Abstract A32: Combination panobinostat and olaparib treatment promotes DNA damage and antitumor immunity in ovarian cancer
Authors: Wilson Andrew J. , Dai Xiaozhuan , Liu Qi , Hiebert Scott , Crispens Marta , Khabele Dineo 
Published: September 2020

Background and Objective: High-grade serous ovarian cancers (HGSOC) retaining functional homologous recombination (HR) have poorer clinical outcomes and show relative resistance to DNA-damaging poly ADP ribose polymerase inhibitors (PARPi). We have shown that epigenetic drugs such as histone deacetylase inhibitors (HDACi) sensitize ovarian cancer cells to PARPi, in part through reduction of HR efficiency. However, these studies were conducted in immunocompromised mouse models, and drug effects on immune cell populations could not be fully examined. In this study, we will identify novel mechanisms of antitumor effects of combined HDACi/PARPi treatment by transcriptome analysis, and test drug effects in an established immune competent mouse model of ovarian cancer.

Methods: HR-proficient SKOV-3 ovarian cancer cells were treated with vehicle (CON), PARPi olaparib (OLA; 10μM), HDACi panobinostat (PANO; 50nM) or OLA/PANO for 12h, and RNA-seq analysis performed. Differentially expressed genes between treatment groups were detected by DESeq2, based on fold change &gt;1.5 and the corrected P value (FDR) &lt;0.05. Functional group analysis of differentially expressed genes was performed using WebGestalt, with enrichment p-values generated by the Fisher’s exact test with Benjamini/Hochberg correction. C57BL/6 mice with intraperitoneal ID8-luc tumors were treated with vehicle, PANO (2.5 mg/kg), OLA (100mg/kg) and OLA/PANO for 4 weeks, starting 30 days after tumor injection. Tumor burden was measured by bioluminescence imaging of the constitutive luc reporter, and harvested tumors assayed for IHC markers of proliferation, apoptosis and DNA damage, and for total (CD3) and cytotoxic (CD8) T cells. Differences in group means were evaluated by Student’s t-test (p&lt;0.05 is significant).

Results: Functional group analysis of RNA-seq data showed significant enrichment of genes involved in cell proliferation, apoptosis, and DNA damage and repair with OLA/PANO treatment compared to CON or OLA alone. For a panel of 37 HR pathway genes, OLA/PANO treatment significantly reduced expression of 20 genes (e.g., BRCA1, BRCA2, WEE1). Examples of other significantly enriched functional pathways were cytokine secretion, inflammatory response genes, T cell activation (e.g., CD274/PD-L1, TNFSF9) and immune cell recruitment (e.g., IL-8, CXCL3). Consistent with these RNA-seq data, combined OLA/PANO treatment significantly reduced ID8-luc tumor burden and cell growth, and increased apoptosis and DNA damage, compared to CON or either drug alone. Moreover, there was increased infiltration of CD8+ T cells into OLA/PANO tumors, indicative of enhanced antitumor immunity.

Conclusions: We have confirmed mechanisms such as reduced HR and identified a novel role for T-cell recruitment for OLA/PANO treatment of ovarian tumors. These findings support expanding the use of PARPi in HR-proficient HGSOC through rational combinations with HDACi and have the potential to benefit a substantial number of women with this devastating disease.

Citation Format: Andrew J. Wilson, Xiaozhuan Dai, Qi Liu, Scott Hiebert, Marta Crispens, Dineo Khabele. Combination panobinostat and olaparib treatment promotes DNA damage and antitumor immunity in ovarian cancer [abstract]. In: Proceedings of the AACR Special Conference on Advances in Ovarian Cancer Research; 2019 Sep 13-16, 2019; Atlanta, GA. Philadelphia (PA): AACR; Clin Cancer Res 2020;26(13_Suppl):Abstract nr A32.