Abstract 4750: The role of drug transporters in the acquired resistance to PBD dimer-containing antibody drug conjugates
Authors: Corbett Simon , Zammarchi Francesca , Howard Philip W , Berkel Patrick H van , Hartley John A 
Published: August 2019

Abstract
Antibody drug conjugates (ADCs) delivering interstrand cross-linking pyrrolobenzodiazepine (PBD) dimers are being evaluated clinically in both hematological and solid tumors. These include ADCT-301, ADCT-402, MEDI3726 and rovalpituzumab tesirine (Rova-T) that contain the payload tesirine which releases the PBD dimer warhead SG3199. An important consideration in the future development of PBD ADCs is the development of clinical acquired resistance. The aim was to generate and characterize in vitro acquired resistant cell lines in both a hematological and solid tumor setting. To generate acquired resistant cells to ADCT-301 (targeting CD25) or warhead SG3199, CD25-positive Karpas-299 cells were incubated with an approximate GI50 dose of the drug for 96 h. Cells were washed and returned to fresh medium until normal cell growth was restored. This was repeated until a stable acquired resistance was established. The level of resistance achieved was &gt;700-fold for the ADC, and 3-fold for the naked PBD. Cross-resistance between the agents was observed and also with an ADC delivering a different PBD dimer. Similarly, resistant cells to ADCT-502 (targeting HER2) or SG3199 were established using HER2-positive NCI-N87 cells incubated with GI50 doses for 144 h. The level of resistance achieved was 8 and 4-fold, respectively, and again, cross-resistance was observed. DNA interstrand cross-linking was measured in the parental and resistant lines treated with equi-molar doses of ADC or SG3199. In every case, the resistant lines produced fewer cross-links indicating an up-stream mechanism of resistance preventing SG3199 from reaching its DNA target. In the Karpas ADCT-301-resistant line, a small (15%) decrease in CD25 cell surface expression could not account for the level of resistance. RT2 Profiler PCR Array for human drug-transporters was used to probe the cell lines. In the Karpas ADCT-301-resistant line three gene products were significantly upregulated: ABCG2 (168-fold), SLCO2A1 (4.6) and ABCC2 (3.5). Significantly upregulated in the Karpas SG3199-resistant cells were SLCO2B1 (15.4), ABCC12 (6.4), ATP7A (4.6), SLC16A2 (2.8), ABCG2 (2.8), SLC7A9 (2.5), ABCB4 (2.3) and ABCC11 (2.1). Upregulation of ABCG2, ABCC2 and SLCO2B1 was confirmed by RT-PCR. In NCI-N87 ADCT-502-resistant cells, ABCG2 (91), SLC22A3 (65), ABCC2 (43), SLCO2B1 (30) and SLC7A7 (6.8) and in NCI-N87 SG3199-resistant cells ABCG2 (115), SLC22A3 (61), SLCO2B1 (54), ABCC2 (36), SLC7A7 (8), AQP7 (6.4) and SLC238A3 (2.9) were upregulated. Upregulation of ABCG2, ABCC2, SLCO2B1, SLC7A7 and SLC22A3 was confirmed by RT-PCR and for ABCG2 and ABCC2 also by western blot. ABCB1(MDR1) was not upregulated in any of the lines. These data show that acquired resistance to both PBD-ADCs and SG3199 can involve specific drug transporters. This has clinical implications as potential biomarkers of resistance and for the rational design of drug combinations.
Citation Format: Simon Corbett, Francesca Zammarchi, Philip W Howard, Patrick H van Berkel, John A Hartley. The role of drug transporters in the acquired resistance to PBD dimer-containing antibody drug conjugates [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4750.