Effect of the BH3 Mimetic Polyphenol (-)-Gossypol (AT-101) on the in vitro and in vivo Growth of Malignant Mesothelioma

Our plain-English summary of Effect of the BH3 Mimetic Polyphenol (-)-Gossypol (AT-101) on the in vitro and in vivo Growth of Malignant Mesothelioma, by M. Benvenuto, R. Mattera, J.I. Sticca, et al (Frontiers in Pharmacology, 2018).

The study

• Authors: M. Benvenuto, R. Mattera, J.I. Sticca, P. Rossi, C. Cipriani, M.G. Giganti, A. Volpi, A. Modesti, L. Masuelli, R. Bei
• Journal: Frontiers in Pharmacology
• Published: 2018;9:1269
• Cited by: 29 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Malignant mesothelioma (MM) is a primary tumor arising from mesothelial cells. The survival of MM patients following traditional chemotherapy is poor, thus innovative treatments for MM are needed. (-)-gossypol (AT-101) is a BH3 mimetic compound which possesses anti-tumoral activity by targeting multiple signaling transduction pathways. Several clinical trials employing AT-101 have been performed and some of them are still ongoing. Accordingly, we investigated the in vitro effects of AT-101 on cell proliferation, cell cycle regulation, pro-survival signaling pathways, apoptosis and autophagy of human (MM-B1, H-Meso-1, and MM-F1) and mouse (#40a) MM cell lines. In addition, we explored the in vivo anti-tumor activities of AT-101 in a mouse model, in which the transplantation of MM cells induces ascites in the peritoneal space. AT-101 inhibited in vitro MM cells survival in a dose- and time-dependent manner and triggered autophagy, but the process was then blocked and was coincident with apoptosis activation. To confirm the effect of AT-101 in inducing the apoptosis of MM cells, MM cells were simultaneously treated with AT-101 and with the caspase inhibitor, Z-VAD-FMK. Z-VAD-FMK was able to significantly reduce the number of cells in the subG1 phase compared to the treatment with AT-101 alone. This result corroborates the induction of cell death by apoptosis following treatment with AT-101. Indeed, Western blotting results showed that AT-101 increases Bax/Bcl-2 ratio, modulates p53 expression, activates caspase 9 and the cleavage of PARP-1. In addition, the treatment with AT-101 was able to: (a) decrease the ErbB2 protein expression; (b) increase the EGFR protein expression; (c) affect the phosphorylation of ERK1/2, p38 and AKT; (d) stimulate JNK1/2 and c-jun phosphorylation. Our in vivo results showed that the intraperitoneal administration of AT-101 increased the median survival of C57BL/6 mice intraperitoneally transplanted with #40a cells and reduced the risk of developing tumors. Our findings may have important implications for the design of MM therapies by employing AT-101 as an anticancer agent in combination with standard therapies.

In plain English

This laboratory study tested AT-101, a form of the cottonseed compound gossypol, on malignant mesothelioma cells. It did not study asbestos exposure. The authors treated three human mesothelioma cell lines (MM-B1, H-Meso-1 and MM-F1) and one mouse line (#40a) with AT-101 in culture. The drug reduced cell survival depending on dose and time. The concentration needed to halve survival after 72 hours ranged from 2.66 to 5.59 micromolar across the lines. After 72 hours at the highest doses, cell death reached 89 to 94 percent depending on the line. Tests pointed to apoptosis (programmed cell death), and a caspase blocker reduced this effect in all human lines. In mice, eight animals per group had #40a cells injected into the abdomen and received AT-101 or corn oil once a week. Median survival was 7 weeks with AT-101 and 4.5 weeks with corn oil. All eight treated mice were eventually euthanized, the last two at 17 weeks because of tumor size. The authors concluded that BH3 mimetics such as AT-101 could be a promising strategy to improve standard therapies.

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 study: experiments on mesothelioma cell lines in culture plus an animal experiment in mice
• Who was studied: Three human malignant mesothelioma cell lines (H-Meso-1, epithelial; MM-B1, biphasic; MM-F1, sarcomatous features) and mouse mesothelioma cell lines 40 and #40a. Groups of 8 C57BL/6 mice aged 6 to 8 weeks were injected into the abdomen with 1 million #40a cells, one week after an injection of pristane.
• Exposure: The drug AT-101, (-)-gossypol. In culture, cells received 1.56 to 25 micromolar or the DMSO solvent alone. In mice, the drug was injected into the abdomen at 0.1 mg in corn oil once a week, compared with corn oil alone. No asbestos exposure was studied.
• Main results:
  • Concentrations reducing cell survival by 50%, after 48 and 72 hours respectively: MM-B1 9.30 and 5.59 micromolar; H-Meso-1 9.24 and 2.66; MM-F1 9.32 and 5.10; #40a 5.44 and 3.87.
  • Cell death percentages after 72 hours at the highest doses were 94, 71 and 22 for MM-B1; 93, 65 and 27 for H-Meso-1; 92, 76 and 23 for MM-F1; and 89, 65 and 29 for #40a (all p less than 0.001).
  • AT-101 raised reactive oxygen species production significantly only in MM-F1 cells, and only at the highest dose. It did not affect production in MM-B1, H-Meso-1 or #40a cells.
  • The caspase inhibitor Z-VAD-FMK significantly reduced AT-101-related apoptosis in all three human cell lines.
  • AT-101 significantly increased the Bax/Bcl-2 ratio in MM-B1, H-Meso-1 and #40a cells. In MM-F1 cells this ratio decreased.
  • The authors interpreted the results as showing that autophagy was triggered and then blocked in MM-B1, H-Meso-1 and #40a cells.
  • AT-101 reduced ErbB2 protein expression in all four cell lines.
  • After 2 weeks, AT-101-treated mice had a smaller mean abdominal circumference than control mice: 6.9 cm versus 7.5 cm.
  • All 8 corn-oil control mice were euthanized for excessive tumor size, four at 4 weeks and four at 5 weeks. The AT-101-treated mice were euthanized at 6 weeks (two), 7 weeks (three) and 8 weeks (one). The remaining two were euthanized at 17 weeks for excessive tumor size.
  • Median survival was 7 weeks in AT-101-treated mice and 4.5 weeks in corn-oil-treated mice (p = 0.0001).
  • In the survival analysis, the hazard ratio for corn-oil-treated mice compared with AT-101-treated mice was 25.19 (95% confidence limits 4.936 to 128.5; p = 0.0001). The authors described this as the risk of developing tumors.
• The authors' conclusion: The authors concluded that AT-101 inhibited mesothelioma cell growth by targeting several signaling pathways and inducing apoptosis, and interfered with tumor growth in mice. They concluded that BH3 mimetics such as AT-101 could be a promising strategy to improve standard therapies for patients with malignant mesothelioma.

Topics

Medical terms in this study, explained in our Lexicon: Mesothelioma, Mesothelial Cells, Chemotherapy, Clinical Trial, Apoptosis, Ascites, EGFR, Median Overall Survival.

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