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Fenretinide (4-HPR) is a synthetic derivative of all-trans-retinoic acid (ATRA) characterised by improved therapeutic properties and toxicological profile relative to ATRA. 4-HPR has been mostly investigated as an anti-cancer agent, but recent studies showed its promising therapeutic potential for preventing metabolic syndrome. Several biological targets are involved in 4-HPR's activity, leading to the potential use of this molecule for treating different pathologies. However, although 4-HPR displays quite well-understood multitarget promiscuity with regards to pharmacology, interpreting its precise physiological role remains challenging. In addition, despite promising results in vitro, the clinical efficacy of 4-HPR as a chemotherapeutic agent has not been satisfactory so far. Herein, we describe the preparation of a library of 4-HPR analogues, followed by the biological evaluation of their anti-cancer and anti-obesity/diabetic properties. The click-type analogue 3 b showed good capacity to reduce the amount of lipid accumulation in 3T3-L1 adipocytes during differentiation. Furthermore, it showed an IC 50 of 0.53±0.8 μM in cell viability tests on breast cancer cell line MCF-7, together with a good selectivity (SI=121) over noncancerous HEK293 cells. Thus, 3 b was selected as a potential PET tracer to study retinoids in vivo, and the radiosynthesis of [ 18 F]3b was successfully developed. Unfortunately, the stability of [ 18 F]3b turned out to be insufficient to pursue imaging studies., (© 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Purpose: By a scaffold shortening strategy, a small series of retinoidal amides fenretinide (4-HPR) analogs have been synthesized from α, β-ionones and tested for their antiproliferative and differentiating activities, and antioxidant effect., Methods: The antiproliferative activity and triggering of apoptosis of our short retinoids were evaluated by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay and 4'-6-diamidino-2-phenylindole staining and microscope evaluation after 3- or 6-day exposure, while their differentiating activity was established by the analysis of the expression of the CD11b marker of differentiation in treated HL60 target cells and by the superoxide production assayed colorimetrically by the nitro blue tetrazolium-reducing activity assay. Finally, the antioxidant activity was determined by the 2,2'-azino-bis-(3-ethylbenzthiazoline-6-sulphonic acid) diammonium salt radical cation decolourisation assay utilizing the antioxidant Trolox (6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid) as reference (Trolox equivalent antioxidant capacity, or TEAC). Docking analysis was performed to study the binding features to the Retinoic Acid Receptor alpha (RARα)., Results: While no pharmacologically relevant antiproliferative activity was evidenced, some of our short retinoids showed a differentiating and antioxidant activity similar to that of 4-HPR. In particular, compound 2b6 displayed a scavenging activity two times more efficient than 4-HPR itself. Finally, the docking analysis showed that these short retinoids, like 4-HPR, bind to the RARα protein with good fitness scores., Conclusion: Our data could pave the way for the design of new potent and less toxic antioxidant and differentiating compounds related to 4-HPR.

Retinoids are a class of compounds with structural similarity to vitamin A. These compounds inhibit the proliferation of many cancer cell lines but have had limited medical application as they are often toxic at therapeutic levels. Efforts to synthesize retinoids with a greater therapeutic index have met with limited success. 4-[(1E)-2-(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-2-naphthalenyl)-1-propen-1-yl]benzoic acid (TTNPB) is one of the most biologically active all-trans-retinoic acid (atRA) analogues and is highly teratogenic. In this study, we show that modification of the TTNPB carboxyl group with an N-(4-hydroxyphenyl)amido (4HPTTNPB) or a 4-hydroxybenzyl (4HBTTNPB) group changes the activity of the compound in cell culture and in vivo. Unlike TTNPB, both compounds induce apoptosis in cancer cells and bind poorly to the retinoic acid receptors (RARs). Like the similarly modified all-trans-retinoic acid (atRA) analogues N-(4-hydroxyphenyl)retinamide (4-HPR/fenretinide) and 4-hydroxybenzylretinone (4-HBR), 4HBTTNPB is a potent activator of components of the ER stress pathway. The amide-linked analogue, 4HPTTNPB, is less toxic to developing embryos than the parent TTNPB, and most significantly, the 4-hydroxybenzyl-modified compound (4HBTTNPB) that cannot be hydrolyzed in vivo to the parent TTNPB compound is nearly devoid of teratogenic liability.

Serum retinol binding protein (sRBP) is released from the liver as a complex with transthyretin (TTR), a process under the control of dietary retinol. Elevated levels of sRBP may be involved in inhibiting cellular responses to insulin and in generating first insulin resistance and then type 2 diabetes, offering a new target for therapeutic attack for these conditions. A series of retinoid analogues were synthesized and examined for their binding to sRBP and their ability to disrupt the sRBP-TTR and sRBP-sRBP receptor interactions. A number inhibit the sRBP-TTR and sRBP-sRBP receptor interactions as well as or better than Fenretinide (FEN), presenting a potential novel dual mechanism of action and perhaps offering a new therapeutic intervention against type 2 diabetes and its development. Shortening the chain length of the FEN derivative substantially abolished binding to sRBP, indicating that the strength of the interaction lies in the polyene chain region. Differences in potency against the sRBP-TTR and sRBP-sRBP receptor interactions suggest variant effects of the compounds on the two loops of sRBP guarding the entrance of the binding pocket that are responsible for these two protein-protein interactions.

Increasing evidence demonstrates that three classes of molecules originally derived from all-trans-retinoic acid and its synthetic analogues, which function by interacting with the retinoid nuclear receptors, exert their anticancer activities through alternative signaling pathways. Thus, the methylene-linked analogues (4-HBR, 4-HPRCG, and 4-HBRCG) of N-(4-hydroxyphenyl) retinamide (4-HPR) and its O-glucuronide metabolite (4-HPROG), the cinnamic acid analogues (3-Cl-AHPC and AHPC/ST1926) of 6-[3'-(1-adamantyl)-4'-hydroxyphenyl)]-2-naphthalenecarboxylic acid, and N-(2,3-dihydro-2,2,4,4-tetramethyl-6-benzothiopyranyl),N'-(4-nitrophenyl)thiourea (SHetA2) induce cancer cell-cycle arrest and apoptosis mediated most likely through mitochondrial and/or endoplasmic reticulum stress responses. Structure-activity relationships and potential for clinical translation as anticancer therapeutics are presented.

Rhabdoid tumors (RTs) are aggressive pediatric malignancies with poor prognosis that arise due to loss of the hSNF5/INI1 tumor suppressor. Molecular studies indicate that cyclin D1, a downstream effector of INI1 is up regulated in RT, and is essential for this tumor formation. Previously we demonstrated that 4-HPR, a synthetic retinoid that targets Cyclin D1, is a potential chemotherapeutic agent for RT. To facilitate further chemical development of this retinoid, and to determine its active moiety, we synthesized small chemical libraries of 4-HPR and tested their cytotoxic effect on RT cells. We synthesized 4-HPR (1) and the derivatives (5a-5n) starting from retinoic acid. First, retinoic acid was converted to acid chloride derivatives, then in the presence of DMF, base, and aniline derivatives, we synthesized the corresponding 4-hydroxy phenyl amine derivatives (5a-5n). This procedure gave 70-90% yield. Then, the 4-HPR derivatives were tested for their ability to inhibit RT cells using an in vitro cell survival assay. We found that the 4-hydroxy group at para-position is essential for cytotoxic activity against RT cells. Furthermore, we identified a few derivatives of 4-HPR with higher cytotoxic potencies than 4-HPR. In addition, we demonstrate that either chloro, fluoro or iodo derivatives at meta-position of phenyl ring retain the cytotoxic activity. Interestingly, substitution of iodo-moiety at meta-position (5j) substantially increased the efficacy (IC(50) approximately 3muM, Fig. 1D). These results indicate that chemical modification of 4-HPR may result in derivatives with increased therapeutic potential for RTs and that halogen substituted 4-HPR that retain the activity can be synthesized for further therapeutic and diagnostic use.

Preclinical models suggest that retinoids inhibit mammary carcinogenesis. The induction of apoptosis is a unique feature of fenretinide, the most-studied retinoid in clinical trials of breast cancer chemoprevention, owing to its selective accumulation in breast tissue and its favorable toxicological profile. In a Phase III breast cancer prevention trial, fenretinide showed a strong trend of reduction of incidence of second breast malignancies in premenopausal women, which was confirmed by 15 years of follow-up. This warrants further research on the mechanisms of action and potential efficacy of fenretinide and provides the rationale for a Phase III primary prevention trial in young women at high risk for breast cancer. This review will highlight the role of fenretinide in breast cancer chemoprevention.

Using solid phase-assisted synthesis and purification, a 49 member library of analogs of the mammary tumor chemopreventive retinoid N-(4-hydroxyphenyl)retinamide (4-HPR) has been prepared. After prescreening for growth inhibitory activity in human mammary tumor cells (MCF-7) in culture, most of those analogs which showed activity (12 of them) were assayed for apoptosis-inducing activity in the MCF-7 cells. At least 3 of the analogs (13, 24, and 28) showed activity approaching that of 4-HPR.

Novel aminophenol analogues were synthesized based on the structure of fenretinide (N-(4-hydroxyphenyl)retinamide, 5), which is a potent anticancer agent. Our findings showed that the anticancer activities of 5 were due to the side chain attached to the aminophenol moiety. A p-octylaminophenol (p-OAP) provided the most potent anticancer activity among p-alkylaminophenols examined. In this study, we investigated anticancer activities against various cancer cell lines by the new aminophenols, p-dodecylaminophenol (1), p-decylaminophenol (2), N-(4-hydroxyphenyl)dodecananamide (3), and N-(4-hydroxyphenyl)decananamide (4), which exhibits a side chain as long as 5. Cell growth of breast cancer (MCF-7, MCF-7/Adr(R)), prostate cancer (DU-145), and leukemia (HL60) cells was suppressed by 1 and 2 in a fashion dependent on the length of the alkyl chain attached to the aminophenol. In contrast, 3 and 4 were extremely weak. Compound 5 was less potent than 1. Cell growth of liver cancer (HepG2) was not markedly affected by these compounds. In addition, apoptosis of HL60 cells was induced by 1 and 2 in a chain length-dependent manner, but not by 3 and 4. Incorporation of compounds into HL60 cells was in the order 1>2=3>4. These results indicated that anticancer activities for 1 and 2 are correlated with their incorporation into cancer cells and their capability to induce apoptosis, but not for 3 and 4. Compound 1, a potent anticancer agent with potency strikingly greater than 5, may potentially be useful in clinic.

All-trans retinoic acid analogues such as N-(4-hydroxyphenyl)retinamide (4-HPR) are effective chemopreventive and chemotherapeutic agents but their utility has been hampered by dose-limiting side effects. The glucuronide derivatives of 4-HPR, the oxygen-linked 4-HPROG and the carbon-linked 4-HPRCG, have been found to be more effective agents. The synthetic route to the fully C-linked analogue of 4-HPROG (4-HBRCG), which employs Suzuki coupling and Umpolung chemistries as key methodologies, is shown. The results of this study show 4-HBRCG to be an effective chemotherapeutic agent in a rat mammary tumor model while being devoid of classical retinoid toxicities.

Retinoic acid and its amide derivative, N-(4-hydroxyphenyl)retinamide (4-HPR), have been proposed as chemopreventative and chemotherapeutic agents. However, their low cytotoxic activity and water solubility limit their clinical use. In this study, we synthesized novel retinoid derivatives with improved cytotoxicity against cancer cells and increased hygroscopicity. Our syntheses were preceded by selective O-acylation and N-acylation, which led to the production of retinoate and retinamide derivatives, respectively, in one pot directly from aminophenol derivatives and retinoic acid without protection. Transcription assays in COS-1 cells indicated that the N-acylated derivatives (2A-5A) and 4-HPR (1A) were much weaker ligands for all three subtypes of retinoic acid receptor (RAR) than all-trans retinoic acid (ATRA), although they showed some selectivity for RARbeta and RARgamma. In contrast, the O-acylated retinoate derivatives (1B-5B) activated all three RAR isotypes without specificity to an extent similar to ATRA. The cytotoxicity was determined using an MTT assay with HCT116 colon cancer cells, and the IC(50) of N-acylated retinamide derivative 4A and O-acylated retinoate derivative 5B was 1.67 microM and 0.65 microM, respectively, which are about five and 13-fold better than that of 4-HPR (8.21 microM), a prototype N-acylated derivative. When retinoate derivative 5B was coupled to organic acid salts, the resulting salt derivatives 5C and 5D had RAR activation and cytotoxicity similar to those of 5B. These data may delineate the relationship between the structure and function of retinoate and retinamide derivatives.

Retinoic acid analogues such as N-(4-hydroxyphenyl)retinamide (4-HPR) are effective chemopreventatives and chemotherapeutics for numerous types of cancer. The C-linked analogue of the O-glucuronide of 4-HPR (4-HPRCG) has been shown to be a more effective agent. The synthetic route to this molecule has been significantly improved by access to a key C-benzyl-glucuronide intermediate through employment of a Suzuki coupling reaction between an exoanomeric methylene sugar and an aryl bromide. Preliminary evidence shows 4-HPRCG has chemotherapeutic activity.

The synthesis of a nonhydrolyzable, carbon-linked analogue (4-HBR) of the retinoid N-(4-hydroxyphenyl)retinamide (4-HPR) using Umpolung methods is described. Preliminary studies of biological activity show 4-HBR is similar to 4-HPR in its actions although a potentially relevant and desirable difference is its reduced suppression of plasma vitamin A levels. These results show that 4-HPR does not have to be hydrolyzed to retinoic acid to produce its chemotherapeutic effects.

The cellular transport, metabolism and biological activity of retinoids are mediated by their specific binding proteins and nuclear receptors. For an understanding of the mode of action of retinoids with potential cancer chemopreventive or other biological activity, it is important to study their interactions with these binding proteins and receptors. In our attempts to understand the action of N-(4-hydroxyphenyl)retinamide (4HPR) and other retinamides in the prevention of cancer, we observed that 4HPR binds to a serum protein with a molecular size of approximately 20,000. The retinoid, however, did not show any binding affinity for cellular retinol-binding protein (CRABP) or for cellular retinoic acid-binding protein (CRABP). However, it showed binding affinity for the nuclear receptors of retinoic acid (RARs) equivalent to 15% of that of retinoic acid. The physicochemical properties of the 4HPR binding protein in the serum were identical to those of serum retinol binding protein (RBP). Antibodies against RBP quantitatively immunoprecipitated the protein-4HPR complex, confirming that the retinoid specifically binds to RBP. Although retinol and 4HPR cross-competed for RBP binding, N-phenylretinamide, in which the 4-hydroxyl group is absent, and N-(4-methoxyphenyl)retinamide, a major cellular metabolite of 4HPR, in which the hydroxyl group is blocked, did not show affinity for the binding protein. The results indicate that the hydroxyl group of 4HPR is essential for binding of this type of retinoid to RBP. Thus, our studies suggest that serum transport of 4HPR may be facilitated by RBP. To bind more efficiently to CRBP, CRABP, or RARs/RXRs, the retinoid may require further metabolic change.