Anti-angiogenic effects of the thienopyridine SR 25989 in vitro and in vivo in a murine pulmonary metastasis model

Abstract

Neovascularisation is a key step in tumour growth and establishment of distant metastases. We have recently demonstrated that the thienopyridine SR 25989 an enantiomer of the anti-aggregant clopidogrel (Plavix 1 ) lacking anti-aggregant activity, inhibits endothelial cell proliferation in vitro by increasing the expression of endogenous thrombospondin-1, a natural potent inhibitor of angiogenesis. The anti-angiogenic effect of SR 25989 was further assessed in vitro in a quantitative assay of angiogenesis comprising a fragment of rat aorta embedded in a fibrin gel and in vivo in a pulmonary metastatic model using C57BL/6 mice inoculated in the foot pad with the highly metastatic melanoma cell line B16 F10. SR 25989 induced a dose dependent inhibition of spontaneous microvessel development in vitro reaching half maximal inhibition at around less than 50 mM and caused platelet derived growth factor induced angiogenesis to regress as a function of thienopyridine concentration. In vivo, SR 25989 did not alter significantly the growth rate of the primary tumour in the foot pad and did not inhibit development of inguinal nodes which appeared after amputation. However, the number and size of lung metastases were reduced in treated animals when examined at the time of sacrifice. In addition, the few metastases over 1 mm 3 did not show any neovascularisation, as confirmed by negative von Willebrand immunostaining and in contrast to intense vascularisation seen in metastases developed by control mice. These results confirm that SR 25989 possesses potent antiangiogenic properties and is able to inhibit metastatic dissemination and growth. The lack of effect on the primary tumour and inguinal nodes illustrates the complexity of the mechanisms involved in tumoural neo-angiogenesis and points out the possibility for distinct processes leading to neovascularisation in primary tumour as opposed to metastases.

Inhibition of Tumor Growth and Metastasis Establishment by Adenovirus-mediated Gene Transfer Delivery of the Antiangiogenic Factor 16K hPRL

“…In accordance with this, a previous study has also shown that treatment with the angiogenesis inhibitor thienopyridine SR 25989 reduces the size and number of lung metastases in a similar metastasis model. 25 Our results show that it should be possible to limit the metastatic process to the development of small metastases that might mostly have only minimal clinical consequences for patients.…”

Initiation of Aspirin Therapy Modulates Angiogenic Protein Levels in Women with Breast Cancer Receiving Tamoxifen Therapy

“…In the laboratory, platelet inhibition by aspirin has been demonstrated to reduce agonist stimulated VEGF and TSP‐1 release from the platelet alpha granule suggesting a plausible mechanism by which local angiogenic protein levels might be controlled in the tumor vasculature micro‐environment in aspirin users . In laboratory models, platelet inhibition by aspirin and thienopyridine derivatives has been demonstrated to decrease angiogenesis, further supporting the suppression of platelet activation as a viable mechanism of influencing tumor angiogenesis …”

“…16 In laboratory models, platelet inhibition by aspirin and thienopyridine derivatives has been demonstrated to decrease angiogenesis, further supporting the suppression of platelet activation as a viable mechanism of infl uencing tumor angiogenesis. 17 We have previously demonstrated that the selective endocrine receptor modulators tamoxifen and aromatase inhibitors (AIs; anastrozole, letrozole, and exemestane) have diff erential eff ects on serum angiogenic protein levels. 18 In that study, tamoxifen use was associated with an increase in serum VEGF levels; a result consistent with higher platelet derived VEGF levels in tamoxifen users as compared to nonusers.…”

VEGF Receptor Inhibitors Block the Ability of Metronomically Dosed Cyclophosphamide to Activate Innate Immunity–Induced Tumor Regression

“…However, this proposed mechanism is not supported by the finding that bona fide anti-angiogenic drugs often show only moderate anti-tumor activity when used as single agents, despite their effectiveness at inhibiting tumor angiogenesis. Examples of this include non-small cell lung cancer (8) and glioblastomas (9) in human patients, 9L gliosarcoma xenografts treated in scid mice (4), and metastatic melanomas in C57BL/6 mice (10). Thus, other mechanisms for the improved anti-tumor effects of metronomic chemotherapy are likely operative.…”