SPARC: A Multipayload ADC Architecture for Programmable Drug Combinations

Drug combination is a cornerstone of modern medicine, particularly in oncology. However, drug combinations often fail due to poor disease site tropism and additive toxicities of composite drugs. Among targeted drug delivery systems for reducing toxicity, the antibody-drug conjugate (ADC) is effective for single cytotoxic payload delivery. Multipayload ADC for combination therapy is mostly limited to two chemotherapeutics at fixed ratios, hampered by a lack of payload combination synergy/toxicity knowledge and complex antibody engineering and linker chemistries. Here we design synergistic payload-antibody ratiometric conjugate (SPARC) based on an elucidation of payload ratio-dependent pharmacology and toxicology of drug combinations delivered by a previously described clinical-stage T1000-ADC linker. Multi-T1000 payload (MTP) moieties are synthesized through a convergent process by orthogonally linking two or more azide-alkyne-modified, clickable T1000 payloads. Direct conjugation of an MTP to a native antibody or combinatorial, sequential conjugation of two MTPs to engineered and native cysteines of THIOMABs leads to a programmable assembly of SPARCs with 2-6 payloads, a total drug antibody ratio (DAR) as high as 30, and a tunable payload ratio from 1 to 10. SPARCs are stable and homogeneous, and conjugation of multiple payloads does not affect antibody binding. SPARCs achieve a more precise pharmacological discrimination in vivo, with lower off-target additive toxicity due to reduced payload release compared to single-payload ADCs but higher efficacy in targeted cells by synergistic/additive interactions among pharmacokinetically synchronized payloads. SPARCs combining Topoisomerase I (TOP1) with DNA Damage Response (DDR) inhibitors outperform single-TOP1 ADCs and free-drug combinations. SPARCs also exhibit improved safety profiles with reduced hematological toxicity and synchronized payload pharmacokinetics. SPARC has the potential to usher in a new generation of ADCs by reusing abandoned drugs as deliverable payloads and represents a transformative approach to precision combination therapy, addressing unmet needs in oncology and other disease areas through programmable, rationally designed drug codelivery.