Abstract 2898: A biparatopic HER2xHER2 antibody drug conjugate with potent anti-tumor activity

A biparatopic HER2xHER2 antibody drug conjugate with potent anti-tumor activity.

The antibody drug conjugate (ADC) Trastuzumab-emtansine (T-DM1) targets the well-characterized breast cancer oncogene HER2 and is active in tumors that express very high levels of HER2 protein. However, tumors expressing intermediate levels of HER2 remain resistant to T-DM1 therapy, apparently due to insufficient lysosomal trafficking of T-DM1. We generated a series of biparatopic HER2xHER2 antibodies in which each arm recognizes a distinct epitope of HER2. One of our HER2xHER2 antibodies bound to cells with greater avidity than Trastuzumab and formed visible cell surface clusters that were efficiently internalized. While some of the internalized HER2xHER2 antibody trafficked to lysosomes and promoted HER2 degradation, a significant fraction recycled back to the plasma membrane through recycling endosomes. To exploit the increased internalization and recycling of the HER2xHER2 antibody, ADCs were generated by site-specific conjugation of Tubulysin A payload through a protease-cleavable linker. Recent data suggest that cleavage of this linker does not require lysosomal trafficking, but can occur in recycling endosomes as well. HER2xHER2-Tubulysin killed cell lines expressing high (IHC3+) and intermediate (IHC2+) HER2 levels with subnanomolar IC50, while exhibiting very weak killing of cells expressing low (IHC1+) HER2 levels (IC50 greater than 10nM). HER2xHER2-Tubulysin induced complete and durable tumor regression and outperformed T-DM1 in a collection of IHC3+ and 2+ tumor xenograft models (including PDX). Our work shows that a detailed understanding of antibody trafficking can enable the design of more effective ADCs and suggests that HER2xHER2-Tubulysin is a potential clinical candidate for HER2 IHC2+ breast cancer.

Citation Format: Andres Perez Bay, Devon Faulkner, Shiwani Tiwari, Carla Castanaro, Xiang Zheng, Arthur Kunz, Thomas Nittoli, Amy Han, William Olson, Gavin Thurston, Christopher Daly, Julian Andreev. A biparatopic HER2xHER2 antibody drug conjugate with potent anti-tumor activity [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 2898.

Clathrin and clathrin adaptor AP-1 control apical trafficking of megalin in the biosynthetic and recycling routes

Megalin (gp330, LRP-2) is a protein structurally related to the low-density lipoprotein receptor family that displays a large luminal domain with multiligand binding properties. Megalin localizes to the apical surface of multiple epithelia, where it participates in endocytosis of a variety of ligands performing roles important for development or homeostasis. We recently described the apical recycling pathway of megalin in Madin–Darby canine kidney (MDCK) cells and found that it is a long-lived, fast recycling receptor with a recycling turnover of 15 min and a half-life of 4.8 h. Previous work implicated clathrin and clathrin adaptors in the polarized trafficking of fast recycling basolateral receptors. Hence, here we study the role of clathrin and clathrin adaptors in megalin’s apical localization and trafficking. Targeted silencing of clathrin or the γ1 subunit of clathrin adaptor AP-1 by RNA interference in MDCK cells disrupted apical localization of megalin, causing its redistribution to the basolateral membrane. In contrast, silencing of the γ2 subunit of AP-1 had no effect on megalin polarity. Trafficking assays we developed using FM4-HA-miniMegalin-GFP, a reversible conditional endoplasmic reticulum–retained chimera, revealed that clathrin and AP-1 silencing disrupted apical sorting of megalin in both biosynthetic and recycling routes. Our experiments demonstrate that clathrin and AP-1 control the sorting of an apical transmembrane protein.

Basolateral sorting of chloride channel 2 is mediated by interactions between a dileucine motif and the clathrin adaptor AP-1

ClC-2 is a ubiquitous chloride channel that regulates cell volume, ion transport, and acid-base balance. Mice knocked out for ClC-2 are blind and sterile. Basolateral localization of ClC-2 in epithelia is mediated by the interaction of a dileucine motif with a highly conserved pocket in the γ1-σ1A hemicomplex of AP-1.

In spite of the many key cellular functions of chloride channels, the mechanisms that mediate their subcellular localization are largely unknown. ClC-2 is a ubiquitous chloride channel usually localized to the basolateral domain of epithelia that regulates cell volume, ion transport, and acid–base balance; mice knocked out for ClC-2 are blind and sterile. Previous work suggested that CLC-2 is sorted basolaterally by TIFS⁸¹²LL, a dileucine motif in CLC-2's C-terminal domain. However, our in silico modeling of ClC-2 suggested that this motif was buried within the channel's dimerization interface and identified two cytoplasmically exposed dileucine motifs, ESMI⁶²³LL and QVVA⁶³⁵LL, as candidate sorting signals. Alanine mutagenesis and trafficking assays support a scenario in which ESMI⁶²³LL acts as the authentic basolateral signal of ClC-2. Silencing experiments and yeast three-hybrid assays demonstrated that both ubiquitous (AP-1A) and epithelium-specific (AP-1B) forms of the tetrameric clathrin adaptor AP-1 are capable of carrying out basolateral sorting of ClC-2 through interactions of ESMI⁶²³LL with a highly conserved pocket in their γ1-σ1A hemicomplex.

Basolateral sorting of the coxsackie and adenovirus receptor through interaction of a canonical YXXPhi motif with the clathrin adaptors AP-1A and AP-1B

The coxsackie and adenovirus receptor (CAR) plays key roles in epithelial barrier function at the tight junction, a localization guided in part by a tyrosine-based basolateral sorting signal, (318)YNQV(321). Sorting motifs of this type are known to route surface receptors into clathrin-mediated endocytosis through interaction with the medium subunit (μ2) of the clathrin adaptor AP-2, but how they guide new and recycling membrane proteins basolaterally is unknown. Here, we show that YNQV functions as a canonical YxxΦ motif, with both Y318 and V321 required for the correct basolateral localization and biosynthetic sorting of CAR, and for interaction with a highly conserved pocket in the medium subunits (μ1A and μ1B) of the clathrin adaptors AP-1A and AP-1B. Knock-down experiments demonstrate that AP-1A plays a role in the biosynthetic sorting of CAR, complementary to the role of AP-1B in basolateral recycling of this receptor. Our study illustrates how two clathrin adaptors direct basolateral trafficking of a plasma membrane protein through interaction with a canonical YxxΦ motif.