DDDR-58. RNA-sequencing to investigate antineoplastic mechanisms of gallium maltolate in glioblastoma

Abstract BACKGROUND Iron fuels rapid proliferation of cancer cells. Gallium (Ga) is a metal that can disrupt iron proteins to inhibit and kill cancer cells. Various mechanisms of action for Ga have been elucidated across several cancer types, often using a first-generation Ga compound (Ga nitrate). These mechanisms include relative intracellular iron depletion, inhibition of ribonucleotide reductase, inhibition of the mitochondrial electron transport chain resulting in oxidative stress, perturbations in zinc homeostasis, and induction of apoptosis. Gallium maltolate (GaM) is a second-generation Ga compound with improved pharmacokinetics. Previous in vitro and animal studies showed efficacy of GaM in treating glioblastoma, leading to a Phase I clinical trial of GaM in recurrent glioblastoma (NCT04319276). Yet, much is left to be understood about mechanisms of GaM in glioblastoma. METHODS Human glioblastoma cells (D54) were cultured in triplicate for 24 or 48h in untreated medium or medium with 30μM GaM. Sequencing was performed using the Illumina NovaSeq6000 platform. Pairwise differential expression was calculated with edgeR. Pathway analysis was performed using Qiagen Ingenuity Pathway Analysis (IPA). RESULTS Transferrin receptor-1 (cellular iron uptake protein) was upregulated with 24 and 48h GaM relative to respective untreated controls, indicating relative iron depletion. GaM caused heme oxygenase-1 and ferritin upregulation, suggestive of oxidant stress. Important proteins in zinc homeostasis (metallothioneins and transporters) showed differential expression with GaM treatment. IPA revealed several affected pathways including Nrf2-mediated antioxidant response and iron homeostasis signaling. Other novel findings included inhibition of matrix metalloproteases, inhibition of S100/calcium, CREB, and FAK signaling, as well as alteration of GPCR and glutaminergic signaling. CONCLUSIONS This data underscores that several previously studied mechanisms of Ga in cancer are also active with GaM in glioblastoma. The many genes and pathways not previously known to be influenced by GaM will provide foundation for future mechanistic studies.