CXCL12 chemokine dimer signaling modulates acute myelogenous leukemia cell migration through altered receptor internalization.

Acute myeloid leukemia (AML) is a malignancy of immature myeloid blast cells with stem-like and chemoresistant cells being retained in the bone marrow through CXCL12-CXCR4 signaling. Current CXCR4 inhibitors mobilize AML cells into the bloodstream where they become more chemosensitive have failed to improve patient survival, likely reflecting persistent receptor localization on target cells. Here we characterize the signaling properties of CXCL12-locked dimer (CXCL12-LD), a bioengineered variant of the dimeric CXCL12 structure. CXCL12-LD binding resulted in lower levels of G protein, ß-arrestin, and intracellular calcium mobilization, consistent with the locked dimer being a partial agonist of CXCR4. Further, CXCL12-LD failed to induce chemotaxis in AML cells. Despite these partial agonist properties, CXCL12-LD increased CXCR4 internalization compared to wildtype and locked-monomer forms of CXCL12. Analysis of a previously published AML transcriptomic data showed CXCR4 positive AML cells co-express genes involved in chemoresistance and maintenance of a blast-like state. The CXCL12-LD partial agonist effectively mobilized stem cells into the bloodstream in mice suggesting a potential role for their use in targeting CXCR4. Together, our results suggest that enhanced internalization by CXCL12-LD partial agonist signaling can avoid pharmacodynamic tolerance and may identify new avenues to better target GPCRs.

Low-dose orthotopic cancer implantation permits measurement of longitudinal functional changes associated with cachexia.

Progressive functional decline is a key element of cancer-associated cachexia. Major barriers to translating preclinical therapies into the clinic include lack of cancer models that accurately mimic functional decline, which develops over time, and use of nonspecific measures, like grip strength, as surrogates for physical function. In this study, we aimed to extend the survival and longevity of a cancer model, to investigate cachexia-related function at the basic science level. Survival extension studies were performed by testing multiple cell lines, dilutions, and vehicle-types in orthotopic implantation of K-rasLSL.G12D/+; Trp53R172H/+; Pdx-1-Cre (KPC)-derived cells. One hundred twenty-eight animals in this new model were assessed for cachexia syndrome phenotype using a battery of anatomical, biochemical, and behavioral techniques. We extended the survival of the KPC orthotopic model to 8-9 wk postimplantation using a relatively low 100-cell dose of DT10022 KPC cells (P < 0.001). In this low-dose orthotopic (LO) model, progressive muscle wasting was detected in parallel to systemic inflammation; skeletal muscle atrophy at the fiber level was detected as early as 3 wk postimplantation compared with controls (P < 0.001). Gait speed in LO animals declined as early as 2 wk postimplantation, whereas grip strength change was a late event. Principal component and regression analyses revealed distinct cachectic and noncachectic animal populations, which we leveraged to show that the gait speed decline was specific to cachexia (P < 0.01), whereas grip strength decline was not (P = 0.19). Gait speed represents an accurate surrogate for cachexia-related physical function as opposed to grip strength.NEW & NOTEWORTHY Previous studies of cancer-induced cachexia have been confounded by the relatively rapid death of animal subjects. Using a lower dose of cancer cells in combination with a battery of behavioral, structural, histological, and biochemical techniques, we show that gait speed is actually the best indicator of functional decline due to cachexia. Future studies are required to define the underlying physiological basis of these findings.

Gait speed is a biomarker of cancer-associated cachexia decline and recovery.

Background: Progressive functional decline is a key element of cancer-associated cachexia. No therapies have successfully translated to the clinic due to an inability to measure and improve physical function in cachectic patients. Major barriers to translating pre-clinical therapies to the clinic include lack of cancer models that accurately mimic functional decline and use of non-specific outcome measures of function, like grip strength. New approaches are needed to investigate cachexia-related function at both the basic and clinical science levels. Methods: Survival extension studies were performed by testing multiple cell lines, dilutions, and vehicle-types in orthotopic implantation of K-ras LSL.G12D/+ ; Trp53 R172H/+ ; Pdx-1-Cre (KPC) derived cells. 128 animals in this new model were then assessed for muscle wasting, inflammation, and functional decline using a battery of biochemical, physiologic, and behavioral techniques. In parallel, we analyzed a 156-subject cohort of cancer patients with a range of cachexia severity, and who required rehabilitation, to determine the relationship between gait speed via six-minute walk test (6MWT), grip strength (hGS), and functional independence measures (FIM). Cachectic patients were identified using the Weight Loss Grading Scale (WLGS), Fearon consensus criteria, and the Prognostic Nutritional Index (PNI). Results: Using a 100-cell dose of DT10022 KPC cells, we extended the survival of the KPC orthotopic model to 8-9 weeks post-implantation compared to higher doses used (p<0.001). In this Low-dose Orthotopic (LO) model, both progressive skeletal and cardiac muscle wasting were detected in parallel to systemic inflammation; skeletal muscle atrophy at the fiber level was detected as early as 3 weeks post-implantation compared to controls (p<0.001). Gait speed in LO animals declined as early 2 week post-implantation whereas grip strength change was a late event and related to end of life. Principle component analysis (PCA) revealed distinct cachectic and non-cachectic animal populations, which we leveraged to show that gait speed decline was specific to cachexia (p<0.01) while grip strength decline was not (p=0.19). These data paralleled our observations in cancer patients with cachexia who required rehabilitation. In cachectic patients (identified by WLGS, Fearon criteria, or PNI, change in 6MWT correlated with motor FIM score changes while hGS did not (r 2 =0.18, p<0.001). This relationship between 6MWT and FIM in cachectic patients was further confirmed through multivariate regression (r 2 =0.30, p<0.001) controlling for age and cancer burden. Conclusion: Outcome measures linked to gait are better associated with cachexia related function and preferred for future pre-clinical and clinical cachexia studies.

Synthesis of fluorinated triphenylphosphonium analogs that improve cancer cell selectivity and in vivo detection.

Triphenylphosphonium (TPP+) compounds like mito-metformin (MMe) target cancer cells by exploiting their hyperpolarized mitochondrial membrane potential. Here, we present a protocol for synthesizing TPP+ analogs with selectivity for mammalian cancer cells, reduced toxicity, and quantifiability using fluorine-19 nuclear magnetic resonance (19F-NMR). We describe steps for treating mammalian cells with mitochondria-targeted compounds, treating and preparing mouse tissue with these compounds, and 19F-NMR detection of MMe analogs in cells and tissue. TPP+-conjugated metformin analogs include para-methoxy (pMeO-MMe) and para-trifluoromethyl MMe (pCF3-MMe) and meta-trifluoromethyl MMe (mCF3-MMe).

Targeted immune activation in pediatric solid tumors: opportunities to complement local control approaches.

Surgery or radiation therapy is nearly universally applied for pediatric solid tumors. In many cases, in diverse tumor types, distant metastatic disease is present and evades surgery or radiation. The systemic host response to these local control modalities may lead to a suppression of antitumor immunity, with potential negative impact on the clinical outcomes for patients in this scenario. Emerging evidence suggests that the perioperative immune responses to surgery or radiation can be modulated therapeutically to preserve anti-tumor immunity, with the added benefit of preventing these local control approaches from serving as pro-tumorigenic stimuli. To realize the potential benefit of therapeutic modulation of the systemic response to surgery or radiation on distant disease that evades these modalities, a detailed knowledge of the tumor-specific immunology as well as the immune responses to surgery and radiation is imperative. In this Review we highlight the current understanding of the tumor immune microenvironment for the most common peripheral pediatric solid tumors, the immune responses to surgery and radiation, and current evidence that supports the potential use of immune activating agents in the perioperative window. Finally, we define existing knowledge gaps that limit the current translational potential of modulating perioperative immunity to achieve effective anti-tumor outcomes.

Fragment-based drug discovery of small molecule ligands for the human chemokine CCL28.

The mucosal chemokine CCL28 is a promising target for immunotherapy drug development due to its elevated expression level in epithelial cells and critical role in creating and maintaining an immunosuppressive tumor microenvironment. Using sulfotyrosine as a probe, NMR chemical shift mapping identified a potential receptor-binding hotspot on the human CCL28 surface. CCL28 was screened against 2,678 commercially available chemical fragments by 2D NMR, yielding thirteen verified hits. Computational docking predicted that two fragments could occupy adjoining subsites within the sulfotyrosine recognition cleft. Dual NMR titrations confirmed their ability to bind CCL28 simultaneously, thereby validating an initial fragment pair for linking and merging strategies to design high-potency CCL28 inhibitors.

DPP4-Truncated CXCL12 Alters CXCR4/ACKR3 Signaling, Osteogenic Cell Differentiation, Migration, and Senescence.

Bone marrow skeletal stem cells (SSCs) secrete many cytokines including stromal derived factor-1 or CXCL12, which influences cell proliferation, migration, and differentiation. All CXCL12 splice variants are rapidly truncated on their N-terminus by dipeptidyl peptidase 4 (DPP4). This includes the common variant CXCL12 alpha (1-68) releasing a much less studied metabolite CXCL12(3-68). Here, we found that CXCL12(3-68) significantly inhibited SSC osteogenic differentiation and RAW-264.7 cell osteoclastogenic differentiation and induced a senescent phenotype in SSCs. Importantly, pre-incubation of SSCs with CXCL12(3-68) significantly diminished their ability to migrate toward CXCL12(1-68) in transwell migration assays. Using a high-throughput G-protein-coupled receptor (GPCR) screen (GPCRome) and bioluminescent resonance energy transfer molecular interaction assays, we revealed that CXCL12(3-68) acts via the atypical cytokine receptor 3-mediated ß-arrestin recruitment and as a competitive antagonist to CXCR4-mediated signaling. Finally, a reverse phase protein array assay revealed that DPP4-cleaved CXCL12 possesses a different downstream signaling profile from that of intact CXCL12 or controls. The data presented herein provides insights into regulation of CXCL12 signaling. Importantly, it demonstrates that DPP4 proteolysis of CXCL12 generates a metabolite with significantly different and previously overlooked bioactivity that helps explain discrepancies in the literature. This also contributes to an understanding of the molecular mechanisms of osteoporosis and bone fracture repair and could potentially significantly affect the interpretation of experimental outcomes with clinical consequences in other fields where CXCL12 is vital, including cancer biology, immunology, cardiovascular biology, neurobiology, and associated pathologies.

Physiology of chemokines in the cancer microenvironment.

Chemokines are chemotactic cytokines whose canonical functions govern movement of receptor-expressing cells along chemical gradients. Chemokines are a physiological system that is finely tuned by ligand and receptor expression, ligand or receptor oligomerization, redundancy, expression of atypical receptors, and non-GPCR binding partners that cumulatively influence discrete pharmacological signaling responses and cellular functions. In cancer, chemokines play paradoxical roles in both the directed emigration of metastatic, receptor-expressing cancer cells out of the tumor as well as immigration of tumor-infiltrating immune cells that culminate in a tumor-unique immune microenvironment. In the age of precision oncology, strategies to effectively harness the power of immunotherapy requires consideration of chemokine gradients within the unique spatial topography and temporal influences with heterogeneous tumors. In this article, we review current literature on the diversity of chemokine ligands and their cellular receptors that detect and process chemotactic gradients and illustrate how differences between ligand recognition and receptor activation influence the signaling machinery that drives cellular movement into and out of the tumor microenvironment. Facets of chemokine physiology across discrete cancer immune phenotypes are contrasted to existing chemokine-centered therapies in cancer.

Fluorinated triphenylphosphonium analogs improve cell selectivity and in vivo detection of mito-metformin.

Triphenylphosphonium (TPP+) conjugated compounds selectively target cancer cells by exploiting their hyperpolarized mitochondrial membrane potential. To date, studies have focused on modifying either the linker or the cargo of TPP+-conjugated compounds. Here, we investigated the biological effects of direct modification to TPP+ to improve the efficacy and detection of mito-metformin (MMe), a TPP+-conjugated probe we have shown to have promising preclinical efficacy against solid cancer cells. We designed, synthesized, and tested trifluoromethyl and methoxy MMe analogs (pCF3-MMe, mCF3-MMe, and pMeO-MMe) against multiple distinct human cancer cells. pCF3-MMe showed enhanced selectivity toward cancer cells compared to MMe, while retaining the same signaling mechanism. Importantly, pCF3-MMe allowed quantitative monitoring of cellular accumulation via 19F-NMR in vitro and in vivo. Furthermore, adding trifluoromethyl groups to TPP+ reduced toxicity in vivo while retaining anti-tumor efficacy, opening an avenue to de-risk these next-generation TPP+-conjugated compounds.

The C-terminal peptide of CCL21 drastically augments CCL21 activity through the dendritic cell lymph node homing receptor CCR7 by interaction with the receptor N-terminus.

The endogenous chemokines CCL19 and CCL21 signal via their common receptor CCR7. CCL21 is the main lymph node homing chemokine, but a weak chemo-attractant compared to CCL19. Here we show that the 41-amino acid positively charged peptide, released through C-terminal cleavage of CCL21, C21TP, boosts the immune cell recruiting activity of CCL21 by up to 25-fold and the signaling activity via CCR7 by ~ 100-fold. Such boosting is unprecedented. Despite the presence of multiple basic glycosaminoglycan (GAG) binding motifs, C21TP boosting of CCL21 signaling does not involve interference with GAG mediated cell-surface retention. Instead, boosting is directly dependent on O-glycosylations in the CCR7 N-terminus. As dictated by the two-step binding model, the initial chemokine binding involves interaction of the chemokine fold with the receptor N-terminus, followed by insertion of the chemokine N-terminus deep into the receptor binding pocket. Our data suggest that apart from a role in initial chemokine binding, the receptor N-terminus also partakes in a gating mechanism, which could give rise to a reduced ligand activity, presumably through affecting the ligand positioning. Based on experiments that support a direct interaction of C21TP with the glycosylated CCR7 N-terminus, we propose that electrostatic interactions between the positively charged peptide and sialylated O-glycans in CCR7 N-terminus may create a more accessible version of the receptor and thus guide chemokine docking to generate a more favorable chemokine-receptor interaction, giving rise to the peptide boosting effect.

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.

Inactivation of the Euchromatic Histone-Lysine N-Methyltransferase 2 Pathway in Pancreatic Epithelial Cells Antagonizes Cancer Initiation and Pancreatitis-Associated Promotion by Altering Growth and Immune Gene Expression Networks.

Pancreatic ductal adenocarcinoma (PDAC) is an aggressive, painful disease with a 5-year survival rate of only 9%. Recent evidence indicates that distinct epigenomic landscapes underlie PDAC progression, identifying the H3K9me pathway as important to its pathobiology. Here, we delineate the role of Euchromatic Histone-lysine N-Methyltransferase 2 (EHMT2), the enzyme that generates H3K9me, as a downstream effector of oncogenic KRAS during PDAC initiation and pancreatitis-associated promotion. EHMT2 inactivation in pancreatic cells reduces H3K9me2 and antagonizes Kras G12D -mediated acinar-to-ductal metaplasia (ADM) and Pancreatic Intraepithelial Neoplasia (PanIN) formation in both the Pdx1-Cre and P48 Cre/+ Kras G12D mouse models. Ex vivo acinar explants also show impaired EGFR-KRAS-MAPK pathway-mediated ADM upon EHMT2 deletion. Notably, Kras G12D increases EHMT2 protein levels and EHMT2-EHMT1-WIZ complex formation. Transcriptome analysis reveals that EHMT2 inactivation upregulates a cell cycle inhibitory gene expression network that converges on the Cdkn1a/p21-Chek2 pathway. Congruently, pancreas tissue from Kras G12D animals with EHMT2 inactivation have increased P21 protein levels and enhanced senescence. Furthermore, loss of EHMT2 reduces inflammatory cell infiltration typically induced during Kras G12D -mediated initiation. The inhibitory effect on Kras G12D -induced growth is maintained in the pancreatitis-accelerated model, while simultaneously modifying immunoregulatory gene networks that also contribute to carcinogenesis. This study outlines the existence of a novel KRAS-EHMT2 pathway that is critical for mediating the growth-promoting and immunoregulatory effects of this oncogene in vivo, extending human observations to support a pathophysiological role for the H3K9me pathway in PDAC.

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.

Targeted biologic inhibition of both tumor cell-intrinsic and intercellular CLPTM1L/CRR9-mediated chemotherapeutic drug resistance.

Recurrence of therapy-resistant tumors is a principal problem in solid tumor oncology, particularly in ovarian cancer. Despite common complete responses to first line, platinum-based therapies, most women with ovarian cancer recur, and eventually, nearly all with recurrent disease develop platinum resistance. Likewise, both intrinsic and acquired resistance contribute to the dismal prognosis of pancreatic cancer. Our previous work and that of others has established CLPTM1L (cleft lip and palate transmembrane protein 1-like)/CRR9 (cisplatin resistance related protein 9) as a cytoprotective oncofetal protein that is present on the tumor cell surface. We show that CLPTM1L is broadly overexpressed and accumulated on the plasma membrane of ovarian tumor cells, while weakly or not expressed in normal tissues. High expression of CLPTM1L is associated with poor outcome in ovarian serous adenocarcinoma. Robust re-sensitization of resistant ovarian cancer cells to platinum-based therapy was achieved using human monoclonal biologics inhibiting CLPTM1L in both orthotopic isografts and patient-derived cisplatin resistant xenograft models. Furthermore, we demonstrate that in addition to cell-autonomous cytoprotection by CLPTM1L, extracellular CLPTM1L confers resistance to chemotherapeutic killing in an ectodomain-dependent fashion, and that this intercellular resistance mechanism is inhibited by anti-CLPTM1L biologics. Specifically, exosomal CLPTM1L from cisplatin-resistant ovarian carcinoma cell lines conferred resistance to cisplatin in drug-sensitive parental cell lines. CLPTM1L is present in extracellular vesicle fractions of tumor culture supernatants and in patients' serum with increasing abundance upon chemotherapy treatment. These findings have encouraging implications for the use of anti-CLPTM1L targeted biologics in the treatment of therapy-resistant tumors.

Targeting PIM1-Mediated Metabolism in Myeloid Suppressor Cells to Treat Cancer.

There is a strong correlation between myeloid-derived suppressor cells (MDSC) and resistance to immune checkpoint blockade (ICB), but the detailed mechanisms underlying this correlation are largely unknown. Using single-cell RNA sequencing analysis in a bilateral tumor model, we found that immunosuppressive myeloid cells with characteristics of fatty acid oxidative metabolism dominate the immune-cell landscape in ICB-resistant subjects. In addition, we uncovered a previously underappreciated role of a serine/threonine kinase, PIM1, in regulating lipid oxidative metabolism via PPARγ-mediated activities. Enforced PPARγ expression sufficiently rescued metabolic and functional defects of Pim1 -/- MDSCs. Consistent with this, pharmacologic inhibition of PIM kinase by AZD1208 treatment significantly disrupted the myeloid cell-mediated immunosuppressive microenvironment and unleashed CD8+ T-cell-mediated antitumor immunity, which enhanced PD-L1 blockade in preclinical cancer models. PIM kinase inhibition also sensitized nonresponders to PD-L1 blockade by selectively targeting suppressive myeloid cells. Overall, we have identified PIM1 as a metabolic modulator in MDSCs that is associated with ICB resistance and can be therapeutically targeted to overcome ICB resistance.

STING Activated Tumor-Intrinsic Type I Interferon Signaling Promotes CXCR3 Dependent Antitumor Immunity in Pancreatic Cancer.

BACKGROUND & AIMS: Pancreatic ductal adenocarcinoma (PDA) is a lethal chemoresistant cancer that exhibits early metastatic spread. The highly immunosuppressive PDA tumor microenvironment renders patients resistant to emerging immune-targeted therapies. Building from our prior work, we evaluated stimulator of interferon genes (STING) agonist activation of PDA cell interferon-α/ß-receptor (IFNAR) signaling in systemic antitumor immune responses. METHODS: PDA cells were implanted subcutaneously to wild-type, IFNAR-, or CXCR3-knockout mice. Tumor growth was monitored, and immune responses were comprehensively profiled. RESULTS: Human and mouse STING agonist ADU-S100 reduced local and distal tumor burden and activated systemic antitumor immune responses in PDA-bearing mice. Effector T-cell infiltration and inflammatory cytokine and chemokine production, including IFN-dependent CXCR3-agonist chemokines, were elevated, whereas suppressive immune populations were decreased in treated tumors. Intratumoral STING agonist treatment also generated inflammation in distal noninjected tumors and peripheral immune tissues. STING agonist treatment of type I IFN-responsive PDA tumors engrafted to IFNAR-/- recipient mice was sufficient to contract tumors and stimulate local and systemic T-cell activation. Tumor regression and CD8+ T-cell infiltration were abolished in PDA engrafted to CXCR3-/- mice treated with STING agonist. CONCLUSIONS: These data indicate that STING agonists promote T-cell infiltration and counteract immune suppression in locally treated and distant tumors. Tumor-intrinsic type I IFN signaling initiated systemic STING-mediated antitumor inflammation and required CXCR3 expression. STING-mediated induction of systemic immune responses provides an approach to harness the immune system to treat primary and disseminated pancreatic cancers.

Mitochondria-targeted magnolol inhibits OXPHOS, proliferation, and tumor growth via modulation of energetics and autophagy in melanoma cells.

INTRODUCTION: Melanoma is an aggressive form of skin cancer for which there are no effective drugs for prolonged treatment. The existing kinase inhibitor antiglycolytic drugs (B-Raf serine/threonine kinase or BRAF inhibitors) are effective for a short time followed by a rapid onset of drug resistance. PRESENTATION OF CASE: Here, we show that a mitochondria-targeted analog of magnolol, Mito-magnolol (Mito-MGN), inhibits oxidative phosphorylation (OXPHOS) and proliferation of melanoma cells more potently than untargeted magnolol. Mito-MGN also inhibited tumor growth in murine melanoma xenografts. Mito-MGN decreased mitochondrial membrane potential and modulated energetic and mitophagy signaling proteins. DISCUSSION: Results indicate that Mito-MGN is significantly more potent than the FDA-approved OXPHOS inhibitor in inhibiting proliferation of melanoma cells. CONCLUSION: These findings have implications in the treatment of melanomas with enhanced OXPHOS status due to metabolic reprogramming or drug resistance.

Increased formation of reactive oxygen species during tumor growth: Ex vivo low-temperature EPR and in vivo bioluminescence analyses.

Previous studies have shown that reactive oxygen species (ROS) such as superoxide or hydrogen peroxide generated at low levels can exert a tumor-promoting role via a redox-signaling mechanism. Reports also suggest that both tumorigenesis and tumor growth are associated with enhanced ROS formation. However, whether ROS levels or ROS-derived oxidative marker levels increase during tumor growth remains unknown. In this study, in vivo bioluminescence imaging with a boronate-based pro-luciferin probe was used to assess ROS formation. Additionally, probe-free cryogenic electron paramagnetic resonance was used to quantify a characteristic aconitase [3Fe4S]+ center that arises in the tumor tissue of mouse xenografts from the reaction of the native [4Fe4S]2+ cluster with superoxide. Results indicated that tumor growth is accompanied by increased ROS formation, and revealed differences in oxidant formation in the inner and outer sections of tumor tissue, respectively, demonstrating redox heterogeneity. Studies using luciferin and pro-luciferin probes enabled the assessment of tumor size, ROS formation, and bioenergetic status (e.g., ATP) in luciferase-transfected mice tumor xenografts. Probe-free ex vivo low-temperature electron paramagnetic resonance can also be translated to clinical studies.