Small heat shock proteins (sHsps) are ubiquitous molecular chaperones that prevent the aggregation of unfolding proteins during proteotoxic stress. In Caenorhabditis elegans, Sip1 is the only sHsp exclusively expressed in oocytes and embryos. Here, we demonstrate that Sip1 is essential for heat shock survival of reproducing adults and embryos. X-ray crystallography and electron microscopy revealed that Sip1 exists in a range of well-defined globular assemblies consisting of two half-spheres, each made of dimeric "spokes." Strikingly, the oligomeric distribution of Sip1 as well as its chaperone activity depend on pH, with a trend toward smaller species and higher activity at acidic conditions such as present in nematode eggs. The analysis of the interactome shows that Sip1 has a specific substrate spectrum including proteins that are essential for embryo development.

Mannose-binding proteins like the macrophage mannose receptor (MR), the dendritic cell-specific intercellular adhesion molecule-3 grabbing non-integrin (DC-SIGN) and mannose-binding lectin (MBL) play crucial roles in both innate and adaptive immune responses. Immunoglobulin fusion proteins of the P-selectin glycoprotein ligand-1 (PSGL-1/mIgG(2b)) carrying mostly O-glycans and, as a control, the α1-acid glycoprotein (AGP/mIgG(2b)) carrying mainly N-linked glycans were stably expressed in the yeast Pichia pastoris. Pichia pastoris-produced PSGL-1/mIgG(2b) was shown to carry O-glycans that mediated strong binding to mannose-specific lectins in a lectin array and were susceptible to cleavage by α-mannosidases including an α1,2- but not an α1,6-mannosidase. Electrospray ionization ion-trap mass spectrometry confirmed the presence of O-glycans containing up to nine hexoses with the penta- and hexasaccharides being the predominant ones. α1,2- and α1,3-linked, but not α1,6-linked, mannose residues were detected by (1)H-nuclear magnetic resonance spectroscopy confirming the results of the mannosidase cleavage. The apparent equilibrium dissociation constants for binding of PNGase F-treated mannosylated PSGL-1/mIgG(2b) to MR, DC-SIGN and MBL were shown by surface plasmon resonance to be 126, 56 and 16 nM, respectively. In conclusion, PSGL-1/mIgG(2b) expressed in P. pastoris carried O-glycans mainly comprised of α-linked mannoses and with up to nine residues. It bound mannose-specific receptors with high apparent affinity and may become a potent targeting molecule for these receptors in vivo.

A key metabolic alteration in tumor cells is an elevated glycolysis rate, resulting in the production of increased amounts of protons and lactate leading to lactic acidosis within the tumor microenvironment. The tumor-promoting effects of lactic acidosis are versatile, ranging from stimulation of proliferation, angiogenesis and metastasis to the reshaping of the tumor immune environment to a tumor-permissive phenotype. In tumors lactate is transported across the plasma membrane by the monocarboxylate transporters 1 and 4 (MCT 1/4) in symport with a proton. While MCT1 is expressed almost ubiquitously at low levels, MCT4 expression is regulated by hypoxia-inducible factor 1α (Hif1α), the central player in the cellular response to hypoxia. Thus, MCT4 is present in hypoxic, highly glycolytic cells. Given their central role in prevention of intracellular acidification and lactate transport, MCTs appear to be indispensable for glycolytic tumor growth. Since MCT4 has the strongest implication on the development and aggressiveness of diverse cancer types it has emerged as a new target for the treatment of solid tumors. We have identified MCT4 specific inhibitors structurally based on an internal compound library using cell-based lactate export assays. A subsequent extensive medicinal chemistry program was able to significantly improve activity and selectivity of the primary structures. Cellular target engagement was verified by cell-based assays like cellular thermal shift assay (CETSA). These efforts resulted in the identification of highly potent, orally bioavailable and selective MCT4 inhibitors (MCT4 IC50 < 20nM; MCT1 IC50 > 100µM) with good physicochemical properties and beneficial pharmacokinetics in mouse. In vivo efficacy and tumor lactate modulation were evaluated in NCI-H358 xenograft and MC38 syngeneic mouse models. Thereby we explore the potential of our MCT4 inhibitor to act as a single anti-cancer agent or to synergize with other established therapies like angiogenesis inhibitors or cancer immunotherapeutics. Citation Format: Nina Hambruch, Barbara Herkert, Christian Gege, Aurelie Mallinger, Johannes Fabian, Olaf Kinzel, Yansong Wang, Gero Fink, Michael Albers, Anette Funk, Annika Bittman-Waetzig, Tilly Fleckenstein, Floriane Braun, Claus Kremoser. Identification of a potent, orally bioavailable and selective MCT4 Inhibitor for the treatment of solid Warburg tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3588.

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