Cyteir Adds $40M for Clinical Test of “Synthetically Lethal” Cancer Drug

Xconomy Boston — 

Cyteir Therapeutics has $40.2 million more in cash to support early-stage tests of a drug intended to treat cancer by targeting a tumor repair mechanism.

The new cash that Cyteir announced Tuesday adds to a Series B round of funding it raised last year. The Lexington, MA-based company says the amount invested in the round now totals $75.2 million. The latest cash infusion was led by Novo Holdings.

Cyteir is developing drugs that tap into genetic interactions that lead to the death of cancer cells, an approach called “synthetic lethality.” The company’s approach focuses on a DNA-damaging protein called activation-inducted cytidine deaminase (AID). While cytidine deaminases are present in healthy tissues, they don’t cause cell death. But Cyteir says that in a wide range of cancers, they become hyperactive and cause elevated levels of DNA damage. Cancers rely on another protein, RAD51, to repair that damage. Cyteir is developing small molecule drugs that block the activity of RAD51 and leave the mutated DNA to build up unchecked, resulting in cell death.

During the annual meeting of the American Association for Cancer Research in March, Cyteir presented preclinical data showing that its lead compound, CYT-0851, could treat B-cell lymphomas and a number of solid tumors, including pancreatic cancer. The company is now testing its experimental drug in humans. The company says its Phase 1/2 study will enroll up to 200 patients with B-cell malignancies and solid tumors.

The company is also developing a test to identify patients whose tumors are abundant with AID, meaning they could potentially be treated with a RAD51 inhibitor.

Other companies have already brought to the market cancer drugs that leverage synthetically lethal interactions. Clovis Oncology (NASDAQ: CLVS) and Tesaro, which is now part of GlaxoSmithKline(NYSE: GSK), are among the companies that have commercialized drugs targeting a cancer-repair enzyme called PARP. Cyteir said its preclinical data suggest its drugs could work in combination with PARP inhibitors, and may also provide a treatment option in cases where cancers have become resistant to PARP-blocking drugs. Another biotech that is trying to develop an alternative to PARP inhibitors is Repare Therapeutics, which closed $82.5 million in Series B funding in September to advance two drugs to clinical testing within the next 18 months.

Cyteir’s addition to its Series B financing includes participation from earlier investors Venrock, DROIA Oncology Ventures, Osage University Partners, Lightstone Ventures, and Celgene (NASDAQ: CELG). As part of the new investment, Karen Hong, a partner at Novo Ventures, is joining the Cyteir board. Novo Ventures provides consulting services to Novo Holdings.

Here’s more on Cyteir’s approach to synthetically lethal cancer drugs.

Pancreatic cancer cells image from the National Cancer Institute