Identification of lipid-phosphatidylserine (PS) as the target of unbiasedly selected cancer specific peptide-peptoid hybrid PPS1.

Tanvi J Desai,Damith Gomika Udugamasooriya,John D Minna,Jason E Toombs,Rolf A Brekken

doi:10.18632/oncotarget.8929

Tanvi J Desai, Damith Gomika Udugamasooriya + Show 3 more

Open Access

https://doi.org/10.18632/oncotarget.8929

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Abstract

Phosphatidylserine (PS) is an anionic phospholipid maintained on the inner-leaflet of the cell membrane and is externalized in malignant cells. We previously launched a careful unbiased selection targeting biomolecules (e.g. protein, lipid or carbohydrate) distinct to cancer cells by exploiting HCC4017 lung cancer and HBEC30KT normal epithelial cells derived from the same patient, identifying HCC4017 specific peptide-peptoid hybrid PPS1. In this current study, we identified PS as the target of PPS1. We validated direct PPS1 binding to PS using ELISA-like assays, lipid dot blot and liposome based binding assays. In addition, PPS1 recognized other negatively charged and cancer specific lipids such as phosphatidic acid, phosphatidylinositol and phosphatidylglycerol. PPS1 did not bind to neutral lipids such as phosphatidylethanolamine found in cancer and phosphatidylcholine and sphingomyelin found in normal cells. Further we found that the dimeric version of PPS1 (PPS1D1) displayed strong cytotoxicity towards lung cancer cell lines that externalize PS, but not normal cells. PPS1D1 showed potent single agent anti-tumor activity and enhanced the efficacy of docetaxel in mice bearing H460 lung cancer xenografts. Since PS and anionic phospholipid externalization is common across many cancer types, PPS1 may be an alternative to overcome limitations of protein targeted agents.

Highlights

Conventional drug development targeting cell surface proteins is challenging in oncology due to the diversity and complexity of cancer [1,2,3]
Further we found that the dimeric version of PPS1 (PPS1D1) displayed strong cytotoxicity towards lung cancer cell lines that externalize PS, but not normal cells
PS is well-known to be externalized in the tumor vascular endothelial cells and on some tumor cells as depicted in Figure 2A compared to normal cells

Summary

INTRODUCTION

Conventional drug development targeting cell surface proteins is challenging in oncology due to the diversity and complexity of cancer [1,2,3]. We hypothesized that identifying compounds that target non-protein based cell surface bio-molecules that are widely expressed across many cancer types would address some of these challenges. We utilized our on-bead two-color (OBTC) combinatorial cell screen to select peptide-peptoid hybrids that discriminate cell www.impactjournals.com/oncotarget surface targets in closely related cell populations [5]. This screening strategy is unbiased in terms of the nature of target selection allowing equal chance to recognize a protein, lipid or a carbohydrate specific to cancer cells. We identified a peptide-peptoid hybrid called PPS1 (Figure 1A) that binds HCC4017 lung cancer cells with limited or no binding to normal HBEC30KT cells. In this study we describe the target identification of our peptide-peptoid hybrid PPS1 and demonstrate that PPS1 has potential as an anti-cancer therapeutic

RESULTS AND DISCUSSION

MATERIALS AND METHODS

CONFLICTS OF INTEREST