G2/M checkpoint inhibition in combination with DNA damaging agents in small cell lung cancer
Small cell lung cancer (SCLC) is typically treated with chemotherapy and radiation with initial success; however, tumors rapidly recur, leading to a dismal 5-year survival rate of 5-10%. AZD1775, a highly selective small molecule inhibitor of WEE1 kinase, has shown promise in combination with DNA damaging agents in treating p53 mutant cancer types, and is currently employed in clinical trials, including SCLC. Ninety percent of small cell lung cancer tumors have a p53 mutation, suggesting they are optimal candidates for treatment with AZD1775. A cell with inactive p53 relies on other proteins, such as WEE1, to govern proper DNA damage repair and cell survival. We hypothesize that WEE1 inhibition in combination with DNA damaging agents will effectively kill p53-deficient SCLC cell lines. AZD1775 and cisplatin were tested in combination both simultaneously and sequentially on cisplatin resistant SCLC cell lines, all of which have p53 mutations. This combination reduced cell viability from the control by up to 28% (p<0.05), while sequential treatment of cisplatin followed with AZD1775 reduced cell viability by up to 55% (p<0.05). Sequential treatment was statistically lower than the simultaneous treatment. The order of treatments did not have a significant effect on cell viability, although a 24-hour delay between treatments was most efficacious. SCLC lines NCI-H526 and NCI-H187 were sensitive to AZD1775 alone (with IC50’s less than 500nM), possibly due to mutations in ATM, a critical regulator in the DNA damage repair pathway, or mutations in SETD2, which has been linked to replicative stress. These cell lines will be investigated to identify additional mechanisms and markers for sensitivity, grounds for rational combinational therapeutic development. As chemotherapeutics alone rarely successfully treat small cell lung cancer, an effective combination treatment, or single agent alternative is needed. Although 90% of small cell lung cancer patients present with p53 mutations, identification of the types of p53 mutants, as well as other genetic players which govern AZD1775 sensitivity, is essential for developing an effective treatment. As more than 50% of all tumors present with p53 mutations, the identified mutations that drive sensitivity to AZD1775 can also guide treatment strategies in other types of cancer.