Copper-based therapeutics increase sodium/iodide symporter (NIS) transcription and enhance radioiodide uptake in thyroid cancer cells

Introduction: New drug approaches are urgently required to improve radioiodide (RAI) uptake for efficient ablation of thyroid cancer cells in RAI-refractory disease. Employing high-throughput screening of FDA-approved compounds we recently identified drugs capable of robust induction of sodium iodide symporter (NIS) activity to promote RAI uptake¹. In particular, a leading drug candidate – the well-established anti-alcoholism drug disulfiram (DSF) – had not been previously implicated in regulating NIS. A better understanding of how DSF can be used to modulate NIS function in vivo is now needed prior to clinical evaluation.

Materials and Methods: NIS function was monitored in vitro by RAI (¹²⁵I) uptake assays, and NIS expression via Western blotting and TaqMan-RTPCR. Technetium-99m pertechnetate (^99mTc) uptake was used to evaluate NIS function in Balb/c mice following intravenous administration.

Results: We demonstrate that the ability of DSF to increase RAI-uptake in thyroid TPC-1 (3.1-fold; P<0.01) and 8505C (4.9-fold; P<0.001) cells can be significantly potentiated by combination with Cu²⁺ to 5.1-fold and 18.9-fold increases respectively. Despite promising data, DSF has poor bioavailability in vivo due to its rapid metabolism to diethyldithiocarbamate (DDC) within the stomach and circulation with subsequent methylation in the liver. Whilst methylated DDC did not have any effect on NIS function, DDC chelated to divalent copper ions [Cu(DDC)₂] was highly effective at increasing RAI uptake (up to 8-fold; P<.001) in multiple thyroid cell types and induced significant NIS protein expression (up to 36.2-fold; 250 nM; P<0.001). Interestingly, a transcriptional effect of Cu(DDC)₂ was revealed via significant induction of NIS mRNA levels in TPC-1 (8.5-fold; P<0.001) and 8505C (104.8-fold; P<0.001) cells. In wild-type Balb/c mice the intraperitoneal administration of albumin nano-encapsulated Cu(DDC)₂ significantly induced thyroidal uptake of technetium-99m (^99mTc) after 30 min (~40% increase; n=11 per group; 3 mg/kg dose; P<0.001), as well as increasing thyroidal mRNA levels of NIS (1.9-fold; P<0.01), thyroid peroxidase (1.8-fold; P<0.001) and thyroglobulin (1.3-fold; P<0.05). Importantly, a significant positive correlation between thyroidal ^99mTc uptake and higher NIS mRNA levels (r_s=0.4477, P=0.0169) was apparent in Cu(DDC)₂-treated mice. Additionally, thyroidal ^99mTc-uptake (P<0.05) and NIS expression (P<0.05) were induced following intravenous administration of albumin nano-encapsulated Cu(DDC)₂ (~30%; n=5; 5 mg/kg dose).

Discussion: Our study demonstrates a promising drug strategy utilising a disulfiram metabolite to enhance NIS function in vivo, with clinical potential to improve treatment effectiveness in RAI-refractory thyroid cancer patients.

Reference: 1. Read ML et al. (2022) Targeting non-canonical pathways as a strategy to modulate the sodium iodide symporter. Cell Chem Biol. 29(3):502-516.e7.