Growth inhibition of myeloid leukemia cells by troglitazone, a ligand for peroxisome proliferator activated receptor γ, and retinoids

Peroxisome proliferator activated receptor gamma (PPAR gamma) plays a central role in the process of adipocyte differentiation. This receptor and its heterodimeric partner, retinoid X receptor alpha (RXR alpha), form a DNA-binding complex that regulates transcription of adipocyte-specific genes. Troglitazone, an antidiabetic drug, has recently been identified as a synthetic ligand for PPAR gamma. We studied the effects of troglitazone on proliferation and differentiation of normal and malignant hematopoietic cells. Expression of PPAR gamma was easily detectable by Western blot analyses in all five myeloid leukemia cell lines. Troglitazone alone (10(-5) M) did not induce differentiation in any of the cell lines; however, this compound suppressed the clonal growth (10-75% of inhibition) of all five myeloid leukemia cell lines. Myelomonocytic U937 cells, which were the most responsive to the growth suppressing effects of troglitazone, were arrested in the G(1) phase of the cell cycle when cultured with this compound. Simultaneous treatment of myeloid leukemia cell lines with both troglitazone and a ligand that specifically binds either RXR (LG100268), or retinoic acid receptors (RAR, ATRA, ALART1550), or both (9-cis RA) resulted in additive suppression of clonal growth. In summary, our studies showed that troglitazone when combined with a retinoid was a moderately potent inhibitor of clonogenic growth of acute myeloid leukemia cells.