Abstracts
2000 Digestive Disease Week

# 2290 26S Proteosome Inhibition Induces Apoptosis and Activation of p21Cip1-Waf-1 in Human Pancreatic Cancer.
Shimul A. Shah, Michael W. Potter, Rocco Ricciardi, Kimberly K. Elbirt, Mark P. Callery, Worcester, MA

Intact 26S proteosome activity promotes the transcription of anti-apoptotic genes. New highly selective 26S proteosome inhibitors are becoming available for testing against human malignancies. We examined whether selective inhibition of the 26S proteosome alone alters proliferation and apoptosis in human pancreatic cancer. Methods: BxPC-3 human pancreatic cancer cells were serum starved for 60 hours. Cells were repleted with media containing 10% serum (FCS) alone or combined with the boronic acid inhibitor PS-341 (100nM; Leukosite, Inc., Cambridge, MA). Proliferation was measured by MTT assay. Apoptosis was determined by FACS analysis (sub-G0 peak) and nuclear morphology (Pap stain). Data were compared by two-tailed t-test (*p<0.05). Activation of caspase-3 and p21Cip1-Waf-1 by 100nM PS-341 were determined by Western blot. Results: Proteosome inhibition with PS-341 significantly blocked mitogen (FCS) induced BxPC-3 cell proliferation. PS-341 alone caused apoptosis to occur as indicated by FACS analysis and nuclear morphology. This corresponds with activation of p21 within 3 hours (Fig), and subsequent activation of caspase-3 within 12 hours (Western not shown). Conclusions: In BxPC-3 pancreatic cancer cells, targeted inhibition (PS- 341) of the 26S proteosome alone blocks proliferation and induces apoptosis as pro-apoptotic kinases become activated. These novel findings support further study of 26S proteosome inhibition in the therapy of human pancreatic cancer.