Evaluation of the antitumor mechanism of antibody‐drug conjugates against tissue factor in stroma‐rich allograft models

Tissue factor (TF) is known to be overexpressed in various cancers including pancreatic cancer. The upregulation of TF expression has been observed not only in tumor cells, but also in tumor stromal cells. Because of the potential of TF as a delivery target, several studies investigated the effectiveness of Ab‐drug conjugates (ADCs) against TF for cancer therapy. However, it is still unclear whether anti‐TF ADC can exert toxicity against both tumor cells and tumor stromal cells. Here, we prepared ADC using a rat anti‐mouse TF mAb (clone.1157) and 2 types of in vivo murine pancreatic cancer models, one s.c. and other orthotopic with an abundant tumor stroma. We also compared the feasibility of bis‐alkylating conjugation (bisAlk) with that of conventional maleimide‐based conjugation (MC). In the s.c. models, anti‐TF ADC showed greater antitumor effects than control ADC. The results also indicated that the bisAlk linker might be more suitable than the MC linker for cancer treatments. In the orthotopic model, anti‐TF ADC showed greater in vivo efficacy and more extended survival time control ADC. Treatment with anti‐TF ADC (20 mg/kg, three times a week) did not affect mouse body weight changes in any in vivo experiment. Furthermore, immunofluorescence staining indicated that anti‐TF ADC delivered agents not only to TF‐positive tumor cells, but also to TF‐positive tumor vascular endothelial cells and other tumor stromal cells. We conclude that anti‐TF ADC should be a selective and potent drug for pancreatic cancer therapy.