Targeting the Redox Balance Pathway Using Ascorbic Acid in sdhb Zebrafish Mutant Larvae

SIMPLE SUMMARY: Thus far, no curative therapies are available for malignant SDHB-associated phaeochromocytomas and paragangliomas (PPGLs). Therapy development is severely hampered by the limited availability of suitable animal models. In this study, we investigated the potential of the sdhb(rmc200) zebrafish model to study SDHB-associated PPGLs using a drug screening approach. One of the key features of cancer initiation and progression is redox imbalance. First, we identified increased reactive oxygen species levels in homozygous sdhb(rmc200) larvae at baseline. Next, we tested the effect of anti- and pro-oxidant ascorbic acid (Vitamin C) on these larvae. We validated the sdhb(rmc200) zebrafish model as a powerful drug screening tool to provide valuable insights into pathomechanisms, which may lead to novel therapeutic targets and therapy development in the future. ABSTRACT: Patients with mutations in the β-subunit of the succinate dehydrogenase (SDHB) have the highest risk to develop incurable malignant phaeochromocytomas and paragangliomas (PPGLs). Therapy development is hindered by limited possibilities to test new therapeutic strategies in vivo. One possible molecular mechanism of SDHB-associated tumorigenesis originates in an overproduction of reactive oxygen species (ROS) due to mitochondrial dysfunction. Ascorbic acid (Vitamin C) has already been shown to act as anti-cancer agent in several clinical trials for various types of cancer. In this study, the potential of the sdhb(rmc200) zebrafish model to study SDHB-associated PPGLs using a drug screening approach was investigated. First, we identified increased basal ROS levels in homozygous sdhb larvae compared to heterozygous and wild-type siblings. Using a semi high-throughput drug screening, the effectiveness of different dosages of anti- and pro-oxidant Vitamin C were assessed to evaluate differences in survival, ROS levels, and locomotor activity. Low-dosage levels of Vitamin C induced a decrease of ROS levels but no significant effects on lifespan. In contrast, high-dosage levels of Vitamin C shortened the lifespan of the homozygous sdhb(rmc200) larvae while not affecting the lifespan of heterozygous and wild-type siblings. These results validated the sdhb(rmc200) zebrafish model as a powerful drug screening tool that may be used to identify novel therapeutic targets for SDHB-associated PPGLs.