Conjugated platinum(IV)-peptide complexes for targeting angiogenic tumor vasculature

The eradication of breast cancer and cancer stem cells using octreotide modified paclitaxel active targeting micelles and salinomycin passive targeting micelles

Tumor stem cells have emerged as the new targets for anti-cancer therapy, besides tumor cells themselves. To eradicate both breast cancer cells and breast cancer stem cells which can not be eliminated by the conventional chemotherapy, octreotide (Oct)-modified paclitaxel (PTX)-loaded PEG-b-PCL polymeric micelles (Oct-M-PTX) and salinomycin (SAL)-loaded PEG-b-PCL polymeric micelles (M-SAL) were developed and investigated in combination. In this study, Oct that targets somatostatin receptors (SSTR) overexpressed in tumors including breast cancer, was coupled to the PEG end of PEG-b-PCL, and all the micelles were prepared using thin film hydration method. Results showed that the particle size of all the micelles was approximately 25-30 nm, and the encapsulation efficiency was >90%. Quantitative and qualitative analysis demonstrated that Oct facilitates the uptake of micelles in SSTR overexpressed breast cancer MCF-7 cells while free Oct inhibited cellular uptake of Oct-modified micelles, revealing the mechanism of receptor-mediated endocytosis. Breast cancer stem cells (side population cells, SP cells) were sorted from MCF-7 cells and identified with the CD44+/CD24- phenotype. M-SAL was capable of decreasing the proportion of SP cells, and its suppression was more potent in SP cells than that in cancer cells. As compared to PTX-loaded micelles (M-PTX), the inhibition of Oct-M-PTX against MCF-7 cells was stronger while such effect significantly increased when applying Oct-M-PTX in combination with M-SAL. In the MCF-7 xenografts, the combination therapy with Oct-M-PTX plus M-SAL produced the strongest antitumor efficacy, in accord with the combination treatment in vitro. Compared with free SAL, M-SAL was found to be more effective in suppressing breast cancer stem cells in vivo. Thus, this combination therapy may provide a strategy to improve treatment of breast cancers for eradication of breast cancer cells together with breast cancer stem cells.

Photocontrolled DNA binding of a receptor-targeted organometallic ruthenium(II) complex

A photoactivated ruthenium(II) arene complex has been conjugated to two receptor-binding peptides, a dicarba analogue of octreotide and the Arg-Gly-Asp (RGD) tripeptide. These peptides can act as "tumor-targeting devices" since their receptors are overexpressed on the membranes of tumor cells. Both ruthenium-peptide conjugates are stable in aqueous solution in the dark, but upon irradiation with visible light, the pyridyl-derivatized peptides were selectively photodissociated from the ruthenium complex, as inferred by UV-vis and NMR spectroscopy. Importantly, the reactive aqua species generated from the conjugates, [(η(6)-p-cym)Ru(bpm)(H(2)O)](2+), reacted with the model DNA nucleobase 9-ethylguanine as well as with guanines of two DNA sequences, (5')dCATGGCT and (5')dAGCCATG. Interestingly, when irradiation was performed in the presence of the oligonucleotides, a new ruthenium adduct involving both guanines was formed as a consequence of the photodriven loss of p-cymene from the two monofunctional adducts. The release of the arene ligand and the formation of a ruthenated product with a multidentate binding mode might have important implications for the biological activity of such photoactivated ruthenium(II) arene complexes. Finally, photoreactions with the peptide-oligonucleotide hybrid, Phac-His-Gly-Met-linker-p(5')dCATGGCT, also led to arene release and to guanine adducts, including a GG chelate. The lack of interaction with the peptide fragment confirms the preference of such organometallic ruthenium(II) complexes for guanine over other potential biological ligands, such as histidine or methionine amino acids.

Spectrum of cellular responses to pyriplatin, a monofunctional cationic antineoplastic platinum(II) compound, in human cancer cells

Pyriplatin, cis-diammine(pyridine)chloroplatinum(II), a platinum-based antitumor drug candidate, is a cationic compound with anticancer properties in mice and is a substrate for organic cation transporters that facilitate oxaliplatin uptake. Unlike cisplatin and oxaliplatin, which form DNA cross-links, pyriplatin binds DNA in a monofunctional manner. The antiproliferative effects of pyriplatin, alone and in combination with known anticancer drugs (paclitaxel, gemcitabine, SN38, cisplatin, and 5-fluorouracil), were evaluated in a panel of epithelial cancer cell lines, with direct comparison to cisplatin and oxaliplatin. The effects of pyriplatin on gene expression and platinum-DNA adduct formation were also investigated. Pyriplatin exhibited cytotoxic effects against human cell lines after 24 hours (IC(50) = 171-443 μmol/L), with maximum cytotoxicity in HOP-62 non-small cell lung cancer cells after 72 hours (IC(50) = 24 μmol/L). Pyriplatin caused a G(2)-M cell cycle block similar to that induced by cisplatin and oxaliplatin. Induction of apoptotsis and DNA damage response was supported by Annexin-V analysis and detection of phosphorylated Chk2 and H2AX. Treatment with pyriplatin increased CDKN1/p21 and decreased ERCC1 mRNA expression. On a platinum-per-nucleotide basis, pyriplatin-DNA adducts are less cytotoxic than those of cisplatin and oxaliplatin. The mRNA levels of genes implicated in drug transport and DNA damage repair, including GSTP1 and MSH2, correlate with pyriplatin cellular activity in the panel of cell lines. Synergy occurred for combinations of pyriplatin with paclitaxel. Because its spectrum of activity differs significantly from those of cisplatin or oxaliplatin, pyriplatin is a lead compound for developing novel drug candidates with cytotoxicity profiles unlike those of drugs currently in use.

Decoration of polymeric micelles with cancer-specific peptide ligands for active targeting of paclitaxel

Polymeric micelles based on poly(ethylene oxide)-b-poly(ε-caprolactone) PEO-b-PCL or poly(ethylene oxide)-b-poly(α-benzyl carboxylate-ε-caprolactone) PEO-b-PBCL block copolymers were prepared and decorated with either c(RGDfK) or p160, a cancer cell-specific peptide ligand, on their surface. The cellular uptake of p160-decorated PEO-b-PBCL micelles containing DiI fluorescent label by MDA-MB-435 cancer cells was assessed and compared to that for c(RGDfK)-decorated micelles. The hydrophobic anticancer drug paclitaxel (PTX) was physically encapsulated into PEO-b-PCL or PEO-b-PBCL micelles (with and without peptide ligands) using a dialysis technique. The effect of the micellar formulation on the specificity of encapsulated PTX against cancer cells was assessed by investigating the in vitro cytotoxicity of free and encapsulated PTX against MDA-MB-435 cancer cell line versus two normal cells, Human Umbilical Vein Endothelial Cells (HUVEC) and MCF10A cells, using the MTT assay. Our results showed both peptide ligands to facilitate the association of micelles with MDA-MB-435 cells. The p160-micelles, however showed better binding and internalizing in MDA-MB-435 cells than c(RGDfK)-micelles. In general, peptide decoration enhanced the selective cytotoxicity of encapsulated PTX against MDA-MB-435 cells over normal HUVEC and MCF10A cells. The extent of this increase in cancer cell specificity for encapsulated PTX was more for p160-decorated micelles than c(RGDfK)-decorated ones.

Overcoming biochemical pharmacologic mechanisms of platinum resistance with a texaphyrin-platinum conjugate

In our effort to investigate further texaphyrin conjugation as a means of increasing delivery and accumulation of known anticancer platinum agents in cancer cells, we have continued our studies on the mode of action of a texaphyrin-platinum conjugate, particularly in cisplatin-resistant tumor cells that are characterized by several mechanisms of resistance, including reduced drug accumulation. Our results provide support for the proposal that intracellular platinum and Pt-DNA adduct levels were significantly increased using our conjugate relative to corresponding Pt controls. Moreover, no differences were found in cellular accumulation and Pt-DNA adduct formation between Pt sensitive and Pt resistant ovarian cells. As a result, resistance to the conjugate was lower than cisplatin in resistant cells. Based on these results we conclude that texaphyrin conjugation provides a promising strategy for overcoming biochemical pharmacologic mechanisms of resistance.

Synthesis, characterization, and cytotoxicity of platinum(IV) carbamate complexes

The synthesis, characterization, and cytotoxicity of eight new platinum(IV) complexes having the general formula cis,cis,trans-[Pt(NH(3))(2)Cl(2)(O(2)CNHR)(2)] are reported, where R = tert-butyl (4), cyclopentyl (5), cyclohexyl (6), phenyl (7), p-tolyl (8), p-anisole (9), 4-fluorophenyl (10), or 1-naphthyl (11). These compounds were synthesized by reacting organic isocyanates with the platinum(IV) complex cis,cis,trans-[Pt(NH(3))(2)Cl(2)(OH)(2)]. The electrochemistry of the compounds was investigated by cyclic voltammetry. The aryl carbamate complexes 7-11 exhibit reduction peak potentials near -720 mV vs Ag/AgCl, whereas the alkyl carbamate complexes display reduction peak potentials between -820 and -850 mV vs Ag/AgCl. The cyclic voltammograms of cis,cis,trans-[Pt(NH(3))(2)Cl(2)(O(2)CCH(3))(2)] (1), cis,cis,trans-[Pt(NH(3))(2)Cl(2)(O(2)CCF(3))(2)] (2), and cis-[Pt(NH(3))(2)Cl(4)] (3) were measured for comparison. Density functional theory studies were undertaken to investigate the electronic structures of 1-11 and to determine their adiabatic electron affinities. A linear correlation (R(2) = 0.887) between computed adiabatic electron affinities and measured reduction peak potentials was discovered. The biological activity of 4-11 and, for comparison, cisplatin was evaluated in human lung cancer A549 and normal MRC-5 cells by the MTT assay. The compounds exhibit comparable or slightly better activity than cisplatin against the A549 cells. In MRC-5 cells, all are equally or slightly less cytotoxic than cisplatin, except for 4 and 5, which are more toxic.

Exploring new near-infrared fluorescent disulfide-based cyclic RGD peptide analogs for potential integrin-targeted optical imaging

We synthesized disulfide-based cyclic RGD pentapeptides bearing a near-infrared fluorescent dye (cypate), represented by cypate-c(CRGDC) (1) for integrin-targeted optical imaging. These compounds were compared with the traditional lactam-based cyclic RGD counterpart, cypate-c(RGDfK) (2). Molecular modeling suggests that the binding affinity of 2 to integrin α(v)β(3) is an order of magnitude higher than that of 1. This was confirmed experimentally, which further showed that substitution of Gly with Pro, Val and Tyr in 1 remarkably hampered the α(v)β(3) binding. Interestingly, cell microscopy with A549 cells showed that 1 exhibited higher cellular staining than 2. These results indicate that factors other than receptor binding affinity to α(v)β(3) dimeric proteins mediate cellular uptake. Consequently, 1 and its analogs may serve as valuable molecular probes for investigating the selectivity and specificity of integrin targeting by optical imaging.

Texaphyrins: tumor localizing redox active expanded porphyrins

Texaphyrins, a class of tumor selective expanded porphyrins capable of coordinating large metals, have been found to act as redox mediators within biological systems. This review summarizes studies involving their experimental use in cancer chemotherapy. Mechanistic insights involving their presumed mode of action are also described, as well as certain structure activity relationships. Finally, newer texaphyrin-based applications associated with targeted drug delivery are presented.

Aminopeptidase N (CD13) as a target for cancer chemotherapy

The enzyme aminopeptidase N (APN, also known as CD13) is a Zn(2+) dependent membrane-bound ectopeptidase that degrades preferentially proteins and peptides with a N-terminal neutral amino acid. Aminopeptidase N has been associated with the growth of different human cancers and suggested as a suitable target for anti-cancerous therapy. Different approaches have been used to develop new drugs directed to this target, including enzyme inhibitors as well as APN-targeted carrier constructs. This review discusses the prevalence and possible function of APN in malignant diseases, mainly solid tumors, as well as its "drugability" evaluated in preclinical in vivo models, and also provides a brief overview of current clinical trials focused on APN.

Targeted delivery of a cisplatin prodrug for safer and more effective prostate cancer therapy in vivo

Targeted delivery and controlled release of inactive platinum (Pt) prodrugs may offer a new approach to improve the efficacy and tolerability of the Pt family of drugs, which are used to treat 50% of all cancers today. Using prostate cancer (PCa) as a model disease, we previously described the engineering of aptamer (Apt)-targeted poly(D,L-lactic-co-glycolic acid)-b-poly(ethylene glycol) (PLGA-b-PEG) nanoparticles (NPs) encapsulating a Pt(IV) prodrug c,t,c[Pt(NH(3))(2)-(O(2)CCH(2)CH(2)CH(2)CH(2)CH(3))(2)Cl(2)] (1) (Pt-PLGA-b-PEG-Apt-NP), which target the extracellular domain of the prostate specific membrane antigen (PSMA), for enhanced in vitro cytotoxicity. Here we demonstrate enhanced in vivo pharmacokinetics (PK), biodistribution, tolerability, and efficacy of Pt-PLGA-b-PEG-Apt-NP (150 ± 15 nm encapsulating ∼5% wt/wt Pt(IV) prodrug) when compared to cisplatin administered in its conventional form in normal Sprague Dawley rats, Swiss Albino mice, and the PSMA-expressing LNCaP subcutaneous xenograft mouse model of PCa, respectively. The 10-d maximum tolerated dose following a single i.v. injection of Pt-PLGA-b-PEG-NP in rats and mice was determined at 40 mg/kg and 5 mg/kg, respectively. PK studies with Pt-PLGA-b-PEG-NP revealed prolonged Pt persistence in systemic blood circulation and decreased accumulation of Pt in the kidneys, a major target site of cisplatin toxicity. Pt-PLGA-b-PEG-Apt-NPs further displayed the significant dose-sparing characteristics of the drug, with equivalent antitumor efficacy in LNCaP xenografts at 1/3 the dose of cisplatin administered in its conventional form (0.3 mg/kg vs. 1 mg/kg). When considering the simultaneous improvement in tolerability and efficacy, the Pt-PLGA-b-PEG-Apt NP provides a remarkable improvement in the drug therapeutic index.

Tuning of lipophilicity and cytotoxic potency by structural variation of anticancer platinum(IV) complexes

A series of bis(carboxylato)dichlorido(ethane-1,2-diamine)platinum(IV) compounds with IC(50) values ranging between 142 μM and 18 nM was investigated with respect to their lipophilicity (by the shake flask method as well as microemulsion electrokinetic chromatography), reduction potential, as well as their cellular accumulation in cancer cells in vitro. In general, the antiproliferative properties of the complexes correlated with their lipophilicity as well as their accumulation, whereas differences in antiproliferative potency could not be explained by reduction potentials since they do not vary significantly within the investigated series of compounds. Only minor effects for complexes featuring polar end groups were detected.

F3-targeted cisplatin-hydrogel nanoparticles as an effective therapeutic that targets both murine and human ovarian tumor endothelial cells in vivo

Recent studies indicate that ovarian cancer may be highly responsive to antivascular therapeutics. We have developed an antivascular tumor therapeutic using the F3 peptide to target cisplatin-loaded nanoparticles (F3-Cis-Np) to tumor vessels. We show that although F3-Cis-Np bind with high specificity to both human ovarian tumor cells and tumor endothelial cells in vitro, they only show cytotoxic activity against the tumor endothelial cells. In vivo these nanoparticles bind primarily to tumor endothelial cells. Therapeutic studies in both flank and orthotopic i.p. murine ovarian tumor models, as well as human tumor xenograft models, show rapid tumor regression with treatment. Treatment was associated with significant vascular necrosis consistent with an antivascular effect. Furthermore, treatment was active in both platinum-sensitive and platinum-resistant cell lines. Importantly, we show that F3-Cis-Np bind to human tumor endothelial cells in vitro and to human tumor vessels in vivo. Therapy targeting human vasculature in vivo with F3-Cis-Np led to near complete loss of all human tumor vessels in a murine model of human tumor vasculature. Our studies indicate that F3-targeted vascular therapeutics may be an effective treatment modality in human ovarian cancer.

Synthesis, characterization, and photophysical properties of three platinum(II) complexes bearing fluorescent analogues of the Di-2-pyridylmethane ligand

Three new ligands of the general formula [RNHCH(py)(2)] (py = pyridine; R = tosyl, Ts-dpm; R = dansyl, Ds-dpm; R = 7-nitro-1,2,3-benzoxadiazole, NBD-dpm) have been synthesized and characterized. Reactions of these ligands with cis-[Pt(DMSO)(2)Cl(2)] (DMSO = dimethyl sulfoxide) in methanol affords [Pt(Ts-dpm)Cl(2)] (1), [Pt(Ds-dpm)Cl(2)] (2), and [Pt(NBD-dpm)Cl(2)] (3). The crystal structures of these complexes reveal bidentate coordination of the ligands to the Pt center with nonplanar chelate rings. Because of inequivalent substituents on the methine carbon atom of the ligands, distinct exo and endo isomers exist in the three complexes. X-ray analyses indicate that 1 crystallizes in the endo conformation, 2 in the exo conformation, and 3 as a mixture of the two conformers. The (1)H NMR and (195)Pt NMR spectra of the complexes display two sets of independent signals corresponding to the chemically inequivalent exo and endo conformers. The exo conformer was determined by 2D NMR spectroscopy to be thermodynamically favored for all three complexes. Density functional theory (DFT), time-dependent DFT, and atoms in molecules calculations were carried out for both conformers of 3 to investigate differences in their electronic structures and to explore intramolecular interactions. In the presence of dioxygen, 1 thermally decomposes at 60 degrees C to form several unidentified products. Compound 2 is thermally stable even in the presence of dioxygen and water but upon light exposure decomposes to form a new platinum(II) species with a (195)Pt NMR shift of -2177 ppm. Compound 3 reacts both thermally and photochemically in the presence of dioxygen and trace amounts of water to form both 4-amino-7-nitro-2,1,3-benzoxadiazole and [Pt(dpk)Cl(2)] (dpk = di-2-pyridyl ketone). Oxidation of 1 and 3 with H(2)O(2) in acetic acid affords a mixture of compounds, two of which contain dpm ligands bound in a tridentate manner to platinum.

Targeted polymeric micelle system for delivery of combretastatin A4 to tumor vasculature in vitro

PURPOSE

To develop an efficient tumor vasculature-targeted polymeric micelle delivery system for combretastatin A4 (CA4), a novel antivascular agent.

METHODS

CA4-loaded micelles were prepared from poly (ethylene glycol)-b-poly (d, l-lactide) copolymers. RGD peptides that target integrins alphavbeta3 and alphavbeta5, markers of angiogenic endothelial cells, were coupled to the surface of micelles. The micelles were characterized in terms of particle size, morphology, drug loading, and drug release. Cellular uptake of micelles was evaluated by fluorometric determination and confocal microscopy. Anti-proliferation of targeted micelles was also evaluated by SRB method.

RESULTS

The mean diameters of CA4-loaded targeted micelles were 25.9 +/- 1.3 nm and spherical in shape. Approximately 4 mg/mL of micellar CA4 loading was obtained with an entrapment efficiency of 97.2 +/- 1.4%. In vitro release studies revealed that targeted micelles release CA4 in a sustained-release manner within 48 h. In vitro cellular uptake studies demonstrated that targeted micelles significantly facilitated the intracellular delivery of the encapsulated agents via integrin-mediated endocytosis. Anti-proliferation studies showed that targeted micelles containing CA4 present superior efficacy over nontargeted micelles.

CONCLUSION

These results suggested that RGD conjugated PEG-PLA micelles loading CA4 have potential as a new formulation for targeting angiogenic tumor vasculature.

Exploring the cellular accumulation of metal complexes

Transition metal complexes offer great potential as diagnostic and therapeutic agents, and a growing number of biological applications have been explored. To be effective, these complexes must reach their intended target inside the cell. Here we review the cellular accumulation of metal complexes, including their uptake, localization, and efflux. Metal complexes are taken up inside cells through various mechanisms, including passive diffusion and entry through organic and metal transporters. Emphasis is placed on the methods used to examine cellular accumulation, to identify the mechanism(s) of uptake, and to monitor possible efflux. Conjugation strategies that have been employed to improve the cellular uptake characteristics of metal complexes are also described.

Polymer--cisplatin conjugate nanoparticles for acid-responsive drug delivery

We report the synthesis of novel acid-responsive therapeutic nanoparticles (NPs) with sub-100 nm size consisting of polymer--cisplatin conjugates. The uniqueness of these drug delivery polymeric NPs lies in the covalent conjugation of each cisplatin drug to the hydrophobic segment of two biocompatible diblock copolymer chains through a hydrazone bond, resulting in highly differential drug release profile at different environmental acidity. We demonstrate that the synthesized polymer--cisplatin conjugates can readily precipitate to form sub-100 nm NPs in aqueous solution due to their very low critical micelle concentration (CMC). The resulting NPs show well-controlled cisplatin loading yield, excellent acid-responsive drug release kinetics, and enhanced in vitro cytotoxicity against ovarian cancer cells as compared to free cisplatin. As an environmentally sensitive drug delivery vehicle, these NPs can potentially minimize the drug loss during NP circulation in the blood, where the pH value is neutral, and trigger rapid intracellular drug release after the NPs are endocytosed by the target cells. This characteristic drug release profile holds the promise to suppress cancer cell chemoresistance by rapidly releasing a high dose of chemotherapy drugs inside the tumor cells, thereby improving the therapeutic efficacy of the drug payload.

Influence of the metal complex-to-peptide linker on the synthesis and properties of bioactive CpMn(CO)3 peptide conjugates

By combining organometallic groups and peptides, a large number of conjugates with interesting new biological properties can be prepared. Especially, attachment to cell-penetrating peptides (CPP) that act as efficient cell delivery vehicles has come to the fore. However, the presence of the metal moiety in such systems can interfere with standard conjugate synthesis procedures which therefore need to be optimized for every new compound. In this work, we report on the preparation of six new cymantrene-sC18 peptide bioconjugates that were prepared by solid phase peptide synthesis (SPPS) techniques. The cymantrene complexes were chosen for their different linker to the peptide, to study the influence of the linker group on cellular uptake and cell viability of the conjugates. Interestingly, the attachment of the metal complex leads to a non-standard cleavage of the Rink amide linker used in the SPPS protocol under trifluoroacetic acid (TFA) treatment, resulting in peptide amides that are N-alkylated at the C-terminus. Furthermore, we found that depending on the type of cymantrene moiety attached, the formation of reactive carbocations which result from decomposition of the resin linker is facilitated and can alkylate the metal complex moiety. Both effects were analyzed by MS/MS studies and cleavage mixtures for efficient elimination of this byproduct formation were identified. Moreover, initial biological testing of the cytotoxicity of one of the bioconjugates gave promising results. Concentration-dependent cell viability studies of Cym1-sC18 on human MCF-7 breast adenocarcinoma cells gave an IC(50) value of 59.8 (+/- 6.7) microM and demonstrate their potential in anticancer chemotherapy.

The alkylating prodrug J1 can be activated by aminopeptidase N, leading to a possible target directed release of melphalan

The alkylating prodrug of melphalan, J1 (melphalanyl-L-p-fluorophenylalanyl ethyl ester) is currently in early clinical trials. Preclinical studies have shown that J1-mediated cytotoxicity is dependent on hydrolytic activity of tumor cells. In this report we have analyzed potential peptidases and esterases of importance for release of free melphalan from J1. Exposure of tumor cell lines to J1 resulted in a significant increased level of free intracellular melphalan, at least tenfold at C(max), compared to exposure to melphalan at the same molar concentration. This efficient intracellular delivery could be inhibited in both magnitude and in time by bestatin, a broad spectrum inhibitor of the aminopeptidases, including the metalloproteinase aminopeptidase N (APN, EC 3.4.11.2.), and ebelactone A, an esterase inhibitor. These effects resulted, as expected, in decreased cytotoxic effects of J1. A specific role of APN in hydrolyzing J1 releasing free melphalan was demonstrated in vitro with pure APN enzyme. By using plasmid-based overexpression of APN or down regulation of endogenous APN with siRNA in different tumor cell lines we here confirm the involvement of APN in J1-mediated cytotoxic and apoptotic signaling. In conclusion, this study demonstrates a role of APN in the activation of the melphalan prodrug J1 and subsequently, its cytotoxicity. Given that APN is shown to be overexpressed in several solid tumors our data suggest that J1 may be activated in a tumor selective manner.

Mitaplatin, a potent fusion of cisplatin and the orphan drug dichloroacetate

The unique glycolytic metabolism of most solid tumors, known as the Warburg effect, is associated with resistance to apoptosis that enables cancer cells to survive. Dichloroacetate (DCA) is an anticancer agent that can reverse the Warburg effect by inhibiting a key enzyme in cancer cells, pyruvate dehydrogenase kinase (PDK), that is required for the process. DCA is currently not approved for cancer treatment in the USA. Here, we present the synthesis, characterization, and anticancer properties of c,t,c-[Pt(NH(3))(2)(O(2)CHCl(2))(2)Cl(2)], mitaplatin, in which two DCA units are appended to the axial positions of a six-coordinate Pt(IV) center. The negative intracellular redox potential reduces the platinum to release cisplatin, a Pt(II) compound, and two equivalents of DCA. By a unique mechanism, mitaplatin thereby attacks both nuclear DNA with cisplatin and mitochondria with DCA selectively in cancer cells. The cytotoxicity of mitaplatin in a variety of cancer cell lines equals or exceeds that of all known Pt(IV) compounds and is comparable to that of cisplatin. Mitaplatin alters the mitochondrial membrane potential gradient (Deltapsi(m)) of cancer cells, promoting apoptosis by releasing cytochrome c and translocating apoptosis inducing factor from mitochondria to the nucleus. Cisplatin formed upon cellular reduction of mitaplatin enters the nucleus and targets DNA to form 1,2-intrastrand d(GpG) cross-links characteristic of its own potency as an anticancer drug. These properties of mitaplatin are manifest in its ability to selectively kill cancer cells cocultured with normal fibroblasts and to partially overcome cisplatin resistance.

Gadolinium texaphyrin (Gd-Tex)-malonato-platinum conjugates: synthesis and comparison with carboplatin in normal and Pt-resistant cell lines

The synthesis of a new PEG-solubilized gadolinium texaphyrin (Gd-Tex) conjugate containing a malonate-Pt(NH(3))(2) moiety is described. The effect of the tumor localizing Gd-Tex macrocycle on platinum activity was evaluated in cell culture. The malonate moiety, analogous to that present in carboplatin, is expected to release an aquated Pt(NH(3))(2) species under physiological conditions. The half-life in phosphate-buffered saline was found to be ca. 3 days at room temperature, and the hydrolytic product released from the conjugate was collected and confirmed as Pt-based by flameless atomic absorption spectrophotometry. Anti-proliferative activity was tested using A549 human lung cancer and A2780 human ovarian cancer cell lines. In both cell lines, the activity of the Gd-Tex conjugate was found to be similar to that of carboplatin. Efficacy against a Pt-resistant ovarian cell line greater than that displayed by carboplatin was also observed.

RGD-modified polymeric micelles as potential carriers for targeted delivery to integrin-overexpressing tumor vasculature and tumor cells

Integrins alphavbeta3 and alphavbeta5 are overexpressed in angiogenic tumor endothelial cells and malignant tumor cells, making them attractive targets for cancer therapy. In this study, an integrin alphavbeta3 and alphavbeta5 binding tripeptide, RGD (Arg-Gly-Asp), was conjugated with the surface of poly(ethylene glycol)-block-poly(D,L-lactide) (PEG-PLA) micelles. A lipophilic fluorescent probe, DiI, was loaded into both the nontargeted methoxy PEG-PLA (mPEG-PLA) micelles and the targeted RGD-modified PEG-PLA micelles. The DiI-loaded targeted micelles had a size of 24.2 nm. The targeted micelles were stable in phosphate buffered saline and exhibited a negligible leakage in culture medium. Transmission electron microscopy analysis showed that targeted micelles were spherical in shape. Cell uptake of DiI-labeled targeted micelles by human umbilical vein endothelial cells and melanoma B16 cells was investigated by spectrophotofluorometry and confocal microscopy techniques. Results revealed that RGD-modified micelles significantly facilitated the intracellular delivery of the encapsulated agents via integrin-mediated endocytosis. This study suggests that RGD-modified PEG-PLA micelles are promising drug carriers for targeted delivery to both angiogenic tumor endothelial cells and tumor cells and that the targeted micelles may be attractive carriers for combination cancer therapy against both targets.

Dual targeting of a thermosensitive nanogel conjugated with transferrin and RGD-containing peptide for effective cell uptake and drug release

In this paper, both arginine-glycine-aspartic acid (RGD)-containing peptide and transferrin (Tf) were conjugated to the thermosensitive poly(N-isopropylacrylamide-co-propyl acrylic acid) (poly(NIPAAm-co-PAAc)) nanogel to prepare a dual-targeting drug carrier. The obtained nanogel was characterized in terms of fluorescence spectroscopy, UV-vis spectroscopy, dynamic light scattering (DLS) and transmission electron microscopy (TEM). In order to track the dual-ligand conjugated nanogel, fluorescein isothiocyanate (FITC) was further conjugated to the nanogel. A cell internalization experiment showed that the dual-ligand conjugated nanogel exhibited obviously enhanced endocytosis by HeLa cells as compared with non-tumorous cells (COS-7 cells). The drug-loaded dual-ligand conjugated nanogel could be transported efficiently into the target tumor cells and the anti-tumor effect was enhanced significantly, suggesting that the dual-ligand conjugated nanogel has great potential as a tumor targeting drug carrier.

Effective photoreduction of a Pt(IV) complex with quantum dots: a feasible new light-induced method of releasing anticancer Pt(II) drugs

Irradiation of CdSe-ZnS quantum dots (QDs) with visible light in the presence of [PtCl(4)(bpy)] (1) (bpy = 2,2'-bipyridine) produced with high efficiency [PtCl(2)(bpy)] (2) by photoinduced electron transfer; a reaction and strategy which opens up new opportunities for cancer therapy.

Solid-phase synthesis and DNA binding studies of dichloroplatinum(ii) conjugates of dicarba analogues of octreotide as new anticancer drugs

The first dichloroplatinum(ii) conjugates of dicarba analogues of octreotide, which is expected to act as a 'tumour-targeting device', have been efficiently synthesized following a stepwise solid-phase approach; these compounds emulate the mechanism of cisplatin since they form a 1,2-intrastrand cross-link with two consecutive guanines of an oligonucleotide.

Novel bis(carboxylato)dichlorido(ethane-1,2-diamine)platinum(IV) complexes with exceptionally high cytotoxicity

(OC-6-33)-Dichlorido(ethane-1,2-diamine)dihydroxidoplatinum(IV) (1) was carboxylated using succinic- or 3-methylglutaric anhydride. The resulting bis(carboxylato)platinum(IV) complexes display free, uncoordinated carboxylic acid groups which were further derivatized with primary aliphatic alcohols. The complexes were characterized in detail by elemental analysis, ESI-MS, FT-IR, as well as multinuclear (1H, 13C, 15N, 195Pt) NMR spectroscopy. Cytotoxic properties were evaluated in four human tumor cell lines originating from ovarian carcinoma (CH1, SK-OV-3), cervical carcinoma (HeLa) and colon carcinoma (SW480) by means of the MTT assay (MTT = 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide). Structure-activity relationships showed that the cytotoxicity increased with increasing lipophilicity of the alcoholate moiety yielding IC50 values in the low micromolar or even low nanomolar range.

Targeted delivery of cisplatin to prostate cancer cells by aptamer functionalized Pt(IV) prodrug-PLGA-PEG nanoparticles

Cisplatin is used to treat a variety of tumors, but dose limiting toxicities or intrinsic and acquired resistance limit its application in many types of cancer including prostate. We report a unique strategy to deliver cisplatin to prostate cancer cells by constructing Pt(IV)-encapsulated prostate-specific membrane antigen (PSMA) targeted nanoparticles (NPs) of poly(D,L-lactic-co-glycolic acid) (PLGA)-poly(ethylene glycol) (PEG)-functionalized controlled release polymers. By using PLGA-b-PEG nanoparticles with PSMA targeting aptamers (Apt) on the surface as a vehicle for the platinum(IV) compound c,t,c-[Pt(NH(3))(2)(O(2)CCH(2)CH(2)CH(2)CH(2)CH(3))(2)Cl(2)] (1), a lethal dose of cisplatin was delivered specifically to prostate cancer cells. PSMA aptamer targeted delivery of Pt(IV) cargos to PSMA(+) LNCaP prostate cancer cells by endocytosis of the nanoparticle vehicles was demonstrated using fluorescence microscopy by colocalization of green fluorescent labeled cholesterol-encapsulated NPs and early endosome marker EEA-1. The choice of linear hexyl chains in 1 was the result of a systematic study to optimize encapsulation and controlled release from the polymer without compromising either feature. Release of cisplatin from the polymeric nanoparticles after reduction of 1 and formation of cisplatin 1,2-intrastrand d(GpG) cross-links on nuclear DNA was confirmed by using a monoclonal antibody for the adduct. A comparison between the cytotoxic activities of Pt(IV)-encapsulated PLGA-b-PEG NPs with the PSMA aptamer on the surface (Pt-NP-Apt), cisplatin, and the nontargeted Pt(IV)-encapsulated NPs (Pt-NP) against human prostate PSMA-overexpressing LNCaP and PSMA(-) PC3 cancer cells revealed significant differences. The effectiveness of PSMA targeted Pt-NP-Apt nanoparticles against the PSMA(+) LNCaP cells is approximately an order of magnitude greater than that of free cisplatin.

Cymantrene conjugation modulates the intracellular distribution and induces high cytotoxicity of a cell-penetrating peptide

The conjugation of cymantrene CpMn(CO)(3) to cell-penetrating peptide hCT(18-32)-k7 alters the intracellular distribution in MCF-7 cells compared to the unmodified peptide, as visualized by fluorescence microscopy, and leads to an increased nuclear accumulation; the peptide and cymantrene compound themselves are not toxic, but the bioconjugate shows a significant cytotoxicity with an IC(50) value of 36 micromol l(-1).

Targeted single-wall carbon nanotube-mediated Pt(IV) prodrug delivery using folate as a homing device

Most low-molecular-weight platinum anticancer drugs have short blood circulation times that are reflected in their reduced tumor uptake and intracellular DNA binding. A platinum(IV) complex of the formula c, c, t-[Pt(NH 3) 2Cl 2(O 2CCH 2CH 2CO 2H)(O 2CCH 2CH 2CONH-PEG-FA)] ( 1), containing a folate derivative (FA) at an axial position, was prepared and characterized. Folic acid offers a means of targeting human cells that highly overexpress the folate receptor (FR). Compound 1 was attached to the surface of an amine-functionalized single-walled carbon nanotube (SWNT-PL-PEG-NH 2) through multiple amide linkages to use the SWNTs as a "longboat delivery system" for the platinum warhead, carrying it to the tumor cell and releasing cisplatin upon intracellular reduction of Pt(IV) to Pt(II). The ability of SWNT tethered 1 to destroy selectively FR(+) vs FR(-) cells demonstrated its ability to target tumor cells that overexpress the FR on their surface. That the SWNTs deliver the folate-bearing Pt(IV) cargos into FR(+) cancer cells by endocytosis was demonstrated by the localization of fluorophore-labeled SWNTs using fluorescence microscopy. Once inside the cell, cisplatin, formed upon reductive release from the longboat oars, enters the nucleus and reacts with its target nuclear DNA, as determined by platinum atomic absorption spectroscopy of cell extracts. Formation of the major cisplatin 1,2-intrastrand d(GpG) cross-links on the nuclear DNA was demonstrated by use of a monoclonal antibody specific for this adduct. The SWNT-tethered compound 1 is the first construct in which both the targeting and delivery moieties have been incorporated into the same molecule; it is also the first demonstration that intracellular reduction of a Pt(IV) prodrug leads to the cis-{Pt((NH 3) 2} 1,2-intrastrand d(GpG) cross-link in nuclear DNA.

Unprecedented twofold intramolecular hydroamination in diam(m)ine-dicarboxylatodichloridoplatinum(IV) complexes - ethane-1,2-diamine vs. ammine ligands

Reaction of (OC-6-13)-bis(2Z-3-carboxyacrylato)dichlorido(ethane-1,2-diamine)platinum(IV) and (OC-6-13)-diamminebis(2Z-3-carboxyacrylato)dichloridoplatinum(IV) with propylamine in the presence of 1,1'-carbonyl diimidazole afforded not the expected amides; instead, beside amide formation, a twofold intramolecular attack of the am(m)ine ligand at the C[double bond, length as m-dash]C bonds was observed involving either both (ethane-1,2-diamine) or only one (ammine) coordinated nitrogen atom(s).