Initial Evaluation of Antibody-conjugates Modified with Viral-derived Peptides for Increasing Cellular Accumulation and Improving Tumor Targeting

Antibody-conjugates (ACs) modified with virus-derived peptides are a potentially powerful class of tumor cell delivery agents for molecular payloads used ...

Université de Sherbrooke

Sherbrooke Institute of Pharmacology

Leukemia stem cells (LSCs) are believed to be responsible for initiating and propagating acute myeloid leukemia (AML) and for causing relapse after treatment. Radioimmunotherapy (RIT) targeting these cells may improve the treatment of AML, but is limited by the low density of target epitopes. Our objective was to study a human polynucleotide kinase/phosphatase (hPNKP) inhibitor that interferes with DNA repair as a radiosensitizer for the Auger electron RIT agent, ¹¹¹In-NLS-7G3, which recognizes the CD123⁺/CD131⁻ phenotype uniquely displayed by LSCs.

The human polynucleotide kinase/phosphatase (hPNKP) inhibitor A12B4C3 radiosensitizes human myeloid leukemia cells to Auger electron-emitting anti-CD123 ¹¹¹In-NLS-7G3 radioimmunoconjugates.

Chimeric IgG1 monoclonal antibody CSL360 recognizes the CD123(+)/CD131(-) phenotype expressed by leukemic stem cells (LSC). Auger electron-emitting (111)In-DTPA-NLS-CSL360 radioimmunoconjugates incorporating nuclear translocation sequence (NLS) peptides bound specifically to Raji cells transfected with CD123 and exhibited a KD of 11nmols/L in a competition receptor-binding assay using CD123-transfected CHO cells. (111)In-DTPA-NLS-CSL360 was bound, internalized and transported to the nucleus of human AML-5 myeloid leukemia cells. The clonogenic survival of AML-5 cells was reduced by (111)In-DTPA-NLS-CSL360 up to 3.7-fold. Isotype control (111)In-DTPA-chIgG1 was 2-fold less cytotoxic, and unlabeled CSL360, DTPA-NLS-CSL360 or free (111)In acetate did not decrease cell survival. These results are promising for further evaluation of (111)In-DTPA-NLS-CSL360 for Auger electron radioimmunotherapy of AML targeting the critical LSC subpopulation.

Auger electron-emitting (111)In-DTPA-NLS-CSL360 radioimmunoconjugates are cytotoxic to human acute myeloid leukemia (AML) cells displaying the CD123(+)/CD131(-) phenotype of leukemia stem cells.

The design of antibody-conjugates (ACs) for delivering molecules for targeted applications in humans has sufficiently progressed to demonstrate clinical efficacy in certain malignancies and reduced systemic toxicity that occurs with standard nontargeted therapies. One area that can advance clinical success for ACs will be to increase their intracellular accumulation. However, entrapment and degradation in the endosomal-lysosomal pathway, on which ACs are reliant for the depositing of their molecular payload inside target cells, leads to reduced intracellular accumulation. Innovative approaches that can manipulate this pathway may provide a strategy for increasing accumulation. We hypothesized that escape from entrapment inside the endosomal-lysosomal pathway and redirected trafficking to the nucleus could be an effective approach to increase intracellular AC accumulation in target cells. Cholic acid (ChAc) was coupled to the peptide CGYGPKKKRKVGG containing the nuclear localization sequence (NLS) from SV-40 large T-antigen, which is termed ChAcNLS. ChAcNLS was conjugated to the mAb 7G3 (7G3-ChAcNLS), which has nanomolar affinity for the cell-surface leukemic antigen interleukin-3 receptor-α (IL-3Rα). Our aim was to determine whether 7G3-ChAcNLS increased intracellular accumulation while retaining nanomolar affinity and IL-3Rα-positive cell selectivity. Competition ELISA and cell treatment assays were performed. Cell fractionation, confocal microscopy, flow cytometry, and Western blot techniques were used to determine the level of antibody accumulation inside cells and in corresponding nuclei. In addition, the radioisotope copper-64 ((64)Cu) was also utilized as a surrogate molecular cargo to evaluate nuclear and intracellular accumulation by radioactivity counting. 7G3-ChAcNLS effectively escaped endosome entrapment and degradation resulting in a unique intracellular distribution pattern. mAb modification with ChAcNLS maintained 7G3 nM affinity and produced high selectivity for IL-3Rα-positive cells. In contrast, 7G3 ACs with the ability to either escape endosome entrapment or traffic to the nucleus was not superior to 7G3-ChAcNLS for increasing intracellular accumulation. Transportation of (64)Cu when complexed to 7G3-ChAcNLS also resulted in increased nuclear and intracellular radioactivity accumulation. Thus, ChAcNLS is a novel mAb functionalizing technology that demonstrates its ability to increase AC intracellular accumulation in target cells through escaping endosome entrapment coupled to nuclear trafficking.

ChAcNLS, a Novel Modification to Antibody-Conjugates Permitting Target Cell-Specific Endosomal Escape, Localization to the Nucleus, and Enhanced Total Intracellular Accumulation.

There is considerable interest in the development of novel and more efficient delivery systems for improving the efficacy of photodynamic therapy (PDT). The authors in this highlighted issue describe the synthesis and the photobiological characterizations of two photosensitizer (PS) conjugates based on β-carboline derivatives covalently conjugated to folic acid (FA) coupled to bovine serum albumin (BSA) as a carrier system specifically targeting cancer cells overexpressing FA receptor alpha (FRα). Accordingly, only the FA-BSA-β-carboline conjugates are internalized specifically in FRα-positive cells and are proved to be phototoxic. On the other hand, albumin-β-carboline conjugates without FA or β-carboline derivatives alone are not internalized and nontoxic. This conjugate is among the first to produce a conjugate composed of a PS and FA molecules that are directly conjugated to BSA. In addition, the in vitro studies are the first evidence that directly conjugated FA-BSA can be used as carriers to selectively enhance cytotoxicity by PDT relative to unmodified PS or nontargeted BSA-PS. This strategy is a positive step forward for the covalent design and construction of a photodynamic nanomedicine for FR-positive tumors.

Development of a Novel Covalent Folate-Albumin-Photosensitizer Conjugate.

(111)In-DTPA-NLS-CSL360 radioimmunoconjugates (RIC) recognize the overexpression of the interleukin-3 receptor α-subchain (CD123) relative to the β-subchain (CD131) on leukemia stem cells (LSC). Our aim was to study Auger electron radioimmunotherapy (RIT) of acute myeloid leukemia (AML) with (111)In-DTPA-NLS-CSL360 in non-obese diabetic severe combined immunodeficiency (NOD/SCID) mice or NOD-Rag1(null)IL2rγ(null) (NRG) mice engrafted with CD123(+) human AML-5 cells.

Paradoxical effects of Auger electron-emitting (111)In-DTPA-NLS-CSL360 radioimmunoconjugates on hCD45(+) cells in the bone marrow and spleen of leukemia-engrafted NOD/SCID or NRG mice.

In vivo imaging of estrogen receptor (ER) densities in human breast cancer is a potential tool to stage disease, guide treatment protocols and follow-up on treatment outcome. Both positron emission tomography (PET) and fluorescence imaging have received ample attention to detect ligand-ER interaction. In this study we prepared BODIPY-estradiol conjugates using 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) as fluorescent probe and estradiol derivatives as ligand and established their relative binding affinity (RBA) for the ERα. The synthesis of the conjugates involves attachment of a BODIPY moiety to the C17α-position of estradiol using Sonogashira or click reactions of iodo-BODIPY or aza-BODIPY with various 17α-ethynylestradiol (EE2) derivatives. The highest RBA for the ERα was observed with the EE2-BODIPY conjugate (7) featuring a linear eight carbon spacer chain. Cell uptake studies and in vivo imaging experiments in an ER-positive mouse tumor model are in progress.

BODIPY-17α-ethynylestradiol conjugates: Synthesis, fluorescence properties and receptor binding affinities.

Despite the high interest and concern due to an increasing incidence and death rate, patients who develop muscle invasive bladder cancer (MIBC) have few options available. However, the past decade has produced many candidate bladder tumor-specific markers but further development of these markers is still needed for creating effective targeted medications to solve this urgent need. Interleukin-5 receptor α-subunit (IL-5Rα) has recently been reported to be involved in MIBC progression. Thus, we aimed to validate IL-5Rα as a target for antibody-conjugates to better manage patients with MIBC. Patients were recruited and their tumors were processed for IL-5Rα immunohistochemical analysis. NOD/SCID mice were also heterotopically implanted with the human MIBC HT-1376 and HT-B9 cell lines and established xenografts immunohistochemically evaluated for IL-5Rα and compared against patient tumors. Using the mAb A14, an antibody-drug conjugate (ADC) and a radiolabeled immunoconjugate (RIC) were developed by conjugating to vinblastine and to the positron emitter copper-64 (Cu), respectively. As a proof-of-concept for ADC and RIC efficacy,cytotoxicity andpositron emission tomography (PET) imaging in tumor-bearing mice were performed, respectively. In addition, as rapid internalization and accumulation are important components for effective antibody-conjugates, we evaluated these aspects in response to IL-5 andCu-A14 treatments. Our findings suggest that although IL-5Rα protein expression is preferentially increased in MIBC, it is rapid IL-5Rα-mediated internalization allowing vinblastine-A14 to have cytotoxic activity andCu-A14 to detect MIBC tumors. This is the first report to elucidate the potential of IL-5Rα as an attractive MIBC target for antibody-conjugate applications.

Jeffrey V. Leyton

Department of Nuclear Medicine and Radiobiology,
Sherbrooke Molecular Imaging Center (CIMS)

Université de Sherbrooke

Initial Evaluation of Antibody-conjugates Modified with Viral-derived Peptides for Increasing Cellular Accumulation and Improving Tumor Targeting

Jeffrey V. Leyton

.css-o250i3{font-size:18px;font-family:Open Sans,sans-serif;line-height:21.6px;}Department of Nuclear Medicine and Radiobiology,Sherbrooke Molecular Imaging Center (CIMS)

Université de Sherbrooke

Initial Evaluation of Antibody-conjugates Modified with Viral-derived Peptides for Increasing Cellular Accumulation and Improving Tumor Targeting

Department of Nuclear Medicine and Radiobiology,
Sherbrooke Molecular Imaging Center (CIMS)