Metformin: Focus on Melanoma

Small molecules targeting mitochondria as an innovative approach to cancer therapy

Cellular death evasion is a defining characteristic of human malignancies and a significant contributor to therapeutic inefficacy. As a result of oncogenic inhibition of cell death mechanisms, established therapeutic regimens seems to be ineffective. Mitochondria serve as the cellular powerhouses, but they also function as repositories of self-destructive weaponry. Changes in the structure and activities of mitochondria have been consistently documented in cancer cells. In recent years, there has been an increasing focus on using mitochondria as a targeted approach for treating cancer. Considerable attention has been devoted to the development of delivery systems that selectively aim to deliver small molecules called "mitocans" to mitochondria, with the ultimate goal of modulating the physiology of cancer cells. This review summarizes the rationale and mechanism of mitochondrial targeting with small molecules in the treatment of cancer, and their impact on the mitochondria. This paper provides a concise overview of the reasoning and mechanism behind directing treatment towards mitochondria in cancer therapy, with a particular focus on targeting using small molecules. This review also examines diverse small molecule types within each category as potential therapeutic agents for cancer.

Metformin regulates the proliferation and motility of melanoma cells by modulating the LINC00094/miR-1270 axis

BACKGROUND

Melanoma is an aggressive tumor with a high mortality rate. Metformin, a commonly prescribed diabetes medication, has shown promise in cancer prevention and treatment. Long noncoding RNAs (lncRNAs) are non-protein-coding RNA molecules that play a key role in tumor development by interacting with cellular chromatins. Despite the benefits of metformin, the anticancer mechanism underlying its effect on the regulation of lncRNAs in melanoma remains unclear.

METHODS

We investigated the lncRNA profiles of human melanoma cells with and without metformin treatment using a next-generation sequencing approach (NGS). Utilizing public databases, we analyzed the expression levels and clinical impacts of LINC00094 and miR-1270 in melanoma. The expression levels of LINC00094 and miR-1270 were verified in human cell lines and clinical samples by real-time PCR and in situ hybridization. The biological roles of LINC00094 and miR-1270 in cell growth, proliferation, cell cycle, apoptosis, and motility were studied using in vitro assays.

RESULTS

We identify a novel long noncoding RNA, namely LINC00094, whose expression considerably decreased in melanoma cells after metformin treatment. In situ hybridization analysis revealed substantially higher expression of LINC00094 in cutaneous melanoma tissue compared with adjacent normal epidermis and normal control tissues (P < 0.001). In nondiabetic patients with melanoma, the overall survival of high LINC00094 expression group was shorter than the low LINC00094 expression group with borderline statistical significance (log-rank test, P = 0.057). Coexpression analysis of LINC00094 indicated its involvement in the mitochondrial respiratory pathway, with its knockdown suppressing genes associated with mitochondrial oxidative phosphorylation, glycolysis, antioxidant production, and metabolite levels. Functional analysis revealed that silencing-LINC00094 inhibited the proliferation, colony formation, invasion, and migration of melanoma cells. Cell cycle analysis following LINC00094 knockdown revealed G1 phase arrest with reduced cell cycle protein expression. Combined TargetScan and reporter assays revealed a direct link between miR-1270 and LINC00094. Ectopic miR-1270 expression inhibited melanoma cell growth and motility while inducing apoptosis. Finally, through in silico analysis, we identified two miR-1270 target genes, CD276 and centromere protein M (CENPM), which may be involved in the biological functions of LINC00094.

CONCLUSIONS

Overall, LINC00094 expression may regulate melanoma cell growth and motility by modulating the expression of miR-1270, and targeting genes of CD276 and CENPM indicating its therapeutic potential in melanoma treatment.

Metformin: Beyond Type 2 Diabetes Mellitus

Metformin was developed from an offshoot of Guanidine. It is known to be the first-line medication for type 2 diabetes mellitus, polycystic ovarian syndrome, and weight reduction. Metformin has also been shown to have effectiveness in the management of non-alcoholic fatty liver disease (NAFLD), liver cirrhosis, and various carcinomas like hepatocellular, colorectal, prostate, breast, urinary bladder, blood, melanoma, bone, skin, lung and so on. This narrative review focuses on the effect of metformin on non-alcoholic fatty liver disease, liver cirrhosis, and hepatocellular carcinoma. The search platforms for the topic were PubMed, Scopus, and Google search engine. Critical words for searching included 'Metformin,' AND 'Indications of Metformin,' AND 'Non-Alcoholic Fatty Liver Disease,' AND 'Metformin mechanism of action,' AND 'NAFLD management,' AND 'NAFLD and inflammation,' AND 'Metformin and insulin,' AND 'Metformin and inflammation,' AND 'Liver cirrhosis,' AND 'Hepatocellular carcinoma.' Lifestyle modification and the use of hypoglycemic agents can help improve liver conditions. Metformin has several mechanisms that enhance liver health, including reducing reactive oxygen species, nuclear factor kappa beta (NF-κB), liver enzymes, improving insulin sensitivity, and improving hepatic cell lipophagy. Long-term use of metformin may cause some adverse effects like lactic acidosis and gastrointestinal disturbance. Metformin long-term overdose may lead to a rise in hydrogen sulfide in liver cells, which calls for pharmacovigilance. Drug regulating authorities should provide approval for further research, and national and international guidelines need to be developed for liver diseases, perhaps with the inclusion of metformin as part of the management regime.

Treatment resistance to melanoma therapeutics on a single cell level

Therapy targeting the BRAF-MEK cascade created a treatment revolution for patients with BRAF mutant advanced melanoma. Unfortunately, 80% patients treated will progress by 5 years follow-up. Thus, it is imperative we study mechanisms of melanoma progression and therapeutic resistance. We created a scRNA (single cell RNA) atlas of 128,230 cells from 18 tumors across the treatment spectrum, discovering melanoma cells clustered strongly by transcriptome profiles of patients of origins. Our cell-level investigation revealed gains of 1q and 7q as likely early clonal events in metastatic melanomas. By comparing patient tumors and their derivative cell lines, we observed that PD1 responsive tumor fraction disappears when cells are propagated in vitro. We further established three anti-BRAF-MEK treatment resistant cell lines using three BRAF mutant tumors. ALDOA and PGK1 were found to be highly expressed in treatment resistant cell populations and metformin was effective in targeting the resistant cells. Our study suggests that the investigation of patient tumors and their derivative lines is essential for understanding disease progression, treatment response and resistance.

Therapeutic implications of the metabolic changes associated with BRAF inhibition in melanoma

Melanoma metabolism can be reprogrammed by activating BRAF mutations. These mutations are present in up to 50% of cutaneous melanomas, with the most common being V600E. BRAF mutations augment glycolysis to promote macromolecular synthesis and proliferation. Prior to the development of targeted anti-BRAF therapies, these mutations were associated with accelerated clinical disease in the metastatic setting. Combination BRAF and MEK inhibition is a first line treatment option for locally advanced or metastatic melanoma harboring targetable BRAF mutations. This therapy shows excellent response rates but these responses are not durable, with almost all patients developing resistance. When BRAF mutated melanoma cells are inhibited with targeted therapies the metabolism of those cells also changes. These cells rely less on glycolysis for energy production, and instead shift to a mitochondrial phenotype with upregulated TCA cycle activity and oxidative phosphorylation. An increased dependence on glutamine utilization is exhibited to support TCA cycle substrates in this metabolic rewiring of BRAF mutated melanoma. Herein we describe the relevant core metabolic pathways modulated by BRAF inhibition. These adaptive pathways represent vulnerabilities that could be targeted to overcome resistance to BRAF inhibitors. This review evaluates current and future therapeutic strategies that target metabolic reprogramming in melanoma cells, particularly in response to BRAF inhibition.

Diabetes Driven Oncogenesis and Anticancer Potential of Repurposed Antidiabetic Drug: A Systemic Review

Diabetes and cancer are two prevalent disorders, pose significant public health challenges and contribute substantially to global mortality rates, with solely 10 million reported cancer-related deaths in 2020. This review explores the pathological association between diabetes and diverse cancer progressions, examining molecular mechanisms and potential therapeutic intersections. From altered metabolic landscapes to dysregulated signaling pathways, the intricate links are delineated, offering a comprehensive understanding of diabetes as a modulator of tumorigenesis. Cancer cells develop drug resistance through mechanisms like enhanced drug efflux, genetic mutations, and altered drug metabolism, allowing them to survive despite chemotherapeutic agent. Glucose emerges as a pivotal player in diabetes progression, and serving as a crucial energy source for cancer cells, supporting their biosynthetic needs and adaptation to diverse microenvironments. Glycation, a non-enzymatic process that produces advanced glycation end products (AGEs), has been linked to the etiology of cancer and has been shown in a number of tumor forms, such as leiomyosarcomas, adenocarcinomas, and squamous cell carcinomas. Furthermore, in aggressive and metastatic breast cancer, the receptor for AGEs (RAGE) is increased, which may increase the malignancy of the tumor. Reprogramming glucose metabolism manifests as hallmark cancer features, including accelerated cell proliferation, angiogenesis, metastasis, and evasion of apoptosis. This manuscript encapsulates the dual narrative of diabetes as a driver of cancer progression and the potential of repurposed antidiabetic drugs as formidable countermeasures. The amalgamation of mechanistic understanding and clinical trial outcomes establishes a robust foundation for further translational research and therapeutic advancements in the dynamic intersection of diabetes and cancer.

In vitro and ex vivo evaluation of chitosan gel containing metformin-loaded polymeric nanoparticles for topical treatment of melanoma

OBJECTIVE

The purpose of this study was to prepare and evaluate chitosan (CS) gel containing metformin hydrochloride (MET)-loaded polycaprolactone (PCL) nanoparticles (NPs) for topical treatment of melanoma.

SIGNIFICANCE

Topical administration of MET-PCL NPs-CS gel improves penetration of drug, decreases side effects, and increases efficacy of treatment.

METHODS

MET-PCL NPs were prepared by double emulsion method. Particle size, charge, encapsulation efficiency (EE), release, and morphology were evaluated. MET-PCL NPs-CS gel formulation was characterized in terms of organoleptic properties, pH, gelling time, viscosity, spreadability, release, and morphology. Cytotoxicity was performed on B16F10 cells. Ex vivo permeability was done with pig skin.

RESULTS

The size, charge, and EE were found to be 180 ± 10 nm, -11.4 mV, and 93%. SEM images showed that NPs were spherical and smooth. An initial burst release followed by a slower release was observed. MET-PCL NPs-CS gel was found to be transparent. The pH was 4.9 ± 0.05. The gelation time was 1.6 ± 0.2 min. The viscosity results confirm pseudoplastic behavior of gel. The spreadability by % area was 392 ± 6.4 cm. The images showed that gelling network of CS gel was composed of suspended NPs. The viscosity was between 554 and 3503 cP. MET-PCL NPs-CS gel showed prolonged release up to 72 h. On B16F10 cells, gel showed higher cytotoxicity compared to MET solution. MET-PCL NPs-CS gel had twofold higher permeability in pig skin compared with MET-CS gel.

CONCLUSION

Topical administration of MET-PCL NPs-CS gel into the skin resulted in improved dermal penetration and this promising approach may be of value in effective treatment of melanoma and other skin cancers.

Delving into the Metabolism of Sézary Cells: A Brief Review

Primary cutaneous lymphomas (PCLs) are a heterogeneous group of lymphoproliferative disorders caused by the accumulation of neoplastic T or B lymphocytes in the skin. Sézary syndrome (SS) is an aggressive and rare form of cutaneous T cell lymphoma (CTCL) characterized by an erythroderma and the presence of atypical cerebriform T cells named Sézary cells in skin and blood. Most of the available treatments for SS are not curative, which means there is an urgent need for the development of novel efficient therapies. Recently, targeting cancer metabolism has emerged as a promising strategy for cancer therapy. This is due to the accumulating evidence that metabolic reprogramming highly contributes to tumor progression. Genes play a pivotal role in regulating metabolic processes, and alterations in these genes can disrupt the delicate balance of metabolic pathways, potentially contributing to cancer development. In this review, we discuss the importance of targeting energy metabolism in tumors and the currently available data on the metabolism of Sézary cells, paving the way for potential new therapeutic approaches aiming to improve clinical outcomes for patients suffering from SS.

Glucagon like peptide-1 receptor agonists and the risk of skin cancer among patients with type 2 diabetes: Population-based cohort study

AIMS

The objective of this study was to determine whether the use of glucagon-like peptide-1 receptor agonists (GLP-1 RAs) is associated with an increased risk of melanoma and nonmelanoma skin cancer, separately, compared with the use of sulfonylureas among patients with type 2 diabetes.

METHODS

Using the United Kingdom Clinical Practice Research Datalink (2007-2019), we assembled two new-user active comparator cohorts. In the first cohort assessing melanoma as the outcome, 11,786 new users of GLP-1 RAs were compared with 208,519 new users of sulfonylureas. In the second cohort assessing nonmelanoma skin cancer as the outcome, 11,774 new users of GLP-1 RAs were compared with 207,788 new users of sulfonylureas. Cox proportional hazards models weighted using propensity score fine stratification were fit to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) of melanoma and nonmelanoma skin cancer, respectively.

RESULTS

Compared with sulfonylureas, GLP-1 RAs were not associated with an increased risk of either melanoma (42.6 vs. 43.9 per 100,000 person-years, respectively; HR 0.96, 95% CI 0.53-1.75) or nonmelanoma skin cancer (243.9 vs. 229.9 per 100,000 person-years, respectively; HR 1.03, 95% CI 0.80-1.33). There was no evidence of an association between cumulative duration of use with either melanoma or nonmelanoma skin cancer. Consistent results were observed in secondary and sensitivity analyses.

CONCLUSIONS

In this population-based cohort study, GLP-1 RAs were not associated with an increased risk of melanoma or nonmelanoma skin cancer, compared with sulfonylureas.

Treatment with the PPARα agonist fenofibrate improves the efficacy of CD8+ T cell therapy for melanoma

Adoptive transfer of tumor antigen-specific CD8+ T cells can limit tumor progression but is hampered by the T cells' rapid functional impairment within the tumor microenvironment (TME). This is in part caused by metabolic stress due to lack of oxygen and glucose. Here, we report that fenofibrate treatment of human ex vivo expanded tumor-infiltrating lymphocytes (TILs) improves their ability to limit melanoma progression in a patient-derived xenograft (PDX) mouse model. TILs treated with fenofibrate, a peroxisome proliferator receptor alpha (PPARα) agonist, switch from glycolysis to fatty acid oxidation (FAO) and increase the ability to slow the progression of autologous melanomas in mice with freshly transplanted human tumor fragments or injected with tumor cell lines established from the patients' melanomas and ex vivo expanded TILs.

Applications of Metformin in Dentistry-A review

Metformin is a versatile drug with numerous medical uses. It is known primarily as an anti-hyperglycemic drug that has become the main oral blood-glucose-lowering medication for managing type 2 diabetes mellitus globally. Its use has been reported in a variety of oral conditions and dentistry in general. Recent clinical trials have indicated the effectiveness of adjunct topical application of metformin in improving the periodontal parameters of patients with diabetes and periodontitis. Additionally, studies have suggested that metformin stimulates odontogenic differentiation and mineral synthesis of stem cells in the tooth pulp. Metformin also stimulates osteoblast proliferation, decreases osteoclast activity and exerts regenerative effects on periodontal bone, thus making it a viable candidate for periodontal regeneration. Metformin monotherapy significantly enhances osseointegration of endosseous implants and has been reported to have anti-cancer effects on oral squamous cell carcinoma by impeding tumor progression. Animal studies have indicated that metformin improves orthodontic tooth movement and resists orthodontic appliance corrosion. This narrative review aims to provide a current summary of research highlighting the prospective uses of metformin in dentistry.

Prognostic and predictive value of metformin in the European Organisation for Research and Treatment of Cancer 1325/KEYNOTE-054 phase III trial of pembrolizumab versus placebo in resected high-risk stage III melanoma

BACKGROUND

Metformin is a commonly prescribed and well-tolerated medication. In laboratory studies, metformin suppresses BRAF wild-type melanoma cells but accelerates the growth of BRAF-mutated cells. This study investigated the prognostic and predictive value of metformin, including with respect to BRAF mutation status, in the European Organisation for Research and Treatment of Cancer 1325/KEYNOTE-054 randomised controlled trial.

METHODS

Patients with resected high-risk stage IIIA, IIIB, or IIIC melanoma received 200 mg of pembrolizumab (n = 514) or placebo (n = 505) every 3 weeks for twelve months. Pembrolizumab prolonged recurrence-free survival (RFS) and distant metastasis-free survival (DMFS) at approximately 42 months median follow-up (Eggermont et al., TLO, 2021). Multivariable Cox regression was used to estimate associations of metformin with RFS and DMFS. Interaction terms were used to model effect modification by treatment and BRAF mutation.

RESULTS

Fifty-four patients (0.5%) used metformin at baseline. Metformin was not significantly associated with RFS (hazard ratio [HR] 0.87, 95% confidence interval [CI] 0.52-1.45) and DMFS (HR 0.82, 95% CI 0.47-1.44). The interaction between metformin and the treatment arm was not significant for either RFS (p = 0.92) or DMFS (p = 0.93). Among patients with mutated BRAF, the association of metformin with RFS (HR 0.70, 95% CI 0.37-1.33) was greater in magnitude though not significantly different to those without mutated BRAF (HR 0.98, 95% CI 0.56-1.69).

CONCLUSIONS

There was no significant impact of metformin use on pembrolizumab efficacy in resected high-risk stage III melanoma. However, larger studies or pooled analyses are needed, particularly to explore a possible effect of metformin in BRAF-mutated melanoma.

Hyaluronic Acid-Coated Chitosan/Gelatin Nanoparticles as a New Strategy for Topical Delivery of Metformin in Melanoma

Metformin is a multipotential compound for treating diabetes II and controlling hormonal acne and skin cancer. This study was designed to enhance metformin skin penetration in melanoma using nanoparticles containing biocompatible polymers. Formulations with various concentrations of chitosan, hyaluronic acid, and sodium tripolyphosphate were fabricated using an ionic gelation technique tailored by the Box-Behnken design. The optimal formulation was selected based on the smallest particle size and the highest entrapment efficiency (EE%) and used in ex vivo skin penetration study. In vitro antiproliferation activity and apoptotic effects of formulations were evaluated using MTT and flow cytometric assays, respectively. The optimized formulation had an average size, zeta potential, EE%, and polydispersity index of 329 ± 6.30 nm, 21.94 ± 0.05 mV, 64.71 ± 6.12%, and 0.272 ± 0.010, respectively. The release profile of the optimized formulation displayed a biphasic trend, characterized by an early burst release, continued by a slow and sustained release compared to free metformin. The ex vivo skin absorption exhibited 1142.5 ± 156.3 μg/cm² of metformin deposited in the skin layers for the optimized formulation compared to 603.2 ± 93.1 μg/cm² for the free metformin. Differential scanning calorimetry confirmed the deformation of the drug from the crystal structure to an amorphous state. The attenuated total reflection Fourier transform infrared results approved no chemical interaction between the drug and other ingredients of the formulations. According to the MTT assay, metformin in nanoformulation exhibited a higher cytotoxic effect against melanoma cancer cells than free metformin (IC₅₀: 3.94 ± 0.57 mM vs. 7.63 ± 0.26 mM, respectively, P < 0.001). The results proved that the optimized formulation of metformin could efficiently decrease cell proliferation by promoting apoptosis, thus providing a promising strategy for melanoma therapy.

Obesity and immune-checkpoint inhibitors in advanced melanoma: A meta-analysis of survival outcomes from clinical studies

Obesity is a chronic inflammatory condition that has been associated with different types of cancer. However, its role in melanoma incidence, progression, and response to immune-checkpoint-inhibitors (ICI) is still controversial. On the one hand, increased levels of lipids and adipokines can promote tumor proliferation and several genes associated with fatty acid metabolism have been found to be upregulated in melanomas. On the other hand, immunotherapy seems to be more effective in obese animal models, presumably due to an increase in CD8 + and subsequent decrease in PD-1 + T-cells in the tumor microenvironment. In humans, several studies have investigated the role of BMI (body mass index) and other adiposity-related parameters as potential prognostic markers of survival in advanced melanoma patients treated with ICI. The aim of this research has been to systematically review the scientific literature on studies evaluating the relationship between overweight/obesity and survival outcomes in patients with advanced melanoma treated with ICI and to perform a meta-analysis on those sharing common characteristics. After screening 1070 records identified through a literature search, 18 articles assessing the role of BMI-related exposure in relation to survival outcomes in ICI-treated patients with advanced melanoma were included in our review. In the meta-analysis of the association between overweight (defined as BMI>25 or BMI 25-30), overall survival (OS), and progression free survival (PFS), 7 studies were included, yielding a summary HR of 0.87 (95% CI: 0.74-1.03) and 0.96 (95% CI: 0.86-1.08), respectively. Our results show that, despite few suggestive findings, the use of BMI as a valuable predictor of melanoma patients' survival in terms of PFS and OS should not be currently recommended, due to the limited evidence available.

Metformin: new applications for an old drug

Metformin is a biguanide, evolved as one of the most widely used medicines. The applications of this component include but are not limited to reducing blood glucose, weight loss, and polycystic ovary syndrome. Studies about other probable indications have emerged, indicating that this agent can also be utilized for other purposes. In this review, applications of metformin are noticed based on the current evidence. Metformin commonly is used as an off-label drug in non-alcoholic fatty liver disease (NAFLD), but it worsens inflammation and should not be used for this purpose, according to the latest research. Metformin decreased the risk of death in patients with liver cirrhosis. It is an effective agent in the prevention and improvement of survival in patients suffering hepatocellular carcinoma. There is evidence of the beneficial effects of metformin in colorectal cancer, early-stage prostate cancer, breast cancer, urothelial cancer, blood cancer, melanoma, and bone cancer, suggesting metformin as a potent anti-tumor agent. Metformin shows neuroprotective effects and provides a potential therapeutic benefit for mild cognitive impairment and Alzheimer's disease (AD). It also has been shown to improve mental function and reduce the incidence of dementia. Another condition that metformin has been shown to slow the progression of is Duchenne muscular dystrophy. Regarding infectious diseases, tuberculosis (TB) and coronavirus disease (COVID-19) are among the conditions suggested to be affected by metformin. The beneficial effects of metformin in cardiovascular diseases were also reported in the literature. Concerning renal function, studies showed that daily oral administration of metformin could ameliorate kidney fibrosis and normalize kidney structure and function. This study reviewed the clinical and preclinical evidence about the possible benefits of metformin based on recent studies. Numerous questions like whether these probable indications of metformin can be observed in non-diabetics, need to be described by future basic experiments and clinical studies.

Monoolein-based nanodispersions for cutaneous co-delivery of methylene blue and metformin: Thermal and structural characterization and effects on the cutaneous barrier, skin penetration and cytotoxicity

This study evaluated the potential of monoolein (MO)-based nanodispersions to promote the cutaneous co-delivery of metformin (MET) and methylene blue (MB) for the treatment of non-melanoma skin cancer. MO-based nanodispersions were obtained using Kolliphor® P407 (KP) and/or sodium cholate (CH), and characterized concerning the structure, thermal stability, ability to disrupt the skin barrier, cutaneous permeation and retention of MB and MET. Additionally, the cytotoxic effect of MO nanodispersions-mediated combination therapy using MET and MB in A431 cells was evaluated. The nanodispersions exhibited nanometric size (<200 nm) and thermal and physical stability. Small angle X-ray scattering studies revealed multiple structures depending on composition. They were able to interact with stratum corneum lipid structure, increasing its fluidity. The effect of MO-nanodispersions on topical/transdermal delivery of MB and MET was composition-dependent. Nanodispersions with low MO content (5 %) and stabilized with KP and CH (0.05-0.10 %) were the most promising, enhancing the cutaneous delivery of MB and MET by 1.9 to 2.2-fold and 1.4 to 1.7-fold, respectively, compared to control. Cytotoxic studies revealed that the most promising MO nanodispersion-mediated combination therapy using MET and MB (1:1) reduced the IC₅₀ by 24-fold, compared to MB solution, and a further reduction (1.5-fold) was observed by MB photoactivation.

Association of metformin use and survival in patients with cutaneous melanoma and diabetes

BACKGROUND

Metformin use has been associated with improved survival in patients with different types of cancer, but research regarding the effect of metformin on cutaneous melanoma (CM) survival is sparse and inconclusive.

OBJECTIVES

To investigate the association between metformin use and survival among patients with CM and diabetes.

METHODS

All adult patients with a primary invasive CM between 2007 and 2014 were identified in the Swedish Melanoma Registry and followed until death, or end of follow-up on 31 December 2017 in this population-based cohort study. Patients with both CM and type 2 diabetes mellitus were assessed further. Overall survival (OS) and melanoma-specific survival (MSS) were the primary endpoints. Cox proportional hazard models estimating crude and adjusted hazard ratios (HRs) and 95% confidence intervals (CIs) were used comparing peridiagnostic use vs. nonuse of metformin. Dose response was evaluated based on defined daily doses.

RESULTS

Among a total of 23 507 patients, 1162 patients with CM and type 2 diabetes mellitus were included in the final cohort, with a median follow-up time of 4.1 years (interquartile range 2.4-6.1). Peridiagnostic metformin use was associated with a significantly decreased risk of death by any cause (HR 0.68, 95% CI 0.57-0.81). Cumulative pre- and postdiagnostic metformin use was also associated with improved OS: the HR for prediagnostic use was 0.90 (95% CI 0.86-0.95) for every 6 months of use and the HR for postdiagnostic use ranged from 0.98 (95% CI 0.97-0.98) for 0-6 months to 0.59 (0.49-0.70) for 24-30 months of use. No association was found for metformin use and MSS.

CONCLUSIONS

Metformin use was associated with improved OS in patients with CM and diabetes regardless of timing (pre-, post- or peridiagnostic use) and followed a dose-response pattern. However, further research regarding the underlying mechanisms is warranted.

Prognostic Relevance of Type 2 Diabetes and Metformin Treatment in Head and Neck Melanoma: Results from a Population-Based Cohort Study

BACKGROUND

Type 2 Diabetes (DM2) and the consecutively daily use of antidiabetic medication are characterized by a frequent prevalence worldwide and were shown to impact the initiation and progression of malignant diseases. While these effects were observed in a variety of malignancies, comprehensive data about the role of DM2 and antidiabetic drugs in the outcome of head and neck melanoma (HNM) patients are missing.

METHODS

This retrospective population-based cohort study included 382 HNM patients from Eastern Bavaria having received tumor resection to negative margins between 2010 and 2017. Recurrence-free survival (RFS) was evaluated with regard to DM2 and routine metformin intake. Statistical analysis was performed by uni- and multivariate analyses. The median follow-up time was 5.6 years.

RESULTS

DM2 was diagnosed in 68 patients (17.8%), routine metformin intake was found in 39 cases (10.2%). The univariate survival analysis revealed impaired 5-year RFS in HNM patients with DM2 compared to non-diabetic controls (p = 0.016; 64.0% and 74.5%, respectively). The multivariate Cox regression substantiated this effect (HR = 1.980, 95% CI = 1.108-3.538, p = 0.021). In detail, the cumulative locoregional recurrence rate displayed the most far-reaching negative effect on the RFS of diabetic HNM patients (HR = 4.173, 95% CI = 1.628-10.697, p = 0.003). For metformin intake, a profound positive effect on the RFS in multivariate statistics was observed, both in the complete cohort (HR = 0.396, 95% CI = 0.177-0.884, p = 0.024) as well as in the cohort of diabetic HNM patients (HR = 0.352, 95% CI = 0.135-0.913, p = 0.032).

CONCLUSIONS

This study emphasizes that DM2 is a relevant comorbid condition in HNM patients, impairing patient survival. Metformin intake was associated with a favorable outcome in HNM patients, providing possible therapeutic implications for future adjuvant treatment regimes.

Options of Therapeutics and Novel Delivery Systems of Drugs for the Treatment of Melanoma

Melanoma is one of the most severe cancerous diseases. The cells employ multiple signaling pathways, such as ERK, HGF/c-MET, WNT, and COX-2 to cause the cell proliferation, survival, and metastasis. Treatment of melanoma, including surgery, chemotherapy, immunotherapy, radiation, and targeted therapy, is based on 4 major or 11 substages of the disease. Fourteen drugs, including dacarbazine, interferon α-2b, interleukin-12, ipilimumab, peginterferon α-2b, vemurafenib, trametinib, talimogene laherparepvec, cobimetinib, pembrolizumab, dabrafenib, binimetinib, encorafenib, and nivolumab, have been approved by the FDA for the treatment of melanoma. All of them are in conventional dosage forms of injection solutions, suspensions, oral tablets, or capsules. Major drawbacks of the treatment are side effects of the drugs and patients' incompliance to them. These are consequences of high doses and long-term treatments for the diseases. Currently more than 350 NCI-registered clinical trials are being carried out to treat advanced and/or metastatic melanoma using novel treatment methods, such as immune cell therapy, cancer vaccines, and new therapeutic targets. In addition, novel delivery systems using biomaterials of the approved drugs have been developed attempting to increase the drug delivery, targeting, stability, bioavailability, thus potentially reducing the toxicity and increasing the treatment effectiveness. Nanoparticles and liposomes have been emerging as advanced delivery systems which can improve drug stability and systemic circulation time. In this review, the most recent findings in the options for treatment and development of novel drug delivery systems for the treatment of melanoma are comprehensively discussed.

Metformin and bladder cancer: Drug repurposing as a potential tool for novel therapy: A review

Bladder cancer (BC) is a common type of cancer worldwide. Currently, the gold standard treatment is transurethral resection of bladder tumor (TUR-Bt) accompanied by intravesical Bacillus Calmette-Guérin (BCG) instillation for patients with middle-to-high-risk non-muscle-invasive bladder cancer (NMIBC). However, intravesical BCG therapy fails in almost 50% of high risk cases, leading to NMIBC persistence or early recurrence. In these patients, the gold standard remains radical cystectomy; however, it can seriously affect the patients' quality of life. Moreover, for patients with muscle-invasive bladder cancer (MIBC), the 5-year survival rate after radical cystectomy with neoadjuvant chemotherapy remains low. Recent discoveries have paved the way for a new era in BC treatment. Metformin is the most widely used oral hypoglycemic drug in clinical practice, being mostly used in the treatment of type 2 diabetes. Epidemiological studies have demonstrated that metformin exerts a potentially positive effect on reducing the incidence and mortality of cancer; therefore, a increasing number of studies have investigated the potential anticancer effects of metformin and its mechanisms of action. This review aims to summarize the evidence for the role of metformin in bladder cancer therapy, including how metformin mediates bladder cancer cell apoptosis.

Formulation and Characterization of Metformin-Loaded Ethosomes for Topical Application to Experimentally Induced Skin Cancer in Mice

To achieve the best treatment of skin cancer, drug penetration inside the deepest layers of the skin is an important scientific interest. We designed an ethosome formulation that serves as a carrier for metformin and measured the in vitro skin permeation. We also aimed to measure the antitumor activity of the optimal ethosomal preparation when applied topically to chemically induced skin cancer in mice. We utilized a statistical Box-Behnken experimental design and applied three variables at three levels: lecithin concentration, cholesterol concentration and a mixture of ethanol and isopropyl alcohol concentrations. All formulations were prepared to calculate the entrapment efficiency %, zeta potential, size of the vesicles and drug release % after 1, 2, 4, 8 and 24 h. The size of the vesicles for the formulations was between 124 ± 14.2 nm and 560 ± 127 nm, while the entrapment efficiency was between 97.8 ± 0.23% and 99.4 ± 0.24%, and the drug release % after 8 h was between 38 ± 0.82% and 66 ± 0.52%. All formulations were introduced into the Box-Behnken software, which selected three formulations; then, one was assigned as an optimal formula. The in vivo antitumor activity of metformin-loaded ethosomal gel on skin cancer was greater than the antitumor activity of the gel preparation containing free metformin. Lower lecithin, high ethanol and isopropyl alcohol and moderate cholesterol contents improved the permeation rate. Overall, we can conclude that metformin-loaded ethosomes are a promising remedy for treating skin cancers, and more studies are warranted to approve this activity in other animal models of skin cancers.

A Clinical Perspective of the Multifaceted Mechanism of Metformin in Diabetes, Infections, Cognitive Dysfunction, and Cancer

In type 2 diabetes, ecological and lifecourse factors may interact with the host microbiota to influence expression of his/her genomes causing perturbation of interconnecting biological pathways with diverse clinical course. Metformin is a plant-based or plant-derived medicinal product used for the treatment of type 2 diabetes for over 60 years and is an essential drug listed by the World Health Organization. By reducing mitochondrial oxidative phosphorylation and adenosine triphosphate (ATP) production, metformin increased AMP (adenosine monophosphate)-activated protein kinase (AMPK) activity and altered cellular redox state with reduced glucagon activity, endogenous glucose production, lipogenesis, and protein synthesis. Metformin modulated immune response by directly reducing neutrophil to lymphocyte ratio and improving the phagocytic function of immune cells. By increasing the relative abundance of mucin-producing and short-chain-fatty-acid-producing gut microbes, metformin further improved the host inflammatory and metabolic milieu. Experimentally, metformin promoted apoptosis and reduced proliferation of cancer cells by reducing their oxygen consumption and modulating the microenvironment. Both clinical and mechanistic studies support the pluripotent effects of metformin on reducing cardiovascular–renal events, infection, cancer, cognitive dysfunction, and all-cause death in type 2 diabetes, making this low-cost medication a fundamental therapy for individualization of other glucose-lowering drugs in type 2 diabetes. Further research into the effects of metformin on cognitive function, infection and cancer, especially in people without diabetes, will provide new insights into the therapeutic value of metformin in our pursuit of prevention and treatment of ageing-related as well as acute and chronic diseases beyond diabetes.

Proline Dehydrogenase/Proline Oxidase (PRODH/POX) Is Involved in the Mechanism of Metformin-Induced Apoptosis in C32 Melanoma Cell Line

The role of proline dehydrogenase/proline oxidase (PRODH/POX) in the mechanism of antineoplastic activity of metformin (MET) was studied in C32 melanoma cells. PRODH/POX is a mitochondrial enzyme-degrading proline that is implicated in the regulation of cancer cell survival/apoptosis. The enzyme is activated by AMP kinase (AMPK). It has been found that MET induced a significant decrease in cell viability and DNA biosynthesis accompanied by an increase in the expressions of AMPK and PRODH/POX in C32 cells. The mechanism for MET-dependent cytotoxicity on C32 cells was found at the level of PRODH/POX-induced ROS generation and activation of Caspase-3 and Caspase-9 expressions in these cells. The effects were not observed in MET-treated PRODH/POX knock-out C32 cells. Of interest is an MET-dependent increase in the concentration of proline, which is a substrate for PRODH/POX. This phenomenon is due to the MET-dependent inhibition of collagen biosynthesis, which is the main proline-utilizing process. It has been found that the underlying mechanism of anticancer activity of MET involves the activation of AMPK, PRODH/POX, increase in the cytoplasmic concentration of proline, inhibition of collagen biosynthesis, and stimulation of PRODH/POX-dependent ROS generation, which initiate the apoptosis of melanoma cells.

The multifaceted roles of mitochondria at the crossroads of cell life and death in cancer

Mitochondria are the cytoplasmic organelles mostly known as the "electric engine" of the cells; however, they also play pivotal roles in different biological processes, such as cell growth/apoptosis, Ca²⁺ and redox homeostasis, and cell stemness. In cancer cells, mitochondria undergo peculiar functional and structural dynamics involved in the survival/death fate of the cell. Cancer cells use glycolysis to support macromolecular biosynthesis and energy production ("Warburg effect"); however, mitochondrial OXPHOS has been shown to be still active during carcinogenesis and even exacerbated in drug-resistant and stem cancer cells. This metabolic rewiring is associated with mutations in genes encoding mitochondrial metabolic enzymes ("oncometabolites"), alterations of ROS production and redox biology, and a fine-tuned balance between anti-/proapoptotic proteins. In cancer cells, mitochondria also experience dynamic alterations from the structural point of view undergoing coordinated cycles of biogenesis, fusion/fission and mitophagy, and physically communicating with the endoplasmic reticulum (ER), through the Ca²⁺ flux, at the MAM (mitochondria-associated membranes) levels. This review addresses the peculiar mitochondrial metabolic and structural dynamics occurring in cancer cells and their role in coordinating the balance between cell survival and death. The role of mitochondrial dynamics as effective biomarkers of tumor progression and promising targets for anticancer strategies is also discussed.

Mitochondrial Metabolism in Melanoma

Melanoma and its associated alterations in cellular pathways have been growing areas of interest in research, especially as specific biological pathways are being elucidated. Some of these alterations include changes in the mitochondrial metabolism in melanoma. Many mitochondrial metabolic changes lead to differences in the survivability of cancer cells and confer resistance to targeted therapies. While extensive work has gone into characterizing mechanisms of resistance, the role of mitochondrial adaptation as a mode of resistance is not completely understood. In this review, we wish to explore mitochondrial metabolism in melanoma and how it impacts modes of resistance. There are several genes that play a major role in melanoma mitochondrial metabolism which require a full understanding to optimally target melanoma. These include BRAF, CRAF, SOX2, MCL1, TRAP1, RHOA, SRF, SIRT3, PTEN, and AKT1. We will be discussing the role of these genes in melanoma in greater detail. An enhanced understanding of mitochondrial metabolism and these modes of resistance may result in novel combinatorial and sequential therapies that may lead to greater therapeutic benefit.

Potential effect of EGCG on the anti-tumor efficacy of metformin in melanoma cells

Metformin, a first-line drug for type 2 diabetes mellitus, has been recognized as a potential anti-tumor agent in recent years. Epigallocatechin-3-gallate (EGCG), as the dominant catechin in green tea, is another promising adjuvant agent for tumor prevention. In the present work, the potential effect of EGCG on the anti-tumor efficacy of metformin in a mouse melanoma cell line (B16F10) was investigated. Results indicated that EGCG and metformin exhibited a synergistic effect on cell viability, migration, and proliferation, as well as signal transducer and activator of transcription 3/nuclear factor-κB (STAT3/NF-κB) pathway signaling and the production of inflammation cytokines. Meanwhile, the combination showed an antagonistic effect on cell apoptosis and oxidative stress levels. The combination of EGCG and metformin also differentially affected the nucleus (synergism) and cytoplasm (antagonism) of B16F10 cells. Our findings provide new insight into the potential effects of EGCG on the anti-tumor efficacy of metformin in melanoma cells.

Biguanides drugs: Past success stories and promising future for drug discovery

Biguanides have attracted much attention a century ago and showed resurgent interest in recent years after a long period of dormancy. They constitute an important class of therapeutic agents suitable for the treatment of a wide spectrum of diseases. Therapeutic indications of biguanides include antidiabetic, antimalarial, antiviral, antiplaque, and bactericidal applications. This review presents an extensive overview of the biological activity of biguanides and different mechanisms of action of currently marketed biguanide-containing drugs, as well as their pharmacological properties when applicable. We highlight the recent developments in research on biguanide compounds, with a primary focus on studies on metformin in the field of oncology. We aim to provide a critical overview of all main bioactive biguanide compounds and discuss future perspectives for the design of new drugs based on the biguanide fragment.

Trend Shifts in Age-Specific Incidence for In Situ and Invasive Cutaneous Melanoma in Sweden

BACKGROUND

The incidence of invasive cutaneous melanoma (CM) is increasing in Sweden. The aim was to present age- and sex-specific trends of the age-standardised incidence and the average annual percentage change (AAPC) for in situ and invasive CM.

METHODS

Joinpoint regression models were used to analyse data from the Swedish Cancer Register and the Swedish Melanoma Registry 1997-2018 (N = 35,350 in situ CM; 59,932 CM).

RESULTS

The AAPC of CM for women was 4.5 (4.1-5.0; p < 0.001) for the period 1997-2018. For men, the APCC was 4.2 (3.0-5.4; p < 0.001), with a significantly higher annual percentage change (APC) for the period 2000-2018 (5.0; 4.6-5.4; p < 0.001) compared to 1997-1999. An increasing annual incidence of CM ≤ 0.6 mm and 0.7 mm Breslow tumour thickness was found for men with a significant incidence shift for the period 2006-2015, respectively. Similarly for women, with a significantly higher APC for CM ≤ 0.6 mm from 2005. The incidence of intermediate thick CM (2.1-4.0 mm) has not increased since 2011. The incidence of CM > 4.0 mm has been increasing among both sexes, with a significantly lower APC among women from 2005.

CONCLUSIONS

The incidence of in situ and low-risk CM ≤ 1.0 mm in tumour thickness has been rising among both sexes since the 2000s.

Targeting nutrient metabolism with FDA-approved drugs for cancer chemoprevention: Drugs and mechanisms

Proliferating cancer cells exhibit metabolic alterations and specific nutritional needs for adapting to their rapid growth. These changes include using aerobic glycolysis, lipid metabolic disorder, and irregular protein degradation. It may be useful to target metabolic abnormalities for cancer chemoprevention. Epidemiological and mechanism-related studies have indicated that many FDA-approved anti-metabolic drugs decrease tumor risk, inhibit tumor growth, or enhance the effect of chemotherapeutic drugs. Drugs targeting nutrient metabolism have fewer side effects with long-term use compared to chemotherapeutic drugs. The characteristics of these drugs make them promising candidates for cancer chemoprevention. Here, we summarize recent discoveries of the chemo-preventive effects of drugs targeting nutrient metabolic pathways and discuss future applications and challenges. Understanding the effects and mechanisms of anti-metabolic drugs in cancer has important implications for exploring strategies for cancer chemoprevention.

Developing an analytical method by HPLC for simultaneous quantification of methylene blue and metformin applied to in vitro skin permeation and retention studies

The aim of this study was to develop an HPLC method for simultaneous quantification of metformin (MET) and methylene blue (MB) in in vitro skin permeation/retention studies, in which retention was evaluated in the different layers of the skin [stratum corneum (SC) and the viable epidermis + dermis (VE + D)]. The method was validated considering the following parameters: specificity, linearity, quantitation limit (LOQ), recovery, precision and accuracy. Calibration curves were obtained using the following six matrices: methanol, water, methanolic extracts from the SC and VE + D spiked with the drugs and drugs extracted from the SC and VE + D. The precision, accuracy and LOQ of the method were evaluated in water and in VE + D and SC, applying the drug extraction process. The results show that the method is selective and linear for both drugs. The precision and accuracy values, independent of matrix and drug, were below the limit of 15%. The LOQ of MB was defined as 0.4 μg/ml in the VE + D and SC and 0.8 μg/ml in water. The LOQ of MET was defined as 0.8 μg/ml in the VE + D and SC and 0.4 μg/ml in the water. The recovery of the method was adequate, consistent and reproducible for the concentration range of 0.4-10 μg/ml for MB (73.3-92.1%) and 0.8-10.0 μg/mL for MET (72.4-94.4%). This method has a potential application in the development of formulation for skin delivery of MB and MET.

Relationship between type 2 diabetes mellitus and markers of cutaneous melanoma aggressiveness: an observational multicentric study in 443 patients with melanoma

BACKGROUND

Some studies have suggested a relationship between type 2 diabetes mellitus (T2DM) and increased incidence of melanoma. Efforts are under way to identify preventable and treatable factors associated with greater melanoma aggressiveness, but no studies to date have examined the relationship between T2DM and the aggressiveness of cutaneous melanoma at diagnosis.

OBJECTIVES

To explore potential associations between T2DM, glycaemic control and metformin treatment and the aggressiveness of cutaneous melanoma.

METHODS

We conducted a cross-sectional multicentric study in 443 patients diagnosed with cutaneous melanoma. At diagnosis, all patients completed a standardized protocol, and a fasting blood sample was extracted to analyse their glucose levels, glycated haemoglobin concentration and markers of systemic inflammation. Melanoma characteristics and aggressiveness factors [Breslow thickness, ulceration, tumour mitotic rate (TMR), sentinel lymph node (SLN) involvement and tumour stage] were also recorded.

RESULTS

The mean (SD) age of the patients was 55·98 (15·3) years and 50·6% were male. The median Breslow thickness was 0·85 mm. In total, 48 (10·8%) patients were diagnosed with T2DM and this finding was associated with a Breslow thickness > 2 mm [odds ratio (OR) 2·6, 95% confidence interval (CI) 1·4-4·9; P = 0·004)] and > 4 mm (OR 3·6, 95% CI 1·7-7·9; P = 0·001), TMR > 5 per mm² (OR 4·5, 95% CI 1·4-13·7; P = 0·009), SLN involvement (OR 2·3, 95% CI 1-5·7; P = 0·038) and tumour stages III-IV (vs. I-II) (OR 3·4, 95% CI 1·6-7·4; P = 0·002), after adjusting for age, sex, obesity, alcohol intake and smoking habits. No significant associations emerged between glycated haemoglobin levels, metformin treatment and melanoma aggressiveness.

CONCLUSIONS

T2DM, rather than glycaemic control and metformin treatment, is associated with increased cutaneous melanoma aggressiveness at diagnosis.

Repurposing of Drug Candidates for Treatment of Skin Cancer

Skin cancers are highly prevalent malignancies that affect millions of people worldwide. These include melanomas and nonmelanoma skin cancers. Melanomas are among the most dangerous cancers, while nonmelanoma skin cancers generally exhibit a more benign clinical pattern; however, they may sometimes be aggressive and metastatic. Melanomas typically appear in body regions exposed to the sun, although they may also appear in areas that do not usually get sun exposure. Thus, their development is multifactorial, comprising endogenous and exogenous risk factors. The management of skin cancer depends on the type; it is usually based on surgery, chemotherapy, immunotherapy, and targeted therapy. In this respect, oncological treatments have demonstrated some progress in the last years; however, current therapies still present various disadvantages such as little cell specificity, recurrent relapses, high toxicity, and increased costs. Furthermore, the pursuit of novel medications is expensive, and the authorization for their clinical utilization may take 10-15 years. Thus, repositioning of drugs previously approved and utilized for other diseases has emerged as an excellent alternative. In this mini-review, we aimed to provide an updated overview of drugs' repurposing to treat skin cancer and discuss future perspectives.

Glucose 6-phosphate dehydrogenase inhibition sensitizes melanoma cells to metformin treatment

Most cancer cells exacerbate the pentose phosphate pathway (PPP) to enhance biosynthetic precursors and antioxidant defenses. Metformin, which is used as a first-line oral drug for the treatment of type 2 diabetes, has been proposed to inhibit the malignant progression of different types of cancers. However, metformin has shown poor efficacy as single agent in several clinical trials. Thus, the aim of the present work was to investigate whether the pharmacological inhibition of G6PDH, the first and rate-limiting enzyme of the PPP, by 6-amino nicotinamide (6-AN) potentiates the antitumoral activity of metformin on different human melanoma cell lines. Our results showed that 6-AN has sensitizing properties to metformin cytotoxicity. The combination of metformin and 6-AN decreased glucose consumption and lactate production, altered the mitochondrial potential and redox balance, and thereby blocked melanoma cell progression, directing cells to apoptosis and necrosis. To our knowledge, this is the first study describing the effect of this combination. Future preclinical studies should be performed to reveal the biological relevance of this finding.

MicroRNA-21-Enriched Exosomes as Epigenetic Regulators in Melanomagenesis and Melanoma Progression: The Impact of Western Lifestyle Factors

DNA mutation-induced activation of RAS-BRAF-MEK-ERK signaling associated with intermittent or chronic ultraviolet (UV) irradiation cannot exclusively explain the excessive increase of malignant melanoma (MM) incidence since the 1950s. Malignant conversion of a melanocyte to an MM cell and metastatic MM is associated with a steady increase in microRNA-21 (miR-21). At the epigenetic level, miR-21 inhibits key tumor suppressors of the RAS-BRAF signaling pathway enhancing proliferation and MM progression. Increased MM cell levels of miR-21 either result from endogenous upregulation of melanocytic miR-21 expression or by uptake of miR-21-enriched exogenous exosomes. Based on epidemiological data and translational evidence, this review provides deeper insights into environmentally and metabolically induced exosomal miR-21 trafficking beyond UV-irradiation in melanomagenesis and MM progression. Sources of miR-21-enriched exosomes include UV-irradiated keratinocytes, adipocyte-derived exosomes in obesity, airway epithelium-derived exosomes generated by smoking and pollution, diet-related exosomes and inflammation-induced exosomes, which may synergistically increase the exosomal miR-21 burden of the melanocyte, the transformed MM cell and its tumor environment. Several therapeutic agents that suppress MM cell growth and proliferation attenuate miR-21 expression. These include miR-21 antagonists, metformin, kinase inhibitors, beta-blockers, vitamin D, and plant-derived bioactive compounds, which may represent new options for the prevention and treatment of MM.

Metabolic Plasticity of Melanoma Cells and Their Crosstalk With Tumor Microenvironment

Cutaneous melanoma (CM) is a highly aggressive and drug resistant solid tumor, showing an impressive metabolic plasticity modulated by oncogenic activation. In particular, melanoma cells can generate adenosine triphosphate (ATP) during cancer progression by both cytosolic and mitochondrial compartments, although CM energetic request mostly relies on glycolysis. The upregulation of glycolysis is associated with constitutive activation of BRAF/MAPK signaling sustained by BRAF^V600E kinase mutant. In this scenario, the growth and progression of CM are strongly affected by melanoma metabolic changes and interplay with tumor microenvironment (TME) that sustain tumor development and immune escape. Furthermore, CM metabolic plasticity can induce a metabolic adaptive response to BRAF/MEK inhibitors (BRAFi/MEKi), associated with the shift from glycolysis toward oxidative phosphorylation (OXPHOS). Therefore, in this review article we survey the metabolic alterations and plasticity of CM, its crosstalk with TME that regulates melanoma progression, drug resistance and immunosurveillance. Finally, we describe hallmarks of melanoma therapeutic strategies targeting the shift from glycolysis toward OXPHOS.

Metformin in combination with JS-K inhibits growth of renal cell carcinoma cells via reactive oxygen species activation and inducing DNA breaks

Metformin (MET) is taken as a principal medication for remedying Type 2 diabetes mellitus. Its anti-tumor effect has been reported increasingly, but the precise mechanism of it remains unclear. This study aims to explore the efficacy of MET and MET combined with nitric oxide donor prodrug JS-K on the proliferation, apoptosis, and DNA damage in human renal cell carcinoma (RCC) cells, and investigate the possible molecular mechanism involved. The cell proliferation was tested through methyl-tetrazolium assay and cell apoptosis was ascertained by flow cytometry. The dihydroethidium and JC-1 fluorescent methods were used to detect Reactive oxygen species (ROS) and mitochondrial transmembrane potential (Δψm), respectively. Proteins associated with apoptosis and DNA damage were evaluated by Western blotting. Results showed that MET and JS-K could suppress cell growth, and the inhibition concentration 50 of treatment with MET combined with JS-K (MET + JS-K) showed more toxicity than individual agents on RCC cells. This augmented toxicity was associated with intracellular reactive oxygen species (ROS) level, mitochondrial membrane potential alteration, and induced DNA breaks. The results of Western blotting showed that the expression level of pro-apoptotic proteins, such as Bax, Bak, caspase-3, and caspase-9, was up-regulated, and the anti-apoptotic protein Bcl-2 was down-regulated after treatment using MET alone and MET + JS-K, correspondingly. Moreover, MET + JS-K inhibited the expression of cellular PCNA and Rad51, and immunofluorescence analysis of γH2AX proved that MET + JS-K enhanced DNA damage. In summary, the results of this research indicated that MET and JS-K inhibited RCC cell growth by activating ROS, targeting mitochondria-dependent apoptotic pathways, and inducing DNA breaks.

Modern Aspects of Immunotherapy with Checkpoint Inhibitors in Melanoma

Although melanoma is one of the most immunogenic tumors, it has an ability to evade anti-tumor immune responses by exploiting tolerance mechanisms, including negative immune checkpoint molecules. The most extensively studied checkpoints represent cytotoxic T lymphocyte-associated protein-4 (CTLA-4) and programmed cell death protein 1 (PD-1). Immune checkpoint inhibitors (ICI), which were broadly applied for melanoma treatment in the past decade, can unleash anti-tumor immune responses and result in melanoma regression. Patients responding to the ICI treatment showed long-lasting remission or disease control status. However, a large group of patients failed to respond to this therapy, indicating the development of resistance mechanisms. Among them are intrinsic tumor properties, the dysfunction of effector cells, and the generation of immunosuppressive tumor microenvironment (TME). This review discusses achievements of ICI treatment in melanoma, reasons for its failure, and promising approaches for overcoming the resistance. These methods include combinations of different ICI with each other, strategies for neutralizing the immunosuppressive TME and combining ICI with other anti-cancer therapies such as radiation, oncolytic viral, or targeted therapy. New therapeutic approaches targeting other immune checkpoint molecules are also discussed.

Clinical outcomes of BRAF plus MEK inhibition in melanoma: A meta-analysis and systematic review

Background

Melanoma is a potentially fatal malignancy with poor prognosis. Several recent studies have demonstrated that combination therapy of BRAF and MEK inhibition achieved better curative effect and appeared less toxic effects. We conducted a meta‐analysis to evaluate the efficacy and safety between BRAF inhibition plus MEK inhibition combination therapy and BRAF inhibition monotherapy in melanoma patients.

Methods

We performed the search in PubMed, EMBASE, and the Cochrane Library from January 2010 to January 2019. Inclusion and exclusion of studies, assessment of quality, outcome measures, data extraction, and synthesis were independently accomplished by two reviewers. Revman 5.3 software was used for the meta‐analysis.

Results

Totally, seven randomized controlled trials involving 3146 patients met our inclusion criteria. Comparing the results of combination therapy and monotherapy, combination therapy significantly improved OS (RR = 1.13; 95% CI, 1.08, 1.19; P < 0.00001), ORR (RR = 1.36; 95% CI, 1.28, 1.45; P < 0.00001), PFS (RR = 0.57; 95% CI, 0.52, 0.63; P < 0.00001) and reduced deaths (RR = 0.78; 95% CI, 0.69, 0.88; P < 0.0001). Skin‐related adverse events such as hyperkeratosis, cutaneous squamous‐cell carcinoma were less compared with monotherapy. However, gastrointestinal events like nausea, diarrhea, and vomiting were at a higher frequency.

Conclusion

Doublet BRAF and MEK inhibition achieved better survival outcomes over single‐agent BRAF inhibition and occurred less skin‐related events, but gastrointestinal events were more in combination therapy.

Metabolic flexibility in melanoma: A potential therapeutic target

Cutaneous melanoma (CM) represents one of the most metastasizing and drug resistant solid tumors. CM is characterized by a remarkable metabolic plasticity and an important connection between oncogenic activation and energetic metabolism. In fact, melanoma cells can use both cytosolic and mitochondrial compartments to produce adenosine triphosphate (ATP) during cancer progression. However, the CM energetic demand mainly depends on glycolysis, whose upregulation is strictly linked to constitutive activation of BRAF/MAPK pathway affected by BRAF^V600E kinase mutant. Furthermore, the impressive metabolic plasticity of melanoma allows the development of resistance mechanisms to BRAF/MEK inhibitors (BRAFi/MEKi) and the adaptation to microenvironmental changes. The metabolic interaction between melanoma cells and tumor microenvironment affects the immune response and CM growth. In this review article, we describe the regulation of melanoma metabolic alterations and the metabolic interactions between cancer cells and microenvironment that influence melanoma progression and immune response. Finally, we summarize the hallmarks of melanoma therapies and we report BRAF/MEK pathway targeted therapy and mechanisms of metabolic resistance.

High Glucose Represses the Anti-Proliferative and Pro-Apoptotic Effect of Metformin in Triple Negative Breast Cancer Cells

Metformin, the most widely prescribed anti-diabetic drug, is shown to possess anti-cancer potential in treatment of cancers, including breast cancer; decreases breast cancer risk; and improves overall survival. However, reports suggest that higher glucose concentrations may negatively impact the anti-cancer efficacy of metformin. Therefore, we examined the anti-cancer potential of metformin in triple-negative breast cancer cells (TNBCs) exposed to different glucose (25 mM, 5.5 mM and zero glucose/glucose-starved) conditions. Our data indicates that a high glucose (25 mM) concentration (mimicking diabetes) significantly abrogated the effect of metformin on cell proliferation, cell death and cell cycle arrest in addition to loss of efficacy in inhibition of the mTOR pathway, a key metabolic pathway in TNBC cells. The mTOR pathway is activated in TNBCs compared to other subtypes of breast cancer, regulates the synthesis of proteins that are critical for the growth and survival of cancer cells and its activation is correlated to poor outcomes among TNBC patients, while also contributing to metastatic progression and development of resistance to chemotherapy/radiotherapy. Our studies were performed in two different types of TNBCs, MDA-MB-231 cells (mesenchymal stem cell-like (MSL)) and MDA-MB-468 (basal like-1 (BL-1)). Interestingly, lower concentrations of metformin (50, 100, 250, and 500 μM) significantly increased cell proliferation in 25 mM glucose exposed MDA-MB-231 cells, an effect which was not observed in MDA-MB-468 cells, indicating that the effective concentration of metformin when used as anti-cancer drug in TNBCs may have to be determined based on cell type and blood glucose concentration. Our data indicates that metformin treatment was most effective under zero glucose/glucose-starved conditions in MDA-MB-468 with a significant increase in the apoptotic population (62.3 ± 1.5%; p-value < 0.01). Under 5.5 mM glucose conditions in both MDA-MB-231 and MDA-MB-468 cells our data showed reduced viability of 73.56 ± 2.53%; p-value < 0.05 and 70.49 ± 1.68%; p-value < 0.001, respectively, along with a significant increase in apoptotic populations of both cell types. Furthermore, metformin (2 mM) inhibited the mTOR pathway and its downstream components under zero glucose/glucose-starved conditions indicating that using metformin in combination with agents that inhibit the glycolytic pathway should be more beneficial for the treatment of triple-negative breast cancers in diabetic individuals.