Sustained Gas6/Axl Signaling Network in the Mes Subtype of Ovarian Cancer As A Molecular Subtype Specific Therapeutic Target.

e17084 Background: Ovarian cancer (OC) is a complex disease demonstrated by the heterogeneity in gene expression molecular subtypes (GEMS). To address the GEMS-specific lethality in OC, we highlight the relevance of how a receptor tyrosine kinase (RTK) differs in the signaling pattern, functional consequences, and therapeutic implications in the context of GEMS. Methods: An enrichment analysis of the human kinome among the OC GEMS was performed to identify top ranking RTKs in each GEMS. A top-ranking RTK for the Mes subtype, AXL, was selected for further studies. AXL activation in GEMS-matched OC cells were analyzed for the downstream signaling cascade by western blotting and Reverse Phase Protein Analysis (RPPA), and in vitro functions. A selective inhibitor to AXL was tested for the attenuation of downstream signaling and functional aggressiveness. Results: AXL is the top-ranking RTK for the poor prognosis Mes subtype. Interestingly, AXL is also expressed, at a lower rank, in the better prognosis Epi-A subtype. Upon ligand stimulation with Gas6, specific to Mes, there is recurrent temporal activation of the extracellular regulated kinase (ERK) signaling downstream of AXL observed by Western blotting. RPPA and proximity ligation assays further show that Gas6/AXL signaling transactivates other RTKs such as cMET, EGFR, and HER2 in Mes, exclusively. This signal amplification downstream to the Gas6/AXL axis alludes to pathway addiction in Mes. Functionally, the recurrent ERK activation results in a motile and invasive phenotype. This further sensitizes Mes to a selective AXL inhibitor, R428, by attenuating the RTK-ERK activation, reducing the in vitro motility and invasion, and inhibiting the in ovo tumor growth in the chick chorio-allantoic membrane (CAM) assay at a lower IC-50 dose compared to Epi-A. Conclusions: Our results imply that the Mes subtype is more sensitive to AXL inhibition, and the RTK crosstalk rewires the system, drastically sensitizing it to RTK node inhibition. The Epi-A subtype retain a linear signaling axis and shows less therapeutic advantage to targeting AXL. Stratifying OC patients based on the GEMS followed by targeting AXL is promising in a prospective clinical setting.