A high density CHO-S transient transfection system: Comparison of ExpiCHO and Expi293.

Chinese Hamster Ovary (CHO) cells are the principal mammalian host used for stable cell line generation and biotherapeutic protein production. Until recently, production of milligrams to grams of protein in CHO transient systems was challenging. As such, Human Embryonic Kidney (HEK293) cells are the most common mammalian cell type used for transient transfection. The post-translational modifications (PTMs) of a protein are dictated in part by the cell line used for expression, and changes in PTMs have been shown to affect both the activity and biophysical properties of proteins. Therefore, it is potentially advantageous to keep the host cell type consistent throughout drug discovery and development. To this end, we compared the ExpiCHO system, a high density CHO-S transient transfection system, to the Expi293 and FreeStyle MAX CHO transient systems. Fourteen proteins were expressed in both the Expi293 and ExpiCHO systems. For a majority of proteins tested, the protein titers observed with the ExpiCHO system were higher than those seen with both the FreeStyle MAX CHO and Expi293 systems. Antibodies expressed using the ExpiCHO system had glycosylation patterns more similar to antibodies produced in stable CHO cell lines than Expi293-derived antibodies. However, culture duration and temperature were found to affect protein titer, monodispersity, enzyme activity, and PTMs and should be carefully selected when using the ExpiCHO system. The ExpiCHO transient transfection systems allows for facile production of milligrams to grams of protein in CHO cells and de-risks the transition from transient to stable material during drug development.

Reversible linkage of two distinct small molecule inhibitors of Myc generates a dimeric inhibitor with improved potency that is active in myc over-expressing cancer cell lines.

We describe the successful application of a novel approach for generating dimeric Myc inhibitors by modifying and reversibly linking two previously described small molecules. We synthesized two directed libraries of monomers, each comprised of a ligand, a connector, and a bioorthogonal linker element, to identify the optimal dimer configuration required to inhibit Myc. We identified combinations of monomers, termed self-assembling dimeric inhibitors, which displayed synergistic inhibition of Myc-dependent cell growth. We confirmed that these dimeric inhibitors directly bind to Myc blocking its interaction with Max and affect transcription of MYC dependent genes. Control combinations that are unable to form a dimer do not show any synergistic effects in these assays. Collectively, these data validate our new approach to generate more potent and selective inhibitors of Myc by self-assembly from smaller, lower affinity components. This approach provides an opportunity for developing novel therapeutics against Myc and other challenging protein:protein interaction (PPI) target classes.

Novel 6-aminofuro[3,2-c]pyridines as potent, orally efficacious inhibitors of cMET and RON kinases.

A series of novel 6-aminofuro[3,2-c]pyridines as kinase inhibitors is described, most notably, OSI-296 (6). We discuss our exploration of structure-activity relationships and optimization leading to OSI-296 and disclose its pharmacological activity against cMET and RON in cellular assays. OSI-296 is a potent and selective inhibitor of cMET and RON kinases that shows in vivo efficacy in tumor xenografts models upon oral dosing and is well tolerated.

Discovery of novel insulin-like growth factor-1 receptor inhibitors with unique time-dependent binding kinetics.

This letter describes a series of small molecule inhibitors of IGF-1R with unique time-dependent binding kinetics and slow off-rates. Structure-activity and structure-kinetic relationships were elucidated and guided further optimizations within the series, culminating in compound 2. With an IGF-1R dissociative half-life (t 1/2) of >100 h, compound 2 demonstrated significant and extended PD effects in conjunction with tumor growth inhibition in xenograft models at a remarkably low and intermittent dose, which correlated with the observed in vitro slow off-rate properties.

Thiamine diphosphate binds to intermediates in the assembly of adenovirus fiber knob trimers in Escherichia coli.

Assembly of the adenovirus (Ad) homotrimeric fiber protein is nucleated by its C-terminal knob domain, which itself can trimerize when expressed as a recombinant protein fragment. The non-interlocked, globular structure of subunits in the knob trimer implies that trimers assemble from prefolded monomers through a dimer intermediate, but these intermediates have not been observed and the mechanism of assembly therefore remains uncharacterized. Here we report that expression of the Ad serotype 2 (Ad2) knob was toxic for thi- strains of Escherichia coli, which are defective in de novo synthesis of thiamine (vitamin B1). Ad2 knob trimers isolated from a thi+ strain copurified through multiple chromatography steps with a small molecule of mass equivalent to that of thiamine diphosphate (ThDP). Mutant analysis did not implicate any specific site for ThDP binding. Our results suggest that ThDP may associate with assembly intermediates and become trapped in assembled trimers, possibly within one of several large cavities that are partially solvent-accessible or buried completely within the trimer interior.