The more recently developed ADCs require the successful delivery of the ADC to the lysosomal compartment for proper release of the toxic payload to the cell.2 Accordingly, a more comprehensive understanding of the molecular mechanisms governing intracellular trafficking, the nuances involved in designing effective elements of the ADC, and the biological interactions that occur between an ADC and a tumor mass is needed for the successful development of efficacious ADCs. these internalized receptors incorporate into endosomes, they are trafficked throughout a complex array of recycling or degradative pathways. Since the discovery of this process, there has been a great deal of emphasis put on identifying ways to efficiently harness receptor-mediated endocytosis as part of a therapeutic strategy through the use of engineered antibody conjugates and other biologic modalities. This idea has gained substantial momentum recently, as our knowledge of the endo/lysosomal system and our ability to engineer antibodies and select appropriate targets has increased. Monoclonal antibodies (mAbs) can achieve selective cytotoxic effects against tumors that overexpress a particular target. This result can be achieved through multiple mechanisms depending on the therapeutic platform used. The mainstay of cancer biologic therapies has concerned naked antibodies, but with advances in antibody engineering, antibodies conjugated to toxic payloads have become increasingly prevalent. Unconjugated mAbs (also referred to as naked) do not have toxic payloads attached to them. Typically, they can act through a number of different mechanisms including receptor downregulation, induction of apoptosis through inhibition of receptor-linked signaling pathways, antibody-dependent cell-mediated cytotoxicity or complement-dependent immunocytotoxicity.1 Alternatively, conjugated mAbs utilize receptor internalization and act as a carrier to deliver the toxic payload to the cancer cell. The more recently developed ADCs require the successful delivery of the ADC to the lysosomal compartment for proper release of the toxic payload to the cell.2 Accordingly, a more comprehensive understanding of the molecular mechanisms governing intracellular trafficking, the nuances involved in designing effective elements of the ADC, and the biological interactions that occur between an ADC and a tumor mass is needed for the successful development of efficacious ADCs. Here, we review recent studies which have ITGA2B explored the ways an antibody can be designed to exploit certain aspects of the endolysosomal system, how engineered antibodies interact with a tumor mass and the biological implications of the chemistry involved in the design of an ADC. Receptor-Mediated Endocytosis and Intracellular Trafficking Dynamics Molecules can be internalized from the Gemilukast surface of eukaryotic cells through a wide array of mechanisms. These include clathrin-independent mechanisms such as Gemilukast phagocytosis, macropinocytosis and caveolin-dependent endocytosis or clathrin-dependent mechanisms such as receptor-mediated endocytosis.3,4 Clathrin-dependent endocytosis is the best characterized and predominant mechanism for the internalization of cell surface receptors and thus provides an ADC with a cell specific entry mechanism.3,4 Clathrin-mediated endocytosis commences with the recruitment of adaptor proteins, accessory proteins and a clathrin polymeric lattice to phosphatidylinositol-4,5-bisphosphate-enriched plasma membrane regions.5 The clathrin adaptors function to select the cargo proteins that will be internalized; the adaptor protein most commonly found to regulate receptor internalization is adaptor complex 2 (AP2), which binds to short linear tyrosine- and dileucine-based sequences on the cytoplasmic tails of receptors.6 Once receptors are selected by adaptor proteins for internalization, clathrin moves from the cytoplasm to adaptor protein-enriched regions of the membrane; the subsequent polymerization of clathrin causes membrane displacement and the formation of the budding vesicle.7 Liberation of the budding vesicle from the plasma membrane is mediated, in part, by the large GTPase, dynamin (Dyn). Dyn is recruited by BinCAmphiphysinCRvs domain-containing proteins, such as amphiphysin, endophilin and sorting nexin 9, which interact Gemilukast with Dyns proline-rich regions through SRC homology 3 domains.8-10 The precise mechanism of vesicle release is presently unclear, but Dyn undergoes a GTP hydrolysis-dependent conformational change that likely helps to mediate scission.11-13 Once individual vesicles are liberated from the plasma membrane, they fuse with each other in the cytoplasm and form the early endosome. The endosome is an extraordinarily complex and compartmentalized system of proteins and lipids functioning in concert to regulate the intracellular distribution of internalized proteins (Fig.?1). Endosomes send cargo through two distinct pathways. The first is cargo recycling that can result in.