Liposomes targeting tumour stromal cells.

Liposomes have found clinical application in cancer therapy in the delivery of cytostatic agents. As a result of the targeted delivery of these toxic molecules to the tumour cells coupled to avoidance of toxicity-sensitive tissues, the therapeutic window is widened. Over the past years the focus of cancer therapy has shifted towards the stromal cells that are present in the tumour. It appears that clinically relevant tumours have acquired the ability to modulate the microenvironment in such a way that a chronic pro-inflammatory and pro-angiogenic state is achieved that contributes to invasion and metastasis and continued proliferation. Over the past years, liposomal formulations have been designed that target key stromal cell types that contribute to tumour growth. At the same time, many promising cell types have not been targeted yet and most of the studies employ drugs that aim at depleting stromal cells rather than modulating their activity towards an anti-tumour phenotype. In this review these target cell types will be addressed. Complementing these targeted formulations with the appropriate drugs to optimally suppress tumour-promoting signals while preserving anti-tumour action will be the challenge for the future.