Structure-based discovery of (S)-2-amino-6-(4-fluorobenzyl)-5,6,11,11a-tetrahydro-1H-imidazo[1',5':1,6]pyrido[3,4-b]indole-1,3(2H)-dione as low nanomolar, orally bioavailable autotaxin inhibitor.

Inhibition of extracellular secreted enzyme autotaxin (ATX) represents an attractive strategy for the development of new therapeutics to treat various diseases and a few inhibitors entered in clinical trials. We herein describe structure-based design, synthesis, and biological investigations revealing a potent and orally bioavailable ATX inhibitor 1. During the molecular docking and scoring studies within the ATX enzyme (PDB-ID: 4ZGA), the S-enantiomer (Gscore = -13.168 kcal/mol) of the bound ligand PAT-494 scored better than its R-enantiomer (Gscore = -9.562 kcal/mol) which corroborated with the reported observation and analysis of the results suggested the scope of manipulation of the hydantoin substructure in PAT-494. Accordingly, the docking-based screening of a focused library of 10 compounds resulted in compound 1 as a better candidate for pharmacological studies. Compound 1 was synthesized from L-tryptophan and evaluated against ATX enzymatic activities with an IC50 of 7.6 and 24.6 nM in biochemical and functional assays, respectively. Further, ADME-PK studies divulged compound 1 as non-cytotoxic (19.02% cell growth inhibition at 20 µM in human embryonic kidney cells), metabolically stable against human liver microsomes (CLint  = 15.6 µl/min/mg; T1/2  = 113.2 min) with solubility of 4.82 µM and orally bioavailable, demonstrating its potential to be used for in vivo experiments.

Lin28b controls a neonatal to adult switch in B cell positive selection.

The ability of B-1 cells to become positively selected into the mature B cell pool, despite being weakly self-reactive, has puzzled the field since its initial discovery. Here, we explore changes in B cell positive selection as a function of developmental time by exploiting a link between CD5 surface levels and the natural occurrence of self-reactive B cell receptors (BCRs) in BCR wild-type mice. We show that the heterochronic RNA binding protein Lin28b potentiates a neonatal mode of B cell selection characterized by enhanced overall positive selection in general and the developmental progression of CD5+ immature B cells in particular. Lin28b achieves this by amplifying the CD19/PI3K/c-Myc positive feedback loop, and ectopic Lin28b expression restores both positive selection and mature B cell numbers in CD19-/- adult mice. Thus, the temporally restricted expression of Lin28b relaxes the rules for B cell selection during ontogeny by modulating tonic signaling. We propose that this neonatal mode of B cell selection represents a cell-intrinsic cue to accelerate the de novo establishment of the adaptive immune system and incorporate a layer of natural antibody-mediated immunity throughout life.

In situ proliferation contributes to accumulation of tumor-associated macrophages in spontaneous mammary tumors.

Infiltration of a neoplasm with tumor-associated macrophages (TAMs) is considered an important negative prognostic factor and is functionally associated with tumor vascularization, accelerated growth, and dissemination. However, the ontogeny and differentiation pathways of TAMs are only incompletely characterized. Here, we report that intense local proliferation of fully differentiated macrophages rather than low-pace recruitment of blood-borne precursors drives TAM accumulation in a mouse model of spontaneous mammary carcinogenesis, the MMTVneu strain. TAM differentiation and expansion is regulated by CSF1, whose expression is directly controlled by STAT1 at the gene promoter level. These findings appear to be also relevant for human breast cancer, in which an interrelationship between STAT1, CSF1, and macrophage marker expression was identified. We propose that, akin to various MU subtypes in nonmalignant tissues, local proliferation and CSF1 play a vital role in the homeostasis of TAMs.

Replenishment of the B cell compartment after doxorubicin-induced hematopoietic toxicity is facilitated by STAT1.

STAT1 serves as an important regulator in the response to pathogens, oncogenic transformation, and genotoxic insults. It exerts these effects by shaping the innate and adaptive immune response and by participating in genotoxic stress pathways, leading to apoptosis and inhibition of cell proliferation. We have investigated the role of STAT1 in hematopoietic toxicity induced by doxorubicin in STAT1-proficient and -deficient mice. Whereas the early genotoxic effect of doxorubicin did not depend on STAT1, expression of STAT1 was required for efficient B lymphocyte repopulation in the recovery phase. We found a lower abundance of lymphocyte precursors in the BM of STAT1-deficient animals, which was particularly evident after doxorubicin-induced hematopoietic toxicity. In accordance, colony-forming assays with STAT1-deficient BM cells revealed a decreased number of pre-B colonies. Differentiation from the pro-B to the pre-B stage was not affected, as demonstrated by unaltered differentiation of purified B cell precursors from BM in the presence of IL-7. With the exception of Sca-1, expression of genes implicated in early lymphocyte development in pro-B cells did not depend on STAT1. Our findings indicate a specific requirement for STAT1 in lymphoid development before differentiation to pre-B cells, which becomes particularly apparent in the recovery phase from doxorubicin-induced hematopoietic toxicity.

Lapatinib and doxorubicin enhance the Stat1-dependent antitumor immune response.

The dual erbB1/2 tyrosine kinase inhibitor lapatinib as well as the anthracycline doxorubicin are both used in the therapy of HER2-positive breast cancer. Using MMTV-neu mice as an animal model for HER2-positive breast cancer, we observed enhanced tumor infiltration by IFN-γ-secreting T cells after treatment with doxorubicin and/or lapatinib. Antibody depletion experiments revealed a contribution of CD8⁺ but not CD4⁺ T cells to the antitumor effect of these drugs. Doxorubicin treatment additionally decreased the content of immunosuppressive tumor-associated macrophages (TAMs) in the tumor bed. In contrast, Stat1-deficient mice were resistant to tumor growth inhibition by lapatinib and/or doxorubicin and exhibited impaired T-cell activation and reduced T-cell infiltration of the tumor in response to drug treatment. Furthermore, Stat1-deficiency resulted in reduced expression of the T-cell chemotactic factors CXCL9, CXCL10, and CXCL11 in the tumor epithelium. The inhibition of TAM infiltration of the tumor by doxorubicin and the immunosuppressive function of TAMs were found to be Stat1 independent. Taken together, the results point to an important contribution toward enhancing T-cell and IFN-γ-based immunity by lapatinib as well as doxorubicin and emphasize the role of Stat1 in building an effective antitumor immune response.