Withaferin A inhibits the proteasome activity in mesothelioma in vitro and in vivo

Our plain-English summary of Withaferin A inhibits the proteasome activity in mesothelioma in vitro and in vivo, by H. Yang, Y. Wang, V.T. Cheryan, et al (PloS One, 2012).

The study

• Authors: H. Yang, Y. Wang, V.T. Cheryan, W. Wu, C.Q. Cui, L.A. Polin, H.I. Pass, Q.P. Dou, A.K. Rishi, A. Wali
• Journal: PloS One
• Published: 2012;7(8):e41214
• Cited by: 48 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

The medicinal plant Withania somnifera has been used for over centuries in Indian Ayurvedic Medicine to treat a wide spectrum of disorders. Withaferin A (WA), a bioactive compound that is isolated from this plant, has anti-inflammatory, immuno-modulatory, anti-angiogenic, and anti-cancer properties. Here we investigated malignant pleural mesothelioma (MPM) suppressive effects of WA and the molecular mechanisms involved. WA inhibited growth of the murine as well as patient-derived MPM cells in part by decreasing the chymotryptic activity of the proteasome that resulted in increased levels of ubiquitinated proteins and pro-apoptotic proteasome target proteins (p21, Bax, IκBα). WA suppression of MPM growth also involved elevated apoptosis as evidenced by activation of pro-apoptotic p38 stress activated protein kinase (SAPK) and caspase-3, elevated levels of pro-apoptotic Bax protein and cleavage of poly-(ADP-ribose)-polymerase (PARP). Our studies including gene-array based analyses further revealed that WA suppressed a number of cell growth and metastasis-promoting genes including c-myc. WA treatments also stimulated expression of the cell cycle and apoptosis regulatory protein (CARP)-1/CCAR1, a novel transducer of cell growth signaling. Knock-down of CARP-1, on the other hand, interfered with MPM growth inhibitory effects of WA. Intra-peritoneal administration of 5 mg/kg WA daily inhibited growth of murine MPM cell-derived tumors in vivo in part by inhibiting proteasome activity and stimulating apoptosis. Together our in vitro and in vivo studies suggest that WA suppresses MPM growth by targeting multiple pathways that include blockage of proteasome activity and stimulation of apoptosis, and thus holds promise as an anti-MPM agent.

In plain English

This was a laboratory study, not a study of people or of asbestos exposure. The authors tested withaferin A, a compound isolated from the medicinal plant Withania somnifera, on malignant pleural mesothelioma cells. They used human cell lines, four of them established in their laboratory from mesothelioma patients, and a mouse mesothelioma cell line (AB12). They also grew AB12 tumors under the skin of female BALB/c mice and gave the mice daily abdominal injections of 5 mg/kg withaferin A or an inactive vehicle. In the cell lines, withaferin A reduced growth by 52% to 67% at the doses reported. It lowered the proteasome's chymotrypsin-like activity (the proteasome is cell machinery that breaks down proteins) and increased signs of programmed cell death. Reducing a protein called CARP-1 interfered with the growth-suppressing effect. In mice, treated tumors averaged 714 cubic millimeters, against 1774 for controls, a 60% inhibition. One treated mouse had no tumor. The authors concluded that withaferin A suppresses mesothelioma growth through multiple pathways and has potential as a future therapy.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Laboratory experiments on mesothelioma cell lines (in vitro) plus an experiment in mice carrying transplanted mouse mesothelioma tumors (allograft); described by the authors as proof-of-concept studies
• Who was studied: Human malignant pleural mesothelioma cell lines: H2373, H2452, H2461 and H2595, established from patients in the authors' laboratory, and H226, obtained from ATCC. Also the AB12 mouse mesothelioma cell line, which was derived from BALB/c mice. For the animal experiment, female BALB/c mice aged 5 weeks were used: n = 5 per group in the methods, 4 per group in the figure legend.
• Exposure: Purified withaferin A, applied to cells at various concentrations. In mice it was given at 5 mg/kg of body weight by daily injection into the abdominal cavity (intraperitoneal); control mice received vehicle. Asbestos exposure was not studied.
• Main results:
  • H2373 cells were the most sensitive, with 52% growth inhibition at a dose printed as 1.25 mM.
  • The H2595, H226, H2452 and AB12 cell lines showed 58, 67, 55 and 55% growth inhibition respectively, at a dose printed as 5 mM.
  • In H2595 human cells, withaferin A caused about 70% inhibition of the proteasome's chymotrypsin-like activity.
  • In AB12 mouse cells, proteasomal activity declined by 52 to 62% over 8 to 24 hours.
  • In H2373 cells, caspase 3/7 activity (a marker of programmed cell death) increased 3.6 to 4.7-fold. In H2595 cells, withaferin A did not activate caspase 3/7.
  • In gene-array analysis of H2373 cells, most of the altered genes were turned down and a small number were turned up. The genes turned down included c-myc, c-fos and c-jun; TIMP-2 was turned up.
  • Knocking down CARP-1 interfered with withaferin A's suppression of mesothelioma cell growth.
  • In mice, control tumors averaged 1774 mm3 and withaferin A-treated tumors 714 mm3, a 60% inhibition.
  • Average tumor weight was 1.42 g in the vehicle group and 0.46 g in the withaferin A group, a 68% reduction. The authors did not show these data.
  • One withaferin A-treated mouse had no tumor.
  • Proteasomal chymotrypsin-like activity was 25% lower in tumors from treated mice than from vehicle-treated mice, and TUNEL staining showed more apoptotic cells in treated tumors.
• The authors' conclusion: The authors concluded that withaferin A targets multiple pathways to suppress mesothelioma growth in vitro and in vivo, and that it has potential as a future anti-mesothelioma therapy.
• Limitations the authors state:
  • The authors said it remains to be clarified whether, and to what extent, withaferin A acts on upstream regulators of the Ras-Raf-Erk pathway to block mesothelioma growth and spread.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Mesothelioma.

Medical terms in this study, explained in our Lexicon: Mesothelioma, Pleural Mesothelioma, Apoptosis, Metastasis.

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