Abstract 3715: Targeted nanotherapy using the PARP inhibitor talazoparib for breast cancer treatment
Authors: Baldwin Paige , Kumar Rajiv , Sridhar Srinivas 
Published: August 2018

Abstract
Introduction: PARP inhibitors exploit defects in DNA repair pathways to selectively target cancerous cells. These drugs are currently delivered orally, but Talazoparib, the most potent PARP inhibitor, exhibits greater toxicity than the others. Systemic administration of nanoparticles bypasses the first-pass metabolism of oral drugs and nanoparticles preferentially accumulate in tumors due to the leaky tumor vasculature. Additionally, nanoparticles can be actively targeted to tumors by conjugating different moieties such as antibodies that recognize overexpressed markers on the tumor cells. NanoTalazoparib (NanoTLZ) has been previously formulated and extensively characterized in breast, ovarian, and lung cancer models. Here we describe further characterization of NanoTLZ and the development of a next generation fluorescently labeled EPCAM targeted formulation of NanoTLZ for the treatment of triple negative breast cancer (TNBC).
Methods: Animals with orthotopic TNBC xenografts were injected with NanoTLZ and at various time points tumor biopsies were taken to assay tumor PAR levels. Blood was collected at various time points and plasma separated for drug extraction and quantification. Pharmacokinetic modeling is underway. Fluorescently labeled NanoTLZ was developed with the addition of Cy5, followed by further improvement via conjugation of anti-EPCAM antibodies. Targeting capability was assessed via laser scanning confocal microscopy after treatment of the TNBC cell line MDA-MB-231 with either non-targeted or targeted NanoTLZ. Therapeutic efficacy studies with targeted NanoTLZ alone and in combination with radiation are underway in an MDA-MB-231 xenograft model.
Results: Pharmacodynamics indicated PAR suppression in tumors within 30 minutes of NanoTLZ treatment. Tumor PAR levels began to increase 24 hours after a single dose but remained significantly lower than control levels up to 72 hours (P&lt;0.005). Characterization of NanoTLZ after the addition of Cy5 and after anti-EPCAM targeting indicated that the formulation remained under 100 nm in diameter with a charge of ~10 mV and equivalent drug loading and release. Cy 5 labeling allowed for visualization of nanoparticle uptake and intracellular fluorescence was 70% greater in cells when treated with EPCAM targeted NanoTLZ compared to non-targeted.
Conclusions: The sustained release of Talazoparib from the nanoformulation decreases tumor PAR levels for up to 72 hours after a single dose, allowing for less frequent administration than the current daily regime used for oral Talazoparib. The targeted formulation of NanoTLZ shares the same physicochemical properties as the untargeted formulation, but is taken up much faster in vitro, suggesting it will allow for greater accumulation at the tumor site making it more effective than the previously tested untargeted NanoTLZ. Supported by ARMY/W81XWH-16-1-0731 and Rivkin Foundation.
Citation Format: Paige Baldwin, Rajiv Kumar, Srinivas Sridhar. Targeted nanotherapy using the PARP inhibitor talazoparib for breast cancer treatment [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 3715.