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1.  Cancerous inhibitor of PP2A is targeted by natural compound celastrol for degradation in non-small-cell lung cancer 
Carcinogenesis  2013;35(4):905-914.
Summary
Celastrol binds CIP2A and enhances CIP2A–CHIP interaction, leading to ubiquitination/degradation of CIP2A and inhibition of lung cancer cells in vitro and in vivo. Celastrol potentiates cisplatin’s efficacy by suppressing the CIP2A–Akt pathway, and therefore CIP2A inhibitors may represent novel therapeutics for cancer.
Cancerous inhibitor of protein phosphatase 2A (CIP2A) is an oncoprotein overexpressed and inversely associated with prognosis in lung and many other human cancers. It modulates phospho-Akt and stabilizes c-Myc, and is required for cell proliferation and malignant transformation, indicating that CIP2A may play an important role in carcinogenesis. We reported here that a small compound celastrol could induce a rapid degradation of CIP2A, through the ubiquitin–proteasome pathway with the carboxyl terminus of Hsp70-interacting protein (CHIP) as the E3 ligase. Celastrol directly bound CIP2A protein and promoted CIP2A–CHIP interaction, leading to subsequent degradation of CIP2A in non-small-cell lung cancer cells. Furthermore, celastrol effectively inhibited cell proliferation and induced apoptosis in non-small-cell lung cancer cells, whereas CIP2A silencing enhanced these effects. Celastrol also suppressed tumor growth in xenograft murine models. In addition, celastrol potentiated the inhibitory effect of cytotoxic agent cisplatin on lung cancer cells in vitro and in vivo via inhibition of CIP2A–Akt pathway. These data indicate that celastrol is a CIP2A-targeting agent that may have therapeutic potentials in lung cancer.
doi:10.1093/carcin/bgt395
PMCID: PMC4319067  PMID: 24293411
2.  Synergy between Proteasome Inhibitors and Imatinib Mesylate in Chronic Myeloid Leukemia 
PLoS ONE  2009;4(7):e6257.
Background
Resistance developed by leukemic cells, unsatisfactory efficacy on patients with chronic myeloid leukemia (CML) at accelerated and blastic phases, and potential cardiotoxity, have been limitations for imatinib mesylate (IM) in treating CML. Whether low dose IM in combination with agents of distinct but related mechanisms could be one of the strategies to overcome these concerns warrants careful investigation.
Methods and Findings
We tested the therapeutic efficacies as well as adverse effects of low dose IM in combination with proteasome inhibitor, Bortezomib (BOR) or proteasome inhibitor I (PSI), in two CML murine models, and investigated possible mechanisms of action on CML cells. Our results demonstrated that low dose IM in combination with BOR exerted satisfactory efficacy in prolongation of life span and inhibition of tumor growth in mice, and did not cause cardiotoxicity or body weight loss. Consistently, BOR and PSI enhanced IM-induced inhibition of long-term clonogenic activity and short-term cell growth of CML stem/progenitor cells, and potentiated IM-caused inhibition of proliferation and induction of apoptosis of BCR-ABL+ cells. IM/BOR and IM/PSI inhibited Bcl-2, increased cytoplasmic cytochrome C, and activated caspases. While exerting suppressive effects on BCR-ABL, E2F1, and β-catenin, IM/BOR and IM/PSI inhibited proteasomal degradation of protein phosphatase 2A (PP2A), leading to a re-activation of this important negative regulator of BCR-ABL. In addition, both combination therapties inhibited Bruton's tyrosine kinase via suppression of NFκB.
Conclusion
These data suggest that combined use of tyrosine kinase inhibitor and proteasome inhibitor might be helpful for optimizing CML treatment.
doi:10.1371/journal.pone.0006257
PMCID: PMC2705802  PMID: 19606213

Results 1-2 (2)