INACCURACY OF ESTIMATIONS OF S PHASE FRACTION BY REDUCTION IN CLONING EFFICIENCY WITH HYDROXYUREA OR TRITIATED THYMIDINE

A. Yen, Caryl Lambek, B. Clarkson

Research output: Contribution to journalArticlepeer-review

2 Scopus citations

Abstract

The current hypothesis, that the fractional reduction of cloning efficiency in semi‐solid culture systems induced by pretreatment of the cells with hydroxyurea (HU) or [3H]TdR equals the fraction of cells initially in S phase, is tested. A lymphoblastoid cell line, SK‐L7, with known cell cycle kinetics was exposed to cytotoxic concentrations of HU or suicidal doses of [3H]TdR and then initiated in semi‐solid and liquid culture. Although approximately 0.6 of the initial population was in S, 1‐hr exposures of HU at concentrations of up to 10‐2 M failed to reduce subsequent cloning efficiency. the 1‐hr exposure to HU did not reduce either the immediate cell number or the gross population doubling rate over 24 hr. A 24‐hr exposure to 10‐3 M HU reduced the cloning efficiency by approximately 98%, confirming the drug's cytotoxic capability. [3H]TdR at doses of 100 μCi/ml for 20–40 min reduced the cloning efficiency by approximately 60 and 70%, respectively. Although no cytotoxicity immediately after exposure was observed in either case, gross population doubling rate in liquid culture was reduced. While HU failed to reduce subsequent cloning efficiency, [3H]TdR reduced cloning efficiency by approximately the fraction of initial cells in S. the above hypothesis, therefore, cannot be applied naïvely as a technique for quantitating the fraction of a clonogenic cell population in S phase.

Original languageEnglish
Pages (from-to)301-308
Number of pages8
JournalCell Proliferation
Volume14
Issue number3
DOIs
StatePublished - May 1981
Externally publishedYes

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