Chengcheng Zhu

A reversible ratiometric sensor for intracellular Cu2+ imaging: metal coordination-altered FRET in a dual fluorophore hybrid

ICT fluorophore benzoxadiazole with its electron-donating group modified as a Cu(2+) chelator was conjugated with coumarin to construct a new ratiometric sensor with reversible intracellular Cu(2+) imaging ability.

A mitochondrion-targeting copper complex exhibits potent cytotoxicity against cisplatin-resistant tumor cells through multiple mechanisms of action

Copper complexes are potential anticancer drugs by virtue of their available redox properties and low toxicity. In this study, a copper(II) complex, [Cu(ttpy-tpp)Br2]Br (simplified as CTB, ttpy-tpp = 4′-p-tolyl-(2,2′:6′,2′′-terpyridyl)triphenylphosphonium bromide), is synthesized and characterized by X-ray crystallography and ESI-MS as a targeted anticancer agent. Triphenylphosphine (TPP) is introduced into the complex for its mitochondrion-targeting ability and lipophilic character. The uptake of CTB by tumor cells and mitochondria was determined by ICP-MS or fluorescence spectrometry. CTB is able to cross the cytoplasmic and mitochondrial membranes of tumor cells and influence the mitochondrial membrane potential more profoundly than the anticancer drug cisplatin. The cytotoxicity of CTB was tested on MCF-7, HeLa, Skov-3, A549 and cisplatin-resistant A549R tumor cells by MTT assay. CTB is more cytotoxic against these cells than cisplatin; particularly, it is highly effective against cisplatin-resistant tumor cells. The interaction between CTB and DNA has been studied by spectroscopic methods and agarose gel electrophoresis. CTB strongly interacts with DNA via intercalation stabilized by electrostatic forces, and displays a significant cleavage activity towards supercoiled pBR322 DNA and cellular DNA through an oxidative mechanism. The cytotoxicity of CTB seems to result from multiple mechanisms of action, including the modification of DNA conformation, generation of reactive oxygen species, scission of DNA strands, and dissipation of mitochondrial membrane potential. The delocalized cationic property and high hydrophilicity of CTB favours its selective accumulation in cancer cells and mitochondria. This study demonstrates that copper complexes with mitochondrion-targeting function could be efficient anticancer drugs immune to the drug resistance of cisplatin.

In Vitro and in Vivo Fluorescent Imaging of a Monofunctional Chelated Platinum Complex Excitable Using Visible Light

The biological fluorescent distribution of a model antitumor monofunctional platinum(II) complex bearing a 7-nitro-2,1,3-benzoxadiazole fluorophore can be visualized in breast carcinoma MCF-7 cells, pulmonary carcinoma A549 cells, kidney epithelial 293T cells, and zebrafish larva.

A monofunctional trinuclear platinum complex with steric hindrance demonstrates strong cytotoxicity against tumor cells.

Polynuclear platinum complexes constitute a special class of hopeful antitumor agents. In this study, a Y-type monofunctional trinuclear platinum complex (MTPC) with 1,3,5-tris(pyridin-2-ylmethoxy)benzene, ammine and chloride as ligands was synthesized and characterized by (1)H NMR and electrospray ionization mass spectrometry (ESI-MS). The DNA binding mode of MTPC was investigated using circular dichroism spectroscopy and gel electrophoresis, and the reactivity of MTPC towards glutathione was studied by (1)H NMR and ESI-MS. The results show that MTPC can affect the conformation of calf-thymus DNA (CT-DNA) significantly and tends to form 1,4-GG rather than 1,2-GG intrastrand crosslinks, which are different from the instance of cisplatin. MTPC reacts with glutathione quite slowly in comparison with cisplatin because of the steric hindrance. The cytotoxicity of MTPC was tested on the human breast cancer cell line MCF-7, the human non-small-cell lung cancer cell line A549, and the human ovarian cancer cell line Skov-3 by the MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assay. MTPC is more potent than or comparable to cisplatin. The cellular inhibition mode of MTPC was examined by flow cytometry using MCF-7 cells. MTPC arrests the cell cycle mainly in G2 or M phase, while cisplatin arrests the cell cycle in S phase. Similar to cisplatin, MTPC kills the cells predominantly through an apoptotic pathway.

A New Approach to Sensitize Antitumor Monofunctional Platinum(II) Complexes via Short Time Photo-Irradiation

Sensitizing the antitumor activity of monofunctional PtII complexes is a reliable approach to developing antitumor agents different from the classic Pt-based drugs. Considering the poor intracellular accumulation of monofunctional PtII complexes, in this study, the photosensitizing monofunctional PtII complex Pt-BA was derived from a weak BODIPY (boron-dipyrromethene)-derived photosensitizer BA, with the purpose to improve its antitumor cytotoxicity via enhancing its intracellular accumulation with a short time photo-irradiation. Photoinduced reactive oxygen species (ROS) determination indicated that the PtII center in Pt-BA is able to improve the photoinduced ROS production ability of BA, which makes Pt-BA a mild photosensitizer. Fluorescence imaging disclosed that dark incubation makes Pt-BA accumulate mainly on the surface of cell membrane, and the later short time photo-irradiation (5 min) promotes distinctly the intracellular accumulation of Pt-BA, which has been confirmed by inductively coupled plasma-mass spectrometry determination. Flow cytometric Annexin V-FITC assay indicated that the short time irradiation of Pt-BA induces in situ the cell membrane damage, which might finally enhance the intracellular accumulation of this monofunctional complex. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay confirmed that the short time photo-irradiation promotes distinctly the antitumor cytotoxicity of Pt-BA against MCF-7, SGC-7901, A549, and HeLa cell lines. The photopromoted antitumor activity of Pt-BA implies that modifying monofunctional PtII complex as a mild photosensitizer to promote its cell accumulation is a useful approach to sensitizing the antitumor activity of monofunctional PtII complex and renders the possibility of monofunctional PtII prodrugs for precise chemotherapy via only short time photoactivation.

A Potential Bone-Targeting Hypotoxic Platinum(II) Complex with an Unusual Cytostatic Mechanism toward Osteosarcoma Cells

Osteosarcoma (OS) is the most common primary pediatric bone tumor lethal to children and adolescents. Chemotherapeutic agents such as cisplatin are not effective for OS because of their poor accessibility to this cancer and severe systemic toxicity. In this study, a lipophilic platinum(II) complex bearing a bisphosphonate bone-targeting moiety, cis-[PtL(NH3)2Cl]NO3 {BPP; L = tetraethyl [2-(pyridin-2-yl)ethane-1,1-diyl]bisphosphonate}, was prepared and characterized by NMR, electrospray ionization mass spectrometry, and single-crystal X-ray crystallography. The cytotoxicity of BPP toward OS cell lines U2OS and MG-63 was tested by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. BPP exhibits moderate inhibition against U2OS cells through a mechanism involving both DNA binding and a mevalonate pathway. The acute toxicity of BPP to mice is 7-fold lower than that of cisplatin. The relative low systemic toxicity may result from the steric hindrance of the ligand, which blocks BPP approaching the bases of DNA. The results suggest that incorporating bisphosphonates into a platinum complex not only enhances its bone-targeting property but also minimizes its reactivity toward DNA and thereby lowers the systematic toxicity of the complex. The diminished cytotoxicity of BPP could be compensated for by increasing the therapeutic dose with marginal harm. This strategy provides a new possibility for overcoming the ineffectiveness and systemic toxicity of platinum drugs in the treatment of OS.

Coumarin/BODIPY Hybridisation for Ratiometric Sensing of Intracellular Polarity Oscillation

With different polarity responses, coumarin and 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) were hybridised to construct polarity fluorescent sensors, CBDP and iso-CBDP, to overcome the disadvantages of solvatochromic sensors in ratiometric polarity sensing. Only CBDP displayed an emission ratio (ICou /IBDP , coumarin to BODIPY emissions) that increased with an exponential dependence on medium relative permittivity over a wide polarity range (ϵr <57.9). This sensing ability of CBDP was not affected by medium pH; viscosity; and most intracellular species, especially reactive oxygen, nitrogen, and sulfur species. Apart from local cytoplasmic polarity quantification through lambda imaging, CBDP enables real-time ratiometric imaging for intracellular polarity oscillation induced by oxidative stimulation. Ratiometric polarity flow cytometry was developed, for the first time, with CBDP, which demonstrated that a high concentration H2 O2 induced cytoplasmic polarity enhancement, whereas pre-incubation with N-acetyl-l-cysteine inhibited this effect.

A novel ratiometric fluorescent probe for Hg2+imaging in biological system

A novel ratiometric fluorescent Hg2+ probe, CDTT, was synthesized based on the changing of intramolecular charge transfer (ICT) process caused by the specific Hg2+ triggered aldehyde recovery. A large excitation shift from 410 nm in the absence of Hg2+ to 485 nm in the presence of Hg2+ was observed. The excitation intensity ratio of F 485/ F 410 increased from 0.06 to 5.02. CDTT exhibited high selectivity and fast response to Hg2+, and its detection limit was determined to be 0.6 ppb, lower than the US EPA standard for drinking water. The ratiometric imaging ability in living cells and 5-day-old zebra fished was confirmed using laser scanning confocal fluorescent microscopy, the preliminary study of the distribution and the toxicity of Hg2+ in zebra fish larvae were also conducted.利用汞离子特异性诱导缩硫醛脱保护，引发分子内电荷转移发生改变的机制，设计合成了一种新型的激发型比例计量汞离子荧光探针. 该探针在与汞离子结合后其最大激发波长由410 nm红移至485 nm，两个波长下的荧光强比值（ F 485 / F 410 ）由0.06增长至5.02. 同时该探针对汞离子表现出了良好的比例计量响应选择性和较快的响应速度，并且检测限低于美国环境保护组织的饮用水标准. 共聚焦造影研究发现，该探针可以应用于活细胞及5天龄斑马鱼幼体中的汞离子的检测. 利用该性质对Hg 2+ 在斑马鱼体内分布及毒性进行了初步的研究.