Cai-Ping Tan

Nuclear Permeable Ruthenium(II) β-Carboline Complexes Induce Autophagy To Antagonize Mitochondrial-Mediated Apoptosis

The role of autophagy in cancer development and response to cancer therapy has been a subject of debate. Here we demonstrate that a series of ruthenium(II) complexes containing a β-carboline alkaloid as ligand can simultaneously induce autophagy and apoptosis in tumor cells. These Ru(II) complexes are nuclear permeable and highly active against a panel of human cancer cell lines, with complex 3 displaying activities greater than those of cisplatin. The antiproliferative potentialities of 1-3 are in accordance with their relative lipophilicities, cell membrane penetration abilities, and in vitro DNA binding affinities. Complexes 1-3 trigger release of reactive oxygen species (ROS) and attenuation of ROS by scavengers reduced the sub-G1 population, suggesting ROS-dependent apoptosis. Inhibition of ROS generation also reduces autophagy, indicating that ROS triggers autophagy. Further studies show that suppression of autophagy using pharmacological inhibitors (3-methyladenine and chloroquine) enhances apoptotic cell death.

Multifunctional QD-based co-delivery of siRNA and doxorubicin to HeLa cells for reversal of multidrug resistance and real-time tracking.

Co-delivery of siRNA and chemotherapeutic agents has been developed to combat multidrug resistance in cancer therapy. Recently, we developed a series of quantum dots (QDs) functionalized by β-cyclodextrin (β-CD) coupled to amino acids, some of which can be used to facilitate the delivery of siRNA. In this study, two CdSe/ZnSe QDs modified with β-CD coupled to L-Arg or L-His were used to simultaneously deliver doxorubicin (Dox) and siRNA targeting the MDR1 gene to reverse the multidrug resistance of HeLa cells. In this co-delivery system, Dox was firstly encapsulated into the hydrophobic cavities of β-CD, resulting in bypass of P-glycoprotein (P-gp)-mediated drug efflux. After complex formation of the mdr1 siRNA with Dox-loaded QDs via electrostatic interaction, significant down-regulation of mdr1 mRNA levels and P-gp expression was achieved as shown by RT-PCR and Western blotting experiments, respectively. The number of apoptotic HeLa cells after treatment with the complexes substantially exceeded the number of apoptotic cells induced by free Dox only. The intrinsic fluorescence of the QDs provided an approach to track the system by laser confocal microscopy. These multifunctional QDs are promising vehicles for the co-delivery of nucleic acids and chemotherapeutics and for real-time tracking of treatment.

Theranostic Iridium(III) Complexes as One- and Two-Photon Phosphorescent Trackers to Monitor Autophagic Lysosomes†

During autophagy, the intracellular components are captured in autophagosomes and delivered to lysosomes for degradation and recycling. Changes in lysosomal trafficking and contents are key events in the regulation of autophagy, which has been implicated in many physiological and pathological processes. In this work, two iridium(III) complexes (LysoIr1 and LysoIr2) are developed as theranostic agents to monitor autophagic lysosomes. These complexes display lysosome-activated phosphorescence and can specifically label lysosomes with high photostability. Simultaneously, they can induce autophagy potently without initiating an apoptosis response. We demonstrate that LysoIr2 can effectively implement two functions, namely autophagy induction and lysosomal tracking, in the visualization of autophagosomal-lysosomal fusion. More importantly, they display strong two-photon excited fluorescence (TPEF), which is favorable for live cell imaging and in vivo applications.

Ruthenium–Arene–β‐Carboline Complexes as Potent Inhibitors of Cyclin‐Dependent Kinase 1: Synthesis, Characterization and Anticancer Mechanism Studies

A series of Ru(II)-arene complexes (1-6) of the general formula [(η(6)-arene)Ru(L)Cl]PF6 (arene=benzene or p-cymene; L=bidentate β-carboline derivative, an indole alkaloid with potential cyclin-dependent kinases (CDKs) inhibitory activities) is reported. All the complexes were fully characterized by classical analytical methods, and three were characterized by X-ray crystallography. Hydrolytic studies show that β-carboline ligands play a vital role in their aqueous behaviour. These complexes are highly active in vitro, with the most active complex 6 displaying a 3- to 12-fold higher anticancer activity than cisplatin against several cancer cell lines. Interestingly, the complexes are able to overcome cross-resistance to cisplatin, and show much lower cytotoxicity against normal cells. Complexes 1-6 may directly target CDK1, because they can block cells in the G2M phase, down-regulate the expression of CDK1 and cyclin B1, and inhibit CDK1/cyclin B in vitro. Further mechanism studies show that the complexes can effectively induce apoptosis through mitochondrial-related pathways and intracellular reactive oxygen species (ROS) elevation.

Co-Delivery of Cisplatin Prodrug and Chlorin e6 by Mesoporous Silica Nanoparticles for Chemo-Photodynamic Combination Therapy to Combat Drug Resistance.

Combination therapy shows great promise in circumventing cisplatin resistance. We report herein the development of a novel nanoscale drug delivery system (nDDS) based nanotherapeutic that combines chemotherapy and photodynamic therapy (PDT) into one single platform to achieve synergistic anticancer capacity to conquer cisplatin resistance. Mesoporous silica nanoparticle (MSNs) was used as the drug delivery vector to conjugate cisplatin prodrug and to load photosensitizer chlorin e6 (Ce6) to afford the dual drug loaded delivery system MSNs/Ce6/Pt. The hybrid nanoparticles have an average diameter of about 100 nm and slightly positive surface charge of about 18.2 mV. The MSNs/Ce6/Pt nanoparticles can be efficiently internalized by cells through endocytosis, thereby achieving much higher cellular Pt uptake than cisplatin in cisplatin-resistant A549R lung cancer cells. After 660 nm light irradiation (10 mW/cm(2)), the cellular reactive oxygen species (ROS) level in MSNs/Ce6/Pt treated cells was elevated dramatically. As a result of these properties, MSNs/Ce6/Pt exhibited very potent anticancer activity against A549R cells, giving a half-maximal inhibitory concentration (IC50) value for the combination therapy of 0.53 μM, much lower than that of cisplatin (25.1 μM). This study suggests the great potential of nDDS-based nanotherapeutic for combined chemo-photodynamic therapy to circumvent cisplatin resistance.

Targeted Cellular Uptake and siRNA Silencing by Quantum‐Dot Nanoparticles Coated with β‐Cyclodextrin Coupled to Amino Acids

Quantum dots (QDs) have the potential to serve as photostable beacons to track siRNA delivery, which is fast becoming an attractive approach to probe gene function in cells. In this paper, we synthesized QD nanoparticles coated with β-cyclodextrin (β-CD) coupled to amino acids with different surface charges (positive, negative, and neutral) through direct ligand-exchange reactions and used them to deliver siRNA. We found that these QDs are diffluent in biological buffer with high colloidal stability and have strong optical emission properties similar to those of tri-n-octylphosphine oxide (TOPO)-coated QDs and also have a long fluorescence lifetime (12.5 ns for L-His-β-CD-coated CdSe/ZnSe QDs). The results of in vitro cytotoxicity and internalization of these modified QDs in normal and cancer cells showed that the β-CD coupled to amino acid outlayers greatly improved the biocompatibility of QDs, and conferred with lower cytotoxicity even at very high concentration. In particular, the L-His-β-CD-coated CdSe/ZnSe QDs presented lower cytotoxicity to these cells (CC(50) value is 180.6±3.4 μg mL(-1) in ECV-304 cells for 48 h). Transmission electron microscope (TEM) images showed that the QDs were localized in vesicles in the cytoplasm of the cells. Furthermore, compared with existing transfection agents, gene-silencing efficiency of the modified QDs was slightly improved for HPV18 E6 gene in HeLa cells by gel electrophoresis analysis. Finally, the unique optical properties of QDs allow visible imaging of siRNA delivery in live cells. Taken together, our study not only provides new insights into the mechanisms of amino acid mediated delivery, but also greatly facilities the monitoring of gene-silencing studies.

Metallomics insights into the programmed cell death induced by metal-based anticancer compounds

Since the discovery of cisplatin more than 40 years ago, enormous research efforts have been dedicated to developing metal-based anticancer agents and to elucidating the mechanisms involved in the action of these compounds. Abnormal metabolism and the evasion of apoptosis are important hallmarks of malignant transformation, and the induction of apoptotic cell death has been considered to be a main pathway by which cytotoxic metal complexes combat cancer. However, many cancers have cellular defects involving the apoptotic machinery, which results in an acquired resistance to apoptotic cell death and therefore reduced chemotherapeutic effectiveness. Over the past decade, it has been revealed that a growing number of cell death pathways induced by metal complexes are not dependent on apoptosis. Metal complexes specifically triggering these alternative cell death pathways have been identified and explored as novel cancer treatment options. In this review, we discuss recent examples of metallomics studies on the different types of cell death induced by metal-based anticancer drugs, especially on the three major forms of programmed cell death (PCD) in mammalian cells: apoptosis, autophagy and regulated necrosis, also called necroptosis.

Histone-Deacetylase-Targeted Fluorescent Ruthenium(II) Polypyridyl Complexes as Potent Anticancer Agents

Histone deacetylases inhibitors (HDACis) have gained much attention as a new class of anticancer agents in recent years. Herein, we report a series of fluorescent ruthenium(II) complexes containing N(1)-hydroxy-N(8)-(1,10-phenanthrolin-5-yl)octanediamide (L), a suberoylanilide hydroxamic acid (SAHA) derivative, as a ligand. As expected, these complexes show interesting chemiphysical properties, including relatively high quantum yields, large Stokes shifts, and long emission lifetimes. The in vitro inhibitory effect of the most effective drug, [Ru(DIP)2L](PF6)2 (3; DIP: 4,7-diphenyl-1,10-phenanthroline), on histone deacetylases (HDACs) is approximately equivalent in activity to that of SAHA, and treatment with complex 3 results in increased levels of the acetylated histone H3. Complex 3 is highly active against a panel of human cancer cell lines, whereas it shows relatively much lower toxicity to normal cells. Further mechanism studies show that complex 3 can elicit cell cycle arrest and induce apoptosis through mitochondria-related pathways and the production of reactive oxygen species. These data suggest that these fluorescent ruthenium(II)-HDACi conjugates may represent a promising class of anticancer agents for potential dual imaging and therapeutic applications targeting HDACs.

Cyclometalated iridium(III)–β-carboline complexes as potent autophagy-inducing agents

Two cyclometalated Ir(III)-β-carboline complexes were identified as potent inducers of autophagic cell death. Autophagy induced by these complexes is ROS-mediated and caspase-independent.

Mono- and Dinuclear Phosphorescent Rhenium(I) Complexes: Impact of Subcellular Localization on Anticancer Mechanisms.

Elucidation of relationship among chemical structure, cellular uptake, localization, and biological activity of anticancer metal complexes is important for the understanding of their mechanisms of action. Organometallic rhenium(I) tricarbonyl compounds have emerged as potential multifunctional anticancer drug candidates that can integrate therapeutic and imaging capabilities in a single molecule. Herein, two mononuclear phosphorescent rhenium(I) complexes (Re1 and Re2), along with their corresponding dinuclear complexes (Re3 and Re4), were designed and synthesized as potent anticancer agents. The subcellular accumulation of Re1-Re4 was conveniently analyzed by confocal microscopy in situ in live cells by utilizing their intrinsic phosphorescence. We found that increased lipophilicity of the bidentate ligands could enhance their cellular uptake, leading to improved anticancer efficacy. The dinuclear complexes were more potent than the mononuclear counterparts. The molecular anticancer mechanisms of action evoked by Re3 and Re4 were explored in detail. Re3 with a lower lipophilicity localizes to lysosomes and induces caspase-independent apoptosis, whereas Re4 with higher lipophilicity specially accumulates in mitochondria and induces caspase-independent paraptosis in cancer cells. Our study demonstrates that subcellular localization is crucial for the anticancer mechanisms of these phosphorescent rhenium(I) complexes.