PKM2 Is Overexpressed in Glioma Tissues, and Its Inhibition Highly Increases Late Apoptosis in U87MG Cells With Low-density Specificity

Abstract

Background/aim: Pyruvate kinase M2 (PKM2) functions as an important rate-limiting enzyme in aerobic glycolysis and is involved in tumor initiation and progression. However, there are few studies on the correlation between PKM2 expression and its role in glioma.

Materials and methods: PKM2 expression was immunohistochemically examined in human brain tumor samples. Furthermore, we studied the effects of two PKM2 inhibitors (shikonin and compound 3K) on the U87MG glioma cell line.

Results: PKM2 was overexpressed in most glioma tissues when compared to controls. Interestingly, glioma-adjacent tissues from showed slight PKM2 overexpression. This suggests that PKM2 overexpression maybe an important trigger factor for glioma tumorigenesis. We found that the PKM2 inhibitor shikonin was effective against U87MG cells at a relatively low dose and was largely dependent on low cellular density compared to the effects of the anticancer drug vincristine. Shikonin highly increased late-apoptosis of U87MG cells. We also demonstrated that autophagy was involved in the increase in late-apoptosis levels caused by shikonin. Although vincristine treatment led to a high level of G₂-phase arrest in U87MG cells, shikonin did not increase G₂ arrest. Co-treatment with two PKM2 inhibitors, shikonin and compound 3K, increased the inhibitory effects.

Conclusion: Combination therapy with PKM2 inhibitors together might be more effective than combination therapy with anticancer drugs. Our findings encourage the application of PKM2-targeting in gliomas, and lay the foundation for the development of PKM2 inhibitors as promising antitumor agents for glioma.

Keywords: PKM2; compound 3K; glioma; shikonin.