Purpose: We have previously shown that osteosarcomas have states of increased interstitial fluid pressure (IFP) which correlate with increased proliferation and chemosensitivity. In this study, we hypothesized that constitutively raised IFP in osteosarcomas regulates angiogenesis. Materials and Methods: Sixteen patients with the clinical diagnosis of osteosarcomas underwent blood flow and IFP readings by the wick-in-needle method at the time and location of open biopsy. Vascularity was determined by capillary density in the biopsy specimens. We performed digital image analysis of immunohistochemical staining for CD31, VEGF-A, VEGF-C and TPA on paraffin-embedded tissue blocks of the biopsy samples. Clinical results were validated in a pressurised cell culture system. Results: IFPs in the tumours (mean 33.5 ± SD 17.2 mmHg) were significantly higher (P = 0.00001) than that in normal tissue (2.9 ± 5.7 mmHg). Pressure readings were significantly higher in low vascularity tumours compared to high vascularity tumours (P <0.001). In the osteosarcoma cell lines, growth in a pressurised environment was associated with VEGF-A downregulation, VEGF-C upregulation and TPA upregulation. The reverse was seen in the OB cell lines. Growth in the HUVEC cell line was not significantly inhibited in a pressurised environment. Immunohistochemical assessment for VEGF-A (P = 0.01), VEGF-C (P = 0.008) and TPA (P = 0.0001) translation were consistent with the findings on PCR. Conclusion: Our data suggest that some molecules in angiogenesis are regulated by changes in IFP.
Solid tumours have states of raised interstitial fluid pressure (IFP) that cause significant changes to their physiology.1-3 We have previously shown that human osteosarcomas respond to this raised IFP by increasing their proliferative state. This proliferative state results in increased sensitivity to chemotherapy – a finding noted both in the in vitro setting in osteosarcoma cells grown in a physiologically replicated high pressure environment and the in vivo setting in a series of patients with osteosarcoma who had chemotherapy.1,4
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