Irvalec Inserts into the Plasma Membrane Causing Rapid Loss of Integrity and Necrotic Cell Death in Tumor Cells

José M Molina-Guijarro,Carlos M Galmarini,Victoria Moneo,Carmen Valenzuela,Carolina García,Carlos Villalobos Jorge,Juan F Martínez-Leal,M Pilar Lillo,Carmen Cuevas,Lucía Núñez,Álvaro Macías,Eva Muñoz,Luis F García-Fernández,Miren David

doi:10.1371/journal.pone.0019042

Abstract

Irvalec is a marine-derived antitumor agent currently undergoing phase II clinical trials. In vitro, Irvalec induces a rapid loss of membrane integrity in tumor cells, accompanied of a significant Ca2+ influx, perturbations of membrane conductivity, severe swelling and the formation of giant membranous vesicles. All these effects are not observed in Irvalec-resistant cells, or are significantly delayed by pretreating the cells with Zn2+. Using fluorescent derivatives of Irvalec it was demonstrated that the compound rapidly interacts with the plasma membrane of tumor cells promoting lipid bilayer restructuration. Also, FRET experiments demonstrated that Irvalec molecules localize in the cell membrane close enough to each other as to suggest that the compound could self-organize, forming supramolecular structures that likely trigger cell death by necrosis through the disruption of membrane integrity.

Highlights

Irvalec (Elisidepsin, PM02734) is a synthetic cyclodepsipeptide closely related to Kahalalide F, a natural antitumor compound isolated from the Hawaiian marine mollusc Elysia rufescens [1]
These membrane changes were not observed in tumor cells with acquired resistance to the compound. These cytotoxic effects could be delayed by pretreating the cells with Zn2+, which has been described as a membrane protector [8]. These results indicate that Irvalec interacts directly with the cell membrane and induces a rapid and severe disorganization of the lipidic bilayer of tumor cells that disturbs the water-electrolyte balance causing necrosis
We evaluated whether exposure to Irvalec was associated with a rapid loss of cell membrane integrity

Summary

Introduction

Irvalec (Elisidepsin, PM02734) is a synthetic cyclodepsipeptide closely related to Kahalalide F, a natural antitumor compound isolated from the Hawaiian marine mollusc Elysia rufescens [1]. Preliminary in vitro and in vivo studies identified Irvalec as a new antiproliferative drug with activity against a broad spectrum of tumor types [Molina-Guijarro JM et al.; AACR Annual Meeting 2009; abstr 888]. Irvalec is currently in phase II clinical studies for squamous non-small cell lung cancer (NSCLC), gastric and esophageal cancer. It was previously reported that Kahalalide F induces a rapid membrane permeabilization, with loss of mitochondrial membrane potential and of lysosomal integrity, and profound general alterations in the cells, including severe cytoplasmic swelling and vacuolization, dilatation and vesiculation of the endoplasmic reticulum, mitochondrial damage and plasma membrane rupture [3,4,5]. Kahalalide F mediates a necrotic cell death type rather than apoptosis that is not associated with DNA degradation or cell cycle blockade [6]

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Results

Conclusion