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Antibody-Drug Conjugates (ADCs) Summary

Core Content

Antibody-drug conjugates (ADCs) represent a significant advancement in targeted cancer therapy, often referred to as "magic bullets" due to their ability to deliver potent cytotoxic agents directly to cancer cells while minimizing damage to healthy tissues. This document outlines the composition, mechanisms, challenges, and future directions of ADCs, highlighting their evolution and expanding applications beyond oncology.

Main Components of ADCs

ADCs consist of three key components:

• Antibody: Acts as a targeted delivery system, guiding the ADC to tumor cells expressing specific antigens. Most ADCs use chimeric or humanized antibodies to reduce immunogenicity.
• Linker: Connects the antibody and the payload. It must remain stable in the bloodstream but cleave efficiently inside the target cell. Linkers can be non-cleavable (remain bound during circulation, release upon lysosomal degradation) or cleavable (release in response to environmental changes like pH or redox potential).
• Payload: The cytotoxic molecule responsible for killing cancer cells. Common payloads include auristatins (MMAE/MMAF), maytansinoids, calicheamicins, and duocarmycins. These payloads are highly toxic and cannot be used as standalone drugs.

Mechanisms of ADCs

ADCs work by:

• Targeting specific antigens on cancer cells
• Delivering the cytotoxic payload directly to the tumor
• Minimizing off-target effects through high specificity and reduced toxicity

Challenges in ADC Development

• Payload stability and toxicity: Early ADCs used traditional chemotherapeutics, which lacked sufficient potency. New payloads are more toxic, requiring careful design to ensure they are only released within the target cell.
• Linker design: Balancing stability in the bloodstream with effective cleavage in the tumor environment is critical. Some linkers may release prematurely, leading to systemic toxicity.
• Antibody selection: While IgG-based antibodies are common, they require precise antigen targeting to avoid harming normal tissues.

Development Landscape

• Currently marketed ADCs: As of 2024, there are 15 approved ADCs, with the majority indicated for breast cancer.
• Clinical trials: 252 ADCs are in clinical trials, and over 700 are in development globally.
• Preclinical stage: Over half of the ADCs are at preclinical development.

Approved ADCs

A Future Beyond Cancer

• The ADC landscape is expanding beyond oncology, with 38 drug candidates in development for non-cancer indications.
• Examples include:
  • Del-desiran: A humanized anti-transferrin receptor mAb conjugated with RNA targeting DM1 protein kinase, currently in Phase III trials for myotonic dystrophy.
  • Delpacibart braxlosiran: In Phase II trials for facioscapulohumeral muscular dystrophy (FSHD).
  • Delpacibart zotadirsen: In Phase II trials for Duchenne's muscular dystrophy (DMD).

Key Case Studies

• Gemtuzumab ozogamicin (Mylotarg): Initially approved in 2000 for AML, it was withdrawn in 2010 due to premature payload release. Reapproved in 2017 with a modified dosing regimen.
• Brentuximab vedotin (Adcetris): Approved for Hodgkin lymphoma and anaplastic large cell lymphoma, and now being explored for non-cancer indications like diffuse scleroderma.

Conclusions

• ADCs have transformed cancer therapy in the last decade by offering targeted, less toxic treatments.
• The success of ADCs depends on the choice of target antigen, payload potency, and linker stability.
• There is a growing push to expand ADC applications to non-cancer diseases, opening new therapeutic avenues.

Q&A

• The presentation concludes with an invitation for questions, indicating ongoing research and development in the ADC field.