Discovery of an Chemical Probe for BCL6 Inhibition by Optimization of Tricyclic Quinolinones.

B-cell lymphoma 6 (BCL6) is a transcriptional repressor and oncogenic driver of diffuse large B-cell lymphoma (DLBCL). Here, we report the optimization of our previously reported tricyclic quinolinone series for the inhibition of BCL6. We sought to improve the cellular potency and exposure of the non-degrading isomer, , of our recently published degrader, .

Optimizing Shape Complementarity Enables the Discovery of Potent Tricyclic BCL6 Inhibitors.

To identify new chemical series with enhanced binding affinity to the BTB domain of B-cell lymphoma 6 protein, we targeted a subpocket adjacent to Val18. With no opportunities for strong polar interactions, we focused on attaining close shape complementarity by ring fusion onto our quinolinone lead series. Following exploration of different sized rings, we identified a conformationally restricted core which optimally filled the available space, leading to potent BCL6 inhibitors.

Improved Binding Affinity and Pharmacokinetics Enable Sustained Degradation of BCL6 .

The transcriptional repressor BCL6 is an oncogenic driver found to be deregulated in lymphoid malignancies. Herein, we report the optimization of our previously reported benzimidazolone molecular glue-type degrader to , a highly potent probe suitable for sustained depletion of BCL6 . We observed a sharp degradation SAR, where subtle structural changes conveyed the ability to induce degradation of BCL6.

Into Deep Water: Optimizing BCL6 Inhibitors by Growing into a Solvated Pocket.

We describe the optimization of modestly active starting points to potent inhibitors of BCL6 by growing into a subpocket, which was occupied by a network of five stably bound water molecules. Identifying potent inhibitors required not only forming new interactions in the subpocket but also perturbing the water network in a productive, potency-increasing fashion while controlling the physicochemical properties. We achieved this goal in a sequential manner by systematically probing the pocket and the water network, ultimately achieving a 100-fold improvement of activity.

Achieving Target Depletion through the Discovery and Optimization of Benzimidazolone BCL6 Degraders.

Deregulation of the transcriptional repressor BCL6 enables tumorigenesis of germinal center B-cells, and hence BCL6 has been proposed as a therapeutic target for the treatment of diffuse large B-cell lymphoma (DLBCL). Herein we report the discovery of a series of benzimidazolone inhibitors of the protein-protein interaction between BCL6 and its co-repressors. A subset of these inhibitors were found to cause rapid degradation of BCL6, and optimization of pharmacokinetic properties led to the discovery of 5-((5-chloro-2-((3,5)-4,4-difluoro-3,5-dimethylpiperidin-1-yl)pyrimidin-4-yl)amino)-3-(3-hydroxy-3-methylbutyl)-1-methyl-1,3-dihydro-2-benzo[]imidazol-2-one (CCT369260), which reduces BCL6 levels in a lymphoma xenograft mouse model following oral dosing.

An RNAi screen of Rho signalling networks identifies RhoH as a regulator of Rac1 in prostate cancer cell migration.

Background: Cell migration is essential for development and tissue repair, but it also contributes to disease. Rho GTPases regulate cell migration, but a comprehensive analysis of how each Rho signalling component affects migration has not been carried out.

Results: Through an RNA interference screen, and using a prostate cancer cell line, we find that approximately 25% of Rho network components alter migration.

HSF1 Is Essential for Myeloma Cell Survival and A Promising Therapeutic Target.

Myeloma is a plasma cell malignancy characterized by the overproduction of immunoglobulin, and is therefore susceptible to therapies targeting protein homeostasis. We hypothesized that heat shock factor 1 (HSF1) was an attractive therapeutic target for myeloma due to its direct regulation of transcriptional programs implicated in both protein homeostasis and the oncogenic phenotype. Here, we interrogate HSF1 as a therapeutic target in myeloma using bioinformatic, genetic, and pharmacologic means.

Oncogenic RAC1 and NRAS drive resistance to endoplasmic reticulum stress through MEK/ERK signalling.

Cancer cells are able to survive under conditions that cause endoplasmic reticulum stress (ER-stress), and can adapt to this stress by upregulating cell-survival signalling pathways and down-regulating apoptotic pathways. The cellular response to ER-stress is controlled by the unfolded protein response (UPR). Small Rho family GTPases are linked to many cell responses including cell growth and apoptosis.

Cleavage of BLOC1S1 mRNA by IRE1 Is Sequence Specific, Temporally Separate from XBP1 Splicing, and Dispensable for Cell Viability under Acute Endoplasmic Reticulum Stress.

The unfolded protein response (UPR) remediates endoplasmic reticulum (ER) stress. IRE1, a component of the UPR, senses misfolded protein and cleaves XBP1 mRNA, which is ligated to code for the prosurvival transcription factor. IRE1 also cleaves other mRNAs preceding their degradation, termed regulated IRE1-dependent mRNA decay (RIDD).

The motor protein myosin 1G functions in FcγR-mediated phagocytosis.

Phagocytosis is the force-dependent complex cellular process by which immune cells engulf particles. Although there has been considerable progress in understanding ligand-receptor-induced actin polymerisation in pushing the membrane around the particle, significantly less is known about how localised contractile activities regulate cup closure in coordination with the actin cytoskeleton. Herein, we show that the unconventional class-I myosin, myosin 1G (Myo1G) is localised at phagocytic cups following Fcγ-receptor (FcγR) ligation in macrophages.

PAK4 phosphorylates myosin regulatory light chain and contributes to Fcγ receptor-mediated phagocytosis.

Phagocytosis of immunoglobulin G-opsonised particles takes place via Fcγ receptor ligation, leading to uptake through an actin-dependent mechanism. Myosin regulatory light chains have previously been reported to control contractility during uptake through the Fcγ receptor. In this study, we show that p21-activated kinase 4 contributes to Fcγ receptor-mediated uptake downstream of actin cup formation by regulating phosphorylation of myosin regulatory light chain.

Enteropathogenic and enterohaemorrhagic Escherichia coli: even more subversive elements.

The human pathogens enteropathogenic and enterohemorrhagic Escherichia coli (EPEC and EHEC) share a unique mechanism of colonization that results from the concerted action of effector proteins translocated into the host cell by a type III secretion system (T3SS). EPEC and EHEC not only induce characteristic attaching and effacing (A/E) lesions, but also subvert multiple host cell signalling pathways during infection. Our understanding of the mechanisms by which A/E pathogens hijack host cell signalling has advanced dramatically in recent months with the identification of novel activities for many effectors.

PAK1 and PAK2 have different roles in HGF-induced morphological responses.

Hepatocyte growth factor (HGF) stimulates dissociation of epithelial cells (scattering) and cell migration. Several Rho GTPases are required for HGF-induced scattering. PAK1 and PAK2 are members of the p21-activated kinase (PAK) family of serine/threonine kinases, and are activated by the Rho GTPases Rac and Cdc42.