Synthesis and evaluation of synthetic retinoid derivatives as inducers of stem cell differentiation

Abstract

All-trans-retinoic acid (ATRA) and its associated analogues are important mediators of cell differentiation and function during the development of the nervous system. It is well known that ATRA can induce the differentiation of neural tissues from human pluripotent stem cells. However, it is not always appreciated that ATRA is highly susceptible to isomerisation when in solution, which can influence the effective concentration of ATRA and subsequently its biological activity. To address this source of variability, synthetic retinoid analogues have been designed and synthesised that retain stability during use and maintain biological function in comparison to ATRA. It is also shown that subtle modifications to the structure of the synthetic retinoid compound impacts significantly on biological activity, as when exposed to cultured human pluripotent stem cells, synthetic retinoid 4-(5,5,8,8-tetramethyl-5,6,7,8-tetrahydronaphthalen-2-ylethynyl)benzoic acid, 4a (para-isomer), induces neural differentiation similarly to ATRA. In contrast, stem cells exposed to synthetic retinoid 3-(5,5,8,8-tetramethyl-5,6,7,8-tetrahydronaphthalen-2-ylethynyl)benzoic acid, 4b (meta-isomer), produce very few neurons and large numbers of epithelial-like cells. This type of structure-activity-relationship information for such synthetic retinoid compounds will further the ability to design more targeted systems capable of mediating robust and reproducible tissue differentiation.

The molecular basis of the interactions between synthetic retinoic acid analogues and the retinoic acid receptors

“…9 Thus, although EC23 and EC19 are chemically similar, they have substantially different biological effects.…”

“…As a result, the linear retinoid ATRA mainly acts as a ligand for RARs while 9CRA exhibits high binding affinity for both the RARs and RXRs. 22,26,27 Although EC23 is more effective than either ATRA or EC19 in differentiation assays, 9 cell-based biological assays cannot be used to elucidate the affinities of synthetic retinoids for RAR receptor types because the specificities of different RARs as drivers of biological responses are poorly understood. Therefore, the molecular basis of the ligand-receptor interactions that underpin these differences in biological activity remains unclear.…”

“…7,8 While 9CRA may also have a cellular role as a ligand to activate transcription factors, a natural physiological function for 13CRA as a transcription-factor ligand is less certain. 5 We have previously described two light-stable synthetic retinoid analogues, EC23 and EC19 (Figure 1, left), 9 differing from each other only in the position of the carboxylic acid group on the terminal substituted ring. EC23 was designed to mimic ATRA, whereas the meta-position carboxylic acid of EC19 changes the effective geometry of the molecule in a similar manner to the alkene geometry differences between ATRA and 13CRA.…”

“…Previous studies showed that EC23 induced neuronal differentiation in pluripotent stem cells at a lower Figure 1: Left, chemical structures of endogenous retinoids ATRA and 9CRA, synthetic retinoids EC23 and EC19, and synthetic retinoid esters EC23Me and EC19Me. 3,9 Right, proposed investigation into the interactions of natural and synthetic retinoids by combining in silico docking studies with an in vitro binding assay.…”

Embryonic stem cell application in drug discovery

“…An outstanding landmark in the past decade has been the development between stem cell biology and chemistry [1][2][3][4][5][6] . The combination of the two fields will likely provide an impetus for revealing intricate molecular interactions and functions under complex cellular differentiation, which offers systems for drug discovery and sources for potential cell therapy [7][8][9][10] .…”