Insights into the anti-angiogenic properties of phosphaplatins ☆ Lu Yang a , Shadi Moghaddas b,1 , Homa Dezvareh b , Louiza Belkacemi b , Steven J. Bark b , Rathindra N. Bose a,b , Loi H. Do a, ⁎ a Departments of Chemistry, University of Houston, Houston, TX 77004, United States b Departments of Biology and Biochemistry, University of Houston, Houston, TX 77004, United States abstract article info Article history: Received 23 May 2016 Received in revised form 19 July 2016 Accepted 26 July 2016 Available online xxxx Phosphaplatins are platinum-based antitumor compounds that, unlike other clinically utilized platinum drugs (i.e. cisplatin, carboplatin, and oxaliplatin), appear to target proteins rather than DNA. Because of their unique mode of action, phosphaplatins are promising drug candidates for cisplatin-resistant cancers. In this study, we discovered that Pt(II) and Pt(IV) phosphaplatins possess diverse antitumor properties. In addition to targeting apoptosis antigen (FAS) and proapoptotic gene products as described previously, phosphaplatins also target an- giogenesis. We demonstrate that phosphaplatins inhibit human umbilical vein endothelial cell (HUVEC) migra- tion and tube formation in vitro and suppress tumor angiogenesis and growth in immunodeficient mice that were inoculated with A2780 ovarian cancer cells in vivo. To provide insight into this novel antitumor mechanism, phosphaplatin-treated HUVECs were found to exhibit lower gene expression levels of vascular endothelial growth factors (VEGFs) and the VEGFR-2 receptor compared to untreated cells. Kinase inhibition studies suggest that phosphaplatins are inhibitors of VEGFR-2. In ligand exchange experiments using both Pt atomic absorption and 31 P NMR spectroscopies, we show that phosphaplatins most likely bind to VEGFR-2 through metal-ligand co- ordination rather than electrostatic interactions. These studies enhance our understanding of the diverse and novel mechanisms of action of the phosphaplatin antitumor agents, which could potentially be used as chemo- therapeutic agents against cisplatin-resistant cancers. © 2016 Elsevier Inc. All rights reserved. 1. Introduction Platinum-based anticancer drugs, such as cisplatin, carboplatin, and oxaliplatin are DNA-targeting chemotherapeutics used widely in treating a variety of cancers, including ovarian, testicular, lung, and bladder cancers [1–4]. Although numerous platinum compounds have been synthesized and tested since the discovery of cisplatin's anti- proliferative properties, their mechanisms of action are generally be- lieved to involve the formation of platinum-DNA lesions and eventual cell destruction via apoptosis [4]. Unfortunately, the non-selective DNA binding tendencies of traditional Pt drugs often cause severe side effects [5]. Furthermore, drug resistance to Pt complexes can develop as a result of efficient removal of platinum-DNA adducts via the nuclear excision repair (NER) pathway or other deactivation pathways [6–8]. To circumvent the limitations of existing platinum chemotherapeutics, we have undertaken a systematic approach to develop non-DNA binding anticancer agents called phosphaplatins (Chart 1) [9–12]. Phosphaplatins comprise platinum complexes that are ligated by diaminocyclohexane (dach) and pyrophosphate ligands. The (1R,2R- diaminocyclohexane)(dihydropyrophosphato)platinum(II) (RRD2) and (1R,2R-diaminocyclohexane)(dihydropyrophosphato)(trans- dihydroxo)platinum(IV) (RRD4) stereoisomers were shown to be high- ly potent against both A2780 and cisplatin-resistant human ovarian cancer cells [10,11]. Initial studies suggested a unique mode of action for these chemotherapeutic agents. No platinum-DNA adducts were detected upon treatment of cancer cells with the phosphaplatins and no nucleotide excision repair, homologous recombination repair, or postreplication repair were observed [12]. Instead, phosphaplatins in- duced overexpression of the death receptor FAS and sphingomyelinase proteins, which suggests protein targeting and activation of an extrinsic apoptotic mechanism. Interestingly, there are scarcely any reports of platinum agents that display anti-angiogenic activity and no currently approved metal- based drugs target angiogenesis in cancer chemotherapy [13,14]. Angio- genesis is the growth of new blood vessels from pre-existing Journal of Inorganic Biochemistry xxx (2016) xxx–xxx ☆ The authors declare the following competing financial interest(s): Phosplatin Therapeutics, LLC (PT), has licensed the compounds disclosed in this article from Ohio University including PT-112, which is currently undergoing phase 1 clinical trial. These compounds were discovered by R.N.B., who held equity interest in the company. However, the funding for this research was not provided by PT. Other authors have no conflict of interest. ⁎ Corresponding author at: Departments of Chemistry, University of Houston, 4800 Calhoun Rd., Houston, TX 77004, United States. E-mail address: loido@uh.edu (L.H. Do). 1 Present address: Harmony School of Discovery, 6270 Barker Cypress Rd., Houston, TX 77084, United States. JIB-10053; No of Pages 12 http://dx.doi.org/10.1016/j.jinorgbio.2016.07.020 0162-0134/© 2016 Elsevier Inc. All rights reserved. Contents lists available at ScienceDirect Journal of Inorganic Biochemistry journal homepage: www.elsevier.com/locate/jinorgbio Please cite this article as: L. Yang, et al., Insights into the anti-angiogenic properties of phosphaplatins, J. Inorg. Biochem. (2016), http://dx.doi.org/ 10.1016/j.jinorgbio.2016.07.020