Zoledronic acid induces apoptosis and S-phase arrest in mesothelioma through inhibiting Rab family proteins and topoisomerase II actions

Our plain-English summary of Zoledronic acid induces apoptosis and S-phase arrest in mesothelioma through inhibiting Rab family proteins and topoisomerase II actions, by S. Okamoto, Y. Jiang, K. Kawamura, et al (Cell Death & Disease, 2014).

The study

• Authors: S. Okamoto, Y. Jiang, K. Kawamura, M. Shingyoji, Y. Tada, I. Sekine, Y. Takiguchi, K. Tatsumi, H. Kobayashi, H. Shimada, K. Hiroshima, M. Tagawa
• Journal: Cell Death & Disease
• Published: 2014;5(11):e1517
• Cited by: 32 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Zoledronic acid (ZOL), a nitrogen-containing bisphosphonate, produced anti-tumor effects through apoptosis induction or S-phase arrest depending on human mesothelioma cells tested. An addition of isoprenoid, geranylgeraniol but not farnesol, negated these ZOL-induced effects, indicating that the ZOL-mediated effects were attributable to depletion of geranylgeranyl pyrophosphates which were substrates for prenylation processes of small guanine-nucleotide-binding regulatory proteins (small G proteins). ZOL-treated cells decreased a ratio of membrane to cytoplasmic fractions in RhoA, Cdc42 and Rab6 but less significantly Rac1 proteins, indicating that these proteins were possible targets for ZOL-induced actions. We further analyzed which small G proteins were responsible for the three ZOL-induced effects, caspase-mediated apoptosis, S-phase arrest and morphological changes, using inhibitors for respective small G proteins and siRNA for Cdc42. ZOL-induced apoptosis is due to insufficient prenylation of Rab proteins because an inhibitor of geranlygeranyl transferase II that was specific for Rab family proteins prenylation, but not others inhibitors, activated the same apoptotic pathways that ZOL did. ZOL suppressed an endogenous topoisomerase II activity, which was associated with apoptosis and S-phase arrest in respective cells because we detected the same cell cycle changes in etoposide-treated cells. Inhibitors for geranlygeranyl transferase I and for RhoA produced morphological changes and disrupted actin fiber structures, both of which were similar to those by ZOL treatments. These data demonstrated that anti-tumor effects by ZOL were attributable to inhibited functions of respective small G proteins and topoisomerase II activity, and suggested that cellular factors were involved in the differential cell cycle changes.

In plain English

This was a laboratory study of human mesothelioma cells grown in culture. It did not involve patients or asbestos exposure. The authors tested zoledronic acid (ZOL), a nitrogen-containing bisphosphonate drug, on human mesothelioma cell lines, mainly MSTO-211H and EHMES-10. ZOL reduced the growth of four cell lines. In MSTO-211H cells it mainly caused apoptosis, a form of programmed cell death. In EHMES-10 cells it mainly caused the cells to stall in the S phase of the cell cycle. Adding geranylgeraniol, but not farnesol, cancelled these effects. Using drugs that block specific cell proteins, the authors found that NE10790, an inhibitor of Rab-family protein modification, produced the same apoptosis signals as ZOL. ZOL also blocked the enzyme topoisomerase II but scarcely topoisomerase I. Etoposide, a topoisomerase II blocker, caused similar cell-cycle changes. The changes in cell shape were linked to Rho-family proteins. The authors concluded that ZOL's anti-tumor effects were attributable to inhibited functions of small G proteins and to reduced topoisomerase II activity, and noted that the effects differed between cell types. They did not identify which Rab proteins were involved.

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 (in vitro) experiments on human mesothelioma cell lines using drugs, specific inhibitors and siRNA
• Who was studied: Human mesothelioma cell lines: MSTO-211H and NCI-H28 (from the American Type Culture Collection) and EHMES-1, EHMES-10 and JMN-1B. MSTO-211H and EHMES-10 were used as the main representative lines. No patients were studied.
• Exposure: Zoledronic acid (a nitrogen-containing bisphosphonate drug). Comparison agents included geranylgeraniol, farnesol, C3 transferase, NSC23766, GGTI-298, NE10790, Cdc42 siRNA, etoposide, topotecan and clodronate. Asbestos exposure was not studied.
• Main results:
  • ZOL suppressed proliferation of four mesothelioma cell lines. It increased dying-cell (sub-G1) fractions in MSTO-211H cells, S-phase populations in EHMES-10 cells, and both in EHMES-1 and JMN-1B cells.
  • Adding geranylgeraniol, but not farnesol, negated the ZOL-induced effects.
  • In MSTO-211H cells, NE10790 (an inhibitor of geranylgeranyl transferase II, specific for Rab family proteins) decreased phosphorylated Akt and Mcl-1 and induced cleavage of caspase-9, caspase-3 and PARP. These were the same changes seen with ZOL.
  • ZOL inhibited topoisomerase II activity but scarcely topoisomerase I activity in MSTO-211H and EHMES-10 cell extracts.
  • Etoposide, a topoisomerase II inhibitor, increased sub-G1 fractions in MSTO-211H cells and increased S- and G2/M-phase populations in EHMES-10 cells, similar to ZOL.
  • The authors judged that ZOL-induced changes in cell shape and disruption of actin fibers were due to inhibition of RhoA and Cdc42. GGTI-298 and C3 transferase caused similar actin disruption, while NE10790 did not.
• The authors' conclusion: The authors concluded that the anti-tumor effects of ZOL in mesothelioma cells were attributable to inhibited functions of small G proteins and to inhibited topoisomerase II activity. They noted that these actions were influenced by cell type differences.
• Limitations the authors state:
  • The study did not determine which Rab family proteins contributed to ZOL-induced apoptosis.
  • The study could not test whether the ATP analogue ApppI was responsible for ZOL-mediated apoptosis because ApppI was unavailable, and further studies are needed to confirm whether ApppI suppresses topoisomerase II.

Topics

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

Related studies

• Zoledronic acid produces antitumor effects on mesothelioma through apoptosis and S-phase arrest in p53-independent and Ras prenylation-independent manners — S. Okamoto, K. Kawamura, et al. (2012)
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• Combination of a third generation bisphosphonate and replication-competent adenoviruses augments the cytotoxicity on mesothelioma — Y. Jiang, B. Zhong, et al. (2016)
• Zoledronic acid overcomes chemoresistance and immunosuppression of malignant mesothelioma — I.C. Salaroglio, I. Campia, et al. (2015)
• Zoledronic acid impairs myeloid differentiation to tumour-associated macrophages in mesothelioma — J.D. Veltman, M.E. Lambers, et al. (2010)
• TRAIL and proteasome inhibitors combination induces a robust apoptosis in human malignant pleural mesothelioma cells through Mcl-1 and Akt protein cleavages — B.Z. Yuan, J. Chapman, et al. (2013)

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