A test that measures the interaction between two proteins, developed by researchers at the Moffitt Cancer Center, could predict which patients with KRAS G12C-mutated non-small-cell-lung cancer (NSCLC) are most likely to respond to KRAS G12C inhibitors.
The proximity ligation assay (PLA) measures the interaction between RAS and RAF, proteins that are part of the RAS/RAF/MAPK pathway and play a key role in the regulation of cell growth and tumorigenesis.
“Our findings could be a game-changer for treating KRAS G12C-mutant NSCLC,” said the study’s first author Ryoji Kato, PhD. “By measuring RAS–RAF interactions, we can potentially help doctors make more informed decisions and provide better treatment outcomes for patients.”
KRAS is the most commonly mutated oncogene in advanced, non-squamous NSCLC in Western countries. Of the various KRAS mutants, KRAS G12C is the most common variant, occurring in 10–13% of advanced, non-squamous NSCLC.
Drugs like sotorasib and adagrasib have been developed to inhibit the mutated KRAS G12C protein from locking the cell into a tumorigenic state. However, response rates generally range from around 35–45% and are lower than the 60–80% response rates achieved with targeted agents for other genetic alterations in NSCLC, namely EGFR and ALK.
Senior author Eric Haura, MD, told Inside Precision Medicine that this is “a good example of where genomics enriches for the population, but there are other factors that may also be important in predicting response. We wanted to understand, with a little bit more precision, which patients are responding, and to apply proteomic biomarkers to gain a next generation view, beyond genomics.”
He added: “Proteins don’t work in isolation, they work as larger molecular machines and complexes, and sometimes when two proteins bind to each other in a cell there’s biological importance to that, and that importance can be captured through this assay format and linked to therapeutic outcome or prognosis.”
Haura and his team developed the RAS–RAF PLA using carefully selected antibodies that measure in situ RAS binding to RAF in cancer samples via immunofluorescence.
They initially tested the assay in NSCLC cell lines, then in animal models, and finally in tumor samples from patients with KRAS G12C-mutated NSCLC. In all three cases they found that higher levels of interaction between RAS and RAF were associated with an increased response to KRAS G12C inhibitors.
Furthermore, in a clinical cohort of 15 patients with advanced NSCLC treated with sotorasib, greater RAS–RAF interaction was associated with increased progression-free survival.
Writing in Clinical Cancer Research, Kato and co-authors say that the study “highlights the importance of evaluating in situ RAS–RAF interactions as a potential predictive biomarker that could enhance current clinical genomics-based platforms.”
Haura, however, is pragmatic about the place the assay may have in current clinical decision-making algorithms. He says that although the test is technically simple compared with genomic assays and could feasibly be carried out in hospital laboratories, it would still need a commercial partner to bring it to a wider audience.
He also points out that “the field of RAS therapeutics is moving so fast that developing an assay for these compounds may already be eclipsed, because we’re already moving into combination therapy and combination with immunotherapy.”
Nonetheless, Haura believes that, importantly, the work provides proof-of-principle that measuring protein–protein interaction offers predictive value in cancer treatment.
“I hope what it does is gets people to think that there are things beyond DNA that we can use as predictive biomarkers,” he said.
