Abstract
Cancer cells are hypersensitive to nutrient limitation because oncogenes constitutively drive glycolytic and TCA (tricarboxylic acid) cycle intermediates into biosynthetic pathways. As the anaplerotic reactions that replace these intermediates are fueled by imported nutrients, the cancer cell's ability to generate ATP becomes compromised under nutrient-limiting conditions. In addition, most cancer cells have defects in autophagy, the catabolic process that provides nutrients from internal sources when external nutrients are unavailable. Normal cells, in contrast, can adapt to the nutrient stress that kills cancer cells by becoming quiescent and catabolic. In the present study we show that FTY720, a water-soluble sphingolipid drug that is effective in many animal cancer models, selectively starves cancer cells to death by down-regulating nutrient transporter proteins. Consistent with a bioenergetic mechanism of action, FTY720 induced homoeostatic autophagy. Cells were protected from FTY720 by cell-permeant nutrients or by reducing nutrient demand, but blocking apoptosis was ineffective. Importantly, AAL-149, a FTY720 analogue that lacks FTY720's dose-limiting toxicity, also triggered transporter loss and killed patient-derived leukaemias while sparing cells isolated from normal donors. As they target the metabolic profile of cancer cells rather than specific oncogenic mutations, FTY720 analogues such as AAL-149 should be effective against many different tumour types, particularly in combination with drugs that inhibit autophagy.