Platinum Conjugates Research Articles

(18-Crown-6)potassium(I) Trichlorido[28-acetyl-3-(tris-(hydroxylmethyl)amino-ethane)betulinic ester-κN]platinum(II): Synthesis and In Vitro Antitumor Activity

Synthesis of platinum(II) conjugate with acetylated betulinic acid tris(hydroxymethyl)aminomethane ester (BATRIS) is presented (BATRISPt). HR-ESI-MS and multinuclear NMR spectroscopy, as well as elemental analysis were used for characterization of BATRISPt. Cytotoxicity (3-(4,5-dimethythiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), crystal violet (CV), and sulforhodamine B (SRB) assays) of BA, BATRIS, BATRISPt, and cisplatin were assessed on seven different tumor cell lines: melanoma B16, colon HCT116 and DLD-1, adenocarcinoma HeLa, breast MCF-7, and anaplastic thyroid tumor 8505C and SW1736; as well as normal MRC-5 fibroblasts. Furthermore, the effect of the mentioned compounds on the apoptosis (Annexin V/PI assay) and autophagy induction (acridine orange (AO) assay) as well as caspase 3, 8, and 9 activation were investigated on the selected B16 melanoma cell line. BATRISPt showed lower activity than BA, BATRIS, or cisplatin. All tested compounds triggered apoptosis in B16 cells. Induction of autophagy was observed in B16 cells exposed only to BATRIS. On the other hand, new conjugate activates caspases 8 and 9 in B16 cells with higher impact than BATRIS or cisplatin alone.

Novel Antitumor Platinum(II) Conjugates Containing the Nonsteroidal Anti-inflammatory Agent Diclofenac: Synthesis and Dual Mechanisms of Antiproliferative Effects

One concept how to improve anticancer effects of conventional metallodrugs consists in conjugation of these compounds with other biologically (antitumor) active agents, acting by a different mechanism. Here, we present synthesis, biological effects, and mechanisms of action of new Pt(II) derivatives containing one or two nonsteroidal anti-inflammatory diclofenac (DCF) ligands also known for their antitumor effects. The antiproliferative properties of these metallic conjugates show that these compounds are potent and cancer cell selective cytotoxic agents exhibiting activity in cisplatin resistant and the COX-2 positive tumor cell lines. One of these compounds, compound 3, in which DCF molecules are coordinated to Pt(II) through their carboxylic group, is more potent than parental conventional Pt(II) drug cisplatin, free DCF and the congeners of 3 in which DCF ligands are conjugated to Pt(II) via a diamine. The potency of 3 is due to several factors including enhanced internalization that correlates with enhanced DNA binding and cytotoxicity. Mechanistic studies show that 3 combines multiple effects. After its accumulation in cells, it releases Pt(II) drug capable of binding/damaging DNA and DCF ligands, which affect distribution of cells in individual phases of the cell cycle, inhibit glycolysis and lactate transport, collapse mitochondrial membrane potential, and suppress the cellular properties characteristic of metastatic progression.

Design of a novel theranostic nanomedicine: synthesis and physicochemical properties of a biocompatible polyphosphazene-platinum(II) conjugate.

To develop a theranostic nanomedicine involving the antitumor-active moiety (dach)Pt(II) (dach: trans-(±)-1,2-diaminocyclohexane) of oxaliplatin (OX), a new biocompatible polyphosphazene carrier polymer was designed by grafting with a methoxy poly(ethylene glycol) (MPEG) to increase duration of circulation in the blood and with aminoethanol (AE) as a spacer group. The antitumor (dach)Pt moiety was conjugated to the carrier polymer using cis-aconitic acid (AA) as a linker, resulting in a polymer conjugate formulated as [NP(MPEG550)(AE-AA)Pt(dach)]n, named “Polyplatin” (PP). PP was found to self-assemble into very stable polymeric nanoparticles with a mean diameter of 55.1 nm and a critical aggregation concentration of 18.5 mg/L in saline. PP could easily be labeled with a fluorescence dye such as Cy5.5 for imaging studies. The time-dependent ex vivo image studies on organ distributions and clearance of Cy-labeled PP have shown that PP accumulated in the tumor with high selectivity by the enhanced permeability and retention effect but was cleared out from all the major organs including the liver in about 4 weeks postinjection. Another time-dependent bioimaging study on distribution and clearance of PP in mouse kidney using laser ablation inductively coupled plasma mass spectroscopy has shown that PP accumulates much less in kidney and is more rapidly excreted than monomeric OX, which is in accord with the very low acute toxicity of PP as shown by its high LD50 value of more than 2000 mg/kg. The pharmacokinetic study of PP has shown that it has a much longer half-life (t1/2β) of 13.3 hours compared with the 5.21 hours of OX and about a 20 times higher area under the curve value of 42,850.8 ng h/mL compared with the 2,320.4 ng h/mL of OX. The nude mouse xenograft trials of PP against the gastric MKN-28 tumor cell line exhibited remarkably better tumor efficacy compared with OX at the higher tolerated dose, with lower systemic toxicity.

A Potent Glucose-Platinum Conjugate Exploits Glucose Transporters and Preferentially Accumulates in Cancer Cells.

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.

A Potent Glucose–Platinum Conjugate Exploits Glucose Transporters and Preferentially Accumulates in Cancer Cells

AbstractThree 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.

Cover Picture: Amphiphilic Cyanine–Platinum Conjugates as Fluorescent Nanodrugs (Chem. Asian J. 2/2016)

Cover Picture: Amphiphilic Cyanine–Platinum Conjugates as Fluorescent Nanodrugs (Chem. Asian J. 2/2016)

Amphiphilic Cyanine-Platinum Conjugates as Fluorescent Nanodrugs.

Two fluorescent nanomedicines based on small molecular cyanine-platinum conjugates have been prepared via a nanoprecipitation method and characterized by transmission electron microscopy (TEM) as well as dynamic light scattering (DLS). The conjugates exhibited an enhanced fluorescence in their nanoparticle formulation compared to that in solution. The nanomedicines could be endocytosed by cancer cells as revealed by confocal laser scanning microscopy (CLSM) and showed high cellular proliferation inhibition. Fluorescent platinum nanomedicines prepared directly from small molecules could be an alternative strategy for developing new drugs with simultaneous cellular imaging and cancer therapy functions.

Synthesis of PtIV‐Biomolecule Conjugates through Click Chemistry

AbstractThe azide‐functionalized PtIV complex {(OC‐6–34)‐chlorido(cyclobutane‐1,1′‐dicarboxylato)(cyclohexane‐1R,2R‐diamine)[2‐hydroxyethyl(2‐{2‐[2‐(2‐azidoethoxy)ethoxy]ethoxy}ethyl)carbamate]platinum(IV)} was synthesized and characterized to obtain a starting complex that was suitable for coupling with appropriate biological carriers in a drug targeting and delivery strategy. The following click reaction (CuI‐catalyzed Huisgen cycloaddition, CuAAC) was successfully applied for coupling with three different model biomolecules that can be exploited for selective targeting of the platinum conjugate toward tumor cells; i.e., the amino acid alanine and the dipeptide lysine‐alanine, both previously alkyne‐functionalized with pent‐4‐ynoic acid, and the hormone 17α‐ethynylestradiol. The title complex demonstrated very good compatibility with both CuAAC reaction and solid‐phase peptide synthesis conditions, making it a suitable antiproliferative fragment for the design of nanovectors.

A dextran-platinum(iv) conjugate as a reduction-responsive carrier for triggered drug release.

Reduction-responsive nano-carriers have been confirmed to be promising for intracellular drug delivery. To develop multifunctional polymer-based drug delivery system, a novel dextran-Pt(iv) conjugate was synthesized by conjugating Pt(iv) to the side chains of the hydrophilic dextran and used for doxorubicin (DOX) delivery. Pt(iv) conjugation could change the hydrophilicity of dextran, leading to the self-assembly of dextran-Pt(iv) conjugates with different morphologies. Pt(iv) segments served as the key components in assembly formation and as the antitumor prodrug. Under a reductive environment, Pt(iv) was found to be reduced to its active Pt(ii) form and cleaved from dextran, shifting the hydrophilic-hydrophobic balance of the dextran-Pt(iv) conjugate. The collapse of the assembly structure due to the partial or complete recovery of the hydrophilicity of dextran led to triggered release of DOX. The DOX-loaded dextran-Pt(iv) conjugate obtained by combining the released hydrophobic DOX and recovered hydrophilic Pt(ii), was found to be very effective as an antitumor agent as demonstrated in in vitro cytotoxicity evaluations. This DOX-loaded dextran-Pt(iv) conjugate system provided a new strategy to trigger the release of hydrophobic and hydrophilic drugs at the same time via single reduction-responsive control to provide an enhanced anti-tumor effect.

Synthesis and properties of a new micellar polyphosphazene–platinum(II) conjugate drug

Aiming at tumor targeting delivery of oxaliplatin using polymer therapy, a new monomeric platinum(II) complex (dach)Pt[HEDM] (dach: trans-(±)-1,2-diaminocyclohexane; HEDM: 2-hydroxyethoxydiethylmalate) was designed to include the antitumor moiety (dach)Pt and HEDM as a linker to the polyphosphazene backbone. This monomeric Pt-complex could easily be grafted to the PEGylated polyphosphazene backbone to prepare a novel polyphosphazene–Pt conjugate, [NP(MPEG550)(dach)Pt(EM)]n [MPEG550: methoxy poly(ethylene glycol) with an average molecular weight of 550; EM: ethoxymalate]. This amphiphilic polyphosphazene–Pt conjugate was found to self-assemble into stable polymeric micelles of a mean diameter of 130nm, which is suitable for passive tumor targeting by enhanced permeability and retention (EPR) effect. Pharmacokinetic study of this polymer conjugate exhibited long blood circulation as expected and longer half-life (t1/2β=9.52h) compared with oxaliplatin (3.47h), and much larger AUC (area under the curve) value (25,831ng·h/mL) compared with oxaliplatin (1194ng·h/mL). Biodistribution study of the polymer conjugate has shown excellent tumor selectivity with the tumor to tissue ratio of 3.84 at 2h post injection and 11.7 at 24h post injection probably due to the EPR effect of the polymer conjugate while no tumor selectivity was observed for monomeric oxaliplatin. Furthermore, accumulation of this polymer conjugate in kidney was much lower compared with oxaliplatin. Also the nude mouse xenograft trial of the polymer conjugate has shown higher antitumor efficacy compared with oxaliplatin.

Photoinduced Reduction of PtIV within an Anti‐Proliferative PtIV–Texaphyrin Conjugate

AbstractInvited for the cover of this issue are the groups of Jonathan Sessler at The University of Texas at Austin and Zahid Siddik at The University of Texas M.D. Anderson Cancer Center in Houston, Texas. The cover picture depicts a tumor‐targeting texaphyrin platinum(IV) conjugate that undergoes controlled reduction and subsequent release of the platinum moiety that can then bind DNA. This conjugate is found to inhibit cell proliferation in ovarian cancer cell lines. Read the full text of the article at 10.1002/chem.201403094.

Lactose targeting oxaliplatin prodrug loaded micelles for more effective chemotherapy of hepatocellular carcinoma.

A sugar active targeting system for the platinum(iv) prodrug [oxaliplatin(iv)-COOH or in short form OxaPt(iv)] of clinically relevant oxaliplatin (OxaPt(ii)) has been reported here for the first time. To achieve this, a series of hydrophilic biocompatible polyurethanes containing free pair-wised pendant amino groups (PU) were synthesized and then lactobionic acid (LA) was grafted to the polyurethane as a targeting moiety, in order to prepare PU-LA conjugates. Thereafter, the prodrug, OxaPt(iv) was introduced into the PU-LA conjugates resulting in the formation of polyurethane platinum(iv) conjugates (PU-LA/Pt) with targeting LA groups. Similarly, PU-Pt conjugates without the LA targeting groups were also prepared. These conjugates were self-assembled into micelles [non-targeting micelles: M(PU-Pt) and targeting micelles: M(PU-LA/Pt)] in water. An in vitro study demonstrated that, compared with M(PU-Pt), M(PU-LA/Pt) demonstrated a lower IC50 (79 μM vs. 126 μM) at 72 h and greater cellular uptake of drugs in HepG2 cells. An in vivo study revealed that M(PU-Pt) and M(PU-LA/Pt) displayed much higher blood drug concentrations and bioavailabilities than the free drug, OxaPt(iv). Moreover, M(PU-LA/Pt) showed enriched distribution in the liver and xenograft H22 tumors as well as better antitumor efficacy. M(PU-LA/Pt) may be a promising polymeric prodrug of the widely used OxaPt(ii) for the clinical treatment of various liver cancers.

A new quantum dot–platinum conjugate for self-assembled nanoconjugates by coordination bonding mediated recognition

A new binding strategy of linking quantum dots (QDs) to magnetic nanoparticles (MNPs) using DNA interaction with metal coordination bonding was developed. Platinum was selected for binding QDs to DNA. This novel self-assembled nanoconjugate would be a new probe for diagnosing a specific disease more accurately with its double modalities, fluorescence and magnetic property.

PH-Triggered Release of Platinum Drugs Conjugated to Micelles via an Acid-Cleavable Linker

A new acid-degradable polymer–platinum conjugate was prepared by postmodification of a POEGMEMA-b-PHEMA block copolymer obtained by RAFT polymerization. A hydrazone linkage, susceptible to hydrolytic cleavage, was formed by reaction of the carbonyl group of a diamino ligand with the hydrazide-modified copolymer. According to NMR kinetic studies, degradation of the hydrazone bond was observed to be more than 10 times faster at pH 5.5 than at pH 7.4. The platinum drug was introduced on the copolymer by permanent conjugation onto the diamino conjugation sites. The platinated amphiphilic copolymer was subsequently self-assembled into nanosized micelles of 27 nm with the platinum drug safely encapsulated in the core. Extended conjugation time however led to cross-linking and to particles of more than 1000 nm. In vitro experiments revealed a high cytotoxicity for the platinum drug-bearing small micelles compared to the polymer before conjugation. In contrast, the large particle did not show any toxicity since the size prevents endocytosis. However, endocytosis and the subsequent location of the micelles in the acidic endosomes or lysosomes are necessary to trigger the release of the toxic platinum drug. In contrast, the small drug loaded micelle exhibited a toxicity superior to the underlying low-molecular-weight drug (IC50 = 10.5 μM vs 17 μM) These hydrolytically degradable nanovectors constitute a promising system for a triggered release of platinum drugs.

Adamantane–platinum conjugate hosted in β-cyclodextrin: Enhancing transport and cytotoxicity by noncovalent modification

This work reports the synthesis of a complex of a carboplatin analog having tethered adamantane that is encapsulated in the hydrophobic cavity of β-cyclodextrin (βCD) and its cytotoxic activity towards human neuroblastoma cells (SK-N-SH). We found that this inclusion complex of βCD adamantane carboplatin analog exhibited higher cytotoxicity towards SK-N-SH cells than carboplatin itself, and the inclusion complex exhibited a higher binding to plasmid pBR322 deoxyribonucleic acid (DNA) than carboplatin. Confocal fluorescence images of SK-N-SH cells treated with βCD having an attached fluorescein isothiocyanate (FITC)-tag exhibited fluorescence in the vicinity of the nuclei of the neuroblastoma cells. Direct measurements of the platinum content in SK-N-SH cells using inductively coupled plasma mass spectrometry (ICP-MS) indicated that the uptake rate of carboplatin was about 4 times higher than βCD adamantane carboplatin analog inclusion complex. When compared to carboplatin, we believe that the higher cytotoxicity of inclusion complex towards SK-N-SH cells is due to its higher DNA binding ability as compared to carboplatin, and more efficient delivery to the nucleus of the cell. This work suggests that the advantage of deliberate noncovalent modification with βCD through host-guest chemistry may also be broadly applicable to other anticancer agents as well.

Water-Soluble Macromolecular Platinum Conjugates Derived from 1,2-Dihydroxyl-Functionalized Carrier Polymers

The class of platinum-containing bioactive agents, including cisplatin as the prototype, and structurally related second- and third-generation compounds, has developed during the past two decades as one of the most important family of antitumor drugs. However, despite a highly valued general antineoplastic performance profile, their unrestricted oncological administration continues to be hampered by pharmacological shortcomings, notably excessive toxicity and induction of drug resistance. This has prompted ongoing intensive development activities in pharmaceutic laboratories worldwide, and one of the most promising approaches emanating from these activities involves the drug conjugation to biomedically functional, water-soluble carrier polymers. Such macromolecular conjugates, judiciously designed and synthesized, provide significant pharmacological advantages over non-polymeric drug systems, notably increased cell specificity and facilitated cell entry, paired with reduced toxicity and resistance problems. In the present project, this technology has been applied specifically to the synthesis of Pt-containing polymers in which the metal is carrier-bound via dihydroxylatoplatinum chelation. In the cancerous target cell, such conjugates will deliver the free bioactive Pt complex hydrolytically for its cytotoxic action. The water-soluble polymeric products, fractionated by dialysis in membrane tubing with molecular-mass cut-off of 25,000, will be submitted to an outside institution for in vitro evaluation of cytotoxic properties.

An androgenic steroid delivery vector that imparts activity to a non-conventional platinum(ii) metallo-drug

A range of androgen conjugates with non-conventional platinum(II) complexes have been synthesised with the aim of targeting tumour cells since many display elevated levels of the androgen receptor. The androgenic platinum conjugates are delivered into selected cells with improved efficiency (when compared to their non-steroidal analogues). The act of conjugating an androgen to a platinum(II) complex resulted in synergistic effects between the metallic centre and the steroidal ligand, creating highly potent platinum(II) complexes from the inactive components.

Poly(amidoamine) dendrimer-supported organoplatinum antitumour agents

While numerous water-soluble biocompatible polymers have been utilized for the construction of drug conjugates that offer significant advantages for drug delivery, poly(amidoamine) (PAMAM) dendrimers are superior in many ways for this purpose. They display nanoscale size, uniform shape, excellent water solubility, low toxicity and high surface functionality. In an attempt to circumvent the toxic side effects associated with the administration of organoplatinum drugs, a polymeric prodrug has been prepared from the treatment of a generation 4.5 PAMAM dendrimer with diaquo(1,2-diaminocyclohexane)platinum(II). A well-defined dendrimer–platinum conjugate containing 40 (1,2-diaminocyclohexane)platinum(II) units coordinated to the dendrimer surface via carboxylate groups is formed. This adduct is well behaved, water soluble, contains a high loading of platinum moieties and displays sustained release of active platinum species over a 24 h period under physiological conditions.

Peptide Targeting of Platinum Anti-Cancer Drugs

Besides various side effects caused by platinum anticancer drugs, they are not efficiently absorbed by the tumor cells. Two Pt-peptide conjugates; cyclic mPeg-CNGRC-Pt (7) and cyclic mPeg-CNGRC-Pten (8) bearing the Asn-Gly-Arg (NGR) targeting sequence, a malonoyl linker, and low molecular weight miniPEG groups have been synthesized. The platinum ligand was attached to the peptide via the carboxylic end of the malonate group at the end of the peptide. The pegylated peptide is nontoxic and highly soluble in water. Platinum conjugates synthesized using the pegylated peptides are also water-soluble with reduced or eliminated peptide immunogenicity. The choice of carboplatin as our untargeted platinum complex was due to the fact that the malonate linker chelates platinum in a manner similar to that of carboplatin. Cell toxicity assay and competition assay on the PC-3 cells (CD13 positive receptors) revealed selective delivery and destruction of PC-3 cells using targeted Pt-peptide conjugates 7 and 8 significantly more than untargeted carboplatin. Platinum uptake on PC-3 cells was 12-fold more for conjugate 7 and 3-fold more for conjugate 8 compared to that of the untargeted carboplatin, indicating selective activation of the CD13 receptors and delivery of the conjugates to CD13 positive cells. Further analysis on effects of conjugates 7 and 8 on PC-3 cells using caspase-3/7, fluorescence microscopy, and DNA fragmentation confirmed that the cells were dying by apoptosis.

Nanoparticulate platinum(II) anticancer drug: Synthesis and characterization of amphiphilic cyclotriphosphazene–platinum(II) conjugates

Novel cyclotriphosphazene–platinum(II) conjugates were prepared by hydrolysis and platination of the amphiphilic cyclotriphosphazenes grafted with equimolar hydrophilic methoxy-poly(ethylene glycol) (MPEG) and hydrophobic oligopeptide. These macromolecular conjugates were found to form stable nanoparticles with a mean diameter of approximately 90–200nm depending on the hydrophobicity of the conjugated (diamine)platinum moieties. The nanoparticulate platinum(II) conjugates have shown temperature and concentration dependent particle sizes. However, the particle sizes of the conjugates were found to decrease to a certain size as the solution concentration was decreased but remained stable even at 10μM, which is enough for systemic delivery by injection. The conjugates exhibited lower in vitro cytotoxicity than cisplatin but reasonably good activity against selected human tumor cell lines.