BackgroundMitochondrial functions are exploited in cancer and provide a validated therapeutic target. However, how this process is regulated has remained mostly elusive and the identification of new pathways that control mitochondrial integrity in cancer is an urgent priority.MethodsWe studied clinically-annotated patient series of primary and metastatic prostate cancer, representative cases of multiple myeloma (MM) and publicly available genetic databases. Gene regulation studies involved chromatin immunoprecipitation, PCR amplification and Western blotting of conditional Myc-expressing cell lines. Transient or stable gene silencing was used to quantify mitochondrial functions in bioenergetics, outer membrane permeability, Ca2+ homeostasis, redox balance and cell death. Tumorigenicity was assessed by cell proliferation, colony formation and xenograft tumour growth.FindingsWe identified Mitochondrial Fission Factor (MFF) as a novel transcriptional target of oncogenic Myc overexpressed in primary and metastatic cancer, compared to normal tissues. Biochemically, MFF isoforms, MFF1 and MFF2 associate with the Voltage-Dependent Anion Channel-1 (VDAC1) at the mitochondrial outer membrane, in vivo. Disruption of this complex by MFF silencing induces general collapse of mitochondrial functions with increased outer membrane permeability, loss of inner membrane potential, Ca2+ unbalance, bioenergetics defects and activation of cell death pathways. In turn, this inhibits tumour cell proliferation, suppresses colony formation and reduces xenograft tumour growth in mice.InterpretationAn MFF-VDAC1 complex is a novel regulator of mitochondrial integrity and actionable therapeutic target in cancer.

Background Cancer cells use specific V-ATPase subunits to activate oncogenic pathways. Therefore, we investigated V-ATPase deregulation in aggressive gliomas and associated signaling. Methods V-ATPase genes expression and associated pathways were analyzed in different series of glioma available from public databases, as well as in patients' cohort. Activation of pathways was analyzed at gene and protein expression levels. A genetic model of glioma in Drosophila melanogaster and mice with GBM patients-derived orthotopic xenografts were used as in vivo models of disease. Findings GBM and recurrent gliomas display a specific V-ATPase signature. Such signature resolves the heterogeneous class of IDH-wild type lower-grade gliomas, identifying the patients with worse prognosis independently from clinical and molecular features (p = 0·03, by Cox proportional-hazards model). In vivo , V-ATPase subunits deregulation significantly impacts tumor growth and proliferation. At the molecular level, GBM-like V-ATPase expression correlates with upregulation of Homeobox genes. Interpretation Our data identify a V-ATPase signature that accompanies glioma aggressiveness and suggest new entry points for glioma stratification and follow-up. Fund This work was supported by Fondazione Cariplo (2014–1148 to VV), Fondazione IRCCS Ca' Granda, and Fondazione INGM Grant in Molecular Medicine 2014 (to VV).

The regulators of mitochondrial cell death in cancer have remained elusive, hampering the development of new therapies. Here, we showed that protein isoforms of mitochondrial fission factor (MFF1 and MFF2), a molecule that controls mitochondrial size and shape, that is, mitochondrial dynamics, were overexpressed in patients with non-small cell lung cancer and formed homo-and heterodimeric complexes with the voltage-dependent anion channel-1 (VDAC1), a key regulator of mitochondrial outer membrane permeability. MFF inserted into the interior hole of the VDAC1 ring using Arg225, Arg236, and Gln241 as key contact sites. A cell-permeable MFF Ser223-Leu243 D-enantiomeric peptidomimetic disrupted the MFF-VDAC1 complex, acutely depolarized mitochondria, and triggered cell death in heterogeneous tumor types, including drug-resistant melanoma, but had no effect on normal cells. In preclinical models, treatment with the MFF peptidomimetic was well-tolerated and demonstrated anticancer activity in patientderived xenografts, primary breast and lung adenocarcinoma 3D organoids, and glioblastoma neurospheres. These data identify the MFF-VDAC1 complex as a novel regulator of mitochondrial cell death and an actionable therapeutic target in cancer.Significance: These findings describe mitochondrial fission regulation using a peptidomimetic agent that disturbs the MFF-VDAC complex and displays anticancer activity in multiple tumor models.