Induction of apoptosis in retinoid-refractory acute myelogenous leukemia by a novel AHPN analog.

Acute myelogenous leukemia (AML) is a heterogeneous disease consisting of a variety of different leukemic subtypes. While acute promyelocytic leukemia displays marked sensitivity to the differentiating effects of trans-retinoic acid (tRA), other subtypes of AML display resistance. We now describe a novel compound (E)-4-[3-(1-adamantyl)-4-hydroxyphenyl]-3-chlorocinnamic acid (3-Cl-AHPC/MM002) that induces apoptosis in the tRA-resistant leukemia cell lines M07e, KG-1, and HL-60R, and in tRA-resistant patient leukemic blasts. The 3-Cl-AHPC totally inhibits leukemia colony formation at concentrations that inhibit committed human bone marrow stem cell proliferation, that is, granulocyte/macrophage colony-forming units (CFU-GMs) by only 30%. Exposure to 3-Cl-AHPC results in caspase activation and the cleavage of poly(adenosine diphosphate) (poly(ADP)) ribose polymerase. While activation of the extracellular signal-regulated kinase (ERK) and p38 pathways is not necessary for 3-Cl-AHPC-mediated apoptosis, maximal apoptosis requires c-Jun N-terminal kinase (JNK) activation. The 3-Cl-AHPC-mediated cleavage of the antiapoptotic B-cell leukemia XL (Bcl-XL) protein to a proapoptotic 18-kDa product is found in both the M07e cell line and patient leukemic blasts. The 3-Cl-AHPC treatment of mice bearing the AML 1498 cell line results in a 3.3-log kill in the leukemic blasts. While 3-Cl-AHPC does not activate retinoic nuclear receptors, it is a potent inducer of apoptosis in AML cells and may represent a novel therapy in the treatment of this disease.

Induction of apoptosis of human B-CLL and ALL cells by a novel retinoid and its nonretinoidal analog.

We have recently described a novel retinoid 6-[3-(1-adamantyl)-4-hydroxyphenyl]-2-naphthalenecarboxylic acid (CD437/AHPN) that induces apoptosis in a number of malignant cell types. We now describe our studies examining the effects of CD437 and a nonretinoidal analog (MM002) on the in vitro proliferation of the ALL-REH cell line, the in vitro and in vivo growth of a novel Epstein-Barr virus-negative (EBV(-)) B-cell chronic lymphocytic leukemia (B-CLL) cell line (WSU-CLL), and primary cultures of human B-CLL and acute lymphoblastic leukemia (ALL) cells. CD437 and MM002 induce apoptosis in both cell lines, as indicated by the activation of caspase-2 and caspase-3, cleavage of poly(adenosine diphosphate-ribose) (poly(ADP-ribose)) polymerase, increase in annexin V binding, and subsequent nuclear fragmentation. CD437-mediated apoptosis was not associated with the modulation of Bcl-2, Bax, or Mcl-1 levels, but was associated with the cleavage of the antiapoptotic protein Bcl-X(L) to a proapoptotic 18-kD form. This cleavage of Bcl-X(L) was dependent on caspase-3 activation since Bcl-X(L) cleavage and apoptosis were inhibited by the caspase-3 inhibitor Z-DVED-fmk. CD437 markedly inhibited the growth of WSU-CLL cells in severe combined immunodeficiency (SCID) mice. Tumor growth inhibition, growth delay, and log cell kill were 85.7%, 21 days, and 2.1, respectively, in the treated mice. Moreover, 1 of the 5 treated mice was tumor-free longer than 150 days and thus was considered cured. Exposure of primary cultures of both B-CLL and ALL cells obtained from patients to CD437 and MM002 resulted in their apoptosis. These results suggest that CD437 and MM002 analogs may have a potential role in the treatment of B-CLL and ALL.