N-(4-HYDROXYPHENYL)RETINAMIDE INDUCES APOPTOSIS IN HUMAN LEUKEMIA HL-60 CELLS AND MEDIATES VIMENTIN DOWN-REGULATION

N-(4-Hydroxyphenyl)retinamide (HPR) is a synthetic retinoid with antic ancer properties and lower toxicity than all-trans retinoic acid (RA). We have studied the effects of HPR on apoptosis and differentiation i n the human promyelocytic leukemia HL-60 cell line. In addition, we ha ve tested the hypothesis that vimentin expression after HPR and RA, ta ken as indirect evidence of the mechanisms of action of the two retino ids, may be different. Quantitative evaluation of the percentage of ap optotic cells was carried out on a cell by cell basis by the flow cyto metric DNA-content in situ-terminal-deoxynucleotydil-transferase (TdT assay). HPR was found to clearly induce apoptosis, while RA: instead, induced differentiation without apoptosis. These data confirm previous observations. Vimentin protein content was evaluated by flow cytometr y with use of monoclonal antibodies simultaneously with DNA content. W e found that HPR treated apoptotic cells were characterized by negativ e vimentin expression, while the HPR treated non apoptotic cells had a bout the same level of vimentin as the RA treated cells. These latter findings suggest that HPR may induce a functional effect (apoptosis) b y a mechanism of action different from that of RA. Further work is nec essary to clarify this finding.