PT  - JOURNAL ARTICLE
AU  - Ismail Kaddour-Djebbar
AU  - Vivek Choudhary
AU  - Vijayabaskar Lakshmikanthan
AU  - Robert Shirley
AU  - Manal El Gaish
AU  - Mohamed Al-Shabrawey
AU  - Belal Al-Husein
AU  - Roger Zhong
AU  - Michael Davis
AU  - Zheng Dong
AU  - Wendy B. Bollag
AU  - M. Vijay Kumar
TI  - Diltiazem Enhances the Apoptotic Effects of Proteasome Inhibitors to Induce Prostate Cancer Cell Death
AID  - 10.1124/jpet.111.188151
DP  - 2012 Jun 01
TA  - Journal of Pharmacology and Experimental Therapeutics
PG  - 646--655
VI  - 341
IP  - 3
4099  - http://jpet.aspetjournals.org/content/341/3/646.short
4100  - http://jpet.aspetjournals.org/content/341/3/646.full
SO  - J Pharmacol Exp Ther2012 Jun 01; 341
AB  - Diltiazem is a calcium channel blocker used to treat cardiovascular ailments. In addition, reports suggest that diltiazem induces cell death, which could make it a drug of choice for the treatment of cancer associated with hypertension. The goal of this research was to determine whether diltiazem is capable of inducing apoptosis in prostate cancer cells, either alone or in combination with the proteasome inhibitors, lactacystin and bortezomib (Velcade). Bortezomib is approved for the treatment of multiple myeloma; unfortunately, it has side effects that limit its utility. Presumably these side effects could be decreased by reducing its dose in combination with another drug. We have previously shown that lactacystin induces apoptosis in LNCaP cells; here, we show that this effect was enhanced by diltiazem. Furthermore, in proteasome inhibitor-resistant DU145 cells, diltiazem alone did not induce apoptosis but decreased cytosolic calcium levels and induced mitochondrial fission; likewise, lactacystin did not induce apoptosis but up-regulated the proapoptotic protein Bik. However, increasing concentrations of diltiazem in combination with lactacystin or bortezomib induced apoptosis in a dose-dependent and synergistic manner. The combination of diltiazem and lactacystin also up-regulated the levels of Bik and released Bak from Bcl-xL, indicating the involvement of the Bcl2 family pathway in this apoptosis. In addition, the drug combination up-regulated GRP78, suggesting also the involvement of endoplasmic reticulum stress in the apoptotic response. Thus, our results demonstrate a potential therapeutic advantage of combining a frequently used calcium channel blocker with proteasome inhibitors in the treatment of prostate cancer.