A Step Towards Development and Bio-evaluation of a Novel Radio-ligand 99mTc-CYX-DTPA Targeting Sigma 2 Receptors.

Introduction: Development of theranostics agents targeted towards particular receptors can effectively help in the management of cancer. The overexpression of the sigma-2 receptor (S2R) in tumors establishes it as a prominent biomarker for cancer cells.

Methods: Radiotheranostics rely on the design of specific molecules having versatility in applications of diagnosis and therapy by merely changing the radioisotope. We have designed a novel radiotheranostic S2R-targeted ligand using cyclohexylpiperazine and performed docking studies to narrow down the potential efficacious ligand. The potential molecule with G-score = -7.0 kcal/mol, was then synthesized using a three steps reaction including conjugation of 2-(4- cyclohexylpiperazine-1-yl)ethyl(CYX) with DTPA chelator. Subsequently, the molecule has been radiolabelled with ^99mTc using stannous chloride as a reducing agent, and a radiolabellieng efficiency of 95.0 ± 0.59% for ^99mTc-CYX-DTPA. As proof of concept, the molecule has been evaluated for its binding affinity and specificity using sigma receptors isolated from the liver membrane homogenates of mice. The binding affinity was found to be K_d = 12.84 ± 0.395 nM; B_max = 0.5258 ± 0.001 fmol/mg, indicating a high affinity for the receptors.

Results: In addition, the molecule was also assessed for biocompatibility using haemolysis analysis and cytotoxicity on HEK cells and MDA-MB-23, wherein the molecule showed no significant cytotoxicity up to 72 h on HEK cells and 32.42% cytotoxicity on MDA-MB-231 cells.

Conclusion: The future work will concentrate on the demonstration of in vivo targeting and sitespecific accumulation of the molecule along with its suitability for theranostics applications.