Deborah J. Marsh

PARP Inhibitors Display Differential Efficacy in Models of BRCA Mutant High-Grade Serous Ovarian Cancer

Several poly (adenosine diphosphate-ribose) polymerase (PARP) inhibitors are now in clinical use for tumours with defects in BReast CAncer genes BRCA1 or BRCA2 that result in deficient homologous recombination repair (HRR). Use of olaparib, niraparib or rucaparib for the treatment of high-grade serous ovarian cancer, including in the maintenance setting, has extended both progression free and overall survival for women with this malignancy. While different PARP inhibitors (PARPis) are mechanistically similar, differences are apparent in their chemical structures, toxicity profiles, PARP trapping abilities and polypharmacological landscapes. We have treated ovarian cancer cell line models of known BRCA status, including the paired cell lines PEO1 and PEO4, and UWB1.289 and UWB1.289+BRCA1, with five PARPis (olaparib, niraparib, rucaparib, talazoparib and veliparib) and observed differences between PARPis in both cell viability and cell survival. A cell line model of acquired resistance to veliparib showed increased resistance to the other four PARPis tested, suggesting that acquired resistance to one PARPi may not be able to be rescued by another. Lastly, as a proof of principle, HRR proficient ovarian cancer cells were sensitised to PARPis by depletion of BRCA1. In the future, guidelines will need to emerge to assist clinicians in matching specific PARPis to specific patients and tumours.

Amphiregulin increases migration and proliferation of epithelial ovarian cancer cells by inducing its own expression via PI3-kinase signaling

The epidermal growth factor receptor (EGFR) is overexpressed in many types of cancer, including epithelial ovarian cancer (EOC), and its expression has been found to correlate with advanced stage and poor prognosis. The EGFR ligand amphiregulin (AREG) has been investigated as a target for human cancer therapy and is known to have an autocrine role in many cancers. A cytokine array identified AREG as one of several cytokines upregulated by EGF in a phosphatidylinositol 3-kinase (PI3-K) dependent manner in EOC cells. To investigate the functional role of AREG in EOC, its effect on cellular migration and proliferation was assessed in two EOC cells lines, OV167 and SKOV3. AREG increased both migration and proliferation of EOC cell line models through activation of PI3-K signaling, but independent of mitogen activated protein kinase (MAPK) signaling. Through an AREG autocrine loop mediated via PI3-K, upregulation of AREG led to increased levels of both AREG transcript and secreted AREG, while downregulation of endogenous AREG decreased the ability of exogenous AREG to induce cell migration and proliferation. Further, inhibition of endogenous AREG activity or metalloproteinase activity decreased EGF-induced EOC migration and proliferation, indicating a role for soluble endogenous AREG in mediating the functional effects of EGFR in inducing migration and proliferation in EOC.

SMARCA4 and SMARCA2 co-deficiency: An uncommon molecular signature defining a subset of rare, aggressive and undifferentiated malignancies associated with defective chromatin remodeling

Genetic mutations and epigenetic modifications affecting multiple cancer-related genes occur synergistically to drive tumorigenesis. Across a wide spectrum of cancers, pathogenic changes have been identified in members of the SWItch/Sucrose Non-Fermentable complex including its two catalytic subunits, SMARCA4 and SMARCA2. During cancer development, it is not uncommon to lose the function of either SMARCA4 or SMARCA2, however, loss of both together has been reported to be synthetic lethal and therefore unexpected. Co-deficiency of SMARCA4 and SMARCA2 occurs as a pathognomonic feature of the early-onset ovarian cancer Small-cell carcinoma of the ovary, hypercalcemic type. The loss of both catalytic subunits is also described in other rare undifferentiated neoplasms including Thoracic SMARCA4-deficient undifferentiated tumors, Malignant rhabdoid tumors and dedifferentiated or undifferentiated carcinomas, predominantly of lung, gastrointestinal, and endometrial origin. This review provides the first extensive characterization of cancers with concurrent SMARCA4 and SMARCA2 loss through the discussion of shared clinical and molecular features. Further, we discuss the mechanisms triggering the loss of catalytic activity, the cellular processes that are dysfunctional as a consequence, and finally, current therapeutic candidates which may selectively target these cancers.

Revealing genetic drivers of ovarian cancer and chemoresistance: insights from whole-genome CRISPR-knockout library screens

Abstract Understanding genetic dependencies in cancer is key to identifying novel actionable drug targets to advance precision medicine. Whole-genome CRISPR-knockout library screening methods have facilitated this goal. Pooled libraries of single guide RNAs (sgRNAs) targeting over 90% of the annotated protein coding genome are used to induce gene knockouts in pre-clinical cancer models. Novel genes of interest are identified by evaluating sgRNA dropout or enrichment following selection pressure application. This method is particularly beneficial for researching cancers where effective treatment strategies are limited. One example of a commonly chemoresistant cancer, particularly at relapse, is the low survival malignancy epithelial ovarian cancer (EOC), made up of multiple histotypes with distinct molecular profiles. CRISPR-knockout library screens in pre-clinical EOC models have demonstrated the ability to predict biomarkers of treatment response, identify targets synergistic with standard-of-care chemotherapy, and determine novel actionable targets which are synthetic lethal with cancer-associated mutations. Robust experimental design of CRISPR-knockout library screens, including the selection of strong pre-clinical cell line models, allows for meaningful conclusions to be made. We discuss essential design criteria for the use of CRISPR-knockout library screens to discover genetic dependencies in cancer and draw attention to discoveries with translational potential for EOC.

Epigenetic Compound Library Screen Identifies Ibrutinib as an Inhibitor of Ovarian Clear Cell Carcinoma Viability

ABSTRACT Background Ovarian clear cell carcinoma (OCCC) is an endometriosis‐associated ovarian cancer subtype. Somatic mutations in OCCC are reported in ARID1A , PIK3CA , and the TERT promoter ( TERTp ), as well as less commonly in KRAS and TP53 among other genes. OCCC is typically resistant to standard‐of‐care chemotherapy, especially after relapse. While recent studies have seen favourable responses to immunotherapy, patients with OCCC face limited therapeutic options. Methods With the objective of discovering new drug treatments for OCCC, we screened OCCC (RMG‐1, JHOC‐5, OV207, OVISE, OVMANA, OVTOKO, and TOV‐21G) and non‐OCCC cell lines with a commercially available epigenetic drug compound library at two concentrations. Based on specified selection criteria, drugs were sought that preferentially inhibited viability of OCCC versus non‐OCCC cells, with subsequent validation in 2D and 3D bioprinted models and exploration of a relevant signalling pathway. Results Taken together, OCCC cell lines were more sensitive to the Bruton's Tyrosine Kinase (BTK) inhibitor ibrutinib than non‐OCCC cells, with some variation in response observed between cell lines in 2D and 3D bioprinted cultures. Furthermore, ibrutinib inhibited PI3K/AKT/mTOR cell survival signalling in some but not all OCCC cell lines, suggesting that this drug functions on additional pathways. Conclusions Ibrutinib is used clinically to treat specific B cell disorders; however, it is not currently approved to treat solid tumours. Data presented in OCCC cell lines complements clinical observations of a therapeutic response to ibrutinib in low‐grade serous ovarian cancer. Ibrutinib demonstrates potential for the treatment of certain rare subtypes of ovarian cancer and should be further investigated.