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Mersana Therapeutics Advancing Anti-Tumor Treatment with Novel Drug-Delivery Technology

Xconomy Boston — 

Mersana Therapeutics is picking up momentum, thanks to the positive data its first anti-cancer drug is generating in a Phase I clinical trial. The study is providing evidence that the Cambridge, MA-based firm’s drug delivery technology works in humans.

The startup’s “Fleximer” technology—which uses sugar-derived polymers to deliver treatments into cells—has the potential to rescue from the scrap heap a number of cancer drugs that proved to be effective in humans but too toxic to gain FDA approval. The firm’s lead treatment, dubbed XMT-1001, has shown that the technology can deliver the anti-cancer agent camptothecin at doses that would be toxic to patients were it not for the delivery system.

This technology could be valuable to big drug companies, which often have to drop development of cancer-killing drugs because of the harm such treatments cause to healthy tissue. The active ingredient in the firm’s lead treatment, camptothecin, has been known for decades for its anti-tumor activity. New York-based drug giant Pfizer and British pharma powerhouse GlaxoSmithKline market chemotherapy treatments related to camptothecin, irinotecan (Camptosar) and topotecan (Hycamtin), respectively. But those treatments can cause severe diarrhea or suppress certain immune functions.

Julie Olson, Mersana’s CEO, told me in a recent interview that the firm’s lead drug, XMT-1001, does not seem to cause severe diarrhea, like irinotecan, nor does it cause serious bladder inflammation like regular camptothecin does. The former Pfizer executive also noted that the sugar-derived polymers that the firm uses to deliver the drug are biodegradable and can be given at relatively high doses without accumulating in peoples’ kidneys, as the peptides used in some other drug-delivery systems sometimes do.

Olson said she has been on the lookout for new investors and potential corporate partners to provide more financial fuel to drive Mersana’s lead drug into Phase II clinical trials, planned to begin next year, and to fund other R&D efforts at the 20-person firm. She hopes to land a financing deal by the end of 2009, from venture backers, a corporate partner, or a combination of the two.

Seven-year-old Mersana has raised a total of more than $30 million. The bulk of the capital came in the $21 million first closing of its Series B round of venture capital, from Fidelity Biosciences in Cambridge and ProQuest Investments, of San Diego, Princeton, NJ, and Montreal, in November 2005. The company’s other investors include Rho Ventures, PureTech Ventures, Harris & Harris Group, the Cape Family Fund, and Lansing Brown Investments. Olson said that the company has since added more than $10 million to the second-round financing in the form of follow-on investments from existing backers.

PureTech, of Boston, was the venture firm that initially helped Mikhail Papisov, a bioengineer at Massachusetts General Hospital, to found Mersana (fka Nanopharma) and license his drug-delivery technology from MGH. Olson, a former vice president of licensing at Pfizer, joined Mersana as chief executive after learning about the startup from PureTech. She said that the startup’s drug-delivery molecules interest her because of their versatility and utility in medicine.

Mersana says it can attach all manner of drugs—including small molecules, proteins, and nucleic acids—to its polymers, and that multiple drugs can be linked to a single polymer molecule. The polymers are designed to hold tightly to the drugs and release them at the optimal time such as inside of target cells, reducing the amount of the unlinked drugs that circulate in the bloodstream, where they could reach healthy tissues and cause side effects.

The firm is studying its molecules’ ability to deliver RNA-interference (RNAi) drugs, which show great promise to mute disease-causing genes but are tricky to get into cells before they are broken down in the body. Olson said that her firm is researching ways to link RNAi drugs to Fleximer molecules along with a compound designed to target specific cells. She hopes that her firm will be able to partner with an RNAi company within the next year to year and a half.

Olson said that her firm is already in touch with developer of RNAi therapies but declined to provide specifics of those discussions. In our other reporting, we’ve covered how Cambridge, MA-based Alnylam Pharmaceuticals (NASDAQ:ALNY) has sought partnerships with other biotech firms and academics to overcome the challenges of delivering its RNAi treatments into cells.