Preclinical pharmacokinetics, pharmacodynamics, and efficacy of RG7116: a novel humanized, glycoengineered anti-HER3 antibody

RG7116 is a novel anti-HER3 therapeutic antibody that inhibits HER3 signalling and induces antibody-dependent cellular cytotoxicity of tumor cells due to a glycoengineered antibody Fc moiety. We investigated the efficacy and pharmacokinetic/pharmacodynamic properties of HER3 signal inhibition by RG7116 in a murine xenograft model of human head and neck cancer. SCID-beige mice bearing FaDu cells were treated with RG7116 at a weekly dose of 0.3-10 mg/kg, and tumor growth control and modulation of selected proteins (HER3 and AKT) were examined. Complete tumor stasis up to Day 46 was observed at a dose > 3 mg/kg, and this dose down-modulated membrane HER3 expression and inhibited HER3 and AKT phosphorylation. Systemic RG7116 exposure was greater than dose-proportional and total clearance declined with increasing dose, indicating that RG7116 elimination is target-mediated. This is consistent with the better efficacy, and the HER3 and pAKT inhibition, that was observed at doses > 1 mg/kg. Tumor regrowth occurred from Day 46 onwards and was associated with HER1 and HER2 upregulation, indicating the activation of alternative HER escape pathways. Modulation of HER3 and phospho-HER3 was also demonstrated in the skin and mucosa of an RG7116-treated cynomolgus monkey, suggesting that these may be useful surrogate tissues for monitoring RG7116 activity. These data confirm the promising efficacy of RG7116 and highlight the value of assessing the PK behavior of the antibody and measuring target protein modulation as a marker of biological activity. Clinical development of RG7116 has now begun, and phase I trials are ongoing.