Chlorotoxin Conjugated with Saporin Reduces Viability of ML-1 Thyroid Cancer Cells In Vitro

BackgroundAlthough differentiated thyroid cancer has good prognosis, radioactive iodine (RAI) resistant thyroid cancer is difficult to treat. Current therapies for progressive RAI resistant thyroid cancer are not very effective. There is an unmet need for better therapeutic agents in this scenario. Studies have shown that aggressive thyroid cancers express matrix metalloproteinase -2 (MMP-2). Chlorotoxin is a selective MMP-2 agonist. Given that Saporin is a well-known ribosome-inactivating protein used for anti-cancer treatment, we hypothesized that Chlorotoxin-conjugated Saporin (CTX-SAP) would inhibit the growth of aggressive thyroid cancer cell lines expressing MMP-2. MethodsThe ML-1 thyroid cancer cell line was used for this study because it is known to express MMP-2. ML-1 cells were treated with a toxin consisting of biotinylated Chlorotoxin bonded with a secondary conjugate of Streptavidin-ZAP containing Saporin (CTX-SAP) from 0 to 600 nM for 72 hours. Then, cell viability was measured via XTT assay at an absorbance of A450-630. Control experiments were set up using Chlorotoxin and Saporin individually at the same varying concentrations. ResultsAfter 7 hours of incubation, there was a statistically significant reduction in cell viability with increasing concentrations of the CTX-SAP conjugate (F=4.286, p=0.0057). In particular, the cell viability of ML-1 cells was decreased by 49.77% with the treatment of 600 nM of CTX-SAP (F=44.24), and the reduction in cell viability was statistically significant (Dunnetts test p<0.0001). In contrast, individual Chlorotoxin or Saporin in increasing concentrations had no significant effect on cell viability using similar assay. ConclusionThis in vitro study demonstrated the efficacy of a CTX-SAP conjugate in reducing the viability of ML-1 thyroid cancer cells in a dose dependent manner. Further studies are needed to delineate the effectiveness of CTX-SAP in the treatment of aggressive thyroid cancer. Our study points towards MMP-2 as a potential target for RAI-resistant thyroid cancer.