Mechanism of melanoma cells selective apoptosis induced by a photoactive NADPH analogue

The role of mitochondria in the resistance of melanoma to PD-1 inhibitors

Malignant melanoma is one of the most common tumours and has the highest mortality rate of all types of skin cancers worldwide. Traditional and novel therapeutic approaches, including surgery, targeted therapy and immunotherapy, have shown good efficacy in the treatment of melanoma. At present, the mainstay of treatment for melanoma is immunotherapy combined with other treatment strategies. However, immune checkpoint inhibitors, such as PD-1 inhibitors, are not particularly effective in the clinical treatment of patients with melanoma. Changes in mitochondrial function may affect the development of melanoma and the efficacy of PD-1 inhibitors. To elucidate the role of mitochondria in the resistance of melanoma to PD-1 inhibitors, this review comprehensively summarises the role of mitochondria in the occurrence and development of melanoma, targets related to the function of mitochondria in melanoma cells and changes in mitochondrial function in different cells in melanoma resistant to PD-1 inhibitors. This review may help to develop therapeutic strategies for improving the clinical response rate of PD-1 inhibitors and prolonging the survival of patients by activating mitochondrial function in tumour and T cells.

Targeting M2 Macrophages with a Novel NADPH Oxidase Inhibitor

ROS in cancer cells play a key role in pathways regulating cell death, stemness maintenance, and metabolic reprogramming, all of which have been implicated in resistance to chemo/ immunotherapy. Adjusting ROS levels to reverse the resistance of cancer cells without impairing normal cell functions is a new therapeutic avenue. In this paper, we describe new inhibitors of NADPH oxidase (NOX), a key enzyme in many cells of the tumor microenvironment. The first inhibitor, called Nanoshutter-1, NS1, decreased the level of tumor-promoting "M2" macrophages differentiated from human blood monocytes. NS1 disrupted the active NADPH oxidase-2 (NOX2) complex at the membrane and in the mitochondria of the macrophages, as shown by confocal microscopy. As one of the characteristics of tumor invasion is hypoxia, we tested whether NS1 would affect vascular reactivity by reducing ROS or NO levels in wire and pressure myograph experiments on isolated blood vessels. The results show that NS1 vasodilated blood vessels and would likely reduce hypoxia. Finally, as both NOX2 and NOX4 are key proteins in tumors and their microenvironment, we investigated whether NS1 would probe these proteins differently. Models of NOX2 and NOX4 were generated by homology modeling, showing structural differences at their C-terminal NADPH site, in particular in their last Phe. Thus, the NADPH site presents an unexploited chemical space for addressing ligand specificity, which we exploited to design a novel NOX2-specific inhibitor targeting variable NOX2 residues. With the proper smart vehicle to target specific cells of the microenvironment as TAMs, NOX2-specific inhibitors could open the way to new precision therapies.

Novel potential NOX2 inhibitors, Dudleya brittonii water extract and polygalatenoside A inhibit intracellular ROS generation and growth of melanoma

Reactive oxygen species (ROS) are key regulators of the proliferation, metastasis, and drug resistance of melanoma, which accounts for 60% of skin cancer deaths. In a previous study, we developed Dudleya brittonii water extract (DBWE) with antioxidant activity, but the mechanism of action and bioactive substances of DBWE have not been fully identified. This study showed altered NADPH oxidase 2 (NOX2) expression and selective inhibition of cytosolic ROS but not mitochondrial ROS in B16-F10 melanoma cells, suggesting the NOX2 inhibitory potential of DBWE. In addition, DBWE inhibited mitochondrial activity, lipid metabolism, and cell cycle in B16-F10 cells. The anti-melanoma effect of DBWE was abrogated by the addition of ROS, and there was no significant change in the melanogenesis pathway. Polygalatenoside A was identified as a candidate bioactive substance in the DBWE aqueous fraction through mass spectrometry, and the DBWE-like anti-melanoma effect was confirmed. These data suggest that DBWE and polygalatenoside A have the potential to prevent and treat melanoma.

The Role of Calcium Signaling in Melanoma

Calcium signaling plays important roles in physiological and pathological conditions, including cutaneous melanoma, the most lethal type of skin cancer. Intracellular calcium concentration ([Ca²⁺]i), cell membrane calcium channels, calcium related proteins (S100 family, E-cadherin, and calpain), and Wnt/Ca²⁺ pathways are related to melanogenesis and melanoma tumorigenesis and progression. Calcium signaling influences the melanoma microenvironment, including immune cells, extracellular matrix (ECM), the vascular network, and chemical and physical surroundings. Other ionic channels, such as sodium and potassium channels, are engaged in calcium-mediated pathways in melanoma. Calcium signaling serves as a promising pharmacological target in melanoma treatment, and its dysregulation might serve as a marker for melanoma prediction. We documented calcium-dependent endoplasmic reticulum (ER) stress and mitochondria dysfunction, by targeting calcium channels and influencing [Ca²⁺]i and calcium homeostasis, and attenuated drug resistance in melanoma management.

Oxidative Stress and Autophagy as Key Targets in Melanoma Cell Fate

Melanoma originates from the malignant transformation of melanocytes and is one of the most aggressive forms of cancer. The recent approval of several drugs has increased the chance of survival although a significant subset of patients with metastatic melanoma do not show a long-lasting response to these treatments. The complex cross-talk between oxidative stress and the catabolic process autophagy seems to play a central role in all aspects of melanoma pathophysiology, from initiation to progression and metastasis, including drug resistance. However, determining the fine role of autophagy in cancer death and in response to redox disruption is still a fundamental challenge in order to advance both basic and translational aspects of this field. In order to summarize the interactions among reactive oxygen and nitrogen species, autophagy machinery and proliferation/growth/death/apoptosis/survival, we provide here a narrative review of the preclinical evidence for drugs/treatments that modulate oxidative stress and autophagy in melanoma cells. The significance and the potential for pharmacological targeting (also through multiple and combination approaches) of these two different events, which can contribute independently or simultaneously to the fate of melanoma, may help to define new processes and their interconnections underlying skin cancer biology and unravel new reliable approaches.

Distinction between 2'- and 3'-Phosphate Isomers of a Fluorescent NADPH Analogue Led to Strong Inhibition of Cancer Cells Migration

Specific inhibition of NADPH oxidases (NOX) and NO-synthases (NOS), two enzymes associated with redox stress in tumor cells, has aroused great pharmacological interest. Here, we show how these enzymes distinguish between isomeric 2′- and 3′-phosphate derivatives, a difference used to improve the specificity of inhibition by isolated 2′- and 3′-phosphate isomers of our NADPH analogue NS1. Both isomers become fluorescent upon binding to their target proteins as observed by in vitro assay and in vivo imaging. The 2′-phosphate isomer of NS1 exerted more pronounced effects on NOS and NOX-dependent physiological responses than the 3′-phosphate isomer did. Docking and molecular dynamics simulations explain this specificity at the level of the NADPH site of NOX and NOS, where conserved arginine residues distinguished between the 2′-phosphate over the 3′-phosphate group, in favor of the 2′-phosphate.

Discovery of a new molecule inducing melanoma cell death: dual AMPK/MELK targeting for novel melanoma therapies

In the search of biguanide-derived molecules against melanoma, we have discovered and developed a series of bioactive products and identified the promising new compound CRO15. This molecule exerted anti-melanoma effects on cells lines and cells isolated from patients including the ones derived from tumors resistant to BRAF inhibitors. Moreover, CRO15 was able to decrease viability of cells lines from a broad range of cancer types. This compound acts by two distinct mechanisms. First by activating the AMPK pathway induced by a mitochondrial disorder. Second by inhibition of MELK kinase activity, which induces cell cycle arrest and activation of DNA damage repair pathways by p53 and REDD1 activation. All of these mechanisms activate autophagic and apoptotic processes resulting in melanoma cell death. The strong efficacy of CRO15 to reduce the growth of melanoma xenograft sensitive or resistant to BRAF inhibitors opens interesting perspective.

Genetic variants in TKT and DERA in the nicotinamide adenine dinucleotide phosphate pathway predict melanoma survival

BACKGROUND

Cutaneous melanoma (CM) is the most lethal type of skin cancers. Nicotinamide adenine dinucleotide phosphate (NADPH) plays an important role in anabolic reactions and tumorigenesis, but many genes are involved in the NADPH system.

METHODS

We used 10,912 single-nucleotide polymorphisms (SNPs) (2018 genotyped and 8894 imputed) in 134 NADPH-related genes from a genome-wide association study (GWAS) of 858 patients from The University of Texas MD Anderson Cancer Center (MDACC) in a single-locus analysis to predict CM survival. We then replicated the results in another GWAS data set of 409 patients from the Nurses' Health Study (NHS) and the Health Professionals Follow-up Study (HPFS).

RESULTS

There were 95 of 858 (11.1%) and 48 of 409 (11.7%) patients who died of CM, respectively. In multivariable Cox regression analyses, we identified two independent SNPs (TKT rs9864057 G > A and deoxyribose phosphate aldolase (DERA) rs12297652 A > G) to be significantly associated with CM-specific survival [hazards ratio (HR) of 1.52, 95% confidence interval (CI) = 1.18-1.96, P = 1.06 × 10^-3 and 1.51 (1.19-1.91, 5.89 × 10^-4)] in the meta-analysis, respectively. Furthermore, an increasing number of risk genotypes of these two SNPs was associated with a higher risk of death in the MDACC, the NHS/HPFS, and their combined data sets (P_trend<0.001, = 0.004 and <0.001, respectively). In the expression quantitative trait loci analysis, TKT rs9864057 G > A and DERA rs12297652 A > G were also significantly associated with higher mRNA expression levels in sun-exposed lower-leg skin (P = 0.043 and 0.006, respectively).

CONCLUSIONS

These results suggest that these two potentially functional SNPs may be valuable prognostic biomarkers for CM survival, but larger studies are needed to validate these findings.

Dysfunctional autophagy induced by the pro-apoptotic natural compound climacostol in tumour cells

Autophagy occurs at a basal level in all eukaryotic cells and may support cell survival or activate death pathways. Due to its pathophysiologic significance, the autophagic machinery is a promising target for the development of multiple approaches for anti-neoplastic agents. We have recently described the cytotoxic and pro-apoptotic mechanisms, targeting the tumour suppressor p53, of climacostol, a natural product of the ciliated protozoan Climacostomum virens. We report here on how climacostol regulates autophagy and the involvement of p53-dependent mechanisms. Using both in vitro and in vivo techniques, we show that climacostol potently and selectively impairs autophagy in multiple tumour cells that are committed to die by apoptosis. In particular, in B16-F10 mouse melanomas climacostol exerts a marked and sustained accumulation of autophagosomes as the result of dysfunctional autophagic degradation. We also provide mechanistic insights showing that climacostol affects autophagosome turnover via p53-AMPK axis, although the mTOR pathway unrelated to p53 levels plays a role. In particular, climacostol activated p53 inducing the upregulation of p53 protein levels in the nuclei through effects on p53 stability at translational level, as for instance the phosphorylation at Ser15 site. Noteworthy, AMPKα activation was the major responsible of climacostol-induced autophagy disruption in the absence of a key role regulating cell death, thus indicating that climacostol effects on autophagy and apoptosis are two separate events, which may act independently on life/death decisions of the cell. Since the activation of p53 system is at the molecular crossroad regulating both the anti-autophagic action of climacostol and its role in the apoptosis induction, it might be important to explore the dual targeting of autophagy and apoptosis with agents acting on p53 for the selective killing of tumours. These findings also suggest the efficacy of ciliate bioactive molecules to identify novel lead compounds in drug discovery and development.

E2F1 inhibition mediates cell death of metastatic melanoma

Melanoma is one of the most lethal cancers when it reaches a metastatic stage. Despite advancements in targeted therapies (BRAF inhibitors) or immunotherapies (anti-CTLA-4 or anti-PD1), most patients with melanoma will need additional treatment. Thus, there is an urgent need to develop new therapeutical approaches to bypass resistance and achieve more prolonged responses. In this context, we were interested in E2F1, a transcription factor that plays a major role in the control of cell cycle under physiological and pathological conditions. Here we confirmed that E2F1 is highly expressed in melanoma cells. Inhibition of E2F1 activity further increased melanoma cell death and senescence, both in vitro and in vivo. Moreover, blocking E2F1 also induced death of melanoma cells resistant to BRAF inhibitors. In conclusion, our studies suggest that targeting the E2F1 signaling pathway may be therapeutically relevant for melanoma.

NADPH Oxidases and Their Roles in Skin Homeostasis and Carcinogenesis

SIGNIFICANCE

Skin protects the body from dehydration, pathogens, and external mutagens. NADPH oxidases are central components for regulating the cellular redox balance. There is increasing evidence indicating that reactive oxygen species (ROS) generated by members of this enzyme family play important roles in the physiology and pathophysiology of the skin. Recent Advances: NADPH oxidases are active producers of ROS such as superoxide and hydrogen peroxide. Different isoforms are found in virtually all tissues. They play pivotal roles in normal cell homeostasis and in the cellular responses to various stressors. In particular, these enzymes are integral parts of redox-sensitive prosurvival and proapoptotic signaling pathways, in which they act both as effectors and as modulators. However, continuous (re)activation of NADPH oxidases can disturb the redox balance of cells, in the worst-case scenario in a permanent manner. Abnormal NADPH oxidase activity has been associated with a wide spectrum of diseases, as well as with aging and carcinogenesis.

CRITICAL ISSUES

Sunlight with its beneficial and deleterious effects induces the activation of NADPH oxidases in the skin. Evidence for the important roles of this enzyme family in skin cancer and skin aging, as well as in many chronic skin diseases, is now emerging.

FUTURE DIRECTIONS

Understanding the precise roles of NADPH oxidases in normal skin homeostasis, in the cellular responses to solar radiation, and during carcinogenesis will pave the way for their validation as therapeutic targets not only for the prevention and treatment of skin cancers but also for many other skin-related disorders. Antioxid. Redox Signal. 28, 1238-1261.

Turning off NADPH oxidase-2 by impeding p67phox activation in infected mouse macrophages reduced viral entry and inflammation

BACKGROUND

Targeting cells of the host immune system is a promising approach to fight against Influenza A virus (IAV) infection. Macrophage cells use the NADPH oxidase-2 (NOX2) enzymatic complex as a first line of defense against pathogens by generating superoxide ions O₂^- and releasing H₂O₂. Herein, we investigated whether targeting membrane -embedded NOX2 decreased IAV entry via raft domains and reduced inflammation in infected macrophages.

METHODS

Confocal microscopy and western blots monitored levels of the viral nucleoprotein NP and p67^phox, NOX2 activator subunit, Elisa assays quantified TNF-α levels in LPS or IAV-activated mouse or porcine alveolar macrophages pretreated with a fluorescent NOX inhibitor, called nanoshutter NS1.

RESULTS

IAV infection in macrophages promoted p67^phox translocation to the membrane, rafts clustering and activation of the NOX2 complex at early times. Disrupting rafts reduced intracellular viral NP. NS1 markedly reduced raft clustering and viral entry by binding to the C-terminal of NOX2 also characterized in vitro. NS1 decrease of TNF-α release depended on the cell type.

CONCLUSION

NOX2 participated in IAV entry and raft-mediated endocytosis. NOX2 inhibition by NS1 reduced viral entry. NS1 competition with p67^phox for NOX2 binding shown by in silico models and cell-free assays was in agreement with NS1 inhibiting p67^phox translocation to membrane-embedded NOX2 in mouse and porcine macrophages.

GENERAL SIGNIFICANCE

We introduce NS1 as a compound targeting NOX2, a critical enzyme controlling viral levels and inflammation in macrophages and discuss the therapeutic relevance of targeting the C-terminal of NADPH oxidases by probes like NS1 in viral infections.