FDA has given the regulatory nod to crizotinib, Pfizer’s ALK inhibitor that has proven very effective in the small portion of the population whose lung cancer is driven by the protein.
Pfizer says the drug, to be sold under the brand name Xalkori, will cost $9,600 per month, and it will provide assistance so that patient co-pays will not exceed $100. It’s the first in a handful of new drugs Pfizer is counting on to help offset the sales drain when the patent expires this fall on its blockbuster cholesterol drug Lipitor.
The approval is notable as the second drug/diagnostic combo to get the FDA green light in recent weeks—Plexxikon/Roche’s melanoma treatment Zelboraf is the other.
Also notable? We call the compound an ALK-inhibitor, but scientists didn’t start out looking for an ALK-inhibitor. Work on crizotinib originated at Sugen, a South San Francisco-based biotech first bought by Pharmacia, which was later acquired by Pfizer. Sugen chemists were intent on finding a molecule that blocked c-Met, a protein implicated in tumor metastasis. They had already struck upon a promising amino pyridine scaffold by the time their activities were moved into Pfizer’s La Jolla site, where lead optimization took place.
An optimized molecule, billed as a c-Met inhibitor, was put into clinical trials. Then, as we wrote last year, scientific discovery and serendipity converged to change the course of the drug’s development:
Researchers led by Hiroyuki Mano, a professor of functional genomics at Japan’s Jichi Medical University, found that when a certain chromosome inverted, a fusion occurred in lung cancer cells between the echinoderm microtubule-associated proteinlike 4 (EML4) gene and the ALK gene. The researchers found that the fusion caused tumor formation in mice. A subsequent test determined that about 7% of lung cancer patients had this fusion gene. In a paper published in Nature, the researchers concluded that ALK would make a good drug target (Nature 2007, 448, 561).
As it happened, Pfizer had just learned it had an ALK inhibitor on its hands. The company and Massachusetts General Hospital had evaluated results from large biochemical and cell-based screens to see whether crizotinib was hitting targets other than c-Met, says James Christensen, director of translational research in Pfizer’s oncology unit. Upon characterizing the hits, the collaborators found that it was blocking ALK’s activity.
Better, crizotinib was just as good at blocking ALK as it was at shutting down c-Met. Pfizer scientists believe the dual activity is due to a similarity in a residue on each protein. Specifically, both c-Met and ALK have a particular tyrosine within one of the three phosphorylation sites, called the activation loop, which seems to be responsible for the compound’s activity.
All in all, pretty cool science that has translated into a very promising treatment for some lung cancer patients.
Leave a Reply