Week 2, June 2025: Antibody Engineering as a Countermeasure to Drug Resistance

Resistance to treatment continues to limit the long-term success of many therapies. In oncology, cancers may evade antibody-based treatments through mechanisms such as antigen loss, impaired intracellular trafficking, or suppression of immune responses. To address these challenges, researchers are developing advanced antibody formats, including dual-payload antibody-drug conjugates (ADCs) and multi-target T-cell engagers, which are designed to maintain efficacy even in the face of resistance. These innovations combine different modes of action to enhance therapeutic durability and reduce the likelihood of escape. Meanwhile, monoclonal antibodies are being applied to the detection of antibiotic resistance, such as β-lactamase enzymes, offering new tools for rapid diagnosis and targeted intervention. Together, these efforts reflect a growing focus on using antibody technologies not only for direct therapeutic action but also to anticipate and overcome resistance across diverse clinical settings. 

Dual-Payload Antibody-Drug Conjugates

In response to the persistent problem of therapeutic resistance driven by tumor heterogeneity, recent research has focused on dual-payload ADCs that integrate different cytotoxic mechanisms within a single platform. These novel constructs combine chemotherapeutic agents and radiotherapeutic isotopes to exploit synergistic interactions and enhance antitumor efficacy where single-payload ADCs fall short. Notably, conjugates such as [²²⁵Ac]Ac-trastuzumab-PEG6-DM1 have shown the ability to eradicate resistant breast cancer models, highlighting the importance of combining alpha emitters with conventional drugs. The inclusion of radiometals emitting beta or Auger electrons, often paired with platinum-based DNA-damaging agents, enables enhanced cytotoxic reach via cross-fire and bystander effects, particularly in solid tumors with spatially heterogeneous cell populations. In parallel, radiolabeled ADCs offer dual utility for both therapeutic and diagnostic (theranostic) applications, as their imageable isotopes facilitate tumor visualization. Design parameters such as the type of radioactive decay, linker chemistry, and drug-to-antibody ratio (DAR) are being optimized to maximize therapeutic index while minimizing off-target effects. Although none of these constructs have yet advanced to clinical trials, preclinical data and human-equivalent dose modeling suggest favorable safety profiles and potent efficacy. 

Overcoming Resistance Mechanisms in ADC Therapy

Despite the clinical success of several FDA-approved ADCs, including trastuzumab emtansine, sacituzumab govitecan, and trastuzumab deruxtecan, almost all patients develop resistance via multiple mechanisms. This resistance arises through various mechanisms: alterations in the target antigen (e.g., reduced expression or heterogeneity), decreased internalization of the ADC-antigen complex, lysosomal dysfunction impeding payload release, and changes in tumor cell sensitivity to the cytotoxic payload. The choice of linker (cleavable versus non-cleavable) further influences ADC performance, particularly in relation to the bystander effect, which is essential for addressing heterogeneous antigen expression. Cleavable linkers facilitate payload diffusion to neighboring cells, enhancing cytotoxic reach, while non-cleavable linkers offer greater serum stability but reduced bystander activity. Additionally, the drug-antibody ratio (DAR) must be optimized to balance therapeutic potency with systemic toxicity. Strategies to overcome resistance include rational design of target antigens, selection of more effective linkers and payloads, and consideration of the immune effector functions conferred by IgG1 isotypes. 

Bispecific Antibody Resistance in Multiple Myeloma

Bispecific T-cell-redirecting antibodies targeting BCMA, GPRC5D, and FcRH5 have demonstrated significant efficacy in multiple myeloma. However, both primary and acquired resistance limit their clinical benefit. Resistance mechanisms are multifactorial and include tumor-related factors such as high tumor burden, antigen loss, and expression of T-cell inhibitory ligands. Primary resistance often correlates with impaired baseline T-cell function, while prolonged exposure can lead to chronic T-cell stimulation and exhaustion. Additionally, the immunosuppressive tumor microenvironment, particularly through CD38+ suppressor cells, further impairs therapeutic response. Combinatorial strategies, such as using CD38-targeting antibodies or developing trispecific antibodies to counteract antigen escape, are being investigated to enhance T-cell activation and improve response durability. Understanding these resistance pathways is essential to optimizing the clinical utility of bispecific antibodies in multiple myeloma. 

Another recent study describes how bispecific T-cell engagers (TCEs), including teclistamab, elranatamab, and talquetamab, have emerged as effective off-the-shelf immunotherapies for triple-class exposed relapsed/refractory multiple myeloma (RRMM). However, approximately one-third of patients exhibit primary resistance, while most initial responders ultimately experience disease progression. Resistance to bispecific TCEs arises through both tumor-intrinsic and tumor-extrinsic mechanisms. Intrinsic mechanisms include loss of the target antigen via chromosome deletions, point mutations, or epigenetic silencing, as well as loss of MHC class I expression, which impairs T-cell receptor (TCR) costimulation. Extrinsic mechanisms involve the expansion of exhausted T-cell clones and the presence of an immunosuppressive microenvironment. Importantly, some resistance pathways selectively impair response to individual TCEs, preserving sensitivity to others. These findings underscore the need for dynamic monitoring of antigen expression and immune contexture to guide the selection and sequencing of bispecific therapies in MM. Optimizing response may also require combination approaches tailored to the molecular and immunological features of each patient’s disease. 

Broadly Reactive Monoclonal Antibodies for Detection Antibiotic Resistance

To address the urgent need for rapid diagnostics in the face of rising antibiotic resistance, researchers from Vilnius University developed monoclonal antibodies (mAbs) targeting a conserved epitope within AmpC β-lactamases, which are enzymes central to resistance against β-lactam antibiotics. Using a bacteriophage-derived nanotube scaffold displaying a universal 17-amino acid AmpC peptide, thirteen mAb-producing hybridoma clones were generated. Eleven of these mAbs exhibited cross-reactivity with diverse recombinant β-lactamases in ELISA and Western blot, and were also capable of detecting native CMY-34 in clinical isolates. Epitope mapping revealed an 11-amino acid conserved region responsible for broad specificity, confirmed through both immunoassays and computational modeling. These mAbs demonstrated compatibility with label-free optical biosensing technologies, such as total internal reflection ellipsometry, highlighting their potential utility in immunosensor platforms. These results offer a novel tool for direct, protein-level detection of β-lactamase activity, complementing current EUCAST-recommended phenotypic assays. Their integration into diagnostic workflows could enhance surveillance and guide appropriate antibiotic use across clinical, veterinary, and environmental applications.