Mersana Adds $4M For Next-Generation “Armed” Cancer Drugs

5/1/12Follow @arleneweintraub

Cambridge, MA-based Mersana Therapeutics is working in one of the hottest areas of biotech research—it’s figuring out new ways to attach potent anti-cancer drugs to specialized molecules that deliver the medicine directly to tumors while sparing healthy tissue. Now the company has added $4 million to a previously disclosed debt round that brought in $10 million all together, according to an SEC filing. Mersana has raised a total of $50 million since it was founded in 2005, says Michael Metzger, the company’s chief operating officer.

Mersana was founded on a technology called Fleximer, which was developed at Massachusetts General Hospital. Fleximer is a type of biodegradable polymer that was originally explored for use in diagnostics and imaging. But Mersana’s founders recognized that Fleximer’s properties made it an ideal carrier for potent payloads of cancer drugs. The company designed a system of linked Fleximer molecules that can remain stable in the bloodstream until they arrive inside cancer cells, at which point they release the drugs they are carrying.

The company initially applied Fleximer to two existing anti-cancer chemicals: camptothecin and fumagillin. Both have well-known tumor-fighting capabilities, but their toxic side effects have made them minimally useful in oncology. Fleximer solves that problem, says Timothy Lowinger, Mersana’s chief scientific officer. “The blood vessels in tumors are known to be somewhat leaky,” Lowinger says. Certain nano-sized particles can leak through those vessels and accumulate in tumors. “But they don’t leak through the healthy vasculature. We can take advantage of that effect,” he says, by designing Fleximer-based molecules that target tumors but don’t build up in health tissue.

Mersana’s fumagillin drug is in early-stage trials and licensed to the Israeli drug giant Teva Pharmaceuticals. Its camptothecin program is approaching mid-stage trials, and the company is hoping to license it out to a development partner, Metzger says.

Out-licensing the earlier programs will help Mersana apply its technology to the next generation of targeted drugs: “antibody-drug conjugates” or ADCs. These are proteins that recognize specific antigens—toxins and other substances expressed by tumors. When the antibodies are linked to cancer-fighting drugs, they home in on those antigens and deliver their drug packages into the tumor cells. Mersana is using Fleximer to attach a range of drug payloads to targeted antibodies. “The future of the company is really predicated on using our technology for that new application,” Metzger says.

On March 7, Mersana formed a collaboration with Endo Pharmaceuticals (NASDAQ: ENDP), based in Chadds Ford, PA, to develop ADCs using the Fleximer technology. The two companies aren’t saying much about the collaboration, except that Endo has chosen one drug target to work on and has the option to

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