Scientific Resources

Chaetocin,a thiodioxopiperazine natural product previously unreported to have anticancer effects,was found to have potent antimyeloma activity in IL-6-dependent and -independent myeloma cell lines in freshly collected sorted and unsorted patient CD138(+) myeloma cells and in vivo. Chaetocin largely spares matched normal CD138(-) patient bone marrow leukocytes,normal B cells,and neoplastic B-CLL (chronic lymphocytic leukemia) cells,indicating a high degree of selectivity even in closely lineage-related B cells. Furthermore,chaetocin displays superior ex vivo antimyeloma activity and selectivity than doxorubicin and dexamethasone,and dexamethasone- or doxorubicin-resistant myeloma cell lines are largely non-cross-resistant to chaetocin. Mechanistically,chaetocin is dramatically accumulated in cancer cells via a process inhibited by glutathione and requiring intact/unreduced disulfides for uptake. Once inside the cell,its anticancer activity appears mediated primarily through the imposition of oxidative stress and consequent apoptosis induction. Moreover,the selective antimyeloma effects of chaetocin appear not to reflect differential intracellular accumulation of chaetocin but,instead,heightened sensitivity of myeloma cells to the cytotoxic effects of imposed oxidative stress. Considered collectively,chaetocin appears to represent a promising agent for further study as a potential antimyeloma therapeutic. View Publication

Drug resistance resulting from emergence of imatinib-resistant BCR-ABL point mutations is a significant problem in advanced-stage chronic myelogenous leukemia (CML). The BCR-ABL inhibitor,nilotinib (AMN107),is significantly more potent against BCR-ABL than imatinib,and is active against many imatinib-resistant BCR-ABL mutants. Phase 1/2 clinical trials show that nilotinib can induce remissions in patients who have previously failed imatinib,indicating that sequential therapy with these 2 agents has clinical value. However,simultaneous,rather than sequential,administration of 2 BCR-ABL kinase inhibitors is attractive for many reasons,including the theoretical possibility that this could reduce emergence of drug-resistant clones. Here,we show that exposure of a variety of BCR-ABL+ cell lines to imatinib and nilotinib results in additive or synergistic cytotoxicity,including testing of a large panel of cells expressing BCR-ABL point mutations causing resistance to imatinib in patients. Further,using a highly quantifiable bioluminescent in vivo model,drug combinations were at least additive in antileukemic activity,compared with each drug alone. These results suggest that despite binding to the same site in the same target kinase,the combination of imatinib and nilotinib is highly efficacious in these models,indicating that clinical testing of combinations of BCR-ABL kinase inhibitors is warranted. View Publication

Recent population studies provide clues that the use of metformin may be associated with reduced incidence and improved prognosis of certain cancers. This drug is widely used in the treatment of type 2 diabetes,where it is often referred to as an insulin sensitizer" because it not only lowers blood glucose but also reduces the hyperinsulinemia associated with insulin resistance. As insulin and insulin-like growth factors stimulate proliferation of many normal and transformed cell types� View Publication

Combined deletion of chromosomes 1p and 19q is associated with improved prognosis and responsiveness to therapy in patients with anaplastic oligodendroglioma. The deletions usually involve whole chromosome arms,suggesting a t(1;19)(q10;p10). Using stem cell medium,we cultured a few tumors. Paraffin-embedded tissue was obtained from 21 Mayo Clinic patients and 98 patients enrolled in 2 North Central Cancer Treatment Group (NCCTG) low-grade glioma trials. Interphase fusion of CEP1 and 19p12 probes detected the t(1;19). 1p/19q deletions were evaluated by fluorescence in situ hybridization. Upon culture,one oligodendroglioma contained an unbalanced 45,XX,t(1;19)(q10;p10). CEP1/19p12 fusion was observed in all metaphases and 74% of interphase nuclei. Among Mayo Clinic oligodendrogliomas,the prevalence of fusion was 81%. Among NCCTG patients,CEP1/19p12 fusion prevalence was 55%,47%,and 0% among the oligodendrogliomas,mixed oligoastrocytomas,and astrocytomas,respectively. Ninety-one percent of NCCTG gliomas with 1p/19q deletion and 12% without 1p/19q deletion had CEP1/19p12 fusion (P textless 0.001,chi(2) test). The median overall survival (OS) for all patients was 8.1 years without fusion and 11.9 years with fusion (P = 0.003). The median OS for patients with low-grade oligodendroglioma was 9.1 years without fusion and 13.0 years with fusion (P = 0.01). Similar significant median OS differences were observed for patients with combined 1p/19q deletions. The absence of alterations was associated with a significantly shorter OS for patients who received higher doses of radiotherapy. Our results strongly suggest that a t(1;19)(q10;p10) mediates the combined 1p/19q deletion in human gliomas. Like combined 1p/19q deletion,the 1;19 translocation is associated with superior OS and progression-free survival in low-grade glioma patients. View Publication

Recognition of tumor-associated Ags (TAAs) on tumor cells by CTLs and the subsequent tumor cell death are assumed to be dependent on TAA protein expression and to correlate directly with the level of peptide displayed in the binding site of the HLA class I molecule. In this study we evaluated whether the levels of Her-2/neu protein expression on human tumor cell lines directly correlate with HLA-A*0201/Her2/neu peptide presentation and CTL recognition. We developed a TCR mimic (TCRm) mAb designated 1B8 that specifically recognizes the HLA-A2.1/Her2/neu peptide (369-377) (Her2(369)-A2) complex. TCRm mAb staining intensity varied for the five human tumor cell lines analyzed,suggesting quantitative differences in levels of the Her2(369)-A2 complex on these cells. Analysis of tumor cell lines pretreated with IFN-gamma and TNF-alpha for Her2/neu protein and HLA-A2 molecule expression did not reveal a direct correlation between the levels of Her2/neu Ag,HLA-A2 molecule,and Her2(369)-A2 complex expression. However,compared with untreated cells,cytokine-treated cell lines showed an increase in Her2(369)-A2 epitope density that directly correlated with enhanced tumor cell death (p = 0.05). Although a trend was observed between tumor cell lysis and the level of the Her2(369)-A2 complex for untreated cells,the association was not significant. These findings suggest that tumor cell susceptibility to CTL-mediated lysis may be predicted based on the level of specific peptide-MHC class I expression rather than on the total level of TAA expression. Further,these studies demonstrate the potential of the TCRm mAb for validation of endogenous HLA-peptide epitopes on tumor cells. View Publication

We previously identified a rearrangement of mixed-lineage leukemia (MLL) gene (also known as ALL-1,HRX,and HTRX1),consisting of an in-frame partial tandem duplication (PTD) of exons 5 through 11 in the absence of a partner gene,occurring in approximately 4%-7% of patients with acute myeloid leukemia (AML) and normal cytogenetics,and associated with a poor prognosis. The mechanism by which the MLL PTD contributes to aberrant hematopoiesis and/or leukemia is unknown. To examine this,we generated a mouse knockin model in which exons 5 through 11 of the murine Mll gene were targeted to intron 4 of the endogenous Mll locus. Mll(PTD/WT) mice exhibit an alteration in the boundaries of normal homeobox (Hox) gene expression during embryogenesis,resulting in axial skeletal defects and increased numbers of hematopoietic progenitor cells. Mll(PTD/WT) mice overexpress Hoxa7,Hoxa9,and Hoxa10 in spleen,BM,and blood. An increase in histone H3/H4 acetylation and histone H3 lysine 4 (Lys4) methylation within the Hoxa7 and Hoxa9 promoters provides an epigenetic mechanism by which this overexpression occurs in vivo and an etiologic role for MLL PTD gain of function in the genesis of AML. View Publication

Granulocyte colony-stimulating factor (GCSF) administration has been linked to the development of monosomy 7 in severe congenital neutropenia and aplastic anemia. We assessed the effect of pharmacologic doses of GCSF on monosomy 7 cells to determine whether this chromosomal abnormality developed de novo or arose as a result of favored expansion of a preexisting clone. Fluorescence in situ hybridization (FISH) of chromosome 7 was used to identify small populations of aneuploid cells. When bone marrow mononuclear cells from patients with monosomy 7 were cultured with 400 ng/ml GCSF,all samples showed significant increases in the proportion of monosomy 7 cells. In contrast,bone marrow from karyotypically normal aplastic anemia,myelodysplastic syndrome,or healthy individuals did not show an increase in monosomy 7 cells in culture. In bone marrow CD34 cells of patients with myelodysplastic syndrome and monosomy 7,GCSF receptor (GCSFR) protein was increased. Although no mutation was found in genomic GCSFR DNA,CD34 cells showed increased expression of the GCSFR class IV mRNA isoform,which is defective in signaling cellular differentiation. GCSFR signal transduction via the Jak/Stat system was abnormal in monosomy 7 CD34 cells,with increased phosphorylated signal transducer and activation of transcription protein,STAT1-P,and increased STAT5-P relative to STAT3-P. Our results suggest that pharmacologic doses of GCSF increase the proportion of preexisting monosomy 7 cells. The abnormal response of monosomy 7 cells to GCSF would be explained by the expansion of undifferentiated monosomy 7 clones expressing the class IV GCSFR,which is defective in signaling cell maturation. View Publication

The RAS proteins undergo farnesylation of a carboxyl-terminal cysteine (the C" of the carboxyl-terminal CaaX motif). After farnesylation� View Publication

Canonical Wnt signaling has emerged as a critical regulatory pathway for stem cells. The association between ectopic activation of Wnt signaling and many different types of human cancer suggests that Wnt ligands can initiate tumor formation through altered regulation of stem cell populations. Here we have shown that mice deficient for the Wnt co-receptor Lrp5 are resistant to Wnt1-induced mammary tumors,which have been shown to be derived from the mammary stem/progenitor cell population. These mice exhibit a profound delay in tumorigenesis that is associated with reduced Wnt1-induced accumulation of mammary progenitor cells. In addition to the tumor resistance phenotype,loss of Lrp5 delays normal mammary development. The ductal trees of 5-week-old Lrp5-/- females have fewer terminal end buds,which are structures critical for juvenile ductal extension presumed to be rich in stem/progenitor cells. Consequently,the mature ductal tree is hypomorphic and does not completely fill the fat pad. Furthermore,Lrp5-/- ductal cells from mature females exhibit little to no stem cell activity in limiting dilution transplants. Finally,we have shown that Lrp5-/- embryos exhibit substantially impaired canonical Wnt signaling in the primitive stem cell compartment of the mammary placodes. These findings suggest that Lrp5-mediated canonical signaling is required for mammary ductal stem cell activity and for tumor development in response to oncogenic Wnt effectors. View Publication

Genes that are strongly repressed after B-cell activation are candidates for being inactivated,mutated,or repressed in B-cell malignancies. Krüppel-like factor 4 (Klf4),a gene down-regulated in activated murine B cells,is expressed at low levels in several types of human B-cell lineage lymphomas and leukemias. The human KLF4 gene has been identified as a tumor suppressor gene in colon and gastric cancer; in concordance with this,overexpression of KLF4 can suppress proliferation in several epithelial cell types. Here we investigate the effects of KLF4 on pro/pre-B-cell transformation by v-Abl and BCR-ABL,oncogenes that cause leukemia in mice and humans. We show that overexpression of KLF4 induces arrest and apoptosis in the G1 phase of the cell cycle. KLF4-mediated death,but not cell-cycle arrest,can be rescued by Bcl-XL overexpression. Transformed pro/pre-B cells expressing KLF4 display increased expression of p21CIP and decreased expression of c-Myc and cyclin D2. Tetracycline-inducible expression of KLF4 in B-cell progenitors of transgenic mice blocks transformation by BCR-ABL and depletes leukemic pre-B cells in vivo. Collectively,our work identifies KLF4 as a putative tumor suppressor in B-cell malignancies. View Publication

Therapeutic mAbs that target tumor-associated Ags on the surface of malignant cells have proven to be an effective and specific option for the treatment of certain cancers. However,many of these protein markers of carcinogenesis are not expressed on the cells' surface. Instead these tumor-associated Ags are processed into peptides that are presented at the cell surface,in the context of MHC class I molecules,where they become targets for T cells. To tap this vast source of tumor Ags,we generated a murine IgG2a mAb,3.2G1,endowed with TCR-like binding specificity for peptide-HLA-A*0201 (HLA-A2) complex and designated this class of Ab as TCR mimics (TCRm). The 3.2G1 TCRm recognizes the GVL peptide (GVLPALPQV) from human chorionic gonadotropin beta presented by the peptide-HLA-A*0201 complex. When used in immunofluorescent staining reactions using GVL peptide-loaded T2 cells,the 3.2G1 TCRm specifically stained the cells in a peptide and Ab concentration-dependent manner. Staining intensity correlated with the extent of cell lysis by complement-dependent cytotoxicity (CDC),and a peptide concentration-dependent threshold level existed for the CDC reaction. Staining of human tumor lines demonstrated that 3.2G1 TCRm was able to recognize endogenously processed peptide and that the breast cancer cell line MDA-MB-231 highly expressed the target epitope. The 3.2G1 TCRm-mediated CDC and Ab-dependent cellular cytotoxicity of a human breast carcinoma line in vitro and inhibited in vivo tumor implantation and growth in nude mice. These results provide validation for the development of novel TCRm therapeutic reagents that specifically target and kill tumors via recognition and binding to MHC-peptide epitopes. View Publication

Multiple myeloma is characterized by the proliferation of clonal plasma cells that have a heterogeneous expression of various cell surface markers,precluding successful use of monoclonal antibodies for therapeutic targeting of the tumor cell. Thymoglobulin (rabbit-derived polyclonal anti-thymocyte globulin),by virtue of its method of preparation,contains antibodies against several B-cell and plasma cell antigens and offers an attractive option for immunotherapy of myeloma. Here,we demonstrate potent anti-myeloma activity of the rabbit anti-thymocyte globulin preparation Thymoglobulin in vitro and in vivo in an animal model of myeloma. Thymoglobulin was able to induce dose- and time-dependent apoptosis of several myeloma cell lines,including those resistant to conventional anti-myeloma agents. Importantly,the anti-myeloma activity was preserved even when myeloma cells were grown with different cytokines demonstrating the ability to overcome microenvironment-mediated resistance. Thymoglobulin induced apoptosis of freshly isolated primary myeloma cells from patients. Using a competitive flow cytometric analysis,we were able to identify the potential antigen targets for Thymoglobulin preparation. Finally,in a plasmacytoma mouse model of myeloma,Thymoglobulin delayed the tumor growth in a dose-dependent manner providing convincing evidence for continued evaluation of this agent in the clinic in patients with myeloma,either alone or in combination with other agents. View Publication