The endosomal-lysosomal system in ADC design and cancer therapy

ABSTRACTIntroduction This discourse delves into the intricate connections between the endosomal-lysosomal system and antibody-drug conjugates (ADCs), shedding light on an essential yet less understood dimension of targeted therapy. While ADCs have revolutionized cancer treatment, resistance remains a formidable challenge, often involving diverse and overlapping mechanisms.Areas covered This discourse highlights the roles of various components within the endosomal machinery, including Rab proteins, in ADC resistance development. It also explores how the transferrin-transferrin receptor and epidermal growth factor-epidermal growth factor receptor complexes, known for their roles in recycling and degradation process, respectively, can offer valuable insights for ADC design. Selected strategies to enhance lysosomal targeting are discussed, and potentially offer solutions to improve ADC efficacy.Expert opinion By harnessing these different insights that connect ADCs with the endosomal-lysosomal system, the field may benefit to shape the next-generation of ADC design for increased efficacy and improved patient outcomes.KEYWORDS: Antibody-drug conjugatesplasma membraneinternalizationendosomelysosometransferrin receptorepidermal growth factor receptorRab proteinsDisclaimerAs a service to authors and researchers we are providing this version of an accepted manuscript (AM). Copyediting, typesetting, and review of the resulting proofs will be undertaken on this manuscript before final publication of the Version of Record (VoR). During production and pre-press, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal relate to these versions also. Article highlightsADCs efficacy relies on intricate interactions with the endosomal-lysosomal system.ADC resistance mechanisms now include dysregulated endosomal-lysosomal processes.Rab GTPases play crucial roles in regulating endosomal-lysosomal dynamics and their functions are significantly altered in cancer cells.Effective ADC design can draw parallels and insights between well-established recycling and degradation systems (TfR and EGFR).Emerging strategies are demonstrating that enhancing lysosomal targeting are essential for ADC therapeutic success in the clinic.Improved understanding of the endosomal-lysosomal system may hold the key to overcoming resistance and enhancing ADC treatment outcomes.Declaration of interestJV Leyton has consulted for Merck and PinotBio in the past 5 years and owns options from Defence Therapeutics Inc. The author has no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed.Reviewer disclosuresPeer reviewers on this manuscript have no relevant financial or other relationships to disclose.Figure 1. ADC resistance involves cellular ejection via exosomes. A) Immuno-electron microscopy images of exosomes obtained from cell culture medium of SK-BR-3 cells treated with immuno-gold labelled T-DM1 (thin arrows). Large arrows indicate exosomes. B) The % survival of SK-BR-3 cells treated with (1) T-DM1 alone and (2) and (3) harvested exosomes from SK-BR-3 cells treated with PBS or T-DM1, respectively. Reprinted from [Citation17], © 2018 Barok et al., licensed under CC BY 4.0.Display full sizeFigure 2. The basic circuitry of the endosomal system. The endosomal system contains a “recycling circuit”, which consists of the plasma membrane (PM), early endosomes, the recycling endosomes, and other various vesicular carriers, a “degradation circuit” which is primarily recognized as the lysosome, and a connecting”feeder” component, which is the endosome sorting complex that contains late endosomes fed by the recycling circuit. The trans-Golgi network communicates with the various endosomal components responding to specific needs through lipid biosynthesis and exchange. There is bidirectional exchange between the recycling circuit and the endosome sorting complex, where internalized cargo is not sent to the degradation circuitry and, instead, recycled back to the cell surface and is known as ‘slow’ recycling. The constant synthesis and exchange of membranes requires significant energy and, hence, 95% of internalized proteins at the cell surface are rapidly recycled to conserve energy. Created with BioRender.com.Display full sizeFigure 3. ADC development in parallel with TfR recycling receptor. Confocal microscopy images of lymphoma cells treated with the A) anti-CD79b mAb SN8 and B) Alexa647-Tf for 3 h at 37 °C in the presence of lysosomal protease inhibitors. Cells were then fixed, permeabilized, and stained with Cy3-conjugated anti-mouse antibody. The SN8 mAb is in red, the lysosomal marker LAMP-1 is in green, and yellow indicates colocalization. Reprinted with permission from [Citation53], © 2007 American Society of Hematology.Display full sizeFigure 4. Improved lysosome targeting improves ADC efficacy. A) SK-BR-3 HER2+ cells incubated with (bottom) and without (top) neratinib for 12 h. Cells were then stained with fluorescently-tagged antibodies specific for HER2 (red) and LAMP1 (green) and examined by confocal microscopy. Reprinted with permission from [Citation72], © 2016 Elsevier Ireland Ltd. B) Schematic showing the current strategy in protocol #11-344 from [Citation74] from patients enrolled in clinical trial (NCT01494662) where patients receive a pan-anti-HER inhibitor in combination with T-DM1. The inhibitor increases T-DM1-HER2 complex internalization and lysosome transport efficiency. Fluorescent green section indicates internalization “activation”. Created with BioRender.com. C) Schematic showing the current strategy for treating patients with S310F mutation in HER2, which increases internalization and treated first with T-DM1 (Drug-to-antibody ratio [DAR] = 3.5) and then switched to T-Dxd (DAR = 8), or vice-versa. Created with BioRender.com.Display full sizeAdditional informationFundingThis paper was funded by the Canadian Institutes of Health Research.