Mixed amine/ammine motifs are important features in newer generation platinum anticancer agents, including the Pt(IV) prodrug satraplatin. One synthetic route that can be used to access platinum molecules with such structures exploits the trans effect during NH₃-mediated cleavage of iodo-bridged platinum(II) dimers of the form [Pt(Am)I(μ-I)]₂, where Am is an amine. A clear picture of the nature of these dimers that is consistent with the reactivity they exhibit has remained elusive. Moreover, technical aspects of this chemistry have impeded its more widespread use. We present here an improved strategy that permits isolation and use of [Pt(Am)I(μ-I)]₂, where Am is cyclohexylamine, within minutes as opposed to weeks, as previously reported. A detailed spectroscopic, crystallographic, and chromatographic investigation of this intermediate in the synthesis of satraplatin is also presented with a discussion of the ability of both cis and trans isomers of the dimer to produce exclusively cis-[Pt(NH₂C₆H₁₁)(NH₃)I₂] upon treatment with NH₃.

The monofunctional platinum complex cis-[Pt(NH3)2Cl(Am)](+), also known as phenanthriplatin, where Am is the N-heterocyclic base phenanthridine, has promising anticancer activity. Unlike bifunctional compounds such as cisplatin, phenanthriplatin can form only one covalent bond to DNA. Another distinguishing feature is that phenanthriplatin is chiral. Rotation about the Pt-N bond of the phenanthridine ligand racemizes the complex, and the question arises as to whether this process is sufficiently slow under physiological conditions to impact its DNA-binding properties. Here we present the results of NMR spectroscopic, X-ray crystallographic, molecular dynamics, and density functional theoretical investigations of diastereomeric phenanthriplatin analogs in order to probe the internal dynamics of phenanthriplatin. These results reveal that phenanthriplatin rapidly racemizes under physiological conditions. The information also facilitated the interpretation of the NMR spectra of small molecule models of phenanthriplatin-platinated DNA. These studies indicate, inter alia, that one diastereomeric form of the complexes cis-[Pt(NH3)2(Am)(R-Gua)](2+), where R-Gua is 9-methyl- or 9-ethylguanine, is preferred over the other, the origin of which stems from an intramolecular interaction between the carbonyl oxygen of the platinated guanine base and a cis-coordinated ammine. The relevance of this finding to the DNA-damaging properties of phenanthriplatin and its biological activity is discussed.

The Pt(IV) complex c,c,t-[Pt(NH3)2Cl2(OH)2] is an important intermediate in the synthesis of Pt(IV) anticancer prodrugs and has been investigated as an anticancer agent in its own right. An analysis of the vibrational spectroscopy of this molecule was previously reported (Faggiani et al., Can. J. Chem. 60:529, 1982), in which crystallographic determination of the structure of the complex permitted a site group approach. The space group, however, was incorrectly assigned. In the present study we have redetermined at high resolution crystal structures of c,c,t-[Pt(NH3)2Cl2(OH)2] and c,c,t-[Pt(NH3)2Cl2(OH)2]·H2O2, which makes possible discussion of the effect of hydrogen bonding on the N-H and O-H vibrational bands. The correct crystallographic site symmetry of the platinum complex in the c,c,t-[Pt(NH3)2Cl2(OH)2] structure is used to conduct a new vibrational analysis using both group-theoretical and modern density functional theory methods. This analysis reveals the nature and symmetry of the "missing band" described in the original publication and suggests a possible explanation for its disappearance.

Platinum compounds are a mainstay of cancer chemotherapy, with over 50% of patients receiving platinum. But there is a great need for improvement. Major features of the cisplatin mechanism of action involve cancer cell entry, formation mainly of intrastrand cross-links that bend and unwind nuclear DNA, transcription inhibition and induction of cell-death programmes while evading repair. Recently, we discovered that platinum cross-link formation is not essential for activity. Monofunctional Pt compounds such as phenanthriplatin, which make only a single bond to DNA nucleobases, can be far more active and effective against a range of tumour types. Without a cross-link-induced bend, monofunctional complexes can be accommodated in the major groove of DNA. Their biological mechanism of action is similar to that of cisplatin. These discoveries opened the door to a large family of heavy metal-based drug candidates, including those of Os and Re, as will be described.

Approximately half of all patients who receive anticancer chemotherapy are treated with a platinum drug. Despite the widespread use of these drugs, the only cure that can be claimed is that of testicular cancer following cisplatin treatment. This article reviews some of our recent work on phenanthriplatin, a cisplatin derivative in which a chloride ion is replaced by phenanthridine, and on one of its analogues, the previously reported pyriplatin. These cationic complexes form monofunctional adducts on DNA that do not significantly distort the duplex, yet efficiently block transcription. Cell-based assays reveal altered cellular uptake properties and a cancer cell-killing profile different from those of established platinum drugs. Mechanistic work, including a crystal structure analysis of platinum-modified DNA in the active site of RNA polymerase II, is discussed herein.

Three rationally designed glucose-platinum conjugates (Glc-Pts) were synthesized and their biological activities evaluated. The Glc-Pts, 1-3, exhibit high levels of cytotoxicity toward a panel of cancer cells. The subcellular target and cellular uptake mechanism of the Glc-Pts were elucidated. For uptake into cells, Glc-Pt 1 exploits both glucose and organic cation transporters, both widely overexpressed in cancer. Compound 1 preferentially accumulates in and annihilates cancer, compared to normal epithelial, cells in vitro.

The platinum drugs, cisplatin, carboplatin, and oxaliplatin, prevail in the treatment of cancer, but new platinum agents have been very slow to enter the clinic. Recently, however, there has been a surge of activity, based on a great deal of mechanistic information, aimed at developing nonclassical platinum complexes that operate via mechanisms of action distinct from those of the approved drugs. The use of nanodelivery devices has also grown, and many different strategies have been explored to incorporate platinum warheads into nanomedicine constructs. In this Review, we discuss these efforts to create the next generation of platinum anticancer drugs. The introduction provides the reader with a brief overview of the use, development, and mechanism of action of the approved platinum drugs to provide the context in which more recent research has flourished. We then describe approaches that explore nonclassical platinum(II) complexes with trans geometry or with a monofunctional coordination mode, polynuclear platinum(II) compounds, platinum(IV) prodrugs, dual-threat agents, and photoactivatable platinum(IV) complexes. Nanoparticles designed to deliver platinum(IV) complexes will also be discussed, including carbon nanotubes, carbon nanoparticles, gold nanoparticles, quantum dots, upconversion nanoparticles, and polymeric micelles. Additional nanoformulations, including supramolecular self-assembled structures, proteins, peptides, metal-organic frameworks, and coordination polymers, will then be described. Finally, the significant clinical progress made by nanoparticle formulations of platinum(II) agents will be reviewed. We anticipate that such a synthesis of disparate research efforts will not only help to generate new drug development ideas and strategies, but also will reflect our optimism that the next generation of approved platinum cancer drugs is about to arrive.

The first near-infrared fluorescent turn-on sensor for the detection of nitroxyl (HNO), the one-electron reduced form of nitric oxide (NO), is reported. The new copper-based probe, CuDHX1, contains a dihydroxanthene (DHX) fluorophore and a cyclam derivative as a Cu(II) binding site. Upon reaction with HNO, CuDHX1 displays a five-fold fluorescence turn-on in cuvettes and is selective for HNO over thiols and reactive nitrogen and oxygen species. CuDHX1 can detect exogenously applied HNO in live mammalian cells and in conjunction with the zinc-specific, green-fluorescent sensor ZP1 can perform multicolor/multianalyte microscopic imaging. These studies reveal that HNO treatment elicits an increase in the concentration of intracellular mobile zinc.

This report presents a novel strategy that facilitates delivery of multiple, specific payloads of Pt(IV) prodrugs using a well-defined supramolecular system. This delivery system comprises a hexanuclear Pt(II) cage that can host four Pt(IV) prodrug guest molecules. Relying on host-guest interactions between adamantyl units tethered to the Pt(IV) molecules and the cage, four prodrugs could be encapsulated within one cage. This host-guest complex, exhibiting a diameter of about 3 nm, has been characterized by detailed NMR spectroscopic measurements. Owing to the high positive charge, this nanostructure exhibits high cellular uptake. Upon entering cells and reacting with biological reductants such as ascorbic acid, the host-guest complex releases cisplatin, which leads to cell cycle arrest and apoptosis. The fully assembled complex displays cytotoxicity comparable to that of cisplatin against a panel of human cancer cells lines, whereas the cage or the Pt(IV) guest alone exhibit lower cytotoxicity. These findings indicate the potential of utilising well-defined supramolecular constructs for the delivery of prodrug molecules.

A series of Pt(IV) prodrugs has been obtained by oxidative halogenation of either cisplatin or carboplatin. Iodobenzene dichloride is a general reagent that cleanly provides prodrugs bearing axial chlorides without the need to prepare intervening Pt(IV) intermediates or handle chlorine gas. Elemental bromine and iodine afford Pt(IV) compounds as well, although in the case of the iodine-mediated oxidation of carboplatin, an amido-bridged Pt(IV) side product also formed. A detailed analysis of the changes in spectroscopic and structural parameters induced by varying the axial halide is presented. A number of recurring motifs are observed in the solid state structures of these compounds.