IntroductionOver the last decade, major advances in the treatment of multiple myeloma (MM) have been reported with the use of autologous stem-cell transplantation [1][2][3][4] and, more recently, of novel agents targeting the tumor clone and the bone marrow microenvironment. 5 In this setting, thalidomide represents a new treatment paradigm because of its alternative mechanisms of action that include disruption of myeloma-bone marrow stromal cell interactions, inhibition of cytokine secretion, and immunomodulatory effects. The observation that increased bone marrow angiogenesis correlates with advanced phases of MM, 6 along with the welldocumented in vitro antiangiogenic activity of thalidomide, 7 led to the investigational use of this agent in patients with advanced and refractory MM. 8 Response rates in the 30% range initially reported by Singhal et al 8 were extended and confirmed by other groups (for a review, see Cavenagh and Oakervee 9 and Dimopoulos et al 10 ). Subsequent combination of thalidomide with dexamethasone increased the rate of response up to 50% to 55%, 11,12 suggesting a synergism between these agents and providing the rationale for their use as primary therapy for patients with symptomatic MM. Results of 3 phase-2 studies with thalidomide-dexamethasone (Thal-Dex) in preparation for subsequent autologous transplantation 13-15 and a randomized comparison of Thal-Dex with dexamethasone alone 16 were promising in terms of response rate and collection of adequate quantities of peripheral blood stem cells (PBSCs). Based on these data, Thal-Dex has been proposed, and is currently accepted at many centers, as a front-line treatment option for patients with symptomatic MM, particularly if it is planned to offer subsequent high-dose therapy with autologous transplantation. However, no comparative study of Thal-Dex with vincristinedoxorubicin-dexamethasone (VAD), the reference treatment used so far to reduce tumor cell mass before autologous transplantation, has been reported. To address this issue, we performed a retrospective matched case-control analysis of 200 patients with symptomatic MM who were primarily treated with Thal-Dex (n ϭ 100) or VAD (n ϭ 100) in preparation for autologous stem-cell transplantation as part of 2 consecutive studies conducted from 1996 to 2004. Table 1; the 2 groups were comparable with respect to the major presenting variables known to potentially affect clinical outcome. Both studies were approved by local ethical committees of participating centers. Informed consent was provided according to the Declaration of Helsinki. Patients, materials, and methods Patients and criteria of matching Study design and treatment regimensBy design of both studies, Thal-Dex and VAD were planned to be administered for 4 months in an attempt to reduce tumor cell mass before collection of PBSCs and subsequent autologous transplantation. Details on treatment regimens were given elsewhere. 4,15 Briefly, thalidomide was given orally at the starting dose of 100 mg/d for 14 days and then increa...

Hematopoiesis, the process by which the hematopoietic stem cells and progenitors differentiate into blood cells of various lineages, involves complex interactions of transcription factors that modulate the expression of downstream genes and mediate proliferation and differentiation signals. Despite the many controls that regulate hematopoiesis, mutations in the regulatory genes capable of promoting leukemogenesis may occur. The FLT3 gene encodes a tyrosine kinase receptor that plays a key role in controlling survival, proliferation and differentiation of hematopoietic cells. Mutations in this gene are critical in causing a deregulation of the delicate balance between cell proliferation and differentiation. In this review, we provide an update on the structure, synthesis and activation of the FLT3 receptor and the subsequent activation of multiple downstream signaling pathways. We also review activating FLT3 mutations that are frequently identified in acute myeloid leukemia, cause activation of more complex downstream signaling pathways and promote leukemogenesis. Finally, FLT3 has emerged as an important target for molecular therapy. We, therefore, report on some recent therapies directed against it.

A high incidence of relapses following induction chemotherapy is a major hindrance to patient survival in acute myelogenous leukemia (AML). There is strong evidence that activation of the phosphoinositide 3 kinase (PI3K)/Akt signaling network plays a significant role in rendering AML blasts drug resistant. An important mechanism underlying drug resistance is represented by overexpression of membrane drug transporters such as multidrug resistance-associated protein 1 (MRP1) or 170-kDa P-glycoprotein (P-gp). Here, we present evidence that MRP1, but not P-gp, expression is under the control of the PI3K/Akt axis in AML blasts. We observed a highly significant correlation between levels of phosphorylated Akt and MRP1 expression in AML cells. Furthermore, incubation of AML blasts with wortmannin, a PI3K pharmacological inhibitor, resulted in lower levels of phosphorylated Akt, downregulated MRP1 expression, and decreased Rhodamine 123 extrusion in an in vitro functional dye efflux assay. We also demonstrate that wortmannin-dependent PI3K/Akt inhibition upregulated p53 protein levels in most AML cases, and this correlated with diminished MRP1 expression and enhanced phosphorylation of murine double minute 2 (MDM2). Taken together, these data suggest that PI3K/Akt activation may lead to the development of chemoresistance in AML blasts through a mechanism involving a p53-dependent suppression of MRP1 expression.