Abstract 1316: PAX8-directed nanotherapeutics for high-grade serous ovarian cancer
Authors: Chandrasekaran Akshaya , Ahmed Mariam , Holub Nicole , Wang Wade , Hammond Paula T. , Elias Kevin M. 
Published: July 2021

Objective: High-grade serous ovarian cancer (HGSOC) is the most common epithelial ovarian cancer subtype. Targeted therapy for HGSOC is challenging as the disease is characterized by copy number variation and not somatic mutations. HGSOC displays well-conserved features such as expression of transcription factor PAX8. We propose employing therapies that capitalize on interactions between PAX8 and specific DNA-binding sites to develop therapeutic approaches to target HGSOC. Our hypothesis is to use a biomimetic approach wherein PAX8 is induced to transcribe an ectopically transfected CRISPR-base editor (BE)-guide RNA (gRNA) plasmid containing a PAX8 binding site in its promoter. The gRNA will impart a dominant-negative allele of ataxia telangiectasia and Rad3-related protein (ATR), which has been shown to be synthetically lethal with mutant p53 in cancer cells. In the presence of PAX8, the plasmid will be transcribed, while in the absence of PAX8, the plasmid is degraded, with minimal toxicity observed in healthy cells.

Methods: PAX8-expressing ovarian cancer cell lines including COV362, Kuramochi, OVCAR8 and OVSAHO or PAX8-null cell lines including MCF-7 and HeLa were transfected with polyplexes bearing the plasmid of interest. Polyplex diameter, polydispersity indices and surface zeta potentials were measured on a Malvern Zetasizer. Polyplexes were imaged for uptake and functionality using fluorescence microscopy and Amnis ImageStream. Polyplex toxicity was assessed in vitro using cell viability assays. Preliminary in vivo experiments to demonstrate luciferase plasmid-bearing polyplexes have been performed in NSG mice. To monitor in vivo transfection efficiencies, we will deliver fluorescently labeled plasmids or luciferase-encoding plasmids to test bio-distribution and pharmacokinetics.

Results: We have synthesized sub-200nm (diameter) polyplexes using the polyamine PPLG-g-azidopropylamine (PPLG) and BE or gRNA plasmids. Using -/- ATR gRNA, we observed that the BE and the gRNA can be efficiently packaged into polymeric nanoplexes and delivered to ovarian cancer cells or control cells to impart a dominant-negative mutant of ATR. Ongoing work includes cell cycle analysis using flow cytometry to monitor checkpoint activation, quantifying percent of total sequencing reads with target base pair conversions and testing gRNAs against other targets for efficacy in ovarian cancer targeting.

Conclusion: Combining nanotechnology and gene editing can improve specificity toward ovarian cancer cells as well as incorporate precision therapy aimed at the underlying genetic architecture of this disease. Due to the synthetic lethality nature of ATR and p53, addition of a combinatorial PARP inhibitor to the proposed therapy will reduce tumor burden. While resistance can develop to ATR inhibitors, ovarian cancer cells are unable to downregulate PAX8, thus ensuring continued response to the PAX8-directed therapy.

Citation Format: Akshaya Chandrasekaran, Mariam Ahmed, Nicole Holub, Wade Wang, Paula T. Hammond, Kevin M. Elias. PAX8-directed nanotherapeutics for high-grade serous ovarian cancer [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 1316.