Antibody–Drug Conjugate that Exhibits Synergistic Cytotoxicity with an Endosome–Disruptive Peptide

Antibody–drug conjugates are an important class of cancer therapeutics. These agents generally bind a specific cell surface receptor, undergo receptor-mediated endocytosis, and enter the endosomal–lysosomal system, where the environment in these organelles facilitates the release of a membrane-permeable cytotoxin. By using a membrane-impermeable cytotoxin, we describe here a method that allows the cytotoxicity of an antibody conjugate to be triggered by co-administration with an endosome-disruptive peptide that exhibits low toxicity. This approach was validated by conjugation of an anionic derivative of the tubulin-binding cytotoxin colchinol methyl ether to lysine residues of the HER2-targeting antibody trastuzumab (Herceptin) via a disulfide. When this antibody binds HER2 on SKBR3 breast cancer cells and undergoes endocytosis, the membrane-impermeable cytotoxin is released, but it becomes trapped in endosomes, resulting in relatively low cytotoxicity (IC50 > 1 μM). However, co-administration with an essentially nontoxic (IC50 > 10 μM) cholesterol-linked endosome-disruptive peptide promotes the release of this small molecule into the cytoplasm, conferring subnanomolar cytotoxic potency (IC50 = 0.11 ± 0.07 nM). Studies of a structurally related fluorophore conjugate revealed that the endosome-disruptive peptide does not substantially enhance cleavage of the disulfide (t1/2 = 8 ± 2 h) within endosomes, suggesting that the mechanism of endosomal escape involves the efflux of some small molecules without facilitating substantial influx of reduced glutathione

https://orcid.org/0000-0002-3346-304X

Sexual dimorphisms in humans and other species exist in visually evident features such as body size and less apparent characteristics, including disease prevalence. Current research is adding to a growing understanding of sex differences in stem cell function and response to external stimuli, including sex hormones such as estrogens. These differences are proving significant and directly impact both the understanding of stem cell processes in tissue repair and the clinical implementation of stem cell therapies. Adult stem cells of the musculoskeletal system, including those used for development and repair of muscle, bone, cartilage, fibrocartilage, ligaments, and tendons, are no exception. Both in vitro and in vivo studies have found differences in stem cell number, proliferative and differentiation capabilities, and response to estrogen treatment between males and females of many species. Maintaining the stemness and reducing senescence of adult stem cells is an important topic with implications in regenerative therapy and aging. As such, this review discusses the effect of estrogens on musculoskeletal system stem cell response in multiple species and highlights the research gaps that still need to be addressed. The following evidence from investigations of sex-related phenotypes in adult progenitor and stem cells are pieces to the big puzzle of sex-related effects on aging and disease and critical information for both fundamental tissue repair and regeneration studies and safe and effective clinical use of stem cells