Cisplatin and Pemetrexed Activate AXL and AXL Inhibitor BGB324 Enhances Mesothelioma Cell Death from Chemotherapy

Our plain-English summary of Cisplatin and Pemetrexed Activate AXL and AXL Inhibitor BGB324 Enhances Mesothelioma Cell Death from Chemotherapy, by D.B. Oien, T. Garay, S. Eckstein, et al (Frontiers in Pharmacology, 2017).

The study

• Authors: D.B. Oien, T. Garay, S. Eckstein, J. Chien
• Journal: Frontiers in Pharmacology
• Published: 2017;8:970
• Cited by: 28 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Reactive oxygen species (ROS) can promote or inhibit tumorigenesis. In mesothelioma, asbestos exposure to serous membranes induces ROS through iron content and chronic inflammation, and ROS promote cell survival signaling in mesothelioma. Moreover, a current chemotherapy regimen for mesothelioma consisting of a platinum and antifolate agent combination also induce ROS. Mesothelioma is notoriously chemotherapy-resistant, and we propose that ROS induced by cisplatin and pemetrexed may promote cell survival signaling pathways, which ultimately may contribute to chemotherapy resistance. In The Cancer Genome Atlas datasets, we found AXL kinase expression is relatively high in mesothelioma compared to other cancer samples. We showed that ROS induce the phosphorylation of AXL, which was blocked by the selective inhibitor BGB324 in VMC40 and P31 mesothelioma cells. We also showed that cisplatin and pemetrexed induce the phosphorylation of AXL and Akt, which was also blocked by BGB324 as well as by N-acetylcysteine antioxidant. AXL knockdown in these cells enhances sensitivity to cisplatin and pemetrexed. Similarly, AXL inhibitor BGB324 also enhances sensitivity to cisplatin and pemetrexed. Finally, higher synergy was observed when cells were pretreated with BGB324 before adding chemotherapy. These results demonstrate cisplatin and pemetrexed induce ROS that activate AXL, and blocking AXL activation enhances the efficacy of cisplatin and pemetrexed. These results suggest AXL inhibition combined with the current chemotherapy regimen may represent an effective strategy to enhance the efficacy of chemotherapy in mesothelioma. This is the first study, to our knowledge, on chemotherapy-induced activation of AXL and cell survival pathways associated with ROS signaling.

In plain English

This was a laboratory study of human malignant pleural mesothelioma (MPM) cells grown in dishes. It did not test asbestos or treat patients. Using tumor RNA data from The Cancer Genome Atlas, the authors found that MPM samples ranked fourth highest for AXL gene expression among 30 cancer types. In two MPM cell lines, VMC40 and P31, the chemotherapy drugs cisplatin and pemetrexed raised levels of reactive oxygen species. The drugs also switched on AXL, which was detectable after 10 minutes, and switched on a related survival protein, Akt, at variable times. BGB324, an experimental AXL blocker, prevented AXL activation and partly reduced Akt activation. Cells also given the antioxidant N-acetylcysteine showed no increase in either. Reducing AXL genetically made the cells more sensitive to both drugs. Giving BGB324 together with chemotherapy produced mostly additive effects. Giving it 4 hours earlier suggested more synergy: in VMC40 cells with pemetrexed, the combination index was 0.74 (below 1 means synergy). BGB324 did not significantly change drug sensitivity in non-cancerous Met-5a cells. The authors concluded that BGB324, especially as a pretreatment, can enhance chemotherapy-induced cell death in MPM cells.

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) study of mesothelioma cell lines, with an analysis of public tumor gene-expression data from The Cancer Genome Atlas
• Who was studied: RNA expression data from 87 MPM samples compared across 30 TCGA cancer datasets; eight human MPM cell lines for protein profiling, mainly VMC40 and P31 for experiments; the nonmalignant mesothelial cell line Met-5a for comparison
• Exposure: Cells were treated with the chemotherapy drugs cisplatin and pemetrexed, the AXL inhibitor BGB324, hydrogen peroxide and the antioxidant N-acetylcysteine. AXL was also reduced genetically with shRNA. No asbestos fibers were tested.
• Main results:
  • In TCGA RNA sequencing data, MPM samples had the fourth highest AXL expression among 30 cancer types (mean log2 value 11.40)
  • In VMC40 and P31 cells, 15 µM cisplatin plus 8 µM pemetrexed produced significantly higher reactive oxygen species than cisplatin alone (p = 0.049 and 0.047). The combination was not significantly different from pemetrexed alone.
  • AXL phosphorylation (activation) increased after 10 minutes of cisplatin or pemetrexed exposure and was blocked by co-treatment with BGB324
  • Cisplatin and pemetrexed induced Akt phosphorylation at variable time points
  • BGB324 only partially reduced chemotherapy-induced Akt phosphorylation
  • Cells co-treated with 4 mM N-acetylcysteine showed no increase in AXL and Akt phosphorylation
  • Cells with AXL knocked down by shRNA were more sensitive to cell death from cisplatin and pemetrexed than control cells
  • When BGB324 was given at the same time as cisplatin or pemetrexed in short-term assays, the combined effects were mostly additive
  • In nonmalignant Met-5a cells, BGB324 did not significantly change GI50 values for cisplatin and pemetrexed
  • With BGB324 given 4 hours before the drugs, clonogenic assays in VMC40 cells gave mean combination indices of 0.91 with 1.4 µM cisplatin and 0.74 with 0.1 µM pemetrexed (values below 1 indicate synergy)
  • With BGB324 plus both cisplatin and pemetrexed together, mean combination indices in VMC40 cells were 0.91 for co-treatment and 0.74 for pretreatment. In P31 cells they were 1.04 for co-treatment and 0.92 for pretreatment.
• The authors' conclusion: The authors concluded that cisplatin and pemetrexed can activate AXL, which BGB324 can block, and that adding BGB324, especially as a pretreatment, can enhance the cell-killing effect of these drugs in MPM cells. They said this may support future in vivo (in living organisms) studies.
• Limitations the authors state:
  • The biochemical mechanism by which reactive oxygen species regulate AXL is unknown
  • It is not known whether the Akt pathway counteracts ROS-induced cell death in their system
  • Further work is needed to understand why pretreatment with BGB324 produced more synergy

Topics

Medical terms in this study, explained in our Lexicon: Cisplatin, Pemetrexed (Alimta), Mesothelioma, Chemotherapy, Reactive Oxygen Species (ROS), Tumorigenesis, Asbestos Exposure, Chronic Inflammation.

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