Sensitization of U937 leukemia cells to doxorubicin by the MG132 proteasome inhibitor induces an increase in apoptosis by suppressing NF-kappa B and mitochondrial membrane potential loss

Cancer Cell International

Georgina Hernández-Flores²  Paulina Gómez-Lomelí⁵  Ruth De Célis²  Oscar González-Ramella⁴  Jorge Ramiro Domínguez-Rodríguez¹  Adriana Aguilar-Lemarroy²  Luis Felipe Jave-Suárez²  José Manuel Lerma-Díaz³  Alejandro Bravo-Cuellar³  Pablo César Ortiz-Lazareno² 

[1] Departamento de Farmacobiología, Centro Universitario de Ciencias Exactas e Ingeniería, UdeG, Jalisco, México;División de Inmunología, Centro de Investigación Biomédica de Occidente (CIBO), Instituto Mexicano del Seguro Social (IMSS), Guadalajara, Jalisco, México;Centro Universitario de los Altos, Universidad de Guadalajara (UdeG), Tepatitlán de Morelos, Jalisco, México;Servicio de Hemato-Oncología Pediatría, OPD Hospital Civil Juan I. Menchaca, Guadalajara, Jalisco, México;Programa de Doctorado en Ciencias Biomédicas Orientación Inmunología, Centro Universitario de Ciencias de la Salud, UdeG, Jalisco, México

关键词: Leukemia;    Doxorubicin;    MG132;    Senescence;    Mitochondrial dysfunction;    Caspase activation;    NF-кB;    Apoptosis;   

Others  :  792365
DOI  :  10.1186/1475-2867-14-13

 received in 2013-07-06, accepted in 2014-01-21,  发布年份 2014

【 摘 要 】

Background

The resistance of cancerous cells to chemotherapy remains the main limitation for cancer treatment at present. Doxorubicin (DOX) is a potent antitumor drug that activates the ubiquitin-proteasome system, but unfortunately it also activates the Nuclear factor kappa B (NF-кB) pathway leading to the promotion of tumor cell survival. MG132 is a drug that inhibits I kappa B degradation by the proteasome-avoiding activation of NF-кB. In this work, we studied the sensitizing effect of the MG132 proteasome inhibitor on the antitumor activity of DOX.

Methods

U937 human leukemia cells were treated with MG132, DOX, or both drugs. We evaluated proliferation, viability, apoptosis, caspase-3, -8, and −9 activity and cleavage, cytochrome c release, mitochondrial membrane potential, the Bcl-2 and Bcl-XL antiapoptotic proteins, senescence, p65 phosphorylation, and pro- and antiapoptotic genes.

Results

The greatest apoptosis percentage in U937 cells was obtained with a combination of MG132 + DOX. Likewise, employing both drugs, we observed a decrease in tumor cell proliferation and important caspase-3 activation, as well as mitochondrial membrane potential loss. Therefore, MG132 decreases senescence, p65 phosphorylation, and the DOX-induced Bcl-2 antiapoptotic protein. The MG132 + DOX treatment induced upregulation of proapoptotic genes BAX, DIABLO, NOXA, DR4, and FAS. It also induced downregulation of the antiapoptotic genes BCL-XL and SURVIVIN.

Conclusion

MG132 sensitizes U937 leukemia cells to DOX-induced apoptosis, increasing its anti-leukemic effectiveness.

【 授权许可】

   
2014 Ortiz-Lazareno et al.; licensee BioMed Central Ltd.

【 图 表 】

Figure 1.

Figure 2.

Figure 3.

Figure 4.

Figure 5.

Figure 6.

Figure 7.

【 参考文献 】

• [1]Kaatsch P: Epidemiology of childhood cancer. Cancer Treat Rev 2010, 36(4):277-285.
• [2]Terracini B: Epidemiology of childhood cancer. Environ Health 2011, 10 Suppl 1:S8.
• [3]Liu J, Yang C, Simpson C, Deryckere D, Van Deusen A, Miley MJ, Kireev D, Norris-Drouin J, Sather S, Hunter D, et al.: Discovery of novel small molecule mer kinase inhibitors for the treatment of pediatric acute lymphoblastic leukemia. ACS Med Chem Lett 2012, 3(2):129-134.
• [4]Pramanik D, Campbell NR, Das S, Gupta S, Chenna V, Bisht S, Sysa-Shah P, Bedja D, Karikari C, Steenbergen C, et al.: A composite polymer nanoparticle overcomes multidrug resistance and ameliorates doxorubicin-associated cardiomyopathy. Oncotarget 2012, 3(6):640-650.
• [5]Osman AM, Al-Harthi SE, Alarabi OM, Elshal MF, Ramadan WS, Alaama MN, Al-Kreathy HM, Damanhouri ZA, Osman OH: Chemosensetizing and cardioprotective effects of resveratrol in doxorubicin- treated animals. Cancer Cell Int 2013, 13(1):52. BioMed Central Full Text
• [6]Osman AM, Bayoumi HM, Al-Harthi SE, Damanhouri ZA, Elshal MF: Modulation of doxorubicin cytotoxicity by resveratrol in a human breast cancer cell line. Cancer Cell Int 2012, 12(1):47. BioMed Central Full Text
• [7]Lerma-Diaz JM, Hernandez-Flores G, Dominguez-Rodriguez JR, Ortiz-Lazareno PC, Gomez-Contreras P, Cervantes-Munguia R, Scott-Algara D, Aguilar-Lemarroy A, Jave-Suarez LF, Bravo-Cuellar A: In vivo and in vitro sensitization of leukemic cells to adriamycin-induced apoptosis by pentoxifylline. Involvement of caspase cascades and IkappaBalpha phosphorylation. Immunol Lett 2006, 103(2):149-158.
• [8]Harati K, Chromik AM, Bulut D, Goertz O, Hahn S, Hirsch T, Klein-Hitpass L, Lehnhardt M, Uhl W, Daigeler A: TRAIL and taurolidine enhance the anticancer activity of doxorubicin, trabectedin and mafosfamide in HT1080 human fibrosarcoma cells. Anticancer Res 2012, 32(7):2967-2984.
• [9]Du BY, Song W, Bai L, Shen Y, Miao SY, Wang LF: Synergistic effects of combination treatment with bortezomib and doxorubicin in human neuroblastoma cell lines. Chemotherapy 2012, 58(1):44-51.
• [10]Cuellar AB, Algara DS, Metzger G, Orbach-Arbouys S: Enhanced activity of mouse peritoneal cells after aclacinomycin administration. Cancer Res 1987, 47(13):3477-3484.
• [11]Liu J, Zheng H, Tang M, Ryu YC, Wang X: A therapeutic dose of doxorubicin activates ubiquitin-proteasome system-mediated proteolysis by acting on both the ubiquitination apparatus and proteasome. Am J Physiol Heart Circ Physiol 2008, 295(6):H2541-H2550.
• [12]DiDonato JA, Mercurio F, Karin M: NF-kappaB and the link between inflammation and cancer. Immunol Rev 2012, 246(1):379-400.
• [13]Mantovani A: Molecular pathways linking inflammation and cancer. Curr Mol Med 2010, 10(4):369-373.
• [14]Park HS, Jun do Y, Han CR, Woo HJ, Kim YH: Proteasome inhibitor MG132-induced apoptosis via ER stress-mediated apoptotic pathway and its potentiation by protein tyrosine kinase p56lck in human Jurkat T cells. Biochem Pharmacol 2011, 82(9):1110-1125.
• [15]Chen D, Dou QP: The ubiquitin-proteasome system as a prospective molecular target for cancer treatment and prevention. Curr Protein Pept Sci 2010, 11(6):459-470.
• [16]Fournier MJ, Gareau C, Mazroui R: The chemotherapeutic agent bortezomib induces the formation of stress granules. Cancer Cell Int 2010, 10:12. BioMed Central Full Text
• [17]Ortiz-Lazareno PC, Hernandez-Flores G, Dominguez-Rodriguez JR, Lerma-Diaz JM, Jave-Suarez LF, Aguilar-Lemarroy A, Gomez-Contreras PC, Scott-Algara D, Bravo-Cuellar A: MG132 proteasome inhibitor modulates proinflammatory cytokines production and expression of their receptors in U937 cells: involvement of nuclear factor-kappaB and activator protein-1. Immunology 2008, 124(4):534-541.
• [18]Montagut C, Tusquets I, Ferrer B, Corominas JM, Bellosillo B, Campas C, Suarez M, Fabregat X, Campo E, Gascon P, et al.: Activation of nuclear factor-kappa B is linked to resistance to neoadjuvant chemotherapy in breast cancer patients. Endocr Relat Cancer 2006, 13(2):607-616.
• [19]Izzo JG, Malhotra U, Wu TT, Ensor J, Luthra R, Lee JH, Swisher SG, Liao Z, Chao KS, Hittelman WN, et al.: Association of activated transcription factor nuclear factor kappab with chemoradiation resistance and poor outcome in esophageal carcinoma. J Clin Oncol 2006, 24(5):748-754.
• [20]Aranovich A, Liu Q, Collins T, Geng F, Dixit S, Leber B, Andrews DW: Differences in the mechanisms of proapoptotic BH3 proteins binding to Bcl-XL and Bcl-2 quantified in live MCF-7 cells. Mol Cell 2012, 45(6):754-763.
• [21]Oiso S, Ikeda R, Nakamura K, Takeda Y, Akiyama S, Kariyazono H: Involvement of NF-kappaB activation in the cisplatin resistance of human epidermoid carcinoma KCP-4 cells. Oncol Rep 2012, 28(1):27-32.
• [22]Reed JC: Bcl-2-family proteins and hematologic malignancies: history and future prospects. Blood 2008, 111(7):3322-3330.
• [23]Bao L, Haque A, Jackson K, Hazari S, Moroz K, Jetly R, Dash S: Increased expression of P-glycoprotein is associated with doxorubicin chemoresistance in the metastatic 4T1 breast cancer model. Am J Pathol 2011, 178(2):838-852.
• [24]Naci D, El Azreq MA, Chetoui N, Lauden L, Sigaux F, Charron D, Al-Daccak R, Aoudjit F: alpha2beta1 integrin promotes chemoresistance against doxorubicin in cancer cells through extracellular signal-regulated kinase (ERK). J Biol Chem 2012, 287(21):17065-17076.
• [25]Steppan I, Reimer D, Sevelda U, Ulmer H, Marth C, Zeimet AG: Treatment of recurrent platinum-resistant ovarian cancer with pegylated liposomal doxorubicin–an evaluation of the therapeutic index with special emphasis on cardiac toxicity. Chemotherapy 2009, 55(6):391-398.
• [26]Gewirtz DA, Holt SE, Elmore LW: Accelerated senescence: an emerging role in tumor cell response to chemotherapy and radiation. Biochem Pharmacol 2008, 76(8):947-957.
• [27]Tsirpanlis G: Cellular senescence and inflammation: a noteworthy link. Blood Purif 2009, 28(1):12-14.
• [28]Ewald JA, Desotelle JA, Wilding G, Jarrard DF: Therapy-induced senescence in cancer. J Natl Cancer Inst 2010, 102(20):1536-1546.
• [29]Saretzki G: Cellular senescence in the development and treatment of cancer. Curr Pharm Des 2010, 16(1):79-100.
• [30]Leontieva OV, Natarajan V, Demidenko ZN, Burdelya LG, Gudkov AV, Blagosklonny MV: Hypoxia suppresses conversion from proliferative arrest to cellular senescence. Proc Natl Acad Sci U S A 2012, 109(33):13314-13318.
• [31]Cavaliere V, Papademetrio DL, Lorenzetti M, Valva P, Preciado MV, Gargallo P, Larripa I, Monreal MB, Pardo ML, Hajos SE, et al.: Caffeic acid phenylethyl ester and MG-132 have apoptotic and antiproliferative effects on leukemic cells but not on normal mononuclear cells. Transl Oncol 2009, 2(1):46-58.
• [32]Naujokat C, Sezer O, Zinke H, Leclere A, Hauptmann S, Possinger K: Proteasome inhibitors induced caspase-dependent apoptosis and accumulation of p21WAF1/Cip1 in human immature leukemic cells. Eur J Haematol 2000, 65(4):221-236.
• [33]Goldberg AL: Functions of the proteasome: from protein degradation and immune surveillance to cancer therapy. Biochem Soc Trans 2007, 35(Pt 1):12-17.
• [34]Chen D, Frezza M, Schmitt S, Kanwar J, Dou QP: Bortezomib as the first proteasome inhibitor anticancer drug: current status and future perspectives. Curr Cancer Drug Targets 2011, 11(3):239-253.
• [35]Chauhan D, Anderson KC: Proteasome inhibition, the pursuit of new cancer therapeutics, and the adaptor molecule p130Cas. BMC Biol 2011, 9:72. BioMed Central Full Text
• [36]Yang F, Teves SS, Kemp CJ, Henikoff S: Doxorubicin, DNA torsion, and chromatin dynamics. Biochim Biophys Acta 2013, 1845(1):84-89.
• [37]Wang S, Konorev EA, Kotamraju S, Joseph J, Kalivendi S, Kalyanaraman B: Doxorubicin induces apoptosis in normal and tumor cells via distinctly different mechanisms. Intermediacy of H(2)O(2)- and p53-dependent pathways. J Biol Chem 2004, 279(24):25535-25543.
• [38]Suzuki F, Hashimoto K, Kikuchi H, Nishikawa H, Matsumoto H, Shimada J, Kawase M, Sunaga K, Tsuda T, Satoh K, et al.: Induction of tumor-specific cytotoxicity and apoptosis by doxorubicin. Anticancer Res 2005, 25(2A):887-893.
• [39]Lipshultz SE, Miller TL, Scully RE, Lipsitz SR, Rifai N, Silverman LB, Colan SD, Neuberg DS, Dahlberg SE, Henkel JM, et al.: Changes in cardiac biomarkers during doxorubicin treatment of pediatric patients with high-risk acute lymphoblastic leukemia: associations with long-term echocardiographic outcomes. J Clin Oncol 2012, 30(10):1042-1049.
• [40]Pang B, Qiao X, Janssen L, Velds A, Groothuis T, Kerkhoven R, Nieuwland M, Ovaa H, Rottenberg S, van Tellingen O, et al.: Drug-induced histone eviction from open chromatin contributes to the chemotherapeutic effects of doxorubicin. Nat Commun 1908, 2013:4.
• [41]Denard B, Lee C, Ye J: Doxorubicin blocks proliferation of cancer cells through proteolytic activation of CREB3L1. eLife 2012, 1:e00090.
• [42]Vantus T, Vertommen D, Saelens X, Rykx A, De Kimpe L, Vancauwenbergh S, Mikhalap S, Waelkens E, Keri G, Seufferlein T, et al.: Doxorubicin-induced activation of protein kinase D1 through caspase-mediated proteolytic cleavage: identification of two cleavage sites by microsequencing. Cell Signal 2004, 16(6):703-709.
• [43]Tao Z, Goodisman J, Penefsky HS, Souid AK: Caspase activation by anticancer drugs: the caspase storm. Mol Pharm 2007, 4(4):583-595.
• [44]Han YH, Moon HJ, You BR, Park WH: The effect of MG132, a proteasome inhibitor on HeLa cells in relation to cell growth, reactive oxygen species and GSH. Oncol Rep 2009, 22(1):215-221.
• [45]Van Geelen CM, Pennarun B, Ek WB, Le PT, Spierings DC, De Vries EG, De Jong S: Downregulation of active caspase 8 as a mechanism of acquired TRAIL resistance in mismatch repair-proficient colon carcinoma cell lines. Int J Oncol 2010, 37(4):1031-1041.
• [46]Gamen S, Anel A, Perez-Galan P, Lasierra P, Johnson D, Pineiro A, Naval J: Doxorubicin treatment activates a Z-VAD-sensitive caspase, which causes deltapsim loss, caspase-9 activity, and apoptosis in Jurkat cells. Exp Cell Res 2000, 258(1):223-235.
• [47]Bagriacik EU, Uslu K, Yurtcu E, Stefek M, Karasu C: Stobadine inhibits doxorubicin-induced apoptosis through a caspase-9 dependent pathway in P815 mastocytoma cells. Cell Biol Int 2007, 31(9):979-984.
• [48]Fulda S, Galluzzi L, Kroemer G: Targeting mitochondria for cancer therapy. Nat Rev Drug Discov 2010, 9(6):447-464.
• [49]Holmuhamedov E, Lewis L, Bienengraeber M, Holmuhamedova M, Jahangir A, Terzic A: Suppression of human tumor cell proliferation through mitochondrial targeting. FASEB J 2002, 16(9):1010-1016.
• [50]Bonnet S, Archer SL, Allalunis-Turner J, Haromy A, Beaulieu C, Thompson R, Lee CT, Lopaschuk GD, Puttagunta L, Bonnet S, et al.: A mitochondria-K + channel axis is suppressed in cancer and its normalization promotes apoptosis and inhibits cancer growth. Cancer Cell 2007, 11(1):37-51.
• [51]Heerdt BG, Houston MA, Augenlicht LH: The intrinsic mitochondrial membrane potential of colonic carcinoma cells is linked to the probability of tumor progression. Cancer Res 2005, 65(21):9861-9867.
• [52]Gogvadze V, Orrenius S, Zhivotovsky B: Mitochondria in cancer cells: what is so special about them? Trends Cell Biol 2008, 18(4):165-173.
• [53]Takahashi A, Ohtani N, Hara E: Irreversibility of cellular senescence: dual roles of p16INK4a/Rb-pathway in cell cycle control. Cell Div 2007, 2:10. BioMed Central Full Text
• [54]Grimes A, Chandra SB: Significance of cellular senescence in aging and cancer. Cancer Res Treat 2009, 41(4):187-195.
• [55]Coppe JP, Desprez PY, Krtolica A, Campisi J: The senescence-associated secretory phenotype: the dark side of tumor suppression. Annu Rev Pathol 2010, 5:99-118.
• [56]Krtolica A, Parrinello S, Lockett S, Desprez PY, Campisi J: Senescent fibroblasts promote epithelial cell growth and tumorigenesis: a link between cancer and aging. Proc Natl Acad Sci U S A 2001, 98(21):12072-12077.
• [57]Rodier F, Campisi J: Four faces of cellular senescence. J Cell Biol 2011, 192(4):547-556.
• [58]Hernandez-Flores G, Ortiz-Lazareno PC, Lerma-Diaz JM, Dominguez-Rodriguez JR, Jave-Suarez LF, Aguilar-Lemarroy Adel C, de Celis-Carrillo R, del Toro-Arreola S, Castellanos-Esparza YC, Bravo-Cuellar A: Pentoxifylline sensitizes human cervical tumor cells to cisplatin-induced apoptosis by suppressing NF-kappa B and decreased cell senescence. BMC Cancer 2011, 11:483. BioMed Central Full Text
• [59]Ohtani N, Takahashi A, Mann DJ, Hara E: Cellular senescence: a double-edged sword in the fight against cancer. Exp Dermatol 2012, 21(Suppl 1):1-4.
• [60]Coppe JP, Patil CK, Rodier F, Sun Y, Munoz DP, Goldstein J, Nelson PS, Desprez PY, Campisi J: Senescence-associated secretory phenotypes reveal cell-nonautonomous functions of oncogenic RAS and the p53 tumor suppressor. PLoS Biol 2008, 6(12):2853-2868.
• [61]Wang YW, Wang SJ, Zhou YN, Pan SH, Sun B: Escin augments the efficacy of gemcitabine through down-regulation of nuclear factor-kappaB and nuclear factor-kappaB-regulated gene products in pancreatic cancer both in vitro and in vivo. J Cancer Res Clin Oncol 2012, 138(5):785-797.
• [62]Sun JG, Chen CY, Luo KW, Yeung CL, Tsang TY, Huang ZZ, Wu P, Fung KP, Kwok TT, Liu FY: 3,5-Dimethyl-H-furo[3,2-g]chromen-7-one as a potential anticancer drug by inducing p53-dependent apoptosis in human hepatoma HepG2 cells. Chemotherapy 2011, 57(2):162-172.
• [63]Hussain AR, Ahmed SO, Ahmed M, Khan OS, Al Abdulmohsen S, Platanias LC, Al-Kuraya KS, Uddin S: Cross-talk between NFkB and the PI3-Kinase/AKT pathway can be targeted in primary effusion lymphoma (PEL) cell lines for efficient apoptosis. PLoS One 2012, 7(6):e39945.
• [64]Yan M, Xu Q, Zhang P, Zhou XJ, Zhang ZY, Chen WT: Correlation of NF-kappaB signal pathway with tumor metastasis of human head and neck squamous cell carcinoma. BMC Cancer 2010, 10:437. BioMed Central Full Text
• [65]Sha M, Ye J, Zhang LX, Luan ZY, Chen YB: Celastrol induces apoptosis of gastric cancer cells by miR-146a inhibition of NF-kappaB activity. Cancer Cell Int 2013, 13(1):50. BioMed Central Full Text
• [66]La Ferla-Bruhl K, Westhoff MA, Karl S, Kasperczyk H, Zwacka RM, Debatin KM, Fulda S: NF-kappaB-independent sensitization of glioblastoma cells for TRAIL-induced apoptosis by proteasome inhibition. Oncogene 2007, 26(4):571-582.
• [67]Zanotto-Filho A, Braganhol E, Battastini AM, Moreira JC: Proteasome inhibitor MG132 induces selective apoptosis in glioblastoma cells through inhibition of PI3K/Akt and NFkappaB pathways, mitochondrial dysfunction, and activation of p38-JNK1/2 signaling. Invest New Drugs 2012, 30(6):2252-2262.
• [68]Zanotto-Filho A, Delgado-Canedo A, Schroder R, Becker M, Klamt F, Moreira JC: The pharmacological NFkappaB inhibitors BAY117082 and MG132 induce cell arrest and apoptosis in leukemia cells through ROS-mitochondria pathway activation. Cancer Lett 2010, 288(2):192-203.
• [69]Sen GS, Mohanty S, Hossain DM, Bhattacharyya S, Banerjee S, Chakraborty J, Saha S, Ray P, Bhattacharjee P, Mandal D, et al.: Curcumin enhances the efficacy of chemotherapy by tailoring p65NFkappaB-p300 cross-talk in favor of p53-p300 in breast cancer. J Biol Chem 2011, 286(49):42232-42247.
• [70]Choi CH, Xu H, Bark H, Lee TB, Yun J, Kang SI, Oh YK: Balance of NF-kappaB and p38 MAPK is a determinant of radiosensitivity of the AML-2 and its doxorubicin-resistant cell lines. Leuk Res 2007, 31(9):1267-1276.
• [71]Yeh PY, Chuang SE, Yeh KH, Song YC, Cheng AL: Involvement of nuclear transcription factor-kappa B in low-dose doxorubicin-induced drug resistance of cervical carcinoma cells. Biochem Pharmacol 2003, 66(1):25-33.
• [72]Zhang W, Ding W, Chen Y, Feng M, Ouyang Y, Yu Y, He Z: Up-regulation of breast cancer resistance protein plays a role in HER2-mediated chemoresistance through PI3K/Akt and nuclear factor-kappa B signaling pathways in MCF7 breast cancer cells. Acta Biochim Biophys Sin (Shanghai) 2011, 43(8):647-653.
• [73]Wang L, Kang F, Li J, Zhang J, Shan B: Overexpression of p65 attenuates celecoxib-induced cell death in MDA-MB-231 human breast cancer cell line. Cancer Cell Int 2013, 13(1):14. BioMed Central Full Text
• [74]Chen KF, Lin JP, Shiau CW, Tai WT, Liu CY, Yu HC, Chen PJ, Cheng AL: Inhibition of Bcl-2 improves effect of LCL161, a SMAC mimetic, in hepatocellular carcinoma cells. Biochem Pharmacol 2012, 84(3):268-277.
• [75]Golbano JM, Loppez-Aparicio P, Recio MN, Perez-Albarsanz MA: Finasteride induces apoptosis via Bcl-2, Bcl-xL, Bax and caspase-3 proteins in LNCaP human prostate cancer cell line. Int J Oncol 2008, 32(4):919-924.
• [76]Carbone C, Melisi D: NF-kappaB as a target for pancreatic cancer therapy. Expert Opin Ther Targets 2012, 16(Suppl 2):S1-S10.
• [77]Sethi G, Sung B, Aggarwal BB: Nuclear factor-kappaB activation: from bench to bedside. Exp Biol Med (Maywood) 2008, 233(1):21-31.
• [78]Suen DF, Norris KL, Youle RJ: Mitochondrial dynamics and apoptosis. Genes Dev 2008, 22(12):1577-1590.
• [79]Altieri DC: Validating survivin as a cancer therapeutic target. Nat Rev Cancer 2003, 3(1):46-54.
• [80]Kannaiyan R, Hay HS, Rajendran P, Li F, Shanmugam MK, Vali S, Abbasi T, Kapoor S, Sharma A, Kumar AP, et al.: Celastrol inhibits proliferation and induces chemosensitization through down-regulation of NF-kappaB and STAT3 regulated gene products in multiple myeloma cells. Br J Pharmacol 2011, 164(5):1506-1521.