Introduction: More than 50% of cancer patients receive radiation therapy at some point during their care. Gold nanoparticles (GNPs) can amplify the radiation dose by facilitating the ejection of low-energy photoelectrons, resulting in increased DNA damage. One of the main challenges of radiation therapy in cancer is to sustain this damage for longer durations. DNA single-strand breaks (SSBs) are repaired by base excision repair, which utilizes Poly(ADP-ribose) polymerase (PARP). PARP inhibition during radiotherapy provides an attractive alternative in maximizing treatment outcomes. Here, we explore a strategy to combine the radiosensitizing effect of GNPs with the DNA-repair inhibiting ability of NanoTalazoparib (nTLZ), a liposomal formulation of the PARP inhibitor, talazoparib (TLZ).

Methods: GNPs were synthesized by reducing AuCl4 using Tetrakis(hydroxymethyl)phosphonium chloride and further PEGylating using heterobifunctional PEGs. A liposomal formulation of TLZ was synthesized using the Nanoassemblr, a microfluidics-based device. Physicochemical characterization of GNPs and nTLZ was carried out using TEM, DLS and release kinetics studies. In vitro studies were carried out to assess the toxicity of the GNPs using MTT assay in non-small cell lung cancer (NSCLC) cell line Calu-6. The therapeutic efficacy of combination treatment using GNPs, nTLZ and radiation was done using clonogenic survival assays. Clonogenic assay was carried out using Calu 6 cells, which were sequentially treated with GNPs (1mg/mL), TLZ (0.5 uM) and nTLZ (0.5 uM) with and without radiation. The radiation doses varied from 0-10Gy for each set of treatments.

Results: PEGylated GNP's showed a hydrodynamic diameter of ~10-12 nm with a spherical morphology whereas nTLZ size was 70 nm encapsulating TLZ at a concentration of ~200 ug/ml. MTT assay showed no toxicity for PEGylated GNPs treated upto a concentration of 3.0 mg/mL. Cells treated with either GNPs, TLZ or nTLZ did not show significant reduction in colony formation, but were reduced with increasing doses of radiation. The survival plots showed a highly additive antiproliferative effect for the GNP + nTLZ combination at all radiation doses, while the free TLZ + GNPs combination was not as effective at inhibiting colony formation. In vivo experiments assessing the combination therapy in a subcutaneous xenograft mice model using Calu 6 are currently under way.

Conclusions: The preliminary in vitro results indicate that the combination of radiosensitizing GNPs with a potent DNA repair enzyme inhibitor, TLZ, has an immense potential as a complimentary combination therapy in conjunction with radiation therapy in treatment of lung cancer.

This work is supported by the CaNCURE program (grant #1CA174650-02), American Lung Association, Dana-Farber Cancer Institute and Brigham and Women's Hospital.

Citation Format: Ana G. Vazquez-Pagan, Paige Baldwin, Ravina M. Ashtaputre, Sijumon Kunjachan, Srinivas Sridhar, Rajiv Kumar, Ross Berbeco. Nanoparticle-mediated concomitant radiation dose amplification and PARP inhibition in lung cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3710.