PAPER www.rsc.org/dalton | Dalton Transactions Synthesis, characterization, and cytotoxicity of dinuclear platinum-bisphosphonate complexes to be used as prodrugs in the local treatment of bone tumours Nicola Margiotta, a Rosa Ostuni, a Valentina Gandin, b Cristina Marzano, b Sara Piccinonna a,c and Giovanni Natile* a Received 22nd September 2009, Accepted 29th October 2009 First published as an Advance Article on the web 16th November 2009 DOI: 10.1039/b919721d For over 30 years cisplatin has been one of the most active antitumour agents in clinical use, nevertheless research for overcoming cisplatin toxicity and resistance or for improving its efficacy has never ceased. In this context we have recently proposed dinuclear Pt complexes with bridging geminal bisphosphonates as novel Pt-prodrugs with potential activity at the bone surface after embedment in inorganic matrices and implantation at the tumour site. In the present paper we report the synthesis and full characterization of four new platinum complexes having a dinuclear structure with a bisphosphonate (2-ammonium-1-hydroxyethane-1,1-diyl-bisphosphonate or 3-ammonium-1-hydroxypropane-1,1-diyl-bisphosphonate, AHBP-H and PAM-H, respectively) acting as a bridging ligand between two platinum moieties (cis-[Pt(NH 3 ) 2 ] 2+ , directly related to cisplatin, and [Pt(cis-1,4-DACH)] 2+ , known to be able to overcome the cisplatin resistance). Moreover, as a preliminary investigation, the in vitro cytotoxicity of the new complexes has been evaluated on a panel of 13 human tumour cell lines including cisplatin- and multidrug-resistant sublines. Introduction Cisplatin is one of the most active antitumour agents in cur- rent clinical use; 1-2 apart from being curative against testicular tumours, 3 it is effective against several other cancers such as ovarian, head and neck, cervical, and bladder. 4-6 Despite its success, treatment with cisplatin is limited by undesirable side ef- fects such as nephrotoxicity, nausea, vomiting, myelosuppression, ototoxicity and neurotoxicity. 7,8 Moreover, tumour resistance to cisplatin (acquired during cycles of therapy or intrinsic in some types of cancers) is another factor that limits its use. 9 Since the serendipitous discovery of the antitumoural activity of cisplatin, 10,11 an intensive research has led to the synthesis of thousands of new platinum compounds with the aim of overcoming cisplatin toxicity and resistance or to improve its efficacy. The use of carrier ligands able to promote the specific accumulation of the drug in target organs or cells has also been exploited as a strategy to overcome the side effects of cisplatin. For instance, platinum complexes containing (aminoalkyl)phosphonic acids 12,13 have been exploited by the group of Keppler 14,15 for their potential use as selective platinum drugs for bone tumours. Those authors were inspired by the analogy between these ligands and geminal bisphosphonates (BPs), commercial drugs, which show affinity for bones and other calcified tissues and are in clinical use for the treatment of hypercalcaemia and skeletal metastases. 16-19 a Dipartimento Farmaco-Chimico, Universit` a degli Studi di Bari “A. Moro”, Via E. Orabona 4, 70125, Bari, Italy. E-mail: natile@farmchim.uniba.it; Fax: +39-080-5442230 b Dipartimento di Scienze Farmaceutiche, Universit` a degli Studi di Padova, Via Marzolo 5, 35131, Padova, Italy c Consorzio Interuniversitario di Ricerca in Chimica dei Metalli nei Sistemi Biologici (C.I.R.C.M.S.B.), Via C. Ulpiani 27, 70125, Bari, Italy The combination of the bisphosphonic functionality with the platinum moiety could promote the specific accumulation of the antitumour drug in the bone with consequent significant improve- ment of the biological effect and reduction of the systemic toxicity. Pharmacological investigations performed on Pt(II) complexes with amino-bis/tris(methylenephosphonate) ligands were a proof of concept demonstrating their superior activity as compared to cisplatin in an orthotopically transplanted rat osteosarcoma model closely resembling the human osteosarcoma. 20,21 A further lowering of the systemic side effects of a drug could be obtained by local administration directly at the site of the tumour and, in this context, we have recently proposed dinuclear Pt complexes with bridging geminal bisphosphonates (Chart 1) as novel Pt-prodrugs with potentiated activity at the Chart 1 Sketches of already reported dinuclear Pt-bisphospho- nate complexes. AHBP-H = 2-ammonium-1-hyroxyethane-1,1-diyl- bisphosphonate; MED = medronate (methane-1,1-diyl-bisphosphonate); PHBP-H = 1-(pyridinium-4-yl)-1-hydroxy-methane-1,1-bisphosphonate. 10904 | Dalton Trans., 2009, 10904–10913 This journal is © The Royal Society of Chemistry 2009 885