Pyrazolo[3,4-d]pyrimidine derivatives, Si306 and pro-Si306, induce oxidative stress and cell death in patient-derived glioblastoma cells

Abstract

Glioblastoma is the most frequent and aggressive brain tumor in adults. The main characteristics of glioblastoma include high proliferation rate, infiltrating nature, and resistance to chemotherapy and radiation. Glioblastoma cells highly express Src tyrosine kinase which has a key role in regulating survival, proliferation, angiogenesis and invasiveness of tumor cells. This tyrosine kinase is also an important regulator of reactive oxygen species production and cellular homeostasis. Anticancer properties of two pyrazolo[3,4-d]pyrimidine derivatives and Src tyrosine kinase inhibitors, Si306 and its prodrug pro-Si306, were investigated in human glioblastoma cell line U87, its multidrug-resistant (MDR) counterpart U87-TxR, and patient-derived glioblastoma cell culture. Si306 and pro-Si306 triggered reactive oxygen species and reactive nitrogen species production in sensitive and MDR glioblastoma cell lines and primary glioblastoma cells as evidenced by elevated levels of superoxide anion, hydrogen peroxide and peroxynitrite anion. Additionally, western blot analysis revealed elevated expression of superoxide dismutase 1, superoxide dismutase 2, and thioredoxin reductase 1 in glioblastoma cells after Si306 and pro-Si306 treatments. The levels of phosphorylated histone H2A.X increased in all glioblastoma cells after treatments with these inhibitors, demonstrating DNA damage. Both compounds also induced significant cell death in primary glioblastoma culture. In addition, the Src tyrosine kinase inhibitors prompted primary glioblastoma cells to enter senescence. The presence of the MDR phenotype did not reduce the activity of the compounds. Overall, the investigated pyrazolo[3,4-d]pyrimidines displayed significant anti-glioblastoma effects making them good candidates for further development as anticancer agents