LAUSR

The approval of osimertinib (AZD9291) as a third generation EGFR inhibitor for treating non-small cell lung cancer (NSCLC) patients with activating EGFR mutations (first-line) or those who have become resistant to 1st generation EGFR inhibitors through the T790M mutation (second-line) have generated tremendous benefits to these NSLCL patients. However, the unavoidable development of acquired resistance to osimertinib limits the long-term benefits of patients. Thus, effective treatment options are urgently needed. Activated Cdc42-associated kinase 1 or ACK1 (also named as TNK2) is a non-receptor tyrosine kinase with oncogenic function. Although ACK1 gene is amplified in lung squamous cell carcinoma, its involvement in lung cancer including regulation of drug resistance has largely not been investigated. We found that inhibition of ACK1 with (R)-9bMS, a specific ACK1 inhibitor, synergized with AZD9291 in inhibiting the growth of EGFR mutant NSCLC cell lines. Similar results were also generated when ACK1 is genetically inhibited through transient shRNA gene knockdown. The combination of AZD9291 and (R)-9bMS enhanced induction of apoptosis as evaluated by detecting annexin V-positive cells with flow cytometry and PARP cleavage using Western blotting. In an in vitro long-term resistance delay assay, the combination of (R)-9bMS and AZD9291 clearly prevented the emergence of AZD9291-resistance as evaluating resistant cell colony formation and growth. Beyond the combination was also effective in inhibiting the growth of EGFR mutant NSCLC cell lines with acquired resistance to AZD9291. In some resistant cell lines, the combinations induced senescence in addition to induction of apoptosis. These preliminary findings suggest that ACK1 inhibition might be a potential and innovative strategy for preventing and overcoming AZD9291 acquired resistance. Hence further in vivo and mechanistic studies are warranted. (This work was supported by the NIH/NCI R01 CA223220 and Winship lung cancer pilot award to SYS; NIH/NCI R01 CA208258, Bankhead Coley Award-6BC08 and Prostate Cancer Foundation (PCF) Challenge award-17CHAL06 to NPM). Citation Format: Jiajia Gu, Xia He, Nupam P. Mahajan, Taofeek K. Owonikoko, Suresh S. Ramalingam, Shi-Yong Sun. Inhibition of ACK1 delays and overcomes acquired resistance of EGFR mutant NSCLC cells to the third generation EGFR inhibitor, osimertinib [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 73.