Abstract 868: Creating a superior, site-specific anti-HER2 antibody-drug conjugate (NG-HER2 ADC) for treatment of solid tumors

Antibody-drug conjugates (ADCs) have emerged as an important class of cancer therapeutics. The FDA approval of Kadcyla (T-DM1), a single agent for treatment of HER2-positive advanced metastatic breast cancer, was a significant milestone in the field of targeted therapy, as the first and only ADC for treatment of solid tumors. Despite the 3-month improvement over standard of care in the median survival, almost all the patients eventually became refractory to T-DM1. We have identified several possible areas for improvement: 1) The potency of T-DM1 as confirmed by the Phase III clinical data is restricted to high HER2 tumors which leaves moderate or low HER2 expressing patients without access to T-DM1 treatment; 2) The 48% overall response rate is indicative of intrinsic resistance to T-DM1 and all T-DM1 treated patients eventually relapse. 3) The randomized lysine conjugation in T-DM1 generates heterogeneity of the product. We have developed a novel, site-specific anti-HER2 ADC (NG-HER2 ADC) and evaluated it in comparative preclinical studies with T-DM1. The results show that the NG-HER2 ADC is ∼ 10 fold more potent than T-DM1 in HER2 3+ xenograft models of breast and gastric cancers. Our proprietary cleavable and permeable linker-payload can mediate bystander effect and this enables potent anti-tumor activity in non-HER2 amplified breast cancer and heterogeneous low HER2 NSCLC PDX models, where T-DM1 is ineffective. Our ADC can overcome T-DM1 resistance in in vitro and in vivo models.. Our site-specific ADC at HNSTD of 9 mg/kg in cynomolgus monkeys showed high AUC, long half-life and had normal clinical observations with no marked neutropenia. On the contrary, conventional conjugates with cleavable linker payloads typically have severe bone marrow toxicity as DLT above 5 mg/kg. The therapeutic index for NG-HER2 ADC is significantly greater than T-DM1 in all models tested. NG-HER2 ADC has a projected clinical efficacious dose of ∼1 mg/kg, compared to 3-5 mg/kg for T-DM1, based on PK/PD modeling. In addition, the activity of the NG-HER2 ADC shows increased infiltration of CD8 positive effector cells, an essential component for immuno-oncology (IO) efficacy, in a syngeneic HER2 overexpressing model. This property potentially allows the combination of the ADC with IO drugs to improve the long-term, overall survival. Our data provides preclinical proof of concept for NG-HER2 ADC with best-in-class potential and is currently being tested in preparation for clinical trials for treatment of HER2 solid tumors. Citation Format: Dangshe Ma, Bitha Narayanan, Kim Marquette, Edmund Graziani, Frank Loganzo, Manoj Charati, Nadira Prashad, Nathan Tumey, Jon Golas, Christine Hosselet, George Hu, Frank Barletta, Alison Betts, Judy Lucas, Chris O’Donnell, Lioudmila Tchistiakova, Hans-Peter Gerber, Puja Sapra. Creating a superior, site-specific anti-HER2 antibody-drug conjugate (NG-HER2 ADC) for treatment of solid tumors. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 868.