The chemical reactivity of the modulating agent WR2721 (ethiofos) and its main metabolites with the antitumor agents cisplatin and carboplatin

A chemical perspective on the clinical use of platinum-based anticancer drugs

Platinum drugs have been a mainstay of cancer chemotherapy since the introduction of cisplatin in the 1970s. Since then, carboplatin and oxaliplatin have been approved world-wide and nedaplatin, lobaplatin, heptaplatin, dicycloplatin, and miriplatin have been approved in individual countries. The three main platinum drugs are not used in isolation but are combined in chemotherapy protocols from a range of 28 drugs that include: anthracyclines, alkylating agents, vinca alkaloids, antimetabolites, topoisomerase inhibitors, taxanes, and monoclonal antibodies. Interestingly, they are not yet used in combination with tyrosine kinase inhibitors or proteasome inhibitors. How platinum drugs are formulated for administration to patients is important to minimise aquation during storage and administration. Cisplatin is typically formulated in saline-based solutions while carboplatin and oxaliplatin are formulated in dextrose. Pharmacokinetics are an important factor in both the efficacy and safety of platinum drugs. This includes the quantity of protein-bound drug in blood serum, how fast the drugs are cleared by the body, and how fast the drugs are degraded and deactivated. Attempts to control platinum pharmacokinetics and side effects using rescue agents, macrocycles, and nanoparticles, and through the design of platinum(IV)-based drugs have not yet resulted in clinically successful outcomes. As cancer is predominantly a disease of old age, many cancer patients who are administered a platinum drug may have other medical conditions which means they may also be taking many non-cancer medicines. The co-administration of non-cancer medicines to patients can potentially affect the efficacy of platinum drugs and/or change the severity of their side effects through drug-drug interactions.

A pilot study of addition of amifostine to melphalan, carboplatin, etoposide, and cyclophosphamide with autologous hematopoietic stem cell transplantation in pediatric solid tumors-A pediatric blood and marrow transplant consortium study

Limited information is available regarding the use of amifostine in pediatric hematopoietic stem cell transplant (HSCT) patients. Melphalan, carboplatin, etoposide +/- cyclophosphamide is a commonly used preparatory regimen in pediatric solid tumor HSCT. Therefore, we decided to determine the feasibility of the addition of amifostine (750 mg/m b.i.d. x 4 d) to melphalan (200 mg/m), carboplatin (1200 mg/m), and etoposide (800 mg/m) (level 1) and escalating doses of cyclophosphamide (3000 mg/m and 3800 mg/m, levels 2 and 3, respectively) followed by autologous HSCT. Thirty-two patients with a variety of pediatric solid tumors were studied. Seventeen patients were accrued at level 1, 9 at level 2, and 6 at level 3. Major toxicities during the administration of the preparatory regimen were hypocalcemia, emesis, and hypotension. Hypocalcemia required aggressive calcium supplementation during the conditioning phase. No dose limiting toxicities were encountered at level 3. Amifostine at 750 mg/m b.i.d. for 4 days can be administered with a double alkylator regimen consisting of melphalan (200 mg/m), cyclophosphamide (up to 3800 mg/m), carboplatin (1200 mg/m), and etoposide (800 mg/m) with manageable toxicities.

Biophysical characterisation of adducts formed between anticancer metallodrugs and selected proteins: new insights from X-ray diffraction and mass spectrometry studies

There is considerable interest today for the reactions of anticancer metallodrugs with proteins as these interactions might feature processes that are crucial for the biodistribution, the toxicity and even the mechanism of action of this important group of anticancer agents. We survey here the results of research activities carried out in our "Laboratory of Metals in Medicine" (Department of Chemistry, University of Florence) during the last three years, concerning the molecular characterisation of adducts formed between platinum, ruthenium and gold metallodrugs and a few model proteins. Valuable structural and functional information on these adducts could be derived from several biophysical studies mainly relying on the application of X-ray diffraction and ESI MS techniques. The value and the limitations of both approaches are outlined through a number of examples. Remarkably, the structural and functional information achieved on the respective metallodrug-protein adducts allowed us to identify some general trends in the reactivity of anticancer metallodrugs with protein targets.

High-Dose Cisplatin With Amifostine: Ototoxicity and Pharmacokinetics

OBJECTIVES/HYPOTHESIS

Ototoxicity is a common side effect of high-dose cisplatin treatment. Thiol-containing chemoprotectors ameliorate cisplatin ototoxicity under experimental conditions. The trial was initiated to test the efficacy of amifostine protection in high-dose cisplatin treatment (125-150 mg/m) for metastatic malignant melanoma, to correlate the ototoxic outcome with cisplatin pharmacokinetics, and to evaluate the importance of using a selective analytical method for the quantification of cisplatin.

STUDY DESIGN

Prospective study of 15 patients with stage IV malignant melanoma.

METHODS

Clinical follow-up of therapeutic response, pure-tone audiometry, and analysis of cisplatin and its monohydrated complex in blood ultrafiltrate by liquid chromatography with postcolumn derivatization were performed. Ultrafiltered blood platinum was analyzed by inductively coupled plasma mass spectrometry.

RESULTS

Ototoxicity and gastrointestinal toxicity were the most prominent side effects. Three patients ultimately required hearing aids. All patients had audiometric changes at one or more frequencies after the second treatment course, and all but one patient reported auditory symptoms. No correlation was found between hearing loss and blood cisplatin pharmacokinetics. Platinum levels determined by inductively coupled plasma mass spectrometry were higher than total platinum levels calculated from cisplatin and monohydrated complex concentrations obtained by liquid chromatography analysis.

CONCLUSION

Ototoxicity was unacceptable despite amifostine treatment. Cisplatin pharmacokinetics during the first treatment course were not predictive of hearing loss. Amifostine caused a lowering of dose-normalized area under the concentration-time curve for cisplatin and monohydrated complex. Use of the unselective inductively coupled plasma mass spectrometry analysis leads to an overestimation of active drug. Selective analysis of cisplatin is especially important when evaluating cisplatin pharmacokinetics during chemoprotector treatment.

Impaired hydrolysis of cisplatin derivatives to aquated species prevents energy-dependent uptake in GLC4 cells resistant to cisplatin

It has been widely stated that cisplatin enters cells by passive diffusion, despite some reports supporting a carrier-mediated mechanism. We have determined the rate of uptake of carboplatin (CBDCA), of cisplatin (CDDP) and of aquated forms, at different values of the extracellular pH, in the small lung-cancer cells GLC4 and GLC4/CDDP, cells resistant to CDDP. The rate of CDDP uptake is about 2-fold lower in resistant cells than in sensitive ones; in ATP-depleted cells this rate is about the same for both cell lines. The rate of CBDCA uptake is about 10-fold lower than that of CDDP and is the same in both cell lines independently of the ATP status of the cells. On the other hand, the rate of uptake of the aquated form of CDDP is approximately 40-fold higher than that of CDDP and is the same in both cell lines, but decreases dramatically in ATP-depleted cells. The plot of the initial rate of uptake of the aquated species as a function of its extracellular concentration shows a tendency to be saturable with k(m)=1.9 mM. In conclusion, our data show that, in sensitive GLC4 cells, passive diffusion of CDDP, probably in its neutral dichloro form, and active uptake of the aquated form contribute to the platinum uptake. The active transport of CDDP involves at least two steps: (1). the hydrolysis of the dichloro species in a deficient Cl(-) space at the level of the plasma membrane, which is the limiting step, and (2). the active transport of the aquated species. In resistant cells, step (1). should be deficient whereas step (2). is the same as in sensitive cells. For CBDCA this mechanism holds; however, step (1). is so low that the active transport does not contribute to the uptake of CBDCA by cells.

The chemical reactivity of BNP7787 and its metabolite mesna with the cytostatic agent cisplatin: comparison with the nucleophiles thiosulfate, DDTC, glutathione and its disulfide GSSG

PURPOSE

BNP7787 is a new chemoprotective agent presently under clinical investigation to protect against cisplatin-induced toxicities, especially nephrotoxicity and neurotoxicity. In the kidneys BNP7787 is postulated to undergo selective conversion into mesna, which can locally detoxify cisplatin. The reactivity of cisplatin with this new chemoprotective agent and with its metabolite mesna was investigated at clinically observed plasma concentrations and compared with the nucleophiles thiosulfate (TS) and DDTC, and with the endogenous compounds glutathione (GSH) and oxidized glutathione (GSSG).

METHODS

Reaction kinetics experiments were performed at 37 degrees C and pH 7.4 in the presence of a high chloride concentration (0.15 M). The degradation of cisplatin was measured over time using HPLC with off-line flameless atomic absorption spectrophotometry.

RESULTS

The degradation half-lives of cisplatin (13.5 microM) with 17.2 m M BNP7787, 340 microM mesna and 17.2 m M mesna were 124 min, about 790 min and 73 min, respectively. Cisplatin reacted at least 9.5 times more slowly with 17.2 mM BNP7787 and 5.5 times more slowly with 17.2 mM mesna than with 17.2 mM of the modulating agents DDTC or TS (i.e. half-lives 11 and 13 min, respectively). The half-lives of cisplatin with 17.2 m M GSH and GSSG (i.e. 122 and 115 min, respectively) were comparable with the half-life obtained with BNP7787. The thiol mesna was shown to be a stronger nucleophile than its corresponding disulfide BNP7787.

CONCLUSIONS

The much slower relative reactivity of BNP7787, the short residence of BNP7787 (approximately 2 h) and the much lower concentration of mesna in the circulation following BNP7787 administration precludes chemical inactivation of cisplatin in the circulation, and thus the antitumor activity of cisplatin is maintained.

Activation of p53 by the cytoprotective aminothiol WR1065: DNA-damage-independent pathway and redox-dependent modulation of p53 DNA-binding activity

WR1065 is an aminothiol with selective cytoprotective effects in normal compared to cancer cells, which is used to protect tissues against the damaging effect of radiation and chemotherapeutic drugs. WR1065 has been shown to induce wild-type p53 accumulation and activation in cultured cells, suggesting a role of p53 in cytoprotection. However, the molecular mechanisms by which WR1065 activates p53 remain unclear. Here, we demonstrated that p53 accumulation by WR1065 in MCF-7 cells did not result from the formation of DNA-damage as measured by DNA fragmentation and Comet assay, nor from oxidative stress as detected by measurement of glutathione levels, lipid peroxidation and reactive oxygen species production. p53 activation by WR1065 was not prevented by inhibition of PI-3 kinases, and was still detectable in MCF-7 cells stably transfected with the oncoprotein E6, which repressed p53 induction by DNA damage. These data provided evidence that WR1065 induces p53 by a pathway different than the one elicited by DNA-damage. Direct reduction by WR1065 of key cysteines in p53 may play an important role in this alternative pathway, as shown by the fact that WR1065 activated the redox-dependent, DNA-binding activity of p53 in vitro.

Kinetic study of the reaction of cisplatin with thiols

The reactions of cisplatin [cis-diamminedichloroplatinum(II), CDDP] with glutathione (GSH) and drug thiols were investigated at 37 degrees C in 100 mM Tris-NO(3), pH approximately 7.4, using a clinically relevant concentration of CDDP (33 micro M), a large excess of GSH (16.5 mM), and [NaCl] of 4.62 mM. The conditions were designed to mimic passage of CDDP through the cytosol. The reactions were studied by UV-absorption spectroscopy, high-pressure liquid chromatography (HPLC), and atomic absorption spectroscopy. The initial rates, detected by UV absorbance, confirmed that the reactions are first order in [CDDP]. The HPLC peak corresponding to CDDP was analyzed for platinum content by atomic absorption spectroscopy, which decreased exponentially with time, confirming that the reactions are first order in [CDDP] and allowing determination of the pseudo first order rate constants (k(1)). For reaction of the dichloro form of CDDP with GSH, the k(1) value was approximately 2.2 x 10(-4) s(-1) (t(1/2) of approximately 53 min), giving the second order rate constant value (k(2)) of approximately 1.3 x 10(-2) M(-)1 s(-1). Reaction of a mixture of the aquated forms of CDDP with GSH gave a lower k(1) value ( approximately 0.9 x 10(-4) s(-1)). Reaction of CDDP with sodium 2-mercaptoethanesulfonate (mesna) gave a k(1) value of approximately 1.8 x 10(-4) s(-1) (t(1/2) of approximately 65 min and k(2) of approximately 1.1 x 10(-2) M(-1) s(-1)). Reaction of CDDP with S-2-(3-aminopropylamino)ethanethiol (WR-1065) gave a k(1) value of approximately 12.0 x 10(-4) s(-1) (t(1/2) of approximately 10 min and k(2) of approximately 7.3 x 10(-2) M(-)1 s(-1)). The relatively slow reaction rate of CDDP with GSH is consistent with the efficient DNA platination by CDDP in the presence of millimolar concentration of GSH in the cytosol.

Exploring the role of the radioprotector amifostine in locally advanced non-small cell lung cancer: Radiation Therapy Oncology Group trial 98-01

The ultimate goal of any strategy in oncology is to enhance the therapeutic ratio, defined as tumor cell kill divided by normal tissue injury. Whereas most trials focus on intensifying therapy, this often increases toxicity so that there is no overall gain in the therapeutic ratio. Radiation Therapy Oncology Group (RTOG) trial 98-01, a phase III study testing the ability of a radioprotector (Amifostine [Ethyol, WR-2721]) to reduce the toxicity of an intensive chemoradiation regimen for locally advanced non-small cell lung cancer (NSCLC), is unique in that it addresses both "sides" of this equation. During the 1990s, thoracic radiotherapy (RT) combined with chemotherapy was accepted as a "new" gold standard for patients with good performance status locally advanced/inoperable NSCLC. This paradigm shift away from RT alone has raised several key questions: What is the optimal method of integrating chemotherapy and RT? Equally importantly, how can the toxicity of combined modality strategies be reduced? This article will review the background underlying RTOG 98-01, a trial exploring the potential role of amifostine in NSCLC.

The sulfhydryl containing compounds WR-2721 and glutathione as radio- and chemoprotective agents. A review, indications for use and prospects

Radio- and chemotherapy for the treatment of malignancies are often associated with significant toxicity. One approach to reduce the toxicity is the concomitant treatment with chemoprotective agents. This article reviews two sulfhydryl compounds, namely the agent WR-2721 (amifostine), a compound recently registered for use in human in many countries, and the natural occurring compound glutathione (GSH). GSH is not registered as a chemoprotective agent. WR-2721 is an aminothiol prodrug and has to be converted to the active compound WR-1065 by membrane-bound alkaline phosphatase. WR-1065 and GSH both act as naturally occurring thiols. No protective effect on the tumour has been found when these compounds are administered intravenously. There is even in vitro evidence for an increased anti-tumour effect with mafosfamide after pretreatment with WR-2721, and in vivo after treatment with carboplatin and paclitaxel. Randomized clinical studies have shown that WR-2721 and GSH decrease cisplatin-induced nephrotoxicity and that WR-2721 reduces radiation radiotherapy-induced toxicity. Side-effects associated with WR-2721 are nausea, vomiting and hypotension, GSH has no side-effects. An exact role of WR-2721 and GSH as chemoprotectors is not yet completely clear. Future studies should examine the protective effect of these drugs on mucositis, cardiac toxicity, neuro- and ototoxicity, the development of secondary neoplasms and their effect on quality of life.

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

Amifostine (Ethyol, WR-2721) is in use in the clinic as a protector against platinum-induced toxicities. We have previously reported that amifostine induced a potentiation of the antitumour activity of carboplatin in human ovarian cancer xenografts. An influence of amifostine on the pharmacokinetics of carboplatin, resulting in higher platinum concentrations in plasma and tissues of the tumour-bearing nude mice, was thought to be the cause of enhancement of the antitumour activity. Therefore, the pharmacokinetics of cisplatin were investigated in tumour-bearing nude mice treated with cisplatin alone or in combination with amifostine. A significant increase in the area under the curve (AUC) of the total platinum concentration in mice treated with amifostine was only observed in the kidney (from 355 to 398 nmol h/g), whereas in the other tissues and plasma no significant changes were measured. The selective protection of normal tissues by amifostine was confirmed by a decrease in the AUC of the cisplatin-DNA adduct levels in normal tissues. The decrease was only significant in the liver (282-240 fmol h/microgram DNA), whereas in tumour tissue a slight increase in the AUC of the cisplatin-DNA adducts could be detected (91.3-110.1 fmol h/microgram DNA). The minor influence of amifostine on the pharmacokinetics of cisplatin may be the reason why amifostine did not potentiate the antitumour activity of cisplatin. The influence of amifostine on cisplatin-DNA adduct levels in normal tissues versus tumour tissues is further evidence for the usefulness of this toxicity modulator in cancer patients.

Pharmacokinetics of amifostine and its metabolites in patients

The pharmacokinetics of the cytoprotective agent amifostine (EthyolR; WR 2721) and its main metabolites (WR 1065 and the disulphides) were studied in patients participating in two phase I trials concerning carboplatin or cisplatin in combination with amifostine. Patients were treated with a single dose or three doses of amifostine (740 or 910 mg/m2). The single or first dose was given as a 15 min i.v. infusion just before administration of the chemotherapeutic agent. The additional two infusions were administered 2 and 4 h thereafter. Amifostine was rapidly cleared from the plasma, due to, at least in part, the fast conversion into WR 1065. A biphasic decrease with a final half-life of 0.8 h was observed. The active metabolite WR 1065 was cleared from the plasma with a final half-life of 7.3 +/- 3.6 h. The short initial half-life of WR 1065 can be explained by its fast uptake in tissues and the formation of disulphides. The disulphides were cleared with a final half-life of 8.4-13.4 h and were detectable for at least 24 h after treatment. They may serve as an exchangeable pool of WR 1065. The amifostine peak values at the end of each 15 min infusion did not accumulate in the multiple dosing schedule. For WR 1065 a trend towards an increase in the peak levels was observed [C1,max: 47.5 +/- 11.9 microM, C2,max: 79.0 +/- 13.2 microM, C3,max: 84.8 +/- 15.1 microM, (n = 6)], whereas a trend towards a small decrease was observed for the peak levels of the disulphides [C1,max: 184.2 +/- 12.6 microM, C2,max: 175.0 +/- 23.7 microM, C3,max: 166.0 +/- 17.2 microM, (n = 6)]. This latter finding might suggest a saturation of the disulphide formation or a change in the uptake or elimination of WR 1065, which would result in higher WR 1065 levels in plasma and tissues, after multiple doses of amifostine.

Influence of single and multiple doses of amifostine on the efficacy and the pharmacokinetics of carboplatin in mice

We have previously reported that amifostine potentiates the anti-tumour activity of carboplatin in mice. The present study was carried out in well-established human ovarian cancer xenografts OVCAR-3, A2780 and FMa grown subcutaneously in the nude mouse. It was found that a single dose of amifostine resulted in a higher increase in the anti-tumour activity of carboplatin than three doses of amifostine. A single dose of amifostine increased the AUC (area under the curve) values of total platinum in plasma ultrafiltrate (30.1 vs 18.2 microM x h), liver (307.7 vs 236.4 nmol g(-1) x h), kidney (500.8 vs 368.3 nmol g(-1) x h) and OVCAR-3 tumour tissue (184.0 vs 146.8 nmol g(-1) x h). Despite this increase in total platinum, a decrease in platinum (Pt)-DNA adduct levels was observed in liver, kidney and bone marrow, which was significant in liver. In tumour tissue an insignificant increase in Pt-DNA adduct levels, specifically the Pt-GG adduct, was observed after treatment with a single dose of amifostine, which may explain the increase in anti-tumour activity. The increase in the AUC of total platinum was probably caused by a reduction in body temperature, which was most severe after three doses of amifostine. The extreme hypothermia may be the reason that three doses of amifostine resulted in less potentiation of the efficacy of carboplatin.

MDA435/LCC6 and MDA435/LCC6MDR1: ascites models of human breast cancer

We have established a novel ascites tumour model (MDA435/LCC6) from the oestrogen receptor-negative, invasive and metastatic MDA-MB-435 human breast cancer cell line. MDA435/LCC6 cells grow as both malignant ascites and solid tumours in vivo in nude mice and nude rats, with a tumour incidence of approximately 100%. Untreated mice develop ascites following i.p. inoculation of 1 x 10(6) cells and have a reproducible life span of approximately 30 days, with all animals dying within a 48 h period. The in vivo response of MDA435/LCC6 ascites to several cytotoxic drugs, including doxorubicin, etoposide (VP-16), BCNU and mitomycin C, closely reflects the activity of these single agents in previously untreated breast cancer patients. MDA435/LCC6 cells also retain the anchorage-dependent and anchorage-independent in vitro growth properties of the parental MDA-MB-435 cells, and can be used in standard in vitro drug screening assays. The drug resistance pattern of the MDA435/LCC6 cells suggests that they may have few active endogenous drug resistance mechanisms. To generate a model for the screening of MDR1-reversing agents, MDA435/LCC6 were transduced with a retroviral vector directing the constitutive expression of the MDR1 cDNA, producing a cell line with a classical MDR1 resistance pattern (MDA435/LCC6MDR1). THese ascites models may be a viable alternative to the murine leukaemia ascites (L1210, P388) and, in conjunction with other breast cancer cell lines, facilitate the in vitro and in vivo screening of new cytotoxic drugs and drug combinations.

Carboplatin combined with amifostine, a bone marrow protectant, in the treatment of non-small-cell lung cancer: a randomised phase II study

Amifostine (WR-2721), a thiol compound, has been shown to protect normal tissue from alkylating agents and cisplatin-induced toxicity without loss of anti-tumour effects. To confirm this result, we conducted a phase II randomised trial to determine if the addition of amifostine reduces the toxicity of carboplatin without loss of anti-tumour activity in patients with inoperable non-small-cell lung cancer (NSCLC). After the first course of carboplatin (600 mg m-2 i.v. infusion), 21 patients were randomised to receive three cycles of carboplatin alone (C arm) or three infusions of amifostine at 910 mg m-2 (CA arm) at 28 day intervals. The amifostine was given 20 min before and at 2 and 4 h after carboplatin. Since the 910 mg m-2 amifostine infusion led to hypotension in six patients, the dosage was reduced by 25%, to 683 mg m-2 t.i.d., in the other four patients. Amifostine was well tolerated at this dose level. Five patients in the CA arm and three in the C arm had their planned treatment discontinued owing to progressive disease (n = 3), amifostine side-effects (hypotension, sneezing and sickness, n = 4), and carboplatin-induced thrombocytopenia (n = 1). Bone marrow and renal function at study entry and after the first course of carboplatin before randomisation were similar in both treatment arms. Twenty courses of carboplatin+amifostine have been compared with 25 courses of carboplatin alone. Although there was no statistically significant difference with respect to haematological values comparing both arms, the median time to platelet recovery (> 100 x 10(9) l-1) (13.5 days vs 21 days; P = 0.04) and the need for hospitalisation for i.v. antibiotic and other supportive treatment tended to be reduced in the CA arm (0/20 vs 6/25 patient courses; P = 0.06). Response rates and median survival (14 vs 9 months) were no different, excluding tumour protection activity by amifostine. These results with a small number of patients suggest that amifostine given with carboplatin may reduce the duration of thrombocytopenia and hospitalisation.

Interactions of drugs with the developing kidney

Interactions between drugs and the kidney are necessary for renal drug elimination, metabolism, and occasionally for therapeutic effect. These interactions may result also in renal toxicity. Understanding the kidney's role in drug-handling helps the clinician to be aware of potential drug interactions and toxicity. Drug disposition, elimination, and toxicity may differ with development and are to be considered when prescribing drugs for children. Nephrotoxicity associated with drugs, although common, is usually reversible with discontinuation of the drug; however, when drug therapy with a well-known nephrotoxic drug (e.g., cisplatin) is necessary, pharmacologic modulators may play a role in limiting the associated nephrotoxicity.

HPLC and 31P NMR characterization of the reaction between antitumor platinum agents and the phosphorothioate chemoprotective agent S-2-(3-aminopropylamino)ethylphosphorothioic acid (WR-2721)

In prior studies, we examined the effects of the radioprotective and chemoprotective agent WR-2721 [S-2-(3-aminopropylamino)ethylphosphorothioic acid] on the in vivo biotransformation of the cisplatin [cis-diamminedichloroplatinum(II)] analog ormaplatin [(d,I)trans-1,2-diaminocyclohexanetetrachloroplatinum(IV), Pt(dach)Cl4, (formerly called tetraplatin)]. Those data suggested that a direct interaction between WR-2721 and ormaplatin and/or the corresponding Pt(II) drug, Pt(dach)Cl2, may be occurring in vivo. This would be in contrast to the generally accepted hypothesis that WR-2721 is a prodrug that must first be converted by alkaline phosphatase to a free thiol compound, WR-1065, before any appreciable reactivity would be evident. However, the major biotransformation product observed in the peritoneal fluid, plasma, and all tissues was Pt(dach)(WR-1065). We report here on further investigations into the in vitro reactivity of Pt(dach) compounds with WR-2721 and WR-1065. Separation of reaction products resulting from incubation of Pt(dach)(malonato) with either WR-2721 or WR-1065 under physiological conditions gave profiles that were indistinguishable by reverse phase HPLC and cation exchange HPLC at two different pHs. 31P NMR characterization of the dephosphorylation of WR-2721 revealed essentially no loss of inorganic phosphate for up to 24 hr when incubated in unbuffered water at 30 degrees. In contrast, when incubated with a 1:1 molar ratio of cisplatin under the same conditions, the WR-2721 signal was decreased markedly in the first 5 min, and had disappeared almost completely by 1 hr. The signal corresponding to inorganic phosphate increased in parallel to the decrease in the WR-2721 signal. No intermediate formation of a complex containing both platinum and phosphate could be detected at any time. These data suggest that the reaction between WR-2721 and platinum complexes results in rapid dephosphorylation of WR-2721, and, consequently, that the reaction products formed with either WR-2721 or WR-1065 and Pt(II) complexes are identical.

Characterization of cisplatin-glutathione adducts by liquid chromatography-mass spectrometry. Evidence for their formation in vitro but not in vivo after concomitant administration of cisplatin and glutathione to rats anc cancer patients

After incubation of equimolar amounts of cisplatin (CDDP) and glutathione (GSH) in phosphate buffer pH 7.4 at 37 degrees C, we detected two CDDP-GSH adducts whose structures, characterized by LC-MS, corresponded to cis-[Pt(NH3)2Cl(SG)] and cis-([Pt(NH3)2Cl]2(mu-SG))+. The latter is a new CDDP-GSH adduct, which was postulated but never structurally characterized so far. Rats and patients were given a 15-min intravenous infusion of CDDP (10 mg/kg to rats and 25 mg/m2 to patients) preceded by a GSH intravenous administration (200 mg/kg to rats as a bolus and 1.5 g/m2 to patients as a 15-min infusion). After the administrations, CDDP-GSH adducts were absent in rat and human plasma ultrafiltrates. The discrepancy between in vitro and in vivo findings can be explained based on pharmacokinetic considerations.

Inhibition of the clastogenic effect of cyclophosphamide by WR-2721 in the bone marrow of mice

The frequency of micronucleated polychromatic erythrocytes in the bone marrow of Swiss mice treated with WR-2721, at a dose of 200 mg/kg or 400 mg/kg body weight, 15 or 30 min prior to cyclophosphamide (CP) administration, at a dose of 200 mg/kg body weight, was determined 24 h after CP treatment. In mice injected with CP, the number of micronuclei in polychromatic erythrocytes was significantly increased in comparison with the controls, and in mice treated with WR-2721 and CP, the frequency of micronucleated polychromatic erythrocytes was distinctly decreased in comparison to those given CP alone. The protective effect of WR-2721 against cyclophosphamide-induced clastogenicity was shown. The effect was dependent on the dose of the thiol agent given, and it was more expressed when WR-2721 was applied at the higher dose, 400 mg/kg body weight. However, the protection by the aminothiol appeared not to depend on the time intervals between WR-2721 and CP administration to the mouse organism.

Drug accumulation and DNA platination in cells exposed to aquated cisplatin species

Since CP always exists in aqueous solution as a mixture of native drug and various aqua and hydroxo species, it is conceivable that one or more of these aquated species is the main form of the drug that enters the cell. To test this hypothesis, we examined the accumulation by 2008 human ovarian carcinoma cells of CP and aquated CP in Cl-, deficient medium. After 24 h in 150 mM NaNO3, HPLC analysis indicated that 54% of the platinum in solution was accounted for by aquated species. Immediately following addition of this solution to Cl- deficient RPMI 1640 medium, the initial concentrations of the aqua and hydroxo species were calculated to be 34-2400-fold higher with pre-aquated CP than with native CP. The cellular platinum accumulation, however, was the same under both conditions and was also identical to that of native CP in normal RPMI. To confirm that aquated species were actually entering the cell, the amount of platinum reaching the DNA was determined. The total platinum levels on DNA were 1.9-fold higher when cells were exposed to pre-aquated CP in Cl- deficient medium compared to CP in regular medium. We conclude that 2008 cells do not preferentially transport an aquated form of CP under these conditions compared to native CP.

Effects of the modulating agent WR2721 on myelotoxicity and antitumour activity in carboplatin-treated mice

The selective modulation of carboplatin [diammine(1,1-cyclo-butanedicarboxylato)platinum(II)]-induced myelotoxicity was investigated in mice, using the protective agent WR2721 [S-2-(3-aminopropylamino)ethyl-phosphorothioic acid, ethiofos]. In female BALB/c mice, WR2721 (200 mg/kg intraperitoneally, i.p.) partly prevented the reduction of in vitro proliferation of whole bone marrow cells and non-adherent cells when administered at different time points relative to 90 mg/kg carboplatin (i.p.). Protection was highest when WR2721 was administered 5 min prior to carboplatin. In vitro proliferation of whole bone marrow cells and non-adherent cells in liquid culture increased from 15% of control for carboplatin alone to 45% when WR2721 was administered 5 min prior to carboplatin. However, WR2721 did not significantly prevent the loss in clonogenic capacity of early hematopoietic progenitors in the bone marrow, as determined by a bilayered soft agar colony forming units assay. In nude mice, bearing well-established subcutaneous human ovarian carcinoma xenografts OVCAR-3, WR2721 (200 mg/kg i.p.) 5 min prior to intravenous carboplatin allowed a 1.5-fold increase in the maximum tolerated dose of carboplatin as determined by overall weight loss. WR2721 alone did not affect tumour growth. However, WR2721 had a potentiating effect on the tumour growth inhibition of a standard dose of carboplatin in this model. Minimal tumour volume compared to control (T/C) decreased from 9.4% with carboplatin alone to 2.2% with WR2721 5 min prior to the same dose of carboplatin. Specific growth delay (SGD) increased from 7.4 to 10.3. With the 1.5-fold increased, equitoxic dose of carboplatin in combination with WR2721, the antitumour activity was only slightly further increased (T/C = 1.4%, SGD = 10.5).

Newer insights into cisplatin nephrotoxicity

OBJECTIVE

To review recent advances in the understanding of the mechanisms of cisplatin nephrotoxicity. Factors affecting this toxicity and agents that may protect against it are discussed.

DATA SOURCES

A MEDLINE search was used to identify pertinent literature including reviews. A manual search of bibliographies was performed to include all articles on the subject.

STUDY SELECTION

All available data relating to the mechanisms, modifying factors, and management of cisplatin nephrotoxicity were assessed.

DATA EXTRACTION

As limited human data are available, all animal studies were included. Articles with hypotheses or suggestions not backed by scientific data were excluded from review.

DATA SYNTHESIS

Cisplatin is one of the most effective agents available for treating a variety of solid tumors. Nephrotoxicity is the dose-limiting factor for the use of this drug. Mechanisms for renal toxicity range from definitive histologic changes found in the proximal convoluted tubules to physiologic and biochemical alterations involving a decrease in mitochondrial respiratory function, enzymatic activity in the respiratory chain and glutathione peroxidase, and effects on cellular calcium homeostasis. Important factors related to nephrotoxicity include age, renal irradiation, and concurrent alcohol intake. Agents that appear promising in attenuating the nephrotoxic effects of cisplatin include loading with NaCl solution and/or mannitol, sodium thiosulfate, WR 2721, glutathione, probenecid, and many other compounds under active investigation.

CONCLUSIONS

Cisplatin is a nephrotoxic drug; however, agents that may make cisplatin therapy more safe and rewarding will be available in the near future.

WR2721 as a modulator of cisplatin- and carboplatin-induced side effects in comparison with other chemoprotective agents: a molecular approach

Cisplatin is an active cytostatic that became successful in the treatment of several types of solid tumours after its nephrotoxic potential was controlled by hydration and diuresis. Thiol compounds were tested to reduce further cisplatin-induced nephrotoxicity. Thiosulphate is rapidly excreted by the kidneys and protects against cisplatin-induced nephrotoxicity by inactivating reactive platinum species in the kidney. Due to inactivation of cisplatin in the circulation, thiosulphate also interferes with its antitumour activity. Therefore, it is mainly used in two-route schedules, whereby cisplatin is delivered locally to the tumour (i.p. or i.a.) while systemic (i.v.) thiosulphate protects the kidneys. Diethyldithiocarbamate was shown to protect against cisplatin-induced nephrotoxicity in several animal models by reversing cellular damage. However, in the clinic it has been less successful, partly due to its central nervous system toxicity. The endogenous thiol compounds glutathione and metallothionein have been shown to reduce cisplatin-induced toxicity both in animal models and in clinical trials. However, the results are rather preliminary and a reduction in therapeutic efficacy may be expected, for both glutathione and metallothionein have been reported to be involved in platinum resistance. The thioether methionine has been shown to reduce cisplatin-induced nephrotoxicity in animal models but it has not yet been tested in the clinic. Cisplatin-induced acute emesis can be sufficiently controlled with a new class of 5-hydroxytryptamine-3 (5HT3)-receptor blockers, but delayed emesis remains a problem. High-dose cisplatin regimens with protection of the kidneys induces ototoxicity, peripheral neuropathy and myelotoxicity, which become dose-limiting. Neurotoxicity was partly reversed by the neurogenerative agent ORG2766, but this agent does not reduce other cisplatin-induced toxicities. Therefore, an agent capable of protecting multiple non-tumour tissues is needed. Carboplatin is a second-generation analogue of cisplatin with less nephro-, neuro- and ototoxicity. Carboplatin is at least as active as cisplatin at its maximum tolerated dose, which is defined by its myelotoxicity. Protection from carboplatin-induced myelotoxicity may be controlled by autologous bone marrow transplantation and/or hematopoietic growth factor infusions. High-dose carboplatin schedules may cause nephrotoxicity, neurotoxicity and ototoxicity. Again, the protection of multiple non-tumour tissues is needed. WR2721 appears to be such a modulating agent capable of protecting multiple non-tumour tissues. It was shown to be preferentially metabolized and taken up as the thiol metabolite WR1065 by non-tumour tissues as compared with (hypoxic) solid tumours. It was shown to protect mice from cisplatin-induced nephrotoxicity and from cisplatin- and carboplatin-induced myelotoxicity without interfering with the antitumour activity.(ABSTRACT TRUNCATED AT 400 WORDS)

The reversal of cisplatin-protein interactions by the modulating agent WR2721 and its metabolites WR1065 and WR33278

The reversibility of cisplatin-protein interactions by the modulating agent WR2721, its active thiol-metabolite WR1065, and the symmetrical disulfide WR33278 was studied using the model compounds (Pt(diethylenetriammine) monofunctionally bound to the sulfur in glutathione (Pt(dien)SG) and Pt(diethylenetriammine) monofunctionally bound to the sulfur in S-methylglutathione (Pt(dien)SMeG). Both model compounds could be quantified by high-performance liquid chromatography (HPLC) with UV detection. The Pt-cysteine-like bond in Pt(dien)SG could not be reversed by any of the WR compounds or by the strong nucleophiles thiosulfate (TS) and diethyldithiocarbamate (DDTC). However, the Pt-methionine-like bond in Pt(dien)SMeG could be reversed by WR1065, although the reversal was slow (k2 = 0.142 M-1 s-1) as compared with that obtained using the modulating agents TS (k2 = 10.1 M-1 s-1) and DDTC (k2 = 3.66 M-1 s-1). WR2721 was hardly able to reverse the Pt-S bond in Pt(dien)SMeG (k2 = 0.00529 M-1 s-1), and WR33278 showed no capacity to do so. The activity of cis-diamminedichloroplatinum(II) (CDDP)-inactivated fumarase was not appreciably restored by any of the WR compounds (16%, 7.7%, and 0 for 20 mM WR1065, WR2721, and WR33278, respectively) in contrast to the strong nucleophile DDTC (61% for 2 mM DDTC). These in vitro studies provide information at the molecular level that may explain why WR2721, in contrast to DDTC, does not provide protection against cisplatin-induced nephrotoxicity when it is given after platinum-containing chemotherapy. The results support the present clinical use of WR2721 prior to the administration of platinum compounds.

Effects of the modulating agent WR2721 and its main metabolites on the formation and stability of cisplatin-DNA adducts in vitro in comparison to the effects of thiosulphate and diethyldithiocarbamate

The influence of the modulating agent WR2721, its active thiol-metabolite WR1065 and the symmetrical disulphide WR33278 on the in vitro formation and stability of cis-diamminedichloroplatinum(II) (cisplatin, CDDP)-DNA adducts was investigated and compared with the effects of the highly nucleophilic modulating agents diethyldithiocarbamate (DDTC) and thiosulphate (TS). Salmon sperm DNA (0.5 mg/mL) was incubated with 25 micrograms/mL (83 microM) cisplatin for 1 hr in 50 mM phosphate buffer, pH 7.2 at 37 degrees in the absence or presence of modulating agent. DDTC and TS were potent inhibitors of the platination of the DNA (95 and 89%, respectively, with 4.2 mM of modulating agent). The WR-compounds were also remarkably active in the inhibition of DNA platination. Prevention of adduct formation in the presence of 4.2 mM WR-compound decreased in the order WR1065 (74%) greater than WR33278 (63%) greater than WR2721 (51%). The prevention of CDDP-DNA adduct formation by WR1065 was strongly concentration-dependent up to 4.2 mM but at higher concentrations this protection hardly increased at all. In the presence of the modulating agents, increased levels of CDDP monofunctionally bound to a guanine residue were observed with a simultaneous decrease in the relative abundance of bifunctional adducts. All modulators were also able to reverse part of the CDDP-DNA adducts formed. After a 2-hr incubation of already platinated salmon sperm DNA with 4.2 mM of modulating agent, the removal of Pt from DNA amounted to about 43% with DDTC, 28% with WR1065 and 13-14% with TS, WR2721 and WR33278. Even CDDP bifunctionally bound to two adjacent guanines in the same DNA strand, which is considered to be a very stable adduct, was partly reversed. Our observations suggest that WR2721, especially when administered prior to or concomitantly with CDDP, can be expected to protect those tissues from CDDP-induced damage to DNA that are able to efficiently dephosphorylate WR2721 followed by uptake of the thiol metabolite WR1065. This stresses the importance of a selective formation and uptake of WR1065 by non-tumour tissues for the successful use of WR2721 as a protective agent in combination with platinum-based cancer chemotherapy.

Effect of WR-2721 on the toxicity and antitumor activity of the combination of carboplatin and 5-fluorouracil

We evaluated the effects of WR-2721 on the toxicity and antitumor activity of the combination of 5-fluorouracil (5FU) and carboplatin (CBDCA) in BALB/c and C57B1/6 mice. On a weekly schedule, i.p. injection of 200 mg/kg WR-2721 at 5 min prior to the administration of this combination enabled us to increase the CBDCA dose from a nontoxic level of 45 mg/kg to a normally toxic dose of 60 mg/kg in non-tumor-bearing BALB/c mice while maintaining the 5FU dose at 100 mg/kg. When WR-2721 was given 30 min before this combination, the CBDCA dose could not be increased to 60 mg/kg without producing drug-related deaths. WR-2721 protected against CBDCA- and 5-FU-induced thrombocytopenia but did not prevent leukopenia or anemia in C57B1/6 mice. The antitumor activity of the combination against colon 26 tumors in BALB/c mice was increased by pretreatment with WR-2721, which facilitated elevation of the CBDCA dose to 60 mg/kg in combination with 100 mg/kg 5FU. These results reveal better therapeutic efficacy for the combination of 5FU and CBDCA following pretreatment with WR-2721.