Dual-payload antibody-drug conjugates: Taking a dual shot

Homogeneous antibody-drug conjugates with dual payloads: potential, methods and considerations

The development of site-specific dual-payload antibody-drug conjugates (ADCs) represents a potential advancement in targeted cancer therapy, enabling the simultaneous delivery of two distinct drugs into the same cancer cells to overcome payload resistance and enhance therapeutic efficacy. Here, we examine various methodologies for achieving site-specific dual-payload conjugation, including the use of multi-functional linkers, canonical amino acids, non-canonical amino acids, and enzyme-mediated methods, all of which facilitate precise control over payload attachment while ensuring homogeneity. We explore the implications of different conjugation techniques on drug-to-antibody ratios and the ratios of the two payloads, as well as their impact on process complexity and manufacturability. Additionally, we address the potential advantages of dual-payload ADCs compared to ADCs combined with traditional chemotherapy or single-payload ADC/ADC combinations. By evaluating these innovative methods, we aim to provide a comprehensive understanding of the current landscape in dual-payload ADC development and outline emerging directions necessary for further advancement of this promising therapeutic strategy.

Maximizing therapeutic potential and safety: Exploring multi/dual-payload antibody conjugates as cancer theranostics

Tumor heterogeneity greatly contributes to the failure of traditional cancer treatments. This leads to tumor relapse, recurrence, and ultimately metastasis, presenting serious clinical challenges. In recent decades, advances in antibody-based immunotherapy have emerged as promising new pillars to combat cancers. Although single payload antibody drug conjugates (ADCs) have resulted in drastic improvements in patient outcomes compared with unconjugated antibodies, multiple de novo and acquired resistance mechanisms inherent with cancer cells have left patients with less than desired outcomes. Newer studies are exploring the use of dual and multiple payload ADCs to enhance effectiveness. These payloads include chemotherapeutic and/or radiotherapeutic agents. The approaches leverage the synergistic effects of the different payloads alongside the immunotherapeutic properties of the antibody carriers. This review presents a comprehensive overview of dual-payload monoclonal antibody conjugates for cancer therapy and diagnosis (theranostics). Additionally, it explores the use of various imageable radiometals that are conjugated to the ADCs for imaging/diagnosis. It discusses the role of radioisotope decay schemes (such as alpha emission, beta emission, or Auger electron emission) along with factors such as linker type and chelator, as well as drug-to-antibody ratio (DAR), which are aimed at enhancing the synergistic effects between the therapeutic payloads while ensuring safety. Because none of these dual-payload ADCs have reached the clinic, this review employs a predictive method to estimate human equivalent dose (HED), maximum tolerable dose (MTD), and radiotoxicity in humans based on preclinical data. Additionally, it discusses the combinatorial behavior of two cytotoxic payloads linked to a monoclonal antibody.

Orthogonal Site-Specific Dual Bioconjugation of Aryl and Alkyl Thiols

We introduce aryl thiols as nucleophiles for site-specific protein and antibody bioconjugation, which allows the orthogonal labeling of native cysteines for double modification strategies. In a high-yielding synthesis, we introduce aromatic thiol substituents in two amino acids (4-SH-L-Phe and 3-SH-L-Tyr), which can be site-specifically incorporated into the C-terminus of a protein using the enzyme tubulin tyrosine ligase (TTL, Tub-tag labeling). In particular, we found that 3-SH-L-tyrosine shows excellent water solubility and incorporation rates, similar to previously described Tyr-derivatives. 2D NMR experiments revealed a pKa value of 5.5 for the aryl thiol modality of 3-SH-L-tyrosine, which matches the pH-dependent reactivity profile toward thiol-selective ethynyl-triazolyl-phosphinate (ETP) electrophiles. Most importantly, we found that the addition of glutathione had no significant effect on the reaction between ETPs and the aryl thiol at pH 7.0 and below, supporting orthogonal reactivity between the aryl and alkyl thiols. We utilized these findings to develop an orthogonal thiol-selective dual bioconjugation protocol for proteins, featuring TTL-ligation to site-specifically incorporate the arylthiol-containing amino acid derivative, followed by aryl thiolate functionalization at pH 5.5 and subsequent conjugation of cysteines at pH 8.3. This dual bioconjugation strategy was used to generate a highly fluorescent photostabilized nanobody and a fully functionalized antibody-drug conjugate carrying two different cytotoxic payloads, which displays potent cytotoxicity toward cells carrying the target antigen in addition to a strong bystander effect.

Immunoconjugates as an Efficient Platform for Drug Delivery: A Resurgence of Natural Products in Targeted Antitumor Therapy

The present review provides a detailed and comprehensive discussion on antibody-drug conjugates (ADCs) as an evolving new modality in the current therapeutic landscape of malignant diseases. The principle concepts of targeted delivery of highly toxic agents forsaken as stand-alone drugs are examined in detail, along with the biochemical and technological tools for their successful implementation. An extensive analysis of ADCs' major components is conducted in parallel with their function and impact on the stability, efficacy, safety, and resistance profiles of the immunoconjugates. The scope of the article covers the major classes of currently validated natural compounds used as payloads, with an emphasis on their structural and mechanistic features, natural origin, and distribution. Future perspectives in ADCs' design are thoroughly explored, addressing their inherent or emerging challenges and limitations. The survey also provides a comprehensive overview of the molecular rationale for active tumor targeting of ADC-based platforms, exploring the cellular biology and clinical relevance of validated tumor markers used as a "homing" mechanism in both hematological and solid tumor malignancies.