Effect Of Ca125/Muc16 On Complement-Dependent Cytotoxicity (Cdc) Of Farletuzumab And Other Cdc-Mediating Antibodies Via Inhibition Of Antibody-C1q Binding

e23082Background: Human cancers employ a number of mechanisms to evade host immune responses. Here we report the effects of the tumor-shed antigen CA125 on suppressing complement-dependent cellular cytotoxicity (CDC). This finding relates to a prespecified subgroup analysis of an 1100 patient Ph3 clinical trial testing the investigational agent farletuzumab, a monoclonal antibody (mAb) to folate receptor alpha, plus standard-of-care chemotherapy in patients with recurrent ovarian cancer. In this study, patients with low levels of CA125 (no greater than 3X the upper limit of normal) treated with farletuzumab compared to placebo demonstrated improvements in both progression free survival (HR 0.49, p = 0.0028) and overall survival (HR 0.44, p = 0.0108). Farletuzumab’s pharmacologic activity is mediated in part through antibody dependent cellular cytotoxicity (ADCC) and CDC. Here we show that CA125 inhibits IgG1- and IgM-mediated CDC by suppressing antibody interaction with the C1q complement-initiating prote...