Mitochondria-targeted vitamin E analogs inhibit breast cancer cell energy metabolism and promote cell death.

BACKGROUND: Recent research has revealed that targeting mitochondrial bioenergetic metabolism is a promising chemotherapeutic strategy. Key to successful implementation of this chemotherapeutic strategy is the use of new and improved mitochondria-targeted cationic agents that selectively inhibit energy metabolism in breast cancer cells, while exerting little or no long-term cytotoxic effect in normal cells. METHODS: In this study, we investigated the cytotoxicity and alterations in bioenergetic metabolism induced by mitochondria-targeted vitamin E analog (Mito-chromanol, Mito-ChM) and its acetylated ester analog (Mito-ChMAc). Assays of cell death, colony formation, mitochondrial bioenergetic function, intracellular ATP levels, intracellular and tissue concentrations of tested compounds, and in vivo tumor growth were performed. RESULTS: Both Mito-ChM and Mito-ChMAc selectively depleted intracellular ATP and caused prolonged inhibition of ATP-linked oxygen consumption rate in breast cancer cells, but not in non-cancerous cells. These effects were significantly augmented by inhibition of glycolysis. Mito-ChM and Mito-ChMAc exhibited anti-proliferative effects and cytotoxicity in several breast cancer cells with different genetic background. Furthermore, Mito-ChM selectively accumulated in tumor tissue and inhibited tumor growth in a xenograft model of human breast cancer. CONCLUSIONS: We conclude that mitochondria-targeted small molecular weight chromanols exhibit selective anti-proliferative effects and cytotoxicity in multiple breast cancer cells, and that esterification of the hydroxyl group in mito-chromanols is not a critical requirement for its anti-proliferative and cytotoxic effect.

Synchronous effects of targeted mitochondrial complex I inhibitors on tumor and immune cells abrogate melanoma progression.

Metabolic heterogeneity within the tumor microenvironment promotes cancer cell growth and immune suppression. We determined the impact of mitochondria-targeted complex I inhibitors (Mito-CI) in melanoma. Mito-CI decreased mitochondria complex I oxygen consumption, Akt-FOXO signaling, blocked cell cycle progression, melanoma cell proliferation and tumor progression in an immune competent model system. Immune depletion revealed roles for T cells in the antitumor effects of Mito-CI. While Mito-CI preferentially accumulated within and halted tumor cell proliferation, it also elevated infiltration of activated effector T cells and decreased myeloid-derived suppressor cells (MDSC) as well as tumor-associated macrophages (TAM) in melanoma tumors in vivo. Anti-proliferative doses of Mito-CI inhibited differentiation, viability, and the suppressive function of bone marrow-derived MDSC and increased proliferation-independent activation of T cells. These data indicate that targeted inhibition of complex I has synchronous effects that cumulatively inhibits melanoma growth and promotes immune remodeling.

Oncostatin M Receptor-Targeted Antibodies Suppress STAT3 Signaling and Inhibit Ovarian Cancer Growth.

Although patients with advanced ovarian cancer may respond initially to treatment, disease relapse is common, and nearly 50% of patients do not survive beyond five years, indicating an urgent need for improved therapies. To identify new therapeutic targets, we performed single-cell and nuclear RNA-seq data set analyses on 17 human ovarian cancer specimens, revealing the oncostatin M receptor (OSMR) as highly expressed in ovarian cancer cells. Conversely, oncostatin M (OSM), the ligand of OSMR, was highly expressed by tumor-associated macrophages and promoted proliferation and metastasis in cancer cells. Ovarian cancer cell lines and additional patient samples also exhibited elevated levels of OSMR when compared with other cell types in the tumor microenvironment or to normal ovarian tissue samples. OSMR was found to be important for ovarian cancer cell proliferation and migration. Binding of OSM to OSMR caused OSMR-IL6ST dimerization, which is required to produce oncogenic signaling cues for prolonged STAT3 activation. Human monoclonal antibody clones B14 and B21 directed to the extracellular domain of OSMR abrogated OSM-induced OSMR-IL6ST heterodimerization, promoted the internalization and degradation of OSMR, and effectively blocked OSMR-mediated signaling in vitro. Importantly, these antibody clones inhibited the growth of ovarian cancer cells in vitro and in vivo by suppressing oncogenic signaling through OSMR and STAT3 activation. Collectively, this study provides a proof of principle that anti-OSMR antibody can mediate disruption of OSM-induced OSMR-IL6ST dimerization and oncogenic signaling, thus documenting the preclinical therapeutic efficacy of human OSMR antagonist antibodies for immunotherapy in ovarian cancer. SIGNIFICANCE: This study uncovers a role for OSMR in promoting ovarian cancer cell proliferation and metastasis by activating STAT3 signaling and demonstrates the preclinical efficacy of antibody-based OSMR targeting for ovarian cancer treatment.

Pancreatic Cancer Cell Migration and Metastasis Is Regulated by Chemokine-Biased Agonism and Bioenergetic Signaling.

Patients with pancreatic ductal adenocarcinoma (PDAC) invariably succumb to metastatic disease, but the underlying mechanisms that regulate PDAC cell movement and metastasis remain little understood. In this study, we investigated the effects of the chemokine gene CXCL12, which is silenced in PDAC tumors, yet is sufficient to suppress growth and metastasis when re-expressed. Chemokines like CXCL12 regulate cell movement in a biphasic pattern, with peak migration typically in the low nanomolar concentration range. Herein, we tested the hypothesis that the biphasic cell migration pattern induced by CXCL12 reflected a biased agonist bioenergetic signaling that might be exploited to interfere with PDAC metastasis. In human and murine PDAC cell models, we observed that nonmigratory doses of CXCL12 were sufficient to decrease oxidative phosphorylation and glycolytic capacity and to increase levels of phosphorylated forms of the master metabolic kinase AMPK. Those same doses of CXCL12 locked myosin light chain into a phosphorylated state, thereby decreasing F-actin polymerization and preventing cell migration in a manner dependent upon AMPK and the calcium-dependent kinase CAMKII. Notably, at elevated concentrations of CXCL12 that were insufficient to trigger chemotaxis of PDAC cells, AMPK blockade resulted in increased cell movement. In two preclinical mouse models of PDAC, administration of CXCL12 decreased tumor dissemination, supporting our hypothesis that chemokine-biased agonist signaling may offer a useful therapeutic strategy. Our results offer a mechanistic rationale for further investigation of CXCL12 as a potential therapy to prevent or treat PDAC metastasis.

A (99m)Tc-labeled triphenylphosphonium derivative for the early detection of breast tumors.

INTRODUCTION: A greater mitochondrial membrane potential in tumor cells has been shown to enhance the accumulation of triphenyl phosphonium derivatives. The aim of this study was to synthesize and characterize (99m)Tc-labeled alkyl triphenyl phosphonium ((99m)Tc-Mito(10)-MAG3) for the early detection of breast tumors. METHODS: Mito(10)-MAG3 was synthesized by coupling (10-aminodecyl)triphenyl phosphonium bromide with NHS-MAG3 and radiolabeled with (99m)Tc. Biodistribution and pharmacokinetics of (99m)Tc-Mito(10)-MAG3 was investigated in female Sprague-Dawley rats. Initially, (99m)Tc-Mito(10)-MAG3 was tested in animals with established breast tumors. In a subsequent longitudinal study, the imaging efficacy of (99m)Tc(10)-Mito-MAG3 for detecting small, nonpalpable breast tumors was assessed after chemically inducting breast carcinoma. Tumors detected by imaging were allowed to grow to palpable size and confirmed by histology. The results were compared with (99m)Tc-MIBI. RESULTS: The synthesis of Mito(10)-MAG3 was confirmed by mass spectrometry. The compound was radiolabeled with (99m)Tc to > 92% in a single step. The radiopharmaceutical exhibited fast blood clearance and low cardiac uptake. In the initial study, using animals with established breast tumors, (99m)Tc-Mito(10)-MAG3 imaging detected small lesions that were missed by palpation. In the longitudinal study, (99m)Tc-Mito(10)-MAG3 exhibited focal uptake in small breast tumors, which were confirmed by histology. CONCLUSIONS: Imaging, using (99m)Tc-Mito(10)-MAG3, allowed the early detection of small neoplastic lesions in the mammary glands. The agent significantly reduced cardiac uptake, compared with (99m)Tc-MBIB. The phosphonium-based derivatives warrant further characterization and development as imaging agents for scintimammography.