Small Molecules for Controlling Stem Cell Differentiation

Abstract

Stem cell homeostasis and differentiation are controlled by the complex interplay of a wide range of signalling pathways and small molecules, including all-trans-retinoic acid (ATRA). The endogenous effects elicited by ATRA, have led to its use in numerous in vitro protocols as a tool for cell differentiation. However, ATRA isomerises and degrades under standard laboratory conditions and furthermore, is rapidly metabolised in vivo, which leads to pleotropic effects and a high efficacious dose response. Consequently, synthetic analogues that are structurally and/or functionally equivalent to ATRA have been developed, as alternative pharmacological tools to further the understanding of this molecular pathway and control cell differentiation.In this study a small library of synthetic retinoids were prepared, which were designed to probe structural size, conformation and biological function, while being more resistant to cellular metabolism and isomerisation. Their stability towards fluorescent light was examined along with their activity in four different stem cell models. Two compounds, AH60 and AH61 were found to inhibit cellular proliferation and induce neural differentiation, through acting on the retinoic acid receptor pathway. Compared to ATRA, AH60 was approximately 10-fold more active, while AH61 was 100-fold more active in two of the cell models tested. These compounds are described comprehensively herein, and should be suitable and convenient alternatives to ATRA and 13cRA for use in in vitro studies carried out by cell and molecular biologists. In addition, an unrelated small molecule, neuropathiazol, has been synthesised to further characterise both the chemistry involved in its production and its biological activity in controlling cell differentiation. This compound was highlighted in the literature as an alternative to ATRA, for inducing neural differentiation in neural progenitor cells. We have further investigated its potential to differentiate other neural stem cell types and pluripotent stem cells. In addition potential analogues of neuropathiazol are discussed, as compounds of this nature are potentially highly useful for selectively controlling neural differentiation.