Dependence Receptors and Cancer: Addiction to Trophic Ligands

Data accumulating over the last 20 years support the notion that some transmembrane receptors are activated not only by their respective ligands but also, differentially, by the withdrawal or absence of these same ligands. In this latter setting, these receptors actively trigger apoptosis. They have been dubbed dependence receptors because their expression confers a state of ligand dependence for survival on the expressing cells. Twenty of these receptors have been identified to date, and several have been shown to inhibit tumor progression by inducing apoptosis. As a corollary, these receptors, or their transduced death signals, are frequently silenced in cancer cells as a selective mechanism to prevent cell death, allowing invasion and metastasis. Drugs aimed at inducing programmed cell death in neoplastic cells by re-engaging the proapoptotic activity induced by unliganded dependence receptors are in late-stage preclinical tests, poised for clinical evaluation. This approach may offer novel opportunities for patient treatments. In this review, we discuss the implications of dependence receptors in limiting cancer progression and address the therapeutic perspectives brought to light by this paradigm.