In vitro activity: Bexarotene treatment at 1 mM and 10 mM for 96 h increases the number of cells with sub-G1 populations and annexin V binding in a dose-dependent manner compared with vehicle controls (DMSO) in well-established CTCL cell lines (MJ, Hut78, and HH), respectively. Bexarotene treatment suppresses the expression of retinoid X receptor alpha and retinoic acid receptor alpha proteins in all three lines compared with untreated controls. Bexarotene treatment decreases the protein levels of survivin, activates caspase-3, and cleaved poly(ADP-Ribose) polymerase, but has no obvious effect on expression of Fas/Fas ligand and bcl-2 proteins in all three CTCL lines. Bexarotene induces a loss of viability and more pronounced inhibition of clonogenic proliferation in HH and Hut-78 cells, whereas the MJ line exhibits resistance. Bexarotene upregulates and activates Bax in sensitive lines, although not enough to signal significant apoptosis. Bexarotene signals both G(1) and G(2)/M arrest by the modulation of critical checkpoint proteins. Bexarotene activates p53 by phosphorylation at Ser15, which influences the binding of p53 to promoters for cell cycle arrest, induces p73 upregulation, and, in concordance, also modulates some p53/p73 downstream target genes, such as p21, Bax, survivin and cdc2.

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