Gritstone bio has brought in bankers to explore “potential value-maximizing strategies” after its phase 2 colorectal cancer vaccine data fell short of the runaway success needed to transform its fortunes.
The California-based biotech ended June with $62 million, leading Evercore ISI analyst Jonathan Miller to conclude that the company's “cash runway is functionally no later than” the end of this year. With time quickly running out, phase 2 data on the GRANITE individualized neoantigen targeting immunotherapy and checkpoint inhibition in microsatellite stable colorectal cancer (MSS-CRC) offered Gritstone a chance to boost its share price.
Instead, Gritstone saw its stock slump 25% to 44 cents after the markets opened Tuesday. The drop followed the release of the interim phase 2 data and accompanying news that Gritstone has begun looking into strategic alternatives.
All patients in the study received standard-of-care chemotherapy. Half the participants also received GRANITE and a checkpoint inhibitor. MSS-CRC, an immunologically cold tumor type, is an indication in which checkpoint inhibitors have failed to move the needle.
Gritstone reported a 21% relative risk reduction of progression or death in the investigational drug arm. The hazard ratio (HR) of 0.79 favored the GRANITE combination but the top end of the 95% confidence interval was 1.50, a result that would mean the control group performed much better than the cancer vaccine.
Miller said that, “on the face of it,” the HR of 0.79 is a good result. The analyst based that view on the fact the trial enrolled people with a metastatic, “ice-cold tumor” and that the “biology is lining up behind clinical benefit,” with antigen-specific T-cell induction across vaccinated patients and correlating to progression-free survival.
The data led Miller to conclude that “there does seem to be activity, more than other oncovaccines have shown in similar settings.” However, the analyst acknowledged the “limitations of the data set,” including the fact that Gritstone has gone from focusing on patients with more aggressive disease in April, when it saw a 0.52 HR in the subpopulation, to making no mention of the subpopulation in the latest update
Miller expects extended follow up to continue to look supportive if Gritstone can keep tracking patients but the biotech’s ability to keep going is in doubt. “They don’t have flexibility to run this data out much further, add [patients], or explore [the] adjuvant setting,” the analyst said.
Gritstone CEO Andrew Allen, M.D., Ph.D., said in the company’s release that the biotech is “excited” by GRANITE’s potential, but the data need “more time to mature.”
“The most recent ‘low and stable’ ctDNA measurements in most GRANITE patients are encouraging since that pattern is not typically seen in patients about to develop disease progression,” Allen added. “The potential PFS benefit observed in MSS-CRC, a notoriously ‘cold’ tumor, suggests opportunity for even greater effects in tumors more typically amenable to immunotherapy.”
In the meantime, Gritstone has engaged Raymond James as a financial advisor to “support the company in exploring and reviewing potential value-maximizing strategies.”