Abstract A74: Identification of novel targetable resistance mechanisms and candidate clinical response biomarkers in drug-resistant ovarian cancer, following single-agent and combination chemotherapy
Authors: Vaidyanathan Aparajitha , Sawers Lynne , Chakravarty Probir , Bray Susan E. , McMullen K. Wendy , Ferguson Michelle J. , Smith Gillian 
Published: August 2018

The aim of our translational research program in Dundee is to develop innovative experimental models to understand the molecular basis of adaptive drug resistance in ovarian cancer patients, extending our findings to the development of novel drug targets, combination chemotherapy approaches, and predictive clinical response biomarkers.

Ovarian cancer is a deadly gynecologic malignancy, frequently diagnosed when the disease is already advanced. First-line treatment options in the UK mandate combination carboplatin and paclitaxel chemotherapy, with olaparib and additional PARP inhibitors under evaluation in patients with specific molecular signatures. While treatment is initially effective in many patients, development of drug resistance frequently limits clinical response to chemotherapy. Our understanding of the underlying molecular mechanisms is limited by lack of cell line models that appropriately mimic typical drug choices and commonly prescribed drug combinations in ovarian cancer patients. To address this issue, we have developed a series of novel drug-resistant cell lines, following treatment of A2780 and additional chemotherapy-naïve parental cells with clinically relevant doses of cisplatin (A2780cisR), carboplatin (A2780carboR), paclitaxel (A2780pacR), olaparib (A2780olapR), and combination carboplatin and paclitaxel chemotherapy (A2780cpR), and have used these cell lines to describe a common ABCB1 (MDR1)-mediated drug resistance mechanism common to A2780pacR and A2780olapR cells (Vaidyanathan et al., Br J Cancer 2016;115:431-41).

More recently, we have used RNASeq (Ion Ampliseq Targeted Sequencing Technology) and Reverse Phase Protein Array (RPPA) analysis to compare the expression of whole-genome mRNA and more than 300 protein and phosphoprotein targets in pairwise comparisons of drug-sensitive and drug-resistant cells—unsupervised hierarchical clustering of these datasets revealed marked differences in expression between paclitaxel, olaparib, and platinum drug-resistant cells, and significant differences in cisplatin and carboplatin-selected cells. Consistent with improved clinical response, our combination A2780cpR line has a unique phenotype, which is distinct from both A2780carboR and A2780pacR cells. Importantly, we have identified significant increases in the expression of targetable phosphoproteins, for example, pATM (Ser1981), pAKT (Tyr308 and Ser473), pCHK1 (Ser296), and pGSK3b (Ser9/Ser21) in A2780cpR cells. In complementary experiments, we have used Taqman Low Density Arrays (TLDAs) to compare the expression of 377 miRNAs in our cell line panel, and have identified multiple differentially expressed miRNAs, both common to all resistant cells and unique to individual drug-resistant phenotypes.

To validate our prioritized candidate phosphoprotein targets and miRNA biomarkers, we have created a unique clinical study, the Dundee Ovarian Cancer Study (DOCS), in which we are creating serial ascites-derived primary cell lines from initially drug-sensitive and subsequently drug-resistant ovarian cancer patients. We are currently using MTT cytotoxicity and colony formation assays in these cell lines to evaluate combination chemotherapy approaches with pathway specific inhibitors to each of our targetable resistance mechanisms, and developing quantitative PCR and immunohistochemical-based methods for evaluation of candidate drug resistance biomarkers in matched serum and plasma samples from DOCS patients.

Our combined laboratory and clinical studies therefore provide a “bench to bedside” approach to molecular characterization and prioritization of novel strategies to combat drug resistance, the major treatment-limiting complication in the clinical management of ovarian cancer patients.

Citation Format: Aparajitha Vaidyanathan, Lynne Sawers, Probir Chakravarty, Susan E. Bray, K. Wendy McMullen, Michelle J. Ferguson, Gillian Smith. Identification of novel targetable resistance mechanisms and candidate clinical response biomarkers in drug-resistant ovarian cancer, following single-agent and combination chemotherapy. [abstract]. In: Proceedings of the AACR Conference: Addressing Critical Questions in Ovarian Cancer Research and Treatment; Oct 1-4, 2017; Pittsburgh, PA. Philadelphia (PA): AACR; Clin Cancer Res 2018;24(15_Suppl):Abstract nr A74.