Validation of 1a and related A3 AR ligands as PPARδ antagonists. (A) The effects of 1a, 1c, 3a, and 23 (1 µM) on the 22 (0.03 µM) induced interaction between fluorescein-C33 coactivator peptides and PPARδ LBD in a TR-FRET PPARδ coactivator assay were evaluated. (B) In a TR-FRET PPARδ corepressor assay with SMRT-ID2 peptides, the activities of 23, 24, and 3a (1 µM) were assessed in the condition that 22 (0.1 µM) existed or not. (C) 23, 24, 3a, and 1c were evaluated in a TR-FRET PPARδ corepressor assay with SMRT-ID2 peptides at various concentrations. For functional validation assay for PPARδ antagonism, hBM-MSCs were differentiated in the IDX condition and co-treated with 23, 24, or 3a in the medium. On the 3rd day in culture, total RNA was extracted and Q-RT-PCR was performed for ANGPTL4 (D) and PDK4 (E). GAPDH was used as an internal control for Q-RT-PCR standardization. Values represent the mean ± SD (n = 3, three independent experiments): (*) p ≤ 0.05 and (**) p ≤ 0.01.