Abstract LB-A03: AXL as a potential mediator of WEE1 inhibitor resistance in small cell lung cancer (SCLC)
Authors: Sen Triparna , Tong Pan , Hoff Jennifer , Stewart C. Allison , Wang Jing , Byers Lauren 
Published: May 2016

Abstract
Background: Wee1 is a protein kinase that plays a key role in regulating the G2 checkpoint and homologous recombination (HR) in response to DNA damage. Recent studies have demonstrated activity of the WEE1 inhibitor, AZD1775 (previously MK1775), in cancers with loss of the tumor suppressor TP53, including colon, pancreatic and breast. Hence, we hypothesize that WEE1 would be an ideal target for monotherapy in small cell lung cancer (SCLC), which is marked by ubiquitous loss of TP53. Moreover, because Wee1 inhibition induces a HR deficient state, dual targeting of Wee1 and PARP (another promising target previously identified in our group and in clinical trial testing) may induce synthetic lethality. In the present study we evaluate the efficacy of AZD1775 alone and with the PARP inhibitor, olaparib, in SCLC and investigate potential predictive biomarkers by proteomic profiling.
Experimental procedures: We evaluated the gene expression of WEE1 in SCLC tumor sample (n = 23) compared to normal lung (n = 42). We then treated with AZD1775 +/- olaparib SCLC cell lines (n = 10). Drug sensitivity (IC50) was correlated with baseline expression level of 200 total or phosphorylated proteins measured by reverse phase protein array (RPPA) to identify potential predictive markers. SCLC cell lines with AZD1775 resistance (n = 3) were treated with TP0903 (10, 20, 40, 80nM) in combination with AZD1775 (0.1nM to 1uM) to test the efficacy of AXL co targeting in augmenting WEE1 inhibitor response.
Results: SCLC tumors have a significantly higher gene expression level of WEE1 as compared to normal lung (p&lt;0.07×10-6). Single-agent WEE1 or PARP inhibition decreased viability of SCLC cells in a dose-dependent manner with AZD1775 being more potent as a single agent treatment (IC50 &lt;100nM in 70% SCLC cell lines) than olaparib (IC50 &lt;1uM in 20% of SCLC cell lines) in a 6day assay. Combination of AZD1775 with olaparib revealed an additive effect in vitro in 90% of SCLC cell lines. Proteomic analysis revealed an association between WEE1 inhibitor resistance and higher levels of AXL and total S6K (p&lt;0.05 for both). In contrast, WEE1 inhibitor sensitivity was associated with elevated basal expression of PDK1 (p&lt;0.002), treatment of SCLC cells with the AXL inhibitor TP0903 (40nM) re-sensitized cells to AZD1775 (IC50 &lt;10nM) in a 6day assay.
Conclusion and significance: The therapeutic options for patients with SCLC are limited and survival is poor. The WEE1 inhibitors are currently in clinical trials for SCLC. However, as with any targeted therapy, primary and secondary drug resistance is an important barrier to clinical benefit which could potentially be addressed with therapeutic combinations. In this study we show the over expression of WEE1 in SCLC and its efficacy as a single agent and in combination with olaparib. Here we also show that the activity of the WEE1 inhibitors might be limited in cancer cells overexpressing of AXL and that AXL 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 inhibition as a mechanism to overcome WEE1 inhibition resistance in SCLC.
Acknowledgement: This work was supported by Uniting Against Lung Cancer grant (LB).
Citation Format: Triparna Sen, Pan Tong, Jennifer Hoff, C. Allison Stewart, Jing Wang, Lauren Byers. AXL as a potential mediator of WEE1 inhibitor resistance in small cell lung cancer (SCLC). [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr LB-A03.