Sudocetaxel Zendusortide (TH1902) triggers the cGAS/STING pathway and potentiates anti-PD-L1 immune-mediated tumor cell killing

The anticancer efficacy of Sudocetaxel Zendusortide (TH1902), a peptide-drug conjugate internalized through a sortilin-mediated process, was assessed in a triple-negative breast cancer-derived MDA-MB-231 immunocompromised xenograft tumor model where complete tumor regression was observed for more than 40 days after the last treatment. Surprisingly, immunohistochemistry analysis revealed high staining of STING, a master regulator in the cancer-immunity cycle. A weekly administration of TH1902 as a single agent in a murine B16-F10 melanoma syngeneic tumor model demonstrated superior tumor growth inhibition than did docetaxel. A net increase in CD45 leukocyte infiltration within TH1902-treated tumors, especially for tumor-infiltrating lymphocytes and tumor-associated macrophages was observed. Increased staining of perforin, granzyme B, and caspase-3 was suggestive of elevated cytotoxic T and natural killer cell activities. Combined TH1902/anti-PD-L1 treatment led to increases in tumor growth inhibition and median animal survival. TH1902 inhibited cell proliferation and triggered apoptosis and senescence in B16-F10 cells in vitro, while inducing several downstream effectors of the cGAS/STING pathway and the expression of MHC-I and PD-L1. This is the first evidence that TH1902 exerts its antitumor activity, in part, through modulation of the immune tumor microenvironment and that the combination of TH1902 with checkpoint inhibitors (anti-PD-L1) could lead to improved clinical outcomes.

Targeting Tyrosinase in Hyperpigmentation: Current Status, Limitations and Future Promises

Hyperpigmentation is a common and distressing dermatologic condition. Since tyrosinase (TYR) plays an essential role in melanogenesis, its inhibition is considered a logical approach along with other therapeutic methods to prevent the accumulation of melanin in the skin. Thus, TYR inhibitors are a tempting target as the medicinal and cosmetic active agents of hyperpigmentation disorder. Among TYR inhibitors, hydroquinone is a traditional lightening agent that is commonly used in clinical practice. However, despite good efficacy, prolonged use of hydroquinone is associated with side effects. To overcome these shortcomings, new approaches in targeting TYR and treating hyperpigmentation are desperately requiredessentialneeded. In line with this purpose, several non-hydroquinone lightening agents have been developed and suggested as hydroquinone alternatives. In addition to traditional approaches, nanomedicine and nanotheranostic platforms have been recently proposed in the treatment of hyperpigmentation. In this review, we discuss the available strategies for the management of hyperpigmentation with a focus on TYR inhibition. In addition, alternative treatment options to hydroquinone are discussed. Finally, we present nano-based strategies to improve the therapeutic effect of drugs prescribed to patients with skin disorders.

A minor metabolite from Curcuma longa effective against metabolic syndrome: results from a randomized, double-blind, placebo-controlled clinical study

Metabolic syndrome (MetS) is characterized by the presence of at least three interrelated risk factors, including central obesity, hypertension, elevated serum triglycerides, low serum high-density lipoproteins, and insulin resistance. Abdominal obesity is considered a predominant risk factor. Lifestyle changes with medications to lower cholesterol, blood sugar, and hypertension are the general treatment approaches. Functional foods and bioactive food ingredients represent versatile tools for addressing different aspects of MetS. In a randomized placebo-controlled clinical study, we evaluated the effect of Calebin A, a minor bioactive phytochemical from Curcuma longa, on metabolic syndrome in obese adults (N = 100), and 94 individuals completed the study (N = 47 in both groups). They were subjected to Calebin A supplementation for 90 days, which resulted in a statistically significant reduction in their body weight, waist circumference, body mass index, low-density lipoprotein-cholesterol, and triglyceride levels compared to those with the placebo. A small but significant increase in high-density lipoprotein-cholesterol levels was also observed in these individuals. Furthermore, Calebin A showed a positive effect on adipokines by reducing circulating leptin levels. Finally, C-reactive protein levels were significantly reduced in Calebin A-supplemented individuals, suggesting a beneficial impact on managing MetS-induced inflammation. Blood glucose levels, insulin resistance, and blood pressure levels were not affected by Calebin A. In conclusion, Calebin A may be an effective supplement for managing abdominal obesity, dyslipidemia, and systemic inflammation in individuals with metabolic syndrome. This study was prospectively registered on the Clinical Trial Registry of India (CTRI) with the registration number CTRI/2021/09/036495. https://ctri.nic.in/Clinicaltrials/advancesearchmain.php.

Melanogenesis and Melasma Treatment

Melanocytes are highly specialised dendritic cells that transfer melanin to keratinocytes in subcellular lysosome-like organelles called melanosomes, where melanin is synthesised and stored. Melanin is a complex pigment that provides colour and photoprotection to the skin, hair, and eyes of mammals. The regulation of melanogenesis includes various mechanisms and factors including genetic, environmental, and endocrine factors. Knowledge of the pigmentation process is important not only to understand hyperpigmentation but also to design treatments and therapies to treat them. Whitening cosmetics with anti-melanogenesis activity are very popular. In the present manuscript, we review the mechanisms and the signalling pathways involved in skin pigmentation and we specifically focus on the alteration of melanogenesis that leads to melasma and results in hyperpigmentation. Finally, current therapies and treatments including topical, oral, and phototherapies are discussed and described, with a special emphasis on the cosmetics’ action.

Anti-Melanogenic Mechanism of Tetrahydrocurcumin and Enhancing Its Topical Delivery Efficacy Using a Lecithin-Based Nanoemulsion

Tetrahydrocurcumin (THC) has been well known for its superior antioxidant properties. Therefore, it is speculated that it might be effective to relieve oxidative stress-induced diseases, such as skin hyperpigmentation. In this work, an in vitro B16F10 melanoma cell model was used to study the impact of THC on the melanogenic process under stressed conditions. It was demonstrated that THC could effectively inhibit the α-MSH (melanocyte-stimulating hormone) induced melanin production in B16F10 melanoma cells and the expressions of three key enzymes involved with the biosynthetic process of melanin, tyrosinase (TYR), tyrosinase-related protein 1 (TRP-1), and tyrosinase-related protein 2 (TRP-2), were all significantly reduced. In addition, an in vitro human keratinocyte cell model was used to investigate the potential protective role of THC on H₂O₂-induced cytotoxicity. It was found that THC could prevent H₂O₂-induced oxidative stress based on the results of both the cell viability study and the intracellular ROS (reactive oxygen species) study assessed by the flow cytometry. Last, THC was formulated into a lecithin based nanoemulsion, and an in vitro Franz diffusion cell study using Strat-M^® membrane concluded that the nanoemulsion could significantly enhance the membrane permeation compared to the unformatted THC suspension. This research demonstrated the anti-melanogenic benefits of THC on the melanoma and keratinocyte cell models and the topical delivery efficacy could be significantly enhanced using a lecithin based nanoemulsion.

Comparative Study of Curcumin and Its Hydrogenated Metabolites, Tetrahydrocurcumin, Hexahydrocurcumin, and Octahydrocurcumin, on Melanogenesis in B16F10 and MNT-1 Cells

Curcumin, a bioactive from Curcuma longa, has been shown to possess anti-melanogenic activity previously; however, the effects of its hydrogenated metabolites (HMs)—Tetrahydrocurcumin (THC), Hexahydrocurcumin (HHC), and Octahydrocurcumin (OHC)—on melanogenesis have not been sufficiently explored. We have studied and compared three HMs (THC, HHC, and OHC) with the parent compound, curcumin (PC), on melanin synthesis in B16F10 mouse and MNT-1 human melanoma cells. Our results demonstrated that all the HMs were nontoxic over the concentration range 5–40 µM, while PC was nontoxic at 5 µM but induced toxicity at 20 and 40 µM in B16F10 cells. All three HMs enhanced melanin synthesis, while PC (5 µM) inhibited it. THC (40 µM) significantly stimulated melanin synthesis to a greater degree than HHC and OHC in both B16F10 and MNT-1 cells; the order of melanogenesis stimulation was THC = OHC > HHC in B16F10 mouse cells, while it was THC > HHC > OHC in MNT-1 cells. HMs stimulated melanogenesis by pathways not involving tyrosinase, as neither the intracellular tyrosinase activity nor the protein levels of tyrosinase were affected. In addition, mushroom tyrosinase activity, using L-Dihydroxyphenylalanine (L-DOPA) as the substrate, showed no direct effects of HMs. In summary, our results demonstrate that the HMs enhanced melanogenesis, which establishes that the hydrogenation of the heptadiene moiety of curcumin leads to a loss of its anti-melanogenic activity and instead results in the stimulation of melanogenesis. This stimulation is not further enhanced upon hydrogenation of the β-diketone, which was noted in MNT-1 cells, although the correlation to the number of keto groups differed in B16F10 cells where HHC was the weakest stimulator of melanogenesis. Collectively, THC with both keto groups intact is the best stimulator. Moreover, our results also validate that the electrophilicity of curcumin is necessary for its anti-melanogenic activity, as the non-electrophilic HMs did not inhibit melanogenesis. Furthermore, our results suggest that THC might hold promise as a stimulator of melanogenesis for treatment of hypopigmentation disorders and anti-graying therapies. Future studies to probe the molecular signaling mechanisms and test whether the pro-melanogenic activity of HMs is retained in primary human melanocytes are warranted.

Simon S. Asoprisnil, a Selective Progesterone Receptor Modulator (SPRM), Inhibits Melanosome Export in B16F10 Cells and HEMn-DP Melanocytes

Previous studies have reported that estrogen hormone promotes melanogenesis while progesterone inhibits it. A selective estrogen receptor modulator (SERM), tamoxifen, has been shown to promote melanogenesis; however, to date, there have been no reports on the effects of a selective progesterone receptor modulator (SPRM) on melanogenesis. In the present study, we hypothesized that asoprisnil (AP), a SPRM, inhibits melanogenesis. AP was tested for cytotoxicity to B16F10 mouse melanoma cells for screening the nontoxic concentrations using MTS cytotoxicity assay. Extracellular and intracellular melanin levels were estimated at nontoxic concentrations of AP. To evaluate the direct effect of AP on tyrosinase enzyme, tyrosinase activity and copper chelating activities were measured. Next, the effects of AP on melanogenesis were tested in normal human melanocytes, neonatal, darkly pigmented (HEMn-DP). Our results demonstrate that AP was nontoxic at a concentration range of 10-50 μM in B16F10 cells; AP at 50 μM significantly suppressed extracellular melanin levels comparable to kojic acid at 500 μM, with no significant effect on intracellular melanin levels. The mechanism of melanogenesis inhibition was studied to assess if AP downregulated tyrosinase activity in cell lysates or in a cell-free system. However, AP was found to increase intracellular tyrosinase activity without any effect on tyrosinase enzyme activity or copper chelating activity in a cell-free system, indicating that AP inhibits melanogenesis by mechanisms other than direct effects on tyrosinase enzyme activity. The capacity of AP to inhibit melanosome export was further validated in HEMn-DP cells; AP significantly suppressed dendricity at concentrations of 20 and 30 μM in the absence of effects on melanin synthesis or intracellular tyrosinase activity. In addition, AP was nontoxic to human keratinocytes (HaCaT) at these concentrations, validating its safety for topical use. Taken together, our preliminary results demonstrate that AP might be repurposed as a candidate therapeutic for treatment of hyperpigmentation disorders via a unique mechanism, which encompasses a selective inhibition of melanosome export.

Inhibitory Effects of the Bioactive Thermorubin Isolated from the Fungus Thermoactinomyces Antibioticus on Melanogenesis

Skin hyperpigmentation disorders arise due to aberrant regulation of melanin synthesis and export. Current treatments include natural compounds like kojic acid and hydroquinone, which suffer from limitations due to adverse reactions. Thermorubin (TR) is a secondary metabolite derived from the fungus Thermoactinomyces antibioticus and has previously demonstrated to possess anti-inflammatory properties by inhibition of matrix metalloproteinases (MMPs), as well as antimicrobial activity. In the current study, we explored whether TR might be a used as a candidate for the treatment of skin hyperpigmentation disorders by studying its effects on melanin synthesis and melanin export in B16F10 mouse melanoma cells and primary human melanocytes derived from darkly-pigmented (DP) skin. Non-toxic doses of TR were first identified in B16F10 mouse melanoma cells. These doses were subsequently tested for their effects on both extracellular and intracellular melanin levels under conditions of basal and hormone-stimulated melanogenesis. Our results demonstrated that TR at 25 µM inhibited total melanin levels with selective inhibition of extracellular melanin in B16F10 cells under both basal and hormone-stimulated conditions. The mechanisms of inhibition did not include tyrosinase inhibition, either in cellular lysates or cell-free system. However, TR potently inhibited activity of α-glucosidase enzyme in vitro and exhibited antioxidant activity. Furthermore, our results with primary human melanocytes from DP skin showed that TR at 10 µM significantly suppressed dendricity along with an increase in accumulation of intracellular melanin. These findings point to a mechanism of action of TR as an exclusive inhibitor of melanosome export. Taken together, our preliminary results demonstrate that TR might offer a novel ingredient as a skin depigmenting agent for inclusion in cosmetic formulations. Further studies delineating molecular mechanisms of hypopigmentation of TR and testing in human skin tissue-equivalents are warranted.