New Pinostilbene Analogues Overcome Anthracycline Resistance in Acute Lymphoplastic Leukemia Ex Vivo.

Anthracylines play a very important role in the treatment of acute lymphoblastic leukemia (ALL) and relapsed ALL in childhood, however resistance to anthracyclines leads to a poor prognosis. In the present study, we have synthesized two new pinostilbene analogues, i.e.

1. trans-3,4′-dihydroxy-5-methoxystilbene and

2. (E)-resveratrol 4′-O-ß-D-glucopyranoside, which are able to overcome anthracycline resistance in childhood acute lymphoblastic leukemia (ALL) ex vivo and induce apoptosis in established leukemia cell lines via mitochondrial pathway.

Apoptosis induction has been investigated by flowcytometric measurement of DNA-fragmentation [LC 50: 10 μM for (1) and (2)], mitochondrial membrane potential reduction and phosphatedylserin-staining on cell membrane surface. Cell death by necrosis could be excluded by a lactatdehydrogenase-release assay. For the first time we analysed the antileukemic and chemopreventive potentials of the pinostilbene analogues (1) and (2) ex vivo in a significant number of primary lymphoblasts of patients suffering from childhood ALL.

Patients: Primary lymphoblasts isolated from 22 children with de novo ALL (median: 6.8 years; range 0,6–16.9 years) and relapsed ALL (median:7.2 years) were tested for ex vivo drug response with the anthracyclines daunorubicin (10 μmol/l) and doxorubicin (10 μmol/l) and two new pinostilbene analogues (1) and (2) (10μmol/l), according to their LC50 values in established cell lines. We could demonstrate in these primary cells that the pinostilbenes (1) and (2) were even more effective as compared with the anthracyclines. Out of 22 patients 14 were female (14 de novo ALL) and 8 were male (6 de novo ALL, 2 relapsed ALL). Within these cell populations following immunologic subgroups were found: c-ALL, pre-B-ALL, pro-B-ALL, T-ALL and pre-T-ALL.

Results: Daunorubicin induced apoptosis in 6 out of 22 lymphoblast populations (response rate 27,3 %). A similar response rate was observed after treatment with doxorubicin: only 5 of 22 lymphoblast populations responded (22,7%). Nevertheless, far higher response rates were observed for (1) with 11/15 (73,3 %; p<0.005) and for (2) with 15/17 (88,2%; p<0.0002, all p-values by t-test). Interestingly, treatment of daunorubicin-resistant lymphoblasts resulted in significant apoptosis induction in 6 out of 10 cell populations after treatment with compound (1) (response rate 60 %) and in 6/6 after treatment with compound (2) (response rate 100%). Furthermore, pinostilbene (2) showed significant synergistic activity with daunorubicin in 2 of 3 lymphoblast populations. We clearly demonstrated that the ex vivo treatment of lymphoblasts from children with de novo and relapsed ALL with the new pinostilbenes (1) and (2) induced significantly higher response rates than daunorubicin or doxorubicin treatment. In conclusion, the high ex vivo sensitivity of anthracycline resistant leukemia cells to pinostilbene treatment reveals the great proapoptotic and chemopreventive potential of this new class of antileukemic agents.