• “In vivo tumor growth inhibition of a mammary carcinoma cell line transfected with shRNA for the progesterone receptor (PR)

LAMB, CAROLINE A.; SALVATIERRA, EDGARDO; LANARI, CLAUDIA; PODHAJCER, OSVALDO

San Diego, EEUU

Congreso; American Association for Cancer Research; 2008

The murine mammary carcinoma cell line (MC4L5) expresses PR. It has a hormone independent pattern of tumor growth as it grows without hormone supply in vivo and in vitro. We used the untransfected cell line (MC4L5-Wt) and stably transfected with the empty vector (MC4L5-pCMV) or with a shRNA that inhibits the mRNA of the PR (MC4L5-O6). In this study we investigated the effect of stably blocking PR on in vitro cell proliferation and on in vivo tumor growth. Stable expression of the shNA inhibited PR expression in 79+-8% as evaluated by Western blot. No significant differences between the three groups were detected in cell proliferation (3H-thymidine uptake) and cell counting assays. On the other hand, significant differences were observed when the three experimental groups were inoculated in female BALB/c mice (1.5x106 cells/mouse). At day 46 post-inocula the cell line MC4L5-Wt had a tumor size of 77.80+-19.83 mm2, the MC4L5-pCMV 66.50+-16.82 mm2 and the MC4L5-O6 9.4+-10.24 mm2 (p<0.001). In two other similar experiments the MC4L5-O6 started to grow and then regressed completely. Lower number of mitosis (Wt: 0.86+-0.09; pCMV: 1.31+-0.10; O6: 0.44+-0.10; p<0.01) and more apoptosis (Wt: 1.47+-0.09; pCMV: 0.88+-0.11; O6: 1.91+-0.43; p<0.05) were observed for the MC4L5-O6 cell line respect to the controls. This data correlated with a weak or absent staining for bromodeoxyuridine. An inhibition in in vivo PR expression was observed by Western blot. The results presented herein demonstrate that PRs are essential for in vivo tumor growth of this cell line, underscoring the idea that PRs are still critical in HI tumor growth. The differences in tumor growth found between the in vivo and the in vitro model indicate that PRs are necessary for tumor formation, for example as an angiogenesis inducer o recruiting tumor stroma, both dispensable in vitro.