Ingenol esters induce apoptosis in Jurkat cells through an AP-1 and NF-κB independent pathway Original Research Article

Abstract Background: Ingenol derivatives have received constant and multidisciplinary attention on account of their pleiotropic pattern of biological activity. This includes activation of protein kinase C (PKC), tumour-promotion, anticancer, and anti-HIV properties, and the possibility of dissecting co-cancerogenic and clinically useful activities has been demonstrated. Certain ingenol esters show powerful anticancer activity, and a structure–activity relationship model to discriminate between their apoptotic and non-apoptotic properties has been developed. Results: The polyhydroxylated southern region of ingenol was selectively modified, using the anticancer and PKC activator ingenol 3,20-dibenzoate (IDB) as a lead compound. The evaluation of IDB analogues in apoptosis assays showed strict structure–activity relationships, benzoylation of the 20-hydroxyl being required to trigger apoptosis through a pathway involving caspase-3 and occurring at the specific cell cycle checkpoint that controls the S–M phase transition. Conversely, a study on the activation of the PKC-dependent transcription factors AP-1 and NF-κB by IDB analogues showed significant molecular flexibility, including tolerance to changes at the 3- and 20-hydroxyls. IDB-induced apoptosis was independent of activation of PKC, since it was not affected by treatment with the non-isoform-selective PKC inhibitor GF 109230X0. Conclusions: Remarkable deviations from the tumour-promotion pharmacophore were observed for both the apoptotic and the PKC-activating properties of IDB analogues, showing that ingenol is a viable template to selectively target crucial pathways involved in tumour promotion and development. Since the apoptotic and the PKC-activating properties of ingenoids are mediated by different pathways and governed by distinct structure–activity relationships, it is possible to dissect them by suitable chemical modification. In this context, the esterification pattern of the 5- and 20-hydroxyls is critica