FLT3 (fms-related tyrosine kinase/Flk2/ Stk-2) is a receptor tyrosine kinase (RTK) primarily expressed on hematopoietic cells. In blasts from acute myelogenous leukemia (AML) patients, 2 classes of FLT3 activating mutations have been identified: internal tandem duplication (ITD) mutations in the juxtamembrane domain (25%-30% of patients) and point mutations in the kinase domain activation loop (7%-8% of patients). FLT3-ITD mutations are the most common molecular defect identified in AML and have been shown to be an independent prognostic factor for decreased survival. FLT3-ITD is therefore an attractive molecular target for therapy. SU11248 is a recently described selective inhibitor with selectivity for split kinase domain RTKs, including platelet-derived growth factor receptors, vascular endothelial growth factor receptors, and KIT. We show that SU11248 also has potent activity against wild-type FLT3 (

Fifteen patients with refractory AML were treated in a phase 1 study with SU11248, an oral kinase inhibitor of fms-like tyrosine kinase 3 (Flt3), Kit, vascular endothelial growth factor (VEGF), and plateletderived growth factor (PDGF) receptors. Separate cohorts of patients received SU11248 for 4-week cycles followed by either a 2-or a 1-week rest period. At the starting dose level of 50 mg (n ‫؍‬ 13), no dose-limiting toxicities were observed. The most frequent grade 2 toxicities were edema, fatigue, and oral ulcerations.

The expression of cytomegalovirus alpha (immediate early) genes is under control of an enhancer that carries signals for strong constitutive expression as well as response elements for transactivation by viral proteins. We have used synthetic oligonucleotides representing the 16, 18 and 19 bp repeat elements within the enhancer to investigate the role of virus‐induced cellular transcription factors in enhancer activation. We show that the transcription factor NF‐kappa B, which binds to the 18 bp repeat, plays a central role in enhancer activation in infected human fibroblasts and that activation is mediated by the product of the viral gene ie1. The simian immunodeficiency virus kappa B site can functionally substitute for the 18 bp element in transient transactivation assays and can also compete efficiently for specific binding to the 18 bp repeat element in vitro. Point mutations in the NF‐kappa B site within the 18 bp element disrupt ie1‐mediated transactivation and binding. We have found that the characteristics of the 18 bp binding factor from human fibroblasts are indistinguishable from NF‐kappa B induced by phorbol ester plus mitogen treatment of T lymphocytes, as determined by gel mobility shift assay as well as protection of the binding site from chemical cleavage. Furthermore, T cell stimulation mediates activation of the viral enhancer via kappa B sites, an observation that may be important in the interaction of cytomegalovirus with the naturally infected human host. Thus, NF‐kappa B plays a central role as a target for enhancer activation via viral and cellular factors.

Mutations in both the viral phosphotransferase gene, UL97, and the DNA polymerase gene, UL54, have been shown to confer ganciclovir resistance to cytomegalovirus (CMV). Moreover, UL54 alterations have been associated with in vitro cross-resistance of CMV to cidofovir. To investigate the relative significance of UL97 versus UL54 alterations in conferring antiviral resistance, phenotypic and genotypic characterization of 28 ganciclovir-resistant clinical CMV isolates was undertaken. Isolates were either low-level ganciclovir-resistant, which have ganciclovir ID50 values > or =8 microM and <30 microM and sensitivity to cidofovir, or high-level ganciclovir-resistant, which have ganciclovir ID50 values > or =30 microM and cross-resistance to cidofovir. Low-level ganciclovir-resistant isolates were associated with UL97 alterations and short periods of ganciclovir treatment, while high-level ganciclovir-resistant isolates were associated with both UL97 and polymerase alterations and were cultured after extended ganciclovir therapy.

The aim of the study was to investigate inhibitory effects of the receptor tyrosine kinase (RTK) inhibitor SU11248 against CSF-1R and osteoclast (OC) formation. We developed an in vivo model of breast cancer metastasis to evaluate efficacy of SU11248 against tumor growth and tumor-induced osteolysis in bone. The in vitro effects of SU11248 on CSF-1R phosphorylation, OC formation and function were evaluated. Effects on 435/HAL-Luc tumor growth in bone were monitored by in vivo bioluminescence imaging (BLI), and inhibition of osteolysis was evaluated by measurement of serum pyridinoline (PYD) concentration and histology. Phosphorylation of the receptor for M-CSF (CSF-1R) expressed by NIH3T3 cells was inhibited by SU11248 with an IC50 of 50-100 nM, consistent with CSF-1R belonging to the class III split kinase domain RTK family. The early M-CSF-dependent phase of in vitro murine OC development and function were inhibited by SU11248 at 10-100 nM. In vivo inhibition of osteolysis was confirmed by significant lowering of serum PYD levels following SU11248 treatment of tumor-bearing mice (P = 0.047). Using BLI, SU11248 treatment at 40 mg/kg/day for 21 days showed 64% inhibition of tumor growth in bone (P = 0.006), and at 80 mg/kg/day showed 89% inhibition (P = 0.001). Collectively, these data suggest that SU11248 may be an effective and tolerated therapy to inhibit growth of breast cancer bone metastases, with the additional advantage of inhibiting tumor-associated osteolysis.

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The expression of a (immediate-early) genes of cytomegalovirus is regulated via a complex enhancer that consists of several different repeat elements. We describe here the autoinduction of expression from the a promoter-enhancer by the most abundant a gene product, a 491-amino-acid nuclear phosphoprotein referred to as iel. We defined the 18-base-pair repeat element within the a enhancer as the signal through which iel acts to regulate gene expression. This element contains an NFKB site that may play an important role in iel autoregulation. Our analysis, which relied on deletions through the enhancer as well as reconstitution of responsiveness to a promoter with synthetic 18-base-pair repeats, strongly implicated iel in the transcriptional transactivation of the a promoter through its enhancer.

IntroductionThe receptor tyrosine kinase (RTK) c-kit is essential for the development of normal hematopoietic cells and has been proposed to play a functional role in acute myeloid leukemia (AML). 1,2 c-Kit is a member of the class III family of RTKs, characterized by an extracellular ligand binding region containing 5 immunoglobulin repeats, a hydrophobic transmembrane domain, and an intracellular kinase domain split by an insert. 3 Binding of the c-kit ligand, stem cell factor (SCF), initiates a signal transduction cascade that includes receptor autophosphorylation and subsequent phosphorylation on numerous intracellular substrates. c-Kit and its ligand play a pivotal role in normal hematopoiesis, as evidenced by naturally occurring murine mutations at the Sl locus, which encodes SCF, as well as in the c-kit receptor itself. These mutations result in varying degrees of macrocytic anemia and a loss of mast cells in addition to deficiencies in gametogenesis and melanogenesis. [4][5][6] In addition to its role in normal hematopoiesis, c-kit is expressed in leukemic blasts in approximately 60% to 80% of AML patients, as assessed by surface immunostaining using antibodies specific to c-kit or by expression of c-kit messenger RNA. 1,7,8 Supporting a functional role for c-kit in AML, increased tyrosine phosphorylation of the receptor, as well as a proliferative response upon SCF stimulation, has been demonstrated in leukemic blasts in most AML cases that were c-kit ϩ . 1,2 The proliferative response to SCF has been shown to be synergistic with granulocytemacrophage colony-stimulating factor (GM-CSF) or interleukin (IL)-3, both of which are known to promote the growth of leukemic cells in vitro.SU5416 and SU6668 are small-molecule inhibitors of RTKs such as Flk-1/KDR that have structural and sequence similarity to c-kit. SU5416 is a more selective and potent inhibitor of the Flk-1/KDR receptor; in contrast, SU6668 exhibits a broader inhibitory target profile, with effects on platelet-derived growth factor (PDGF) receptor and fibroblast growth factor (FGF) receptor in addition to Flk-1/KDR. 9,10 Both compounds have been shown to exhibit selectivity with respect to other tyrosine kinases, for example, with inhibitory concentration of 50% (IC 50 ) above 10 M for epidermal growth factor (EGF) receptor, Src, Met,10 In cell-based and preclinical animal models, both compounds have also been shown to exhibit antiangiogenic properties. SU5416 inhibits vascular endothelial growth factor (VEGF)-induced and SU6668 VEGF-and FGF-induced proliferation of human umbilical vein endothelial cells in culture; however, neither compound potently inhibits the growth of tumor cells grown in culture. 9,10 In addition, both compounds inhibit the growth of a variety of tumor cells grown as subcutaneous xenografts in athymic mice; furthermore, SU6668 has been shown to regress established xenograft tumors in mice. 9,10 Intravital fluoresence videomicroscopy in mouse tumor xenograft models has demonstrated that SU5416 and SU6668 also inhibit tumor...