title: Phase I study of (6R)-5,10-dideazatetrahydrofolate: a folate antimetabolite inhibitory to de novo purine synthesis.
abstract: BACKGROUND
  Cancer chemotherapy with folate antimetabolites has been traditionally targeted at the enzyme dihydrofolate reductase and is based on the requirement of dividing tumor cells for a supply of thymidylate and purines. However, a new compound, 5,10-dideazatetrahydrofolate (DDATHF, whose 6R diastereomer is also known as Lometrexol), has become available that prevents tumor cell growth by inhibiting the first of the folate-dependent enzymes involved in de novo purine synthesis, glycinamide ribonucleotide formyltransferase.
  
  
  OBJECTIVE
  We investigated the toxicity and therapeutic activity of DDATHF in a phase I clinical trial.
  
  
  METHODS
  DDATHF was given at one of the following dose levels to 33 patients (16 females and 17 males) with malignant solid tumors: 3.0 mg/m2 per week (level A) to 10 patients, 4.5 mg/m2 per week (level B) to 13 patients, or 6.0 mg/m2 per week (level C) to 10 patients. Each drug cycle consisted of three weekly injections of DDATHF followed by a 2-week rest prior to redosing in the next cycle.
  
  
  RESULTS
  Of 33 patients, 27 received at least one full cycle of DDATHF. Thrombocytopenia was the major dose-limiting toxicity, and it was severe in one of 10 patients during the first cycle and in two of four patients during the second cycle. Because of cumulative toxicity at 6.0 mg/m2, second or later cycles were abbreviated to two weekly doses. Stomatitis was generally mild, but it was dose-limiting in one patient. Neutropenia was infrequent and mild, and normocytic anemia requiring blood transfusion was common with repeat dosing. Leucovorin was given for grade 2 or greater thrombocytopenia and resulted in hematologic recovery within 1 week in all eight patients so treated. Without leucovorin, the thrombocytopenia lasted from 7 to 49 days in three patients. A partial response was noted in one patient with non-small-cell lung cancer and a minor response in one patient with breast cancer. Three patients with colorectal cancer achieved stable disease for greater than 3 months with improvement in carcinoembryonic antigen levels in one patient.
  
  
  CONCLUSIONS
  DDATHF has an unusual pattern of toxicity with repetitive dosing, and humans with advanced cancer are considerably more sensitive than would be predicted from previous animal studies. Although doses of 6.0 mg/m2 per week on our schedule have been determined to be safe, repeated cycles require careful monitoring because of cumulative toxic effects.
  
  
  CONCLUSIONS
  Additional phase I studies of DDATHF that relate toxicity to folate intake and tissue folate pools appear warranted.
authors.affiliation: Department of Medicine, University of Southern California, Los Angeles.
authors.forename: M S
authors.initials: MS
authors.lastname: Ray
authors.forename: F M
authors.initials: FM
authors.lastname: Muggia
authors.forename: C G
authors.initials: CG
authors.lastname: Leichman
authors.forename: S M
authors.initials: SM
authors.lastname: Grunberg
authors.forename: R L
authors.initials: RL
authors.lastname: Nelson
authors.forename: R W
authors.initials: RW
authors.lastname: Dyke
authors.forename: R G
authors.initials: RG
authors.lastname: Moran
mesh_terms: D000328:Adult; D000368:Aged; D004334:Drug Administration Schedule; D005260:Female; D005493:Folic Acid Antagonists / Q000008:administration & dosage / Q000009:adverse effects / Q000627:therapeutic use*; D006402:Hematologic Diseases / Q000139:chemically induced / Q000188:drug therapy; D006801:Humans; D002955:Leucovorin / Q000627:therapeutic use; D008297:Male; D008875:Middle Aged; D009369:Neoplasms / Q000188:drug therapy; D011687:Purines / Q000378:metabolism; D013763:Tetrahydrofolates / Q000008:administration & dosage / Q000009:adverse effects / Q000627:therapeutic use*; D016896:Treatment Outcome
chemical_list: D005493:Folic Acid Antagonists; D011687:Purines; D013763:Tetrahydrofolates; C045894:lometrexol; D002955:Leucovorin