Phase I Clinical and Pharmacological Study of O6-Benzylguanine Followed by Carmustine in Patients with Advanced Cancer1
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Vol. 6, 3025–3031, August 2000 Clinical Cancer Research 3025 Phase I Clinical and Pharmacological Study of O6-Benzylguanine Followed by Carmustine in Patients with Advanced Cancer1 Richard L. Schilsky,2 M. Eileen Dolan,3 dose-limiting toxicity of BG combined with carmustine and Donna Bertucci, Reginald B. Ewesuedo, was cumulative in some patients. The neutrophil nadir oc- Nicholas J. Vogelzang, Sridhar Mani, curred at a median of day 27, with complete recovery in most patients by day 43. Nonhematological toxicity included Lynette R. Wilson, and Mark J. Ratain fatigue, anorexia, increased bilirubin, and transaminase el- Department of Medicine, Section of Hematology-Oncology, Cancer evation. Recommended doses for Phase II testing are 120 Research Center and Committee on Clinical Pharmacology, mg/m2 BG given with carmustine at 40 mg/m2. BG rapidly University of Chicago, Chicago, Illinois 60637 disappeared from plasma and was converted to a major metabolite, O6-benzyl-8-oxoguanine, which has a 2.4-fold ABSTRACT higher maximal concentration and 20-fold higher area un- O6-benzylguanine (BG) is a potent inactivator of the der the concentration versus time curve than BG. AGT DNA repair protein O6-alkylguanine-DNA alkyltransferase activity in peripheral blood mononuclear cells was rapidly (AGT) that enhances sensitivity to nitrosoureas in tumor cell and completely suppressed at all of the BG doses. The rate lines and tumor-bearing animals. The major objectives of of AGT regeneration was more rapid for patients treated this study were to define the optimal modulatory dose and with the lowest dose of BG but was similar for BG doses 2 associated toxicities of benzylguanine administered alone ranging from 20–120 mg/m . In conclusion, coadministra- and in combination with carmustine; to define the maxi- tion of BG and carmustine is feasible in cancer patients, but mally tolerated dose and associated toxicities of carmustine the maximal dose of carmustine that can be safely adminis- administered with benzylguanine and to describe the phar- tered with BG is approximately one-third of the standard macokinetics of BG in humans and its effects on AGT clinical dose. Bone marrow suppression, which may be cu- depletion and recovery in peripheral blood mononuclear mulative, is the dose-limiting toxicity of the combination. cells. Patients with histologically confirmed advanced solid Prolonged AGT suppression is likely attributable primarily 6 tumors or lymphoma that had failed to respond to standard to the effect of O -benzyl-8-oxoguanine. therapy or for which no standard therapy was available were eligible to participate in this study. Patients initially INTRODUCTION received BG as a 1-h i.v. infusion without carmustine. After The DNA repair protein AGT4 (1) plays an important role a 14-day washout (i.e., without therapy) period, patients in the protection of cells from the cytotoxic effects of alkylni- received BG as a 1-h i.v. infusion followed, 1 h later, by a trosoureas and methylating agents. AGT removes adducts from 15-min i.v. infusion of carmustine. Cycles of chemotherapy the O6 position of guanine in DNA through covalent binding of were repeated every 6 weeks. Cohorts of patients received the alkyl group to a cysteine residue on the protein within the BG doses ranging from 10 to 120 mg/m2 and carmustine active site (1). During this process, irreversible inactivation of doses ranging from 13 to 50 mg/m2. Plasma and urine the protein occurs and the synthesis of new protein molecules is samples were collected and analyzed for BG, and O6-benzyl- required to regenerate AGT activity. 8-oxoguanine concentrations and AGT activity was deter- There is an inverse relationship between the level of AGT mined in peripheral blood mononuclear cells. and the sensitivity of tumor cells grown in culture and as There was no toxicity attributable to BG alone at any xenografts to the cytotoxic effects of alkylnitrosoureas (1). dose tested. Bone marrow suppression was the primary and Increased AGT activity has been found in many human solid tumors including colon cancer (2), malignant melanoma (3), lung cancer, gliomas (4, 5), and others (6), and may account for the relative ineffectiveness of nitrosourea therapy in these dis- Received 12/6/99; accepted 2/15/00. eases. Inactivation of AGT leads to an enhancement of the The costs of publication of this article were defrayed in part by the cytotoxic effects of chloroethylnitrosoureas (e.g., carmustine) payment of page charges. This article must therefore be hereby marked and methylating agents (e.g., dacarbazine, temozolomide) in advertisement in accordance with 18 U.S.C. Section 1734 solely to both cell culture and animal tumor xenograft models (7–9). indicate this fact. 1 Supported by USPHS Grants CA14599 (to R. L. S.), CA67098 (to M. E. D.), and CA69852 (to M. J. R.) from the National Cancer Insti- tute, NIH, Bethesda, MD, and by Grant MO1 RR00055 to The General Clinical Research Center, University of Chicago. 4 The abbreviations used are: AGT, O6-alkylguanine-DNA alkyltrans- 2 To whom requests for reprints should be addressed: Division of the ferase; BCNU, bischloronitrosourea, carmustine; BG, O6-benzylgua- Biological Sciences, University of Chicago, 5841 South Maryland nine; MTD, maximally tolerated dose; PBMC, peripheral blood mono- Avenue, MC1000, Chicago, IL 60637. Phone: (773) 834-3914; Fax: nuclear cell; BG max, maximal dose of BG; DLT, dose-limiting (773) 834-3915; E-mail: [email protected]. toxicity; DLCO, carbon monoxide diffusion capacity; AUC, area under 3 Author has disclosed a financial interest in Procept, a company that has the concentration versus time curve; 8-oxo-BG, O6-benzyl-8-oxogua- licensed O6-benzylguanine. nine. 3026 Phase I Trial of Benzylguanine plus Carmustine Therefore, various strategies have been attempted to deplete creatinine level less than 1.7 mg/dl or measured creatinine cells of AGT and thereby increase the sensitivity of tumor cells clearance of at least 60 ml/min. Patients must have been off of to carmustine and related agents. all previous anticancer therapy for at least 4 weeks (6 weeks if Agents that methylate DNA, such as streptozotocin and the previous therapy included mitomycin C or a nitrosourea) and dacarbazine, deplete AGT activity incompletely and produce must have recovered from the toxic effects of any prior therapy. significant clinical toxicity (10). BG, a low-molecular-weight Patients were excluded from the study if they had a significant AGT substrate, binds readily to the same cysteine residue on cardiac, pulmonary, neurological, endocrine, gastrointestinal, AGT that is used for alkyl group transfer and inactivates the rheumatological, dermatological, or allergic disorder that would protein stoichiometrically, requiring micromolar concentrations make administration of the therapy hazardous or would obscure and only minutes of exposure to completely inactivate AGT (11, the interpretation of adverse effects. Pregnant and lactating 12). Once AGT is inactivated, cells become vulnerable to killing women were also excluded, and all of the patients with repro- by nitrosoureas because lesions that are present at the O6 posi- ductive potential were required to use an effective contraceptive tion of guanine cannot be repaired until new AGT synthesis method during treatment and for 2 months after completion of occurs (13–16). There is a strong correlation between the degree treatment if they were sexually active. All of the patients gave of sensitization that can be achieved and the level of AGT written informed consent according to institutional and federal activity in cells, with little or no BG-induced enhancement of guidelines. BCNU cytotoxicity occurring in cells that express low levels of Study Design. The initial goal of the study was to define AGT and the greatest enhancement observed in cells with high the dose of BG that produced maximal AGT suppression in AGT activity (13). BCNU preceded by BG treatment results in human PBMCs without excessive toxicity and to define the time significantly greater growth inhibition of human brain and colon course of this inhibition. Once this dose of BG was defined, tumor xenografts in nude mice compared with that observed in cohorts of patients were to be treated at a fixed dose of BG and animals treated with BCNU alone (8, 17). at increasing doses of BCNU to determine the MTD of BCNU Preclinical toxicology studies in mice and dogs revealed given with BG. Thus, patients who were enrolled in the study BG alone to be nontoxic. When combined with BCNU, bone initially received BG as a 1-h i.v. infusion without BCNU. After marrow toxicity was dose-limiting, and the MTD of BCNU was a 14-day washout period, patients received the assigned dose of 2- to 3-fold lower in mice and 6-fold lower in dogs than in the BG as a 1-h i.v. infusion followed, 1 h later, by a 15-min i.v. absence of BG (18, 19). infusion of BCNU. Cycles of chemotherapy were repeated every On the basis of the strong preclinical evidence that BG 6 weeks as long as the patient’s tumor was stable or responding administration could potentially reverse resistance to alkylnitro- to treatment and the patient did not experience DLT. 2 soureas, we conducted a Phase I study of the combination of BG The starting dose of BG was 10 mg/m . Escalation of the and BCNU in patients with advanced cancer. The major objec- BG dose occurred in increments of 100% until maximal AGT tives of the study were to define the optimal modulatory dose suppression was observed in PBMCs 6 h after dosing or until the and associated acute and cumulative toxicities of BG adminis- appearance of grade 1–2 toxicity attributable to BG. Dose es- tered alone and in combination with BCNU; to define the MTD calation of BG was to continue until AGT suppression of at least and associated acute and cumulative toxicities of BCNU admin- 90% was observed in at least two of three patients in two istered with BG; to determine the time course of AGT depletion successive dose cohorts (BG max).