A phase I pharmacokinetic and pharmacodynamic study of the DNA methyltransferase 1 inhibitor MG98 administered twice weekly

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Abstract
Background: Hypermethylation and inactivation of tumor suppressor genes by the enzyme DNA methyltransferase may lead to neoplastic transformation. MG98, a phosphorothioate antisense oligodeoxynucleotide that is a specific inhibitor of mRNA for human DNA methyltransferase 1 (DNMT1), was evaluated in a phase I study. Patients and methods: MG98 was given as a 2 h i.v. infusion twice weekly three weeks out of every four to patients with solid tumors. Pharmacokinetic evaluation was performed on days 1 and 15 of cycle 1 and mRNA expression of DNMT1 was measured in peripheral blood mononuclear cells (PBMCs). Results: Nineteen patients were entered onto the study. A total of 74 cycles (range 1–18 cycles) were administered at dose levels from 40 to 480 mg/m2. Dose limiting toxicity was seen in two of three patients at 480 mg/m2 and consisted of a constellation of fever, chills, fatigue and, in one case, confusion beginning within 6 h after the first infusion. Other toxic effects included fatigue, anorexia, nausea, vomiting and diarrhea, reversible elevations in transaminases and partial thromboplastin time. Pharmacokinetic evaluation showed Cmax and AUC to be dose proportional with low inter- and intra-patient variability. No consistent changes in DNMT1 mRNA expression were noted in PBMCs. One partial response was documented in a patient with renal cell carcinoma treated at 80 mg/m2. Conclusions: The recommended dose of MG98 was 360 mg/m2 given by 2 h infusion twice a week for three weeks out of every four. Phase II trials using this dose and schedule are underway.