Approaching Sites of Action of Temozolomide for Pharmacological and Clinical Studies in Glioblastoma

Abstract

Temozolomide (TMZ), together with bulk resection and focal radiotherapy, is currently a standard of care for glioblastoma. Absorption, distribution, metabolism, and excretion (ADME) parameters, together with the mode of action of TMZ, make its biochemical and biological action difficult to understand. Accurate understanding of the mode of action of TMZ and the monitoring of TMZ at its anatomical, cellular, and molecular sites of action (SOAs) would greatly benefit precision medicine and the development of novel therapeutic approaches in combination with TMZ. In the present perspective article, we summarize the known ADME parameters and modes of action of TMZ, and we review the possible methodological options to monitor TMZ at its SOAs. We focus our descriptions of methodologies on mass spectrometry-based approaches, and all related considerations are taken into account regarding the avoidance of artifacts in mass spectrometric analysis during sampling, sample preparation, and the evaluation of results. Finally, we provide an overview of potential applications for precision medicine and drug development.

Targeting Glioblastoma via Selective Alteration of Mitochondrial Redox State

“…However, it should be noted that the effect of vitamin C on demethylation of histones may antagonize the anticancer effect of DNA-alkylating drugs, such as temozolomide. MGMT promoter methylation is the key mechanism of MGMT gene silencing and predicts a favorable outcome in patients with glioblastoma who are exposed to alkylating agent chemotherapy [95,96]. We found that M/A did not abolish or decrease the cytotoxic effect of temozolomide in isolated glioblastoma cells (Figure S4, see the Supporting Materials).…”

Quantification of Biologically Active DNA Alkylation in Temozolomide-Exposed Glioblastoma Cell Lines by Ultra-Performance Liquid Chromatography–Tandem Mass Spectrometry: Method Development and Recommendations for Validation

“…Mass spectrometric (MS) quantification of temozolomide (TMZ)-induced DNA modifications would represent an ideal pharmacodynamic approach to monitor TMZ action in precision oncology and drug development for glioblastoma (GBM) . Among DNA modifications triggered by TMZ, the methylation of 2′-deoxyguanosine (2dGO) at the O6 position is the known one mainly responsible for TMZ action .…”

“…Mass spectrometric (MS) quantification of temozolomide (TMZ)-induced DNA modifications would represent an ideal pharmacodynamic approach to monitor TMZ action in precision oncology and drug development for glioblastoma (GBM) . Among DNA modifications triggered by TMZ, the methylation of 2′-deoxyguanosine (2dGO) at the O6 position is the known one mainly responsible for TMZ action . O6-methyl-2′-deoxyguanosine (O6-m2dGO) can be repaired by the methylguanine methyl transferase (MGMT), which is unfunctional in a majority of GBM patients, especially in the presence of mutations of isocitrate dehydrogenase (IDH) .…”

“…Although the quantification of O6-m2dGO would allow to evaluate the biologically active chemical modifications of DNA induced by TMZ, it is challenged by the existence of a large majority of other alkylated species such as N7-methyl-2′-deoxyguanosine (N7-m2dGO) in DNA and methylated guanosines in RNA. Indeed, O6-m2dGO represent only 5–10% of the nucleoside alkylation in DNA, while TMZ also leads to the alkylation of guanines at N7-position . N7-m2dGO is repaired by the base excision repair machinery, which is rarely inactive in GBM .…”

“…N7-m2dGO is therefore biologically inactive but represents 60–80% of nucleoside alkylation induced by TMZ. N7-m2dGO represents a major analytical issue for the quantification of O6-m2dGO since both species present the same mass, as well as their fragments, N7-methylguanine (N7-mG) and O6-methylguanine (O6-mG), respectively . In addition, alkylation induced by TMZ is not specific to DNA but also affects RNA.…”