Raymond Wai-Yin Sun

Gold(III) Porphyrin 1a Induced Apoptosis by Mitochondrial Death Pathways Related to Reactive Oxygen Species

Apoptosis is a tightly controlled multistep mechanism of cell death, and mitochondria are considered to play a central role in this process. Mitochondria initiate two distinct apoptosis pathways, one caspase-dependent and the other caspase-independent. In addition, mitochondrial production of reactive oxygen species (ROS) seems to play a role in cell death. Most chemotherapeutic agents induce apoptosis through at least one of these pathways. The post-initiation mechanisms of gold(III) porphyrin 1a were investigated in this study. HONE1 cells exposed to gold(III) porphyrin 1a underwent apoptosis after 24 hours. Functional proteomic studies revealed the alteration of several cytoplasmic protein expressions in HONE1 cells after treatment with the drug. These proteins include enzymes participating in energy production and proteins involved in cellular redox balance. There was a quick attenuation of mitochondrial membrane potential (DeltaPsi(m)) with the alterations of Bcl-2 family proteins, the release of cytochrome c, and apoptosis-inducing factor (AIF) following gold(III) porphyrin 1a treatment. Cytochrome c in turn activated caspase-9 and caspase-3. Cotreatment with caspase inhibitor (zVAD-fmk) showed that the activated caspases worked in conjunction with AIF-initiated apoptosis pathways. Further study showed that ROS played a part in gold(III) porphyrin 1a-induced apoptosis by regulating DeltaPsi(m). In summary, gold(III) porphyrin 1a induced apoptosis through both caspase-dependent and caspase-independent mitochondrial pathways, and intracellular oxidation affected gold(III) porphyrin 1a-induced apoptosis. These results support a role for gold(III) porphyrin 1a as a promising anticancer drug lead and as a possible novel therapeutic agent directed toward the mitochondria.

Therapeutic applications of gold complexes: lipophilic gold(III) cations and gold(I) complexes for anti-cancer treatment

Gold and its complexes have long been known to display unique biological and medicinal properties. Extensive cell-based (in vitro) and animal (in vivo) studies have revealed the potent anti-cancer activities of diverse classes of gold(I) and gold(III) complexes. Most of the reported anti-cancer active gold complexes are highly cytotoxic and unstable under physiological conditions, which hamper their development to be launched clinically. Several clinical reports showed that lipophilic organic cations are promising anti-cancer drug candidates targeting to mitochondria. Through metal-ligand coordination, gold(I) and gold(III) ions can form stable lipophilic cations containing organic ligands having tunable lipophilicity and diverse functionalities. The present highlight summarizes the recent development of lipophilic gold(III) cations and gold(I) complexes with promising anti-cancer activities.

Luminescent cyclometalated platinum(II) complexes containing N-heterocyclic carbene ligands with potent in vitro and in vivo anti-cancer properties accumulate in cytoplasmic structures of cancer cells

Contrary to most platinum-based anti-cancer agents which target DNA, coordination of N-heterocyclic carbene (NHC) ligands to cyclometalated platinum(II) complexes confers these luminescent complexes to other cellular target(s). The strong Pt–Ccarbene bond(s) renders the platinum(II) complexes to display unique photophysical properties and enhanced stability against biological reduction and ligand exchange reactions. The platinum complexes described in this work are highly cytotoxic and display high specificity to cancerous cells. Among them, [(C^N^N)PtII(N,N′-nBu2NHC)]PF6 (1a, where HC^N^N = 6-phenyl-2,2′-bipyridine) with a lipophilic carbon chain on the carbene ligand induces apoptosis in cancer cells, demonstrates an enhancing synergistic effect with cisplatin in vitro, and displays potent in vivo activities using nude mice models. As this complex is strongly emissive, its cellular localization can be traced using emission microscopy. In contrast to common platinum-based anti-cancer agents, 1a does not accumulate in the vicinity of DNA but preferentially accumulates in cytoplasmic structures including sites where active survivin, an inhibitor of apoptosis (IAP), is located. In vitro, 1a significantly inhibits the expression of survivin, activates poly(ADP-ribose) polymerase (PARP) and induces apoptosis in cancer cells. Given the ease of structural modification of NHC ligand to alter the overall biological activities, these [(C^N^N)PtII(NHC)]+ complexes having unique photophysical properties provide an entry to a new class of potential anti-cancer drug leads.

Cyclometalated gold(III) complexes with N-heterocyclic carbene ligands as topoisomerase I poisons

A panel of stable [Au(R-C--N--C)(N-heterocyclic carbene)](+) complexes displays prominent in vitro anticancer properties; [Au(C--N--C)(IMe)]CF(3)SO(3) (1, IMe = 1,3-dimethylimidazol-2-ylidene) significantly poisons topoisomerase I in vitro and suppresses tumor growth in nude mice model.

Stable Anticancer Gold(III)–Porphyrin Complexes: Effects of Porphyrin Structure

In the design of physiologically stable anticancer gold(III) complexes, we have employed strongly chelating porphyrinato ligands to stabilize a gold(III) ion [Chem. Commun. 2003, 1718; Coord. Chem. Rev. 2009, 253, 1682]. In this work, a family of gold(III) tetraarylporphyrins with porphyrinato ligands containing different peripheral substituents on the meso-aryl rings were prepared, and these complexes were used to study the structure-bioactivity relationship. The cytotoxic IC(50) values of [Au(Por)](+) (Por=porphyrinato ligand), which range from 0.033 to >100 microM, correlate with their lipophilicity and cellular uptake. Some of them induce apoptosis and display preferential cytotoxicity toward cancer cells than to normal noncancerous cells. A new gold(III)-porphyrin with saccharide conjugation [Au(4-glucosyl-TPP)]Cl (2a; H(2)(4-glucosyl-TPP)=meso-tetrakis(4-beta-D-glucosylphenyl)porphyrin) exhibits significant cytostatic activity to cancer cells (IC(50)=1.2-9.0 microM) without causing cell death and is much less toxic to lung fibroblast cells (IC(50)>100 microM). The gold(III)-porphyrin complexes induce S-phase cell-cycle arrest of cancer cells as indicated by flow cytometric analysis, suggesting that the anticancer activity may be, in part, due to termination of DNA replication. The gold(III)-porphyrin complexes can bind to DNA in vitro with binding constants in the range of 4.9 x 10(5) to 4.1 x 10(6) dm(3) mol(-1) as determined by absorption titration. Complexes 2a and [Au(TMPyP)]Cl(5) (4a; [H(2)TMPyP](4+)=meso-tetrakis(N-methylpyridinium-4-yl)porphyrin) interact with DNA in a manner similar to the DNA intercalator ethidium bromide as revealed by gel mobility shift assays and viscosity measurements. Both of them also inhibited the topoisomerase I induced relaxation of supercoiled DNA. Complex 4a, a gold(III) derivative of the known G-quadruplex-interactive porphyrin [H(2)TMPyP](4+), can similarly inhibit the amplification of a DNA substrate containing G-quadruplex structures in a polymerase chain reaction stop assay. In contrast to these reported complexes, complex 2a and the parental gold(III)-porphyrin 1a do not display a significant inhibitory effect (<10%) on telomerase. Based on the results of protein expression analysis and computational docking experiments, the anti-apoptotic bcl-2 protein is a potential target for those gold(III)-porphyrin complexes with apoptosis-inducing properties. Complex 2a also displays prominent anti-angiogenic properties in vitro. Taken together, the enhanced stabilization of the gold(III) ion and the ease of structural modification render porphyrins an attractive ligand system in the development of physiologically stable gold(III) complexes with anticancer and anti-angiogenic activities.

A High-Symmetry Coordination Cage from 38- or 62-Component Self-Assembly

Artificial molecular architecture from a large number of subcomponents (>50) via self-assembly remains a formidable challenge for chemists. Reaction of 38 components [14 Ni(2+) and 24 N-methyl-1-(4-imidazolyl)methanimine] under solvothermal conditions reproducibly leads to the formation of a high-symmetry coordination cage. This polyhedral cage can also be obtained in high yield by self-assembly of 62 commercially available subcomponents (24 methylamine, 24 4-formylimidazole, and 14 Ni(2+)) under mild conditions involving synchronized formation of both dynamic covalent bonds and coordination bonds. Guest molecules (e.g., water, methylamine, and methanol) are randomly imprisoned in the cage.

A Gold(III) Porphyrin Complex with Antitumor Properties Targets the Wnt/β-catenin Pathway

Gold(III) complexes have shown promise as antitumor agents, but their clinical usefulness has been limited by their poor stability under physiological conditions. A novel gold(III) porphyrin complex [5-hydroxyphenyl-10,15,20-triphenylporphyrinato gold(III) chloride (gold-2a)] with improved aqueous stability showed 100-fold to 3,000-fold higher cytotoxicity than platinum-based cisplatin and IC50 values in the nanomolar range in a panel of human breast cancer cell lines. Intraductal injections of gold-2a significantly suppressed mammary tumor growth in nude mice. These effects are attributed, in part, to attenuation of Wnt/beta-catenin signaling through inhibition of class I histone deacetylase (HDAC) activity. These data, in combination with computer modeling, suggest that gold-2a may represent a promising class of anticancer HDAC inhibitor preferentially targeting tumor cells with aberrant Wnt/beta-catenin signaling.

Gold(III) compound is a novel chemocytotoxic agent for hepatocellular carcinoma

Recently, a series of gold(III) meso‐tetraarylporphyrins that are stable against demetallation in physiological conditions have been synthesized. In the present study, the antitumor effects of one of these compounds, gold(III) meso‐tetraarylporphyrin 1a (gold‐1a) was investigated in an orthotopic rat hepatocellular carcinoma (HCC) model as well as using a HCC cell line. The rat HCC model was induced by injection of rat hepatoma cells, McA‐RH7777, into the left lobe of the liver. Seven days after tumor cell inoculation, gold‐1a was injected directly into the tumor nodule at different doses, followed by the same doses via intraperitoneal injection twice a week. Gold‐1a administration significantly prolonged the survival of HCC‐bearing rats. Importantly, gold‐1a induced necrosis as well as apoptosis in the tumor tissues, but not in the normal liver tissues. Furthermore, gold‐1a treatment neither caused significant drop in body weight of the rats nor affected plasma aspartate aminotransferase level. In the in vitro studies, we observed that gold‐1a treatment inhibited the proliferation of McA‐RH7777 cells. Gold‐1a upregulated genes that increase apoptosis, stabilize p53, decrease proliferation and downregulated genes playing roles in angiogenesis, invasion, and metabolism, as demonstrated by microarray. In particular, the compound upregulated 2 members of the growth arrest and DNA damage (Gadd) inducible gene family, Gadd34 and Gadd153. Suppression of Gadd34 and Gadd153 in McA‐RH7777 cells by small hairpin RNA reduced the gold‐1a‐induced apoptosis and growth inhibition, indicating that gold‐1a mediated its effects via upregulation of Gadd34 and Gadd153. Results from our study demonstrated that gold‐1a might be a novel promising chemocytotoxic agent for treating HCC.

Organogold(III) Supramolecular Polymers for Anticancer Treatment

Gold cures: the depicted gold(III) complex self-assembles into supramolecular polymers which form nanofibrillar networks that display sustained cytotoxicity and can also act as carriers for other cytotoxic agents.

Gold(III) porphyrin complex is more potent than cisplatin in inhibiting growth of nasopharyngeal carcinoma in vitro and in vivo

Nasopharyngeal carcinoma (NPC) is a common neoplasm in Southeastern Asia, and cisplatin‐containing regimens for combinational chemotherapy are widely used for treating locally recurrent or metastatic diseases. However, resistance to cisplatin is not infrequently seen and its associated side effects may be life‐threatening. In this report, another metallo‐pharmaceutical agent gold(III) porphyrin complex [Au(TPP)]Cl was investigated in comparison to cisplatin for its in vitro and in vivo anticancer effects. Through induction of the intrinsic apoptosis pathway, [Au(TPP)]Cl exhibited 100‐fold higher potency than cisplatin in killing NPC cells, including cisplatin‐sensitive and cisplatin‐resistant variants, and also an variant harboring the Epstein‐Barr virus. In addition, a safety concentration window was demonstrated, allowing [Au(TPP)]Cl to kill tumors with minimal cytotoxicity to noncancerous cells. More importantly, weekly intraperitoneal injection of 3 mg/kg [Au(TPP)]Cl was more effective than the same dose of cisplatin in inducing tumor apoptosis in vivo and remarkably inhibited tumor growth in animals without any noticeable side effect. [Au(TPP)]Cl therefore is a promising chemotherapeutic agent that deserves further development as a novel drug for the treatment of advanced NPC, in particular, for cases with cisplatin‐resistance.