Human epidermal growth factor receptor 2 (HER2) may serve as a valid target for diagnosis of cancer. The probes with capability for near-infrared window one region II (NIR-II) and positron emission tomography (PET) dual-modal imaging are highly desired for HER2-positive tumor detection. Herein, three HER2-targeted peptides were designed and further modified with indocyanine green (ICG) and 2,2′,2″,2″-(1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrayl)­tetraacetic acid (DOTA), which were used for NIR-II imaging and complexation with 68Ga for PET. Among the resulted probes (DOTA-ZC01-ICG, DOTA-KSP-ICG, and DOTA-ZC02-ICG), NIR-II imaging revealed that DOTA-ZC02-ICG had the best tumor imaging performance in SKOV3 tumor-bearing mice. The highest T/N ratio (5.4) was achieved at 4 h post-injection. Furthermore, DOTA-ZC02-ICG was radiolabeled with 68Ga to generate [68Ga]-DOTA-ZC02-ICG for PET, and it clearly delineated at 0.5, 1, and 2 h post-injection. The tumor uptake reached 1.9 %ID/g at 0.5 h, and the tumor uptakes were significantly inhibited in the blocking study (p < 0.05). Overall, it provides a promising technique for tumor dual-modal imaging and a new molecular scaffold for developing HER2-targeted theranostic agents.

Molecular targets serve a crucial role in drug development. Herein, we discovered a novel peptide that can specifically target the human epidermal growth factor receptor 2 (HER2) and thus named it Herceptide. In our study, Herceptide was conjugated to the near-infrared fluorescent dye indocyanine green (ICG) to obtain a probe, ICG-Herceptide. Importantly, specific binding to HER2 was revealed by molecular docking, surface plasmon resonance analysis, and competition assays. The probe showed high binding affinity (K D = 1.03 nM) and fast binding property (k on = 0.44 min −1 ). In vivo near-infrared window two (NIR-II, 1000−1700 nm) imaging in HER2-overexpressed SKOV3 tumor-bearing mice demonstrated a high tumor-to-normal tissue signal ratio (T/N = 7.3) at 8 h postinjection. In the blocking study, ICG-Herceptide coinjected with Herceptide only showed a weak tumor signal. In other HER2 high-expression tumors, such as non-small-cell lung cancer A549 and gastric cancer MKN45, the tumor-to-normal tissue signal ratios (T/N) were 4.1 and 4.7, respectively. In contrast, HER2 low-expression tumor MDAMB231 shows no imaging contrast between the tumor and normal tissues. Furthermore, tumor resection was successfully performed under the guidance of the ICG-Herceptide-based NIR-II imaging in subcutaneous SKOV3 mice models. The biocompatibility study indicated that the probe had no observable toxicity to cells and tissues. Overall, these results demonstrate that ICG-Herceptide is a promising optical probe for the diagnosis and localization of HER2-overexpressing tumors. Moreover, Herceptide is a novel HER2targeting peptide and can be further used for developing theranostic agents.

As an important cancer-associated fibroblast-specific biomarker, fibroblast activation protein (FAP) has become an attractive target for tumor diagnosis and treatment. However, most FAP-based radiotracers showed inadequate uptake and short retention in tumors. In this study, we designed and synthesized a novel FAP ligand (DOTA-GPFAPI-04) through assembling three functional moieties: a quinoline-based FAP inhibitor for specifically targeting FAP, a FAP substrate Gly−Pro as a linker for increasing the FAP protein interaction, and a 2,2′,2″,2‴-(1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrayl)tetraacetic acid (DOTA) chelator for radiolabeling with different radionuclides. The FAP targeting ability of DOTA-GPFAPI-04 was investigated by molecular docking studies. DOTA-GPFAPI-04 was then radiolabeled with 68 Ga to give [ 68 Ga]Ga-DOTA-GPFAPI-04 for positron emission tomography (PET) imaging of glioblastoma. [ 68 Ga]Ga-DOTA-GPFAPI-04 exhibited a purity of >98% and high stability analyzed by radio-HPLC in saline and mouse serum. Cell uptake studies demonstrated the targeting specificity of the probe. Further in vivo pharmacokinetic studies in normal mice demonstrated the quick clearance of the probe. Moreover, compared with the widely studied [ 68 Ga]Ga-FAPI-04, [ 68 Ga]Ga-DOTA-GPFAPI-04 showed much higher U87MG tumor uptake values (4.467 ± 0.379 for [ 68 Ga]Ga-DOTA-GPFAPI-04 and 1.267 ± 0.208% ID/g for [ 68 Ga]Ga-FAPI-04 at 0.5 h post-injection, respectively). The area under the curve based on time−activity curve (TAC) analysis for tumor radioactivity in small animal models was 422.5 for [ 68 Ga]Ga-DOTA-GPFAPI-04 and 98.14 for [ 68 Ga]Ga-FAPI-04, respectively, demonstrating that the former had longer tumor retention time. The tumor-to-muscle (T/M) ratio for [ 68 Ga]Ga-DOTA-GPFAPI-04 reached 9.15 in a U87MG xenograft animal model. PET imaging and blocking assays showed that [ 68 Ga]Ga-DOTA-GPFAPI-04 had specific tumor uptake. In summary, this study demonstrates the successful synthesis and evaluation of a novel FAPI targeting probe, [ 68 Ga]Ga-DOTA-GPFAPI-04, with a Gly−Pro sequence. It shows favorable in vivo glioblastoma imaging properties and relatively long tumor retention, highlighting DOTA-GPFAPI-04 as a promising molecular scaffold for developing FAP targeting tumor theranostic agents.

Metrics & MoreArticle RecommendationsI n the last paragraph of the Introduction section, change "In this study, we first identified that the molecular target of a peptide (RSLWSDFYASASRGP) screened from phage display is the human epidermal growth factor receptor 2 (HER2). 1 " to "In this study, we first identified that the molecular target of a peptide (RSLWSDFYASASRGP) screened from phage display reported previously 1 is the human epidermal growth factor receptor 2 (HER2)."■ REFERENCES