INDUCTION OF DIFFERENTIATION AND APOPTOSIS BYAPAG-1 IN ACUTE PROMYELOCYTIC LEUKAEMIA CELLS: P8

This study was carried out to evaluate the potential of APAG-1, anaturally occurring diterpenoid lactone as a differentiating agent inacute promyelocytic leukaemia cells (APL): HL-60 (late FAB-M2),NB4 (FAB-M3) and NB4-R2 (NB4 cell line made resistant to all-trans retinoic acid (ATRA)). In an earlier study, APAG-1showed antitumour activity in breast cancer models (Stanslas et al.2001, Eur J Cancer, 37 (Suppl. 6): 169). In this study APAG-1 ex- hibited 2- and 3-fold increased efficiency in killing HL-60 (IC50 =2.4 ± 0.5 μM) and NB4-R2 (IC50 = 1.5 ± 0.3 μM) cells, respectively compared with NB4 cells (IC50 = 4.5 ± 0.5 μM) (p<0.001). The induction of differentiation in NB4 cells was assessed by theability of the cells to produce superoxide, measured by thereduction of nitroblue tetrazolium (NBT) dye. APAG-1 induced alinear kinetic differentiation effect throughout the 96 hr exposureat IC50 concentration. Failure of retinoic acid receptor (RAR) antag-onist AGN 193109 to reverse the cytotoxic effect of APAG-1 sugg-ests that this compound exerts its effect through an RAR indepe-ndent signalling pathway to induce differentiation, unlike ATRA. Morphologically, APAG-1 induced apoptosis and this was laterconfirmed by the presence of internucleosomal DNAfragmentation of 200 bp ladders on agarose gel electrophoresis. Inconclusion, the abilities of APAG-1 to be effective against primaryNB4 cells by inducing differentiation and apoptosis, and its killingeffect on ATRA-resistant APL cells at a concentration range that isachievable in the plasma i.e. 3 – 30 μM (Stanslas et al. 2001, Eur JCancer, 37 (Suppl. 6): 169) suggest that APAG-1 may be useful inthe treatment of primary and ATRA-relapse APL