Abstract A03: PARP inhibitor nanotherapy for ovarian cancer.
Authors: Baldwin Paige , Ohman Anders , Thong Jeremy , Tangutoori Shifalika , Dinulescu Daniela , Sridhar Srinivas 
Published: May 2016

Introduction: Poly-ADP-Ribose Polymerase (PARP) inhibitor therapy exploits a synthetic lethality strategy in ovarian cancers specifically endowed with inherent damage in DNA repair or transcription pathways. Talazoparib and Olaparib are potent PARP inhibitors that are currently indicated for oral inhibitor therapy in several clinical trials for a variety of cancers. Oral administration of these inhibitors typically results in poor bioavailability and tumor accumulation. Here we report the first novel nanoformulations NanoTalazoparib and NanoOlaparib, thus enabling a platform which provides a safe vehicle for parenteral administration specifically targeted to the tumor, thereby increasing the bioavailability while reducing systemic toxicity.

Methods: Three nanoparticle (~120nm size) formulations NanoOlaparib, NanoOlaparibPt and NanoTalazoparib, have been successfully formulated and tested in vitro on several cancer cell lines. KURAMOCHI, SKOV3, and OVSAHO were cultured in RPMI + 10% FBS. JHOS2 was cultured in RPMI + 10% FBS +1% Non-Essential Amino Acids. PA1, COV318, 403, 404, 4412, and 4306 were all cultured in DMEM + 10% FBS. 403 and 404 were derived from tumors of BRCA2-/-¬, PTEN-/-, and TP53mut mice. 4306 and 4412 4306 were developed from conditional LSL-K-rasG12D/+/PTENloxP/loxP mice.

Dose Response: Cell lines were exposed to either Olaparib or NanoOlaparib concentrations ranging from 0 to 100 µM. Each cell line was treated for a total of four doubling cycles to ensure that the percent viability for each cell line was comparable. Cell viability was ascertained with an MTS assay, to measure the metabolic activity of the cells.

Pt synergism: The synergism due to chemosensitization using cisplatin was studied for both therapies using isobolograms developed from a delayed viability assay.

Results: In vitro studies PA1 is highly sensitive to NanoOlaparib which may be attributed to genetic instability at 11/13 polymorphic loci, each containing (CA)¬n microsatellites. Microsatellite instability has the potential to cause mutations in critical genes that contain coding repeat sequences. This suggests that the genetic instability in PA1 leads to downstream mutations conferring sensitivity to PARP inhibitors.

The murine cell lines, 403, 404 are the next most sensitive group to this treatment due to there triply mutated genomic profile. The high sensitivity of 4412 and 4306 cell lines suggests that PTEN deletion confers similar sensitivity to PARP inhibitors as a BRCA2 deletion. Loss of PTEN has been shown to lead to spontaneous DSBs, chromosomal instability, and defects in homologous recombination. While it was expected that cell lines with BRCA1/2 mutations would be some of the most sensitive to these treatments, the results indicate that BRCA mutations and deletions are just as susceptible as PTEN deletions while high genetic instability shows the greatest sensitivity.

NanoTalazoparib is 10-100 times more potent than Olaparib. The cell line dependence is similar to Olaparib except for the overall lower magnitudes.

In vivo studies A pilot study was carried out in an endometrial OvCa murine model with KRaS-PTEN deletion to test the nanoformulations for biocompatibility and therapeutic efficacy. Bioluminescence images show tumor suppression of more than a nearly a factor of 3. All formulations were well tolerated. Studies in BRCA2-/-¬/ PTEN-/-/TP53mut GEMM also showed good therapeutic response to i.p. administration.

Conclusions: Robust nanoparticle formulations of NanoTalazoparib and NanoOlaparib have been successfully demonstrated for in vitro and in vivo administrations. These results show that NanoOlaparib and NanoTalazoparib amplify the therapeutic efficacy of PARP inhibition and imply a very promising role for the nanoformulation in ovarian and other cancers.

This work was supported by the DOD Ovarian Cancer Research Program under Army- W81XWH-14-1-0092.

Citation Format: Paige Baldwin, Anders Ohman, Jeremy Thong, Shifalika Tangutoori, Daniela Dinulescu, Srinivas Sridhar. PARP inhibitor nanotherapy for ovarian cancer. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Ovarian Cancer Research: Exploiting Vulnerabilities; Oct 17-20, 2015; Orlando, FL. Philadelphia (PA): AACR; Clin Cancer Res 2016;22(2 Suppl):Abstract nr A03.