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SAN DIEGO — Peering through a microscope more than a half century ago, researchers made a head-scratching finding: they spotted tiny rings of DNA in tumor cells that were largely absent in healthy cells. Now, a San Diego biotech company is targeting these loops of genetic material to try to control the growth and spread of deadly tumors.

Boundless Bio is testing a small-molecule drug against what scientists call extrachromosomal DNA, in an initial clinical trial of patients with solid tumors. The company, which last week reported that it has dosed its first patient, announced on Tuesday that it raised $100 million to bankroll the ongoing trial as well as future work around other therapies.


The company expects to have data on the safety of its drug, BBI-355, by the end of this year and early signs of its effectiveness by the first half of 2024. Success isn’t guaranteed, as about 90% of drugs that enter clinical trials fail along the way. But if it beats those odds, Boundless will have developed the first-ever extrachromosomal DNA-directed therapy.

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