Cytosine arabinoside does not cause differentiation in vitro of CFU-GM in marrow from normal, myelodysplastic or ANLL subjects

The effect of rh-cytokines on the sensitivity of normal human CFU-GM progenitors to Ara-C and on the S-phase activity of light density human bone marrow cells

This study examines the effect of pre-incubation in liquid phase of normal human CFU-GM progenitors with recombinant human (rh) cytokines prior to exposure to cytosine arabinoside (Ara-C) in clonogenic culture. Light density marrow cells (LMDCs) were preincubated in Biorich (chemically defined serum-free complete medium) with G + GM-CSF or IL-3 prior to semi-solid culture with Ara-C (10(-4) M-10(-12) M). Cell cycle analysis was performed by flow cytometry pre- and post-rh-cytokine treatment. Data from 26 normal marrows studied clonogenically, demonstrated a 60% reduction in CFU-GM with 10(-4) M Ara-C. Preincubation in Biorich medium with the addition of G + GM-CSF or IL-3 caused a significant enhancement of sensitivity to Ara-C across the dose curve. Biorich medium alone had an apparent protective effect resulting in amelioration of the cytotoxic effect of Ara-C. Cell cycle analysis of eight subjects showed significant recruitment into S-phase following pre-treatment with cytokines. A reduction in S-phase activity was noted in cells pre-incubated in Biorich alone. In summary, it would appear that cytokines can enhance the sensitivity of normal CFU-GM to Ara-C in vitro possibly due to an increase in S-phase activity. Pre-incubation in nutrient medium without cytokines resulted in cell quiescence.