Combination therapy of established cancer using a histone deacetylase inhibitor and a TRAIL receptor agonist

Abstract

Histone deacetylase inhibitors (HDACi) and agents such as recombinant tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and agonistic anti-TRAIL receptor (TRAIL-R) antibodies are anticancer agents that have shown promise in preclinical settings and in early phase clinical trials as monotherapies. Although HDACi and activators of the TRAIL pathway have different molecular targets and mechanisms of action, they share the ability to induce tumor cell-selective apoptosis. The ability of HDACi to induce expression of TRAIL-R death receptors 4 and 5 (DR4/DR5), and induce tumor cell death via the intrinsic apoptotic pathway provides a molecular rationale to combine these agents with activators of the TRAIL pathway that activate the alternative (death receptor) apoptotic pathway. Herein, we demonstrate that the HDACi vorinostat synergizes with the mouse DR5-specific monoclonal antibody MD5-1 to induce rapid and robust tumor cell apoptosis in vitro and in vivo. Importantly, using a preclinical mouse breast cancer model, we show that the combination of vorinostat and MD5-1 is safe and induces regression of established tumors, whereas single agent treatment had little or no effect. Functional analyses revealed that rather than mediating enhanced tumor cell apoptosis via the simultaneous activation of the intrinsic and extrinsic apoptotic pathways, vorinostat augmented MD5-1-induced apoptosis concomitant with down-regulation of the intracellular apoptosis inhibitor cellular-FLIP (c-FLIP). These data demonstrate that combination therapies involving HDACi and activators of the TRAIL pathway can be efficacious for the treatment of cancer in experimental mouse models.

Identification of an acetylation-dependant Ku70/FLIP complex that regulates FLIP expression and HDAC inhibitor-induced apoptosis

“…Although a number of studies have shown that HDAC inhibitor-mediated downregulation of FLIP sensitises various cancer cell lines to death ligands, such as TRAIL, 23,27,28 to our knowledge, no previous studies have directly examined whether FLIP downregulation is a sufficient death signal for apoptosis induction when these agents are administered as single agents. We found that FLIP downregulation in response to HDAC inhibitors results in caspase 8-and DR5-mediated apoptosis, phenocopying the mechanism of apoptosis that we previously observed in CRC cells following siRNA-mediated downregulation of FLIP.…”

“…However, our findings agree with a recent study in breast cancer models, which also found that SAHA-induced FLIP downregulation was post-transcriptional. 23 In addition, a related pan-HDAC inhibitor Panobinostat (LBH589) was recently reported to cause FLIP polyubiquitination and proteasomal degradation in pancreatic cancer cells. 24 Collectively, these findings suggest that SAHA causes Ku70 acetylation, resulting in the disruption of its interaction with FLIP leading to degradation of FLIP by the UPS.…”

The BCL-2 protein family, BH3-mimetics and cancer therapy

“…Similar protection from chemotherapeutic drug-induced apoptosis can be afforded by overexpression of any of the other prosurvival BCL-2 family members. [134][135][136][137] Studies using gene-targeted mice or RNAi-mediated gene knockdown in cell lines revealed which pro-apoptotic BCL-2 family members are critical for cell killing by which anticancer agent. Consistent with the notion that BAX and BAK have essential overlapping functions in the BCL-2-regulated apoptotic pathway, cells from Bax −/− Bak −/− mice are markedly resistant to diverse anticancer agents.…”

AMPK-independent down-regulation of cFLIP and sensitization to TRAIL-induced apoptosis by AMPK activators

“…To overcome this resistance, TRAIL-induced signaling is being studied alone or in combination with different sensitizing agents, such as chemotherapeutic drugs, cytokines and inhibitors of survival pathways [4][5][6].…”