Payload Selection to Maximize Multiple Mechanisms of Action for High Avidity Low Affinity Antibody Drug Conjugates

(30 lines) Antibody Drug Conjugates (ADCs) have made tremendous progress in the clinic with 9 new FDA approvals in the past six years and increasing use in combination with other agents, including first-line cancer therapies. ADCs have shown striking responses in combination with immune checkpoint inhibitors (ICIs), and these drugs are ideal agents for immunotherapy due to immunogenic cell death (ICD) from the payload, selective delivery that avoids immune suppression, and direct immune activation via the antibody Fc-domain. However, a major challenge in developing ADC immunotherapeutics and combinations is the lack of mouse cell sensitivity to payloads in syngeneic models and deficiency of humanized models to capture immunosuppressive effects. Therefore, there is an urgent need to outline how ADCs drive immune responses so more effective agents and combinations can be pursued in the clinic. The long-term goal of this research is to quantify the mechanisms behind ADC immune activation to design clinically effective ADC therapeutic combinations. We have identified unique payloads with high potency in mouse and human cells, thereby enabling the study of ADC immune effects at clinically relevant doses. The objective of this proposal is to use these novel payloads to delineate the mechanisms behind ADC immune stimulation and rationally design immunostimulatory ADC therapies. Our central hypothesis, backed by data in multiple syngeneic models and enabled by the unique payloads and protein design from our research groups, is that selective Fc-receptor binding ADCs with enhanced Fc-effector function ‘carrier doses’ of antibody will elicit maximum ICD and Fc-effector function to drive strong innate and adaptive immunity. We have engineered High Avidity Low Affinity (HALA) antibodies that automatically “tune” the number of ADC payloads delivered per cell based on the expression level, enabling efficient delivery in both high and low expression tumors. By modulating the antibody target affinity and Fc domains, we can rationally and independently control ADC payload delivery to cancer cells and immune cells while maximizing Fc-effector function. This unique toolbox will be used to test our central hypothesis through three specific aims: identify the most effective payload class for immune stimulation at clinically relevant doses, engineer the Fc-domains on the ADC and carrier antibody to maximize Fc-effector function and Fc-mediated payload delivery, and select the class of immune agonist payload to induce durable complete responses. We will first compare the immune effects of two major classes of ADC payloads in solid tumors, microtubule inhibitors and topoisomerase inhibitors, for ICD and Tcell recruitment. Next, we will selectively delivery these payloads to cancer and/or immune cells via Fc-engineered antibodies to isolate the impact of Fc-effector function from Fc-mediated payload delivery. Finally, we will leverage innate immune agonists to overcome the myeloid suppression within the tumor microenvironment seen with previous ADC therapy. The successful completion of these aims will enable the design of effective ADC regimens for inducing durable complete responses via selective immune activation. Project Number: 1R01CA292699-01A1 | Fiscal Year: 2026 | NIH Institute/Center: National Cancer Institute (NCI) | Principal Investigator: Greg Thurber (+1 co-PI) | Institution: UNIVERSITY OF MICHIGAN AT ANN ARBOR, ANN ARBOR, MI | Award Amount: $646,671 | Activity Code: R01 | Study Section: Translational Immuno-oncology Study Section[TIO] View on NIH RePORTER: https://reporter.nih.gov/project-details/11363939