SENSITIZATION OF HELA CELLS TO TRAIL-INDUCED APOPTOSIS VIA AMPLIFICATION OF DEATH RECEPTOR SIGNALING: NOVEL BIOLOGICAL ACTIVITY OF THE SMALL MOLECULE COMPOUND LY303511

Abstract

The TNF receptor family member TRAIL (TNF-related apoptosis inducing ligand) has shown promise as a target-specific agent against certain classes of tumor cells, without exhibiting cytotoxicity towards normal cells. However, despite this preferential sensitivity, resistance to TRAIL remains a clinical problem. To that end, a plethora of compounds are under investigation for their ability to revert tumor cells¿ responsiveness to TRAIL. We recently demonstrated that the phosphatidylinositide-3-kinase (PI3K) inhibitor, LY294002, and its inactive analog LY303511 (LY30), sensitized tumor cells to drug-induced apoptosis, independent of PI3K/Akt pathway. Thus, we investigated the effect of LY30 on TRAIL-induced apoptosis in human cancer cell lines. Preincubation of cells with LY30 significantly amplified TRAIL signaling as evidenced by enhanced DNA fragmentation, caspases 2, 3, 8, and 9 activation, and inhibition of tumor colony formation. We link this execution signal to the ability of LY30 to oligomerize and upregulate DR4/5 and downregulate cFLIPS, thus facilitating assembly and signaling via the death initiating signaling complex. The subsequent processing/activation of caspase 8 and cleavage of its substrate, the BH3 protein Bid, recruits mitochondrial initiated apoptotic events culminating in activation of caspase 9. Functional knockdown of death receptors abolished the TRAIL-sensitizing ability of LY30 and restored viability to the cells. Thus, we highlighted the potential of LY30, or structurally similar compounds, as an adjuvant in tumor cells for TRAIL-induced cell death.