BU-32: a novel proteasome inhibitor for breast cancer.
BACKGROUND
Proteasome inhibition provides an attractive approach to cancer therapy and may have application in the treatment of breast cancer. However, results of recent clinical trials to evaluate the effect of the proteasome inhibitor Bortezomib (Velcade, also called PS-341) in metastatic breast cancer patients have shown limited activity when used as a single agent. This underscores the need to find new and more efficacious proteasome inhibitors. In this study, we evaluate the efficacy of the novel proteasome inhibitor BU-32 (NSC D750499-S) using in vitro and in vivo breast cancer models.


METHODS
We have recently synthesized a novel proteasome inhibitor (BU-32) and tested its growth inhibitory effects in different breast cancer cells including MCF-7, MDA-MB-231, and SKBR3 by in vitro cytotoxicity and proteasomal inhibition assays. The apoptotic potential of BU32 was tested using flow cytometry and analyzing cell cycle regulatory proteins. In vivo tumor xenograft studies for solid tumor as well as tumor metastasis were conducted using MDA-MB-231-GFP cells.


RESULTS
We report for the first time that BU-32 exhibits strong cytotoxicity in a panel of cell lines: MDA-MB-231 (IC50 = 5.8 nM), SKBR3 (IC50 = 5.7 nM) and MCF-7 cells (IC50 = 5.8 nM). It downregulates a wide array of angiogenic marker genes and upregulates apoptotic markers, including Bid and Bax. Incubation of MDA-MB-231 cells with BU-32 results in the accumulation of cell cycle inhibitor proteins p21 and p27 and stabilization of the tumor suppressor protein p53. Studies in in vivo solid tumor and metastasis models show significant effect with a 0.06 mg/kg dose of BU-32 and marked reduction in tumor burden in the skeleton.


CONCLUSIONS
We have shown that BU-32 is effective in cultured breast cancer cells and in breast cancer xenografts. The results suggest its potential benefit in breast cancer treatment.
Agyin
Joseph K
JK
Department of Biochemistry, University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Drive, San Antonio, TX 78229, USA. agyinj@uthscsa.edu
Santhamma
Bindu
B
Nair
Hareesh B
HB
Roy
Sudipa S
SS
Tekmal
Rajeshwar R
RR
D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D001859:Bone Neoplasms / Q000188:drug therapy / Q000201:enzymology / Q000235:genetics / Q000556:secondary; D001897:Boronic Acids / Q000494:pharmacology; D000069286:Bortezomib; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000201:enzymology / Q000235:genetics / Q000473:pathology; D048708:Cell Growth Processes / Q000187:drug effects; D045744:Cell Line, Tumor; D002918:Chymotrypsin / Q000037:antagonists & inhibitors / Q000378:metabolism; D005260:Female; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D016328:NF-kappa B / Q000096:biosynthesis / Q000235:genetics; D011480:Protease Inhibitors / Q000494:pharmacology*; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D061988:Proteasome Inhibitors; D011719:Pyrazines / Q000494:pharmacology; D011720:Pyrazoles / Q000494:pharmacology*; D023041:Xenograft Model Antitumor Assays
D001897:Boronic Acids; D016328:NF-kappa B; C547394:NSC D750499-S; D011480:Protease Inhibitors; D061988:Proteasome Inhibitors; D011719:Pyrazines; D011720:Pyrazoles; D000069286:Bortezomib; D002918:Chymotrypsin; D046988:Proteasome Endopeptidase Complex