Systems analysis of apoptotic priming in ovarian cancer identifies vulnerabilities and predictors of drug response

Abstract

The lack of effective chemotherapies for high-grade serous ovarian cancers (HGS-OvCa) has motivated a search for alternative treatment strategies. Here, we present an unbiased systems-approach to interrogate a panel of 14 well-annotated HGS-OvCa patient-derived xenografts for sensitivity to PI3K and PI3K/mTOR inhibitors and uncover cell death vulnerabilities. Proteomic analysis reveals that PI3K/mTOR inhibition in HGS-OvCa patient-derived xenografts induces both pro-apoptotic and anti-apoptotic signaling responses that limit cell killing, but also primes cells for inhibitors of anti-apoptotic proteins. In-depth quantitative analysis of BCL-2 family proteins and other apoptotic regulators, together with computational modeling and selective anti-apoptotic protein inhibitors, uncovers new mechanistic details about apoptotic regulators that are predictive of drug sensitivity (BIM, caspase-3, BCL-XL) and resistance (MCL-1, XIAP). Our systems-approach presents a strategy for systematic analysis of the mechanisms that limit effective tumor cell killing and the identification of apoptotic vulnerabilities to overcome drug resistance in ovarian and other cancers.

Combined MEK and BCL-2/XL Inhibition Is Effective in High-Grade Serous Ovarian Cancer Patient–Derived Xenograft Models and BIM Levels Are Predictive of Responsiveness

“…Because mutations in the genes of the MEK/ERK pathway that occur in HGSOC do not predict the activation of the pathway in tumor samples, we measured the relative activation status at the protein level using RPPA on lysates of short-term in vitro cultures of ascites cells from the PDX models. We previously described a workflow for the harvest and culture of these cells (referred to here as PDX ascites cells) for in vitro drug-sensitivity studies and molecular characterization (29). We measured the protein levels of several members of the MEK/ERK pathway, including upstream positive activators (pRAF, pMEK1, and pERK) and downstream targets (pp90RSK, pYB-1, and pElk1), and calculated a pathway activation score by adding the values of all these proteins (as described previously; ref.…”

“…Ascites cells were harvested from PDX models and were allowed to recover for 4 days in vitro in primary ovarian growth medium previously described (29). Cells were seeded in 96-well plates in MCDB105 þ M199 medium, supplemented with 2% HI-FBS and 1% penicillin/streptomycin.…”

Novel Targeting of Transcription and Metabolism in Glioblastoma

“…Mcl-1 has been characterized mostly in hematologic malignancies. However, some reports demonstrated aberrant expression of Mcl-1 in some solid tumors, including GBM (25)(26)(27). Our findings of TG02-induced reduction of Mcl-1 and Survivin expression suggested a potential mitochondrial dysfunction in TG02-treated GBM.…”

Critical questions in ovarian cancer research and treatment: Report of an American Association for Cancer Research Special Conference

“…Combining targeting of the MEK pathway with inhibition of the anti‐apoptotic proteins BCL‐2/XL navitoclax (ABT‐263) was more effective in reducing cell number and increasing cell death than single agents in the majority of PDX models assessed in vitro and in vivo. Moreover, high pretreatment protein levels of BIM predicted response to combination therapy …”

“…Moreover, high pretreatment protein levels of BIM predicted response to combination therapy. 36 Assay of plasma ctDNA promises to identify relevant targets for therapy. A panel of 508 cancer genes has been used to identify actionable mutations and copy number alterations in patients with HGSOC.…”