Abstract
Acute lymphoblastic leukemia (ALL) is the most common malignant disease in childhood. Despite a relatively good prognosis approximately one fourth of the patients suffers from relapse and, consequently, a worse prognosis. Only 40 % of these children with relapsed ALL will survive. Patients who fail to achieve a complete remission in chemotherapy do not survive. This explains the need for new compounds that may overcome resistance against clinically employed cytostatic drugs. Here we describe a new class of iron-containing nucleosides that overcome drug resistance in vitro and ex vivo. Analyses of apoptosis induction in primary lymphoblasts from 30 children with de novo ALL and relapsed ALL showed that these iron-containing nucleoside analogs are far more potent as compared with conventional nucleoside analogs employed in clinical therapy of childhood ALL (cytosinarabinoside: p < 0.0064). Furthermore we demonstrate ex vivo these novel nucleoside analogs overcome drug resistance against fludarabine (p<0.0162) and doxorubicin (p<0.002).
Additional experiments revealed that the prototype of iron-containing nucleoside analogs, N69, specifically induced apoptosis, as evidenced by DNA fragmentation, dissipation of the mitochondrial membrane potential and activation of caspase-3. All those events occurred in the absence of cellular lysis, i. e. in the absence of release of lactate dehydrogenase from the cells, thereby excluding N69-induced necrosis.
N69-induced cell death was functionally characterized by the use of different cellular model systems being devoid of defined molecular parts of the apoptosis machinery. According to those results, the CD95-dependent apoptosis cascade is not involved in N69-induced cell death. Furthermore, N69 triggers apoptosis in a Bax-independent manner in the essentially Bax-free prostata carcinoma cell line DU145. Thus, N69 is able to break the Bax-related drug resistance that plays an important role in the therapy of relapsed ALL in childhood. In addition, we could show that N69-induced apoptosis even proceeds in the absence of caspase-3 expression. We demonstrate here that N69 still exerts a considerable apoptosis-inducing effect in the caspase-3-deficient, multi drug-resistant (i. e. taxol-, epirubicin- and etoposide-resistant) mamma carcinoma cell line MCF-7. Taken together, iron-containing nucleosides comprise a totally new, very promising class of cytostatic agents for cancer and leukemia therapy, especially for the therapy of relapsed ALL in childhood. Future studies will aim to elucidate the target structures of these new compounds and to demonstrate N69-mediated anti-cancer activity in vivo. First experiments in mice show a good tolerability of N69.
Programmed Cell Death Induced by Modulated Electrohyperthermia