Nutritional Access Modulates Activity of a Small Molecule Enhancer of Endosomal Escape

Abstract

For siRNA drugs to be relevant in tumors, poor endosomal escape of these drugs needs to be addressed. Endosomal escape can occur when the endolysosomal membrane is damaged and can be visualized by endogenously expressed fluorescent galectin-9 functioning as damage sensors. Tumor cells have unstable membranes and central parts of tumors have low nutrient levels contributing to reactive oxygen species which can induce membrane damage. We show that nutrient depletion alone does not induce endolysosomal membrane damage in HeLa and MCF7 cells or in HeLa spheroids. Serum depletion, however, enhanced endolysosomal membrane damage in HeLa cells when combined with the membrane destabilizing drug chloroquine, a cationic amphiphilic drug. This effect was almost completely abolished when depleting the cells of glucose, even when serum was present. This phenomenon could not be seen with other cationic amphiphilic drugs like siramesine and loperamide. In a functional experiment, co-treatment with chloroquine and siGFP significantly improved knockdown of GFP in the presence but not in the absence of glucose. Our results have implications for the development of chloroquine as an endosomal escape enhancer of RNA therapeutics in tumor contexts and stresses the importance of considering nutrient levels and tumor size in future screenings.