Observations on the Effects of Residualization and Dehalogenation on the Utility of -Succinimidyl Ester Acylation Agents for Radioiodination of the Internalizing Antibody Trastuzumab.

Trastuzumab is an antibody used for the treatment of human epidermal growth factor receptor 2 (HER2)-overexpressing breast cancers. Since trastuzumab is an internalizing antibody, two factors could play an important role in achieving high uptake and prolonged retention of radioactivity in HER2-positive tumors after radioiodination-residualizing capacity after receptor-mediated internalization and susceptibility to dehalogenation. To evaluate the contribution of these two factors, trastuzumab was radiolabeled using the residualizing reagent -succinimidyl 4-guanidinomethyl-3-[*I]iodobenzoate ([*I]SGMIB) and the nonresidualizing reagent -succinimidyl-3-[*I]iodobenzoate ([*I]SIB), both of which are highly dehalogenation-resistant.

d-Amino Acid Peptide Residualizing Agents for Protein Radioiodination: Effect of Aspartate for Glutamate Substitution.

The residualizing prosthetic agent -(3-[I]iodobenzoyl)-Lys⁵--maleimido-Gly¹-d-GEEEK ([I]IB-Mal-d-GEEEK) showed promise for the radioiodination of monoclonal antibodies (mAbs) that bind to internalizing molecular targets. Although enhanced tumor uptake was achieved in these studies, elevated kidney accumulation also was observed, particularly with low-molecular-weight, single-domain antibody fragments (sdAbs). Here, we developed an analogous agent (IB-Mal-d-GDDDK), in which glutamate residues (E) were replaced with aspartates (D) to determine whether this modification could decrease renal uptake.

Astatine-211 labeled anti-HER2 5F7 single domain antibody fragment conjugates: radiolabeling and preliminary evaluation.

Introduction: Derived from heavy chain only camelid antibodies, ~15-kDa single-domain antibody fragments (sdAbs) are an attractive platform for developing molecularly specific imaging probes and targeted radiotherapeutics. The rapid tumor accumulation and normal tissue clearance of sdAbs might be ideal for use with At, a 7.2-h half-life α-emitter, if appropriate labeling chemistry can be devised to trap At in cancer cells after sdAb binding.

(2S)-2-(3-(1-Carboxy-5-(4-211At-Astatobenzamido)Pentyl)Ureido)-Pentanedioic Acid for PSMA-Targeted α-Particle Radiopharmaceutical Therapy.

Unlabelled: Alpha-particle emitters have a high linear energy transfer and short range, offering the potential for treating micrometastases while sparing normal tissues. We developed a urea-based, At-labeled small molecule targeting prostate-specific membrane antigen (PSMA) for the treatment of micrometastases due to prostate cancer (PC).

Methods: PSMA-targeted (2S)-2-(3-(1-carboxy-5-(4-At-astatobenzamido)pentyl)ureido)-pentanedioic acid (At- 6: ) was synthesized.

Preclinical Evaluation of 18F-Labeled Anti-HER2 Nanobody Conjugates for Imaging HER2 Receptor Expression by Immuno-PET.

Unlabelled: The human growth factor receptor type 2 (HER2) is overexpressed in breast as well as other types of cancer. Immuno-PET, a noninvasive imaging procedure that could assess HER2 status in both primary and metastatic lesions simultaneously, could be a valuable tool for optimizing application of HER2-targeted therapies in individual patients. Herein, we have evaluated the tumor-targeting potential of the 5F7 anti-HER2 Nanobody (single-domain antibody fragment; ∼13 kDa) after (18)F labeling by 2 methods.

N-Succinimidyl 3-((4-(4-[(18)F]fluorobutyl)-1H-1,2,3-triazol-1-yl)methyl)-5-(guanidinomethyl)benzoate ([(18)F]SFBTMGMB): a residualizing label for (18)F-labeling of internalizing biomolecules.

Residualizing labeling methods for internalizing peptides and proteins are designed to trap the radionuclide inside the cell after intracellular degradation of the biomolecule. The goal of this work was to develop a residualizing label for the (18)F-labeling of internalizing biomolecules based on a template used successfully for radioiodination. N-Succinimidyl 3-((4-(4-[(18)F]fluorobutyl)-1H-1,2,3-triazol-1-yl)methyl)-5-(bis-Boc-guanidinomethyl)benzoate ([(18)F]SFBTMGMB-Boc2) was synthesized by a click reaction of an azide precursor and [(18)F]fluorohexyne in 8.

Synthesis and evaluation of 4-[18F]fluoropropoxy-3-iodobenzylguanidine ([18F]FPOIBG): A novel 18F-labeled analogue of MIBG.

Introduction: Radioiodinated meta-iodobenzylguanidine (MIBG), a norepinephrine transporter (NET) substrate, has been extensively used as an imaging agent to study the pathophysiology of the heart and for the diagnosis and treatment of neuroendocrine tumors. The goal of this study was to develop an (18)F-labeled analogue of MIBG that like MIBG itself could be synthesized in a single radiochemical step. Towards this end, we designed 4-fluoropropoxy-3-iodobenzylguanidine (FPOIBG).

D-Amino acid peptide residualizing agents bearing N-hydroxysuccinimido- and maleimido-functional groups and their application for trastuzumab radioiodination.

Introduction: Proteins that undergo receptor-mediated endocytosis are subject to lysosomal degradation, requiring radioiodination methods that minimize loss of radioactivity from tumor cells after this process occurs. To accomplish this, we developed the residualizing radioiodination agent N(ϵ)-(3-[(*)I]iodobenzoyl)-Lys(5)-N(α)-maleimido-Gly(1)-D-GEEEK (Mal-D-GEEEK-[(*)I]IB), which enhanced tumor uptake but also increased kidney activity and necessitates generation of sulfhydryl moieties on the protein. The purpose of the current study was to synthesize and evaluate a new D-amino acid based agent that might avoid these potential problems.

N-Succinimidyl guanidinomethyl iodobenzoate protein radiohalogenation agents: influence of isomeric substitution on radiolabeling and target cell residualization.

Introduction: N-succinimidyl 4-guanidinomethyl-3-[(*)I]iodobenzoate ([(*)I]SGMIB) has shown promise for the radioiodination of monoclonal antibodies (mAbs) and other proteins that undergo extensive internalization after receptor binding, enhancing tumor targeting compared to direct electrophilic radioiodination. However, radiochemical yields for [(131)I]SGMIB synthesis are low, which we hypothesize is due to steric hindrance from the Boc-protected guanidinomethyl group ortho to the tin moiety. To overcome this, we developed the isomeric compound, N-succinimidyl 3-guanidinomethyl-5-[(131)I]iodobenzoate (iso-[(131)I]SGMIB) wherein this bulky group was moved from ortho to meta position.

Radiolabeling and in vitro evaluation of (67)Ga-NOTA-modular nanotransporter--a potential Auger electron emitting EGFR-targeted radiotherapeutic.

Introduction: Modular nanotransporters (MNTs) are vehicles designed to transport drugs from the cell surface via receptor-mediated endocytosis and endosomal escape to nucleus. Hence their conjugation to Auger electron emitters, can cause severe cell killing, by nuclear localization. Herein we evaluate the use of MNT as a platform for targeted radiotherapy with (67)Ga.

Improved tumor targeting of anti-HER2 nanobody through N-succinimidyl 4-guanidinomethyl-3-iodobenzoate radiolabeling.

Unlabelled: Nanobodies are approximately 15-kDa proteins based on the smallest functional fragments of naturally occurring heavy chain-only antibodies and represent an attractive platform for the development of molecularly targeted agents for cancer diagnosis and therapy. Because the human epidermal growth factor receptor type 2 (HER2) is overexpressed in breast and ovarian carcinoma, as well as in other malignancies, HER2-specific Nanobodies may be valuable radiodiagnostics and therapeutics for these diseases. The aim of the present study was to evaluate the tumor-targeting potential of anti-HER2 5F7GGC Nanobody after radioiodination with the residualizing agent N-succinimidyl 4-guanidinomethyl 3-(125/131)I-iodobenzoate (*I-SGMIB).

Targeting breast carcinoma with radioiodinated anti-HER2 Nanobody.

Introduction: With a molecular weight an order of magnitude lower than antibodies but possessing comparable affinities, Nanobodies (Nbs) are attractive as targeting agents for cancer diagnosis and therapy. An anti-HER2 Nb could be utilized to determine HER2 status in breast cancer patients prior to trastuzumab treatment. This provided motivation for the generation of HER2-specific 5F7GGC Nb, its radioiodination and evaluation for targeting HER2 expressing tumors.

Modular nanotransporters: a versatile approach for enhancing nuclear delivery and cytotoxicity of Auger electron-emitting 125I.

Background: This study evaluates the potential utility of a modular nanotransporter (MNT) for enhancing the nuclear delivery and cytotoxicity of the Auger electron emitter 125I in cancer cells that overexpress the epidermal growth factor receptor (EGFR).

Methods: MNTs are recombinant multifunctional polypeptides that we have developed for achieving selective delivery of short-range therapeutics into cancer cells. MNTs contain functional modules for receptor binding, internalization, endosomal escape and nuclear translocation, thereby facilitating the transport of drugs from the cell surface to the nucleus.

Comparison of receptor affinity of natSc-DOTA-TATE versus natGa-DOTA-TATE.

Background: 44Sc as a positron emitter can be an interesting alternative to 68Ga (T½=67.71 min) due to its longer half-life (T½=3.97 h).

Comparative study on DOTA-derivatized bombesin analog labeled with 90Y and 177Lu: in vitro and in vivo evaluation.

Introduction: The aim of the study was to compare in vitro and in vivo a novel DOTA-chelated bombesin (BN) analog of the amino acid sequence, QRLGNQWAVGHLM-CONH(2) (BN[2-14]NH(2)), labeled with (90)Y and (177)Lu, for its potential use in targeted radiotherapy of tumors expressing gastrin releasing peptide (GRP) receptors. The same amino acid sequence, but with different chelator, referred as BN1.1 (Gly-Gly-Cys-Aca-QRLGNQWAVGHLM-CONH(2)), has already been studied and reported; however, the DOTA-chelated one, suitable for labeling with M(+3) type radiometals, was not yet described.