinic sometime next year. Cheruvu added that the raise will give them enough funding to push it through Phase IIa studies, which will provide initial proof-of-concept.

The biotech’s pursuit of an anti-CD47 program comes at a time where others like AbbVie and Zai Lab are winding down their respective CD47 cancer programs after magrolimab was put on clinical hold by the FDA due to safety issues, raising concerns about the target.

Cheruvu was quick to assuage such concerns, noting that they took safety into consideration early on in the design of their molecule. Basson added, “There are a number of proprietary modifications that limit those adverse effects that have been seen before in oncology, in addition to the sheer potency of the molecule — allowing us to dose at much, much lower levels that are used in oncology.”

The founding team outside of Leeper and Weissman includes Lou Lange and the late John Martin, the former CEO of Gilead who built the company up from its HIV franchise. Leeper told Endpoints that Lange and Martin are both important mentors to him, and that they helped the biotech build its management team and attract investors, as well as well-known cardiologists as scientific advisors.

“We were very sad about his untimely passing, and we continue to honor his memory today,” Leeper said of Martin. “There’s a plaque in our headquarters in his memory. We hope to one day have a program for fellows that can be named in his memory as our research efforts grow.”

As for future programs, Bitterroot plans to look outside of CD47. Cheruvu said aside from the biotech’s own discovery efforts, it is also looking at assets from academia and industry. “We think CD47 is really the tip of the iceberg in terms of what can be done in the cardiovascular space,” he said.

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