Preclinical evaluation of 99m Tc-labeled LHRH as GnRH receptor imaging

Abstract

Breast cancer stands as the principal cause of cancer-related mortality among women in the developed world. Notably, receptors of Luteinizing Hormone-Releasing Hormone (LHRH or GnRH) exhibit overexpression in this malignancy. This study aimed to develop a new molecular prove [99mTc] Tc-HYNIC-GSG-LHRH(D-Lys6)/Tricine/Nicotinic Acid (NA) as a novel molecular imaging agent for breast cancer. HYNIC-GSG-LHRH(D-Lys6) was acquired and radiolabeled with [99mTc] Tc. The radiochemical purity and stability in different conditions were evaluated by Instant thin-layer chromatography (ITLC) and High performance liquid chromatography (HPLC). Lipophilicity was performed by the distribution coefficient test. In vitro cell binding studies were performed in different human and mice breast cancer cell lines (MDA-MB-231, MDA-MB-435, MCF-7, BT474 and 4T1) as well as in normal murine fibroblasts (NIH-3T3) and CHO-K1 as negative control. Biodistribution studies were performed in normal Balb/c mice and 4T1 tumor-bearing Balb/c mice up to 6 h post-injection. SPECT/CT images were performed in 4T1 tumor-bearing Balb/c mice up to 5 h post injection (p.i). [99mTc] Tc-HYNIC-GSG-LHRH(D-Lys6)/Tricine/NA complex was labeled with a high radiochemical purity (> 98%) and stable up to 4 hs. It presented a good hydrophilicity (Log P = − 2.82 ± 0.04). It also yields a relevant and specific binding in all breast cell lines evaluated. Biodistributions studies showed a high renal clearance and low unspecific binding (< 2% Act/g) in most organs, as well as appreciable tumor uptake (5.8 ± 0.5%ID/g 1 h p.i) and high tumor/muscle ratio (maximum of 30.5 ± 11.2 at 1 h p.i). SPECT/CT of 4T1-tumor bearing Balb/c mice images revealed similar results to biodistribution studies, with a Tumor/Non-Tumor ration of > 3.5 at all times evaluated. In vivo blockage studies showed specificity for the LHRH-R; demonstrating a substantial potential for in vivo visualization of LHRH-R expression in breast cancer.