Lovastatin inhibits VEGFR and AKT activation: synergistic cytotoxicity in combination with VEGFR inhibitors

Our plain-English summary of Lovastatin inhibits VEGFR and AKT activation: synergistic cytotoxicity in combination with VEGFR inhibitors, by T.T. Zhao, D. Trinh, C.L. Addison, et al (PloS One, 2010).

The study

• Authors: T.T. Zhao, D. Trinh, C.L. Addison, J. Dimitroulakos
• Journal: PloS One
• Published: 2010;5(9):e12563
• Cited by: 27 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Background: In a recent study, we demonstrated the ability of lovastatin, a potent inhibitor of mevalonate synthesis, to inhibit the function of the epidermal growth factor receptor (EGFR). Lovastatin attenuated ligand-induced receptor activation and downstream signaling through the PI3K/AKT pathway. Combining lovastatin with gefitinib, a potent EGFR inhibitor, induced synergistic cytotoxicity in a variety of tumor derived cell lines. The vascular endothelial growth factor receptor (VEGFR) and EGFR share similar activation, internalization and downstream signaling characteristics.

Methodology/principal Findings: The VEGFRs, particularly VEGFR-2 (KDR, Flt-1), play important roles in regulating tumor angiogenesis by promoting endothelial cell proliferation, survival and migration. Certain tumors, such as malignant mesothelioma (MM), also express both the VEGF ligand and VEGFRs that act in an autocrine loop to directly stimulate tumor cell growth and survival. In this study, we have shown that lovastatin inhibits ligand-induced VEGFR-2 activation through inhibition of receptor internalization and also inhibits VEGF activation of AKT in human umbilical vein endothelial cells (HUVEC) and H28 MM cells employing immunofluorescence and Western blotting. Combinations of lovastatin and a VEGFR-2 inhibitor showed more robust AKT inhibition than either agent alone in the H28 MM cell line. Furthermore, combining 5 µM lovastatin treatment, a therapeutically relevant dose, with two different VEGFR-2 inhibitors in HUVEC and the H28 and H2052 mesothelioma derived cell lines demonstrated synergistic cytotoxicity as demonstrated by MTT cell viability and flow cytometric analyses.

Conclusions/significance: These results highlight a novel mechanism by which lovastatin can regulate VEGFR-2 function and a potential therapeutic approach for MM through combining statins with VEGFR-2 inhibitors.

In plain English

This was a laboratory study of cells, not of patients. Asbestos exposure was not studied. The authors tested lovastatin, a cholesterol-lowering statin drug, on human umbilical vein endothelial cells (HUVEC) and on two human malignant mesothelioma cell lines, H28 and H2052. In HUVEC, lovastatin reduced the movement of VEGFR-2 receptors into cells after stimulation with the growth factor VEGF. In HUVEC and H28 cells, it reduced breakdown of the receptor. Lovastatin reduced VEGF-triggered activation of a cell-survival signal called AKT in a dose-dependent way, though less efficiently in H28 cells. In H28 cells, lovastatin combined with the VEGFR inhibitor KRN633 blocked this signal more strongly than either drug alone. In a combination index analysis at 5 micromolar lovastatin, H28 cells scored 0.58 with the inhibitor ZM323881 (synergy by the authors' definition) and 1 with KRN633 (an additive effect). H2052 cells and HUVEC scored below 1 with both inhibitors. In both mesothelioma cell lines, the combinations caused more programmed cell death (apoptosis) than either drug alone. The authors concluded that combining statins with VEGFR-2 inhibitors is a potential therapeutic approach for mesothelioma.

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) cell-culture experiments
• Who was studied: Human umbilical vein endothelial cells (HUVEC) and two human malignant mesothelioma cell lines, NCI-H28 and NCI-H2052, obtained from the American Type Culture Collection; no patients were studied
• Exposure: No asbestos exposure was studied. Cells were treated with lovastatin (doses from 0.5 to 25 micromolar, printed as "mM" in the text) and with the growth factor VEGF165 (50 ng/ml). Two VEGFR inhibitors were used alone or combined with lovastatin: KRN633 (inhibits VEGFR 1, 2 and 3) and ZM323881 (selective for VEGFR-2). Rapamycin and siRNA against VEGFR-2 were also used.
• Main results:
  • In HUVEC treated with lovastatin for 24 hours, adding VEGF165 produced significantly less of the intracellular staining pattern that indicates the receptor VEGFR-2 being taken into the cell
  • Lovastatin inhibited VEGF-induced internalization and degradation of VEGFR-2 in HUVEC and H28 mesothelioma cells
  • Lovastatin inhibited VEGF-induced AKT activation in a dose-dependent manner. This was readily detectable at 1 micromolar in HUVEC and less efficient in H28 cells.
  • In control HUVEC, about 26% of cells were apoptotic, compared with about 13% when VEGF165 was added. VEGF could reduce lovastatin-induced apoptosis at 1 micromolar lovastatin but had no significant effect at 2 micromolar.
  • In H28 mesothelioma cells, lovastatin combined with KRN633 inhibited the AKT pathway more than either agent alone
  • At 5 micromolar lovastatin, H28 cells had a combination index of 0.58 with ZM323881 (below 1 means synergism) and 1 with KRN633 (1 means an additive effect, by the authors' definition)
  • H2052 mesothelioma cells and HUVEC had combination index values below 1 (synergism) with both VEGFR inhibitors
  • In both mesothelioma cell lines (H28 and H2052), 5 micromolar lovastatin combined with either VEGFR inhibitor caused more apoptosis than either agent alone; apoptosis with the combination was not reported for HUVEC
  • Silencing VEGFR-2 with siRNA increased lovastatin-induced cytotoxicity in H2052 and H28 cells compared with control siRNA (P less than 0.001)
• The authors' conclusion: The authors concluded that the results highlight a novel mechanism regulating VEGFR-2 function and a potential novel therapeutic approach for malignant mesothelioma, combining statins with VEGFR-2 inhibitors
• Limitations the authors state:
  • Data on statin use in mesothelioma patients treated with VEGFR inhibitors were not available because there were not enough such patients for analysis
  • The mechanism by which lovastatin inhibits EGFR and VEGFR function requires further study

Topics

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

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