title: Resistance to 6-thioguanine in spontaneously cycling and in mitogen-stimulated human peripheral lymphocytes.
abstract: Spontaneously cycling lymphocytes (in cell division in cultures without addition of phytohemagglutinin, PHA) go through the various phases of the first division with the same kinetics as PHA-stimulated cells. In samples from 10 referents, the frequency of spontaneously cycling lymphocytes varied from 8.9 X 10(-5)-9.5 X 10(-3) as indicated with autoradiography on cells in (S + G2) phase determined by flow sorting. In PHA-stimulated samples from the same persons the frequency of 6-thioguanine (TG)-resistant variants was between 4 X 10(-7) and 2.6 X 10(-6), which indicates that most of the spontaneously cycling cells were TG-sensitive. With lymphocytes from one of the referents it was found that: (i) in the presence of 2 X 10(-4) M TG, more than 97% of the spontaneously cycling cells were inhibited before or in early S phase, and (ii) when a flow cytometer was set to sort out TG-resistant cells in late S + G2 phase after 48 h incubation in medium with PHA, the contribution of TG-resistant cells from the spontaneously cycling fraction amounted to less than 2% of the total number of resistant cells.
mesh_terms: D002453:Cell Cycle / Q000187:drug effects; D002478:Cells, Cultured; D004351:Drug Resistance; D006801:Humans; D008213:Lymphocyte Activation / Q000187:drug effects; D008214:Lymphocytes / Q000187:drug effects / Q000502:physiology*; D010835:Phytohemagglutinins; D013866:Thioguanine / Q000633:toxicity*
chemical_list: D010835:Phytohemagglutinins; D013866:Thioguanine