26-Trifluoro-(E)-9,10-dehydro-12,13-desoxyepothilone B [Fludelone (Flu)] has shown broad antitumor activity in solid tumor models. In the present study, we showed, in vitro, that Flu significantly inhibited multiple myeloma (MM) cell proliferation (with 1-15 nM IC 50), whereas normal human bone marrow stromal cells (HS-27A and HS-5 lines) were relatively resistant (10-to 15-fold higher IC 50). Cell-cycle analysis demonstrated that Flu caused G2͞M phase arrest and induced cell apoptosis. After Flu treatment, caspase-3, -8, and -9 were activated, cytochrome c and second mitochondrial-derived activator of caspase were released to the cytosol, and c-Jun N-terminal kinase was activated, indicating that mitochondria were involved in the apoptosis. Flu toxicity to human hematopoietic stem cells was evaluated by CD34 ؉ cell-apoptosis measurements and hematopoietic-progenitor assays. There was no significant toxicity to noncycling human CD34 ؉ cells. We Epothilones have emerged as a highly promising family of microtubule-stabilizing agents. The epothilones have higher solubility in water than paclitaxel and are poorer substrates for the P-glycoprotein, proving more effective than paclitaxel against tumors showing multidrug resistance (5, 6). Epothilones also have a simpler molecular architecture, which has allowed for the total synthesis of the natural epothilones and many synthetic analogs.Our group achieved the total synthesis, and the structure-activity relationship evaluation, of several epothilones (9-11). This work soon led to the synthesis of 12,13-desoxyepothilone B (dEpoB), which proved highly effective in various in vivo xenograft tumor models (10, 11). More recently, we reported the total synthesis of (E)-9,10-dehydro-12, 13-desoxyepothilone B (9) and 26-trifluoro-(E)-9,10-dehydro-12,13-desoxyepothilone B, named Fludelone (Flu) (12). In mice, Flu appears to have a particularly broad therapeutic index in vivo. It seems to be curative over a range of tumor types, without tumor relapse upon suspension of treatment. Moreover, Flu is orally available and is completely curative against human tumor xenografts by parenteral and oral therapy. In addition, treatment with Flu gave complete tumor remission against Taxol-resistant tumors (10, 12). These very promising antitumor data were obtained in s.c. solid tumor models; however, drug efficacy in orthotopic models has not been investigated. In the present study, we focused on the evaluation of the anti-multiplemyeloma (MM) effects of the second generation analog Flu, in comparison with dEpoB, in a disseminated MM model. Our data demonstrated that Flu had a profound antitumor activity in human MM both in vitro and in vivo, indicating that this compound might be a promising agent against MM, particularly in late-stage refractory disease.
Materials and MethodsCell Lines and Primary Specimens. For information about cell lines and primary specimens, see Supporting Materials and Methods, which is published as supporting information on the PNAS web site.Reagents. Flu and dEpoB...