Retinoids play a major role in a wide variety of biological functions, such as cell differentiation, proliferation and embryonic development in vertebrates. 1 All-trans-retinoid acid (ATRA, Fig. 1), 13-cis-retinoid acid (13-cis-RA, Fig. 1), 9-cis-retinoid acid (9-cis-RA, Panretin®, Fig. 1) and more recently the RXR selective LGD1069 (Targretin®, Fig. 1), have been administered for treatment of numerous skin diseases like psoriasis, acne, Karposi's ...