Integrative Metallomics Studies of Toxic Metal(loid) Substances at the Blood Plasma–Red Blood Cell–Organ/Tumor Nexus

Globally, an estimated 9 million deaths per year are caused by human exposure to environmental pollutants, including toxic metal(loid) species. Since pollution is underestimated in calculations of the global burden of disease, the actual number of pollution-related deaths per year is likely to be substantially greater. Conversely, anticancer metallodrugs are deliberately administered to cancer patients, but their often dose-limiting severe adverse side-effects necessitate the urgent development of more effective metallodrugs that offer fewer off-target effects. What these seemingly unrelated events have in common is our limited understanding of what happens when each of these toxic metal(loid) substances enter the human bloodstream. However, the bioinorganic chemistry that unfolds at the plasma/red blood cell interface is directly implicated in mediating organ/tumor damage and, therefore, is of immediate toxicological and pharmacological relevance. This perspective will provide a brief synopsis of the bioinorganic chemistry of AsIII, Cd2+, Hg2+, CH3Hg+ and the anticancer metallodrug cisplatin in the bloodstream. Probing these processes at near-physiological conditions and integrating the results with biochemical events within organs and/or tumors has the potential to causally link chronic human exposure to toxic metal(loid) species with disease etiology and to translate more novel anticancer metal complexes to clinical studies, which will significantly improve human health in the 21st century.

Application of a Novel Metallomics Tool to Probe the Fate of Metal-Based Anticancer Drugs in Blood Plasma: Potential, Challenges and Prospects

Although metallodrugs are used to treat a variety of human disorders and exhibit a remarkable diversity of therapeutic properties, they constitute only a tiny minority of all medicinal drugs that are currently on the market. This undesirable situation must be partially attributed to our general lack of understanding the fate of metallodrugs in the extremely ligand-rich environment of the bloodstream. The challenge of gaining insight into these bioinorganic processes can be overcome by the application of 'metallomics tools', which involve the analysis of biological fluids (e.g., blood plasma) with a separation method in conjunction with multi-element specific detectors. To this end, we have developed a metallomics tool that is based on size-exclusion chromatography (SEC) hyphenated to an inductively coupled plasma atomic emission spectrometer (ICP-AES). After the successful application of SEC-ICPAES to analyze plasma for endogenous copper, iron and zinc-metalloproteins, it was subsequently applied to probe the metabolism of a variety of metal-based anticancer drugs in plasma. The versatility of this metallomics tool is exemplified by the fact that it has provided insight into the metabolism of individual Pt-based drugs, the modulation of the metabolism of cisplatin by sulfur-containing compounds, the metabolism of two metal-based drugs that contain different metals as well as a bimetallic anticancer drug, which contained two different metals. After adding pharmacologically relevant doses of metallodrugs to plasma, the temporal analysis of aliquots by SEC-ICP-AES allows to observe metal-protein adducts, metallodrug-derived degradation products and the parent metallodrug(s). This unique capability allows to obtain comprehensive insight into the fate of metal-based drugs in plasma and can be extended to in vivo studies. Thus, the application of this metallomics tool to probe the fate of novel metalcomplexes that exert the desired biological activity in plasma has the potential to advance more of these to animal/preclinical studies to fully explore the potential that metallodrugs inherently offer.

Design, synthesis and pharmacological screening of novel renoprotective methionine-based peptidomimetics: Amelioration of cisplatin-induced nephrotoxicity

Cisplatin (CP) is an effective chemotherapeutic agent for treatment of various types of cancer, however efforts are needed to reduce its toxic side effect. Previous studies revealed promising effect of peptides in decreasing CP induced nephrotoxicity. Herein, novel Met-based peptidomimetics were synthesized using N-acylbenzotriazole as acylating agent in high yield. Evaluation of renoprotective effect of the synthesized targets on CP treated kidney cell line (LLC-PK1) revealed that pretreatment with 1/3 IC₅₀ of targets II, IIIa-g attenuated CP induced cell death where the IC₅₀ of CP was raised from 3.28 µM to 9.25-41.1 µM. The most potent compounds IIIg, II and IIIb exhibited antioxidative stress in CP-treated LLC-PK1 cells as confirmed by raising GSH/GSSG ratio and SOD concentration as well as decreasing ROS and MDA. Additionally, in vivo experiments using Sprague Dawley rats showed renoprotective effect of IIIg against CP-induced nephrotoxicity as evidenced by improved results of renal function tests and attenuated CP-induced renal structural injury. Moreover, antioxidant activity of IIIg was demonstrated via its ability to reduce renal MDA level and up-regulate renal antioxidant element GSH level. Further, immunohistochemistry of renal specimens showed the ability of IIIg to restore CP-induced suppression of Nrf2. Interestingly, in vivo and in vitro studies demonstrated that IIIg had no effect on CP antiproliferative activity. An assessment of the ADMET properties revealed that targets IIIg, II and IIIb showed good drug-likeness in terms of their physicochemical, pharmacokinetic properties. The findings presented here showcase that IIIg is a promising renoprotective candidate with antioxidative stress potential.

Nephroprotective effects of eriocitrin via alleviation of oxidative stress and DNA damage against cisplatin-induced renal toxicity

Background

Cisplatin, a common anti-neoplastic drug used in the medical industry for cancer treatment has shown adverse nephrotoxic effects. This research targets to demonstrate the protective measure of eriocitrin, a bioactive flavonoid, against cisplatin-induced renal toxicity in rats.

Materials and methods

Rats of normal control and model groups were treated with saline whereas experimental groups received oral administration of eriocitrin (25 and 50 mg/kg b.w.) for 10 days and a single intraperitoneal (i.p.) injection of cisplatin (8 mg/kg b.w.) was given on the 7th day for all except normal control group. Blood serum, urine, and kidney tissue samples were collected for analysis.

Results

Cisplatin-induced rats demonstrated significant renal toxicity and damage. Eriocitrin dose-dependently reversed the effects by decreasing the proteinuria in urine, and urea, creatinine, lipid peroxidation, nitric oxide (NO) and pro-inflammatory cytokine levels (TNF-α, IL-1β) in serum. The tissue levels of reduced glutathione (GSH), superoxide dismutase (SOD) and catalase (CAT) were increased, whereas the levels of tissue DNA fragmentation and serum PARP-1 and Caspase-3 were reduced against model group. Histopathological modulations were supporting the protective effect of eriocitrin.

Conclusion

Eriocitrin has significant nephroprotective effects against cisplatin-induced renal toxicity by alleviating oxidative stress, preventing apoptosis and DNA damage.

D-Methionine Ameliorates Cisplatin-Induced Muscle Atrophy via Inhibition of Muscle Degradation Pathway

Cisplatin induces anorexia, weight loss, loss of adipose tissue, skeletal muscle atrophy, and serious adverse effects that can cause premature termination of chemotherapy. The aim of this study was to use an animal model to assess cisplatin therapy (3 cycles) with and without d-methionine to investigate its protective effects on cisplatin-induced anorexia and skeletal muscle wasting. Wistar rats were divided into 3 groups and treated as follows: saline as control (group 1), intraperitoneal cisplatin once a week for 3 weeks (group 2), and intraperitoneal cisplatin once a week for 3 weeks plus oral administration of d-methionine (group 3). Tissue somatic index (TSI), gastric emptying index (GEI), and feeding efficiency were measured. Both hepatic lipid metabolism and muscle atrophy-related gene expressions and C2C12 myotubes were determined by polymerase chain reaction. Micro-computed tomography (micro-CT) was used to conduct assessment of bone microarchitecture indices. Pathological changes of the gastric mucosa were assessed by hematoxylin and eosin staining after euthanizing the animals. d-Methionine increased food intake, weight gain, gastric emptying, and feeding efficiency, as well as decrease stomach contents, after cisplatin injections. Cisplatin caused shortening of myofibers. Cisplatin-induced muscle mass wasting was mediated by the elevation of mRNA expressions of MAFbx and MuRF-1 in ubiquitin ligases in muscle tissue homogenate. The mRNA expressions of MyoD and myogenin, markers of muscle differentiation, declined following cisplatin administration. The administration of d-methionine not only led to significant improvements in myofiber diameter and cross-sectional fiber areas but also reversed muscle atrophy-related gene expression. However, there were no significant changes in stomach histology or microarchitecture of trabecular bone among the study groups. The results indicate that d-methionine has an appetite-enhancing effect and ameliorates cisplatin-induced adipose and muscle tissue loss during cisplatin-based chemotherapy.

Development of Second-Generation CDK2 Inhibitors for the Prevention of Cisplatin-Induced Hearing Loss

There are currently no FDA-approved therapies to prevent the hearing loss associated with the usage of cisplatin in chemotherapeutic regimens. We recently demonstrated that the pharmacologic inhibition with kenpaullone or genetic deletion of CDK2 preserved hearing function in animal models treated with cisplatin, which suggests that CDK2 is a promising therapeutic target to prevent cisplatin-induced ototoxicity. In this study, we identified two lead compounds, AT7519 and AZD5438, from a focused library screen of 187 CDK2 inhibitors, performed in an immortalized cell line derived from neonatal mouse cochleae treated with cisplatin. Moreover, we screened 36 analogues of AT7519 and identified analogue 7, which exhibited an improved therapeutic index. When delivered locally, analogue 7 and AZD5438 both provided significant protection against cisplatin-induced ototoxicity in mice. Thus, we have identified two additional compounds that prevent cisplatin-induced ototoxicity in vivo and provided further evidence that CDK2 is a druggable target for treating cisplatin-induced ototoxicity.

Protective Effect of D-Methionine on Body Weight Loss, Anorexia, and Nephrotoxicity in Cisplatin-Induced Chronic Toxicity in Rats

D-methionine is a sulfur-containing amino acid that can act as a potent antioxidant. Anorexia and nephrotoxicity are side effects of cisplatin. The protective effects of D-methionine on cisplatin-induced anorexia and renal injury were investigated. The model of chronic cisplatin administration (5 mg/kg body weight) involved intraperitoneal injection on days 1, 8, and 15 and oral D-methionine (300 mg/kg body weight) coadministration daily for 20 days. On the 21st day of treatment, food intake and body weight in the cisplatin-treated group significantly decreased by 52% and 31%, respectively, when compared with a control group. D-methionine coadministration with cisplatin decreased food intake and body weight by 29% and 8%, respectively. In cisplatin-treated rats, white blood cell, mean corpuscular volume, and platelet values significantly decreased, while mean corpuscular hemoglobin concentration significantly increased by 8.6% when compared with control rats. Cisplatin administration resulted in significantly decreased feeding efficiency, elevated renal oxidative stress, and reduced antioxidative activity. Leukocyte infiltration, tubule vacuolization, tubular expansion, and swelling were observed in the kidneys of cisplatin-treated rats. Oral D-methionine exhibited an antianorexic effect, with improvement in food intake, feeding efficiency, and hematological toxicities, as well as a protective effect against nephrotoxicity by elevated antioxidative activity. D-methionine may serve as a chemoprotectant in patients receiving cisplatin as part of a chemotherapy regimen.

Tuning the metabolism of the anticancer drug cisplatin with chemoprotective agents to improve its safety and efficacy

Numerous in vivo studies have shown that the severe toxic side-effects of intravenously administered cisplatin can be significantly reduced by the co-administration of sulfur-containing 'chemoprotective agents'. Using a metallomics approach, a likely biochemical basis for these potentially useful observations was only recently uncovered and appears to involve the reaction of chemoprotective agents with cisplatin-derived Pt-species in human plasma to form novel platinum-sulfur complexes (PSC's). We here reveal aspects of the structure of two PSC's and establish the identification of an optimal chemoprotective agent to ameliorate the toxic side-effects of cisplatin, while leaving its antineoplastic activity largely intact, as a feasible research strategy to transform cisplatin into a safer and more effective anticancer drug.

He-Wei granules (HWKL) combat cisplatin-induced nephrotoxicity and myelosuppression in rats by inhibiting oxidative stress, inflammatory cytokines and apoptosis

He-Wei granules (HWKL) combat cisplatin-induced nephrotoxicity and myelosuppression in rats by inhibiting oxidative stress, inflammatory cytokines and apoptosis

Ameliorative effect of an oxovanadium (IV) complex against oxidative stress and nephrotoxicity induced by cisplatin

OBJECTIVE

The present study was designed to investigate the chemoprotective efficacy of an L-cysteine-based oxovanadium (IV) complex, namely, oxovanadium (IV)-L-cysteine methyl ester complex (VC-IV) against cisplatin (CDDP)-induced renal injury in Swiss albino mice.

METHODS

CDDP was administered intraperitoneally (5 mg/kg body weight) and VC-IV was administered orally (1 mg/kg body weight) in concomitant and 7 days pre-treatment schedule.

RESULTS

CDDP-treated mice showed marked kidney damage and renal failure. Administration of VC-IV caused significant attenuation of renal oxidative stress and elevation of antioxidant status. VC-IV also significantly decreased serum levels of creatinine and blood urea nitrogen, and improved histopathological lesions. Western blot analysis of the kidneys showed that VC-IV treatment resulted in nuclear translocation of nuclear factor E2-related factor 2 (Nrf2) through modulation of cytosolic Kelch-like ECH-associated protein 1. Thus, VC-IV stimulated Nrf2-mediated activation of antioxidant response element (ARE) pathway and promoted expression of ARE-driven cytoprotective proteins, heme oxygenase 1 and NAD(P)H:quinone oxidoreductase 1, and enhanced activity of antioxidant enzymes. Interestingly, VC-IV did not alter the bioavailability and renal accumulation of CDDP in mice.

DISCUSSION

In this study, VC-IV exhibited strong nephroprotective efficacy by restoring antioxidant defense mechanisms and hence may serve as a promising chemoprotectant in cancer chemotherapy.

An oxovanadium(IV) complex protects murine bone marrow cells against cisplatin-induced myelotoxicity and DNA damage

Cisplatin (CDDP) is one of the first-line anticancer drugs that has gained widespread use against various forms of human malignancies. But, the therapeutic outcome of CDDP therapy is limited due to its adverse effects including myelotoxicity and DNA damage which may lead to the subsequent risk of developing secondary cancer. Hence, in search of a suitable cytoprotectant, this study investigated the probable protective efficacy of an oxovanadium(IV) complex, namely oxovanadium(IV)-L-cysteine methyl ester complex (VC-IV) against CDDP-induced myelosuppression and genotoxic damage in the bone marrow cells of Swiss albino mice. CDDP was administered intraperitoneally (5 mg/kg b.w.) and VC-IV was administered orally (1 mg/kg b.w.) in concomitant and 7 d pretreatment schedule. Treatment with VC-IV in CDDP-treated mice significantly (p < 0.01) enhanced bone marrow cell proliferation and inhibited cell death in the bone marrow niche indicating improvement of CDDP-induced myelotoxicity. The organovanadium compound also significantly (p < 0.01) reduced the percentage of chromosomal aberrations, the frequency of micronuclei formation, and the extent of DNA damage. The observed chemoprotective effect of VC-IV was attributed to its anti-oxidant efficacy which significantly (p < 0.01) attenuated CDDP-induced generation of free radicals, and restored (p < 0.01) the levels of oxidized and reduced glutathione. Hence, VC-IV may serve as a promising candidate for future development to decrease the deleterious effects of CDDP in the bone marrow cells of cancer patients and associated secondary complications.

Physiologically relevant plasma d,l-homocysteine concentrations mobilize Cd from human serum albumin

Although low-level chronic exposure of humans to cadmium (Cd(2+)) can result in a variety of adverse health effects, little is known about the role that its interactions with plasma proteins and small molecular weight (SMW) ligands in the bloodstream may play in delivering this metal to its target organs. To gain insight, a Cd-human serum albumin (HSA) 1:1 (molar ratio) complex was analyzed by size exclusion chromatography (SEC) coupled on-line to a flame atomic absorption spectrometer (FAAS). Using a phosphate buffered saline (PBS)-buffer mobile phase, the stability of the Cd-HSA complex was investigated in the presence of 2.0mM of SMW ligands, including taurine, acetaminophen, l-methionine, l-cysteine (Cys), d,l-homocysteine (hCys) or l-cysteine methyl-ester (Cys-Me). While taurine, acetaminophen and l-methionine did not affect its integrity, Cys, hCys and Cys-Me completely abstracted Cd from HSA. Subsequent investigations into the effect of 1.5, 1.0 and 0.5mM Cys and hCys on the integrity of the Cd-HSA complex revealed clear differences with regard to the nature of the eluting SMW-Cd species between these structurally related endogenous thiols. Interestingly, the Cd-specific chromatograms that were obtained for 0.5mM hCys revealed the elution of an apparent mixture of the parent Cd-HSA complex with a significant contribution of a structurally uncharacterized CdxhCysy species. Since this hCys concentration is encountered in blood plasma of hyperhomocysteinemia patients and since previous studies by others have revealed that a SH-containing carrier mediates the uptake of Cd into hepatocytes, our results suggest that plasma hCys may play a role in the toxicologically relevant translocation of Cd from the bloodstream to mammalian target organs.

Modulation of the metabolism of cis-platin in blood plasma by glutathione

The anticancer drug cis-platin (CP) is in worldwide clinical use to treat a variety of cancers, but is inherently associated with severe toxic side effects. Previous animal studies revealed that its neurotoxicity can be significantly reduced by the coadministration of l-glutathione (GSH) without affecting the anticancer effect. The underlying molecular mechanism, however, has remained elusive. Since the bloodstream is a likely biological compartment where CP-derived hydrolysis products may react with GSH, we have employed a recently developed metallomics tool to gain insight into the interaction of CP and GSH in rabbit plasma in vitro. After the addition of increasing GSH/CP molar ratios to plasma (25:1, 50:1, and 100:1), the determination of the Pt distribution 5 min and 2 h later revealed the formation of a Pt–GSH complex that did not bind to plasma proteins. The simultaneously obtained Zn distribution in plasma revealed a progressively more pronounced perturbation of the Zn metalloproteome with increasing GSH/CP molar ratios at the 5 min time point, which partially reversed at the 2 h time point. The formation of Pt–GSH species in plasma is therefore likely to be directly involved in the process by which GSH protects mammalian organisms from CP-induced neurotoxicity, nephrotoxicity, and possibly other organ-based toxicities.

Advanced LC-analysis of human plasma for metallodrug metabolites

Understanding the fate of metallodrugs in the bloodstream is critical to assess if the parent drug has a reasonable probability to reach the intended target tissue and to predict toxic side-effects. To gain insight into these processes, we have added pharmacologically relevant doses of metallodrugs to blood plasma and applied an LC-method to directly analyze the latter for metallodrug metabolites. Using human or rabbit plasma, this LC-method was employed to gain insight into the metabolism of clinically used as well as emerging anticancer metallodrugs and to unravel the mechanisms by which small molecular weight compounds that - when co-administered with a metallodrug - decrease the toxic side-effects of the metallodrug by modulating its metabolism. The results suggest that the developed LC-method is useful to probe the fate of biologically active novel metal-complexes in plasma to help select those which may be advanced to animal/clinical studies to ultimately develop safer metallodrugs.

Fortification of blood plasma from cancer patients with human serum albumin decreases the concentration of cisplatin-derived toxic hydrolysis products in vitro

While cisplatin (CP) is still one of the world's bestselling anticancer drugs, its intravenous administration is inherently associated with severe, dose limiting toxic side-effects. Although the molecular basis of the latter are not well understood, biochemical transformations of CP in blood and the interaction of the generated platinum species with plasma proteins likely play a critical role since these processes will ultimately determine which platinum-species reach the intended tumor cells as well as non-target cells. Compared to healthy subjects, cancer patients often have decreased plasma human serum albumin (HSA) concentrations. Little, however, is known about how the plasma HSA concentration will affect the metabolism of CP. To gain insight, we obtained blood plasma from healthy adults (n = 20, 42 ± 4 g HSA per L) and pediatric cancer patients (n = 11, 26 ± 7 g HSA per L). After the incubation of plasma at 37 °C, a pharmacologically relevant dose of CP was added and the Pt-distribution therein was determined by size-exclusion chromatography coupled on-line to an inductively coupled plasma atomic emission spectrometer. At the 2 h time point, a 5.9% increase of toxic CP-derived hydrolysis products was detected in pediatric cancer patient plasma, while 9.8% less platinum was protein bound compared to plasma from healthy controls. These in vitro results suggest that the elevated concentration of highly reactive free CP-derived hydrolysis products in plasma may cause the toxic side-effects in cancer patients. More importantly, the deliberate increase of the plasma HSA concentration in cancer patients prior to CP treatment would represent a simple strategy to possibly alleviate the fraction of patients that suffer from drug induced toxic side-effects.