Genetic heterogeneity of the vasculogenic phenotype parallels angiogenesis; Implications for cellular surrogate marker analysis of antiangiogenesis.

Development of antiangiogenic therapies would be significantly facilitated by quantitative surrogate pharmacodynamic markers. Circulating peripheral blood endothelial cells (CECs) and/or their putative progenitor subset (CEPs) have been proposed but not yet fully validated for this purpose. Herein, we provide such validation by showing a striking correlation between highly genetically heterogeneous bFGF- or VEGF-induced angiogenesis and intrinsic CEC or CEP levels measured by flow cytometry, among eight different inbred mouse strains. Moreover, studies using genetically altered mice showed that levels of these cells are affected by regulators of angiogenesis, including VEGF, Tie-2, and thrombospondin-1. Finally, treatment with a targeted VEGFR-2 antibody caused a dose-dependent reduction in viable CEPs that precisely paralleled its previously and empirically determined antitumor activity.

Targeting cyclooxygenase-2 reduces overt toxicity toward low-dose vinblastine and extends survival of juvenile mice with Friend disease.

PURPOSE: To test the efficacy of selective therapy against cyclooxygenase-2 in combination with a low-dose regimen of a cytotoxic agent in the treatment of juvenile hematopoietic malignancies in the experimental model, Friend disease. EXPERIMENTAL DESIGN: Juvenile erythroleukemic mice (n = 8) received no treatment, celecoxib (1600 mg/kg/d), vinblastine (0.5 microg/g twice weekly), vehicle controls, or celecoxib + vinblastine combination (n = 9) over a 6-month period from time of tumor induction. Overt toxicity was assessed daily and recorded weekly. RESULTS: Among randomly selected mice from celecoxib treatment groups, plasma concentrations ranged from 2 to 6 micromol/L. As a single agent, celecoxib was not associated with any apparent toxicity. Monotherapy with vinblastine, however, caused early mortality marked by severe diarrhea, lethargy, and weight loss. At the tested doses, neither vinblastine nor celecoxib enhanced survival as monotherapies. Coadministration of these two drugs alleviated the overt toxicity associated with vinblastine and resulted in a significant increase in survival (P < 0.05). Survivors sampled throughout the study showed a trend to decreased weight loss and hematocrit levels among all groups, but significance was evidenced earlier in the vinblastine monotherapy group overall (P < 0.05). Despite similar degree of splenomegaly, histologic analysis revealed preserved splenic mantle architecture from mice given combination therapy compared with those sampled from mice on all other monotherapies, exhibiting a more diffuse burden of blasts and destruction of germinal centers. CONCLUSION: We propose that addition of a selective cyclooxygenase-2 inhibitor to a modified low-dose conventional chemotherapeutic regimen protects juvenile mice with Friend disease from succumbing to low-dose cytotoxicity, in part, by neutralizing acute inflammatory responses.

Friend virus-induced erythroleukemias: a unique and well-defined mouse model for the development of leukemia.

Retroviruses lacking oncogenes have been known to induce various types of cancer when inoculated into animals. Among these, Friend virus, discovered by Charlotte Friend in 1957, is capable of inducing erythroleukemias when injected into susceptible strains of mice. Since its discovery, this murine model of leukemogenesis has been extensively used to study the multistage nature of cancer. In the past two decades, several oncogenes and tumour suppressor genes, which play critical roles in the induction and progression of Friend erythroleukemia, have been identified. Retroviral insertional activation of Fli-1 and Spi-1/PU.1, as well as loss of tumour suppressor genes such as p53 or p45 NFE2 have been shown to be critical for the induction and progression of Friend virus-induced erythroleukemias. The majority of these genetic changes have also been implicated in various types of human neoplastic transformations. In this review we will discuss the genetic changes associated with Friend Disease, the temporal order during induction and progression of disease, and the function of these genes in both normal erythroid development as well as malignant transformation.

Optimal biologic dose of metronomic chemotherapy regimens is associated with maximum antiangiogenic activity.

Low-dose metronomic chemotherapy is a promising therapeutic cancer treatment strategy thought to have an antiangiogenic basis. However, the advantages of reduced toxicity, increased efficacy in some cases, and ability to combine chemotherapy administered long term in this way with targeted therapies can be compromised by the empiricism associated with determining the optimum biologic dose (OBD). Using 4 distinct metronomic chemotherapy regimens in 4 different preclinical tumor models, including a hematologic malignancy, we established the OBD by determining the maximum efficacy associated with minimum or no toxicity. We then found each OBD to be strikingly correlated with the maximum reduction in viable peripheral blood circulating vascular endothelial growth factor receptor 2-positive (VEGFR-2+) endothelial precursors (CEPs). These results suggest that CEPs may serve as a pharmacodynamic biomarker to determine the OBD of metronomic chemotherapy regimens.

The splenic microenvironment is a source of proangiogenesis/inflammatory mediators accelerating the expansion of murine erythroleukemic cells.

The stromal compartments of hematopoietic organs (eg, spleen) are known to influence the viability and growth of diseased hematopoietic progenitors. Here we have used Friend murine leukemia virus (F-MuLV)-induced erythroleukemia to investigate factors of the splenic microenvironment that may make it fertile for the expansion and survival of malignant erythroblasts. We found that splenectomized, erythroleukemic mice exhibited extended survival compared with age-matched sham controls. In vitro, the proliferation of primary erythroleukemic cells cocultured with leukemic-derived splenic adherent cells or their conditioned media was found to be significantly higher than that observed in cocultures with healthy-derived adherent splenic cells. Cytokine protein arrays revealed that F-MuLV-infected splenocytes secreted elevated levels of interleukin-6 (IL-6), vascular endothelial growth factor-A (VEGF-A), macrophage chemoattractant protein-5 (MCP-5), soluble tumor necrosis factor receptor-1 (sTNFR1), IL-12p70, tumor necrosis factor-alpha (TNF-alpha), and IL-2 over normal splenocytes. Medium supplemented with both VEGF-A and MCP-5 could sustain proliferation of primary erythroleukemic cells in vitro, and significant proliferative suppression was observed upon addition of neutralizing antibodies to either of these factors. Furthermore, in vivo administration of a neutralizing antibody to VEGF-A extended survival times of erythroleukemic mice in comparison with controls. These findings suggest that VEGF-A and MCP-5 are potentially pivotal paracrine mediators occurring within the diseased splenic microenvironment capable of promoting disease acceleration and expansion of erythroleukemic blasts.