Abstract 5507: Characterization of ADC bystander killing in admixed tumor model

Abstract

Abstract We have previously described an admixed tumor model, consisting of the CD30+ ALCL cell line Karpas 299 and CD30- Karpas-35R (SGN-35 resistant) cells, to study the phenomenon of ‘bystander killing’ of antigen negative tumor cells by antibody-drug conjugates (ADCs) in tumors with a heterogeneous target expression profile. Here we study the contribution of payload membrane permeability and target expression in bystander killing. We hypothesize that membrane permeability of payloads may impact bystander killing in addition to their intrinsic potency. Monomethyl auristatin E (MMAE)-based ADCs utilizing the cleavable linkers valine-citrulline (vc) or glucuronide (gluc) release the membrane permeable MMAE. As a result, antiCD30-vcMMAE and antiCD30-glucMMAE showed similar bystander killing in vivo. We then compared the more membrane permeable payloads, MMAE and pyrrolobenzodiazepine dimer (PBD), to those that are less permeable, monomethyl auristatin F (MMAF) and auristatin T (AT), as antiCD30 conjugates in this model. We found that antiCD30-AT and antiCD30-vcMMAF killed only CD30+ tumor cells in admixed tumors, while antiCD30-MMAE, antiCD30-GlucMMAE and antiCD30-PBD killed both CD30+ and CD30- cells. These results suggest that membrane permeability is one of the key factors determining in vivo bystander killing. To elucidate the role of antigen positive cells in bystander killing in this model, we varied the implant ratio of CD30+ cells and evaluated ADC activity in vivo. Flow cytometric analysis and CD30 immunohistochemistry confirmed a corresponding change of CD30+ cell percentage in the resulting admixed tumors (∼40%, 70%, or 80%). Treatment with ADCs in these tumors demonstrated that antiCD30-vcMMAE induced remissions in tumors with 70 or 80% CD30+ cells, whereas antiCD30-PBD produced remissions in all three admixed tumor ratios. Collectively, these data confirm that membrane permeable payloads can kill antigen negative cells in vivo. We hypothesize that the enhanced bystander killing by PBD-based ADCs may result from the intrinsic potency of the small molecule and/or membrane permeability. This information will be useful to consider when designing future ADCs. Citation Format: Fu Li, Kim Kissler Emmerton, Mechthild Jonas, Xinqun Zhang, Che-Leung Law. Characterization of ADC bystander killing in admixed tumor model. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5507. doi:10.1158/1538-7445.AM2015-5507