A Comparative Analysis of NOX4 Protein Expression in Malignant and Non-Malignant Thyroid Tumors

The comparative analysis of the expression of the reactive oxygen species-generating NADPH oxidase NOX4 from TCGA data shows that the NOX4 transcript is upregulated in papillary thyroid carcinomas (PTC)-BRAF^V600E tumors compared to PTC-BRAF^wt tumors. However, a comparative analysis of NOX4 at the protein level in malignant and non-malignant tumors is missing. We explored NOX4 protein expression by immunohistochemistry staining in malignant tumors (28 classical forms of PTC (C-PTC), 17 follicular variants of PTC (F-PTC), and three anaplastic thyroid carcinomas (ATCs)) and in non-malignant tumors (six lymphocytic thyroiditis, four Graves' disease, ten goiters, and 20 hyperplasias). We detected the BRAF^V600E mutation by Sanger sequencing and digital droplet PCR. The results show that NOX4 was found to be higher (score ≥ 2) in C-PTC (92.9%) compared to F-PTC (52.9%) and ATC (33.3%) concerning malignant tumors. Interestingly, all C-PTC-BRAF^V600E expressed a high score for NOX4 at the protein level, strengthening the positive correlation between the BRAF^V600E mutation and NOX4 expression. In addition, independent of the mutational status of BRAF, we observed that 90% of C-PTC infiltrating tumors showed high NOX4 expression, suggesting that NOX4 may be considered a complementary biomarker in PTC aggressiveness. Interestingly, NOX4 was highly expressed in non-malignant thyroid diseases with different subcellular localizations.

Abstract 2937: Preclinical evaluation of new therapeutic strategies on SDHB invalidated clones from human pheochromocytoma cells

Introduction: Malignant paraganglioma/pheochromocytoma (MPP) are very rare neuroendocrine tumors with heterogeneous prognostic and no gold-standard treatment. MPP can be associated with germline mutations at SDHB gene which encode for a TCA enzyme, the succinate dehydrogenase that catalyzes the oxidation of succinate to fumarate. When mutated, SDHB losses its function, leading to succinate accumulation by inhibiting 2-oxoglutarate dependent dioxygenases involved in methylation and angiogenesis. Thus alkylating agents, antiagniogenic and demethylating drugs are potential strategies for MPP patients.

Aim: This project aimed to establish preclinical models of SDHB invalidated human cell line and to characterize new therapeutic strategies.

Material & Methods: Invalidation of SDHB gene has been performed using the CRISPR-Cas9 technology on a human pheochromocytoma cell line (hPHEO1). Isogenic clones have been characterized at the genetic, cellular, proteic, and enzymatic levels through sequencing, immunohistochemistry, western-blotting and enzymatic assays, respectively. The antiproliferative effects of three drugs (temozolomide, sunitinib, azacytidine) have been explored and half maximal inhibitory concentrations (IC50) have been determined on the parental cell line and the 4 clones using the WST1® assay.

Results: Four heterozygote isogenic clones have been obtained with 3 different genetic alterations (deletion-insertion). Expression of Ki67 was increased in the SDHB+/- clones. SDHB expression was partially reduced in clones 1 and 2 and almost totally suppressed in clones 3 and 4. For temozolomide and sunitinib, IC50 were significantly lower in SDHB+/- clones (~140 µM for temozolomide and ~1.4 µM for sunitinib) compared to the parental cell line (~1300 µM for temozolomide and ~6 µM for sunitinib) whereas IC50 were similar for azacytidine (~3.5 µM). No significant difference was observed between clones.

Conclusion: In this study we obtained 4 SDHB invalidated isogenic clones from the human hPHEO1 cell line, pretty useful for preclinical evaluations in this rare disease. In agreement with literature clones were more sensitive to temozolomide but also to sunitinib. Metabolomic characterization of hPHEO1 and SDHB+/- clones is currently under investigation at baseline and after IC50 treatment of the 3 therapeutic strategies. Drugs’ combinations will be studied in a further step.

Citation Format: Constance Lamy, Julien Hadoux, Sylvere Durand, Abir Alghuzlan, Julie Riviere, Deborah Lefevre, Amaury Bongers, Jean-Yves Scoazec, Eric Baudin, Angelo Paci, Sophie Broutin. Preclinical evaluation of new therapeutic strategies on SDHB invalidated clones from human pheochromocytoma cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2937.