Phorboid 20-homovanillates induce apoptosis through a VR1-independent mechanism

Background: Vanilloids, such as capsaicin and resiniferatoxin (RTX), are re cognized at the cell surface by vanilloid receptor type 1(VR1), which has r ecently been cloned. VRI mediates the effects of capsaicin and RTX in VR1-e xpressing cells, but vanilloids can induce apoptosis through a pathway not mediated by VR1. Phorboid 20-homovanillates can be used to investigate cell death induced by vanilloids. Results: 12,1 3-Diacylphorbol-20 homovanillates were prepared by the sequen tial esterification of the natural polyol. Phorbol 15-phenylacetate 13-acet ate 20-homovanillate (PPAHV) induced apoptosis in Jurkat cells to the same extent as RTX. Apoptosis was preceded by an increase in intracellular react ive oxygen species and by the loss of mitochondrial transmembrane potential . PPAHV-induced apoptosis was mediated by a pathway involving caspase-3 act ivation and was initiated at the S phase of the cell cycle. The cell-death pathway triggered by VRI activation was studied in 293T cells transfected w ith the cloned rat vanilloid receptor. In this system, capsaicin and PPAHV induced cell death by an apparent necrotic mechanism, which was selectively inhibited by the competitive vanilloid receptor antagonist capsazepine. In terestingly, phorbol-12,13-bisnonanoate-20-hemovanillate, an analogue of PP AHV, induced cell death in VR1-transfected cells but could not trigger apop tosis in the Jurkat cell line. Conclusions: Vanilloids can induce cell death through different signalling pathways. The cell death induced in a VR1-independent manner has the hallma rk of apoptosis, whereas the cell death mediated by vanilloids binding to V R1 is seemingly necrotic. Phorboid homovanillates that have antitumour and anti-inflammatory activities but lack the undesirable side effects of the n atural vanilloids could be developed as potential drugs.