Yangzhong Liu

Combating the Drug Resistance of Cisplatin Using a Platinum Prodrug Based Delivery System

Platinum-based anticancer drugs are widely used in the clinic for the treatment of a broad spectrum of human malignancies. These drugs are administered to 40–80% of all patients undergoing cancer chemotherapy, either as single agents or in combination with other agents. However, their application is limited by the presence of side effects and drug resistance. Although some tumors are intrinsically resistant to platinumbased drugs, other tumors acquire resistance only after initial treatment. The sensitivity of cells toward platinum-based drugs, such as cisplatin, is dependent on DNA platination because DNA is the ultimate drug target of cisplatin. Tumor cells can acquire cisplatin resistance, that is, can achieve a reduction in the level of DNA platination, through several mechanisms, for example, through reduced drug uptake, through drug deactivation in cells, through DNA repair, and through increased drug efflux. Several cellular processes can be associated with sensitivity of cells toward cisplatin. The uptake of cisplatin into cells is facilitated by the copper transport protein (Ctr1), which is expressed in low levels in some cisplatin-resistant cells. Metallothionein (MT) is a thiol-rich protein that binds strongly to many heavy-metal ions, including platinum(II). MT plays a role in cellular detoxification by sequestering these heavy-metal compounds, and an increased concentration of this protein in cells is associated with low efficacy of cisplatin. The small peptide glutathione (GSH), which also has high affinity toward cisplatin and is found in increased concentrations in some cisplatin-resistant cells, can play a similar role. Additionally, DNA repair proteins (such as NER) and efflux proteins (such as P-type ATPases) can also reduce the efficacy of cisplatin and contribute to cisplatin resistance. To avoid the problems of resistance associated with the use of cisplatin, several types of nonclassical platinum complexes have been developed, including trans-coordinated complexes, polynuclear platinum complexes, and platinum(IV) complexes. These platinum complexes differ from cisplatin in their uptake pathway, their reactivity toward cellular proteins, and their DNA binding modes. Because of these differences, some of these nonclassical platinum complexes, such as trans-EE, BBR3464, and satraplatin, have shown promising activity in cisplatin-resistant cells. These findings suggest that the design of platinum-based drugs that have different responses to cellular processes is a feasible approach toward circumventing the problems of resistance that affect the use of cisplatin. Drug delivery systems have drawn particular attention in recent years because they can facilitate the delivery of platinum-based drugs, thus enhancing drug efficacy. A number of drug delivery systems have been developed for the delivery of platinum-based drugs. These systems have been based on polymers, solid lipids, and inorganic nanoparticles; the latter can be further subdivided into magnetic iron oxide, single-walled carbon nanotubes, metallofullerene nanoparticles, gold nanoparticles, nanoscale metal-organic frameworks, and mesoporous silica microparticles. [17] Some of these systems have entered clinical trials. With the conjugation of biologically active molecules, some delivery systems have shown high selectivity in targeting tumor cells. Although the use of drug-delivery systems has been successful in improving the efficacy of platinum-based drugs, it remains a challenge to develop drug conjugates that combat drug resistances. We have previously reported that PEGylated gold nanorods (PEG-GNRs) can facilitate the delivery of platinum(IV) prodrugs and significantly enhance the cytotoxicity of these prodrugs in tumor cells. Herein, we report that the use of this drug-delivery system avoids the drug resistance that affects the use of cisplatin. We show that impaired drug uptake that results from the low expression of Ctr1 in the cisplatin-resistant cells A549R can be overcome by using a conjugate of a cisplatin prodrug and PEGylated gold nanorods (Pt-PEG-GNRs conjugate); this conjugate facilitates the delivery of the platinum-based drug into cells through endocytosis. Additionally, the platinum(IV) prodrug is less susceptible to deactivation by the detoxification protein MT and the peptide GSH, which were found in high concentrations in A549R cells. Consequently, the Pt-PEGGNRs conjugate was highly cytotoxic to tumor cells, especially cisplatin-resistant cells. [*] Y. Min, S. Chen, G. Ma, Prof. Y. Liu CAS Key Laboratory of Soft Matter Chemistry and Department of Chemistry University of Science and Technology of China Hefei, Anhui, 230026 (China) E-mail: liuyz@ustc.edu.cn

The ligation of aspirin to cisplatin demonstrates significant synergistic effects on tumor cells

Asplatin, a fusion of aspirin and cisplatin, exhibits significant cytotoxicity in tumor cells and almost fully overcomes the drug resistance of cisplatin resistant cells. Asplatin is highly accumulated in cancer cells and is activated upon the reduction by ascorbic acid.

Identification of [PtCl2(phen)] Binding Modes in Amyloid‐β Peptide and the Mechanism of Aggregation Inhibition

Platinum phenanthroline complexes inhibit amyloid-β (Aβ) aggregation and reduce Aβ-caused neurotoxicity [Proc. Natl. Acad. Sci., 2008, 105, 6813-6818]. In this study, we investigated the interactions of Aβ(1-16) with [PtCl(2)(phen)] (phen=1,10-phenanthroline) using HPLC, ESI-MS, and NMR spectroscopy , and characterized the identity of products using tandem mass spectrometry. Results indicated that the phenanthroline ligand could induce noncovalent interactions between Aβ peptide and platinum complexes, leading to rapid Aβ platination. Multiple products were generated in the reaction, in which His6/His14 chelation was preferentially formed. Coordination of Asp7, His13, and Lys16 was also detected in other products. The majority of products were monoplatinated adducts with binding of the {Pt(phen)} scaffold, which impeded intermolecular interactions between Aβ peptides. Moreover, noncovalent interactions were confirmed by the interaction between Aβ peptide and [Pt(phen)(2)]Cl(2). The synergistic roles of the phen ligand and platinum(II) atom in the inhibition of Aβ aggregation are discussed.

pK(a) coupling at the intein active site: implications for the coordination mechanism of protein splicing with a conserved aspartate.

Protein splicing is a robust multistep posttranslational process catalyzed by inteins. In the Mtu RecA intein, a conserved block-F aspartate (D422) coordinates different steps in protein splicing, but the precise mechanism is unclear. Solution NMR shows that D422 has a strikingly high pK(a) of 6.1, two units above the normal pK(a) of aspartate. The elevated pK(a) of D422 is coupled to the depressed pK(a) of another active-site residue, the block-A cysteine (C1). A C1A mutation lowers the D422 pK(a) to normal, while a D422G mutation increases the C1 pK(a) from 7.5 to 8.5. The pK(a) coupling and NMR structure determination demonstrate that protonated D422 serves as a hydrogen bond donor to stabilize the C1 thiolate and promote the N-S acyl shift, the first step of protein splicing. Additionally, in vivo splicing assays with mutations of D422 to Glu, Cys, and Ser show that the deprotonated aspartate is essential for splicing, most likely by deprotonating and activating the downstream nucleophile in transesterification, the second step of protein splicing. We propose that the sequential protonation and deprotonation of the D422 side chain is the coordination mechanism for the first two steps of protein splicing.

Methionine Can Favor DNA Platination by trans‐Coordinated Platinum Antitumor Drugs

Cisplatin (cis-DDP) and its cis-coordinated analogues, carboplatin and oxaliplatin, have been successfully used in the treatment of testicular and other solid tumors, but applications are restricted by side effects and intrinsic and acquired resistances. The discovery of trans-coordinated platinum complexes with antitumor activity provides a novel approach for cancer chemotherapy. Among several types of transplatinum complexes, trans-[PtCl2{E-HN=C(OCH3)CH3}2] (trans-EE) raised particular interest because of its higher cytotoxicity than the cis isomer and its activity towards several cis-DDP-resistant tumor cells. Mechanistic studies indicated that trans-EE has different DNA binding modes relative to cis-DDP, although their reaction rates were similar. DNAmodified by trans-EE could not be recognized by high-mobility group (HMG), the protein that interferes with DNA repair of cis-DDP adducts, whereas histone H1 could bind to trans-EE-modified DNA and prevent DNA polymerization and repair. A recent study also indicated that methionine was the preferable binding site of trans-EE in the reaction with cytochrome c, and different binding modes were observed between cisand trans-platinum complexes. Many cellular molecules, including proteins, peptides, and also some small molecules, can play significant roles in the functioning of and resistance to drugs, such as DNA platination, drug transport, and efflux. Sulfur-containing proteins are of special interest because of their high affinity for platinum, their abundance (e.g. albumin), and their involvement in metal-ion transport (e.g. the copper transporter protein CTR1, which contains methionine-rich extracellular motifs and appears to be involved in platinum-drug transport through the cell membrane). Kinetic studies indicated that the S platination of l-methionine (Met) or Nacetyl-l-methionine (AcMet) was kinetically preferred, whereas N7 coordination of guanine was thermodynamically favored. Studies using the model compound [PtCl(dien)] showed that the migration of platinum from S-Met to N7guanine (G–N7) was fairly slow (t1/2= 21–147 h at 310 K depending on DNA sequence), which was obviously slower than the direct DNA platination by [PtCl(dien)]. Although Met could slightly increase the rate of platination of cis-DDP to guanosine monophosphate (GMP), the reaction with synthetic DNA showed that the presence of Met actually inhibited platination on both single strand (ss) and double strand (ds) DNA. Herein we show that the platination rates of both GMP and DNA are substantially enhanced by a Met ligand bound to trans-EE. Moreover the reaction is highly pH-dependent. This enhancement has been observed for all nucleotides used in this work, including monomeric GMP, synthetic ssand dsDNA, and natural DNA. It has been observed that the formation of a Met intermediate is about seven times faster than G–N7 platination (Figure S1 in the Supporting Information). Accordingly, DNA platination is significantly faster via a Met intermediate (Scheme 1). On the basis of activity studies and the formation of this type of adducts also in the cellular system, it is suggested that the mechanism of trans-EE could differ substantially from that of conventional cisplatinum compounds.

Synthesis of a ratiometric fluorescent peptide sensor for the highly selective detection of Cd2

A novel ratiometric fluorescent peptidyl chemosensor (Dansyl-Cys-Pro-Gly-Cys-Trp-NH(2), D-P5) for metal ions detection has been synthesized via Fmoc solid-phase peptide synthesis. The chemosensor exhibited a high selectivity for Cd(2+) over other metal ions including competitive transition and Group I and II metal ions in neutral pH. The fluorescence emission intensity of D-P5 was significantly enhanced in the presence of Cd(2+) by fluorescent resonance energy transfer (FRET) and chelation enhanced fluorescence (CHEF) effects. The binding stoichiometry, detection limit, binding affinity, reversibility and pH sensitivity of the sensor for Cd(2+) were investigated.

Copper binding promotes the interaction of cisplatin with human copper chaperone Atox1

Cu(I) binding promotes the platination of Atox1, although cisplatin binds to the copper coordination sites. In addition, Cu(I) binding enhances the competition of Atox1 with DTT in the reaction of cisplatin. These results indicate that cuprous ions could regulate the cellular trafficking of cisplatin.

Trans‐Platinum/Thiazole Complex Interferes with Sp1 Zinc‐Finger Protein

Abstract No trafficking: The antitumor-active trans-platinum/thiazole complex trans-PtTz demonstrated high reactivity to the transcription factor Sp1, which is overexpressed in tumor cells. The binding of trans-PtTz disrupts the DNA interaction with Sp1 in vitro and prevents the protein trafficking from the cytoplasm into the nucleus.

Cisplatin binds to human copper chaperone Cox17: the mechanistic implication of drug delivery to mitochondria

Cox17 facilitates the platinum accumulation in mitochondria, which contributes to the overall cytotoxicity of cisplatin.

Tris-(2-carboxyethyl) phosphine significantly promotes the reaction of cisplatin with Sp1 zinc finger protein

A widely used reducing agent tris-(2-carboxyethyl) phosphine significantly promotes the reaction of cisplatin with Sp1 zinc finger protein. This discovery clarifies the reactivity of cisplatin towards Sp1 zinc finger protein and implies that the reactions of platinum drugs could be largely influenced by small molecules with a strong trans effect.