Cytochalasan Alkaloids as TRAIL Sensitizers from an Endophytic Fungus Chaetomium sp.

Two new cytochalasans with a rare 6/6/5/5/7 pentacyclic ring system, named chaetoconvosins C−D (1−2), together with two known congeners (3−4), were isolated from the fermentation of an endophytic fungus, Chaetomium sp. SG-01, harbored in the fibrous roots of Schisandra glaucescens Diels. Their structures including the absolute configuration were elucidated by extensive spectroscopic (HRESIMS, NMR, and ECD) and X-ray crystallographic analyses. The TRAIL sensitivity of 1–4 in a TRAIL-resistant HT29 colorectal cancer cell line was evaluated, which revealed that co-treatment of 1–4 at 50 µM with TRAIL (150 ng/mL) reduced the HT29 cell viability by 19.0%, 24.1%, 17.9%, and 15.5%, respectively, compared to treatment with 1–4 alone.

Oxaliplatin resistance in colorectal cancer enhances TRAIL sensitivity via death receptor 4 upregulation and lipid raft localization

Colorectal cancer (CRC) remains a leading cause of cancer death, and its mortality is associated with metastasis and chemoresistance. We demonstrate that oxaliplatin-resistant CRC cells are sensitized to TRAIL-mediated apoptosis. Oxaliplatin-resistant cells exhibited transcriptional downregulation of caspase-10, but this had minimal effects on TRAIL sensitivity following CRISPR-Cas9 deletion of caspase-10 in parental cells. Sensitization effects in oxaliplatin-resistant cells were found to be a result of increased DR4, as well as significantly enhanced DR4 palmitoylation and translocation into lipid rafts. Raft perturbation via nystatin and resveratrol significantly altered DR4/raft colocalization and TRAIL sensitivity. Blood samples from metastatic CRC patients were treated with TRAIL liposomes, and a 57% reduction of viable circulating tumor cells (CTCs) was observed. Increased DR4/lipid raft colocalization in CTCs was found to correspond with increased oxaliplatin resistance and increased efficacy of TRAIL liposomes. To our knowledge, this is the first study to investigate the role of lipid rafts in primary CTCs.

Oxaliplatin Resistance in Colorectal Cancer Enhances TRAIL Sensitivity Via Death Receptor 4 Upregulation and Lipid Raft Localization

Colorectal cancer (CRC) remains a leading cause of cancer death, and its mortality is associated with metastasis and resistance to chemotherapy. We demonstrate that oxaliplatin-resistant (OxR) CRC cells are sensitized to TRAIL-mediated apoptosis. Oxaliplatin-resistant cells exhibited transcriptional downregulation of caspase-10, but this effect was of little consequence to TRAIL sensitivity following CRISPR-Cas9 depletion of caspase-10. OxR cells were found to have increased expression of DR4, as well as significantly enhanced DR4 palmitoylation and translocation into lipid rafts. Raft perturbation via nystatin and resveratrol significantly altered DR4/raft colocalization and TRAIL sensitivity. Blood samples from metastatic CRC patients were treated with TRAIL liposomes, and a 57% reduction of viable circulating tumor cells (CTCs) was observed. The degree of DR4/lipid raft colocalization in CTCs was found to increase over time in patients receiving chemotherapy treatment. To our knowledge, this is the first study to investigate the role of lipid rafts in primary CTCs.

Choline kinase alpha impairment overcomes TRAIL resistance in ovarian cancer cells

Background Choline kinase-α (ChoKα/CHKA) overexpression and hyper-activation sustain altered choline metabolism conferring the cholinic phenotype to epithelial ovarian cancer (OC), the most lethal gynecological tumor. We previously proved that CHKA down-modulation reduced OC cell aggressiveness and increased sensitivity to in vitro chemotherapeutics’ treatment also affecting intracellular content of one-carbon metabolites. In tumor types other than ovary, methionine decrease was shown to increase sensitivity to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-receptor 2 triggering. These effects were suggestive of a potential role for ChoKα in regulating susceptibility to TRAIL cytokine. Methods The relationship between ChoKα/CHKA and TRAIL-receptor 2 (TRAIL-R2) expression was investigated in silico in OC patients’ GEO datasets and in vitro in a panel of OC cell lines upon transient CHKA silencing (siCHKA). The effect of siCHKA on metabolites content was assessed by LC-MS. The triggered apoptotic signalling was studied following soluble-TRAIL or anti-TRAIL-R2 agonist antibody treatment. Lipid rafts were isolated by Triton X-100 fractionation. Preclinical ex vivo studies were performed in OC cells derived from patients’ ascites using autologous PBLs as effectors and a bispecific anti-TRAIL-R2/anti-CD3 antibody as triggering agent. Results Here we demonstrate that siCHKA specifically overcomes resistance to TRAIL-mediated apoptosis in OC cells. Upon siCHKA we detected: a significant sensitization to caspase-dependent apoptosis triggered by both soluble TRAIL and anti-TRAIL-R2 agonist antibody, a specific increase of TRAIL-R2 expression and TRAIL-R2 relocation into lipid rafts. In siCHKA-OC cells the acquired TRAIL sensitivity was completely reverted upon recovery of ChoKα expression but, at variance of other tumor cell types, TRAIL sensitivity was not efficiently phenocopied by methionine deprivation. Of note, we were also able to show that siCHKA sensitized tumor cells derived ex vivo from OC patients’ ascites to the cytotoxic activity of autologous lymphocytes redirected by a bispecific anti-TRAIL-R2/anti-CD3 antibody. Conclusions Our findings suggest that ChoKα/CHKA impairment, by restoring drug-induced or receptor-mediated cell death, could be a suitable therapeutic strategy to be used in combination with chemotherapeutics or immunomodulators to improve OC patients’ outcome.

Tristetraprolin Posttranscriptionally Downregulates TRAIL Death Receptors

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) has attracted attention as a potential candidate for cancer therapy. However, many primary cancers are resistant to TRAIL, even when combined with standard chemotherapy. The mechanism of TRAIL resistance in cancer cells has not been fully elucidated. The TRAIL death receptor (DR) 3′-untranslated region (3′-UTR) is reported to contain AU-rich elements (AREs) that are important for regulating DR mRNA stability. However, the mechanisms by which DR mRNA stability is determined by its 3′-UTR are unknown. We demonstrate that tristetraprolin (TTP), an ARE-binding protein, has a critical function of regulating DR mRNA stability. DR4 mRNA contains three AREs and DR5 mRNA contains four AREs in 3′-UTR. TTP bound to all three AREs in DR4 and ARE3 in DR5 and enhanced decay of DR4/5 mRNA. TTP overexpression in colon cancer cells changed the TRAIL-sensitive cancer cells to TRAIL-resistant cells, and down-regulation of TTP increased TRAIL sensitivity via DR4/5 expression. Therefore, this study provides a molecular mechanism for enhanced levels of TRAIL DRs in cancer cells and a biological basis for posttranscriptional modification of TRAIL DRs. In addition, TTP status might be a biomarker for predicting TRAIL response when a TRAIL-based treatment is used for cancer.