Toxicity, biodistribution and radioprotective capacity of l-homocysteine thiolactone in CNS tissues and tumors in rodents: comparison with prior results with phosphorothioates

Alexander M. Spence, Janet S. Rasey, Lori Dwyer-Hansen, Zdenka Grunbaum, John Livesey, Lay Chin, Norma Nelson, Donna Stein, Kenneth A. Krohn, Francis Ali-Osman

Research output: Contribution to journalArticlepeer-review

13 Scopus citations

Abstract

l-Homocysteine thiolactone (L-HCTL) was evaluated for its potential as an intravenously-administered central nervous system (CNS) radioprotector in C3H mice and F344 rats. Toxicity assessments in the mouse yielded a LD50 of 297 mg/kg and in the rat 389 mg/kg. Biodistribution studies in tumor-bearing mice showed that brain specimens contained more label at 10 min than the tumors but less at 30 or 60 min. Brain uptake relative to the tumors, the brain/tumor ratio, ranged between 0.5 and 3.3. The cervical spinal cord of non-tumor-bearing rats was irradiated with 32 Gy 137Cs with or without prior treatment with l-HCTL following which the time to forelimb or hindlimb paralysis was measured to determine the relative protective factors (RPFs) for this radiation dose. For forelimb paralysis the RPF was 1.9 (± 1.0, SD) and for hindlimb it was 2.0 (± 1.1, SD). 36B-10 glioma cells irradiated in vitro with or without l-HCTL and assayed for colony forming capacity demonstrated a dose modifying factor (DMF) of only 1.15 (±0.16, SE). Rats bearing intracerebral 36B-10 glioma received 137Cs irradiation with or without l-HCTL after which the tumors were similarly assayed in vitro. From this the glioma DMF was 1.2 (±0.30, SE). Compared to prior results with phosphorothioates our data show that the toxicity of l-HCTL is roughly the same as WR2721, WR77913 and WR3689 and that it distributes at higher levels in the CNS after systemic administration. l-HCTL may well equal these phosphorothioates at protecting normal CNS tissue without requiring administration directly into the cerebrospinal fluid-containing spaces and it does not protect the 36B-10 glioma.

Original languageEnglish (US)
Pages (from-to)216-226
Number of pages11
JournalRadiotherapy and Oncology
Volume35
Issue number3
DOIs
StatePublished - Jun 1995

Keywords

  • Brain neoplasm
  • CNS
  • Phosphorothioate
  • Radioprotection
  • l-Homocysteine thiolactone

ASJC Scopus subject areas

  • Hematology
  • Oncology
  • Radiology Nuclear Medicine and imaging

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