The Effect of Albumin-Binding Moiety on Tumor Targeting and Biodistribution Properties of 67Ga-Labeled Albumin Binder-Conjugated Alpha-Melanocyte-Stimulating Hormone Peptides

Jingli Xu; Fabio Gallazzi; Darrell R Fisher; Rene Gonzalez; Yubin Miao

doi:10.1089/cbr.2021.0273

. 2022 Feb 8;37(1):47–55. doi: 10.1089/cbr.2021.0273

The Effect of Albumin-Binding Moiety on Tumor Targeting and Biodistribution Properties of ⁶⁷Ga-Labeled Albumin Binder-Conjugated Alpha-Melanocyte-Stimulating Hormone Peptides

Jingli Xu ¹, Fabio Gallazzi ², Darrell R Fisher ³, Rene Gonzalez ⁴, Yubin Miao ^1,^✉

PMCID: PMC8865629 PMID: 34762521

Abstract

Background: The purpose of this study was to examine the effect of 4-p-(tolyl)butyric acid as an albumin-binding (ALB) moiety on tumor targeting and biodistribution properties of ⁶⁷Ga-labeled albumin binder-conjugated alpha-melanocyte-stimulating hormone peptides.

Materials and Methods: DOTA-Lys(ALB)-G/GG/GGG-Nle-CycMSH_hex {1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid-Lys(ALB)-Gly/GlyGly/GlyGlyGly-Nle-c[Asp-His-DPhe-Arg-Trp-Lys]-CONH₂} were synthesized with 4-p-(tolyl)butyric acid serving as an ALB moiety. The melanocortin-1 receptor (MC1R)-binding affinities of the peptides were determined on B16/F10 melanoma cells. The biodistribution of ⁶⁷Ga-DOTA-Lys(ALB)-G/GG/GGG-Nle-CycMSH_hex was examined on B16/F10 melanoma-bearing C57 mice at 2 h postinjection to select a lead peptide for further evaluation. The melanoma targeting and imaging properties of ⁶⁷Ga-DOTA-Lys(ALB)-GGNle-CycMSH_hex {⁶⁷Ga-ALB-G2} were determined on B16/F10 melanoma-bearing C57 mice.

Results: The IC₅₀ value of DOTA-Lys(ALB)-G/GG/GGG-Nle-CycMSH_hex {ALB-G1, ALB-G2, ALB-G3} was 0.67 ± 0.07, 0.5 ± 0.09 and 0.51 ± 0.03 nM on B16/F10 cells, respectively. ⁶⁷Ga-ALB-G2 was further evaluated as a lead peptide because of its higher tumor uptake (30.25 ± 3.24%ID/g) and lower kidney uptake (7.09 ± 2.22%ID/g) than ⁶⁷Ga-ALB-G1 and ⁶⁷Ga-ALB-G3 at 2 h postinjection. The B16/F10 melanoma uptake of ⁶⁷Ga-ALB-G2 was 15.64 ± 4.55, 30.25 ± 3.24, 26.76 ± 3.23, and 10.71 ± 1.21%ID/g at 0.5, 2, 4, and 24 h postinjection, respectively. The B16/F10 melanoma lesions were clearly visualized by SPECT/CT using ⁶⁷Ga-ALB-G2 as an imaging probe at 2 h postinjection.

Conclusions: The introduction of 4-p-(tolyl)butyric acid as an ALB moiety increased the blood retention, and resulted in higher tumor/kidney ratio of ⁶⁷Ga-ALB-G2 as compared with its counterpart without an albumin binder. However, the resulting high uptake of ⁶⁷Ga-ALB-G2 in blood and liver need to be further reduced to facilitate its therapeutic application when replacing ⁶⁷Ga with therapeutic radionuclides.

Keywords: albumin-binding moiety, alpha-melanocyte-stimulating hormone, melanocortin-1 receptor, melanoma targeting

Introduction

Malignant melanoma is the most lethal form of skin cancer due to the extreme aggressiveness of melanoma metastasis. Approximately 100,350 new cases and 6850 fatalities occurred in the United States in 2020.¹ Despite the significant improvement of new immunotherapy on melanoma treatment over the past decade,^2–7 the 5-year survival is only 35% for metastatic melanoma patients.⁷ There is a great need to develop new theranostic agents for metastatic melanoma. Melanocortin-1 receptor (MC1R) is a distinct melanoma target because of its overexpression on both melanotic and amelanotic human melanoma samples.^8–10 We have developed a new class of MC1R-targeted radiolabeled lactam-cyclized α-melanocyte-stimulating hormone (α-MSH) peptides, building upon the key backbone of GGNle-CycMSH_hex {Gly-Gly-Nle-c[Asp-His-DPhe-Arg-Trp-Lys]-CONH₂}, for melanoma imaging and therapy over the years.^11–20 Different radiometal chelators, namely hydrazinonicotinamide (HYNIC), 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) and 1,4,7-triazacyclononane-1,4,7-triyl-triacetic acid (NOTA), were utilized for radiolabeling of diagnostic and therapeutic radionuclides, including ^99mTc, ¹¹¹In, ²⁰³Pb, ^67/68Ga, ⁶⁴Cu, ¹⁷⁷Lu, and ⁹⁰Y for melanoma imaging and therapy.^11–20 These radiolabeled α-MSH peptides generally exhibited high melanoma uptake and rapid urinary clearance. Our first-in-human study clearly demonstrated the clinical relevance of MC1R and the feasibility of utilizing ⁶⁸Ga-DOTA-GGNle-CycMSH_hex to target MC1R for human melanoma imaging.¹⁰ Remarkably, the melanoma metastases in brain, lung, connective tissue, and intestines were clearly visualized using ⁶⁸Ga-DOTA-GGNle-CycMSH_hex as an imaging probe.¹⁰

Dumelin et al. identified a class of portable albumin binders from a DNA-encoded chemical library.²¹ Specifically, 4-p-(iodophenyl)butyric acid-D-Lys-Ac displayed 3.2 μM of dissociation constant (K_d = 3.2 μM) and 4-p-(tolyl)butyric acid-D-Lys-Ac exhibited a more than one order of magnitude higher K_d value (K_d = 52 μM).²¹ Both albumin-binding (ALB) moieties have been utilized as strong and weak albumin binders in radiolabeled folate and prostate-specific membrane antigen (PSMA) ligands to improve their tumor uptake.^22–28 For instance, Umbricht et al. prepared ¹⁷⁷Lu-PSMA-ALB-53 using 4-p-(iodophenyl)butyric acid and ¹⁷⁷Lu-PSMA-ALB-56 using 4-p-(tolyl)butyric acid, and compared their biodistribution properties in PC-3 PIP tumor-bearing mice. Despite that both ¹⁷⁷Lu-PSMA-ALB-56 and ¹⁷⁷Lu-PSMA-ALB-53 displayed similar area under the curve (AUC) value in tumor, the tumor/blood, tumor/kidney, and tumor/liver AUC ratios of ¹⁷⁷Lu-PSMA-ALB-56 were between three-fold and five-fold higher than those of ¹⁷⁷Lu-PSMA-ALB-53.²⁷ This interesting report suggested that 4-p-(tolyl)butyric acid might be a better ALB moiety than 4-p-(iodophenyl)butyric acid because of the dramatic reduced uptake of ¹⁷⁷Lu-PSMA-ALB-56 in blood, kidney, and liver.²⁷

^67/68Ga-DOTA-GGNle-CycMSH_hex exhibited high melanoma uptake and potential for single photon emission computed tomography (SPECT) and positron emission tomography (PET) imaging of melanoma in our previous reports.^10,13 Thus, we were interested whether the ALB moiety could affect the tumor targeting and biodistribution property of ⁶⁷Ga-DOTA-GGNle-CycMSH_hex. In this study, they attached 4-p-(tolyl)butyric acid to the epsilon amino group of lysine {Lys(ALB)} and conjugated DOTA to the alpha amino group of lysine to yield DOTA-Lys(ALB)-GNle-CycMSH_hex, DOTA-Lys(ALB)-GGNle-CycMSH_hex, and DOTA-Lys(ALB)-GGGNle-CycMSH_hex peptides, respectively. It was unknown whether the bulky Lys(ALB) moiety could affect the nanomolar MC1R-binding affinity of the Nle-CycMSH_hex motif. Therefore, we used one to three glycines as linkers to separate the DOTA-Lys(ALB) and Nle-CycMSH_hex. We synthesized the DOTA-Lys(ALB)-G/GG/GGG-Nle-CycMSH_hex peptides using fluorenylmethoxycarbonyl (Fmoc) chemistry, determined their MC1R binding affinities on B16/F10 melanoma cells, prepared their ⁶⁷Ga-conjugates, and examined their biodistribution and tumor targeting properties on B16/F10 melanoma-bearing C57 mice in this study.

Materials and Methods

Chemicals and reagents

Amino acids and resin were purchased from Advanced ChemTech, Inc., (Louisville, KY) and Novabiochem (San Diego, CA). DOTA(tBu)₃ was purchased from CheMatech, Inc., (Dijon, France) for peptide synthesis. ¹²⁵I-Tyr²-[Nle⁴, D-Phe⁷]-α-MSH {¹²⁵I-(Tyr²)-NDP-MSH} was obtained from PerkinElmer, Inc., (Waltham, MA) for in vitro binding assay. ⁶⁷GaCl₃ was purchased from Lantheus Medical Imaging (North Billerica, MA) for radiolabeling. B16/F10 murine melanoma cells were received from American Type Culture Collection (Manassas, VA). All other chemicals used in this study were purchased from Thermo Fisher Scientific (Waltham, MA) and used without further purification.

Peptide synthesis

DOTA-Lys(ALB)-GNle-CycMSH_hex (ALB-G1), DOTA-Lys(ALB)-GGNle-CycMSH_hex (ALB-G2), and DOTA-Lys(ALB)-GGGNle-CycMSH_hex (ALB-G3) were synthesized using Fmoc chemistry. Generally, 70 μmol of resin, 210 μmol of each Fmoc-protected amino acid and DOTA(tBu)₃ were used for the synthesis. Briefly, the linear intermediate scaffolds of Dde-Lys(Fmoc)-Gly-Nle-Asp(O-2-PhiPr)-His(Trt)-DPhe-Arg(Pbf)-Trp(Boc)-Lys(Mtt), Dde-Lys(Fmoc)-Gly-Gly-Nle-Asp(O-2-PhiPr)-His(Trt)-DPhe-Arg(Pbf)-Trp(Boc)-Lys(Mtt), and Dde-Lys(Fmoc)-Gly-Gly-Gly-Nle-Asp(O-2-PhiPr)-His(Trt)-DPhe-Arg(Pbf)-Trp(Boc)-Lys(Mtt) were synthesized on Sieber amide resin by an Advanced ChemTech multiple-peptide synthesizer (Louisville, KY). The 4-p-(tolyl)butyric acid was coupled to each intermediate scaffold after the removal of Fmoc on the epsilon amino group of lysine. Then the DOTA(tBu)₃ was coupled to each scaffold after the removal of Dde on the alpha amino group of lysine by 2% hydrazine. The protecting groups of Mtt and 2-phenylisopropyl were selectively removed and the linear peptides were cleaved from the resin during single reaction, treating with a mixture of 3.5% of trifluoroacetic acid (TFA), and 5% of thioanisole. The cyclization reaction was achieved by an overnight reaction at 25°C in dimethylformamide (DMF) using benzotriazole-1-yl-oxy-tris-pyrrolidino-phosphonium-hexafluorophosphate (PyBOP) as a coupling agent in the presence of N,N-diisopropylethylamine (DIPEA). After the cyclization reaction, all protecting groups were totally removed by treating with a mixture of TFA, thioanisole, phenol, water, ethanedithiol, and triisopropylsilane (87.5:2.5:2.5:2.5:2.5:2.5) for 2 h at 25°C. The peptides were precipitated and washed with ice-cold ether four times, and purified by reverse-phase high-pressure liquid chromatography (RP-HPLC) on a Grace Vydac C-18 analytical column (Vydac 218TP54, Deerfield, IL) using the following gradient at a 1 mL/min flowrate. The mobile phase consisted of solvent A (20 mM HCl aqueous solution) and solvent B (100% CH₃CN). The gradient was initiated and kept at 72:28 A/B for 3 min followed by a linear gradient of 72:28 A/B to 62:38 A/B over 20 min. Then, the gradient was changed from 62:38 A/B to 10:90 A/B over 3 min followed by an additional 5 min at 10:90 A/B. Thereafter, the gradient was changed from 10:90 A/B to 72:28 A/B over 3 min. The purified peptides were characterized by liquid chromatography–mass spectrometry (LC-MS).

In vitro competitive binding assay

The MC1R binding affinities of ALB-G1, ALB-G2, and ALB-G3 were determined on B16/F10 melanoma cells by in vitro competitive receptor-binding assay. The receptor-binding assay was replicated in triplicate. The B16/F10 cells (0.5 × 10⁵ cells/well, n = 3) were incubated at room temperature (25°C) for 2 h with ∼30,000 counts per minute (cpm) of ¹²⁵I-(Tyr²)-NDP-MSH in the presence of 10⁻¹³ to 10⁻⁵ M of the peptide in 0.3 mL of binding medium {modified Eagle's medium with 25 mM N-(2-hydroxyethyl)-piperazine-N’-(2-ethanesulfonic acid), pH 7.4, 0.2% bovine serum albumin (BSA), 0.3 mM 1,10-phenanthroline}. The binding medium was aspirated after the incubation. The cells were rinsed twice with 0.5 mL of ice-cold pH 7.4, 0.2% BSA/0.01 M phosphate buffered saline (PBS) and lysed in 0.5 mL of 1 N NaOH for 5 min. The cells were harvested and measured in a Wallac 1480 automated gamma counter (PerkinElmer, NJ). The IC₅₀ value was calculated using the Prism software (GraphPad Software, La Jolla, CA).

Preparation and specific binding of ⁶⁷Ga-ALB-G1, ⁶⁷Ga-ALB-G2, and ⁶⁷Ga-ALB-G3

⁶⁷Ga-ALB-G1, ⁶⁷Ga-ALB-G2, and ⁶⁷Ga-ALB-G3 were prepared in a 0.25 M NH₄OAc-buffered solution (pH 4.5). Briefly, 20 μL of ⁶⁷GaCl₃ (37–74 MBq in 0.1 M HCl aqueous solution), 10 μL of 1 mg/mL peptide aqueous solution, and 200 μL of 0.25 M NH₄OAc (pH 4.5) were added into a reaction vial and incubated at 75°C for 20 min. The pH of each reaction mixture was 4. After the incubation, 10 μL of 0.05% EDTA (ethylenediaminetetraacetic acid) aqueous solution was added into the reaction vial to scavenge potentially unbound ⁶⁷Ga³⁺ ions. The radiolabeled complexes were purified to single species by a Waters RP-HPLC (Milford, MA) on a Grace Vydac C-18 analytical column (Vydac 218TP54, Deerfield, IL) using the following gradient at a 1 mL/min flowrate. The mobile phase consisted of solvent A (20 mM HCl aqueous solution) and solvent B (100% CH₃CN). The gradient was initiated and kept at 72:28 A/B for 3 min followed by a linear gradient of 72:28 A/B to 62:38 A/B over 20 min. Then, the gradient was changed from 62:38 A/B to 10:90 A/B over 3 min followed by an additional 5 min at 10:90 A/B. Thereafter, the gradient was changed from 10:90 A/B to 72:28 A/B over 3 min. Each purified peptide sample was purged with N₂ gas for 15 min to remove the acetonitrile. The pH of the final solution was adjusted to 7.4 with 0.1 N NaOH and sterile saline for specific binding and animal studies.

The specific binding of ⁶⁷Ga-ALB-G1, ⁶⁷Ga-ALB-G2, and ⁶⁷Ga-ALB-G3 was determined on B16/F10 melanoma cells, respectively. Briefly, the B16/F10 cells (1 × 10⁶ cells/tube, n = 3) were incubated at 25°C for 2 h with ∼11.1 KBq of each ⁶⁷Ga-peptide with or without 10 μg (6.07 nmol) of unlabeled NDP-MSH (with sub-nanomolar MC1R binding affinity) in 0.3 mL of binding medium {modified Eagle's medium with 25 mM N-(2-hydroxyethyl)-piperazine-N′-(2-ethanesulfonic acid), pH 7.4, 0.2% BSA, 0.3 mM 1,10-phenathroline}. After the incubation, the cells were rinsed twice with 0.5 mL of ice-cold pH 7.4, 0.2% BSA/0.01 M PBS, lysed with 0.5 mL of 1 M NaOH for 5 min, collected, and measured in a Wallac 1480 automated gamma counter (PerkinElmer, NJ).

Biodistribution and imaging studies

All animal studies were conducted in compliance with Institutional Animal Care and Use Committee approval. C57 mice were purchased from Charles River Laboratory (Wilmington, MA). Each C57 mouse was subcutaneously inoculated with 1 × 10⁶ B16/F10 cells on the right flank to generate melanoma tumors, and monitored twice a week. Ten days postinoculation, the tumor weights reached ∼0.2 g and the melanoma-bearing mice were used for biodistribution and imaging studies. The biodistribution properties of ⁶⁷Ga-ALB-G1, ⁶⁷Ga-ALB-G2, and ⁶⁷Ga-ALB-G3 were determined on B16/F10 melanoma-bearing C57 mice at 2 h postinjection first to select one peptide for further evaluation. Because ⁶⁷Ga-ALB-G2 displayed more favorable tumor-targeting property than ⁶⁷Ga-ALB-G1 and ⁶⁷Ga-ALB-G3, the full biodistribution of ⁶⁷Ga-ALB-G2 was further examined on B16/F10 melanoma-bearing C57 mice.

For full biodistribution of ⁶⁷Ga-ALB-G2, each melanoma-bearing mouse was injected with 0.037 MBq of ⁶⁷Ga-ALB-G2 through the tail vein. The specificity of the tumor uptake of ⁶⁷Ga-ALB-G2 was determined by coinjecting 10 μg (6.07 nmol) of unlabeled NDP-MSH. Mice were sacrificed at 0.5, 2, 4, and 24 h postinjection, and tumors and organs of interest were harvested, weighed, and counted. Blood values were taken as 6.5% of the whole body weight. The melanoma imaging property of ⁶⁷Ga-ALB-G2 was examined on B16/F10 melanoma-bearing C57 mice. Approximately 11.1 MBq of ⁶⁷Ga-ALB-G2 was injected in each B16/F10 melanoma-bearing C57 mouse through the tail vein. SPECT imaging study was performed at 2 h postinjection. CT data were collected followed by SPECT data acquisition. Reconstructed SPECT/CT data were visualized using VivoQuant (Invicro, Boston, MA).

Statistical analysis

Statistical analysis was performed using the Student's t-test for unpaired data. A 95% confidence level was chosen to determine the significance of difference in cellular binding, and tumor, blood, liver, and kidney uptake between ⁶⁷Ga-ALB-G2 with or without NDP-MSH blockade. The differences at the 95% confidence level (p < 0.05) were considered significant.

Results

The schematic structures of three peptides are presented in Figure 1. The peptides were synthesized and purified by HPLC. After the HPLC purification, all peptides displayed greater than 90% purity. The retention time of ALB-G1, ALB-G2, and ALB-G3 was 11.6, 9.8, and 10 min, respectively. The identities of the peptides were confirmed by mass spectrometry. The found molecular weights of ALB-G1, ALB-G2, and ALB-G3 matched their calculated molecular weights. The found molecular weights of ALB-G1, ALB-G2, and ALB-G3 were 1713.6, 1770.7, and 1827.7, respectively. In vitro competitive binding curves of ALB-G1, ALB-G2, and ALB-G3 on B16/F10 melanoma cells are shown in Figure 2. The IC₅₀ value of ALB-G1, ALB-G2, and ALB-G3 was 0.67 ± 0.07, 0.5 ± 0.09, and 0.51 ± 0.03 nM on B16/F10 cells, respectively.

FIG. 1. — Schematic structures of DOTA-Lys(ALB)-GNle-CycMSH_hex (ALB-G1), DOTA-Lys(ALB)-GGNle-CycMSH_hex (ALB-G2), and DOTA-Lys(ALB)-GGGNle-CycMSH_hex (ALB-G3).

FIG. 2. — *In vitro* competitive binding curves of ALB-G1 (▲), ALB-G2 (●), and ALB-G3 (■). The IC₅₀ value of ALB-G1, ALB-G2, and ALB-G3 was 0.67 ± 0.07, 0.5 ± 0.09, and 0.51 ± 0.03 nM on B16/F10 melanoma cells, respectively.

⁶⁷Ga-ALB-G1, ⁶⁷Ga-ALB-G2, and ⁶⁷Ga-ALB-G3 were readily prepared in 0.25 M NH₄OAc-buffered solution with greater than 90% radiolabeling yields. ⁶⁷Ga-ALB-G1, ⁶⁷Ga-ALB-G2, and ⁶⁷Ga-ALB-G3 were completed separated from their excess nonlabeled peptides by HPLC. The specific activity was ∼4.0045 × 10⁴ mCi/μmol for ⁶⁷Ga-ALB-G1, ⁶⁷Ga-ALB-G2, and ⁶⁷Ga-ALB-G3. Radioactive HPLC profiles of ⁶⁷Ga-ALB-G1, ⁶⁷Ga-ALB-G2, and ⁶⁷Ga-ALB-G3 and their specific binding on B16/F10 melanoma cells are presented in Figure 3. The retention time of ⁶⁷Ga-ALB-G1, ⁶⁷Ga-ALB-G2, and ⁶⁷Ga-ALB-G3 was 14.9, 11, and 11.4 min, respectively. The radiochemical purity of ⁶⁷Ga-ALB-G1, ⁶⁷Ga-ALB-G2, and ⁶⁷Ga-ALB-G3 was greater than 95%, respectively. All three peptides exhibited receptor-mediated binding on B16/F10 cells. Approximately 77%, 72%, and 69% of ⁶⁷Ga-ALB-G1, ⁶⁷Ga-ALB-G2, and ⁶⁷Ga-ALB-G3 was blocked by peptide blockade, respectively.

FIG. 3. — Radioactive HPLC profiles **(A)** ⁶⁷Ga-ALB-G1, **(B)** ⁶⁷Ga-ALB-G2, and **(C)** ⁶⁷Ga-ALB-G3. The retention time of ⁶⁷Ga-ALB-G1, ⁶⁷Ga-ALB-G2, and ⁶⁷Ga-ALB-G3 was 14.9, 11, and 11.4 min, respectively. Specific binding **(D)** of ⁶⁷Ga-ALB-G1, ⁶⁷Ga-ALB-G2, and ⁶⁷Ga-ALB-G3 on B16/F10 melanoma cells with (*black*) and without (*white*) peptide blockade, respectively.

The biodistribution results of ⁶⁷Ga-ALB-G1, ⁶⁷Ga-ALB-G2, and ⁶⁷Ga-ALB-G3 at 2 h postinjection are presented in Table 1. The tumor uptake of ⁶⁷Ga-ALB-G2 was higher compared with ⁶⁷Ga-ALB-G1 and ⁶⁷Ga-ALB-G3 at 2 h postinjection, although the difference was not statistically different. The tumor uptake of ⁶⁷Ga-ALB-G1, ⁶⁷Ga-ALB-G2, and ⁶⁷Ga-ALB-G3 was 25.84 ± 6.13, 30.25 ± 3.24, and 24.52 ± 6.83%ID/g at 2 h postinjection, respectively. The blood uptake of ⁶⁷Ga-ALB-G1 and ⁶⁷Ga-ALB-G2 was 8.13 ± 1.42 and 8.79 ± 3.06%ID/g, whereas the blood uptake of ⁶⁷Ga-ALB-G3 was 4.94 ± 1.15%ID/g at 2 h postinjection. Meanwhile, ⁶⁷Ga-ALB-G2 and ⁶⁷Ga-ALB-G3 exhibited similar liver uptake as 4.73 ± 0.99 and 3.29 ± 0.5%ID/g, whereas ⁶⁷Ga-ALB-G1 displayed a higher liver uptake as 8.31 ± 1.27%ID/g at 2 h postinjection. All three peptides showed similar renal uptake between 6.68 ± 1.11 and 7.62 ± 1.08%ID/g at 2 h postinjection. They further evaluated the full biodistribution property of ⁶⁷Ga-ALB-G2 at 0.5, 4, and 24 h postinjection because of its high tumor uptake and tumor/kidney ratio.

Table 1.

Biodistribution Comparison Among ⁶⁷Ga-ALB-G1, ⁶⁷Ga-ALB-G2, and ⁶⁷Ga-ALB-G3 on B16/F10 Melanoma-Bearing C57 Mice at 2 h Postinjection

Tissues	⁶⁷Ga-ALB-G1	⁶⁷Ga-ALB-G2	⁶⁷Ga-ALB-G3
	Percent injected dose/gram (%ID/g)
Tumor	25.84 ± 6.13	30.25 ± 3.24	24.52 ± 6.83
Brain	0.43 ± 0.16	0.33 ± 0.16	0.22 ± 0.05
Blood	8.13 ± 1.42	8.79 ± 3.06	4.94 ± 1.15
Heart	3.39 ± 0.29	2.76 ± 0.89	1.77 ± 0.4
Lung	4.63 ± 1.65	3.93 ± 1.23	2.42 ± 0.81
Liver	8.31 ± 1.27	4.73 ± 0.99	3.29 ± 0.5
Spleen	1.76 ± 0.68	1.35 ± 0.62	0.91 ± 0.26
Stomach	2.47 ± 0.6	2.83 ± 0.94	1.85 ± 0.26
Kidneys	6.68 ± 1.11	7.09 ± 2.22	7.62 ± 1.08
Muscle	0.71 ± 0.43	0.42 ± 0.2	0.25 ± 0.09
Pancreas	1.09 ± 0.68	0.63 ± 0.19	0.48 ± 0.09
Bone	2.46 ± 0.98	1.11 ± 0.36	0.66 ± 0.18
Skin	2.69 ± 1.34	2.58 ± 0.45	1.93 ± 0.49

	Percent injected dose (%ID)
Intestines	2.4 ± 0.17	3.53 ± 1.08	2.3 ± 0.42
Urine	48.73 ± 4.73	56.11 ± 4.37	60.17 ± 9.18

	Uptake ratio of tumor/normal tissue
Tumor/blood	3.18 ± 0.62	3.44 ± 1.02	4.96 ± 0.94
Tumor/kidney	3.87 ± 0.65	4.27 ± 1.64	3.22 ± 1.17
Tumor/lung	5.58 ± 1.3	7.70 ± 3.71	10.13 ± 4.09
Tumor/liver	3.11 ± 0.94	6.40 ± 0.85	7.45 ± 1.26
Tumor/muscle	36.39 ± 12.98	72.02 ± 36.65	98.08 ± 43.17

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The data were presented as percent injected dose/gram or as percent injected dose (Mean ± SD, n = 5).

The full biodistribution results of ⁶⁷Ga-ALB-G2 are presented in Table 2. The accumulation of ⁶⁷Ga-ALB-G2 in the tumor was rapid and high, with 15.64 ± 4.55%ID/g at 0.5 h postinjection. The tumor uptake of ⁶⁷Ga-ALB-G2 was 30.25 ± 3.24 and 26.76 ± 3.23%ID/g %ID/g at 2 h and 4 h postinjection, and gradually decreased to 10.71 ± 1.21%ID/g at 24 h postinjection. Approximately 85% of the tumor uptake was blocked at 2 h postinjection, demonstrating that the tumor uptake was MC1R medicated. The blood uptake was 17.18 ± 1.83 and 8.79 ± 3.06%ID/g at 0.5 and 2 h postinjection, quickly reduced to 2.46 ± 0.37%ID/g at 4 h postinjection, and gradually decreased to 0.16 ± 0.23%ID/g at 24 h postinjection. The liver uptake was 7.77 ± 0.8 and 4.73 ± 0.99%ID/g at 0.5 and 2 h postinjection, gradually reduced to 3.85 ± 0.32 and 2.11 ± 0.1%ID/g at 4 and 24 h postinjection. The renal uptake was 8.13 ± 1.24, 7.09 ± 2.22, 4.5 ± 0.84, and 2.49 ± 0.3%ID/g at 0.5, 2, 4, and 24 h postinjection, respectively. The injection of peptide blockade did not significantly reduce the renal uptake, suggesting that the renal uptake was not MC1R mediated. Figure 4 illustrates the representative maximum intensity projection SPECT/CT image of a B16/F10 melanoma-bearing C57 mouse using ⁶⁷Ga-ALB-G2 as an imaging probe at 2 h postinjection. The tumor lesions were clearly visualized by ⁶⁷Ga-ALB-G2, which was in agreement with its biodistribution results.

Table 2.

Biodistribution of ⁶⁷Ga-ALB-G2 on B16/F10 Melanoma-Bearing C57 Mice

Tissues	0.5 h	2 h^a	4 h	24 h	2 h NDP blockade
	Percent injected dose/gram (%ID/g)
Tumor	15.64 ± 4.55	30.25 ± 3.24	26.76 ± 3.23	10.71 ± 1.21	4.47 ± 1.25^*
Brain	0.63 ± 0.12	0.33 ± 0.16	0.15 ± 0.04	0.03 ± 0.03	0.29 ± 0.1
Blood	17.18 ± 1.83	8.79 ± 3.06	2.46 ± 0.37	0.16 ± 0.23	7.56 ± 2.2
Heart	6.16 ± 0.4	2.76 ± 0.89	0.77 ± 0.1	0.16 ± 0.03	2.69 ± 0.71
Lung	6.45 ± 2.59	3.93 ± 1.23	1.57 ± 0.28	0.22 ± 0.21	2.73 ± 0.74
Liver	7.77 ± 0.8	4.73 ± 0.99	3.85 ± 0.32	2.11 ± 0.1	4.68 ± 0.62
Spleen	2.8 ± 0.49	1.35 ± 0.62	0.8 ± 0.29	0.45 ± 0.23	0.79 ± 0.4
Stomach	3.53 ± 1.42	2.83 ± 0.94	1.13 ± 0.44	0.55 ± 0.15	2.35 ± 2.25
Kidneys	8.13 ± 1.24	7.09 ± 2.22	4.5 ± 0.84	2.49 ± 0.3	6.55 ± 0.83
Muscle	1.36 ± 0.81	0.42 ± 0.2	0.10 ± 0.11	0.01 ± 0.02	0.12 ± 0.06
Pancreas	1.33 ± 0.21	0.63 ± 0.19	0.17 ± 0.05	0.09 ± 0.12	0.38 ± 0.09
Bone	2.02 ± 0.53	1.11 ± 0.36	0.65 ± 0.4	0.44 ± 0.71	0.68 ± 0.27
Skin	5.66 ± 0.88	2.58 ± 0.45	1.28 ± 0.38	0.44 ± 0.52	1.72 ± 0.47

	Percent injected dose (%ID)
Intestines	3.15 ± 0.12	3.53 ± 1.08	2.42 ± 0.76	0.67 ± 0.2	2.71 ± 1.11
Urine	21.38 ± 1.27	56.11 ± 4.37	73.72 ± 2.79	91.25 ± 0.39	68.59 ± 2.72

	Uptake ratio of tumor/normal tissue
Tumor/blood	0.91 ± 0.17	3.44 ± 1.02	10.88 ± 1.9	66.94 ± 25.52	0.59 ± 0.05
Tumor/kidney	1.92 ± 0.52	4.27 ± 1.64	5.95 ± 1.39	4.3 ± 0.35	0.68 ± 0.14
Tumor/lung	2.42 ± 0.92	7.70 ± 3.71	17.04 ± 3.94	48.68 ± 16.73	1.64 ± 0.47
Tumor/liver	2.01 ± 0.35	6.40 ± 0.85	6.95 ± 0.79	5.08 ± 0.49	0.96 ± 0.17
Tumor/muscle	11.5 ± 7.69	72.02 ± 36.65	267.6 ± 173.6	1071 ± 111.53	37.25 ± 25.27

Open in a new tab

The data were presented as percent injected dose/gram or as percent injected dose (Mean ± SD, n = 5).

^{^a}

2 h Data were cited from Table 1 for comparison.

^{^*}

p < 0.05 for determining significance of differences in tumor, blood, liver, and kidney uptake between ⁶⁷Ga-ALB-G2 with or without peptide blockade at 2 h postinjection.

FIG. 4. — Representative maximum intensity projection SPECT/CT image of a B16/F10 melanoma-bearing C57 mouse using ⁶⁷Ga-ALB-G2 as an imaging probe at 2 h postinjection. The melanoma lesions (T) are highlighted with an *arrow* on the image.

Discussion

The promising biodistribution results of ¹⁷⁷Lu-PSMA-ALB-53 and ¹⁷⁷Lu-PSMA-ALB-56 clearly suggested 4-p-(tolyl)butyric acid as an interesting ALB moiety.²⁷ In this study, they attached 4-p-(tolyl)butyric acid to Nle-CycMSH_hex peptide with one to three glycine linkers to examine its influence on tumor uptake and distribution profiles of ⁶⁷Ga-ALB-G1, ⁶⁷Ga-ALB-G2, and ⁶⁷Ga-ALB-G3 peptides on B16/F10 melanoma-bearing mice. Apparently, ⁶⁷Ga-ALB-G1 was more hydrophobic than ⁶⁷Ga-ALB-G2 and ⁶⁷Ga-ALB-G3 because of its longer HPLC retention time. Interestingly, the liver uptake of ⁶⁷Ga-ALB-G1 was almost two-fold compared with ⁶⁷Ga-ALB-G2 and ⁶⁷Ga-ALB-G3, reflecting the hydrophobicity of ⁶⁷Ga-ALB-G1. The tumor uptake of ⁶⁷Ga-ALB-G2 was higher compared with ⁶⁷Ga-ALB-G1 and ⁶⁷Ga-ALB-G3, whereas the renal uptake was similar among these three ⁶⁷Ga-ALB-peptides. In terms of blood clearance, ⁶⁷Ga-ALB-G3 exhibited the fastest blood clearance among these three ⁶⁷Ga-ALB-peptides at 2 h postinjection.

Figure 5 illustrated the uptake comparison in tumor, blood, liver, and kidneys between ⁶⁷Ga-DOTA-Lys(ALB)-GGNle-CycMSH_hex (⁶⁷Ga-ALB-G2) and their previously published ⁶⁷Ga-DOTA-GGNle-CycMSH_hex (⁶⁷Ga-G2).¹³ First of all, the tumor uptake of ⁶⁷Ga-ALB-G2 was slightly higher than ⁶⁷Ga-G2 at 2 h and 4 h postinjection, and 42% higher than ⁶⁷Ga-G2 at 24 h postinjection. Meanwhile, the blood uptake of ⁶⁷Ga-ALB-G2 was 9-fold and 4.6-fold higher than ⁶⁷Ga-G2 at 2 h and four postinjection, and 45% lower than ⁶⁷Ga-G2 at 24 h postinjection. High blood uptake of ⁶⁷Ga-ALB-G2 at 2 h and 4 h postinjection clearly demonstrated the ALB effect of 4-p-(tolyl)butyric acid. The liver uptake of ⁶⁷Ga-ALB-G2 was approximately between 4-fold and 5.5-fold higher than ⁶⁷Ga-G2 at 2, 4, and 24 h postinjection. Interestingly, the renal uptake of ⁶⁷Ga-ALB-G2 was only 80%, 53%, and 44% of ⁶⁷Ga-G2 at 2, 4, and 24 h postinjection, respectively. The decreased renal uptake of ⁶⁷Ga-ALB-G2 was likely attributed to the long circulation of ⁶⁷Ga-ALB-G2 in blood and high accumulation of ⁶⁷Ga-ALB-G2 in liver as compared with ⁶⁷Ga-G2 without ALB moiety.

FIG. 5. — Comparison of uptake in tumor, blood, liver, and kidneys between ⁶⁷Ga-DOTA-Lys(ALB)-GGNle-CycMSH_hex (⁶⁷Ga-ALB-G2) and ⁶⁷Ga-DOTA-GGNle-CycMSH_hex (⁶⁷Ga-G2) at 2, 4, and 24 h postinjection. The data of ⁶⁷Ga-DOTA-GGNle-CycMSH_hex were cited from their previous work (ref. 13) for comparison.

The introduction of 4-p-(tolyl)butyric acid as an ALB moiety extended the blood retention and resulted in higher tumor/kidney ratio of ⁶⁷Ga-ALB-G2 as compared with its counterpart without an albumin binder. However, the resulting high uptake of ⁶⁷Ga-ALB-G2 in blood and liver might become a concern when replacing the diagnostic ⁶⁷Ga to therapeutic radionuclides for therapy applications. Especially, high blood uptake may potentially lead to bone marrow toxicity and bone marrow may become the dose-limiting organ for therapy. From therapeutic perspective, it is optimal to achieve the maximum therapeutic efficacy with minimal normal organ toxicity. However, in reality, there is always a delicate balance between the therapeutic effectiveness and dose-limiting organ toxicity. The therapeutic dose needs to be carefully selected based on the dosimetry to minimize the radiation to normal organs.

Recently, Kramer et al. reported the feasibility, dosimetry, and tolerance of ¹⁷⁷Lu-PSMA-ALB-56 in patients with metastatic castration-resistant prostate cancer.²⁹ As compared with ¹⁷⁷Lu-PSMA-617, ¹⁷⁷Lu-PSMA-ALB-56 exhibited longer retention in blood, up to 2.3-fold higher accumulation in tumor, and similar uptake in salivary.³⁰ However, the doses to kidneys and red marrow also significantly increased for ¹⁷⁷Lu-PSMA-ALB-56, resulting in the red marrow as a dose-limiting organ for ¹⁷⁷Lu-PSMA-ALB-56 rather than the kidney as a dose dose-limiting organ for ¹⁷⁷Lu-PSMA-617.³⁰ This interesting report suggested that more research efforts would be needed to optimize the concept of ALB PSMA ligands. Recently, Deberle et al. utilized ibuprofen as an ALB moiety through diaminobutyric acid (DAB) in PSMA ligands, and identified ¹⁷⁷Lu-Ibu-DAB-PSMA as a more favorable compound, which displayed 60% more tumor/blood ratio than ¹⁷⁷Lu-PSMA-ALB-56.³⁰ Accordingly, it would be interesting to investigate whether ibuprofen could be used as an ALB moiety to improve tumor/blood ratio of α-MSH peptides in future studies.

Conclusions

The introduction of 4-p-(tolyl)butyric acid as an ALB moiety increased the blood circulation, and resulted in higher tumor/kidney ratio of ⁶⁷Ga-ALB-G2 as compared with its counterpart without an albumin binder. However, the resulting high uptake of ⁶⁷Ga-ALB-G2 in blood and liver needs to be further reduced to facilitate its therapeutic application when replacing ⁶⁷Ga with therapeutic radionuclides.

Disclosure Statement

No competing financial interests exist.

Funding Information

This work was supported by NIH grant R01CA225837.

References

1. Siegel RL, Miller KD, Jemal A. Cancer statistics, 2020. CA Cancer J Clin 2020;70:7. [DOI] [PubMed] [Google Scholar]
2. Chapman PB, Hauschild A, Robert C, et al. BRIM-3 Study Group. Improved survival with vemurafenib in melanoma with BRAF V600E mutation. N Engl J Med 2011;364:2507. [DOI] [PMC free article] [PubMed] [Google Scholar]
3. Sosman JA, Kim KB, Schuchter L, et al. Survival in BRAF V600-mutant advanced melanoma treated with vemurafenib. N Engl J Med 2012;366:707. [DOI] [PMC free article] [PubMed] [Google Scholar]
4. Hodi FS, O'Day SJ, McDermott DF, et al. Improved survival with ipilimumab in patients with metastatic melanoma. N Engl J Med 2010;363:711. [DOI] [PMC free article] [PubMed] [Google Scholar]
5. Weber JS, O'Day S, Urba W, et al. Phase I/II study of ipilimumab for patients with metastatic melanoma. J Clin Oncol 2008;26:5950. [DOI] [PubMed] [Google Scholar]
6. Topalian SL, Sznol M, McDermott DF, et al. Survival, durable tumor remission, and long-term safety in patients with advanced melanoma receiving nivolumab. J Clin Oncol 2014;32:1020. [DOI] [PMC free article] [PubMed] [Google Scholar]
7. Weiss SA, Wolchok JD, Sznol M. Immunotherapy of melanoma: Facts and hopes. Clin Cancer Res 2019;25:5191. [DOI] [PMC free article] [PubMed] [Google Scholar]
8. Siegrist W, Solca F, Stutz S, et al. Characterization of receptors for alpha-melanocyte-stimulating hormone on human melanoma cells. Cancer Res 1989;49:6352. [PubMed] [Google Scholar]
9. Tatro JB, Wen Z, Entwistle ML, et al. Interaction on an α-melanocyte stimulating hormone-diptheria toxin fusion protein with melanotropin receptors in human metastases. Cancer Res 1992;52:2545. [PubMed] [Google Scholar]
10. Yang J, Xu J, Gonzalez R, Lindner T, et al. ⁶⁸Ga-DOTA-GGNle-CycMSH_hex targets the melanocortin-1 receptor for melamoma imaging. Sci Transl Med 2018;10:eaau4445. [DOI] [PMC free article] [PubMed] [Google Scholar]
11. Guo H, Yang J, Gallazzi F, et al. Reduction of the ring size of radiolabeled lactam bridge-cyclized alpha-MSH peptide resulting in enhanced melanoma uptake. J Nucl Med 2010;51:418. [DOI] [PMC free article] [PubMed] [Google Scholar]
12. Guo H, Yang J, Gallazzi F, et al. Effects of the amino acid linkers on melanoma-targeting and pharmacokinetic properties of Indium-111-labeled lactam bridge-cyclized α-MSH peptides. J Nucl Med 2011;52:608. [DOI] [PMC free article] [PubMed] [Google Scholar]
13. Guo H, Gallazzi F, Miao Y. Ga-67-labeled lactam bridge-cyclized alpha-MSH peptides with enhanced melanoma uptake and reduced renal uptake. Bioconjug Chem 2012;23:1341. [DOI] [PMC free article] [PubMed] [Google Scholar]
14. Guo H, Miao Y. Cu-64-labeled lactam bridge-cyclized alpha-MSH peptides for PET imaging of melanoma. Mol Pharm 2012;9:2322. [DOI] [PMC free article] [PubMed] [Google Scholar]
15. Guo H, Gallazzi F, Miao Y. Design and evaluation of new Tc-99m-labeled lactam bridge-cyclized alpha-MSH peptides for melanoma imaging. Mol Pharm 2013;10:1400. [DOI] [PMC free article] [PubMed] [Google Scholar]
16. Guo H, Miao Y. Introduction of an aminooctanoic acid linker enhances uptake of Tc-99m-labeled lactam bridge-cyclized alpha-MSH peptide in melanoma. J Nucl Med 2014;55:2057. [DOI] [PMC free article] [PubMed] [Google Scholar]
17. Guo H, Miao Y. Melanoma targeting property of a Lu-177-labeled lactam bridge-cyclized alpha-MSH peptide. Bioorg Med Chem Lett 2013;23:2319. [DOI] [PMC free article] [PubMed] [Google Scholar]
18. Yang J, Xu J, Cheuy L, et al. Evaluation of a novel Pb-203-labeled lactam-cyclized alpha-melanocyte-stimulating hormone peptide for melanoma targeting. Mol Pharm 2019;16:1694. [DOI] [PMC free article] [PubMed] [Google Scholar]
19. Xu J, Yang J, Gonzalez R, et al. Melanoma-targeting property of Y-90-labeled lactam-cyclized alpha-melanocyte-stimulating hormone peptide. Cancer Biother Radiopharm 2019;34:597. [DOI] [PMC free article] [PubMed] [Google Scholar]
20. Qiao Z, Xu J, Gonzalez R, et al. Novel [^99mTc]-tricarbonyl-NOTA-conjugated lactam-cyclized alpha-MSH peptide with enhanced melanoma uptake and reduced renal uptake. Mol Pharm 2020;17:3581. [DOI] [PMC free article] [PubMed] [Google Scholar]
21. Dumelin CE, Trüssel S, Buller F, et al. A portable albumin binder from a DNA-encoded chemical library. Angew Chem Int Ed 2008;47:3196. [DOI] [PubMed] [Google Scholar]
22. Müller C, Struthers H, Winiger C, et al. DOTA conjugate with an albumin-binding entity enables the first folic acid-targeted ¹⁷⁷Lu-radionuclide tumor therapy in mice. J Nucl Med 2013;54:124. [DOI] [PubMed] [Google Scholar]
23. Farkas R, Siwowska K, Ametamey SM, et al. ⁶⁴Cu- and ⁶⁸Ga-based PET imaging of folate receptor-positive tumors: Development and evaluation of an albumin-binding NODAGA-folate. Mol Pharm 2016;13:1979. [DOI] [PubMed] [Google Scholar]
24. Siwowska K, Haller S, Bortoli F, et al. Preclinical comparison of albumin-binding radiofolates: Impact of linker entities on the in vitro and in vivo properties. Mol Pharm 2017;14:523. [DOI] [PubMed] [Google Scholar]
25. Benešová M, Umbricht CA, Schibli R, et al. Albumin-binding PSMA ligands: Optimization of the tissue distribution profile. Mol Pharm 2018;15:934. [DOI] [PubMed] [Google Scholar]
26. Umbricht CA, Benešová M, Hasler R, et al. Design and preclinical evaluation of an albumin-binding PSMA ligand for ⁶⁴Cu-based PET imaging. Mol Pharm 2018;15:5556. [DOI] [PubMed] [Google Scholar]
27. Umbricht CA, Benešová M, Schibli R, et al. Preclinical development of novel PSMA-targeting radioligands: Modulation of albumin-binding properties to improve prostate cancer therapy. Mol Pharm 2018;15:2297. [DOI] [PubMed] [Google Scholar]
28. Borgna F, Deberle LM, Cohrs S, et al. Combined application of albumin-binding [¹⁷⁷Lu]Lu-PSMA-ALB-56 and fast-cleared PSMA inhibitors: Optimization of the pharmacokinetics. Mol Pharm 2020;17:2044. [DOI] [PubMed] [Google Scholar]
29. Kramer V, Fernández R, Lehnert W, et al. Biodistribution and dosimetry of a single dose of albumin-binding ligand [¹⁷⁷Lu]Lu-PSMA-ALB-56 in patients with mCRPC. Eur J Nucl Med Mol Imaging 2021;48:893. [DOI] [PMC free article] [PubMed] [Google Scholar]
30. Deberle LM, Benešová M, Umbricht CA, et al. Development of a new class of PSMA radioligands comprising ibuprofen as an albumin-binding entity. Theranostics 2020;10:1678. [DOI] [PMC free article] [PubMed] [Google Scholar]

[B1] 1. Siegel RL, Miller KD, Jemal A. Cancer statistics, 2020. CA Cancer J Clin 2020;70:7. [DOI] [PubMed] [Google Scholar]

[B2] 2. Chapman PB, Hauschild A, Robert C, et al. BRIM-3 Study Group. Improved survival with vemurafenib in melanoma with BRAF V600E mutation. N Engl J Med 2011;364:2507. [DOI] [PMC free article] [PubMed] [Google Scholar]

[B3] 3. Sosman JA, Kim KB, Schuchter L, et al. Survival in BRAF V600-mutant advanced melanoma treated with vemurafenib. N Engl J Med 2012;366:707. [DOI] [PMC free article] [PubMed] [Google Scholar]

[B4] 4. Hodi FS, O'Day SJ, McDermott DF, et al. Improved survival with ipilimumab in patients with metastatic melanoma. N Engl J Med 2010;363:711. [DOI] [PMC free article] [PubMed] [Google Scholar]

[B5] 5. Weber JS, O'Day S, Urba W, et al. Phase I/II study of ipilimumab for patients with metastatic melanoma. J Clin Oncol 2008;26:5950. [DOI] [PubMed] [Google Scholar]

[B6] 6. Topalian SL, Sznol M, McDermott DF, et al. Survival, durable tumor remission, and long-term safety in patients with advanced melanoma receiving nivolumab. J Clin Oncol 2014;32:1020. [DOI] [PMC free article] [PubMed] [Google Scholar]

[B7] 7. Weiss SA, Wolchok JD, Sznol M. Immunotherapy of melanoma: Facts and hopes. Clin Cancer Res 2019;25:5191. [DOI] [PMC free article] [PubMed] [Google Scholar]

[B8] 8. Siegrist W, Solca F, Stutz S, et al. Characterization of receptors for alpha-melanocyte-stimulating hormone on human melanoma cells. Cancer Res 1989;49:6352. [PubMed] [Google Scholar]

[B9] 9. Tatro JB, Wen Z, Entwistle ML, et al. Interaction on an α-melanocyte stimulating hormone-diptheria toxin fusion protein with melanotropin receptors in human metastases. Cancer Res 1992;52:2545. [PubMed] [Google Scholar]

[B10] 10. Yang J, Xu J, Gonzalez R, Lindner T, et al. ⁶⁸Ga-DOTA-GGNle-CycMSH_hex targets the melanocortin-1 receptor for melamoma imaging. Sci Transl Med 2018;10:eaau4445. [DOI] [PMC free article] [PubMed] [Google Scholar]

[B11] 11. Guo H, Yang J, Gallazzi F, et al. Reduction of the ring size of radiolabeled lactam bridge-cyclized alpha-MSH peptide resulting in enhanced melanoma uptake. J Nucl Med 2010;51:418. [DOI] [PMC free article] [PubMed] [Google Scholar]

[B12] 12. Guo H, Yang J, Gallazzi F, et al. Effects of the amino acid linkers on melanoma-targeting and pharmacokinetic properties of Indium-111-labeled lactam bridge-cyclized α-MSH peptides. J Nucl Med 2011;52:608. [DOI] [PMC free article] [PubMed] [Google Scholar]

[B13] 13. Guo H, Gallazzi F, Miao Y. Ga-67-labeled lactam bridge-cyclized alpha-MSH peptides with enhanced melanoma uptake and reduced renal uptake. Bioconjug Chem 2012;23:1341. [DOI] [PMC free article] [PubMed] [Google Scholar]

[B14] 14. Guo H, Miao Y. Cu-64-labeled lactam bridge-cyclized alpha-MSH peptides for PET imaging of melanoma. Mol Pharm 2012;9:2322. [DOI] [PMC free article] [PubMed] [Google Scholar]

[B15] 15. Guo H, Gallazzi F, Miao Y. Design and evaluation of new Tc-99m-labeled lactam bridge-cyclized alpha-MSH peptides for melanoma imaging. Mol Pharm 2013;10:1400. [DOI] [PMC free article] [PubMed] [Google Scholar]

[B16] 16. Guo H, Miao Y. Introduction of an aminooctanoic acid linker enhances uptake of Tc-99m-labeled lactam bridge-cyclized alpha-MSH peptide in melanoma. J Nucl Med 2014;55:2057. [DOI] [PMC free article] [PubMed] [Google Scholar]

[B17] 17. Guo H, Miao Y. Melanoma targeting property of a Lu-177-labeled lactam bridge-cyclized alpha-MSH peptide. Bioorg Med Chem Lett 2013;23:2319. [DOI] [PMC free article] [PubMed] [Google Scholar]

[B18] 18. Yang J, Xu J, Cheuy L, et al. Evaluation of a novel Pb-203-labeled lactam-cyclized alpha-melanocyte-stimulating hormone peptide for melanoma targeting. Mol Pharm 2019;16:1694. [DOI] [PMC free article] [PubMed] [Google Scholar]

[B19] 19. Xu J, Yang J, Gonzalez R, et al. Melanoma-targeting property of Y-90-labeled lactam-cyclized alpha-melanocyte-stimulating hormone peptide. Cancer Biother Radiopharm 2019;34:597. [DOI] [PMC free article] [PubMed] [Google Scholar]

[B20] 20. Qiao Z, Xu J, Gonzalez R, et al. Novel [^99mTc]-tricarbonyl-NOTA-conjugated lactam-cyclized alpha-MSH peptide with enhanced melanoma uptake and reduced renal uptake. Mol Pharm 2020;17:3581. [DOI] [PMC free article] [PubMed] [Google Scholar]

[B21] 21. Dumelin CE, Trüssel S, Buller F, et al. A portable albumin binder from a DNA-encoded chemical library. Angew Chem Int Ed 2008;47:3196. [DOI] [PubMed] [Google Scholar]

[B22] 22. Müller C, Struthers H, Winiger C, et al. DOTA conjugate with an albumin-binding entity enables the first folic acid-targeted ¹⁷⁷Lu-radionuclide tumor therapy in mice. J Nucl Med 2013;54:124. [DOI] [PubMed] [Google Scholar]

[B23] 23. Farkas R, Siwowska K, Ametamey SM, et al. ⁶⁴Cu- and ⁶⁸Ga-based PET imaging of folate receptor-positive tumors: Development and evaluation of an albumin-binding NODAGA-folate. Mol Pharm 2016;13:1979. [DOI] [PubMed] [Google Scholar]

[B24] 24. Siwowska K, Haller S, Bortoli F, et al. Preclinical comparison of albumin-binding radiofolates: Impact of linker entities on the in vitro and in vivo properties. Mol Pharm 2017;14:523. [DOI] [PubMed] [Google Scholar]

[B25] 25. Benešová M, Umbricht CA, Schibli R, et al. Albumin-binding PSMA ligands: Optimization of the tissue distribution profile. Mol Pharm 2018;15:934. [DOI] [PubMed] [Google Scholar]

[B26] 26. Umbricht CA, Benešová M, Hasler R, et al. Design and preclinical evaluation of an albumin-binding PSMA ligand for ⁶⁴Cu-based PET imaging. Mol Pharm 2018;15:5556. [DOI] [PubMed] [Google Scholar]

[B27] 27. Umbricht CA, Benešová M, Schibli R, et al. Preclinical development of novel PSMA-targeting radioligands: Modulation of albumin-binding properties to improve prostate cancer therapy. Mol Pharm 2018;15:2297. [DOI] [PubMed] [Google Scholar]

[B28] 28. Borgna F, Deberle LM, Cohrs S, et al. Combined application of albumin-binding [¹⁷⁷Lu]Lu-PSMA-ALB-56 and fast-cleared PSMA inhibitors: Optimization of the pharmacokinetics. Mol Pharm 2020;17:2044. [DOI] [PubMed] [Google Scholar]

[B29] 29. Kramer V, Fernández R, Lehnert W, et al. Biodistribution and dosimetry of a single dose of albumin-binding ligand [¹⁷⁷Lu]Lu-PSMA-ALB-56 in patients with mCRPC. Eur J Nucl Med Mol Imaging 2021;48:893. [DOI] [PMC free article] [PubMed] [Google Scholar]

[B30] 30. Deberle LM, Benešová M, Umbricht CA, et al. Development of a new class of PSMA radioligands comprising ibuprofen as an albumin-binding entity. Theranostics 2020;10:1678. [DOI] [PMC free article] [PubMed] [Google Scholar]

PERMALINK

The Effect of Albumin-Binding Moiety on Tumor Targeting and Biodistribution Properties of ⁶⁷Ga-Labeled Albumin Binder-Conjugated Alpha-Melanocyte-Stimulating Hormone Peptides

Jingli Xu

Fabio Gallazzi

Darrell R Fisher

Rene Gonzalez

Yubin Miao

Abstract

Introduction