Synergistic effects of PARP inhibition and cholesterol biosynthesis pathway modulation.

An in-depth multi-omic molecular characterisation of poly(adenosine 5'-diphosphate [ADP]-ribose) polymerase (PARP) inhibitors revealed a distinct poly-pharmacology of niraparib (Zejula®) mediated by its interaction with lanosterol synthase (LSS), which is not observed with other PARP inhibitors. Niraparib, in a similar way to the LSS inhibitor Ro-48-8071, induced activation of the 24,25-epoxysterol shunt pathway, which is a regulatory signalling branch of the cholesterol biosynthesis pathway. Interestingly, the combination of a LSS inhibitor with a PARP inhibitor that does not bind to LSS, such as olaparib, had an additive effect on killing of cancer cells to levels comparable to Niraparib as single agent. In addition, the combination of PARP inhibitors and statins, inhibitors of HMGCR, an enzyme catalysing the rate-limiting step in the mevalonate pathway, had a synergistic effect on tumor cell killing in cell lines and patient-derived ovarian tumor organoids. These observations suggest that concomitant inhibition of cholesterol biosynthesis pathway and PARP activity might result in stronger efficacy of these inhibitors against tumor types highly dependent on cholesterol metabolism.

Discovery of GSK251: A Highly Potent, Highly Selective, Orally Bioavailable Inhibitor of PI3Kδ with a Novel Binding Mode.

Optimization of a previously reported lead series of PI3Kδ inhibitors with a novel binding mode led to the identification of a clinical candidate compound 31 (GSK251). Removal of an embedded Ames-positive heteroaromatic amine by reversing a sulfonamide followed by locating an interaction with Trp760 led to a highly selective compound 9. Further optimization to avoid glutathione trapping, to enhance potency and selectivity, and to optimize an oral pharmacokinetic profile led to the discovery of compound 31 (GSK215) that had a low predicted daily dose (45 mg, b.i.d) and a rat toxicity profile suitable for further development.

Discovery of GSK8612, a Highly Selective and Potent TBK1 Inhibitor.

The serine/threonine protein kinase TBK1 (Tank-binding Kinase-1) is a noncanonical member of the IkB kinase (IKK) family. This kinase regulates signaling pathways in innate immunity, oncogenesis, energy homeostasis, autophagy, and neuroinflammation. Herein, we report the discovery and characterization of a novel potent and highly selective TBK1 inhibitor, GSK8612. In cellular assays, this small molecule inhibited toll-like receptor (TLR)3-induced interferon regulatory factor (IRF)3 phosphorylation in Ramos cells and type I interferon (IFN) secretion in primary human mononuclear cells. In THP1 cells, GSK8612 was able to inhibit secretion of interferon beta (IFNß) in response to dsDNA and cGAMP, the natural ligand for STING. GSK8612 is a TBK1 small molecule inhibitor displaying an excellent selectivity profile and therefore represents an ideal probe to further dissect the biology of TBK1 in models of immunity, neuroinflammation, obesity, or cancer.

Discovery of a Highly Selective Tankyrase Inhibitor Displaying Growth Inhibition Effects against a Diverse Range of Tumor Derived Cell Lines.

The availability of high quality probes for specific protein targets is fundamental to the investigation of their function and their validation as therapeutic targets. We report the utilization of a dedicated chemoproteomic assay platform combining affinity enrichment technology with high-resolution protein mass spectrometry to the discovery of a novel nicotinamide isoster, the tetrazoloquinoxaline 41, a highly potent and selective tankyrase inhibitor. We also describe the use of 41 to investigate the biology of tankyrase, revealing the compound induced growth inhibition of a number of tumor derived cell lines, demonstrating the potential of tankyrase inhibitors in oncology.