Cellular accumulation and cytotoxicity of macromolecular platinum complexes in cisplatin-resistant tumor cells

Improved Targeting and Safety of Doxorubicin through a Novel Albumin Binding Prodrug Approach

Human serum albumin (HSA) improves the pharmacokinetic profile of drugs attached to it, making it an attractive carrier with proven clinical success. In our previous studies, we have shown that Caveolin-1 (Cav-1) and caveolae-mediated endocytosis play important roles in the uptake of HSA and albumin-bound drugs. Doxorubicin is an FDA-approved chemotherapeutic agent that is effective against multiple cancers, but its clinical applicability has been hampered by its high toxicity levels. In this study, a doxorubicin-prodrug was developed that could independently and avidly bind HSA in circulation, called IPBA-Dox. We first developed and characterized IPBA-Dox and confirmed that it can bind albumin in vitro while retaining a potent cytotoxic effect. We then verified that it efficiently binds to HSA in circulation, leading to an improvement in the pharmacokinetic profile of the drug. In addition, we tested our prodrug for Cav-1 selectivity and found that it preferentially affects cells that express relatively higher levels of Cav-1 in vitro and in vivo. Moreover, we found that our compound was well tolerated in vivo at concentrations at which doxorubicin was lethal. Altogether, we have developed a doxorubicin-prodrug that can successfully bind HSA, retaining a strong cytotoxic effect that preferentially targets Cav-1 positive cells while improving the general tolerability of the drug.

In vitro and in vivo accumulation of the anticancer Ru complexes [RuII(cym)(HQ)Cl] and [RuII(cym)(PCA)Cl]Cl

The cellular accumulation and the underlying mechanisms for the two ruthenium-based anticancer complexes [RuII(cym)(HQ)Cl] 1 (cym = η6-p-cymene, HQ = 8-hydroxyquinoline) and [RuII(cym)(PCA)Cl]Cl 2 (PCA = N-fluorophenyl-2-pyridinecarbothioamide) were investigated in HCT116 human colorectal carcinoma cells. The results showed that the cellular accumulation of both complexes increased over time and with higher concentrations, and that 2 accumulates in greater quantities in cells than 1. Inhibition studies of selected cellular accumulation mechanisms indicated that both 1 and 2 may be transported into the cells by both passive diffusion and active transporters, similar to cisplatin. Efflux experiments indicated that 1 and 2 are subjected to efflux through a mechanism that does not involve p-glycoprotein, as addition of verapamil did not make any difference. Exploring the influence of the Cu transporter by addition of CuCl2 resulted in a higher accumulation of 1 and 2 whilst the amount of Pt detected was slightly reduced when cells were treated with cisplatin. Complexes 1 and 2 were further explored in zebrafish where accumulation and distribution were determined with ICP-MS and LA-ICP-MS. The results correlated with the in vitro observations and zebrafish treated with 2 showed higher Ru contents than those treated with 1. The distribution studies suggested that both complexes mainly accumulated in the intestines of the zebrafish.

Circumventing Physicochemical Barriers of Cyclometalated Gold(III) Dithiocarbamate Complexes with Protein-Based Nanoparticle Delivery to Enhance Anticancer Activity

Optimizing the bioavailability of drug candidates is crucial to successful drug development campaigns, especially for metal-derived chemotherapeutic agents. Nanoparticle delivery strategies can be deployed to overcome physicochemical limitations associated with drugs to improve bioavailability, pharmacokinetics, efficacy, and minimize toxicity. Biodegradable albumin nanoconstructs offer pragmatic solutions for drug delivery of metallodrugs with translational benefits in the clinic. In this work, we explored a logical approach to investigate and resolve the physicochemical drawbacks of gold(III) complexes with albumin nanoparticle delivery to improve solubility, enhance intracellular accumulation, circumvent premature deactivation, and enhance anticancer activity. We synthesized and characterized stable gold(III) dithiocarbamate complexes with a variable degree of cyclometalation such as phenylpyridine (C^N) or biphenyl (C^C) Au(III) framework and different alkyl chain lengths. We noted that extended alkyl chain lengths impaired the solubility of these complexes in biological media, thus adversely impacting potency. Encapsulation of these complexes in bovine serum albumin (BSA) reversed solubility limitations and improved cancer cytotoxicity by ∼25-fold. Further speciation and mechanism of action studies demonstrate the stability of the compounds and alteration of mitochondria bioenergetics, respectively. We postulate that this nanodelivery strategy is a relevant approach for translational small-molecule gold drug delivery.

Critical evaluation of cell lysis methods for metallodrug studies in cancer cells

Intracellular accumulation studies are a key step in metallodrug development but often variable results are obtained. Therefore, we aimed here to investigate different protocols for efficient and reproducible lysis of cancer cells in terms of protein content in lysates and in cell uptake studies of the Ru anticancer complex [chlorido(8-oxyquinolinato)(η6-p-cymene)ruthenium(II)] ([Ru(cym)(HQ)Cl]). The physical lysis methods osmosis and sonication were chosen for comparison with chemical lysis with the radioimmunoprecipitation assay (RIPA) buffer. Based on the protein content and the total Ru accumulated in the lysates, the latter determined using inductively coupled plasma-mass spectrometry, RIPA buffer was the most efficient lysis method. Measurements of plastic adsorption blanks revealed that the higher Ru content determined in the RIPA buffer lysis samples may be due a higher amount of Ru extracted from the plastic incubation plates compared with osmosis and sonication. Overall, we found that the choice of lysis method needs to be matched to the information sought and we suggest the least disruptive osmosis method might be the best choice for labile drug-biomolecule adducts. Minimal differences were found for experiments aimed at measuring the overall cell uptake of the Ru complex.

Single-cell and bulk ICP-MS investigation of accumulation patterns of Pt-based metallodrugs in cisplatin-sensitive and -resistant cell models

In research enabling preclinical development and attaining a deeper understanding of the behavior of metallodrugs in cancer cells with acquired resistance, intracellular Pt accumulation could be considered an important biomarker and analytical focus. In this work, Pt accumulation patterns in terms of the number of cells and Pt mass in single cells were precisely defined by using inductively coupled plasma-mass spectrometry (ICP-MS) operating in a fast time-resolved analysis mode. This technique is otherwise known as single-cell (SC)-ICP-MS. By applying the nascent and validated SC-ICP-MS technique, comparisons across three Pt drugs (cisplatin, carboplatin, and oxaliplatin) in the A2780 and A2780cis ovarian cancer cell models could be made. Additional roles of transporters on top of passive diffusion and the drugs' bioactivity could be postulated. The SC-ICP-MS-based observations also served as a cross-validation point to augment preexisting research findings on Pt-resistance mechanisms. Conjectures regarding S and Fe metabolism were also derived based on an additional and direct ICP-MS analysis of endogenous elements. Overall, our work not only confirms the utility of SC-ICP-MS in chemotherapeutic research, but also provided insights into further ICP-MS-based analytical capacities to be developed.

The copper transporter CTR1 and cisplatin accumulation at the single-cell level by LA-ICP-TOFMS

More than a decade ago, studies on cellular cisplatin accumulation via active membrane transport established the role of the high affinity copper uptake protein 1 (CTR1) as a main uptake route besides passive diffusion. In this work, CTR1 expression, cisplatin accumulation and intracellular copper concentration was assessed for single cells revisiting the case of CTR1 in the context of acquired cisplatin resistance. The single-cell workflow designed for in vitro experiments enabled quantitative imaging at resolutions down to 1 µm by laser ablation-inductively coupled plasma-time-of-flight mass spectrometry (LA-ICP-TOFMS). Cisplatin-sensitive ovarian carcinoma cells A2780 as compared to the cisplatin-resistant subline A2780cis were investigated. Intracellular cisplatin and copper levels were absolutely quantified for thousands of individual cells, while for CTR1, relative differences of total CTR1 versus plasma membrane-bound CTR1 were determined. A markedly decreased intracellular cisplatin concentration accompanied by reduced copper concentrations was observed for single A2780cis cells, along with a distinctly reduced (total) CTR1 level as compared to the parental cell model. Interestingly, a significantly different proportion of plasma membrane-bound versus total CTR1 in untreated A2780 as compared to A2780cis cells was observed. This proportion changed in both models upon cisplatin exposure. Statistical analysis revealed a significant correlation between total and plasma membrane-bound CTR1 expression and cisplatin accumulation at the single-cell level in both A2780 and A2780cis cells. Thus, our study recapitulates the crosstalk of copper homeostasis and cisplatin uptake, and also indicates a complex interplay between subcellular CTR1 localization and cellular cisplatin accumulation as a driver for acquired resistance development.

Laser-responsive multi-functional nanoparticles for efficient combinational chemo-photodynamic therapy against breast cancer

Herein, novel laser-responsive multi-functional nanoparticles (NPs-Lip@PTX/CyA/Ce6) were fabricated with bovine serum albumins (BSA) based nanoparticles, which simultaneously carried chemotherapeutic drug paclitaxel (PTX) and P-gp inhibitor cyclosporin A (CyA), as core and photosensitizer agent Chlorin e6 (Ce6) loaded Tf-modified liposomal bilayer as shell. NPs-Lip@PTX/CyA/Ce6 exhibited apparent core-shell structure morphology with particle size of 160.9 ± 1.7 nm and zeta potential of - 26.7 ± 0.6 mV, indicating their excellent stability in aqueous solution. Besides, NPs-Lip@PTX/CyA/Ce6 possessed laser-responsive release profiles upon laser irradiation at specific wavelength, which was favor to exert efficient combinatorial chemo-photodynamic therapy and effectively reverse the multiple drug resistance (MDR). Under laser irradiation, as expected, NPs-Lip@PTX/CyA/Ce6 demonstrated superb intracellular ROS productivity and fantastic in vitro and in vivo anti-cancer therapy effect but absent of systemic toxicity. In conclusion, the nano-drug delivery system would be prospectively applied in clinic as resultful therapeutic tactic for investing compositional chemo-photodynamic therapy synergistically.

A novel protein-drug conjugate, SSH20, demonstrates significant efficacy in caveolin-1-expressing tumors

In recent years, human serum albumin (HSA) has been characterized as an ideal drug carrier in the cancer arena. Caveolin-1 (Cav-1) has been established as the principal structural protein of caveolae and, thus, critical for caveolae-mediated endocytosis. Cav-1 has been shown to be overexpressed in cancers of the lung and pancreas, among others. We found that Cav-1 expression plays a critical role in both HSA uptake and response to albumin-based chemotherapies. As such, developing a novel albumin-based chemotherapy that is more selective for tumors with high Cav-1 expression or high levels of caveolar-endocytosis could have significant implications in biomarker-directed therapy. Herein, we present the development of a novel and effective HSA-SN-38 conjugate (SSH20). We find that SSH20 uptake decreases significantly by immunofluorescence assays and western blotting after silencing of Cav-1 expression through RNA interference. Decreased drug sensitivity occurs in Cav-1-depleted cells using cytotoxicity assays. Importantly, we find significantly reduced sensitivity to SSH20 in Cav-1-silenced tumors compared to Cav-1-expressing tumors in vivo. Notably, we show that SSH20 is significantly more potent than irinotecan in vitro and in vivo. Together, we have developed a novel HSA-conjugated chemotherapy that is potent, effective, safe, and demonstrates improved efficacy in high Cav-1-expressing tumors.

Metal- and metalloid-based compounds to target and reverse cancer multidrug resistance

Drug resistance remains the major cause of cancer treatment failure especially at the late stage of the disease. However, based on their versatile chemistry, metal and metalloid compounds offer the possibility to design fine-tuned drugs to circumvent and even specifically target drug-resistant cancer cells. Based on the paramount importance of platinum drugs in the clinics, two main areas of drug resistance reversal strategies exist: overcoming resistance to platinum drugs as well as multidrug resistance based on ABC efflux pumps. The current review provides an overview of both aspects of drug design and discusses the open questions in the field. The areas of drug resistance covered in this article involve: 1) Altered expression of proteins involved in metal uptake, efflux or intracellular distribution, 2) Enhanced drug efflux via ABC transporters, 3) Altered metabolism in drug-resistant cancer cells, 4) Altered thiol or redox homeostasis, 5) Altered DNA damage recognition and enhanced DNA damage repair, 6) Impaired induction of apoptosis and 7) Altered interaction with the immune system. This review represents the first collection of metal (including platinum, ruthenium, iridium, gold, and copper) and metalloid drugs (e.g. arsenic and selenium) which demonstrated drug resistance reversal activity. A special focus is on compounds characterized by collateral sensitivity of ABC transporter-overexpressing cancer cells. Through this approach, we wish to draw the attention to open research questions in the field. Future investigations are warranted to obtain more insights into the mechanisms of action of the most potent compounds which target specific modalities of drug resistance.

Intracellular delivery of oxaliplatin conjugate via cell penetrating peptide for the treatment of colorectal carcinoma in vitro and in vivo

Pt-based drugs are one of the main active agents in colorectal cancer treatment. However, drug resistance and dose-dependent side effects are the main barriers that restrict their clinical applications. As an alternative approach to these issues, we designed and synthesized a cell penetrating peptide (CPP) octaarginine-oxaliplatin conjugate that quickly and successfully delivered oxaliplatin into colon cancer cells. The CPP octaarginine is a well-studied cationic peptide that can play a role as a drug delivery vector. In this work, an octaarginine CPP (RRRRRRRR) was conjugated with oxaliplatin via a specific heterobifunctional linker. The in vitro studies showed the conjugate had affinity toward mitochondria inside cells and the MTT assay confirmed that conjugate is active in low micromolar range against colon cancer cells, requiring much lower concentrations than the oxaliplatin alone to reach IC₅₀. More importantly, in the in vivo mouse study, the conjugate effectively inhibited tumor growth and showed considerably high antitumor activity, demonstrating the conjugate can perform well in vivo. This strategy may offer a new approach for designing oxaliplatin derivatives or prodrugs with remarkable therapeutic capabilities.

Amphiphilic block polymer-based self-assembly of high payload nanoparticles for efficient combinatorial chemo-photodynamic therapy

Combinatorial chemo-photodynamic therapy is regared as effective cancer therapy strategy, which could be realized via multiple nano-drug delivery system. Herein, novel high payload nanoparticles stabilized by amphiphilic block polymer cholesterol-b-poly(ethylene glycol) (PEG)₂₀₀₀ (Chol-PEG₂₀₀₀) were fabricated for loading chemotherapeutic drug 10-hydroxycamptothecin (HCPT) and photosensitizer chlorin e6 (Ce6). The obtained HCPT/Ce6 NPs showed uniform rod-like morphology with a hydration diameter of 178.9 ± 4.0 nm and excellent stability in aqueous solution. HCPT and Ce6 in the NPs displayed differential release profile, which was benefit for preferentially exerting the photodynamic effect and subsequently enhancing the sensitivity of the cells to HCPT. Under laser irradiation, the NPs demonstrated fantastic in vitro and in vivo anticancer efficiency due to combinational chemo-photodynamic therapy, enhanced cellular uptake effectiveness, and superb intracellular ROS productivity. Besides, the NPs were proved as absent of systemic toxicity. In summary, this nanoparticle delivery system could be hopefully utilized as effective cancer therapy strategy for synergistically exerting combined chemo-photodynamic therapy in clinic.

Efficacy and Safety of Human Serum Albumin-Cisplatin Complex in U87MG Xenograft Mouse Models

Cisplatin (cis-diamminedichloroplatinum (II), CDDP) is a chemotherapeutic drug widely used against many solid tumors. A pharmacokinetics study found that CDDP can bind to human serum albumin (HSA), which is the most abundant plasma protein in serum. HSA has the advantage of being a nanocarrier and can accumulate in tumors by passive targeting and active targeting mediated by the secreted protein acidic and rich in cysteine (SPARC). In this study, we investigated the possibility of using a CDDP-HSA complex (HSA-CDDP) as a SPARC-mediated therapeutic agent. To investigate the HSA-dependent therapeutic effect of HSA-CDDP, we used two types of U87MG glioma cells that express SPARC differently. HSA-CDDP was highly taken up in SPARC expressing cells and this uptake was enhanced with exogenous SPARC treatment in cells with low expression of SPARC. The cytotoxicity of HSA-CDDP was also higher in SPARC-expressing cells. In the tumor model, HSA-CDDP showed a similar tumor growth and survival rate to CDDP only in SPARC-expressing tumor models. The biosafety test indicated that HSA-CDDP was less nephrotoxic than CDDP, based on blood markers and histopathology examination. Our findings show that HSA-CDDP has the potential to be a novel therapeutic agent for SPARC-expressing tumors, enhancing the tumor targeting effect by HSA and reducing the nephrotoxicity of CDDP.

Novel carrier-free nanoparticles composed of 7-ethyl-10-hydroxycamptothecin and chlorin e6: Self-assembly mechanism investigation and in vitro/in vivo evaluation

The combination therapy strategy based on both chemotherapy and photodynamic therapy (PDT) exhibits great potential for advanced cancer treatment. Multimodal nanodrug delivery systems based on both chemotherapeutic drug and photodynamic agent have been proven to possess excellent synergistic efficacy. In this study, 7-ethyl-10-hydroxycamptothecin (SN38) and chlorin e6 (Ce6) were co-assembled into novel carrier-free nanoparticles (SN38/Ce6 NPs) via simple antisolvent precipitation method. As expected, SN38/Ce6 NPs exhibited uniform morphology with a particle size of around 150 nm and a zeta potential of about -30 mV, good stability in aqueous solution/at lyophilized state and high cellular uptake efficiency against murine mammary carcinoma (4T1) cell lines. Besides, enhanced singlet oxygen generation capacity of the nanoparticles was both observed in test-tube and in 4T1 cell lines in contrast with Ce6 injection. Moreover, a ∼85 % inhibition rate of SN38/Ce6 NPs with laser was detected, which was significantly higher (P < 0.05) than those without laser (∼65 %) and injections (less than 20 %), verified the excellent synergistic antitumor efficacy of the nanoparticles due to combined chemo-photodynamic therapy, enhanced tumor accumulation and higher cellular internalization. Notably, chemical thermodynamic method and molecular dynamics (MD) simulations supplied solid data and visual images to estimate the driving forces for the self-assembly process of the carrier-free nanoparticles as primary hydrophobic interactions (π-π stacking) and subordinate hydrogen bonds. Conclusively, the above self-assembled carrier-free nanoparticles represented a promising synergistic anticancer strategy capable of maximal therapeutic efficacy and minimal systemic toxicity. Moreover, the application of thermodynamic method together with MD simulations in the investigation of NPs self-assembly process also provided new ideas for the assembly mechanism exploration of more complicated nanodrug delivery system.

Critical assessment of different methods for quantitative measurement of metallodrug-protein associations

Quantitative screening for potential drug-protein binding is an essential step in developing novel metal-based anticancer drugs. ICP-MS approaches are at the core of this task; however, many applications lack in the capability of large-scale high-throughput screenings and proper validation. In this work, we critically discuss the analytical figures of merit and the potential method-based quantitative differences applying four different ICP-MS strategies to ex vivo drug-serum incubations. Two candidate drugs, more specifically, two Pt(IV) complexes with known differences of binding affinity towards serum proteins were selected. The study integrated centrifugal ultrafiltration followed by flow injection analysis, turbulent flow chromatography (TFC), and size exclusion chromatography (SEC), all combined with inductively coupled plasma-mass spectrometry (ICP-MS). As a novelty, for the first time, UHPLC SEC-ICP-MS was implemented to enable rapid protein separation to be performed within a few minutes at > 90% column recovery for protein adducts and small molecules. Graphical abstract Quantitative screening for potential drug-protein binding is an essential step in developingnovel metal-based anticancer drugs.

HSA-based multi-target combination therapy: regulating drugs' release from HSA and overcoming single drug resistance in a breast cancer model

Multi-drug delivery systems, which may be promising solution to overcome obstacles, have limited the clinical success of multi-drug combination therapies to treat cancer. To this end, we used three different anticancer agents, Cu(BpT)Br, NAMI-A, and doxorubicin (DOX), to build human serum albumin (HSA)-based multi-drug delivery systems in a breast cancer model to investigate the therapeutic efficacy of overcoming single drug (DOX) resistance to cancer cells in vivo, and to regulate the drugs' release from HSA. The HSA complex structure revealed that NAMI-A and Cu(BpT)Br bind to the IB and IIA sub-domain of HSA by N-donor residue replacing a leaving group and coordinating to their metal centers, respectively. The MALDI-TOF mass spectra demonstrated that one DOX molecule is conjugated with lysine of HSA by a pH-sensitive linker. Furthermore, the release behavior of three agents form HSA can be regulated at different pH levels. Importantly, in vivo results revealed that the HSA-NAMI-A-Cu(BpT)Br-DOX complex not only increases the targeting ability compared with a combination of the three agents (the NAMI-A/Cu(BpT)Br/DOX mixture), but it also overcomes DOX resistance to drug-resistant breast cancer cell lines.

Facilitating the Cellular Accumulation of Pt-Based Chemotherapeutic Drugs

Cisplatin, carboplatin, and oxaliplatin are Pt-based drugs used in the chemotherapeutic eradication of cancer cells. Although most cancer patient cells initially respond well to the treatment, the clinical effectiveness declines over time as the cancer cells develop resistance to the drugs. The Pt-based drugs are accumulated via membrane-bound transporters, translocated to the nucleus, where they trigger various intracellular cell death programs through DNA interaction. Here we illustrate how resistance to Pt-based drugs, acquired through limitation in the activity/subcellular localization of canonical drug transporters, might be circumvented by the facilitated uptake of Pt-based drug complexes via nanocarriers/endocytosis or lipophilic drugs by diffusion.

Suppression of chloride voltage-gated channel 3 expression increases sensitivity of human glioma U251 cells to cisplatin through lysosomal dysfunction

The mechanism of cisplatin resistance is complex. Previous studies have indicated that chloride voltage-gated channel 3 (CLCN3) is associated with drug resistance; however, the mechanisms are not fully understood. Therefore, the present study explored the involvement of CLCN3 in cisplatin resistance in human glioma U251 cells. The effects of combined cisplatin treatment and CLCN3 suppression on cultured U251 cells were investigated. The decreased viability of cisplatin-treated U251 cells indicated the cytotoxic effects of CLCN3 silencing. Expression of the apoptosis-related gene TP53 and caspase 3 activation were enhanced in cisplatin-treated U251 cells. Furthermore, the ratio of BCL2/BAX expression was decreased. Notably, CLCN3 suppression promoted cisplatin-induced cell damage in U251 cells. Thus, the combined use of cisplatin and CLCN3 antisense had additive effects in U251 cells. In addition, the present results indicated that CLCN3 suppression decreased lysosome stabilization in U251 cells treated with cisplatin. To conclude, the present results indicated that CLCN3 suppression can sensitize glioma cells to cisplatin through lysosomal dysfunction.

Are cucurbiturils better drug carriers for bent metallocenes? Insights from theory

Bent metallocenes (BM) have anti-tumor properties but they face a serious drug efficacy problem due to poor aqueous solubility and rapid hydrolysis under physiological conditions. These two problems can be fixed by encapsulating them in host molecules such as cyclodextrin (CD), cucurbituril (CB) etc. Experimentally, CD-BM, CB-BM host-guest complexes have been investigated to check the efficiency of the drug delivery and efficiency of the encapsulated drug. CB has been reported to be a better host than CD but the reasons for this has not been figured out. This can be done by finding out the mechanism of binding and the nature of the binding forces in both the inclusion complexes. This is exactly done here by performing a DFT study at BP86/TZP level on CB-BM host-guest systems. For comparison CD-BM with β-cyclodextrin as host have been studied. Four BMs (Cp₂MCl₂, M=Ti, V, Nb, Mo) and their corresponding cations (Cp₂MCl⁺, Cp₂M²⁺) are chosen as guests and they are encapsulated into cucurbit-[6]-uril (CB[6]) and cucurbit-[7]-uril(CB[7]) host systems. Computations reveal that CB[7] accommodates well the BMs over CB[6] due to their larger cavity size and also CB[7] is found to be a better host than β-cyclodextrin. BMs enter vertically rather than horizontally into the CB cavity. The reversible binding of BMs within CB[7] is controlled by various non-bonding interactions and mainly by hydrogen bonding between the portal oxygen atoms and Cp protons as revealed by QTAIM analysis. On the other hand, the interaction between the wall nitrogen atoms in CB[7] and chlorine atoms attached to the metal in BM strengthens the M-Cl bonds that prevents rapid hydrolysis of M-Cl and M-Cp bonds saving the drug. Comparatively, BMs experience less electrostatic attraction and more Pauli repulsion within β-cyclodextrin cavity and this affects the drug binding with CD. This makes β-cyclodextrin a less suitable drug carrier for BMs than CBs. Among the four BMs, niobocene binds strongly and titanocene binds weakly with CBs. EDA clearly shows that all the interactions between the guest and host are non-covalent in nature and electrostatic interactions outperform high-repulsion resulting in stable complexes. Cations form stronger complexes than neutral BMs. FMO analysis reveals that neutral BMs are less reactive compared to their cations and complexes are more reactive in CB[6] environment due to excess strain. QTAIM analysis helps to bring out the newer insights in these types of host-guest systems.

Developing an anticancer copper(II) pro-drug based on the nature of cancer cell and human serum albumin carrier IIA subdomain: mouse model of breast cancer

Human serum albumin (HSA)-based drug delivery systems are promising for improving delivery efficiency, anticancer activity and selectivity of anticancer agents. To rationally guide to design HSA carrier for anticancer metal agent, we built a breast mouse model on developing anti-cancer copper (Cu) pro-drug based on the nature of IIA subdomain of HSA carrier and cancer cells. Thus, we first synthesized a new Cu(II) compound derived from tridentate (E)-N'-(5-bromo-2-hydroxybenzylidene)benzohydrazide Schiff base ligand (HL) containing 2 potential leaving groups [indazole (Ind) and NO3-], namely, [Cu(L)(Ind)NO3]. Structural analysis of the HSA complex showed that Cu(L)(Ind)(NO3) could bind to the hydrophobic pocket of the HSA IIA subdomain. Lys199 and His242 coordinate with Cu2+ by replacing the indazole and NO3 ligands of [Cu(L)(Ind)NO3]. The release behavior of the Cu compound from the HSA complex is different at different pH levels. [Cu(L)(Ind)NO3] can enhance cytotoxicity by 2 times together with HSA specifically in cancer cells but has no such effect on normal cells in vitro. Importantly, our in vivo results showed that the HSA complex displayed increased selectivity and capacity to inhibit tumor growth and was less toxic than [Cu(L)(Ind)NO3] alone.

Intracellular glutathione-depleting polymeric micelles for cisplatin prodrug delivery to overcome cisplatin resistance of cancers

The intrinsic or acquired cisplatin resistance of cancer cells frequently limits the final therapeutic efficacy. Detoxification by the high level of intracellular glutathione (GSH) plays critical roles in the majority of cisplatin-resistant cancers. In this report, we designed an amphiphilic diblock copolymer composed of poly(ethylene glycol) (PEG) and polymerized phenylboronic ester-functionalized methacrylate (PBEMA), PEG-b-PBEMA, which can self-assemble into micelles in aqueous solutions to load hydrophobic cisplatin prodrug (Pt(IV)). Pt(IV)-loaded PEG-b-PBEMA micelles (PtBE-Micelle) reverse cisplatin-resistance of cancer cells through improving cellular uptake efficiency and reducing intracellular GSH level. We found that the cellular uptake amount of platinum from PtBE-Micelle was 6.1 times higher than that of free cisplatin in cisplatin-resistant human lung cancer cells (A549R). Meanwhile, GSH concentration of A549R cells was decreased to 32% upon treatment by PEG-b-PBEMA micelle at the phenyl borate-equivalent concentration of 100μM. PtBE-Micelle displayed significantly higher cytotoxicity toward A549R cells with half maximal inhibitory concentration (IC₅₀) of cisplatin-equivalent 0.20μM compared with free cisplatin of 33.15μM and Pt(IV)-loaded PEG-b-poly(ε-caprolactone) micelles of cisplatin-equivalent 0.75μM. PtBE-Micelle can inhibit the growth of A549R xenograft tumors effectively. Accordingly, PEG-b-PBEMA micelles show great potentials as drug delivery nanocarriers for platinum-based chemotherapy toward cisplatin-resistant cancers.

Penetration and drug delivery of albumin nanoparticles into pancreatic multicellular tumor spheroids

Albumin-based nanoparticles have been exploited as a useful carrier for the efficient delivery of anti-cancer drugs. In this study, albendazole was encapsulated into bovine serum albumin (BSA)-polycaprolactone (PCL) conjugates and the formed nanoparticles with a size about 100 nm were used to treat pancreatic carcinoma cells. In addition, two more types of albendazole-loaded BSA nanoparticles, 10 nm and 200 nm ones, were prepared using a desolvation method. The albendazole-loaded BSA nanoparticles were evaluated with both 2D cultured AsPC-1 cells and 3D multicellular tumor spheroids (MCTS). Their anti-tumor effects were also compared. BSA-PCL nanoparticles and 200 nm BSA nanoparticles showed noticeable cytotoxicity to 2D cultured AsPC-1 cells when compared to the free drug. The penetration of BSA-PCL nanoparticles and 200 nm BSA nanoparticles, especially the BSA-PCL nanoparticles, enabled effective delivery of albendazole into pancreatic MCTS. BSA-PCL nanoparticles also showed a better inhibition effect on the growth of pancreatic MCTS than the 200 nm counterpart. Although 10 nm BSA nanoparticles inhibited the growth of MCTS, the inhibitory effect was even less than that of free albendazole. In addition, it is also found that SPARC protein facilitates the penetration and drug delivery of albumin nanoparticle since treatment using anti-SPARC antibody decreased the efficacy of drug loaded BSA nanoparticles.

Comparison of different sample preparation methods for platinum determination in cultured cells by graphite furnace atomic absorption spectrometry

BACKGROUND

Platinum-based agents are widely used in chemotherapy against solid tumors and insufficient intracellular drug accumulation is one of the leading causes of platinum resistance which is associated with poor survival of tumor patients. Thus, the detection of intracellular platinum is pivotal for studies aiming to overcome platinum resistance. In the present study, we aimed to establish a reliable graphite furnace atomic absorption spectrometry (GFAAS)-based assay to quantify the intracellular platinum content for cultured cells.

METHODS

Several most commonly applied cell preparation methods, including 0.2% HNO3, 0.2% Triton X-100, concentrated nitric acid, RIPA combined with concentrated nitric acid and hydroxide, followed by GFAAS for platinum detection were compared in ovarian, cervical and liver cancer cell lines to obtain the optimal one, and parameters regarding linearity, accuracy, precision and sensitivity were evaluated. Influence of other metals on platinum detection and the storage conditions of samples were also determined.

RESULTS

The treatment of cells with 0.2% HNO3 was superior to other approaches with fewer platinum loss and better repeatability. The recovery rate and precision of this method were 97.3%-103.0% and 1.4%-3.8%, respectively. The average recoveries in the presence of other metals were 95.1%-103.1%. The detection limit was 13.23 ug/L. The recovery rate of platinum remained acceptable even in cell samples stored in -20 °C or -80 °C for two months.

DISCUSSION

After comparison, we found that 0.2% HNO3 was optimal for intracellular platinum quantification based on GFAAS, which presented values compatible with that of inductively-coupled plasma mass-spectrometry (ICP-MS), and this is partially attributed to the simplicity of this method. Moreover, the assay was proved to be accurate, sensitive, cost-effective and suitable for the research of platinum-based antitumor therapy.

An albumin-based tumor-targeted oxaliplatin prodrug with distinctly improved anticancer activity in vivo

An oxaliplatin-based platinum(iv) drug which specifically binds to albumin after i.v. application led to several complete responses in tumor-bearing mice.

The design of targeted platinum(iv) prodrugs is a very promising approach to enhance the low selectivity of platinum(ii) drugs towards cancerous tissue in order to reduce the impact on healthy tissue and, consequently, the often severe side-effects. Herein, we report a set of mono-functionalized cis- and oxaliplatin-based platinum(iv) complexes bearing a maleimide moiety, which allows selective binding to serum albumin in the bloodstream. This leads not only to a prolonged plasma half-life by avoidance of fast renal clearance, but also to preferential accumulation of the drug in the tumor tissue due to the EPR-effect. Additionally, analogous succinimide-functionalized derivatives were prepared to verify the influence of the maleimide moiety. First experiments showed that all the maleimide compounds are stable and also possess good albumin-binding properties in whole serum. Further analytical studies on in vivo samples proved the highly increased plasma half-life, as well as tumor accumulation of the maleimide-functionalized substances. In vivo antitumor experiments with CT-26-bearing mice showed that, in contrast to the cisplatin derivatives, the oxaliplatin-based complexes had exceptionally better activity than the free drug resulting in the cure of the majority of treated mice. Subsequent analysis suggested that a distinctly faster reduction as well as reduced tumor accumulation of the cisplatin derivative might explain the worse performance compared to the oxaliplatin(iv) complexes. Taken together, a novel lead platinum(iv) complex with outstanding antitumor activity is presented, which will now be further developed towards clinical phase I trials.

Anticancer activity of Ru- and Os(arene) compounds of a maleimide-functionalized bioactive pyridinecarbothioamide ligand

With the aim of increasing the accumulation of Ru anticancer agents in the tumor, a targeted delivery strategy based on a maleimide anchor for the biological vector human serum albumin (HSA) was developed. A group of piano stool Ru- and Os(η⁶-arene) complexes carrying a maleimide-functionalized N-phenyl-2-pyridinecarbothioamide (PCA) ligand was designed allowing for covalent conjugation to biological thiols. The complexes were characterized by NMR spectroscopy, ESI-MS, elemental analysis and single-crystal X-ray diffraction analysis. The compounds were shown to undergo halido/aqua ligand exchange reactions in aqueous solution, depending mainly on the metal center and the nature of the halide. In vitro cytotoxicity studies revealed low potency which is explained by the observed high reactivity of the maleimide to the thiol of l-cysteine (Cys), while the metal center itself shows little affinity to amino acids of the model protein lysozyme.

Developing an Anticancer Copper(II) Pro-Drug Based on the His242 Residue of the Human Serum Albumin Carrier IIA Subdomain

To increase delivery efficiency, anticancer activity, and selectivity of anticancer metal agents in vivo, we proposed to develop the anticancer metal pro-drug based on His242 residue of the human serum albumin (HSA) carrier IIA subdomain. To confirm our hypothesis, we prepared two Cu(II) compounds [Cu(P4 mT)Cl and Cu(Bp44 mT)Cl] by modifying Cu(II) compound ligand structure. Studies with two HSA complex structures revealed that Cu(P4 mT)Cl bound to the HSA subdomain IIA via hydrophobic interactions, but Cu(Bp44 mT)Cl bound to the HSA subdomain IIA via His242 replacement of a Cl atom of Cu(Bp44 mT)Cl, and a coordination to Cu(2+). Furthermore, Cu(II) compounds released from HSA could be regulated at different pHs. In vivo data revealed that the HSA-Cu(Bp44 mT) complex increased copper's selectivity and capacity of inhibiting tumor growth compared to Cu(Bp44 mT)Cl alone.

An experimental and theoretical approach on the kinetics and mechanism for the formation of a four-membered (S, S) chelated Pt(ii) complex

A biomolecular substitution reaction on a Pt(ii) complex by a dithiocarbamate derivative has been studied experimentally and theoretically, and the resultant product complex is a four-membered (S, S) chelate possessing cytotoxic properties.

Albumin–polymer conjugate nanoparticles and their interactions with prostate cancer cells in 2D and 3D culture: comparison between PMMA and PCL

Using proteins as the hydrophilic moiety can dramatically improve the biodegradability and biocompatibility of self-assembled amphiphilic nanoparticles in the field of nanomedicine.

VP, Dasgupta S, Bose K JC, Mukherjee S, Linert W, Moi SC. Benzimidazole based Pt(ii) complexes with better normal cell viability than cisplatin: synthesis, substitution behavior, cytotoxicity, DNA binding and DFT study

Water soluble Pt(ii) complexes with higher viability towards normal cells and comparable cytotoxicity to cancer cells as compared to cisplatin.

VP, Mitra I, Saha R, K. JCB, Reddy Dodda S, Linert W, Moi SC. In vitro model reaction of sulfur containing bio-relevant ligands with Pt(ii) complex: kinetics, mechanism, bioactivity and computational studies

In vitrodrug reservoir model reactions of thiols with novel Pt(ii) complex were investigated in aqueous medium and the complex and its substituted products show remarkable anticancer property.

Ligand substitution reaction on a platinum(ii) complex with bio-relevant thiols: kinetics, mechanism and bioactivity in aqueous medium

Kinetics of the interaction between [Pt(pic)(H₂O)₂](ClO₄)₂and selected thiols has been studied in aqueous medium as a function of [complex], [thiol], pH and temperature at constant ionic strength.

Contrasting cellular uptake pathways for chlorido and iodido iminopyridine ruthenium arene anticancer complexes

The pathways involved in cellular uptake and accumulation of iminopyridine complexes of general formula [Ru(η(6)-p-cymene)(N,N-dimethyl-N'-[(E)-pyridine-2-ylmethylidene]benzene-1,4-diamine)X]PF(6) bearing two different halido ligands X = Cl or I, have been explored. The ratio of passive/active cellular accumulation of Ru in A2780 human ovarian cancer cells is compared and contrasted with cisplatin. Also, saturation of cellular uptake, time-dependence of cellular influx/efflux equilibria, together with endocytotic pathways such as caveolae and facilitated diffusion are investigated and discussed. Temperature dependence studies of Ru accumulation in the A2780 cells show that in contrast to cisplatin (CDDP) and chlorido complex , which are taken up largely through active transport, the iodido complex enters cells via passive transport. The cellular efflux of Ru is slow (ca. 25% retained after 72 h) and is partially inhibited by verapamil, implicating the P-gp protein in the efflux mechanism. Ouabain inhibition experiments suggest that the cellular uptake of these ruthenium complexes relies at least in part on facilitated diffusion, and in particular is dependent on the membrane potential. In addition the finding that depletion of cellular ATP with antimycin A had little effect on cellular Ru accumulation from iodido complex is consistent with passive diffusion. In contrast, ATP depletion caused a major increase in cellular accumulation of ruthenium from chlorido complex .

Genetic polymorphism of copper transporter protein 1 is related to platinum resistance in Chinese non-small cell lung carcinoma patients

1. Chemotherapeutic resistance to platinum-based anticancer drugs is a major obstacle in the successful treatment of lung cancer. Cellular uptake and platinum accumulation are considered the most important factors contributing to platinum resistance. The copper transporter family is the major plasma membrane transporter for platinum uptake. Copper transporter protein 1 (CTR1) plays an essential role in cisplatin influx and is closely related to platinum resistance by influencing platinum uptake and accumulation. The aim of the present study was to determine whether CTR1 polymorphisms are associated with platinum resistance in non-small cell lung carcinoma (NSCLC) patients. 2. A total of 282 incident Chinese Han NSCLC patients were enrolled in the study and followed up at three different institutions. All patients underwent at least two cycles of platinum-based chemotherapy. Twenty single-nucleotide polymorphisms of CTR1 were detected from genomic DNA samples. 3. Genetic polymorphisms of CTR1 at rs7851395 and rs12686377 were associated with platinum resistance in NSCLC patients. Patients with a GT haplotype presented with increased susceptibility to platinum resistance (P < 0.05), whereas an AG haplotype contributed to longer survival (P < 0.05). 4. In conclusion, a significant relationship was found between rs7851395 and rs12686377 polymorphisms and platinum resistance, as well as clinical outcomes, in Chinese NSCLC patients. Thus, CTR1 plays an essential role in platinum resistance and could be considered a predictive marker for the pretreatment evaluation of NSCLC patients.

Theoretical prediction of the complexation behaviors of antitumor platinum drugs with cucurbiturils

The inclusion complex formation ability between CB[n] (n = 6-9) and Pt-drugs (oxaliplatin, nedaplatin, carboplatin, and cisplatin) in gas phase as well as water phases has been investigated using the using density functional theory. The results reveal the existence of several stable inclusion complexes in aqueous solution with high solvation energies compared to the guest and host molecule. It has been shown that the formation of complexes between CB[6] and Pt-drugs resulted in structural change in the CB[6], with the calculated deformation energies being higher for the inclusion complexes. The inclusion complexes are stabilized by the hydrogen bonding and the charge transfer between the Pt-drugs and the CB[n] host. Calculated enthalpy and Gibbs free energy of formation in aqueous solution revels that the formation of CB[7]-oxaliplatin is spontaneous, and hence its experimental synthesis is feasible. Among the CB's studied, CB[8]-Pt-drug inclusion complexes have exothermic enthalpy and low Gibbs free energy of formation. Computed (1)NMR spectra in CB[7]-oxaliplatin showed high chemical shielding for the cyclohexane ring, indicating the existence of charge transfer in the inclusion complex. The amine protons in the guest Pt-drugs are shielded due to the hydrogen bonding interaction with CB's oxygen portal.