Cancer Targeting Potential of 99mTc-Finasteride in Experimental Model of Prostate Carcinogenesis

Target specific uptake of a newly synthesized radiolabeled 5α-reductase inhibitor “Tc-99m-17-Oxo-17a-Aza-D-Homo-5-Androsten-3β-yl phenoxyacetate (Tc-99m-17a-Aza Steroid)” in rat prostatic neoplastic lesions

Objective:

Considering the 5α-reductase (5AR) inhibitory activity of the oximes and the importance of the ester group in increasing the anti-androgenic property, we reasoned to synthesize a compound having a lactam group in ring D and an ester group at the 3 β position of the androsterone nucleus. The study aims to radiolabel 17-oxo-17a-aza-D-homo-5-androsten-3β-yl phenoxyacetate (17a-aza steroid) with Tc-99m to evaluate its targeted uptake in experimentally induced prostate carcinogenesis in rats.

Materials and Methods:

The prediction of the optimal interaction and binding affinity of Tc-99m-17-oxo-17a-aza-D-homo-5-androsten-3 β-ylphenoxyacetate (Tc-99m-17a-aza steroid) toward 5AR inhibitor was done using Biopredicta Vlife MDS tool. Tc-99m-17a-aza steroid was developed by direct radiolabeling protocol. The radio-pharmacological characteristics (serum stability, plasma protein-binding ability, and lipophilicity) of the complex were evaluated. Further, the bio-distribution studies of the complex were performed in rats with experimentally induced prostate carcinogenesis.

Results:

The in-silico analysis exhibits favorable binding of Tc-99m-17a-aza toward 5AR with D score-130.97. The radiochemical purity of Tc-99m-17a-aza was 96.79%. The radio-complex maintained stability in the rat serum for a period of 6 h (hours). Plasma protein binding and Log Po/w value were observed to be 86.23 ± 7.08% and 0.118 ± 0.045, respectively. A significantly enhanced percent-specific uptake was observed in the prostate of rats with induced prostate carcinogenesis.

Conclusion:

The study concludes that Tc-99m-17a-aza exhibits prostate specificity and can be explored further for its potential as a radionuclide imaging probe.

Targeting 5α-reductase with 99mTc labeled dutasteride derivatives for prostate imaging

To assess the suitability of 99mTc labeled 5α-reductase (5α-Rds) inhibitors for non-invasive targeting of prostate cancer (PCa) using Male Sprague Dawely Rat (MSDR) model. In this work, dutasteride (Cpd-1) a 5α-Rds inhibitor was derivatized to its dithiocarbamate analogue (Cpd-2) for subsequent synthesis of 99mTc(CO)3-dutasteride dithiocarbamate (Cpd-3) using tricarbonyl technique. To determine the structure of Cpd-3, for the first time a reference Re(CO)3-dutasteride dithiocarbamate (Cpd-4) was synthesized and characterized with NMR, ESIMS, HPLC and elemental analysis. HPLC was used to establish the identity of Cpd-3 using Cpd-4 as a reference standard. The suitability of Cpd-3 as a new 5α-Rds targeting agent was investigated, both in vitro and vivo. The Cpd-3 has shown ≥98 % in vitro stability at room temperature and was remained ≥90 % stable up to 6 h. In serum Cpd-3 has revealed an analogous behavior with a small decrease in stability after 16 h. High uptake (26.25 ± 1.10 %, after 4 h of i.v.) of Cpd-3 was observed in the prostate (target tissue) of MSDR model with reasonably good target to non-target ratio. Blocking the target site with excess Cpd-2 considerably decreased the uptake of Cpd-3 to 4.10 ± 0.75 % in PCa. High in vitro stability in saline and serum and in vivo uptake in prostate of MSDR model plausibly attracts the opportunity of using Cpd-3 as a novel radiopharmaceutical for non invasive targeting of prostate.