Lentiviral knockdown of HAS3 in OSC1 cells inhibited tumour growth after xenografting of transduced cells into nude mice. (A) Nude mice received subcutaneous injections of 106 OSC1 cells that had been transduced in vitro with a lentivirus containing either scrambled shRNA (control) or shHAS3. Tumour growth as assessed by calliper measurements; mean ± SEM, n = 6 (control), 7 (shHAS3); *, p < 0.05. (B) Representative fpVCT images of mice after 65 days. Average tumour volumes after sacrification of mice at the end of the experiment as measured by fpVCT showed also a significant reduction in tumour volume in the shHAS3 group. (C) H&E revealed changes in tumour morphology strikingly similar to those after 4-MU (compare Figure 2). (D) Tumour stroma was visualised by alpha-smooth muscle actin staining (red). (E) Xenografting shHAS3 tumour cells caused redistributed hyaluronan staining specifically localised to the outer layer of tumour cell clusters. Scale bars, 200 μm. Shown are representative images of n = 6 (control) and n = 7 (shHAS3) experiments.