Can Arena's latest safety study help satisfy FDA's cancer worries?

Hoping to assuage FDA concerns about the evidence of cancer seen in animal studies of the weight drug lorcaserin, Arena Pharmaceuticals is preparing to offer regulators evidence that the drug doesn't accumulate in the brains of humans nearly as much as in rats. Investigators drew that conclusion after testing for levels of the drug in plasma and cerebrospinal fluid, concluding that patients' brains were exposed to 1.7 times the level of the drug found in plasma, far lower than the 24 times plasma exposure seen in rats' brains.

For Arena ($ARNA), the data represents part of its response to regulators who wanted to see more cancer safety data on the obesity treatment before they would provide an approval. By demonstrating that relatively low levels of the drug stay in the brain, they hope to convince regulators it can't be responsible for triggering a slow-growing cancer. The next step is to assure regulators on signs of mammary tumors, which Arena is betting can be settled with a short, 6-month study.

"Previously, when we submitted our application, we estimated a certain level of risk," Arena VP Christen Anderson tells Bloomberg. "What we're now saying is that the risk to humans relative to rats is a lot lower than previously estimated."

Analysts, though, have been anything but certain that Arena and its partner Eisai can resolve worries at the FDA, which has already scuttled Orexigen's Contrave with demands for a new trial while leaving a big question mark over the future of Vivus's Qnexa. All three biotechs had been engaged in a closely-watched race to the FDA with what they had hoped would be the first new weight drug to gain approval in more than a decade.  The FDA has raised a high bar on the safety of new weight drugs and Arena will be expected to mount a strong case in its favor to avoid a demand for a much more costly study.

- read the Arena release
- and here's the story from Bloomberg