Advances in biosynthesis of 7-Dehydrocholesterol through de novo cell factory strategies

7-Dehydrocholesterol (7-DHC) is an important sterol for maintaining human health and is present in the skin. After sun exposure, 7-DHC in the skin is converted to vitamin D3 to strengthen the immune system. In recent years, synthetic biology has gained importance due to the effective and efficient production of various important compounds using microorganisms. Despite the understanding of the mechanisms and pathways of 7-DHC biosynthesis, achieving higher production yields remains a significant challenge. This review aims to provide a comprehensive overview of the current state of 7-DHC biosynthesis. Various synthetic strategies including optimization of rate-limiting enzymes, metabolic fluxes, redox balance, and subcellular localization are discussed. Moreover, the role of omics technology in designing important proteins and gene editing techniques for strain modification to efficiently synthesize 7-DHC will also be discussed.

Comparative study of ergosterol and 7-dehydrocholesterol and their endoperoxides: Generation, identification, and impact in phospholipid membranes and melanoma cells

Melanoma is an aggressive cancer that has attracted attention in recent years due to its high mortality rate of 80%. Damage caused by oxidative stress generated by radical (type I reaction) and singlet oxygen, 1O2 (type II reaction) oxidative reactions may induce cancer. Thus, studies that aim to unveil the mechanism that drives these oxidative damage processes become relevant. Ergosterol, an analogue of 7-dehydrocholesterol, important in the structure of cell membranes, is widely explored in cancer treatment. However, to date little is known about the impact of different oxidative reactions on these sterols in melanoma treatment, and conflicting results about their effectiveness complicates the understanding of their role in oxidative damage. Our results highlight differences among ergosterol, 7-dehydrocholesterol (7-DHC), and cholesterol in membrane properties when subjected to distinct oxidative reactions. Furthermore, we conducted a comparative study exploring the mechanisms of cell damage by photodynamic treatment in A375 melanoma. Notably, endoperoxides from ergosterol and 7-DHC generated by 1O2 showed superior efficacy in reducing the viability of A375 cells compared to their precursor molecules. We also describe a step-by-step process to produce and identify endoperoxides derived from ergosterol and 7-DHC. While further studies are needed, this work provides new insights for understanding cancer cell death induced by different oxidative reactions in the presence of biologically relevant sterols.

Novel Lipid-Based Carriers of Provitamin D3: Synthesis and Spectroscopic Characterization of Acylglycerol Conjugated with 7-Dehydrocholesterol Residue and Its Glycerophospholipid Analogue

The aim of this research was to design and synthesize new lipid conjugates of 7-DHC that could serve as a new storage form of esterified provitamin D3, increasing the reservoir of this biomolecule in the epidermis and enabling controlled production of vitamin D3 even during periods of sunlight deficiency. Acylglycerol and glycerophospholipid containing succinate-linked provitamin D3 at the sn-2 position of the glycerol backbone were synthesized from dihydroxyacetone (DHA) and sn-glycerophosphocholine (GPC), respectively. The three-step synthesis of 1,3-dipalmitoyl-2-(7-dehydrocholesterylsuccinoyl)glycerol involved the esterification of DHA with palmitic acid, reduction of the carbonyl group, and conjugation of the resulting 1,3-dipalmitoylglycerol with 7-dehydrocholesterol hemisuccinate (7-DHC HS). The use of NaBH3CN as a reducing agent was crucial to avoid acyl migration and achieve the final product with 100% regioisomeric purity. For the preparation of 1-palmitoyl-2-(7-dehydrocholesterylsuccinoyl)-sn-glycero-3-phosphocholine, a two-step process was applied, involving the esterification of GPC at the sn-1 position with palmitic acid, followed by the conjugation of 1-palmitoyl-sn-glycero-3-phosphocholine with 7-DHC HS. Alongside the main product, a small amount of its regioisomer with provitamin D3 linked at the sn-1 position and palmitic acid at the sn-2 position was detected, indicating acyl migration from the sn-1 to the sn-2 position in the intermediate 1-palmitoyl-sn-glycerophosphocholine. The synthesized novel lipids were fully characterized using spectroscopic methods. They can find applications as novel lipid-based prodrugs as additives to sunscreen creams.

Nano-assemblies from J-aggregated dyes to improve the selectivity of a H2S-activatable photosensitizer

We report J-aggregates of a boron dipyrromethene derivative (BDP-Nit) as an H₂S-activatable nano-photosensitizer. The closely packed BDP-Nit in J-aggregates exhibits high selectivity to H₂S over biothiols to produce an active photosensitizer.

Nanomaterials-based photosensitizers and delivery systems for photodynamic cancer therapy

The increasing cancer morbidity and mortality requires the development of high-efficiency and low-toxicity anticancer approaches. In recent years, photodynamic therapy (PDT) has attracted much attention in cancer therapy due to its non-invasive features and low side effects. Photosensitizer (PS) is one of the key factors of PDT, and its successful delivery largely determines the outcome of PDT. Although a few PS molecules have been approved for clinical use, PDT is still limited by the low stability and poor tumor targeting capacity of PSs. Various nanomaterial systems have shown great potentials in improving PDT, such as metal nanoparticles, graphene-based nanomaterials, liposomes, ROS-sensitive nanocarriers and supramolecular nanomaterials. The small molecular PSs can be loaded in functional nanomaterials to enhance the PS stability and tumor targeted delivery, and some functionalized nanomaterials themselves can be directly used as PSs. Herein, we aim to provide a comprehensive understanding of PDT, and summarize the recent progress of nanomaterials-based PSs and delivery systems in anticancer PDT. In addition, the concerns of nanomaterials-based PDT including low tumor targeting capacity, limited light penetration, hypoxia and nonspecific protein corona formation are discussed. The possible solutions to these concerns are also discussed.

Bioorthogonal Assembly Based on Metallophilic Interactions for Selective Imaging and PDT Treatment of Cancer Cells

Precise control of the luminescence and singlet oxygen generation is important for selective photo-theranostics applications. In this work, bioorthogonal assembly based on d10···d10 metallophilic interactions was first proposed for selective...

7-dehydrocholesterol suppresses melanoma cell proliferation and invasion via Akt1/NF-κB signaling

Melanoma is the most lethal cutaneous cancer with a high metastatic rate worldwide, causing ~55,500 deaths annually. Although the selective B-Raf oncogene serine/threonine-kinase (BRAF) inhibitors, dabrafenib and vemurafenib, have been approved for the treatment of BRAF-mutant metastatic melanoma, the 5-year survival rate remains unfavorable due to acquired therapy resistance. Therefore, it is of great importance to develop alternative therapeutic drugs and uncover their mechanisms for the treatment of melanoma. 7-dehydrocholesterol (7-DHC) has been demonstrated to inhibit melanoma, but the mechanism is unclear. Therefore, the present study aimed to elucidate the mechanisms of the inhibitory effect of 7-DHC in melanoma cells via analyzing the proliferation, migration, apoptosis, cell cycle and transcriptional sequencing of melanoma cells treated with 7-DHC, as well as constructing a gene signature according to public data of patients with melanoma. In the present study, 7-DHC, the precursor of vitamin D₃, was able to induce apoptosis and inhibit cell proliferation and invasion of melanoma cells in a dose-dependent manner. RNA sequencing of melanoma cells treated with different concentrations of 7-DHC revealed that, compared with untreated melanoma cells, 65 genes were downregulated, and genes involved in the regulation of NF-ĸB import into the nucleus and NF-ĸB signaling were significantly repressed. Consistently, the Akt kinase family was one of most common somatic mutation hotspots in patients with melanoma according to The Cancer Genome Atlas enrichment analysis. Furthermore, 7-DHC decreased the phosphorylation of Akt1-Ser473 rather than that of MEK1, and the decreased phosphorylation of Akt1 subsequently inhibited the translocation of free RELA proto-oncogene NF-κB subunit to the nucleus. Finally, by intersecting downregulated genes by 7-DHC treatment and upregulated genes in patients with melanoma, a 7-DHC gene signature was identified, which was negatively associated with the prognosis. Overall, the present results demonstrated that 7-DHC suppressed melanoma cell proliferation and invasion via the Akt1/NF-ĸB signaling pathway, and 7-DHC key target genes were negatively associated with the prognosis. These findings highlight the potential application of 7-DHC for the treatment of melanoma in the future.

Smart use of “ping-pong” energy transfer to improve the two-photon photodynamic activity of an Ir(iii) complex

A two-photon excited “Ping-Pong” type energy transfer process is for the first time disclosed for enhancing two-photon PDT.