What a difference a methylene makes: replacing Glu with Asp or Aad in the Lys-urea-Glu pharmacophore of PSMA-targeting radioligands to reduce kidney and salivary gland uptake

Abstract

The aim of this study was to investigate the effect of replacing Glu in the Lys-urea-Glu PSMA-targeting pharmacophore of [ 68 Ga]Ga-HTK03041 with a close analog on the uptake of kidneys, salivary glands and PSMA-expressing tumor xenografts. Methods: HTK03161, HTK03149 and HTK03189A/B were obtained by replacing Glu in HTK03041 with Asp, Aad (L-2-aminoadipic acid) and Api (2-aminopimelic acid), respectively. PSMA binding affinities were measured by competition binding assays. PET imaging and biodistribution studies of 68 Ga-labeled ligands were performed in LNCaP tumor-bearing mice. The best candidate HTK03149 was selected and radiolabeled with 177 Lu, and SPECT imaging and biodistribution studies were performed in LNCaP tumor-bearing mice. Radiation dosimetry calculation was conducted using the OLINDA software. Radioligand therapy study was performed in LNCaP tumor-bearing mice treated with [ 177 Lu]Lu-HTK03149 (9.3-148 MBq), [ 177 Lu]Lu-PSMA-617 (37 MBq) or nat Lu-HTK03149 (500 pmol). Results: PSMA binding affinities (K i ) of Ga-HTK03161, Ga-HTK03149, Ga-HTK03189A and Lu-HTK03149 were 3.88±0.66, 6.99±0.80, 550±35.7 and 1.57±0.42 nM, respectively. PET imaging showed that all 68 Ga-labeled HTK03161, HTK03149 and HTK03189A/B were excreted mainly via the renal pathway and had minimal uptake in all organs/tissues including kidneys and salivary glands. Tumor xenografts were clearly visualized in PET images of [ 68 Ga]Ga-HTK03161 and [ 68 Ga]Ga-HTK03149 but were barely visualized using [ 68 Ga]Ga-HTK03189A/B. Tumor uptake values for [ 68 Ga]Ga-HTK03161, [ 68 Ga]Ga-HTK03149, [ 68 Ga]Ga-HTK0189A and [ 68 Ga]Ga-HTK03189B were 12.7±1.91, 19.1±6.37, 2.10±0.28 and 0.67±0.15 %IA/g, respectively at 1h post-injection, and their average kidney and salivary gland uptake values were 2.13-4.41 and 0.20-0.23 %IA/g, respectively. Longitudinal SPECT imaging studies showed that [ 177 Lu]Lu-HTK03149 was excreted mainly through the renal pathway with high uptake in LNCaP tumors and minimal uptake in all normal organs/tissues. The tumor uptake of [ 177 Lu]Lu-HTK03149 peaked at 4h post-injection (20.9±2.99 %IA/g) and the uptake was sustained over time. Compared to [ 177 Lu]Lu-PSMA-617, [ 177 Lu]Lu-HTK03149 had 145% increase in tumor absorbed dose but 70% less in kidney absorbed dose, leading to an 7.1-fold increase in tumor-to-kidney absorbed dose ratio. Radioligand therapy studies showed that only half of the [ 177 Lu]Lu-PSMA-617 injected dosage was needed for [ 177 Lu]Lu-HTK03149 to achieve the same median surv...

Synthesis and Preclinical Evaluation of Three Novel 68Ga-Labeled Bispecific PSMA/FAP-Targeting Tracers for Prostate Cancer Imaging

“…The following supporting information can be downloaded at: . Detailed synthetic procedures and results for the preparation of bispecific ligands and their nat Ga/ 68 Ga-complexed analogs; Table S1: HPLC purification conditions and MS characterizations of DOTA-conjugated precursors; Table S2: HPLC purification conditions and MS characterizations of nonradioactive Ga-complexed standards; Table S3: HPLC conditions for the purification and quality control of 68 Ga-labeled tracers; Table S4: Biodistribution and uptake ratios of 68 Ga-labeled PSMA/FAP bispecific tracers, HTK03041 and FAPI-04 in LNCaP tumor-bearing mice; Table S5: Biodistribution and uptake ratios of 68 Ga-labeled PSMA/FAP bispecific tracers, HTK03041 and FAPI-04 in HEK293T:hFAP tumor-bearing mice [ 26 , 47 , 48 , 49 , 50 ].…”

Novel 68Ga-Labeled Pyridine-Based Fibroblast Activation Protein-Targeted Tracers with High Tumor-to-Background Contrast

“…Ga complexation of AV02053 and AV02070 was conducted in NaOAc buffer (0.1 M, pH 4.2–4.5) for nonradioactive standards and in HEPES buffer (2 M, pH 5.0) for 68 Ga labeling, as previously reported ( Tables S2 and S3 ) [ 32 , 33 ]. Ga-AV02053 and Ga-AV02070 were obtained in 42 and 22% yields, respectively.…”

Imidazolium‐methylene‐trifluoroborate: A novel radioprosthetic group validated with preclinical 18F‐Positron Emission Tomography imaging of Prostate Specific Membrane Antigen in mice

“…In light of this success, a number of new PSMA-targeting diagnostics, therapeutics, and theranostics are advancing in pre-clinical and clinical trials. [4][5][6][7][8][9][10][11] For a majority of these agents, the lysineglutamate-ureido scaffold (EUK) serves as the primary binding motif that tightly associates with the PSMA target with high affinity and selectivity.…”

“…A prime example is prostate cancer (PCa), where diagnostic agents and companion therapeutics have increased patient survival; in just the past year, the FDA approved 18 F‐Pylarify™ 2 as a diagnostic agent for imaging the prostate‐specific membrane antigen (PSMA) to detect the metastatic spread of PCa and 177 Lu‐Pluvicto™ as a targeted radiotherapeutic that recognizes the same target 3 and is used to treat patients with end‐stage disease. In light of this success, a number of new PSMA‐targeting diagnostics, therapeutics, and theranostics are advancing in pre‐clinical and clinical trials 4–11 . For a majority of these agents, the lysine‐glutamate‐ureido scaffold (EUK) serves as the primary binding motif that tightly associates with the PSMA target with high affinity and selectivity.…”