ABSTRACT
Colorectal cancer (CRC) is the fourth cause of death from cancer worldwide mainly due to the high incidence of drug-resistance. During a screen for new actionable targets in drug-resistant tumours we recently identified p65BTK - a novel oncogenic isoform of Bruton's tyrosine kinase. Studying three different cohorts of patients here we show that p65BTK expression correlates with histotype and cancer progression. Using drug-resistant TP53-null colon cancer cells as a model we demonstrated that p65BTK silencing or chemical inhibition overcame the 5-fluorouracil resistance of CRC cell lines and patient-derived organoids and significantly reduced the growth of xenografted tumours. Mechanistically, we show that blocking p65BTK in drug-resistant cells abolished a 5-FU-elicited TGFB1 protective response and triggered E2F-dependent apoptosis. Taken together, our data demonstrated that targeting p65BTK restores the apoptotic response to chemotherapy of drug-resistant CRCs and gives a proof-of-concept for suggesting the use of BTK inhibitors in combination with 5-FU as a novel therapeutic approach in CRC patients. © 2019 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.
Subject(s)
Antineoplastic Combined Chemotherapy Protocols/therapeutic use , Colonic Neoplasms/drug therapy , Protein Kinase Inhibitors/administration & dosage , Agammaglobulinaemia Tyrosine Kinase/antagonists & inhibitors , Agammaglobulinaemia Tyrosine Kinase/metabolism , Animals , Antineoplastic Combined Chemotherapy Protocols/pharmacology , Apoptosis/drug effects , Colonic Neoplasms/genetics , Colonic Neoplasms/pathology , Disease Progression , Drug Resistance, Neoplasm/drug effects , Drug Synergism , E2F Transcription Factors/metabolism , Fluorouracil/administration & dosage , Fluorouracil/pharmacology , Genes, p53 , Humans , Mice, Nude , Molecular Targeted Therapy/methods , Neoplasm Staging , Organoids/drug effects , Protein Isoforms/antagonists & inhibitors , Protein Isoforms/metabolism , Protein Kinase Inhibitors/pharmacology , Transforming Growth Factor beta1/metabolism , Tumor Cells, Cultured , Xenograft Model Antitumor Assays/methodsABSTRACT
Glycogen Synthase Kinase-3 alpha (GSK3A) and beta (GSK3B) isoforms are encoded by distinct genes, are 98% identical within their kinase domain and perform similar functions in several settings; however, they are not completely redundant and, depending on the cell type and differentiative status, they also play unique roles. We recently identified a role for GSK3B in drug resistance by demonstrating that its inhibition enables necroptosis in response to chemotherapy in p53-null drug-resistant colon carcinoma cells. We report here that, similarly to GSK3B, also GSK3A silencing/inhibition does not affect cell proliferation or cell cycle but only abolishes growth after treatment with DNA-damaging chemotherapy. In particular, blocking GSK3A impairs DNA repair upon exposure to DNA-damaging drugs. As a consequence, p53-null cells overcome their inability to undergo apoptosis and mount a necroptotic response, characterized by absence of caspase activation and RIP1-independent, PARP-dependent AIF nuclear re-localization. We therefore conclude that GSK3A is redundant with GSK3B in regulating drug-resistance and chemotherapy-induced necroptosis and suggest that inhibition of only one isoform, or rather partial inhibition of overall cellular GSK3 activity, is enough to re-sensitize drug-resistant cells to chemotherapy.