HER2-targeted ADC DX126-262 combined with chemotherapy demonstrates superior antitumor efficacy in HER2-positive gastric cancer.

Gastric cancer is a common malignant tumor with high incidence and mortality. The overexpression of Human epidermal growth factor receptor 2 (HER2) is associated with increased metastatic potential and poor clinical outcome in gastric cancer. Despite the proven clinical response rates of approved HER2-targeted therapies, including Trastuzumab combined with chemotherapy, their limited long-term clinical benefits and inevitable disease progression still pose significant challenges to the clinical treatment of gastric cancer. Hence, exploring novel strategies to enhance therapeutic outcomes for HER2-positive patients is extremely crucial and urgent. Here, we reported that DX126-262, a novel HER2-targeted antibody-drug conjugate, generated by conjugating a potent Tubulysin B analogue (Tub-114) to humanized anti-HER2 monoclonal antibody, exhibited a significant synergistic inhibitory effect with both Cisplatin and 5-FU in HER2-positive gastric cancer NCI-N87 cells. Moreover, the triple-drug combination strategy of DX126-262 combined with Cisplatin and 5-FU showed much better in vitro and in vivo therapeutic efficacy than monotherapy or double-drug combination (Cisplatin plus 5-FU) or first-line standard-of-care (SOC, Herceptin plus Cisplatin and 5-FU), and comparable or even superior in vivo efficacy than third-line SOC (DS-8201a) in NCI-N87 cells and xenograft models. Meanwhile, the triple-drug combination therapy did not exhibit superimposed toxicity. Taken together, our findings provide compelling evidence that DX126-262 in combination with Cisplatin and 5-FU exerts synergistic antitumor activity and is a promising strategy to improve the clinical efficacy of HER2-positive advanced or metastatic gastric cancer.