Greater effect seen with co-mutation
KRAS is commonly co-mutated, so the investigators performed an exploratory analysis to see if the presence of other mutations – STK11, KEAP1, and TP53 – might affect the results of adagrasib.
A greater objective response rate was seen in patients with the STK11 mutation than in those without it (64% and 33%, respectively). STK11 is associated with poorer responses to immune checkpoint inhibitors.
“We hypothesized that adagrasib treatment recruits T cells into the tumor and that T-cell infiltration may reverse STK11-mediated immune suppression,” Dr. Riely said. This theory seemed to be borne out with further analyses, though Dr. Greystoke raised doubts. There was no sign of STK11 mutations having any effect on response rates with adagrasib in preclinical studies.
Patients with KEAP1 as a co-mutation had a lower response rate than that of those without it (36% and 48%, respectively), which is in keeping with what might be expected. KEAP1 is known to be associated to a poor response to chemotherapy and immunotherapy.
“I think this data is very provocative but needs to be confirmed in larger cohorts,” Dr. Greystoke said. It could mean that adagrasib has the potential to turn a “cold tumor, hot,” enabling the use of immunotherapies.
A new cohort has been included in the KRYSTAL-1 study to further evaluate how having both the KRAS G12C and STK11 mutations may affect treatment with adagrasib.
Data could support drug combination
The adagrasib data lend support to the combination of KRAS G12C inhibitors with other molecularly-targeted treatments for NSCLC, Dr. Greystoke said, such as with tyrosine kinase inhibitors or immunotherapies. He noted that high steady-state levels of adagrasib were detected in the blood, and these levels were well above those needed for potential efficacy.
“This gives us confidence that if we do need to drop the dose below the recommended phase 2 dose to allow potential combinations with a small-molecule inhibitor due to overlapping toxicity or overlapping pharmacokinetics, that it is safe to do and shouldn’t [have an] impact on efficacy,” Dr. Greystoke said. “Overall, all this information will help us drive forward the next round of clinical trials of probably a combination of treatments.”
The KRYSTAL-1 study is supported by Mirati Therapeutics, Inc. Dr. Riely disclosed relationships with Mirati Therapeutics, Merck, Novartis, Pfizer, Takeda, and Roche. Dr. Greystoke was not involved in the study but disclosed relationships with Amgen, AstraZeneca, Boehringer-Ingelheim, Bristol-Myers Squibb, Merck, Novartis, Pfizer, Lilly, Takeda, and Roche.