Introduction:Colony stimulating factors such as G-CSF modulate proliferation and differentiation of cells in the bone marrow and influence the activation and survival of peripheral leukocytes. However, the effects of G-CSF are not restricted to hematopoietic cells. Several solid tumors like bladder and ovarian carcinoma are known to be stimulated by G-CSF, gallbladder cancer expresses G-CSF receptors.Clinically, recombinant G-CSF is used more and more to overcome neutropenic periods during chemotherapy for cancer. Also, it has been shown to support liver regeneration after partial hepatectomy in mice: Whilst survival with liver regeneration was observed in mice treated with G-CSF after partial hepatectomy extending the critical remnant liver mass of >0.8% of their body weight, untreated mice died of liver failure.Approximately 50% of patients with colorectal cancer (CRC) develop liver metastases, but only 10% of those patients qualify for a curative liver resection for reasons including pattern and anatomic distribution of those metastases.Hence, understanding of G-CSF effects on liver CRC metastasis is mandatory as a first step towards a future clinical application of the observed G-CSF stimulus on liver regeneration. Methods and Results:In 5 CRC cell lines, murine CT26 and human Caco2, SW480, SW620 and DLD1, effects of recombinant G-CSF were determined.Proliferation assays comparing G-CSF challenged cells using AlamarBlue showed a diminished growth compared to placebo. LDH assays were performed to rule out direct toxicity of G-CSF. Immunohistochemistry was used to localize the G-CSF-receptor. Unlike in hematopoietic cells, the receptor in CRC cells was found to be cytoplasmic and not membrane standing.In RT-PCR and Western Blot analysis, a 6-fold upregulation of the G-CSF receptor was detected in G-CSF-treated cells compared to placebo challenged cells.Transwell migration and Matrigel invasion assays simulating conditions in basal membranes showed no difference between G-CSF- and placebo-treated cells (1,2,3,4 and 5 days) permeating the membrane.Similarly, FACS analysis performed to determine cell cycle arrest and apoptosis after stimulation with G-CSF and placebo also showed no difference.Conclusion:In contrast to other malignancies, growth and tumorigenicity of colorectal carcinoma does not seem to be stimulated by G-CSF in vitro. Effects of G-CSF on these cells differ from hematopoietic cells in receptor expression and localization. Further studies are necessary to determine in vivo effects of G-CSF on colorectal cells.