Cancer cells share several properties, high proliferation potential, reprogramed metabolism, and resistance to apoptotic cues. Acquiring these hallmarks involves changes in key oncogenes and non-oncogenes essential for cancer cell survival and prosperity, and is accompanied by the increased energy requirements of proliferating cells. Mitochondria occupy a central position in cell life and death with mitochondrial bioenergetics, biosynthesis, and signaling are critical for tumorigenesis. Voltage-dependent anion channel 1 (VDAC1) is situated in the outer mitochondrial membrane (OMM) and serving as a mitochondrial gatekeeper. VDAC1 allowing the transfer of metabolites, fatty acid ions, Ca²⁺, reactive oxygen species, and cholesterol across the OMM and is a key player in mitochondrial-mediate apoptosis. Moreover, VDAC1 serves as a hub protein, interacting with diverse sets of proteins from the cytosol, endoplasmic reticulum, and mitochondria that together regulate metabolic and signaling pathways. The observation that VDAC1 is over-expressed in many cancers suggests that the protein may play a pivotal role in cancer cell survival. However, VDAC1 is also important in mitochondria-mediated apoptosis, mediating release of apoptotic proteins and interacting with anti-apoptotic proteins, such as B-cell lymphoma 2 (Bcl-2), Bcl-xL, and hexokinase (HK), which are also highly expressed in many cancers. Strategically located in a “bottleneck” position, controlling metabolic homeostasis and apoptosis, VDAC1 thus represents an emerging target for anti-cancer drugs. This review presents an overview on the multi-functional mitochondrial protein VDAC1 performing several functions and interacting with distinct sets of partners to regulate both cell life and death, and highlights the importance of the protein for cancer cell survival. We address recent results related to the mechanisms of VDAC1-mediated apoptosis and the potential of associated proteins to modulate of VDAC1 activity, with the aim of developing VDAC1-based approaches. The first strategy involves modification of cell metabolism using VDAC1-specific small interfering RNA leading to inhibition of cancer cell and tumor growth and reversed oncogenic properties. The second strategy involves activation of cancer cell death using VDAC1-based peptides that prevent cell death induction by anti-apoptotic proteins. Finally, we discuss the potential therapeutic benefits of treatments and drugs leading to enhanced VDAC1 expression or targeting VDAC1 to induce apoptosis.

Hepatocellular carcinoma (HCC) is the third most lethal cancer worldwide. Despite progress in identifying risk factors, the incidence of HCC is increasing. Moreover, therapeutic options are limited and survival is poor. Therefore, alternative and innovative therapeutic strategies are urgently required. R-Tf-D-LP4, a cell-penetrating peptide derived from the mitochondrial multifunctional protein the voltage-dependent anion channel (VDAC1), is identified here as a highly effective liver cancer treatment. Recently, we demonstrated that R-Tf-D-LP4 induced apoptosis and inhibited tumor growth in mouse models. We now demonstrate that R-Tf-D-LP4 induced apoptosis in cancer liver-derived cell lines and inhibited tumor growth in three different liver cancer mouse models. These included diethylnitrosamine (DEN)-induced HCC, metabolically high-fat diet-induced HCC, and using a subcutaneous HepG2 cell xenograft model. Intravenous injection of the peptide into tumor-carrying DEN-treated mice resulted in dose-dependent inhibition of tumor growth up to complete tumor elimination. TUNEL staining of liver sections demonstrated peptide-induced apoptosis. Hematoxylin/eosin and Sirius red staining of liver sections showed decreased fibrotic formation. Immunohistochemical staining demonstrated reduced numbers of α-SMA-expressing cells in R-Tf-D-LP4-treated mouse livers. Additionally, macrophage presence in liver tissue was reduced in R-Tf-D-LP4-treated mice. Liver sections from DEN-treated mice showed steatohepatic pathology, reflected as fatty liver, inflammation, ballooning degeneration, and fibrosis; all were eliminated upon peptide treatment. Peptide treatment also inhibited tumor development in a nonalcoholic steatohepatitis-hepatocellular carcinoma mouse model induced by HFD. In HepG2 subcutaneous tumor xenografts, R-Tf-D-LP4 inhibited tumor growth.

CONCLUSION:

These results show that the VDAC1-based peptide R-Tf-D-LP4 has multiple effects on liver cancer cells, leading to impairment of cell energy and metabolism homeostasis, induction of apoptosis, and elimination of liver cancer-associated processes, and thus represents a promising therapeutic approach for liver cancer.

Mitochondrial VDAC1 mediates cross talk between the mitochondria and other parts of the cell by transporting anions, cations, ATP, Ca²⁺ , and metabolites and serves as a key player in apoptosis. As such, VDAC1 is involved in two important hallmarks of cancer development, namely energy and metabolic reprograming and apoptotic cell death evasion. We previously developed cell-penetrating VDAC1-derived peptides that interact with hexokinase (HK), Bcl-2, and Bcl-xL to prevent the anti-apoptotic activities of these proteins and induce cancer cell death, with a focus on leukemia and glioblastoma. In this study, we demonstrated the sensitivity of a panel of genetically characterized cancer cell lines, differing in origin and carried mutations, to VDAC1-based peptide-induced apoptosis. Noncancerous cell lines were less affected by the peptides. Furthermore, we constructed additional VDAC1-based peptides with the aim of improving targeting, selectivity, and cellular stability, including R-Tf-D-LP4, containing the transferrin receptor internalization sequence (Tf) that allows targeting of the peptide to cancer cells, known to overexpress the transferrin receptor. The mode of action of the VDAC1-based peptides involves HK detachment, interfering with the action of anti-apoptotic proteins, and thus activating multiple routes leading to an impairment of cell energy and metabolism homeostasis and the induction of apoptosis. Finally, in xenograft glioblastoma, lung, and breast cancer mouse models, R-Tf-D-LP4 inhibited tumor growth while inducing massive cancer cell death, including of cancer stem cells. Thus, VDAC1-based peptides offer an innovative new conceptual framework for cancer therapy.