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Background Although ADCs offer a safer and more effective way to deliver cytotoxic agents, cytotoxicity relies heavily on the payload, with antibodies serving mainly as carriers. We aimed to develop an ADC that combines payload-mediated cytotoxicity with potent immunotherapeutic properties for treating pancreatic cancer, enabling a multipronged, potentially safer treatment for a broad patient population since less than 50% of patients with advanced pancreatic cancer tolerate combination chemotherapy. Combining immune-mediated cytotoxicity with payload-mediated cytotoxicity will provide a more potent tumor cell kill and reduce risks for the development of therapy-resistance.Methods We developed a tetravalent antibody (ADoBind) targeting FRα, expressed in up to 80% of PDAC, to showcase its intrinsic antitumor activity. Two ADCs were created: one with a noncleavable SMCC linker conjugated to DM1 (ADoBind-DM1) to isolate ADoBind’s direct effects for proof-of-concept, and another (MC001) with a cleavable linker conjugated to MMAE (AdoBind-MMAE) to evaluate therapeutic efficacy in PDAC.Results A pair of v-genes encoding a high-affinity FRα antibody was isolated from a human phage display library and cloned into an expression vector to produce a tetravalent ADoBind antibody that crosslinks two monomeric IgG1 by a disulfide bond, created from a S444C mutation on the heavy chain ( figure 1). Two ADCs were successfully produced: ADoBind-DM1 (average DAR 8) and ADoBind-MMAE (average DAR 7.6). First, the naked tetravalent ADoBind antibody showed greater avidity and a much larger area under the curve (AUC) serum concentrations compared to its monomeric counterpart in a single dose pharmacokinetic study in balb/c mice. ADoBind antibody exhibited a more effective ADCC than its monomeric IgG1 counterpart, although both did not mediate CDC. In FRα-expressing OV90 tumor cells, ADoBind-DM1 exhibited a significantly lower IC50 than the monomeric ADC. In vivo, ADoBind-DM1 inhibited tumor growth, indicating not only efficient tumor cell internalization but also tissue penetration. ADoBind-MMAE was tested in a single-dose SCID mouse PDAC model (SU.86.86 cells) and showed, at a mole/kg equivalent, 5-fold greater tumor inhibition than its monomeric form (figure 2). Mice treated with ADoBind-MMAE ADC showed improved survival.Conclusions Harnessing the intrinsic antitumor activity of the antibody backbone is key, especially with cleavable linkers that may release payloads before internalization. Combining this with payload-mediated cytotoxicity offers dual mechanisms of action, reducing the risk of resistance. Our data provides preclinical support for the ADoBind platform and justifies advancing MC001 to further development for pancreatic cancer treatment. MC001 is currently in IND-enabling stage of development.Ethics Approval All animal experiments were carried out under the Sanyou Biopharmaceuticals Laboratory Animal Ethics Committee.Abstract 996 Figure 1Structure of MC001Abstract 996 Figure 2Single-dose in vivo studies of MC001 in a mouse model of pancreatic cancer