Effects of hematopoietic growth factors on malignant nonhematopoietic cells.

We have assayed modulation of clonal growth of cell lines from human solid tumors in vitro by recombinant human interleukin-6 (rhIL-6), rhIL-3, rh granulocyte-macrophage colony-stimulating factor (GM-CSF), rhG-CSF, rhM-CSF, and rh erythropoietin. Effects of hematopoietic growth factors were also tested in the tritiated thymidine uptake assay. No reproducible and significant modulation of clonal growth was found with rhIL-6, rhM-CSF, and rhEPO. The other cytokines showed stimulation of colony formation in some cell lines from colorectal adenocarcinomas and bladder and lung cancers with the following order of activity: rhIL-3 greater than or equal to rhGM-CSF greater than rhG-CSF. Growth stimulation was only found in clonal assays; it was abolished by neutralizing antibodies and was highly dependent on culture conditions. Stimulation could be masked by elevation of serum concentration and there was an inverse correlation between spontaneous plating efficacy of the control cells and growth stimulation by the factor with the highest activity of the colony-stimulating factor at suboptimal growth conditions. Growth inhibition by the cytokines was not observed. We could not establish autocrine loops for the growth modulation by the cytokines in the cell lines tested so far. Furthermore, we xenotransplanted some responsive cell lines into athymic mice and observed their in vivo growth under systemic application of rhIL-3 and rhGM-CSF or vehicle. There was no significant alteration of the tumor growth by these cytokines at plasma levels sufficient for in vitro growth stimulation. In conclusion, tumor growth stimulation by rhGM-CSF and rhIL-3 as potential hazards for their clinical application in cancer patients in conjunction with cytotoxic chemotherapy is unlikely.