Abstract
Failures in treating glioma have made it necessary to search for new therapies, especially those that have immunological properties. Amitriptyline (AMI) is not only used in the treatment of major depression but is also effective in the therapy for neuropathic and chronic cancer pain. Previous data have indicated anticancer and anti-inflammatory effects of AMI. However, at present, its effect on glioma cells in combination with the standard treatment, namely temozolomide (TEMO, the first-line cytostatic) and radiotherapy, has not been investigated. It would also be interesting to determine whether the mechanism of the immunomodulatory action of AMI is associated with its effect on the programmed death ligand-1 (PD-L1) expression, a key target for anticancer therapies. In the present study, the effect of AMI or its concomitant use with AMI and TEMO and/or radiation (10 Gy) on the viability, mortality (MTT, Trypan blue), proliferation (BrdU), colony forming (microscopic analysis) of C6 glioma cells and PD-L1 expression (enzyme immunoassay) was investigated. Although AMI induced the anticancer effects, it attenuated the effects of radiation. In radiated cell cultures, the combination of AMI and TEMO provoked the formation of larger glioma cell colonies and reversed the cellular effects of radiation. Moreover, AMI suppressed the expression of PD-L1 in cells that had been exposed to or had not been exposed to radiation, whereas radiation enhanced its expression. Because AMI exhibited promising anticancer properties including an interesting, previously unknown immunomodulatory effect, it appears that its potential therapeutic should be verified in an in vivo study.