Dexamethasone pretreatment impairs the thymidylate synthase inhibition mediated flare in thymidine salvage pathway activity in non-small cell lung cancer

Abstract

IntroductionSuccessful inhibition of thymidylate synthase (TS) by pemetrexed, a TS inhibitor, results in a reproducible transient burst or “flare” in thymidine salvage pathway activity at 2 hrs. of therapy which can be measurable with FLT-PET ([18F]fluorothymidine-positron emission tomography) in non-small cell lung cancer (NSCLC). Routine administration of dexamethasone with pemetrexed-based therapy could potentially confound this imaging approach since dexamethasone is known to inhibit expression of thymidine kinase 1, a key enzyme in the thymidine salvage pathway. Here we examine the potential impact of dexamethasone on the TS inhibition-mediated thymidine salvage pathway “flare” in NSCLC.Materials and methodsIn order to determine NSCLC cell line sensitivity to dexamethasone and pemetrexed, IC50 studies were performed on NSCLC cell lines H23, H1975, H460, H1299. TS inhibition-mediated “flare” in thymidine salvage pathway activity was then measured at 2hrs. of exposure to pemetrexed and cisplatin in NSCLC cells lines following using 3H-thymidine incorporation assays under the following conditions: control (no chemotherapy or dexamethasone), or treated with pemetrexed and cisplatin without dexamethasone, with 24 hrs. pre-treatment of dexamethasone or with dexamethasone administered together with chemotherapy. These conditions were chosen to model the delivery of pemetrexed-based therapy in the clinic.ResultsThe IC50 of H23, H1975, H460, H1299 for dexamethasone and pemetrexed were 40, 5.9, 718, 362 μM and 0.22, 0.73, 0.14 and 0.66 μM respectively. Significant blunting of the thymidine salvage pathway “flare” is observed at 2hrs. of pemetrexed-based therapy when dexamethasone sensitive cell lines H23 and H1975 were pretreated with dexamethasone but not when dexamethasone was given together with pemetrexed therapy or in the setting of dexamethasone resistance (H460 and H1299).Conclusion24 hr. pretreatment with dexamethasone, but not same day co-administration of dexamethasone with therapy, impairs the TS inhibition-mediated “flare” in thymidine salvage pathway activity in NSCLC.

Impact of the APE1 Redox Function Inhibitor E3330 in Non-Small Cell Lung Cancer Cells Exposed to Cisplatin: Increased Cytotoxicity and Impairment of Cell Migration and Invasion

“…According to two complementary cell viability assays, cisplatin displayed a concentration-and time-dependent cytotoxic effect with IC50 values ranging from approximately 10 to 16 µ M for 72 h, being more than two-fold higher for a shorter incubation period of 48 h. Considering the results available in the literature, the effect of cisplatin in H1975 cells viability herein obtained is comparable to those described by other authors using different methodologies such as sulforhodamine B assay (IC50 = 8.31 µ M [27]) and MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay (IC50 = 6.71 µ M [42] and IC50 = 11 µ M [43]) for the same 72 h incubation period. As for 48 h of cisplatin incubation in the same cell line, our results differ from the study of Zhao et al [44] that found an IC50 value of 3 µ M using the MTT assay.…”

Role of 3'-Deoxy-3'-[18F] Fluorothymidine Positron Emission Tomography-Computed Tomography as a Predictive Biomarker in Argininosuccinate Synthetase 1-Deficient Thoracic Cancers Treated With Pegargiminase

“…FLT-PET imaging provides additional validation of arginine auxotrophic thoracic cancers, especially MPM, in which there are several resistance mechanisms, including ASS1 re-expression (i.e., recycling of citrulline to arginine), autophagy, and metabolic support by macrophages and other stromal cells, which affect subsequent disease progression. 31 …”

“…FLT-PET imaging provides additional validation of arginine auxotrophic thoracic cancers, especially MPM, in which there are several resistance mechanisms, including ASS1 reexpression (i.e., recycling of citrulline to arginine), autophagy, and metabolic support by macrophages and other stromal cells, which affect subsequent disease progression. 31 Early phase combination trials of ADI-PEG 20 with chemotherapy are reporting increased efficacy, owing to synergistic and additive mechanisms of cytotoxicity in various cancer types, accompanied by more sustained arginine depletion with the slower emergence of anti-ADI-PEG 20 antibodies. 13,[32][33][34] In thoracic cancers, this multimodality strategy has progressed to a randomized phase 3 study of ADI-PEG 20 (or placebo) PemCis focusing on chemorefractory (nonepithelioid) MPM which is expected to report final results in 2022 (ATOMIC-meso, ClinicalTrials.gov identifier: NCT02709512).…”

Application of Metabolic Reprogramming to Cancer Imaging and Diagnosis

“…Furthermore, there is an ongoing study to evaluate 18F-FLT uptake in non-small cell lung cancer following pemetrex treatment. Because of the response and activation of the dexamethasone/pemetrexed thymidine salvage pathway inhibited by dexamethasone/pemetrexed [132], the authors hypothesize that this strategy can be detected as an increase in FLT tumor uptake that subsequently decreases with reduced proliferation. In this study, the FLT response had a good overall survival rate that was twice that of no response.…”