Induction of white cell proliferation due to haematopoietic growth factors is associated with an increase in multiple forms of dihydrofolate reductase in non-neutropenic cancer patients

OBJECTIVE: Granulocyte-colony stimulating factor [G-CSF] and granulocyte macrophage-colony stimulating factor [GM-CSF] are frequently used in cancer patients to overcome the granulocytopenic effects of chemotherapy, and also to mobilize the stem cells. The mobilized stem cells are collected from the peripheral blood and used for transplantation following high doses of chemotherapy. However, the molecular mechanism by which these colony stimulating factors [CSFs] bring about proliferation of myeloid precursor cells is not clearly known. Dihydrofolate reductase [DHFR], which has an established role in DNA synthesis, could be a link between administration of CSF and stem cell proliferation. The purpose of this study was to investigate whether CSFs induce white cell proliferation by producing multiple forms of DHFR. METHODS: Twelve patients with non-haematological malignancies were treated with either G-CSF or GM-CSF to mobilize stem cells. Nine healthy subjects were treated with placebo as controls. Blood samples were obtained before and after stimulation with CSFs or placebo. White blood cells were separated and concentrations of both active DHFR and immunoreactive nonfunctional form of DHFR were determined in their cytoplasm using methotrexate-binding assay and enzyme-linked immunosorbent assay, respectively. Total leucocytes count [TLC] was also monitored before and after stimulation with CSFs or placebo. There was a significant [P < 0.05] increase in concentration of immunoreactive nonfunctional form of DHFR and TLC following stimulation with CSFs. There was an increase in concentration of active DHFR as well, however, this did not reach statistical significance. In the placebo-treated subjects, no significant increase in active DHFR, immunoreactive nonfunctional form of enzyme or TLC was observed. However, it was noticed that the base-line values of active DHFR and immunoreactive nonfunctional form of enzyme in leucocytes of cancer patients were higher than the base-line values in leukocytes of normal healthy subjects. Our data suggest that colony stimulating factors induce white cell proliferation by increasing levels of multiple forms of DHFR

effect of theophylline on the production of colony stimulating factor [CSF] by the lung

The effect of theophylline on colony stimulating factor production by the lung tissue was investigated. Addition of various concentrations of theophylline to the lung conditioned medium enhanced CSF production at 10 .microg/ml and at higher concentrations showed an inhibitory effect. Determination of the phosphate content of the medium showed a decrease at 1-3 hours of incubation. Addition of AMP to the cultures in the presence of theophylline had no effect on the CSF production but compensated phosphate content of the lung cultures. Exogenous cAMP or its dibutyryl derivative also stimulated CSF production. On the other hand IBMX, another inhibitor of phosphodiesterases, exerted similar effect as theophylline. The results suggest that cAMP regulates CSF production by the lung