Loss of DRAK2 signaling enhances allogeneic transplant survival by limiting effector and memory T cell responses

Intramolecular Dearomative Inverse-Electron-Demand Diels Alder Strategy for the Total Synthesis of (+)-Alstonlarsine A

An evolution of a synthetic route leading to a successful enantioselective total synthesis of monoterpenoid indole alkaloid (+)-alstonlarsine A is represented. The unique 9-azatricyclo[4.3.1.03,8]decane core was assembled through an efficient domino sequence comprising enamine formation in situ, followed by intramolecular dearomative inverse-electron-demand Diels Alder reaction. The preparation of the tricyclic dihydrocyclohepta[b]indole key intermediate via the intramolecular Horner-Wadsworth-Emmons reaction required a development of a new general method for the introduction of the phosphonoacetate moiety into the indole C-2 position, through copper-carbenoid insertion. The modular nature of the represented synthetic approach makes it suitable for the synthesis of analogues with different substituents' patterns.

New insights into the characteristics of DRAK2 and its role in apoptosis: From molecular mechanisms to clinically applied potential

As a member of the death-associated protein kinase (DAPK) family, DAP kinase-associated apoptosis-inducing kinase 2 (DRAK2) performs apoptosis-related functions. Compelling evidence suggests that DRAK2 is involved in regulating the activation of T lymphocytes as well as pancreatic β-cell apoptosis in type I diabetes. In addition, DRAK2 has been shown to be involved in the development of related tumor and non-tumor diseases through a variety of mechanisms, including exacerbation of alcoholic fatty liver disease (NAFLD) through SRSF6-associated RNA selective splicing mechanism, regulation of chronic lymphocytic leukemia and acute myeloid leukemia, and progression of colorectal cancer. This review focuses on the structure, function, and upstream pathways of DRAK2 and discusses the potential and challenges associated with the clinical application of DRAK2-based small-molecule inhibitors, with the aim of advancing DRAK2 research.

A novel and efficient method to induce allospecific CD8+ memory T lymphocytes

The aim of the current study was to establish a simple method for effectively inducing memory T lymphocytes by the intraperitoneal injection of spleen lymphocytes into mice. In total, 75 mice were divided into the following groups: an injection group administered three doses of spleen lymphocytes (1 × 10⁶, 5 × 10⁶, and 1 × 10⁷ cells), a transplantation group in which a 0.25‐cm² skin section from C57BL/6 mice was transplanted onto the back of the recipient, and a control group in which an equal volume of phosphate‐buffered saline was injected. At 1, 2, or 3 months following transplantation, the following parameters were evaluated: quantity of T lymphocytes, percentage of cluster of differentiation 8⁺ (CD8⁺) memory T cells, and proliferation index of purified CD8⁺ memory T cells. No significant differences among groups were detected at 1 month (p > .05). However, the injection group administered 1 × 10⁶ cells exhibited the highest proportion of CD8⁺ memory T cells among all groups at 2 months, and the proportions of CD8⁺ T cells were higher in the three injection groups than in the skin transplantation and control groups at 3 months. The proportions of memory T cells were higher in the injection groups administered 5 × 10⁶ or 1 × 10⁷ cells than in the skin transplantation and control groups at 3 months. The newly established method effectively induces memory T lymphocytes via the intraperitoneal injection of spleen lymphocytes in vivo and has potential applications in the field of immunotherapy.

Discovery of indirubin derivatives as new class of DRAK2 inhibitors from high throughput screening

DRAK2 is a serine/threonine kinase belonging to the death-associated protein kinase (DAPK) family and has emerged as a promising drug target for the treatment of autoimmune diseases and cancers. To identify small molecule inhibitors for DRAK2, we performed a high throughput screening campaign using in-house chemical library and identified indirubin-3'-monoximes as novel class of DRAK2 inhibitors. Among the compounds tested, compound 16 exhibited the most potent inhibitory activity against DRAK2 (IC50=0.003μM). We also propose that compound 16 may bind to the ATP-binding site of the enzyme based on enzyme kinetics and molecular docking studies.

High-dose immunosuppressant alters the immunological status of New Zealand white rabbits following skin transplantation

The aim of this study was to investigate the effect of an immunosuppressant on the immunological status of New Zealand white rabbits after skin grafting, and to evaluate a method for monitoring the immunological status of subjects with skin transplants. The rabbits were randomly divided into allograft rejection, autograft tolerance, nontransplant, allograft low-dose immunosuppressant and allograft high-dose immunosuppressant groups. The rabbits in the low- and high-dose immunosuppressant groups were treated with cyclosporine A intravenously 8 h prior to skin transplantation and once daily following transplantation at doses of 2 and 25 mg/kg, respectively. At 12 days after skin transplantation, the spleens of donor (female) rabbits and recipient (male) rabbits were harvested for the preparation of single-cell suspensions. The splenocytes from recipient and donor rabbits were labeled with 0.3 or 6 µM carboxy fluorescein diacetate succinimidyl ester, respectively, and a mixed cell suspension was prepared. The final preparation was intravenously injected into recipient New Zealand white rabbits. The ratio of the two fluorescently labeled cell populations in the peripheral blood was measured using flow cytometry at 1, 2, 4 and 8 h after the injection, and the cell death rate was calculated. Histological analysis was also performed on samples collected at the time of splenectomy. The cell death rates of the allograft rejection and low-dose immunosuppressant groups reached their highest levels 8 h after the injection of spleen cell suspension. Allogeneic spleen cells from donor male rabbits were almost completely removed within 8 h of injection. The cell death rate increased slowly in the nontransplant, autograft and high-dose immunosuppressant groups without specificity. This study provides a specific method for the in vivo monitoring of the immunological status of patients after skin grafting. This method can quickly and accurately detect the immunological status of recipients following the injection of a mixed splenocyte suspension, thereby indicating the strength of immune rejection by the immune systems of the recipients.

Drak2 is not required for tumor surveillance and suppression

Drak2 is a promising therapeutic target to treat organ-specific autoimmune diseases such as type 1 diabetes and multiple sclerosis without causing generalized immune suppression. Inhibition of Drak2 may also prevent graft rejection following organ transplantation. However, Drak2 may function as a critical tumor suppressor, which would challenge the prospect of targeting Drak2 for therapeutic treatment. Thus, we examined the susceptibility of Drak2 (-/-) mice in several tumor models. We show that Drak2 is not required to prevent tumor formation in a variety of settings. Therefore, Drak2 does not function as an essential tumor suppressor in in vivo tumor models. These data further validate Drak2 as a viable therapeutic target to treat autoimmune disease and graft rejection. Importantly, these data also indicate that while Drak2 may induce apoptosis when overexpressed in cell lines, it is not an essential tumor suppressor.

Discovery of dual death-associated protein related apoptosis inducing protein kinase 1 and 2 inhibitors by a scaffold hopping approach

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.

Synthesis and structure-activity relationship studies of 2-(1,3,4-oxadiazole-2(3H)-thione)-3-amino-5-arylthieno[2,3-b]pyridines as inhibitors of DRAK2

In recent years, DAPK-related apoptosis-inducing protein kinase 2 (DRAK2) has emerged as a promising target for the treatment of a variety of autoimmune diseases and for the prevention of graft rejection after organ transplantation. However, medicinal chemistry optimization campaigns for the discovery of novel small-molecule inhibitors of DRAK2 have not yet been published. Screening of a proprietary compound library led to the discovery of a benzothiophene analogue that displays an affinity constant (Kd) value of 0.25 μM. Variation of the core scaffold and of the substitution pattern afforded a series of 5-arylthieno[2,3-b]pyridines with strong binding affinity (Kd = 0.008 μM for the most potent representative). These compounds also show promising activity in a functional biochemical DRAK2 enzyme assay, with an IC50 value of 0.029 μM for the most potent congener. Selectivity profiling of the most potent compounds revealed that they lack selectivity within the DAPK family of kinases. However, one of the less potent analogues is a selective ligand for DRAK2 and can be used as starting point for the synthesis of selective and potent DRAK2 inhibitors.