The anti-tumor agent, p-DDAP potently suppresses proliferation through apoptosis in human neuroblastoma NB-39-nu cells

[Prevention and Treatment of Cancer with Vitamin A and Its Derivatives: Cell Differentiation and Proliferation]

Normal differentiation and proliferation of cells are essential for maintaining homeostasis. Following the successful completion of whole genome sequencing, protein modification has been attracted increasing attention in order to understand the roles of protein diversification in protein function and to elucidate molecular targets in mechanisms of signal transduction. Vitamin A is an essential nutrient for health maintenance. It is present as β-carotene in green and yellow vegetables and retinyl ester in animal products and absorbed into the body from the intestines. After ingestion, it is converted to retinol and oxidized in target cells to retinal, which plays critical roles in vision. It is then further oxidized to retinoic acid (RA), which exhibits a number of effects prior to being metabolized by cytochrome P450 and excreted from the body. Since RA exhibits cell differentiation-inducing actions, it is used as a therapeutic agent for patients with acute promyelocytic leukemia. The current paper describes: (1) HL60 cell differentiation and cell differentiation induction therapy by RA; (2) roles played by RA and retinal and their mechanisms of action; (3) retinoylation, post-translational protein-modified by RA, a novel non-genomic RA mechanism of action without RA receptor; (4) new actions of β-carotene and retinol in vivo and (5) potent anticancer effects of p-dodecylaminophenol (p-DDAP), a novel vitamin A derivative created from the RA derivative fenretinide. We propose that nutritional management of vitamin A can be effective at preventing and treating diseases, and that p-DDAP is a promising anticancer drug.

Examination of aminophenol-containing compounds designed as antiproliferative agents and potential atypical retinoids

Retinoic acid (RA, 1), an oxidized form of vitamin A, binds to retinoic acid receptors (RAR) and retinoid X receptors (RXR) to regulate gene expression and has important functions such as cell proliferation and differentiation. Synthetic ligands regarding RAR and RXR have been devised for the treatment of various diseases, particularly promyelocytic leukemia, but their side effects have led to the development of new, less toxic therapeutic agents. Fenretinide (4-HPR, 2), an aminophenol derivative of RA, exhibits potent antiproliferative activity without binding to RAR/RXR, but its clinical trial was discontinued due to side effects of impaired dark adaptation. Assuming that the cyclohexene ring of 4-HPR is the cause of the side effects, methylaminophenol was discovered through structure-activity relationship research, and p-dodecylaminophenol (p-DDAP, 3), which has no side effects or toxicity and is effective against a wide range of cancers, was developed. Therefore, we thought that introducing the motif carboxylic acid found in retinoids, could potentially enhance the anti-proliferative effects. Introducing chain terminal carboxylic functionality into potent p-alkylaminophenols significantly attenuated antiproliferative potencies, while a similar structural modification of weakly potent p-acylaminophenols enhanced growth inhibitory potencies. However, conversion of the carboxylic acid moieties to their methyl esters completely abolished the cell growth inhibitory effects of both series. Insertion of a carboxylic acid moiety, which is important for binding to RA receptors, abolishes the action of p-alkylaminophenols, but enhances the action of p-acylaminophenols. This suggests that the amido functionality may be important for the growth inhibitory effects of the carboxylic acids.

Vitamin A in health care: Suppression of growth and induction of differentiation in cancer cells by vitamin A and its derivatives and their mechanisms of action

Vitamin A is an important micro-essential nutrient, whose primary dietary source is retinyl esters. In addition, β-carotene (pro-vitamin A) is a precursor of vitamin A contained in green and yellow vegetables that is converted to retinol in the body after ingestion. Retinol is oxidized to produce visual retinal, which is further oxidized to retinoic acid (RA), which is used as a therapeutic agent for patients with promyelocytic leukemia. Thus, the effects of retinal and RA are well known. In this paper, we will introduce (1) vitamin A circulation in the body, (2) the actions and mechanisms of retinal and RA, (3) retinoylation: another RA mechanism not depending on RA receptors, (4) the relationship between cancer and actions of retinol or β-carotene, whose roles in vivo are still unknown, and (5) anti-cancer actions of vitamin A derivatives derived from fenretinide (4-HPR). We propose that vitamin A nutritional management is effective in the prevention of cancer.

Anticancer efficacy of p-dodecylaminophenol against high-risk and refractory neuroblastoma cells in vitro and in vivo

Neuroblastoma is an aggressive and drug-resistant refractory cancer. The human high-risk neuroblastoma cell line, SK-N-AS (non-amplified N-myc) is derived from stromal cells and it is resistant to treatment with retinoic acid (1, RA), which is a chemotherapeutic agent used to induce neuronal cellular differentiation of neuroblastomas. We have developed p-dodecylaminophenol (3, p-DDAP), based on N-(4-hydroxyphenyl)retinamide (2, 4-HPR), a synthetic amide of 1, since 1 and 2 are associated with the side-effect of nyctalopia. In order to evaluate the effects of 3 on high-risk neuroblastomas, we employed SK-N-AS cells as well asa second high-risk human neuroblastoma cell line, IMR-32, which is derived from neuronal cells (amplified N-myc, drug sensitive). Compound 3 suppressed cell growth of SK-N-AS and IMR-32 cells more effectively than 1, 2, p-decylaminophenol (4, p-DAP), N-(4-hydroxyphenyl)dodecananamide (5, 4-HPDD) or N-(4-hydroxyphenyl)decananamide (6, 4-HPD). In SK-N-AS cells, 3 induced G₀/G₁ arrest and apoptosis to a greater extent than 1 and 2. In IMR-32 cells, 3 induced apoptosis to a similar extent as 1 and 2, potentially by inhibiting N-myc expression. In addition, i.p. administration of 3 suppressed tumor growth in SK-N-AS-implanted mice in vivo. Since 3 showed no effects on blood retinol concentrations, in contrast to reductions following the administration of 2, it exhibited excellent anticancer efficacy against high-risk neuroblastoma SK-N-AS and IMR-32 expressing distinct levels of N-myc. Compound 3 may have potential for clinical use in the treatment of refractory neuroblastoma with reduced side effects.