Therapeutic utilization of tetrodotoxin for treating carcinomas: a comparative molecular docking and dosage adjustment study

Samenvatting

Background: Cancer metastasis is facilitated by voltage-gated sodium channels (VGSCs) through the extracellular matrix (ECM) degradation. VGSCs play a pivotal role in cancer invasion during its epithelial-mesenchymal transition; hence, decreasing treatability. Tetrodotoxin (TTX) is a potent, selective neurotoxin that blocks VGSCs, particularly Nav1.7, which is overexpressed in carcinomas, especially type II endometrial and ductal carcinomas. TTX is found mainly in puffer fish (Fugu) and other marine and terrestrial animals used in traditional Japanese cuisine. TTX carries the potential for therapeutic applications; however, it’s limited by a high toxicity and narrow therapeutic index (NTI), requiring precise dosage control for medicinal use [38]. Thus, TTX appropriate adjustment could give novel anti-metastatic agent, while maintaining a non-toxic concentration for human, what is very important. Limited insights exist on TTX's toxicology and therapeutic potential. 

Objective: This study employed a multifaceted approach to evaluate the therapeutic potential of TTX in inhibiting carcinoma metastasis while ensuring concentrations remain within non-toxic levels for humans. Due to the hazardous nature of TTX, Carbamazepine (CBZ), an anticonvulsant known to block Nav1.7, was selected as a reference compound. CBZ's established pharmacokinetic profile and lower toxicity allowed for safer experimental handling and provided a comparative baseline for TTX's efficacy. Since collecting volumetric data on CBZ, according to Mohr’s method, was unfeasible due to its fully molecular composition, Verapamil was introduced as a similar channel-blocking drug in chloride salt form.

Methods: Verapamil chloride was used for precipitation titration to estimate CBZ’s effective (ED50), toxic (TD50), and lethal (LD50) doses. This was done by using the ED50 of Verapamil and transcribing it to CBZ, as they have very similar TI. Similar tactics were carried out for the determination of the ED50 of TTX in concentration form, yielding its therapeutic dose. TI of TTX was calculated. Molecular Docking analysis of both CBZ and TTX’s interaction with Nav1.7, independently 5 times using 20 starting conformations for each compound, with the virtual box size not exceeding 27,000 Å.

Results: In silico analysis showed that TTX binds to Nav1.7 within a pocket, demonstrating lower affinity but greater efficacy due to site-specific interactions, while CBZ binds on a more exposed level with less efficacy. Volumetric dosage-adjustment analysis indicated that, while TTX has NTI ≈ 1.6, careful administration could allow localized carcinoma treatment at 1.737×10⁻⁸ mol cm⁻³/kg. The findings support the hypothesis that TTX, in controlled dosage-adjustment and targeted delivery, could inhibit carcinoma metastasis. 

Conclusion: TTX has the potential to inhibit the invasion of carcinoma cells, especially those of ductal and type II endometrial carcinomas, by selectively blocking Nav1.7. Careful dosage control and targeted drug delivery systems (which would vary with the stage of the cancer’s development) are necessary to minimize systemic toxicity. Further research is required to practically develop safe administration methods to enhance TTX’s therapeutic viability, with in vivo methodologies.

Keywords: Cancer, tetrodotoxin (TTX), voltage-gated sodium channels (VGSCs), carbamazepine (CBZ), novel anti-metastatic agent, verapamil, bioactive, functional food.