Abstract 367: Sub-group of ovarian cancer patients with hyperactive RAS network signaling identified: Dynamic pathway activity test identifies patients that may benefit from PI3K/mTOR or PI3K/mTOR/BCL inhibitors
Authors: Rossetti Stefano , Broege Aaron , Sabat Joanna , Wiley Shu , Khan Salmaan , Kuzmicki Catherine , MacNeil Ian , Sullivan Brian , Laing Lance 
Published: July 2021

Abstract
Background: Dysregulated RAS signaling through GPCRs is reported in ovarian cancer (OC), but no sub-groups of OC patients with actionable RAS genetic variants have been found. The complex mechanisms that link RAS nodes can trigger adaptation when a single RAS node is inhibited. Thus, inhibition of multiple RAS nodes may be required for durable antitumor responses. To identify patients with dysregulated RAS signaling tumors that may respond to RAS node inhibitors, an assay using an impedance biosensor was developed. The CELsignia RAS Activity Test measures GPCR-initiated signaling activity and PI3K, mTOR, and BCL's role in transducing this activity in live tumor cells. The current study set out to characterize the prevalence of dysregulated RAS signaling initiated by a GPCR in OC patients and the role played by PI3K, mTOR and BCL.
Methods: Fresh tumor specimens from 32 OC patients and 18 OC cell lines (84% HGS, 13% endometrioid, 3% clear cells) were used to derive test cell samples. Dynamic live cell response to a GPCR agonist (LPA), a PI3K-α inhibitor (GDC-0077), a pan-PI3K inhibitor (copanlisib), a pan-PI3K/mTOR inhibitor (gedatolisib), and a BCL inhibitor (navitoclax) was measured using an xCELLigence impedance biosensor (Agilent Technologies). From these responses, the gross amount of GPCR-initiated signaling and corresponding participation of PI3K-α, all Class 1 PI3K-isoforms, mTORC1, and BCL was quantified and converted to a signaling score. Correlative analyses using FACS markers (RPS6, AKT, ERK, caspase 3) were performed.
Results: Hyperactive RAS signaling (RASs+) initiated by GPCR pathways was found in 14 of 50 (28%; 95% CI=17%-42%) tumors. The signaling scores were bimodally distributed; for the 14 RASs+ and the 36 RASs- patient tumors, the mean scores were 569 (SD 282) and 55 (SD 78), respectively. For RASs+ tumors, inhibition of all Class 1 PI3K-isoforms attenuated, on average, 57% of the GPCR signaling, while inhibition of PI3K-α alone had only a nominal inhibitory effect. When mTOR inhibition was combined with pan-PI3K inhibition, GPCR signaling was further attenuated by 29%. More complete attenuation of RAS-signaling occurred when PI3K, mTOR, and BCL were simultaneously inhibited. Early apoptosis markers (RPS6, AKT, ERK, caspase 3) were found most significantly in RASs+ tumors with pan-PI3K/mTOR inhibition and to a greater degree with pan-PI3K/mTOR/BCL inhibition. No apoptosis markers were found in RASs- tumors regardless of which RAS node was inhibited.
Conclusions: These findings suggest that a significant sub-group of OC patients have a RAS-involved oncogenic driver that is responsive ex vivo to pan-PI3K/mTOR and pan-PI3K/mTOR/BCL inhibitors. A clinical trial to evaluate treatment response of this patient sub-group to combined PI3K/mTOR or PI3K/mTOR/BCL inhibitors is warranted.
Citation Format: Stefano Rossetti, Aaron Broege, Joanna Sabat, Shu Wiley, Salmaan Khan, Catherine Kuzmicki, Ian MacNeil, Brian Sullivan, Lance Laing. Sub-group of ovarian cancer patients with hyperactive RAS network signaling identified: Dynamic pathway activity test identifies patients that may benefit from PI3K/mTOR or PI3K/mTOR/BCL inhibitors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 367.