Pharmacokinetics of cisplatin with and without amifostine in tumour-bearing nude mice

Physiologically-Based Modeling and Interspecies Prediction of Cisplatin Pharmacokinetics

The goal of this work was to develop a physiologically-based pharmacokinetic (PBPK) modeling framework for cisplatin. The model was constructed based on 11 published data sets from rodents; and rabbit, dog, and human data were used to evaluate its utility in predicting plasma and tissue distribution of platinum in larger species, including humans. The model included biotransformation of cisplatin into mobile (k1) and fixed (k2) metabolites in all tissues, and subsequent conversion of fixed metabolites to mobile metabolites (k3) due to protein degradation and turnover. The model successfully captured complex pharmacokinetics of platinum in rodents, and all parameters were estimated with sufficient precision. A separate k2 parameter was estimated for each included tissue, and the relationship between the rates of formation of mobile and fixed metabolites was established through a scaling factor (k1=k2·SF, SF=0.74). For interspecies predictions, k1 and k2 were shared across all species, and k3 was scaled allometrically based on protein turnover rate (with an exponent of -0.28). Scaled PBPK model provided a good prediction of total platinum profiles in humans and reasonably captured platinum measurements in human tissues (as obtained from autopsy).

Development and evaluation of a theranostic probe with RGD peptide introduced platinum complex to enable tumor-specific accumulation

Cisplatin (CDDP) has been widely used for chemotherapy. However, it has several unfavorable side effects due to its low tumor selectivity. In this study, we designed, synthesized, and evaluated Pt(IV)-[c(RGDyK)]₂ (9), in which two molecules of an RGD peptide are introduced as a carrier molecule to cancer into oxoplatin, a Pt(IV) prodrug of CDDP, to enhance cancer selectivity. Furthermore, we prepared and evaluated Pt(IV)-[c(RGDyK)]{[¹²⁵I]c[RGDy(3-I)K]} ([¹²⁵I]10) for a preliminary step of nuclear medicine imaging and theranostics. Compound 9 inhibited cell growth in the cell viability assay and, [¹²⁵I]10 was highly accumulated in tumor tissues (1 h: 3.53 ± 0.53 %ID/g) in the biodistribution study. These results indicate that implementing RGD peptides into oxoplatin enabled tumor-specific accumulation, and combining [^123/124I]10 and 9 for diagnostic imaging and therapy could be useful for cancer theranostics.

Identification of the xenobiotic-metabolizing enzyme arylamine N-acetyltransferase 1 as a new target of cisplatin in breast cancer cells: molecular and cellular mechanisms of inhibition

Arylamine N-acetyltransferase 1 (NAT1) is a phase II xenobiotic-metabolizing enzyme that plays an important role in the biotransformation of aromatic drugs and carcinogens. NAT1 activity has long been associated with susceptibility to various cancers. Evidence for a role of NAT1 in malignant progression has also been obtained, particularly for breast and prostate cancer. Cisplatin is widely used in chemotherapy against human cancers, and it is thought to act principally by forming DNA adducts. However, recent studies have suggested that some of the pharmacological and/or toxicological effects of cisplatin may be due to the direct targeting and inhibition of certain cellular enzymes. We show here that the exposure of breast cancer cells, known to express functional NAT1 enzyme, to therapeutically relevant concentrations of cisplatin impairs the catalytic activity of endogenous NAT1. Endogenous NAT1 was also found to be inactivated, in vivo, in the tissues of mice treated with cisplatin. Mechanistic studies with purified human NAT1 indicated that this inhibition resulted from the irreversible formation of a cisplatin adduct with the active-site cysteine residue of the enzyme. Kinetic studies suggested that NAT1 interacts rapidly with cisplatin, with a second-order rate inhibition constant of 700 M(-1) min(-1). This rate constant is one the highest ever reported for the reaction of cisplatin with a biological macromolecule. Few enzymes have been clearly shown to be inactivated by cisplatin. We provide here molecular and cellular evidence suggesting that NAT1 is one of the targets of cisplatin in cells.

Metabolism of Cisplatin to a nephrotoxin in proximal tubule cells

Cisplatin, a commonly used chemotherapeutic agent, is nephrotoxic. The mechanism by which cisplatin selectively kills the proximal tubule cells was heretofore unknown. Recent studies in mice and rats have shown that the nephrotoxicity of cisplatin can be blocked by acivicin or (aminooxy)acetic acid, the same enzyme inhibitors that block the metabolic activation of a series of nephrotoxic halogenated alkenes. In this study, it was hypothesized that cisplatin is activated in the kidney to a toxic metabolite through the same pathway that has been shown to activate the halogenated alkenes. This activation begins with the formation of a glutathione-conjugate that is metabolized to a cysteinyl-glycine-conjugate, to a cysteine-conjugate, and finally to a reactive thiol. In this study, a protocol was developed in which confluent monolayers of LLC-PK(1) cells were exposed to clinically relevant concentrations of cisplatin or cisplatin-conjugate for 3 h. Cell viability was assayed at 72 h. The role of gamma-glutamyl transpeptidase (GGT) and cysteine-S-conjugate beta-lyase in the metabolism of each of the cisplatin-conjugates was investigated. Pre-incubation of cisplatin with glutathione, cysteinyl-glycine, or N-acetyl-cysteine to allow for the spontaneous formation of cisplatin-conjugates increased the toxicity of cisplatin toward LLC-PK(1) cells. Inhibition of GGT activity showed that GGT was necessary only for the toxicity of the cisplatin-glutathione-conjugate. Inhibition of cysteine-S-conjugate beta-lyase reduced the toxicity of each of the cisplatin-conjugates. These data demonstrate that metabolism of cisplatin in proximal tubule cells is required for its nephrotoxicity. The elucidation of this pathway provides new targets for the inhibition of cisplatin nephrotoxicity.

Flow cytometric detection of apoptotic bone marrow cells with fractional DNA content after application of WR-2721, cyclophosphamide, cisplatin, and exposure of mice to gamma rays

Little is known about the mechanisms of apoptosis triggered in normal cells of the haemopoietic system by the aminothiol WR-2721 (Amifostine), chemotherapeutic drugs, and ionizing radiation; thus, the present study was undertaken to evaluate the effects of WR-2721, cyclophosphamide (CP), cisplatin (CDDP), and 60Co gamma rays on induction of apoptotic DNA degradation in bone marrow cells. Adult male Swiss mice were treated with WR-2721 (400 mg/kg b.wt.), CP (200 mg/kg b.wt.), and CDDP (10 mg/kg b.wt.), and exposed to 6 Gy 60Co gamma rays. Alterations in the number of apoptotic cells with fractional DNA content and also the cell cycle position of the non-apoptotic cells were determined in the bone marrow at 7 and 24 hours after treatment of mice with these agents, using flow cytometric assay of the controlled extraction of low-MW DNA from apoptotic cells. The chemotherapeutic drugs CP and CDDP and 60Co gamma rays triggered apoptosis and affected the cell cycle position of the non-apoptotic cells in the mouse bone marrow. The pretreatment of mice with WR-2721 resulted in the modulatory action of the aminothiol on induction of apoptotic cell death and changes in the cell cycle distribution of the non-apoptotic cells caused by the DNA-damaging agents. The patterns of changes in the frequency of apoptotic cells and the cell cycle position of the non-apoptotic cells, observed in the bone marrow, were dependent on the agent(s) applied and the time interval after application of the drug(s) and exposure of mice to gamma rays. Understanding of the mechanisms responsible for triggering of apoptotic cell death and disturbing of the cell cycle by the DNA-damaging agents, and modulation of the apoptotic and cell cycle pathways by the aminothiol WR-2721, can lead to more effective therapy and chemo- and radio-protection of normal cells.

Cisplatin-loaded polymer-metal complex micelle with time-modulated decaying property as a novel drug delivery system

PURPOSE

The pharmacological activity and pharmacokinetics of cisplatin (CDDP)-loaded polymeric micelles were examined to reveal their usefulness as a novel tumor-directed drug carrier system of CDDP.

METHODS

In biodistribution assay, free CDDP or CDDP-loaded micelles were administered intravenously to Lewis lung carcinoma-bearing mice. Antitumor activity and nephrotoxicity were respectively evaluated by the measurement of tumor size and plasma blood urea nitrogen (BUN) after single bolus i.v. administration of each drug.

RESULTS

The time profile of the plasma Pt level after the injection of the micelles exhibited a time-modulated disappearance as observed in saline in vitro. The micelles exhibited 5.2- and 4.6-fold higher AUC of Pt in the plasma and tumor, respectively, with minimal change in the kidney, in comparison with free CDDP, suggesting that prolonged circulation of Pt in circulation and specific accumulation in the tumor were achieved utilizing the micellar drug carrier system. Administration of the micelles at the dose exhibiting antitumor activity similar to free CDDP did not increase the plasma BUN, whereas free CDDP induced its remarkable increase.

CONCLUSION

CDDP-loaded micelles restrained nephrotoxicity, which is the dose-limiting factor of CDDP, while exhibiting tumor-specific accumulation. Thus, CDDP-loaded micelles are expected to be a novel formulation of CDDP for clinical use.

WR-2721: inhibitor of cisplatin-induced micronuclei

The modulatory effect of S-2-/3-aminopropylamino/ethyl-phosphorothioic acid, (WR-2721, Amifostine) on induction of micronuclei by cis-diamminedichloroplatinum[II] (CDDP) was studied. The adult, male Swiss mice were treated with WR-2721, at a dose of 200 mg/kg or 400 mg/kg body weight, and/or with CDDP, at a dose 5 mg/kg or 10 mg/kg body weight. WR-2721 was given alone or 30 min before CDDP administration. The frequency of micronucleated polychromatic erythrocytes (MNPCEs) and also the number of polychromatic erythrocytes (PCEs) in the bone marrow and peripheral blood, at 24 h after the drug application, were determined. After administration of CDDP, the frequency of MNPCEs distinctly increased, and the number of PCEs decreased. As compared with the animals injected with CDDP only, in mice treated with WR-2721 before CDDP application, the number of MNPCEs was reduced and the frequency of PCEs was increased. However, WR-2721 given alone, without subsequent administration of cis-diamminedichloroplatinum[II], caused an increase in the number of micronucleated polychromatic erythrocytes and a decrease in the number of PCEs. The geno- and cyto-toxicity and chemoprotection were dependent on the doses of the agents WR-2721 and CDDP applied. In mice injected with CDDP and/or WR-2721, the patterns of changes in the frequency of MNPCEs and PCEs were similar in the bone marrow and peripheral blood, respectively. The protective effect of the aminothiol compound WR-2721 against induction of micronuclei and apoptotic cell death in the erythropoietic system by CDDP was shown.

The cytoprotective aminothiol WR1065 activates p21waf-1 and down regulates cell cycle progression through a p53-dependent pathway

The phosphoaminothiol WR1065, the active metabolite of the pro-drug amifostine (WR2721), protects cultured cells and tissues against cytotoxic exposure to radiation or chemotherapeutic agents. We show here that WR1065 and the pro-drug WR2721 activate the p53 tumor suppressor protein and induce the expression of the cyclin-dependent kinase inhibitor p21waf-1 in the breast cancer cell line MCF-7, and in the mouse fibroblast cell line balb/c 3T3. Using two MCF-7 derived cell lines, MN1 and MDD2, we show that induction of p21waf-1 is detectable in MN1 (expressing a functional p53) but not in MDD2 (p53 disabled). These effects are observed at concentrations of WR1065 (0.5 to 1 mM) identical to those required to protect against cytotoxicity by hydrogen peroxide. Induction of p53 is not prevented by addition of aminoguanidine, an inhibitor of Cu-dependent amine-oxidases which blocks the extra-cellular degradation of WR1065 into toxic metabolites. Moreover, spermidine, a natural polyamine structurally related to amifostine, does not activate p53. Induction of p53 by WR1065 results in a delay in the G1/S transition in MCF-7 and MN-1 cells, but not in the p53 disabled cells MDD2. These data indicate that WR1065, a polyamine analog with thiol anti-oxidant properties, activates a cell cycle check-point involving p53.

Effects of amifostine on cisplatin induced DNA adduct formation and toxicity in malignant glioma and normal tissues in rat

The chemoprotective effect of amifostine (WR2721) was studied in a BDIX rat model with intracerebral BT4C glioma implants. Twenty-one rats were given cisplatin 5 mg/kg i.p., 21 were given amifostine 200 mg/kg i.p. + cisplatin 5 mg/kg i.p. Ten rats served as untreated controls. An immunohistochemical method for analysis of cisplatin-DNA adducts was used to elucidate the adduct formation in tumor, normal brain and kidney. Tumor volume and serum creatinine level were analysed 10 days after treatment. In animals pretreated with amifostine there was a delayed adduct formation rate in the normal brain, and in the kidney cortex the number of tubular cells with extremely high adduct level was reduced. No difference in adduct formation was seen in tumors. Tumor volume was significantly larger following amifostine + cisplatin (66% of controls) compared to cisplatin alone (38% of controls). Weight loss was, however, severe in rats given cisplatin alone. In the tumor growth study only 3 out of 11 rats treated with cisplatin 5 mg/kg alone survived until time of sacrifice at 10 days, whereas all those pretreated with amifostine survived. Mean serum creatinine was 48 micromol/l (controls), 146 micromol/l (cisplatin) and 59 micromol/l (amifostine + cisplatin). A marked reduction of histopathological renal changes was found when amifostine was added. Amifostine thus significantly reduced general and renal toxicity of cisplatin. The tumor growth retardation was stronger when cisplatin was given alone but this is probably related to general toxicity and malnutrition indirectly supported by the fact that amifostine did not significantly reduce cisplatin-DNA adduct formation in tumors. The results of the present study suggest that amifostine may have a role in increasing the therapeutic ratio of cisplatin, also in the treatment of malignant glioma.

Pharmacodynamics of cisplatin in human head and neck cancer: correlation between platinum content, DNA adduct levels and drug sensitivity in vitro and in vivo

Total platinum contents and cisplatin-DNA adduct levels were determined in vivo in xenografted tumour tissues in mice and in vitro in cultured tumour cells of head and neck squamous cell carcinoma (HNSCC), and correlated with sensitivity to cisplatin. In vivo, a panel of five HNSCC tumour lines growing as xenografts in nude mice was used. In vitro, the panel consisted of five HNSCC cell lines, of which four had an in vivo equivalent. Sensitivity to cisplatin varied three- to sevenfold among cell lines and tumours respectively. However, the ranking of the sensitivities of the tumour lines (in vivo), also after reinjection of the cultured tumour cells, did not coincide with that of the corresponding cell lines, which showed that cell culture systems are not representative for the in vivo situation. Both in vitro and in vivo, however, significant correlations were found between total platinum levels, measured by atomic absorption spectrophotometry (AAS), and tumour response to cisplatin therapy at all time points tested. The levels of the two major cisplatin-DNA adduct types were determined by a recently developed and improved 32P post-labelling assay at various time points after cisplatin treatment. Evidence is presented that the platinum-AG adduct, in which platinum is bound to guanine and an adjacent adenine, may be the cytotoxic lesion because a significant correlation was found between the platinum-AG levels and the sensitivities in our panel of HNSCC, in vitro as well as in vivo. This correlation with the platinum-AG levels was established at 1 h (in vitro) and 3 h (in vivo) after the start of the cisplatin treatment, which emphasizes the importance of early sampling.