99mTc-Labeled D-Type PTP as a Plectin-Targeting Single-Photon Emission Computed Tomography Probe for Hepatocellular Carcinoma Imaging

Plectin, a scaffolding protein overexpressed in tumor cells, plays a significant role in hepatocellular carcinoma (HCC) proliferation, invasion, and migration. However, the use of L-type peptides for targeting plectin is hindered by their limited stability and retention. We designed a D-type plectin-targeting peptide (^DPTP) and developed a novel single-photon emission computed tomography (SPECT) probe for HCC imaging. The ^DPTP targeting ability was evaluated in vitro using flow cytometry and ex vivo fluorescence imaging. ^99mTc radiolabeling was performed using tricine and ethylenediamine-N,N'-diacetic acid (EDDA) as coligands after modification with 6-hydrazino nicotinamide (HYNIC) at the N termini of ^DPTP. The radiochemical purity (RCP), in vitro stability, and binding affinity of the prepared ^99mTc-HYNIC-^DPTP were analyzed. Tumor uptake, metabolic stability, biodistribution, and pharmacokinetics of ^99mTc-HYNIC-^DPTP were investigated and compared with those of ^99mTc-labeled L-type PTP (^99mTc-HYNIC-PTP) in HCC tumor-bearing mice. ^DPTP could be efficiently radiolabeled with ^99mTc using the HYNIC/tricine/EDDA system with a high RCP and good in vitro stability. Compared with the L-type PTP, ^DPTP exhibited improved targeting ability, and ^99mTc-HYNIC-^DPTP displayed higher tumor uptake, better metabolic stability, longer blood circulation time, and lower kidney retention, resulting in superior imaging performance and biodistribution in vivo. ^99mTc-HYNIC-^DPTP has great potential as a novel SPECT probe for diagnosing HCC.