Osteogenic differentiation of human mesenchymal stem cells (hMSCs) is classically thought to be mediated by different cytokines such as the bone morphogenetic proteins (BMPs). Here, we report that cell adhesion to extracellular matrix (ECM), and its effects on cell shape and cytoskeletal mechanics, regulates BMP-induced signaling and osteogenic differentiation of hMSCs. Using micropatterned substrates to progressively restrict cell spreading and flattening against ECM, we demonstrated that BMP-induced osteogenesis is progressively antagonized with decreased cell spreading. BMP triggered rapid and sustained RhoA/Rho-associated protein kinase (ROCK) activity and contractile tension only in spread cells, and this signaling was required for BMPinduced osteogenesis. Exploring the molecular basis for this effect, we found that restricting cell spreading, reducing ROCK signaling, or inhibiting cytoskeletal tension prevented BMP-induced SMA/mothers against decapentaplegic (SMAD)1 c-terminal phosphorylation, SMAD1 dimerization with SMAD4, and SMAD1 translocation into the nucleus. Together, these findings demonstrate the direct involvement of cell spreading and RhoA/ROCK-mediated cytoskeletal tension generation in BMP-induced signaling and early stages of in vitro osteogenesis, and highlight the essential interplay between biochemical and mechanical cues in stem cell differentiation.

Kal/bat, a polyketide, isolated to high purity (>95%) is characterized by strong and selective antibacterial activity against Staphylococcus species (minimum inhibitory concentration, 0.05 microg/mL), and no resistance was observed in strains already resistant to commonly used antibiotics. The kal/bat biosynthesis gene cluster was determined to a 62 kb genomic region of Pseudomonas fluorescens BCCM_ID9359. The kal/bat gene cluster consists of 16 open reading frames (ORF), encoding a hybrid PKS-NRPS system, extended with trans-acting tailoring functions. A full model for kal/bat biosynthesis is postulated and experimentally tested by gene inactivation, structural confirmation (using NMR spectroscopy), and complementation. The structural and microbiological study of biosynthetic kal/bat analogs revealed the importance of the carbamoyl group and 17-keto group for antibacterial activity. The mechanism of self-resistance lies within the production of an inactive intermediate, which is activated in a one-step enzymatic oxidation upon export. The genetic basis and biochemical elucidation of the biosynthesis pathway of this antibiotic will facilitate rational engineering for the design of novel structures with improved activities. This makes it a promising new therapeutic option to cope with multidrug-resistant clinical infections.

Serratia plymuthica strain RVH1, initially isolated from an industrial food processing environment, displays potent antimicrobial activity towards a broad spectrum of Gram-positive and Gram-negative bacterial pathogens. Isolation and subsequent structure determination of bioactive molecules led to the identification of two polyamino antibiotics with the same molecular structure as zeamine and zeamine II as well as a third, closely related analogue, designated zeamine I. The gene cluster encoding the biosynthesis of the zeamine antibiotics was cloned and sequenced and shown to encode FAS, PKS as well as NRPS related enzymes in addition to putative tailoring and export enzymes. Interestingly, several genes show strong homology to the pfa cluster of genes involved in the biosynthesis of long chain polyunsaturated fatty acids in marine bacteria. We postulate that a mixed FAS/PKS and a hybrid NRPS/PKS assembly line each synthesize parts of the backbone that are linked together post-assembly in the case of zeamine and zeamine I. This interaction reflects a unique interplay between secondary lipid and secondary metabolite biosynthesis. Most likely, the zeamine antibiotics are produced as prodrugs that undergo activation in which a nonribosomal peptide sequence is cleaved off.

There are currently no approved drugs for the treatment of emerging viral infections, such as dengue and Ebola. Adaptor associated kinase 1 (AAK1) is a cellular serine/threonine protein kinase that functions as a key regulator of the clathrin-associated host adaptor proteins and *

BatG is a trans-2-enoyl-ACP reductase, encoded in the kalimantacin/batumin (kal/bat) biosynthesis operon. It is not essential for the production of the kal/bat secondary metabolite. Instead, BatG is an isoform of FabI, conferring full resistance to target bacteria. It also complements FabI in its role in fatty acid biosynthesis. The identification of FabI as the antibacterial target is important to assess clinical potential of the kalimantacin/batumin antibiotics against Staphylococcus aureus.

DRAK2 emerged as a promising drug target for the treatment of autoimmune diseases and to prevent graft rejection after organ transplantation. Screening of a compound library in a DRAK2 binding assay led to the identification of an isothiazolo[5,4-b]pyridine derivative as a novel ligand for DRAK2, displaying a Kd value of 1.6 μM. Subsequent medicinal chemistry work led to the discovery of a thieno[2,3-b]pyridine derivative with strong DRAK2 binding affinity (Kd = 9 nM). Moreover, this compound also behaves as a functional inhibitor of DRAK2 enzymatic activity, displaying an IC50 value of 0.82 μM, although lacking selectivity, when tested against DRAK1. This paper describes for the first time functionally active dual DRAK1 and DRAK2 inhibitors that can be used as starting point for the synthesis of chemical tool compounds to study DRAK1 and DRAK2 biology, or they can be considered as hit compounds for hit-to-lead optimization campaigns in drug discovery programs.

Nucleoside and nucleotide analogues are essential antivirals in the treatment of infectious diseases such as human immunodeficiency virus (HIV), hepatitis B virus (HBV), hepatitis C virus (HCV), herpes simplex virus (HSV), varicella-zoster virus (VZV), and human cytomegalovirus (HCMV). To celebrate the 80th birthday of Prof. Dr. Erik De Clercq on 28 March 2021, this review provides an overview of his contributions to eight approved nucleos(t)ide drugs: (i) three adenosine nucleotide analogues, namely tenofovir disoproxil fumarate (Viread®) and tenofovir alafenamide (Vemlidy®) against HIV and HBV infections and adefovir dipivoxil (Hepsera®) against HBV infections; (ii) two thymidine nucleoside analogues, namely brivudine (Zostex®) against HSV-1 and VZV infections and stavudine (Zerit®) against HIV infections; (iii) two guanosine analogues, namely valacyclovir (Valtrex®, Zelitrex®) against HSV and VZV and rabacfosadine (Tanovea®-CA1) for the treatment of lymphoma in dogs; and (iv) one cytidine nucleotide analogue, namely cidofovir (Vistide®) for the treatment of HCMV retinitis in AIDS patients. Although adefovir dipivoxil, stavudine, and cidofovir are virtually discontinued for clinical use, tenofovir disoproxil fumarate and tenofovir alafenamide remain the most important antivirals against HIV and HBV infections worldwide. Overall, the broad-spectrum antiviral potential of nucleos(t)ide analogues supports their development to treat or prevent current and emerging infectious diseases worldwide.

Herein we describe the synthesis and in vitro and in vivo activity of thiazolo[5,4-d]pyrimidines as a novel class of immunosuppressive agents, useful for preventing graft rejection after organ transplantation. This research resulted in the discovery of a series of compounds with potent activity in the mixed lymphocyte reaction (MLR) assay, which is well-known as the in vitro model for in vivo rejection after organ transplantation. The most potent congeners displayed IC(50) values of less than 50 nM in this MLR assay and hence are equipotent to cyclosporin A, a clinically used immunosuppressive drug. One representative of this series was further evaluated in a preclinical animal model of organ transplantation and showed excellent in vivo efficacy. It validates these compounds as new promising immunosuppressive drugs.