A112, a tamibarotene dimethylaminoethyl ester, may inhibit human leukemia cell growth more potently than tamibarotene

摘要

A112 is a tamibarotene dimethylaminoethyl ester considered a candidate compound for the treatment of acute promyelocytic leukemia (APL) and acute myeloid leukemia (AML). Our goal in this study was to evaluate the efficacy of anti-cancer activity, beginning by studying its inhibitory effects on leukemia cells and then comparing it to tamibarotene. A112 effectively inhibited the growth of HL-60 and NB4 cells as estimated by the 3-(4,5-dimethylthiazol-2-yl)- 2,5-diphenyltetrazolium bromide (MTT) assay. The inhibitory effect of A112 was confirmed in mice in which A112 delayed the growth of HL-60 xenografts after 3 weeks' injection. The efficacy of A112 on leukemia cell growth was stronger than that of tamibarotene at the same dosage. The detection of A112 and tamibarotene in plasma of rats showed that A112 might sustain release of its hydrolysate tamibarotene, and the concentration was maintained at a higher level and for a longer time than that of tamibarotene injection. We studied the differentiation morphologies of leukemic cells exposed to A112 or tamibarotene. The number of differentiated NB4 cells was increased, suggesting that A112 possessed differentiation activity in the inhibition of leukemia growth. Further studies showed that the expression of CD11b, a marker of terminal granulocyte differentiation, was increased as estimated by flow cytometry with a direct immunofluorescence assay. A112 was found to induce the activation of CCAAT/enhancer-binding protein β (C/EBPβ) and cyclin-dependent kinase (CDK) inhibitors p21 Waf1/cip1 and p27 Kip1 while cell growth was inhibited. These activities of A112 were greater than those of tamibarotene. The higher efficacy of A112 was also evidenced by induction of apoptosis in leukemia cells. A112 induced a greater number of annexin V-positive cells than did tamibarotene as measured by flow cytometry analysis. Treatment of mice with A112 resulted in stronger terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining in HL-60 xenografts. Western blot analysis revealed that A112 increased the expression of caspase-3, caspase-9 and cleaved poly(ADP-ribose) polymerase (PARP) in leukemia cells both in vitro and in vivo, indicating that induction of apoptosis was involved in the inhibition of leukemia growth. Taken together, these results suggest that A112 is a highly effective derivative of trans retinoic acid and a potential candidate compound for the treatment of leukemia.