Abstract 991: Secretory phospholipase A2 as a trigger for drug release in the treatment of triple-negative breast cancer
Authors: Jasper Shanese L. , Skarupa Elena B. , Cummings Brian S. , Arnold Robert D. 
Published: August 2019

Abstract
Triple negative breast cancer describes a subgroup of breast cancers which are negative for the estrogen and progesterone receptors as well as the HER2 protein. As such, triple negative breast cancers have seen little benefit from the targeted therapies developed for the treatment of breast cancer. To address this challenge, we examined an alternative target within the tumor as well as the tumor environment. Secretory phospholipase A2 (sPLA2) cleave phospholipids at sn-2 ester bonds, releasing lysophospholipids and fatty acids, and are over expressed in several pathologies including breast cancer. Herein, we evaluated the therapeutic activity of secretory phospholipase A2 responsive liposomes (SPRL) compared to the clinically used, sterically-stabilized, pegylated liposomes (SSL) for in vitro response in a triple-negative breast cancer (TNBC) model. In these studies, SSL and SPRL formulations were made according to previous studies and resulted in three formulations SSL, SPRL- E and SPRL-G. SPRL were made by the addition of either DSPE (SPRL-E) or DSPG (SPRL-G). Doxorubicin was used as the drug of choice and Dox-loaded liposomes were prepared by remote-loading using an ammonium sulfate gradient. Toxicity studies were performed by the use of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) or resazurin while uptake studies were performed by fluorescence microscopy and flow cytometry. Briefly, cells were seeded at a density of 10,000 cells per well and subjected to free doxorubicin or liposomal doxorubicin in concentrations from 0 - 100 µM. At the appropriate time points, 0-72 hours, cells were harvested for studies. Treatment of breast cancer cells with doxorubicin encapsulated in SSL and SPRL resulted in cytotoxicity in the MDA-MB-231 cells line comparable to free drug with an IC50 of approximately 3 µM at the 72 hour time point. In tracking of drug and liposome delivery, we demonstrated that drug uptake was liposome-dependent, as encapsulation of doxorubicin in SPRL resulted in greater intracellular drug levels compared to SSL. These data show the therapeutic activity of SPRL compared to SSL, and suggest that SPRL may be useful for the treatment of TNBC. Two-dimensional models do not fully recapitulate the complexity of barriers to drug delivery, nor the effect of multiple cell types. Therefore, ongoing studies are examining the utility of these liposome formulations in three-dimensional co-cultures that include macrophages and fibroblasts. In this model, we hope to assess the ability of the tumor microenvironment to alter drug release.
Citation Format: Shanese L. Jasper, Elena B. Skarupa, Brian S. Cummings, Robert D. Arnold. Secretory phospholipase A2 as a trigger for drug release in the treatment of triple-negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 991.