Association of renal tubular hyaline droplets with lymphoma in CD-1 mice.

In mice, hyaline droplets in renal proximal tubules have been associated with histiocytic sarcoma but have not been reported with lymphoma. Tissues from CD-1 mice in a 2-year carcinogenicity bioassay were examined microscopically. Twenty-five mice with hyaline droplets in renal tubules were identified. Immunohistochemistry to detect IgA, IgG, IgM, lysozyme, albumin, CD3, and CD79a was performed on kidneys of 21 affected mice. Hyaline droplets were present in the kidneys of 11 mice with lymphoma (1 male, 10 female), of which 1 female also had histiocytic sarcoma. Hyaline droplets were also present in 7 other mice with histiocytic sarcoma, 2 with chronic progressive nephropathy, 3 with renal cortical tubular necrosis, and 2 with granulocytic leukemia. Five of the 11 lymphomas were CD3+, indicating a T lymphocyte origin. Hyaline droplets in mice with lymphoma did not stain for IgA, IgG, or IgM, except in one questionable case. Results of other immunohistochemical stains were inconclusive. Although the droplet composition could not be determined immunohistochemically, the study findings indicate that renal tubular hyaline droplets may be associated with lymphoma in mice.

ABT-888 confers broad in vivo activity in combination with temozolomide in diverse tumors.

PURPOSE: ABT-888, currently in phase 2 trials, is a potent oral poly(ADP-ribose) polymerase inhibitor that enhances the activity of multiple DNA-damaging agents, including temozolomide (TMZ). We investigated ABT-888+TMZ combination therapy in multiple xenograft models representing various human tumors having different responses to TMZ. EXPERIMENTAL DESIGN: ABT-888+TMZ efficacy in xenograft tumors implanted in subcutaneous, orthotopic, and metastatic sites was assessed by tumor burden, expression of poly(ADP-ribose) polymer, and O(6)-methylguanine methyltransferase (MGMT). RESULTS: Varying levels of ABT-888+TMZ sensitivity were evident across a broad histologic spectrum of models (55-100% tumor growth inhibition) in B-cell lymphoma, small cell lung carcinoma, non-small cell lung carcinoma, pancreatic, ovarian, breast, and prostate xenografts, including numerous regressions. Combination efficacy in otherwise TMZ nonresponsive tumors suggests that TMZ resistance may be overcome by poly(ADP-ribose) polymerase inhibition. Profound ABT-888+TMZ efficacy was seen in experimental metastases models that acquired resistance to TMZ. Moreover, TMZ resistance was overcome in crossover treatments, indicating that combination therapy may overcome acquired TMZ resistance. Neither tumor MGMT, mismatch repair, nor poly(ADP-ribose) polymer correlated with the degree of sensitivity to ABT-888+TMZ. CONCLUSIONS: Robust ABT-888+TMZ efficacy is observed across a spectrum of tumor types, including orthotopic and metastatic implantation. As many TMZ nonresponsive tumors proved sensitive to ABT-888+TMZ, this novel combination may broaden the clinical use of TMZ beyond melanoma and glioma. Although TMZ resistance may be influenced by MGMT, neither MGMT nor other mechanisms of TMZ resistance (mismatch repair) precluded sensitivity to ABT-888+TMZ. Underlying mechanisms of TMZ resistance in these models are not completely understood but likely involve mechanisms independent of MGMT.

Correlation of tumor growth suppression and methionine aminopetidase-2 activity blockade using an orally active inhibitor.

This laboratory and others have shown that agents that inhibit the in vitro catalytic activity of methionine aminopeptidase-2 (MetAP2) are effective in blocking angiogenesis and tumor growth in preclinical models. However, these prototype MetAP2 inhibitors are clearly not optimized for therapeutic use in the clinic. We have discovered an orally active class of MetAP2 inhibitors, the anthranilic acid sulfonamides exemplified by A-800141, which is highly specific for MetAP2. This orally bioavailable inhibitor exhibits an antiangiogenesis effect and a broad anticancer activity in a variety of tumor xenografts including B cell lymphoma, neuroblastoma, and prostate and colon carcinomas, either as a single agent or in combination with cytotoxic agents. We also have developed a biomarker assay to evaluate in vivo MetAP2 inhibition in circulating mononuclear cells and in tumors. This biomarker assay is based on the N-terminal methionine status of the MetAP2-specific substrate GAPDH in these cells. In cell cultures in vitro, the sulfonamide MetAP2 inhibitor A-800141 caused the formation of GAPDH variants with an unprocessed N-terminal methionine. A-800141 blocked tumor growth and MetAP2 activity in a similar dose-response in mouse models, demonstrating the antitumor effects seen for A-800141 are causally connected to MetAP2 inhibition in vivo. The sulfonamide MetAP2 inhibitor and GAPDH biomarker in circulating leukocytes may be used for the development of a cancer treatment.

Preclinical activity of ABT-869, a multitargeted receptor tyrosine kinase inhibitor.

ABT-869 is a structurally novel, receptor tyrosine kinase (RTK) inhibitor that is a potent inhibitor of members of the vascular endothelial growth factor (VEGF) and platelet-derived growth factor (PDGF) receptor families (e.g., KDR IC50 = 4 nmol/L) but has much less activity (IC50s > 1 micromol/L) against unrelated RTKs, soluble tyrosine kinases, or serine/threonine kinases. The inhibition profile of ABT-869 is evident in cellular assays of RTK phosphorylation (IC50 = 2, 4, and 7 nmol/L for PDGFR-beta, KDR, and CSF-1R, respectively) and VEGF-stimulated proliferation (IC50 = 0.2 nmol/L for human endothelial cells). ABT-869 is not a general antiproliferative agent because, in most cancer cells, >1,000-fold higher concentrations of ABT-869 are required for inhibition of proliferation. However, ABT-869 exhibits potent antiproliferative and apoptotic effects on cancer cells whose proliferation is dependent on mutant kinases, such as FLT3. In vivo ABT-869 is effective orally in the mechanism-based murine models of VEGF-induced uterine edema (ED50 = 0.5 mg/kg) and corneal angiogenesis (>50% inhibition, 15 mg/kg). In tumor growth studies, ABT-869 exhibits efficacy in human fibrosarcoma and breast, colon, and small cell lung carcinoma xenograft models (ED50 = 1.5-5 mg/kg, twice daily) and is also effective (>50% inhibition) in orthotopic breast and glioma models. Reduction in tumor size and tumor regression was observed in epidermoid carcinoma and leukemia xenograft models, respectively. In combination, ABT-869 produced at least additive effects when given with cytotoxic therapies. Based on pharmacokinetic analysis from tumor growth studies, efficacy correlated more strongly with time over a threshold value (cellular KDR IC50 corrected for plasma protein binding = 0.08 microg/mL, >or=7 hours) than with plasma area under the curve or Cmax. These results support clinical assessment of ABT-869 as a therapeutic agent for cancer.