New Rigosertib Study Shows Mechanism Of Action A study published in the medical journal Molecular Cancer detailed how rigosertib's action through the RAS pathway could improve the response to checkpoint inhibitors. Rigosertib is currently in a Phase 1 clinical trial in combination with the PD-1 inhibitor Opdivo (nivolumab) to improve response rates in lung cancer.Turning "Cold" Tumors "Hot" Drugs in the checkpoint inhibitor category block the mechanism that allows cancer cells to avoid recognition by the immune system. Response rates for checkpoint inhibitors vary from about 10% to 40% depending on the tumor. The new publication supports observations in prior rigosertib trials by demonstrating increases in immune cell populations and responses.Study Results: The study in a murine (mouse) model of melanoma showed that rigosertib's action on the RAS pathway could lead to both cell death and immune cell proliferation. Importantly, these cells were in the tumor microenvironment and led to improved tumor responses. Response Rates Improved: The study tested rigosertib in combination with both a PD-1 inhibitor and a CTLA-4 inhibitor and found an increase from about 50% inhibition of tumor growth for the two checkpoint inhibitors alone to about 70% inhibition for the combination with rigosertib.Conclusion: The data from the preclinical models support the theorized mechanism of action. Rigosertib was able to kill cells through the RAS pathway and stimulate an increased immune response. We see this as important data that supports the observations seen in previous trials, and justify continued use in the Phase 1 trial. We reiterate our Outperform rating an $11 price target. Read More >>