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

select two more. Endo will finance all development, manufacturing, and commercialization of the projects. If all three targets are pursued, Mersana could receive up to $270 million in milestone payments, plus royalties on worldwide sales.

Metzger says Endo proved to be an ideal partner. “They’re a specialty pharmaceutical company with an ongoing discovery effort in oncology, and specifically in antibody drug conjugates,” he says. “They have a very interesting antibody they wanted to deploy and they needed a technology like ours to make it work. Their expertise and resources were important to us.”

Mersana will continue to pursue a two-pronged development plan—investing in its own molecules while partnering with more companies like Endo that are interested in ADCs, Metzger says. Mersana’s venture investors include PureTech Ventures, Fidelity Biosciences, Rho Ventures, and ProQuest Investments.

Mersana isn’t the only biotech company that’s working on new methods for attaching drug payloads to nanoparticles. Cambridge, MA-based Cerulean is currently in clinical trials with CRLX101, a drug made of nanoparticles that carry camptothecin to cancer cells. And a number of companies are working on ADCs, including Roche unit Genentech and Seattle Genetics, the latter of which has made a big market impact with brentuximab vedotin (Adcetris), an armed antibody that has been shown to significantly shrink tumors in Hodgkin’s disease and anaplastic large-cell lymphoma.

The folks at Mersana are neither surprised nor concerned about the competition. “Our technology is more diverse and flexible than other technologies,” Metzger contends. “We’re able to work with lots of different payloads that are either already available or are being developed. We think we’re introducing some key advantages that the field will come to appreciate as we collaborate with partners and advance our own programs.”

Lowinger says he expects early results from marketed drugs like Seattle Genetics’ ADC to fuel the enthusiasm for the armed-antibody approach. “You’re not prolonging someone’s life for two or three months but really seeing the tumor shrink away,” he says. “This is realizing the dream of the magic bullet.”

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