Influence of Fc Modifications and IgG Subclass on Biodistribution of Humanized Antibodies Targeting L1CAM

Impact of site-specific conjugation strategies on the pharmacokinetics of antibody conjugated radiotherapeutics

Antibody radionuclide conjugates are an emerging modality for targeted imaging and potent therapy of disseminated disease. Coupling of radionuclides to monoclonal antibodies (mAbs) is typically achieved by applying non-site-specific labelling techniques. With the ambition of reducing variability, increasing labelling efficacy and stability, several site-specific conjugation strategies have been developed in recent years for toxin- and fluorophore-mAb conjugates. In this study, we studied two site-specific labelling strategies for the conjugation of the macrocyclic chelating agent, DOTA, to the anti-Leucine Rich Repeat Containing 15 (LRRC15) mAb DUNP19. Specifically, one approach utilized a DOTA-bearing peptide (FcIII) with a strong affinity for the fragment crystallizable (Fc) domain of the human IgG1 of DUNP19 (DUNP19LF-FcIII-DOTASS), while the other leveraged a chemo-enzymatic technique to substitute the N-linked bi-antennary oligosaccharides in the human IgG1 Fc domain with DOTA (DUNP19LF-gly-DOTASS). To assess if these methods impact the antibody's binding properties and targeting efficacy, comparative in vitro and in vivo studies of the generated DUNP19-conjugates were performed. While the LRRC15 binding of both radioimmunoconjugates remained intact, the conjugation methods had different impacts on their abilities to interact with FcRn and FcγRs. In vitro assessments of DUNP19LF-FcIII-DOTASS and DUNP19LF-gly-DOTASS demonstrated markedly decreased affinity for FcRn and FcγRIIIa (CD16), respectively. DUNP19LF-FcIII-DOTASS demonstrated increased blood and tissue kinetics in vivo, confirming loss of FcRn binding. While the ablated FcγR interaction of DUNP19LF-gly-DOTASS had no immediate impact on in vivo biodistribution, reduced immunotherapeutic effect can be expected in future studies as a result of reduced NK-cells interaction. In conclusion, our findings underscore the necessity for meticulous consideration and evaluation of mAb labelling strategies, extending beyond mere conjugation efficiency and radiolabeling yields. Notably, site-specific labelling methods were found to significantly influence the immunological impact of Fc interactions. Therefore, it is of paramount importance to consider the intended diagnostic or therapeutic application of the construct and to adopt conjugation strategies that ensure the preservation of critical pharmacological properties and functionality of the antibody in use.

Afucosylated broadly neutralizing antibodies enhance clearance of HIV-1 infected cells through cell-mediated killing

Broadly neutralizing antibodies (bNAbs) targeting the HIV-1 envelope glycoprotein (Env) have the capacity to delay viral rebound when administered to people with HIV-1 (PWH) during anti-retroviral therapy (ART) interruption. To further enhance the performance of bNAbs through their Fc effector functions, in particular NK cell-mediated killing of HIV-1 infected cells, we have produced a panel of glyco-engineered (afucosylated) bNAbs with enhanced affinity for Fc gamma receptor IIIa. These afucosylated anti-HIV-1 bNAbs enhance NK cell activation and degranulation compared to fucosylated counterparts even at low antigen density. NK cells from PWH expressing exhaustion markers PD-1 and TIGIT are activated in a similar fashion by afucosylated bNAbs as NK cell from HIV-1 negative individuals. Killing of HIV-1 infected cells is most effective with afucosylated bNAbs 2G12, N6, PGT151 and PGDM1400, whereas afucosylated PGT121 and non-neutralizing antibody A32 only induce minor NK cell-mediated killing. These data indicate that the approach angle and affinity of Abs influence the capacity to induce antibody-dependent cellular cytotoxicity. Thus, afucosylated bNAbs have the capacity to induce NK cell-mediated killing of infected cells, which warrants further investigation of afucosylated bNAb administration in vivo, aiming for reduction of the viral reservoir and ART free durable control.

Engineered Antibodies as Cancer Radiotheranostics

Radiotheranostics is a rapidly growing approach in personalized medicine, merging diagnostic imaging and targeted radiotherapy to allow for the precise detection and treatment of diseases, notably cancer. Radiolabeled antibodies have become indispensable tools in the field of cancer theranostics due to their high specificity and affinity for cancer-associated antigens, which allows for accurate targeting with minimal impact on surrounding healthy tissues, enhancing therapeutic efficacy while reducing side effects, immune-modulating ability, and versatility and flexibility in engineering and conjugation. However, there are inherent limitations in using antibodies as a platform for radiopharmaceuticals due to their natural activities within the immune system, large size preventing effective tumor penetration, and relatively long half-life with concerns for prolonged radioactivity exposure. Antibody engineering can solve these challenges while preserving the many advantages of the immunoglobulin framework. In this review, the goal is to give a general overview of antibody engineering and design for tumor radiotheranostics. Particularly, the four ways that antibody engineering is applied to enhance radioimmunoconjugates: pharmacokinetics optimization, site-specific bioconjugation, modulation of Fc interactions, and bispecific construct creation are discussed. The radionuclide choices for designed antibody radionuclide conjugates and conjugation techniques and future directions for antibody radionuclide conjugate innovation and advancement are also discussed.

MIB Guides: Measuring the Immunoreactivity of Radioimmunoconjugates

Immunoglobulins, both full-length antibodies and smaller antibody fragments, have long been regarded as effective platforms for diagnostic and therapeutic radiopharmaceuticals. The construction of radiolabeled immunoglobulins (i.e., radioimmunoconjugates) requires the manipulation of the biomolecule through the attachment of a radiohalogen or the bioconjugation of a chelator that is subsequently used to coordinate a radiometal. Both synthetic approaches have historically relied upon the stochastic modification of amino acids within the immunoglobulin, a process which poses a risk to the structural and functional integrity of the biomolecule itself. Not surprisingly, radioimmunoconjugates with impaired antigen binding capacity will inevitably exhibit suboptimal in vivo performance. As a result, the biological characterization of any newly synthesized radioimmunoconjugate must include an assessment of whether it has retained its ability to bind its antigen. Herein, we provide straightforward and concise protocols for three assays that can be used to determine the immunoreactivity of a radioimmunoconjugate: (1) a cell-based linear extrapolation assay; (2) a cell-based antigen saturation assay; and (3) a resin- or bead-based assay. In addition, we will provide a critical analysis of the relative merits of each assay, an examination of the inherent limitations of immunoreactivity assays in general, and a discussion of other approaches that may be used to interrogate the biological behavior of radioimmunoconjugates.

Site-Specific Photoaffinity Bioconjugation for the Creation of 89Zr-Labeled Radioimmunoconjugates

PURPOSE

Site-specific approaches to bioconjugation produce well-defined and homogeneous immunoconjugates with potential for superior in vivo behavior compared to analogs synthesized using traditional, stochastic methods. The possibility of incorporating photoaffinity chemistry into a site-specific bioconjugation strategy is particularly enticing, as it could simplify and accelerate the preparation of homogeneous immunoconjugates for the clinic. In this investigation, we report the synthesis, in vitro characterization, and in vivo evaluation of a site-specifically modified, 89Zr-labeled radioimmunoconjugate created via the reaction between an mAb and an Fc-binding protein bearing a photoactivatable 4-benzoylphenylalanine residue.

PROCEDURES

A variant of the Fc-binding Z domain of protein A containing a photoactivatable, 4-benzoylphenylalanine residue - Z(35BPA) - was modified with desferrioxamine (DFO), combined with the A33 antigen-targeting mAb huA33, and irradiated with UV light. The resulting immunoconjugate - DFOZ(35BPA)-huA33 - was purified and characterized via SDS-PAGE, MALDI-ToF mass spectrometry, surface plasmon resonance, and flow cytometry. The radiolabeling of DFOZ(35BPA)-huA33 was optimized to produce [89Zr]Zr-DFOZ(35BPA)-huA33, and the immunoreactivity of the radioimmunoconjugate was determined with SW1222 human colorectal cancer cells. Finally, the in vivo performance of [89Zr]Zr-DFOZ(35BPA)-huA33 in mice bearing subcutaneous SW1222 xenografts was interrogated via PET imaging and biodistribution experiments and compared to that of a stochastically labeled control radioimmunoconjugate, [89Zr]Zr-DFO-huA33.

RESULTS

HuA33 was site-specifically modified with Z(35BPA)-DFO, producing an immunoconjugate with on average 1 DFO/mAb, high in vitro stability, and high affinity for its target. [89Zr]Zr-DFOZ(35BPA)-huA33 was synthesized in 95% radiochemical yield and exhibited a specific activity of 2 mCi/mg and an immunoreactive fraction of ~ 0.85. PET imaging and biodistribution experiments revealed that high concentrations of the radioimmunoconjugate accumulated in tumor tissue (i.e., ~ 40%ID/g at 120 h p.i.) but also that the Z(35BPA)-bearing immunoPET probe produced higher uptake in the liver, spleen, and kidneys than its stochastically modified cousin, [89Zr]Zr-DFO-huA33.

CONCLUSIONS

Photoaffinity chemistry and an Fc-binding variant of the Z domain were successfully leveraged to create a novel site-specific strategy for the synthesis of radioimmunoconjugates. The probe synthesized using this method - DFOZ(35BPA)-huA33 - was well-defined and homogeneous, and the resulting radioimmunoconjugate ([89Zr]Zr-DFOZ(35BPA)-huA33) boasted high specific activity, stability, and immunoreactivity. While the site-specifically modified radioimmunoconjugate produced high activity concentrations in tumor tissue, it also yielded higher uptake in healthy organs than a stochastically modified analog, suggesting that optimization of this system is necessary prior to clinical translation.

In Vivo Biorthogonal Antibody Click for Dual Targeting and Augmented Efficacy in Cancer Treatment

Antibody-drug conjugates (ADCs) have emerged as promising therapeutics for cancer treatment; however, their effectiveness has been limited by single antigen targeting, potentially leading to resistance mechanisms triggered by tumor compensatory pathways or reduced expression of the target protein. Here, we present antibody-ADC click, an approach that harnesses bioorthogonal click chemistry for in vivo dual receptor targeting, irrespective of the levels of the tumor's expression of the ADC-targeting antigen. Antibody-ADC click enables targeting heterogeneity and enhances antibody internalization and drug delivery inside cancer cells, resulting in potent toxicity. We conjugated antibodies and ADCs to the bioorthogonal click moieties tetrazine (Tz) and trans-cyclooctene (TCO). Through sequential antibody administration in living biological systems, we achieved dual receptor targeting by in vivo clicking of antibody-TCO with antibody-Tz. We show that the clicked antibody therapy outperformed conventional ADC monotherapy or antibody combinations in preclinical models mimicking ADC-eligible, ADC-resistant, and ADC-ineligible tumors. Antibody-ADC click enables in vivo dual-antigen targeting without extensive antibody bioengineering, sustains tumor treatment, and enhances antibody-mediated cytotoxicity.

Fc-engineered monoclonal antibodies to reduce off-target liver uptake

BACKGROUND

Radiolabeled-antibodies usually display non-specific liver accumulation that may impair image analysis and antibody biodistribution. Here, we investigated whether Fc silencing influenced antibody biodistribution. We compared recombinant 89Zr-labeled antibodies (human IgG1 against different targets) with wild-type Fc and with mutated Fc (LALAPG triple mutation to prevent binding to Fc gamma receptors; FcγR). After antibody injection in mice harboring xenografts of different tumor cell lines or of immortalized human myoblasts, we analyzed antibody biodistribution by PET-CT and conventional biodistribution analysis.

RESULTS

Accumulation in liver was strongly reduced and tumor-specific targeting was increased for the antibodies with mutated Fc compared with wild-type Fc.

CONCLUSION

Antibodies with reduced binding to FcγR display lower liver accumulation and better tumor-to-liver ratios. These findings need to be taken into account to improve antibody-based theragnostic approaches.

Antibody Engineering for Nuclear Imaging and Radioimmunotherapy

Radiolabeled antibodies have become indispensable tools in nuclear medicine. However, the natural roles of antibodies within the immune system mean that they have several intrinsic limitations as a platform for radiopharmaceuticals. In recent years, the field has increasingly turned to antibody engineering to circumvent these issues while retaining the manifold benefits of the immunoglobulin framework. In this "Focus on Molecular Imaging" review, we cover recent advances in the application of antibody engineering to immunoPET, immunoSPECT, and radioimmunotherapy. Specifically, we address how antibody engineering has been used to improve radioimmunoconjugates on four fronts: optimizing pharmacokinetics, facilitating site-specific bioconjugation, modulating Fc interactions, and creating bispecific constructs.