Cytotoxicity of the new antimetabolite-bisphosphonate (5-FdU-alendronate) in comparison to standard therapeutics on breast and ovarian cancer cell lines in the ATP tumor chemosensitivity assay

Abstract

Bisphosphonates (BPs) are bone specific palliative therapeutics that reduce tumorand cancer treatment-induced skeletal complication [1–3]. Further, they are an effective treatment for preventing skeletal-related events in patients with bone metastasis and may preserve functional independence as well as quality of life. Besides their action on osteoclasts short-term treatment with zoledronic acid has a clear anti-tumour effect on breast cancer cells which is supposed to be mediated by inhibiting the mevalonate pathway [4, 5]. All BPs share a common P-C-P “backbone” with two phosphonate (PO3) groups covalently linked to carbon. BPs are analogues of pyrophosphates where the PO-P linkage is replaced by P-C-P. The central carbon atom is generally linked to two geminate phosphates, a tertiary hydroxyl group and a variable side chain. The chemical properties, the mode of action and the therapeutic efficacy are more or less determined by the variable side chain. The tertiary hydroxyl group supports the bone-binding of the geminate phosphate groups. As bone is the most common site for metastasis from solid tumors and the majority of patients suffering of those malignancies develop bone metastasis at some point of their disease, there is a high demand for the development of more effective therapeutics against tumor-induced bone disease. In search of new treatment options, chemical modification approaches with BPs have been chosen as potential methods in order to enhance and prolong pharmacological effects in bone along with reducing adverse effect in other tissues [6]. Cytostatica like methotrexate [7], doxorubicin [8] or cisplatin [9] have been covalently attached via a chemical linkage to the terminal amino group of amino-BPs. The obtained conjugates should survive in the circulation, bind to the mineral matrix of the bone and subsequently release both, BPs as well as the linked cytostatica, by cleavage of the conjugates in the bone microenvironment. However, the cytostatic activities of these conjugates were evaluated in certain in vitro cell assays as well as in animal models and proved to be modest. Thus, it is to claim that the amide binding between the BPs and the cytostatica was perhaps not the postulated optimal linkage, being either too stable or too unstable in vivo to provide the desired concentration of cytostatic compounds in the bone [6]. In another approach the conjugation of BPs with the well-established antimetabolites 5-fluorodeoxyuridine (5FdU) and ara-cytidine (araC) was performed by condensation of the low cytostatic active etidronate or medronate with the 5′-monophosphates of 5-FdU or araC (see Fig. 1). The obtained nucleoside-5′-triphosphate analogs S. Schott :M. Wallwiener Department of Gynaecology and Obstetrics, National Center for Tumour Diseases (NCT) , University of Heidelberg, 69115 Heidelberg, Germany