Heme Oxygenase-1 and Its Role in Colorectal Cancer.

Heme oxygenase-1 (HO-1) is an enzyme located at the endoplasmic reticulum, which is responsible for the degradation of cellular heme into ferrous iron, carbon monoxide and biliverdin-IXa. In addition to this main function, the enzyme is involved in many other homeostatic, toxic and cancer-related mechanisms. In this review, we first summarize the importance of HO-1 in physiology and pathophysiology with a focus on the digestive system. We then detail its structure and function, followed by a section on the regulatory mechanisms that control HO-1 expression and activity. Moreover, HO-2 as important further HO isoform is discussed, highlighting the similarities and differences with regard to HO-1. Subsequently, we describe the direct and indirect cytoprotective functions of HO-1 and its breakdown products carbon monoxide and biliverdin-IXa, but also highlight possible pro-inflammatory effects. Finally, we address the role of HO-1 in cancer with a particular focus on colorectal cancer. Here, relevant pathways and mechanisms are presented, through which HO-1 impacts tumor induction and tumor progression. These include oxidative stress and DNA damage, ferroptosis, cell cycle progression and apoptosis as well as migration, proliferation, and epithelial-mesenchymal transition.

The Mitochondrial Disruptor Devimistat (CPI-613) Synergizes with Genotoxic Anticancer Drugs in Colorectal Cancer Therapy in a Bim-Dependent Manner.

Colorectal cancer is one of the most frequent tumor entities, with an increasing incidence and mortality in younger adults in Europe and the United States. Five-year survival rates for advanced colorectal cancer are still low, highlighting the need for novel targets in colorectal cancer therapy. Here, we investigated the therapeutic potential of the compound devimistat (CPI-613) that targets altered mitochondrial cancer cell metabolism and its synergism with the antineoplastic drugs 5-fluorouracil (5-FU) and irinotecan (IT) in colorectal cancer. Devimistat exerted a comparable cytotoxicity in a panel of established colorectal cancer cell lines and patient-derived short-term cultures independent of their genetic and epigenetic status, whereas human colonic epithelial cells were more resistant, indicating tumor selectivity. These findings were corroborated in intestinal organoid and tumoroid models. Mechanistically, devimistat disrupted mitochondrial membrane potential and severely impaired mitochondrial respiration, resulting in colorectal cancer cell death induction independent of p53. Combination treatment of devimistat with 5-FU or IT demonstrated synergistic cell killing in colorectal cancer cells as shown by Combenefit modeling and Chou-Talalay analysis. Increased cell death induction was revealed as a major mechanism involving downregulation of antiapoptotic genes and accumulation of proapoptotic Bim, which was confirmed by its genetic knockdown. In human colorectal cancer xenograft mouse models, devimistat showed antitumor activity and synergized with IT, resulting in prolonged survival and enhanced therapeutic efficacy. In human tumor xenografts, devimistat prevented IT-triggered p53 stabilization and caused synergistic Bim induction. Taken together, our study revealed devimistat as a promising candidate in colorectal cancer therapy by synergizing with established antineoplastic drugs in vitro and in vivo.

Targeting Altered Energy Metabolism in Colorectal Cancer: Oncogenic Reprogramming, the Central Role of the TCA Cycle and Therapeutic Opportunities.

Colorectal cancer (CRC) is among the most frequent cancer entities worldwide. Multiple factors are causally associated with CRC development, such as genetic and epigenetic alterations, inflammatory bowel disease, lifestyle and dietary factors. During malignant transformation, the cellular energy metabolism is reprogrammed in order to promote cancer cell growth and proliferation. In this review, we first describe the main alterations of the energy metabolism found in CRC, revealing the critical impact of oncogenic signaling and driver mutations in key metabolic enzymes. Then, the central role of mitochondria and the tricarboxylic acid (TCA) cycle in this process is highlighted, also considering the metabolic crosstalk between tumor and stromal cells in the tumor microenvironment. The identified cancer-specific metabolic transformations provided new therapeutic targets for the development of small molecule inhibitors. Promising agents are in clinical trials and are directed against enzymes of the TCA cycle, including isocitrate dehydrogenase, pyruvate dehydrogenase kinase, pyruvate dehydrogenase complex (PDC) and α-ketoglutarate dehydrogenase (KGDH). Finally, we focus on the α-lipoic acid derivative CPI-613, an inhibitor of both PDC and KGDH, and delineate its anti-tumor effects for targeted therapy.