A Phase I and Pharmacokinetic Study of LY 231514 , the Multitargeted Antifolate

LY231514 is a novel antifolate that principally inhibits thymidylate synthase, but with additional folate-dependent enzyme targets. A Phase I study of single-agent LY231514 administered as a daily i.v. infusion over 10 minutes for 5 days, repeated every 3 weeks, was conducted to evaluate the maximum tolerated dose, pharmacokinetic profile, and antitumor activity of the drug using this schedule. Thirty-eight patients with advanced malignancies that were refractory or not amenable to standard therapy were treated with a total of 1 16 courses of LY231514, escalating treatment doses through 10 dose levels, from 0.2-5.2 mg/m2/day. No objective clinical responses were observed, although minor antitumor activity not fulfilling the response criteria was seen in three patients. A maximum tolerated dose of 4.0 mg/m2/day was determined, with neutropenia as the predominant dose-limiting toxicity. Reversible disturbances of liver biochemistry, fulfilling the protocol definitions of dose-limiting toxicity, were also observed. Other toxicities included diarrhea, mucositis, skin rash, and fatigue. Pharmacokinetic studies were performed at all treatment levels. Analysis showed a linear relation between administered dose and both maximum plasma concentration (Cmax) and area under the plasma concentration/time curve. The drug was cleared with a day 1 total body clearance of 108.9 ± 38.8 mI/minim2, with plasma concentrations declining with a mean harmonic terReceived 5/13/97; revised 12/9/97; accepted 12/19/97. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. 1 To whom requests for reprints should be addressed, at Department of Clinical Oncology, Clatterbridge Centre for Oncology, Wirral, Merseyside L63 4JY, United Kingdom. Phone: 44-151-334-1 155: Fax: 44-151482-7675; E-mail: alecm@ccotrust.co.uk. minal half-life of 1.4 ± 0.98 h. When given by this schedule, LY231514 is tolerable, and Phase II studies are in progress. INTRODUCTION LY23 I S I 4 (N-[4-[2-(2-amino-3,4-dihydro-4-oxo-7Hpyrollo[2,3-d]pyrimidin-5-yl)ethylj-benzoyl]-L-glutamic acid disodium salt) is a novel antifobate with a pyrrole ring replacing the pyrazine ring in the pterine portion of fobic acid, and the benzylic nitrogen in the bridge portion substituted by a methylene group. LY231514 has been developed as an inhibitor of TS2 (I) but also has important secondary enzymatic targets; this feature may confer a therapeutic advantage over other folate analogues. The biochemical locus of LY23 I 5 14 is TS ( 1 , 2), a folatedependent enzyme catalyzing the conversion of dUMP to dTMP, the precursor of the nucleotide dTTP. TS is a twosubstrate enzyme, and this reaction requires the presence of the reduced folate cofactor 5,10-methylenetetrahydrofolate; TS is the only de nova intracellular source of thymidylate. In vitro work has shown that LY23lSl4 also inhibits additional folatedependent enzymes (2) including dihydrofolate reductase and GARFT involved in de novo purine synthesis. Furthermore, end product reversal experiments using the CCRF-CEM human leukemia cell line suggest that these alternative targets are relevant to the cytotoxicity of LY231514, because both thymidine and hypoxanthine are required to circumvent LY23 1514-induced cell death (2). LY231514 gains entry to the cell predominantly via the reduced folate carrier and, once localized intracellularly. is an excellent substrate for polyglutamation by the enzyme folylpolyglutamate synthase. Pentaglutamate forms, the predominant intracellular species, acquire approximately an 80-fold gain in affinity for human TS (K1 glu5 = 1.3 nM; parent compound = 109 nM) and a 140-fold gain in affinity for murine GARFT (K1 glu = 65 nM; parent compound = 9300 nM; Ref. 2). In addition, polyglutamation confers polarity on the molecule, increasing intracellular retention. LY23lSb4 has demonstrated good activity in preclinical model systems, exhibiting potent in vitro cytotoxicity toward the CCRF-CEM human leukemia cell line (IC50 = 7 ng/ml) and, in animal studies, exhibiting growth suppression of the methotrexate-resistant VRC5 and GC3 human colon xenografts by 8094% (1). Animal toxicology has been studied in mice and beagle dogs and is described in more detail elsewhere (3). In mice, the single iv. dose producing death in 50% of animals was greater than 1574 mg/kg, possibly due to this species’ high circulating 2 The abbreviations used are: TS, thymidylate synthase: MTD. maximum tolerated dose: PK. pharmacokinetic: GARFT, glycinamide ribonucleotide formyltransferase: DLI, dose-limiting toxicity: C’FC. Common Toxicity Criteria; AUC. area under the curve: 5-Hi. 5-fluorouracil. Research. on November 11, 2017. © 1998 American Association for Cancer clincancerres.aacrjournals. org Downloaded from Table 1 Patient characteristics Total enrolled 38 Male/female 19/19 Performance status 0 7 2 Median age (range; yr) Prior therapy None Radiotherapy Chemotherapy Tumor types Colorectal Pancreas Melanoma Lung Gall bladder Others 26 5 53 (33-73)