Clinical Positioning of the IAP Antagonist Tolinapant (ASTX660) in Colorectal Cancer

Abstract

Inhibitors of apoptosis proteins (IAPs) are intracellular proteins, with important roles in regulating cell death, inflammation, and immunity. Here, we examined the clinical and therapeutic relevance of IAPs in colorectal cancer. We found that elevated expression of cIAP1 and cIAP2 (but not XIAP) significantly correlated with poor prognosis in patients with microsatellite stable (MSS) stage III colorectal cancer treated with 5-fluorouracil (5FU)-based adjuvant chemotherapy, suggesting their involvement in promoting chemoresistance. A novel IAP antagonist tolinapant (ASTX660) potently and rapidly downregulated cIAP1 in colorectal cancer models, demonstrating its robust on-target efficacy. In cells co-cultured with TNFa to mimic an inflammatory tumor microenvironment, tolinapant induced caspase-8-dependent apoptosis in colorectal cancer cell line models; however, the extent of apoptosis was limited because of inhibition by the caspase-8 paralogs FLIP and, unexpectedly, caspase-10. Importantly, tolinapant-induced apoptosis was augmented by FOLFOX in human colorectal cancer and murine organoid models in vitro and in vivo, due (at least in part) to FOLFOX-induced downregulation of class I histone deacetylases (HDAC), leading to acetylation of the FLIP-binding partner Ku70 and downregulation of FLIP. Moreover, the effects of FOLFOX could be phenocopied using the clinically relevant class I HDAC inhibitor, entinostat, which also induced acetylation of Ku70 and FLIP downregulation. Further analyses revealed that caspase-8 knockout RIPK3-positive colorectal cancer models were sensitive to tolinapant-induced necroptosis, an effect that could be exploited in caspase-8-proficient models using the clinically relevant caspase inhibitor emricasan. Our study provides evidence for immediate clinical exploration of tolinapant in combination with FOLFOX in poor prognosis MSS colorectal cancer with elevated cIAP1/2 expression.

Discovery of Novel Histone Deacetylase 6 (HDAC6) Inhibitors with Enhanced Antitumor Immunity of Anti-PD-L1 Immunotherapy in Melanoma

“…Jurkat T cells were treated with different concentrations (0.1–2.0 μM) of XP5 and XP19 . As depicted in Figure , compounds XP5 and XP19 were able to upregulate the expression levels of acetylated Ku70 significantly and dose-dependently but showed no effect on the Ku70 levels, which is in agreement with previous studies. − In addition, XP5 and XP19 also significantly increased the expression of Bax (a pro-apoptotic protein) and downregulated Bcl-2 (an anti-apoptotic protein).…”

“…Therefore, Ku70 is a potential target of HDAC inhibitors and plays an important role during the induction of apoptosis by HDACis . Meanwhile, many studies indicate that HDACis could enhance Ku70 acetylation, abolish DNA repair, and lead to cell cycle arrest and apoptosis. − …”

ATF6α contributes to rheumatoid arthritis by inducing inflammatory cytokine production and apoptosis resistance

“…BIRC3 (cellular IAP2) belongs to the human inhibitors of apoptosis protein (IAP) family ( 35 ), is one of the eight members. Previous studies have shown that BIRC3 is a multi-functional protein, as demonstrated by its ability to regulate not only caspases and apoptosis, but also inflammatory signaling, immunity, mitogenic kinase signaling, and cell proliferation ( 36 ). In classical TNF-α signaling in RA FLSs, BIRC2/BIRC3 forms a complex with TNFR2 and TRAF2 to further activate the NF-κB and MAPK pathways ( 37 , 38 ).…”

The cross talk of ubiquitination and chemotherapy tolerance in colorectal cancer

“…Inhibition of XIAP expression enhances the sensitization of CRC cells to 5-FU (Zhao et al 2017 ). High expression of cIAP1 and cIAP2 was significantly associated with poor prognosis in patients with CRC treated with 5-FU, and further studies revealed that downregulation of cIAP2 effectively enhanced 5-FU sensitivity through the apoptotic pathway (Crawford et al 2021 ). Ubiquitination and degradation of SMAD Family Member 4(SMAD4) increased upon physical interaction with TRIM47, leading to upregulation of the C–C motif chemokine ligand 15(CCL15) expression and chemotherapy resistance in response to 5-FU therapy (Liang et al 2019 ).…”

“…Tolinapant (ASTX660), a novel IAP antagonist, efficiently and rapidly downregulated cIAP1 expression in a CRC model. Additionally, FOLFOX was shown to promote tolinapant-induced apoptosis in human CRC and murine organ models, providing evidence for the clinical exploration of tolinapant in combination with FOLFOX for the treatment of cIAP1-expressing CRC with poor prognosis and high microsatellite stability (Crawford et al 2021 ).…”