Role of tyrosine kinases in lymphocyte activation: targets for drug intervention

Fyn nanoclustering requires switching to an open conformation and is enhanced by FTLD-Tau biomolecular condensates

Fyn is a Src kinase that controls critical signalling cascades and has been implicated in learning and memory. Postsynaptic enrichment of Fyn underpins synaptotoxicity in dementias such as Alzheimer's disease and frontotemporal lobar degeneration with Tau pathology (FTLD-Tau). The FLTD P301L mutant Tau is associated with a higher propensity to undergo liquid-liquid phase separation (LLPS) and form biomolecular condensates. Expression of P301L mutant Tau promotes aberrant trapping of Fyn in nanoclusters within hippocampal dendrites by an unknown mechanism. Here, we used single-particle tracking photoactivated localisation microscopy to demonstrate that the opening of Fyn into its primed conformation promotes its nanoclustering in dendrites leading to increased Fyn/ERK/S6 downstream signalling. Preventing the auto-inhibitory closed conformation of Fyn through phospho-inhibition or through perturbation of its SH3 domain increased Fyn's nanoscale trapping, whereas inhibition of the catalytic domain had no impact. By combining pharmacological and genetic approaches, we demonstrate that P301L Tau enhanced both Fyn nanoclustering and Fyn/ERK/S6 signalling via its ability to form biomolecular condensates. Together, our findings demonstrate that Fyn alternates between a closed and an open conformation, the latter being enzymatically active and clustered. Furthermore, pathogenic immobilisation of Fyn relies on the ability of P301L Tau to form biomolecular condensates, thus highlighting the critical importance of LLPS in controlling nanoclustering and downstream intracellular signalling events.

Ouabain stimulates a Na+/K+-ATPase-mediated SFK-activated signalling pathway that regulates tight junction function in the mouse blastocyst

The Na(+)/K(+)-ATPase plays a pivotal role during preimplantation development; it establishes a trans-epithelial ionic gradient that facilitates the formation of the fluid-filled blastocyst cavity, crucial for implantation and successful pregnancy. The Na(+)/K(+)-ATPase is also implicated in regulating tight junctions and cardiotonic steroid (CTS)-induced signal transduction via SRC. We investigated the expression of SRC family kinase (SFK) members, Src and Yes, during preimplantation development and determined whether SFK activity is required for blastocyst formation. Embryos were collected following super-ovulation of CD1 or MF1 female mice. RT-PCR was used to detect SFK mRNAs encoding Src and Yes throughout preimplantation development. SRC and YES protein were localized throughout preimplantation development. Treatment of mouse morulae with the SFK inhibitors PP2 and SU6656 for 18 hours resulted in a reversible blockade of progression to the blastocyst stage. Blastocysts treated with 10(-3) M ouabain for 2 or 10 minutes and immediately immunostained for phosphorylation at SRC tyr418 displayed reduced phosphorylation while in contrast blastocysts treated with 10(-4) M displayed increased tyr418 fluorescence. SFK inhibition increased and SFK activation reduced trophectoderm tight junction permeability in blastocysts. The results demonstrate that SFKs are expressed during preimplantation development and that SFK activity is required for blastocyst formation and is an important mediator of trophectoderm tight junction permeability.

Fluorinated cyclitols as useful biological probes of phosphatidylinositol metabolism

A number of deoxyfluoro cyclitols have been synthesized and evaluated as probes of the phosphatidylinositol pathway (PtdIns pathway), most notably 5-deoxy-5-fluoro-myo-inositol, which is incorporated into the pathway at about 25% the level of myo-inositol itself. Unfortunately, none of the cyclitols have proved effective in limiting cell proliferation, as the cells are able to 'synthesize around' the fraudulent cyclitols using natural myo-inositol as substrate. Inhibitors for 3-phosphatidylinositol kinase, which has importance in a number of pathological conditions, including cancer, have been intensively investigated. 3-Deoxy-3-fluoro-myo-inositol is incorporated into the PtdIns pathway; however, only related phosphatidyl derivatives, for example, a methyl ether derivative of the 3-deoxy inositol, showed significant antiproliferative activity. Synthesis of the deoxyfluoro analogues most often has been accomplished by DAST fluoro-de-hydroxylation of the appropriate cyclitol, generally leading to products of inversion.

General Model for Estimation of the Inhibition of Protein Kinases Using Monte Carlo Simulations

Monte Carlo statistical mechanics simulations were used in combination with the extended linear response (ELR) approach to develop a model to predict the activities of kinase inhibitors. One hundred forty eight inhibitors of three protein kinases, cyclin-dependent kinase 2 (CDK2), lymphocyte-specific kinase (Lck), and p38 mitogen-activated protein kinase were considered. The inhibitor sets for the individual kinases were analyzed first, and ELR models using only three descriptors were obtained with correlation coefficients, r(2), of 0.7-0.8. Models for each pair of kinases were then developed and used to predict the activities of the inhibitors for the remaining kinase with resultant q(2) values of 0.71 (CDK2), 0.70 (Lck), and 0.54 (p38). Finally, the three datasets were combined to yield a general ELR model for kinase inhibition; with just three physically reasonable descriptors, EXX, DeltaHB(total), and DeltaSASA, the r(2) and leave-one-out q(2) are 0.69 and 0.67. The optimization of the model was confirmed using a genetic algorithm. The descriptors reflect the structural requirements for strong inhibition: good steric and electrostatic complementarities between inhibitor and protein, limited loss of hydrogen bonds for the inhibitor upon binding, and increased burial of surface area of the inhibitor.

Discovery of 2-amino-heteroaryl-benzothiazole-6-anilides as potent p56(lck) inhibitors

A series of structurally novel benzothiazole based small molecule inhibitors of p56(lck) was prepared to elucidate their structure-activity relationships (SAR), selectivity and cell activity in the T-cell proliferation assay. BMS-350751 (2) and BMS-358233 (3) are identified as potent Lck inhibitors with excellent cellular activities against T-cell proliferation.

Molecular design, synthesis, and structure-Activity relationships leading to the potent and selective p56(lck) inhibitor BMS-243117

A series of structurally novel benzothiazole based small molecule inhibitors of p56(lck) were prepared to elucidate their structure-activity relationships (SARs), selectivity and cell activity in the T-cell proliferation assay. BMS-243117 (compound 2) is identified as a potent, and selective Lck inhibitor with good cellular activity (IC(50)=1.1 microM) against T-cell proliferation.

Optimization of 2-phenylaminoimidazo[4,5-h]isoquinolin-9-ones: orally active inhibitors of lck kinase

The tyrosine kinase p56lck (lck) is essential for T cell activation; thus, inhibitors of lck have potential utility as autoimmune agents. Our initial disclosure of a new class of lck inhibitors based on the phenylaminoimidazoisoquinolin-9-one showed reasonable cellular activity but did not work in vivo upon oral administration. Our current work highlights the further use of rational drug design and molecular modeling to produce a series of lck inhibitors that demonstrate cellular activity below 100 nM and are as efficacious as cyclosporin A in an in vivo mouse model of anti-CD3-induced IL-2 production.

Discovery of 2-phenylamino-imidazo[4,5-h]isoquinolin-9-ones: a new class of inhibitors of lck kinase

An imidazo[4,5-h]isoquinolin-7,9-dione (1) was identified as an adenosine 5'-triphosphate competitive inhibitor of lck by high throughput screening. Initial structure-activity relationship studies identified the dichlorophenyl ring and the imide NH as important pharmacophores. A binding model was constructed to understand how 1 binds to a related kinase, hck. These results suggested that removing the gem-dimethyl group and flattening the ring would enhance activity. This was realized by converting 1 to the imidazo[4,5-h]isoquinolin-9-one (20), resulting in an 18-fold improvement in potency against lck and a 50-fold increase in potency in a cellular assay.

Pyrrolo[2,3-d]pyrimidines containing diverse N-7 substituents as potent inhibitors of Lck

A series of pyrrolo[2,3-d]pyrimidines was synthesized and evaluated as inhibitors of Lck. Lck accommodates a diverse set of substituents at N-7. Altering the substituent at N-7 provided compound 13, an orally available lck inhibitor which inhibited TCR mediated IL-2 production after oral dosing.

Therapeutically targeting lymphocyte energy metabolism by high-dose glucocorticoids

Lymphocytes use a considerable amount of energy, mainly in the form of ATP, especially when they become stimulated following activation by antibodies or mitogens. Cellular respiration is the major energy source, and in quiescent cells the ATP produced is used to drive protein synthesis and sodium transport. In stimulated cells there is significantly higher ATP production to balance the higher ATP demand of specific processes resulting from activation. The major ATP-consuming processes under these conditions are protein synthesis and Na(+),K(+)-ATPase (about 20% each), while Ca(2+)-ATPase and RNA/DNA syntheses contribute about 10% each. There is a wealth of available information about glucocorticoid effects on lymphocytes, but here we focus on the extent to which this lymphocyte bioenergetic machinery is targeted by glucocorticoids when they are used therapeutically at high doses. High-dose glucocorticoids have been shown recently to interfere with processes that are essential for the activation and maintenance of lymphocytes, such as sodium and potassium transport. Therefore, in this article we describe the bioenergetics of lymphocytes in resting, activated, and glucocorticoid-treated states and present a concept for discussion to describe the relationship among these states in fundamental and clinical terms.

Substrate specificity and inhibitor profile of human recombinant p56lck from a baculovirus expression vector

p56lck, a member of the src family of non-receptor protein receptor kinases, is required for normal signal transduction through the T cell receptor. Inappropriate T cell activation and proliferation has been identified as an early event in auto-immune disease-agents which control T cell activation through modulation of p56lck kinase activity could therefore be potential therapeutic agents for a range of pathological conditions. To identify p56lck inhibitors, we have established an assay system suitable for the high throughput screening of compound libraries. The assay uses enzyme purified from baculovirus infected SF9 cells, and a novel peptidic substrate identified by L. Cantley from a degenerate combinatorial peptide library. We have used this assay system to screen a number of different compounds as potential inhibitors of p56lck. In addition, peptides based on the substrate sequence were also tested to identify a sequence that could be used in the rational design of peptide inhibitors of p56lck.