P38 MAP Kinase inhibition promotes primary tumour growth via VEGF independent mechanism

Background: The surgical insult induces an inflammatory response that activates P38 MAP kinases and solid tumours can also release cytokines. Therfore inhibition of these pathways may reduce tumour growth We set out to examine the effects of P38-MAPK inhibition on apoptosis, proliferation, VEGF release and cell cycle effects in-vitro and on primary tumour growth in-vivo. Methods: 4T-1 cells (2 x 10(5)cells/well) were incubated, in 24 well plates with control, 25, 50 or 100 ng/ml of SB-202190 for 24 hours. Cells were subsequently asessed for apoptosis, proliferation, VEGF release and cell cycle analysis. Balb-c mice each received 1 x 10(6) 4T1 cells subcutaneously in the flank and were then randomised to receive control or SB202190 (2.5 mu M/kg) by intraperitoneal injection daily. Tumour size was measured alternate days and at day 24 animals were sacrificed and serum VEGF assessed. Results: P38-MAPK inhibition in-vitro resulted in a significant reduction in proliferation (75.2 +/- 8.4% vs. 100 +/- 4.3%, p < 0.05) and G(1) cell cycle phase(35.9 +/- 1.1% vs. 32.5 +/- 0.6%, p < 0.05) but no significant changes in apoptosis or VEGF levels. In-vivo, P38-MAPK inhibition resulted in an increase in primary tumour growth (155.6 +/- 34.9 vs. 86.7 +/- 18.2 mm(3), p < 0.05). P38-MAPK inhibition also lowered circulating VEGF levels but this difference was not significant (101.9 +/- 27.1 eta g/ml compared to 158.6 +/- 27.1 eta g/ml) Conclusion: These findings demonstrate that P38- MAPK inhibition in-vitro reduces proliferation and G1 cell cycle phase as well as promoting primary tumour growth in-vivo. These effects would appear to be independent of VEGF.