Platinum–bisphosphonate complexes have proven to be inactive chemotherapeutics targeted for malignant mesothelioma because of inappropriate hydrolysis

Molecular dynamics simulation study of DNA conformation changes caused by the dinuclear platinum(II) complexes with the bisphosphonate group

Bisphosphonate (BP) has been widely used as a bone-targeting group, and the BP-modified platinum(II) complexes have shown potential to as anticancer drugs against bone-related diseases, such as osteosarcoma. DNA conformation changes induced by the BP-modified dinuclear platinum(II) complexes have been investigated using molecular dynamics simulations. The results indicated that the BP-modified dinuclear platinum(II) complexes coordinated to DNA results in DNA structural distortions, including twisting, unwinding and bending. Furthermore, the rigidity of the bridging linkers in the BP-modified platinum(II) complex may induce more significant DNA structural distortions with same spans. The results provide the detail information of DNA conformational changes induced by the BP-modified platinum(II) complexes with different flexibility of bridging linkers, and are helpful for exploring novel platinum-based antitumor drugs.

Targeting of radioactive platinum-bisphosphonate anticancer drugs to bone of high metabolic activity

Platinum-based chemotherapeutics exhibit excellent antitumor properties. However, these drugs cause severe side effects including toxicity, drug resistance, and lack of tumor selectivity. Tumor-targeted drug delivery has demonstrated great potential to overcome these drawbacks. Herein, we aimed to design radioactive bisphosphonate-functionalized platinum (^195mPt-BP) complexes to confirm preferential accumulation of these Pt-based drugs in metabolically active bone. In vitro NMR studies revealed that release of Pt from Pt BP complexes increased with decreasing pH. Upon systemic administration to mice, Pt-BP exhibited a 4.5-fold higher affinity to bone compared to platinum complexes lacking the bone-seeking bisphosphonate moiety. These Pt-BP complexes formed less Pt-DNA adducts compared to bisphosphonate-free platinum complexes, indicating that in vivo release of Pt from Pt-BP complexes proceeded relatively slow. Subsequently, radioactive ^195mPt-BP complexes were synthesized using ^195mPt(NO₃)₂(en) as precursor and injected intravenously into mice. Specific accumulation of ^195mPt-BP was observed at skeletal sites with high metabolic activity using micro-SPECT/CT imaging. Furthermore, laser ablation-ICP-MS imaging of proximal tibia sections confirmed that ^195mPt BP co-localized with calcium in the trabeculae of mice tibia.

A Potential Bone-Targeting Hypotoxic Platinum(II) Complex with an Unusual Cytostatic Mechanism toward Osteosarcoma Cells

Osteosarcoma (OS) is the most common primary pediatric bone tumor lethal to children and adolescents. Chemotherapeutic agents such as cisplatin are not effective for OS because of their poor accessibility to this cancer and severe systemic toxicity. In this study, a lipophilic platinum(II) complex bearing a bisphosphonate bone-targeting moiety, cis-[PtL(NH₃)₂Cl]NO₃ {BPP; L = tetraethyl [2-(pyridin-2-yl)ethane-1,1-diyl]bisphosphonate}, was prepared and characterized by NMR, electrospray ionization mass spectrometry, and single-crystal X-ray crystallography. The cytotoxicity of BPP toward OS cell lines U2OS and MG-63 was tested by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. BPP exhibits moderate inhibition against U2OS cells through a mechanism involving both DNA binding and a mevalonate pathway. The acute toxicity of BPP to mice is 7-fold lower than that of cisplatin. The relative low systemic toxicity may result from the steric hindrance of the ligand, which blocks BPP approaching the bases of DNA. The results suggest that incorporating bisphosphonates into a platinum complex not only enhances its bone-targeting property but also minimizes its reactivity toward DNA and thereby lowers the systematic toxicity of the complex. The diminished cytotoxicity of BPP could be compensated for by increasing the therapeutic dose with marginal harm. This strategy provides a new possibility for overcoming the ineffectiveness and systemic toxicity of platinum drugs in the treatment of OS.

Bifunctional Platinum(II) Complexes with Bisphosphonates Substituted Diamine Derivatives: Synthesis and In vitro Cytotoxicity

A series of N,N'-dibisphosphonate-containing 1,3-propanediamine derivatives (L1 - L6) and their corresponding dichloridoplatinum(II) complexes (1 - 6) have been synthesized and characterized by elemental analysis, ¹ H-NMR, ¹³ C-NMR, ³¹ P-NMR and HR-MS spectra. The in vitro antitumor activities of compounds L1 - L6 and 1 - 6 were tested by WST-8 assay with Cell Counting Kit-8, indicating that platinum-based complexes 1 - 6 showed higher cytotoxicity than corresponding ligands L1 - L6 against A549 and MG-63, especially complex 2 which displayed comparable cytotoxicity to those of cisplatin and zoledronate after 48 h incubation. In addition, complexes 1 - 6 were more active in vitro on osteosarcoma cell line MG-63 than normal osteoblast cell line hFOB 1.19. The structure-activity relationship has been summarized based on the in vitro cytotoxicity of three series of platinum complexes from this and our previous studies. The in vitro bone affinity of platinum complexes was also tested by hydroxyapatite (HAP) chromatography in terms of capacity factor K'. Besides, in this paper, representative complex 2, which has been proved to be a promising antitumor agent with high cytotoxicity and bone HAP binding property, was investigated for its mechanism of action producing cell death against MG-63.

Pros and cons of bifunctional platinum(IV) antitumor prodrugs: two are (not always) better than one

This article evaluates the efficacy and applicability of bifunctional prodrugs consisting of a six-coordinate Pt(iv) octahedral core and one or more bioactive molecules. The platinum(iv) complexes release upon reduction the corresponding cytotoxic Pt(ii) agents and the bioactive molecules, able to inhibit some biochemical mechanisms of cancer growth and/or prevent the deactivation of the Pt(ii) metabolites.

Dinuclear Pt(II)-bisphosphonate complexes: a scaffold for multinuclear or different oxidation state platinum drugs

Geminal bisphosphonates (BPs), used in the clinic for the treatment of hypercalcaemia and skeletal metastases, have been also exploited for promoting the specific accumulation of platinum antitumor drugs in bone tissue. In this work, the platinum dinuclear complex [{Pt(en)}(2)(μ-AHBP-H(2))](+) (1) (the carbon atom bridging the two phosphorous atoms carrying a 2-ammonioethyl and a hydroxyl group, AHBP-H(2)) has been used as scaffold for the synthesis of a Pt(II) trinuclear complex, [{Pt(en)}(3)(μ-AHBP)](+) (2), and a Pt(IV) adamantane-shaped dinuclear complex featuring an oxo-bridge, [{Pt(IV)(en)Cl}(2)(μ-O)(μ-AHBP-H(2))](+) (3) (X-ray structure). Compound 2 undergoes a reversible, pH dependent, rearrangement with a neat switch point around pH = 5.4. Compound 3 undergoes a one-step electrochemical reduction at E(pc) = -0.84 V affording compound 1. Such a potential is far lower than that of glutathione (-0.24 V), nevertheless compound 3 can undergo chemical reduction to 1 by GSH, most probably through a different (inner-sphere) mechanism. In vitro cytotoxicity of the new compounds, tested against murine glioma (C6) and human cervix (HeLa) and hepatoma (HepG2) cell lines, has shown that, while the Pt(IV) dimer 3 is inactive up to a concentration of 50 μM, the two Pt(II) polynuclear compounds 1 and 2 have a cytotoxicity comparable to that of cisplatin with the trinuclear complex 2 generally more active than the dinuclear complex 1.

Polyoxometalates functionalized by bisphosphonate ligands: synthesis, structural, magnetic, and spectroscopic characterizations and activity on tumor cell lines

We report the synthesis and characterization of eight new Mo, W, or V-containing polyoxometalate (POM) bisphosphonate complexes with metal nuclearities ranging from 1 to 6. The compounds were synthesized in water by treating Mo(VI), W(VI), V(IV), or V(V) precursors with biologically active bisphosphonates H(2)O(3)PC(R)(OH)PO(3)H(2) (R = C(3)H(6)NH(2), Ale; R = CH(2)S(CH(3))(2), Sul and R = C(4)H(5)N(2), Zol, where Ale = alendronate, Sul = (2-Hydroxy-2,2-bis-phosphono-ethyl)-dimethyl-sulfonium and Zol = zoledronate). Mo(6)(Sul)(2) and Mo(6)(Zol)(2) contain two trinuclear Mo(VI) cores which can rotate around a central oxo group while Mo(Ale)(2) and W(Ale)(2) are mononuclear species. In V(5)(Ale)(2) and V(5)(Zol)(2) a central V(IV) ion is surrounded by two V(V) dimers bound to bisphosphonate ligands. V(6)(Ale)(4) can be viewed as the condensation of one V(5)(Ale)(2) with one additional V(IV) ion and two Ale ligands, while V(3)(Zol)(3) is a triangular V(IV) POM. These new POM bisphosphonates complexes were all characterized by single-crystal X-ray diffraction. The stability of the Mo and W POMs was studied by (31)P NMR spectroscopy and showed that all compounds except the mononuclear Mo(Ale)(2) and W(Ale)(2) were stable in solution. EPR measurements performed on the vanadium derivatives confirmed the oxidation state of the V ions and evidenced their stability in aqueous solution. Electrochemical studies on V(5)(Ale)(2) and V(5)(Zol)(2) showed reduction of V(V) to V(IV), and magnetic susceptibility investigations on V(3)(Zol)(3) enabled a detailed analysis of the magnetic interactions. The presence of zoledronate or vanadium correlated with the most potent activity (IC(50)~1-5 μM) against three human tumor cell lines.

Novel oximato-bridged platinum(II) di- and trimer(s): synthetic, structural, and in vitro anticancer activity studies

Novel platinum complexes of trans geometry [PtCl(2){(Z)-R(H)C═NOH}(2)] [R = Me (1), Et (3)] and [PtCl(2){(E)-R(H)C═NOH}{(Z)-R(H)C═NOH}] [R = Me (2), Et (4)] as well as the classic trans-[PtCl(2)(R(2)C═NOH)(2)] [R = Me, Et] were reacted with an equivalent amount of silver acetate in acetone solution at ambient temperature, resulting in formation of unprecedented head-to-tail-oriented oximato-bridged dimers [PtCl{μ-(Z)-R(H)C═NO}{(Z)-R(H)C═NOH}](2) [R = Me (5), Et (7)], [PtCl{μ-(Z)-R(H)C═NO}{(E)-R(H)C═NOH}](2) [R = Me (6), Et (8)], and [PtCl(μ-R(2)C═NO)(R(2)C═NOH)](2) [R = Me (9), Et (10)], correspondingly. The dimeric species feature a unique six-membered diplatinacycle and represent the first example of oxime ligands coordinated to platinum via the oxygen atom. All complexes were characterized by elemental analyses, electrospray ionization mass spectrometry, IR and multinuclear ((1)H, (13)C, and (195)Pt) NMR spectroscopy, as well as X-ray diffraction in the cases of dimers 6 and 9. Furthermore, the crystal and molecular structures of a trimeric oximato-bridged complex 11 comprising three platinum units connected in a chain way were established. The cytotoxicity of both dimers and the respective monomers was comparatively evaluated in three human cancer cell lines: cisplatin-sensitive CH1 cells as well as cisplatin-resistant SW480 and A549 cells, whereupon structure-activity relationships were drawn. Thus, it was found that dimerization results in a substantial (up to 7-fold) improvement of IC(50) values of (aldoxime)Pt(II) compounds, whereas for the analogous complexes featuring ketoxime ligands the reverse trend was observed. Remarkably, the novel dimers yielded no cross-resistance with cisplatin in SW480 cells, exhibiting up to 2-fold enhanced cytotoxicity in comparison with the CH1 cell line and thereby possessing a promising potential to overcome resistance toward platinum anticancer drugs. The latter point was also confirmed by investigating the potency of apoptosis induction in the case of one monomer as well as one dimer; the investigated complexes proved to be strong apoptotic agents which could induce cell death even in the cisplatin-resistant SW480 cell line.