Mirati Therapeutics hopes to later this year win U.S. approval of only the second drug able to target tumors spurred by mutations in an elusive gene called KRAS.
Updated clinical trial results disclosed Thursday show the San Diego biotech's drug to be roughly as effective as the first, Amgen's Lumakras, in treating a common form of advanced lung cancer. Lumakras won a milestone clearance from the Food and Drug Administration last spring and the agency is expected to make a decision on Mirati's therapy, called adagrasib, by December.
The new data were revealed in a study abstract published ahead of the American Society of Clinical Oncology's annual meeting next month and are the first to emerge since an update from Mirati last September. Treatment with adagrasib shrank tumors in 43% of the 112 patients included in the analysis and held cancer in check for a median of 6.5 months, as measured by what's known as progression-free survival.
Study participants, almost all of whom were previously treated with chemotherapy and immunotherapy, lived a median of just over one year, the data show.
Mirati's results mirror those recently reported by Amgen after two years of follow-up from the early study that led to Lumakras' approval. In that trial, Lumakras led to a response rate of 41%, median progression-free survival of 6.3 months and median overall survival of 12.5 months.
Yet, Mirati's data also signal adagrasib treatment comes with a high rate of side effects rated as more severe, with 43% of patients in the study experiencing reactions classified as Grade 3 or Grade 4. Two patients died; one from pulmonary hemorrhage and the other from cardiac failure. In the latter patient, who had a history of heart problems, Mirati said there were no signs of heart rhythm disturbances that can sometimes warn of a drug-related effect.
Adagrasib has been closely followed as the nearest rival to Lumakras, which Amgen has marked as a future blockbuster product. While the KRAS gene is frequently mutated in lung, colon and pancreatic cancers, targeting it with drugs remained out of researchers' reach for more than three decades. Only recently did scientists learn how best to design treatments that could latch onto the protein produced by mutant KRAS and help shut it down.
Lumakras was the first result of that breakthrough, but Mirati leads a lengthening list of biotech and pharmaceutical companies aiming to follow Amgen to market. While the most recent data suggest adagrasib can match Lumakras, some of the efficacy data are on the lower end of expectations recently set out in a note by analysts at Jefferies.
Investors' focus has also shifted to how well the drugs might work in combination with other drugs, like Merck & Co.'s Keytruda. There, Mirati has presented preliminary findings in a handful of patients.
Additional data on how well adagrasib works in treating cancer that's metastasized into the central nervous system will be disclosed in a late-breaking presentation at ASCO on June 6.
Shares in Mirati fell by more than 30% in Friday morning trading on news of the ASCO data, depressing the biotech's valuation below $3 billion — far from the heights of late 2020, when the company was worth as much as $12 billion.
Both adagrasib and Lumakras target a specific type of KRAS mutation known as G12C that's present in about 13% to 14% of lung tumors and less commonly in colon and pancreatic cancer. Results for adagrasib and Lumakras in the latter two tumor types have been less impressive than in lung, particularly when the drugs have been tested on their own.
Mirati and Amgen are also running larger, confirmatory studies of their respective drugs in lung cancer. Results from Amgen's Phase 3 trial are expected in the third quarter and, if positive, could help the company convert Lumakras' conditional approval to a full clearance. As Mirati is seeking an accelerated approval for adagrasib, a standard clearance for Lumakras could complicate the biotech's regulatory plans.
Editor's note: This story has been updated to reflect trading in Mirati shares on Friday.