Figure 6

Lapatinib significantly enhances the anti-tumor activity of proteasome inhibitors in vitro and in vivo . (A) Triple-negative MDA-MB-231 and HS-578 T breast cancer cells were pre-treated with 1 μM lapatinib for three days followed by addition or not of 50 nM bortezomib for 48 hours. Protein cleavage of PARP and caspase 3 were then examined by Western blot analysis with anti-PARP and anti-caspase 3 specific antibodies. (B) Triple-negative MDA-MB-231 and HS-578 T breast cancer cells were pre-treated with 1 μM lapatinib or 1 μM gefitinib for three days followed by addition or not of 0.3 μM MG-132 or 50 nM bortezomib for seven days. The cell viability was determined by crystal violet staining. (C,D) MDA-MB-231 cells were injected into the mammary fat pad of SCID mice followed by treatment with lapatinib, bortezomib or lapatinib plus bortezomib, respectively. The growth rate of xenograft tumor was determined by measurement of tumor size (C). The expression of p65 and apoptotic protein Bax in the xenograft tumor in response to these treatments was examined by immunohistochemical staining with anti-p65 and anti-Bax specific antibodies (D). PARP, poly ADP ribose polymerase; SCID, severe combined immunodeficiency.