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

Neuroprotective Role of Selected Antioxidant Agents in Preventing Cisplatin-Induced Damage of Human Neurons In Vitro

Chemotherapy-induced peripheral neuropathy (CIPN) is a side effect of platinum-based chemotherapy and decreases the quality of life of cancer patients. We compared neuroprotective properties of several agents using an in vitro model of terminally differentiated human cells NT2-N derived from cell line NT2/D1. Sodium azide and an active metabolite of amifostine (WR1065) increase cell viability in simultaneous treatment with cisplatin. In addition, WR1065 protects the non-dividing neurons by decreasing cisplatin caused oxidative stress and apoptosis. Accumulation of Pt in cisplatin-treated cells was heterogeneous, but the frequency and concentration of Pt in cells were lowered in the presence of WR1065 as shown by X-ray fluorescence microscopy (XFM). Transition metals accumulation accompanied Pt increase in cells; this effect was equally diminished in the presence of WR1065. To analyze possible chemical modulation of Pt-DNA bonds, we examined the platinum L_III near edge spectrum by X-ray absorption spectroscopy. The spectrum found in cisplatin-DNA samples is altered differently by the addition of either WR1065 or sodium azide. Importantly, a similar change in Pt edge spectra was noted in cells treated with cisplatin and WR1065. Therefore, amifostine should be reconsidered as a candidate for treatments that reduce or prevent CIPN.

Amifostine increases cure rate of cisplatin on ascites hepatoma 22 via selectively protecting renal thioredoxin reductase

It has been demonstrated via in vitro experiments that the anti-cancer drug cisplatin (CDDP) can inactivate thioredoxin reductase (TrxR), a molecular target for cancer therapy. The present study in mice revealed that CDDP at pharmacological doses inhibited TrxR activity in both ascitic hepatoma 22 (H22) cells and kidney, leading to suppression of H22 cells proliferation along with nephrotoxicity. Amifostine, a clinical used cytoprotective agent, protected against CDDP-induced TrxR inactivation in kidney but not in H22 cells. Such an excellent selective modulation of amifostine on TrxR led us to exploit the potential of amifostine in increasing cure rate of CDDP on cancer. In mice, CDDP at the doses of 5 and 7.5 mg/kg once weekly for 4 weeks could not completely control H22 ascites development and the cure rate was no more than 12.5%; CDDP 9 mg/kg by the same schedule prominently suppressed the ascites development, but finally resulted in 87.5% mortality caused by CDDP toxicity. Thus, these dose-dependent therapeutic results well recapitulated the clinical dilemma of chemotherapy on cancer. However, co-treatment of CDDP (9 mg/kg) and amifostine largely reduced CDDP toxicity, and obtained a cure rate as high as 87.5%. Overall, the present study demonstrates both pharmacological and toxicological effects of CDDP involve TrxR inactivation, and the large enhancement on CDDP cure rate in H22 ascites model by using amifostine is, at least in part, ascribed to its selective modulation on TrxR.

Cisplatin interaction with cysteine and methionine, a theoretical DFT study

Interactions of hydrated cisplatin complexes with sulphur-containing amino acids cysteine and methionine were explored. The square-planar cis-[Pt(NH3)2(H2O)X]+ complexes (where X=Cl- and OH-) were chosen as mono- and dihydrated reactants. Calculations using density functional theory (DFT) techniques with B3LYP functional were performed. The isolated molecules and the supermolecular approaches were employed for the determination of the reaction energies. Bond dissociation energies (BDE) were estimated in the model of isolated molecules and supermolecules were used for the determination of the association energies between the two interacting parts. Formation of monodentate complexes by replacing the aqua-ligand with the S, N, and O-sites of both amino acids represents an exothermic process. The highest BDE was found in cysteine structures for the Pt-S coordination. The bonding energy is about 114 kcal/mol, which is comparable with cisplatin-guanine adducts. Analogous BDE for methionine complexes is smaller by about 40 kcal/mol. This correlates well with the known fact that cysteine forms irreversible cisplatin adducts while similar adducts in the methionine case are reversible. The formation of chelate structures is an exothermic reaction only for the hydroxo-form of reactants in the supermolecular approach where additional association interactions between the released water and chelate molecules sufficiently stabilize the final product.

Cytoprotection in Acute Myelogenous Leukemia (AML) therapy

Planning therapy for acute myelogenous leukemia (AML) is difficult because of the heterogeneous nature of the disease and varying patient age at presentation. Cytogenetics and patient age at the time of diagnosis are two major factors determining treatment outcome in AML. Patients with poor-risk cytogenetics have much lower complete remission rates than other groups. In addition, AML in patients greater than 55 to 60 years of age often exhibits a resistant phenotype, more akin to secondary AML or AML arising from myelodysplastic syndromes. This group is also characterized by lower complete remission rates, and often requires the delivery of intensive therapy to a patient population that is the least likely to tolerate it. At the Jefferson Health System (Philadelphia, PA), we wished to develop a regimen that was maximally intensive to treat stubborn disease, but gentle enough to be given to all patients regardless of age. Toward this end, 33 patients received a maximal dose of the cytoprotective agent, amifostine, before each infusion of idarubicin in the "7 + 3" regimen, escalating the dose of idarubicin in a phase I fashion to a maximum dose of 24 mg/m2 . The data indicate that the addition of amifostine to "7 + 3" AML induction therapy enables a substantial escalation of the idarubicin dose through the 21-mg/m2 dose level, without a concomitant increase in side effects, thus providing a regimen that is both intensive and applicable to patients of all ages. Currently, phase II studies are ongoing on a national basis to evaluate the efficacy of this regimen.

Rationale for a phase I/II radiation dose-escalation study with concurrent amifostine (Ethyol) and infusional 5-FU chemotherapy for preoperative treatment of unresectable or locally recurrent rectal carcinoma

Rectal adenocarcinoma almost invariably requires extirpative surgery to be cured. Although radiation therapy and concurrent chemotherapy often will elicit dramatic responses, the treatment morbidity limits the tolerable dose of radiation to about 45 to 50 Gy. Strategies to reduce procto/enteritis may permit higher doses of radiation to be delivered. This report reviews a recently activated radiation dose-escalation study that combines the radioprotector amifostine (Ethyol, WR-2721) with 3-dimensionally planned radiation therapy and concurrent infusional 5-fluorouracil chemotherapy.

Drug interactions in palliative care

PURPOSE

This review of drug interactions in palliative care examines the relevant literature in this area and summarizes the information on interactions of drugs, nutrients, and natural products that are used in the palliative care setting. Particular emphasis is placed on describing the newer information on the cytochrome P450 (CYP) system and the interactions of opioids, antidepressants, and the antitussive, dextromethorphan.

METHODS

We performed a search of the MEDLINE database of the time period from 1966 until April 1998, using medical subject headings such as the names of selective serotonin reuptake inhibitors and other relevant medications in palliative care. Literature reviewed included both human and animal articles as well as non-English literature. Bibliographies of these articles and the personal libraries of several palliative care specialists were reviewed. Software developed by The Medical Letter-The Drug Interaction Program was also used.

RESULTS

Drug interactions can be categorized in several ways. Drug-drug interactions are the most well known and can be kinetic, dynamic, or pharmaceutical. Pharmacokinetic interactions can involve CYP 2D6, which acts on drugs such as codeine and is responsible for its conversion to morphine. Poor metabolizers, either genotypic or due to phenocopying, are at risk for undertreatment if not recognized. Pharmacodynamic interactions with dextromethorphan may produce serotonin syndrome.

CONCLUSION

Drug interactions are important in palliative care as in other aspects of medicine. These interactions are similar to those seen in other areas of medical care but have significant consequences in pain management. Failure to recognize these interactions can lead to either overdosing or undertreatment.

[Chemoprotectors. Mechanisms of action and clinical applications]

Toxicity of chemotherapy remains an important point in the care of patients with malignancies. Since a few years, new compounds without any intrinsic anti tumoral activity have been developed to decrease the toxicity or to enhance the activity of anti-cancer drugs. From those used against the toxic activity of anti-cancer drugs, two classes could be isolated: the chemoprotectors that interact through a specific of chemotherapy in normal cells, and the chemocorrectors that enhance the spontaneous recovery after exposition to cytotoxic drugs. The most widely used chemoprotector remains the 2-mercaptoethanesulfonate (mesna) which protects against the bladder toxicity of ifosfamide and cyclophosphamide. However, two new drugs, amifostine and dextrazoxane have been recently or will be approved in France against the toxicity of cisplatin and anthracyclines, respectively. Mechanism of action and clinical applications of these new drugs in cancer chemotherapy are reviewed.

The preclinical basis for broad-spectrum selective cytoprotection of normal tissues from cytotoxic therapies by amifostine (Ethyol)

Administered prior to cytotoxic chemotherapy or radiation, the aminothiol amifostine provides broad-spectrum cytoprotection of various normal tissues without attenuating antitumour response. The basis for the selectivity of action resides in the anabolism of amifostine at the normal tissue site by membrane-bound alkaline phosphatase. Dephosphorylation to the free thiol, WR-1065, is followed by rapid uptake into normal tissues by a carrier mediated, facilitated diffusion process; in contrast, uptake into tumour tissue is slow to negligible. Preclinical studies have shown that pretreatment with amifostine provides protection of normal tissues from the cytotoxic effects of alkylating agents, organoplatinums, anthracyclines, taxanes and radiation. Normal tissues protected include bone marrow, kidney, neural tissues, the heart, intestinal crypt cells and pulmonary tissues. Additionally, the mutagenic and carcinogenic effects of these modalities are also attenuated. With respect to bone marrow, preclinical studies have shown significant protection of progenitor cells that give rise to the red and white cells and platelets. Comparative in vitro and in vivo studies using murine and human tumour xenografts show no decrease of antitumour effects of these same therapies despite the protection of normal organs. The unique preclinical profile of amifostine serves as a model for the clinical development programme for this important new broad-spectrum cytoprotective agent.

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).

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)

Cytotoxic and cytostatic effects of antitumor agents induced at the plasma membrane level

A variety of antitumor agents inhibit cell proliferation by interacting with the plasma membrane. They act as growth factor antagonists, growth factor receptor blockers, interfere with mitogenic signal transduction or exert direct cytotoxic effects. The P-glycoprotein encoded by the MDR1 gene represents a transmembrane protein which catalyzes the efflux of various antitumor agents. This membrane protein is the target of compounds acting as Multi-Drug Resistance (MDR)-modulators. Finally, several established antitumor agents which are considered to represent DNA-targeted drugs, including anthracyclines, platinum complexes and alkylating agents, cause a variety of membrane lesions. Their contribution to the antitumor activity of these drugs is discussed.