Retinoids in Cutaneous Squamous Cell Carcinoma

Structure-Activity Relationships and Therapeutic Applications of Retinoids in View of Potential Benefits from Drug Repurposing Process

Vitamin A, an essential micronutrient, is integral to various biological processes crucial for organismal development and maintenance. Dietary sources of vitamin A encompass preformed retinol, retinyl esters, and provitamin A carotenoids. Retinoic acid (RA), a key component, plays pivotal roles in vision, cell proliferation, apoptosis, immune function, and gene regulation. Drug repurposing, an effective strategy for identifying new therapeutic applications for existing drugs, has gained prominence in recent years. This review seeks to provide a comprehensive overview of the current research landscape surrounding retinoids and drug repurposing. The scope of this review encompasses a comprehensive examination of retinoids and their potential for repurposing in various therapeutic contexts. Despite their efficacy in treating dermatological conditions, concerns about toxicity persist, driving the search for safer and more potent retinoids. The molecular mechanisms underlying retinoid activity involve binding to retinoic acid receptors (RARs) and retinoid X receptors (RXRs), leading to transcriptional regulation of target genes. This review seeks to shed light on the possibilities for repurposing retinoids to cover a wider spectrum of therapeutic uses by exploring recent scientific progress. It also aims to offer a more comprehensive understanding of the therapeutic prospects of retinoids and the broader impact of drug repositioning in contemporary medicine.

UV and visible light exposure to hair leads to widespread changes in the hair lipidome

OBJECTIVE

Scalp hair is among the most exposed parts of the human body, yet the impact of visible and UV light on hair lipids, an important structural component of hair, is poorly researched. We have used lipidomics, a broad-based approach to measure lipids in samples, which has hitherto not been applied to UV-exposed hair in the published literature, and could allow for a wider understanding of how UV light impacts on specific hair lipids.

METHODS

Mixed blonde Caucasian hair switches were divided into two groups of five, with half of the hair switches exposed to UV and visible light mimicking normal daytime exposure and half left unexposed. LC-MS lipidomics was used to profile the lipids in the hair samples.

RESULTS

A total of 791 lipids and 32 lipid classes with tentative identifications were detected in the hair samples. Nineteen lipid classes and 397 lipids differed between UV-treated and non-treated hair. The main lipid classes that differed were vitamin A fatty acid esters, sterol esters, several ceramides, mono-, di- and triglycerides, phosphatidylethanolamines (all decreased in UV-exposed hair) and bismonoacylglycerolphosphates, acylcarnitines and acylglycines (all increased in UV-exposed hair). Most detected lipids were decreased in UV-exposed hair, supporting earlier work that has found that UV exposure causes oxidation of lipids which would result in a decrease in most lipid classes.

CONCLUSION

Light exposure to hair has a widespread impact on the hair lipidome. This study also adds to the emerging literature on the hair lipidome, broadening the range of lipid classes reported in hair.

Conformationally Defined Rexinoids for the Prevention of Inflammation and Nonmelanoma Skin Cancers

Compound 1 is a potent rexinoid that is highly effective in cancer chemoprevention but elevates serum triglycerides. In an effort to separate the lipid toxicity from the anticancer activity of 1, we synthesized four new analogs of rexinoid 1, of which three rexinoids did not elevate serum triglycerides. Rexinoids 3 and 4 are twice as potent as rexinoid 1 in binding to Retinoid X receptor (RXR). All-trans retinoic acid (ATRA) plays a key role in maintaining skin homeostasis, and rexinoids 3-6 are highly effective in upregulating the genes responsible for the biosynthesis of ATRA. Inflammation plays a key role in skin cancer, and rexinoids 3 and 4 are highly effective in diminishing LPS-induced inflammation. Rexinoids 3 and 4 are highly effective in preventing UVB-induced nonmelanoma skin cancer (NMSC) without displaying any overt toxicities. Biophysical studies of rexinoids 3 and 5 bound to hRXRα-ligand binding domain (LBD) reveal important conformational and dynamical differences in the ligand binding domain.

Retinoid metabolism: new insights

Vitamin A (retinol) is a critical micronutrient required for the control of stem cell functions, cell differentiation, and cell metabolism in many different cell types, both during embryogenesis and in the adult organism. However, we must obtain vitamin A from food sources. Thus, the uptake and metabolism of vitamin A by intestinal epithelial cells, the storage of vitamin A in the liver, and the metabolism of vitamin A in target cells to more biologically active metabolites, such as retinoic acid (RA) and 4-oxo-RA, must be precisely regulated. Here, I will discuss the enzymes that metabolize vitamin A to RA and the cytochrome P450 Cyp26 family of enzymes that further oxidize RA. Because much progress has been made in understanding the regulation of ALDH1a2 (RALDH2) actions in the intestine, one focus of this review is on the metabolism of vitamin A in intestinal epithelial cells and dendritic cells. Another focus is on recent data that 4-oxo-RA is a ligand required for the maintenance of hematopoietic stem cell dormancy and the important role of RARβ (RARB) in these stem cells. Despite this progress, many questions remain in this research area, which links vitamin A metabolism to nutrition, immune functions, developmental biology, and nuclear receptor pharmacology.

PKMYT1 regulates the proliferation and epithelial‑mesenchymal transition of oral squamous cell carcinoma cells by targeting CCNA2

Oral squamous cell carcinoma (OSCC) has gradually become a global public health issue in recent years. Therefore, the current study aimed to explore the mechanism of OSCC development and to identify a potential target that may be used in its treatment. The expression of protein kinase, membrane-associated tyrosine/threonine 1 (PKMYT1) and cyclin A2 (CCNA2) in SCC-9 cells was determined prior to and following transfection with short hairpin RNA targeting PKMYT1. Cell proliferation, colony-forming ability, migration and invasion were determined using Cell Counting Kit-8, colony formation, wound healing and Transwell assays, respectively. Furthermore, the expression of epithelial-mesenchymal transition (EMT)- and migration-related proteins were evaluated using western blot analysis. Additionally, co-immunoprecipitation was used to verify the binding of PKMYT1 and CCNA2. The results revealed that PKMYT1 was highly expressed in OSCC cells and that PKMYT1 knockdown could inhibit proliferation, colony formation, migration, invasion, EMT and CCNA2 expression in SCC-9 cells. In addition, PKMYT1 was demonstrated to bind to CCNA2, and knocking down PKMYT1 resulted in inhibitory effects on cell proliferation, colony formation ability, migration, invasion and EMT by downregulating CCNA2 expression. PKMYT1 was observed to regulate the proliferation, migration and EMT of OSCC cells by targeting CCNA2, which may be used in the future to improve OSCC treatment.

Retinoic acid exerts sexually dimorphic effects on muscle energy metabolism and function

The retinol dehydrogenase Rdh10 catalyzes the rate-limiting reaction that converts retinol into retinoic acid (RA), an autacoid that regulates energy balance and reduces adiposity. Skeletal muscle contributes to preventing adiposity, by consuming nearly half the energy of a typical human. We report sexually dimorphic differences in energy metabolism and muscle function in Rdh10+/- mice. Relative to wild-type (WT) controls, Rdh10+/- males fed a high-fat diet decrease reliance on fatty-acid oxidation and experience glucose intolerance and insulin resistance. Running endurance decreases 40%. Rdh10+/- females fed this diet increase fatty acid oxidation and experience neither glucose intolerance nor insulin resistance. Running endurance increases 220%. We therefore assessed RA function in the mixed-fiber type gastrocnemius muscles (GM), which contribute to running, rather than standing, and are similar to human GM. RA levels in Rdh10+/- male GM decrease 38% relative to WT. Rdh10+/- male GM increase expression of Myog and reduce Eif6 mRNAs, which reduce and enhance running endurance, respectively. Cox5A, complex IV activity, and ATP decrease. Increased centralized nuclei reveal existence of muscle malady and/or repair in GM fibers. Comparatively, RA in Rdh10+/- female GM decreases by less than half the male decrease, from a more modest decrease in Rdh10 and an increase in the estrogen-induced retinol dehydrogenase Dhrs9. Myog mRNA decreases. Cox5A, complex IV activity, and ATP increase. Centralized GM nuclei do not increase. We conclude that Rdh10/RA affects whole body energy use and insulin resistance partially through sexual dimorphic effects on skeletal muscle gene expression, structure, and mitochondria activity.