Background: WEE1 inhibitors (WEEi) are a novel class of small molecule inhibitors that are now under early clinical trials for small cell lung cancer (SCLC). WEE1 is a protein kinase that plays a key role in regulating the G2 checkpoint in response to DNA damage. Moreover, because WEE1 inhibition induces a HR deficient state, dual targeting of WEE1 and PARP (another promising target previously identified in our group) may induce synthetic lethality. In the present study we evaluate the efficacy of AZD1775 alone and with the PARP inhibitor, olaparib; investigate the mechanisms of primary resistance to AZD1775 in SCLC models; and assess the combinatorial efficacy of AZD1775 treatment with the chemotherapy drug, temozolomide (TMZ), that has shown promise in patients with recurrent SCLC and has been included in the National Comprehensive Cancer Network guidelines for standard treatment for SCLC.

Results: Combination of AZD1775 with olaparib revealed an additive effect in vitro in 90% of SCLC cell lines. AZD1775 combined with TMZ synergistically decreased viability, increased DNA damage and apoptosis in SCLC cell lines (n=10) irrespective of MGMT status or initial response to AZD1775 alone. However, unlike the sensitive cells, SCLC cell lines showing primary resistance to AZD1775 had an intact DNA repair mechanism (after DNA damage), which may contribute to the resistance mechanism. Proteomic analysis revealed AXL (receptor tyrosine kinase) and phospho-S6K (S240/244) as markers of AZD1775 resistance and treatment with AXL inhibitor, TP0903 (40nM), resensitized the cells to AZD1775. Pre and post-AZD1775 treated samples revealed sustained activation of mTOR pathway in AZD1775 primary resistant lines. We further demonstrated that pre-treatment of the cells with the mTOR inhibitor everolimus sensitized SCLC cells to AZD1775 by causing downregulation of AKT/mTOR pathway.

Conclusion: WEE1 inhibitors are currently in clinical trials for SCLC patients. However, as with any targeted therapy, drug resistance is an important barrier to clinical benefit which could be addressed with therapeutic combinations. We show the efficacy of single agent AZD1775 and in combination with olaparib. WEE1 inhibitor, AZD1775 synergizes with TMZ irrespective of MGMT status in all tested in vitro models which warrants further clinical investigation. We also show that the activity of the WEE1 inhibitors might be limited in cancer cells overexpressing of AXL and activated mTOR pathway and that AXL and mTOR inhibition re-sensitized the cells to AZD1775. Our work supports further exploration of the combination of PARP and WEE1 in SCLC and also the possibility of AXL/mTOR inhibition as a mechanism to overcome WEE1 inhibition resistance in SCLC. SCLC is a disease with very limited therapeutic options and no targeted agents with proven benefit; thus the results from this study have clear translational benefit.

Citation Format: Triparna Sen, Pan Tong, Lixia Diao, You Hong-Fan, C. Allison Stewart, John V. Heymach, Jing Wang, Lauren A. Byers. WEE1 inhibitor activity correlates to AXL/mTOR expression and exhibits synergy with temozolomide (TMZ) in small cell lung cancer (SCLC) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 298. doi:10.1158/1538-7445.AM2017-298