Bisphosphonate drugs inhibit osteoclastic bone resorption and are widely used to treat skeletal complications in patients with tumor-induced osteolysis. We now show that zoledronic acid, a new generation bisphosphonate with a heterocyclic imidazole substituent, is also a potent inhibitor of angiogenesis. In vitro, zoledronic acid inhibits proliferation of human endothelial cells stimulated with fetal calf serum, basic fibroblast growth factor (bFGF), and vascular endothelial growth factor (IC(50) values 4.1, 4.2, and 6.9 microM, respectively), and modulates endothelial cell adhesion and migration. In cultured aortic rings and in the chicken egg chorioallantoic membrane assay, zoledronic acid reduces vessel sprouting. When administered systemically to mice, zoledronic acid potently inhibits the angiogenesis induced by subcutaneous implants impregnated with bFGF [ED(50), 3 microg/kg (7.5 nmol/kg) s.c.]. These findings indicate that zoledronic acid has marked antiangiogenic properties that could augment its efficacy in the treatment of malignant bone disease and extend its potential clinical use to other diseases with an angiogenic component.

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Cryptolepine hydrochloride is an indoloquinoline alkaloid isolated from the roots of Cryptolepis sanguinolenta. It is characterized by a multiplicity of host-mediated biological activities, including antibacterial, antiviral, and antimalarial properties. To date, the molecular basis for its diverse biological effects remains largely uncertain. Several lines of evidence strongly suggest that DNA might correspond to its principal cellular target. Consequently, we studied the strength and mode of binding to DNA of cryptolepine by means of absorption, fluorescence, circular, and linear dichroism, as well as by a relaxation assay using DNA topoisomerases. The results of various optical and gel electrophoresis techniques converge to reveal that the alkaloid binds tightly to DNA and behaves as a typical intercalating agent. In DNAase I footprinting experiments it was found that the drug interacts preferentially with GC-rich sequences and discriminates against homo-oligomeric runs of A and T. This study has also led to the discovery that cryptolepine is a potent topoisomerase II inhibitor and a promising antitumor agent. It stabilizes topoisomerase II-DNA covalent complexes and stimulates the cutting of DNA at a subset of preexisting topoisomerase II cleavage sites. Taking advantage of the fluorescence of the indoloquinoline chromophore, fluorescence microscopy was used to map cellular uptake of the drug. Cryptolepine easily crosses the cell membranes and accumulates selectively into the nuclei rather than in the cytoplasm of B16 melanoma cells. Quantitative analyses of DNA in cells after Feulgen reaction and image cytometry reveal that the drug blocks the cell cycle in G2/M phases. It is also shown that the alkaloid is more potent at inhibiting DNA synthesis rather than RNA and protein synthesis. Altogether, the results provide direct evidence that DNA is the primary target of cryptolepine and suggest that this alkaloid is a valid candidate for the development of tumor active compounds.

Bone sialoprotein (BSP) is a secreted glycoprotein primarily found in sites of biomineralization. Recently, we demonstrated that BSP is strongly upregulated in osteotropic cancers and particularly those that exhibit microcalcifications. BSP contains an Arg-Gly-Asp (RGD) motif found in other adhesive molecules that interact with cellular integrins. In bone, BSP has been shown to mediate the attachment of osteoblasts and osteoclasts via alpha(v)beta(3) integrin receptors. Ligands for alpha(v)beta(3) integrin are considered to play a central role during angiogenesis. Therefore, we used human umbilical vein endothelial cells (HUVECs) to study the potential role of BSP in angiogenesis. We found that purified eukaryotic recombinant human BSP (rhBSP) is able to promote both adhesion and chemotactic migration of HUVECs in a dose-dependent manner. These interactions involve HUVEC alpha(v)beta(3) integrin receptors and the RGD domain of BSP. Indeed, HUVECs attach to a recombinant BSP fragment containing the RGD domain, whereas this response is not observed with the same fragment in which RGD has been mutated to Lys-Ala-Glu (KAE). A cyclic RGD BSP peptide inhibits both adhesion and migration of HUVECs to rhBSP. Moreover, anti-alpha(v)beta(3) but not anti-alpha(v)beta(5) monoclonal antibodies also prevent BSP-mediated adhesion and migration of HUVECs. We observed that both rhBSP and the RGD BSP recombinant fragment stimulated ongoing angiogenesis on the chorioallantoic chick membrane assay. BSP angiogenic activity was inhibited by anti-alpha(v)beta(3) antibody, and the KAE BSP fragment was inactive. Our findings represent the first report implicating BSP in angiogenesis. BSP could play a critical role in angiogenesis associated with bone formation and with tumor growth and metastatic dissemination.

Cryptolepine, matadine, and serpentine are three indoloquinoline alkaloids isolated from the roots of African plants: Cryptolepis sanguinolenta, Strychnos gossweileri, and Rauwolfia serpentina, respectively. For a long time, these alkaloids have been used in African folk medicine in the form of plant extracts for the treatment of multiple diseases, in particular as antimalarial drugs. To date, the molecular basis for their diverse biological effects remains poorly understood. To elucidate their mechanism of action, we studied their interaction with DNA and their effects on topoisomerase II. The strength and mode of binding to DNA of the three alkaloids were investigated by spectroscopy. The alkaloids bind tightly to DNA and behave as typical intercalating agents. All three compounds stabilize the topoisomerase II-DNA covalent complex and stimulate the cutting of DNA by topoisomerase II. The poisoning effect is more pronounced with cryptolepine than with matadine and serpentine, but none of the drugs exhibit a preference for cutting at a specific base. Cryptolepine which binds 10-fold more tightly to DNA than the two related alkaloids proves to be much more cytotoxic toward B16 melanoma cells than matadine and serpentine. The cellular consequences of the inhibition of topoisomerase II by cryptolepine were investigated using the HL60 leukemia cell line. The flow cytometry analysis shows that the drug alters the cell cycle distribution, but no sign of drug-induced apoptosis was detected when evaluating the internucleosomal fragmentation of DNA in cells. Cryptolepine-treated cells probably die via necrosis rather than via apoptosis. The results provide evidence that DNA and topoisomerase II are the primary targets of cryptolepine, matadine, and serpentine.

Different retrospective studies have shown that microvessel counting (MVC) is an independent prognostic marker for clinical outcome in breast cancer. The aim of this study was to evaluate the prognostic value of MVC alone or in association with classical clinicopathological parameters, as well as the reproducibility of the technique. We analyzed a retrospective series of 216 cases of breast carcinoma. Tissue sections were stained for Factor-VIII-related antigen. Microvessel quantification was performed at x400 magnification in the three most vascular areas of the tumors (hot spots). Mean and highest values were studied. Furthermore, a semi-quantitative evaluation of MVC was performed by use of an image-analysis system. The effect of multiple factors on survival was tested under a Cox multivariate proportional hazards model. In ten cases, a study of the reproducibility was done by evaluating MVC in different sections of the same block and in different blocks of a same tumor. There was no association between MVC (determined at a microscopic level or by image analysis) and overall survival or relapse-free survival. No association was found with tumor size, tumor grade, and lymph-node status. The study of reproducibility showed a very high intra-tumoral variation of MVC. The intra-individual coefficient of variation (CV) varied between 20 and 80%. This study did not show any significant correlation between angiogenesis, as assessed by MVC, and relapse-free survival or overall survival in infiltrating breast carcinomas. The low reproducibility of the MVC for the same tumors suggests that this technique must still be optimized before routine application.

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Zoledronate exhibits antiangiogenic properties in vitro and in vivo. Integrins alphavbeta3 and alphavbeta5 are involved in angiogenesis. Because zoledronate inhibits endothelial cell adhesion, the authors explored the hypothesis that it could alter these integrins recruitment to focal adhesion sites. Human umbilical vein endothelial cells (HUVECs) were treated with zoledronate or with mevalonate pathway intermediates geranylgeraniol (GGOH) and farnesol (FOH). Zoledronate generated a significant decrease in alphavbeta3 and alphavbeta5 expression at HUVEC cell surface using flow cytometry and immunofluorescence. This inhibition was reversed by GGOH but not by FOH. Cells cotreated with zoledronate and GGOH were able to attach to vitronectin through alphavbeta3 and alphavbeta5, as confirmed by the use of specific function-blocking antibodies. The authors showed that zoledronate alters endothelial cell integrin-mediated adhesion. This effect is likely to contribute to the previously demonstrated antiangiogenic effect of zoledronate. Whether this mechanism of action also applies to metastatic tumor cells is under investigation.