Synthesis and evaluation of 4-[18F]fluorothalidomide for the in vivo studies of angiogenesis

Biological evaluation of both enantiomers of fluoro-thalidomide using human myeloma cell line H929 and others

Over the last few years, thalidomide has become one of the most important anti-tumour drugs for the treatment of relapsed-refractory multiple myeloma. However, besides its undesirable teratogenic side effect, its configurational instability critically limits any further therapeutic improvements of this drug. In 1999, we developed fluoro-thalidomide which is a bioisostere of thalidomide, but, in sharp contrast to the latter, it is configurationally stable and readily available in both enantiomeric forms. The biological activity of fluoro-thalidomide however, still remains virtually unstudied, with the exception that fluoro-thalidomide is not teratogenic. Herein, we report the first biological evaluation of fluoro-thalidomide in racemic and in both (R)- and (S)-enantiomerically pure forms against (in vitro) H929 cells of multiple myeloma (MM) using an annexin V assay. We demonstrate that all fluoro-thalidomides inhibited the growth of H929 MM cells without any in-vivo activation. Furthermore, we report that the enantiomeric forms of fluoro-thalidomide display different anti-tumour activities, with the (S)-enantiomer being noticeably more potent. The angiogenesis of fluoro-thalidomides is also investigated and compared to thalidomide. The data obtained in this study paves the way towards novel pharmaceutical research on fluoro-thalidomides.

Proliferating and quiescent human umbilical vein endothelial cells (HUVECs): a potential in vitro model to evaluate contrast agents for molecular imaging of angiogenesis

BACKGROUND

The design of highly specific contrast agents for molecular imaging of angiogenesis requires the availability of adequate in vitro models. In this context, we investigated the applicability of a potential in vitro model based on human umbilical vein endothelial cells (HUVECs) mimicking physiological and angiogenic vasculature.

METHODS

HUVECs in supplemented medium were used to mimic proliferating neovasculature (stimulated HUVECs), whereas quiescent non-proliferating endothelium was modeled by alteration of medium supplements (unstimulated HUVECs). The features of both culture subsets were compared with features of angiogenic and physiological vessels in vivo described in the literature using different techniques. Testing of the cell model was performed by specific labeling of CD105 and VEGFR2 with fluorophores and consecutive imaging using a planar near-infrared fluorescence (NIRF) imager.

RESULTS

Light microscopy revealed tubular alignment of unstimulated HUVECs, which was absent in stimulated HUVECs. Proliferation assay confirmed a high level of proliferation in stimulated HUVECs but almost no cell proliferation in unstimulated HUVECs. Flow cytometry revealed an up-regulation of CD105, but not of VEGFR2 on stimulated HUVECs. CD105 and VEGFR2 gene expression was detectable both in proliferating and in non-proliferating cells. NIRF-imaging revealed highest fluorescence signal for CD105 in proliferating endothelial cells. No relevant fluorescence signal could be observed for VEGFR2.

CONCLUSION

The established cell model exhibits features of physiological and angiogenic vasculature. NIRF-imaging using the proposed model was feasible. We conclude that the presented cell model might be useful in future angiogenesis applications, like evaluating new fluorophores and other contrast media.