Photosensitizer-thioglycosides enhance photodynamic therapy by augmenting cellular uptake.

Photodynamic therapy (PDT) uses photosensitizing agents along with light to ablate tissue, including cancers. Such light-driven localized delivery of free-radical oxygen to kill target tissue depends on photosensitizer cell penetration efficacy. While the attachment of monosaccharides and disaccharides to photosensitizers has been shown to potentially provide improved photosensitizer delivery, the range of glycan entities tested thus far is limited. We sought to expand such knowledge by coupling N-acetylglucosamine (GlcNAc) to pyropheophorbides as thioglycosides, and then testing photosensitizer efficacy. To this end, GlcNAc was conjugated to both pyropheophorbide-a and methyl pyropheophorbide-a. Among the entities tested, the conjugation of N-acetylglucosamine to methyl pyropheophorbide-a ('PSe') as thioglycoside enhanced cell uptake both in the presence and absence of human serum proteins, relative to other compounds tested. The enhanced PSe penetrance into cells resulted in higher cell death upon illumination with 665 nm light. While acting as a potent photosensitizer, PSe did not affect cellular carbohydrate profiles. Overall, the study presents a new pyropheophorbide glycoconjugate with strong in vitro PDT efficacy.

Efficient inhibition of O-glycan biosynthesis using the hexosamine analog Ac5GalNTGc.

There is a critical need to develop small-molecule inhibitors of mucin-type O-linked glycosylation. The best-known reagent currently is benzyl-GalNAc, but it is effective only at millimolar concentrations. This article demonstrates that Ac5GalNTGc, a peracetylated C-2 sulfhydryl-substituted GalNAc, fulfills this unmet need. When added to cultured leukocytes, breast cells, and prostate cells, Ac5GalNTGc increased cell-surface VVA binding by ∼10-fold, indicating truncation of O-glycan biosynthesis. Cytometry, mass spectrometry, and western blot analysis of HL-60 promyelocytes demonstrated that 50-80 µM Ac5GalNTGc prevented elaboration of 30%-60% of the O-glycans beyond the Tn-antigen (GalNAcα1-Ser/Thr) stage. The effect of the compound on N-glycans and glycosphingolipids was small. Glycan inhibition induced by Ac5GalNTGc resulted in 50%-80% reduction in leukocyte sialyl-Lewis X expression and L-/P-selectin-mediated rolling under flow conditions. Ac5GalNTGc was pharmacologically active in mouse. It reduced neutrophil infiltration to sites of inflammation by ∼60%. Overall, Ac5GalNTGc may find diverse applications as a potent inhibitor of O-glycosylation.

Thioglycosides Are Efficient Metabolic Decoys of Glycosylation that Reduce Selectin Dependent Leukocyte Adhesion.

Metabolic decoys are synthetic analogs of naturally occurring biosynthetic acceptors. These compounds divert cellular biosynthetic pathways by acting as artificial substrates that usurp the activity of natural enzymes. While O-linked glycosides are common, they are only partially effective even at millimolar concentrations. In contrast, we report that N-acetylglucosamine (GlcNAc) incorporated into various thioglycosides robustly truncate cell surface N- and O-linked glycan biosynthesis at 10-100 µM concentrations. The >10-fold greater inhibition is in part due to the resistance of thioglycosides to hydrolysis by intracellular hexosaminidases. The thioglycosides reduce ß-galactose incorporation into lactosamine chains, cell surface sialyl Lewis-X expression, and leukocyte rolling on selectin substrates including inflamed endothelial cells under fluid shear. Treatment of granulocytes with thioglycosides prior to infusion into mouse inhibited neutrophil homing to sites of acute inflammation and bone marrow by ∼80%-90%. Overall, thioglycosides represent an easy to synthesize class of efficient metabolic inhibitors or decoys. They reduce N-/O-linked glycan biosynthesis and inflammatory leukocyte accumulation.

Glycosphingolipids on Human Myeloid Cells Stabilize E-Selectin-Dependent Rolling in the Multistep Leukocyte Adhesion Cascade.

OBJECTIVE: Recent studies suggest that the E-selectin ligands expressed on human leukocytes may differ from those in other species, particularly mice. To elaborate on this, we evaluated the impact of glycosphingolipids expressed on human myeloid cells in regulating E-selectin-mediated cell adhesion. APPROACH AND RESULTS: A series of modified human cell lines and primary neutrophils were created by targeting UDP-Glucose Ceramide Glucosyltransferase using either lentivirus-delivered shRNA or CRISPR-Cas9-based genome editing. Enzymology and mass spectrometry confirm that the modified cells had reduced or abolished glucosylceramide biosynthesis. Glycomics profiling showed that UDP-Glucose Ceramide Glucosyltransferase disruption also increased prevalence of bisecting N-glycans and reduced overall sialoglycan expression on leukocyte N- and O-glycans. Microfluidics-based flow chamber studies demonstrated that both the UDP-Glucose Ceramide Glucosyltransferase knockouts and knockdowns display ≈60% reduction in leukocyte rolling and firm adhesion on E-selectin bearing stimulated endothelial cells, without altering cell adhesion to P-selectin. Consistent with the concept that the glycosphingolipids support slow rolling and the transition to firm arrest, inhibiting UDP-Glucose Ceramide Glucosyltransferase activity resulted in frequent leukocyte detachment events, skipping motion, and reduced diapedesis across the endothelium. Cells bearing truncated O- and N-glycans also sustained cell rolling on E-selectin, although their ability to be recruited from free fluid flow was diminished. CONCLUSIONS: Glycosphingolipids likely contribute to human myeloid cell adhesion to E-selectin under fluid shear, particularly the transition of rolling cells to firm arrest.

Collagen XXIV (Col24α1) promotes osteoblastic differentiation and mineralization through TGF-ß/Smads signaling pathway.

Collagen XXIV (Col24α1) is a recently discovered fibrillar collagen. It is known that mouse Col24α1 is predominantly expressed in the forming skeleton of the mouse embryo, as well as in the trabecular bone and periosteum of the newborn mouse. However, the role and mechanism of Col24α1 in osteoblast differentiation and mineralization remains unclear. By analyzing the expression pattern of Col24α1, we confirmed that it is primarily expressed in bone tissues, and this expression gradually increased concomitant with the progression of osteoblast differentiation. Through the use of a lentivirus vector-mediated interference system, silencing Col24α1 expression in MC3T3-E1 murine preosteoblastic cells resulted in significant inhibition of alkaline phosphatase (ALP) activity, cell mineralization, and the expression of osteoblast marker genes such as runt-related transcription factor 2 (Runx2), osteocalcin (OCN), ALP, and type I collagen (Col I). Subsequent overexpression not only rescued the deficiency in osteoblast differentiation from Col24α1 silenced cells, but also enhanced osteoblastic differentiation in control cells. We further revealed that Col24α1 interacts with integrin ß3, and silencing Col24α1 up-regulated the expression of Smad7 during osteoblast differentiation while at the same time inhibiting the phosphorylation of the Smad2/3 complex. These results suggest that Col24α1 imparts some of its regulatory control on osteoblast differentiation and mineralization at least partially through interaction with integrin ß3 and the transforming growth factor beta (TGF-ß) /Smads signaling pathway.