Multi-focal control of mitochondrial gene expression by oncogenic MYC provides potential therapeutic targets in cancer.

Despite ubiquitous activation in human cancer, essential downstream effector pathways of the MYC transcription factor have been difficult to define and target. Using a structure/function-based approach, we identified the mitochondrial RNA polymerase (POLRMT) locus as a critical downstream target of MYC. The multifunctional POLRMT enzyme controls mitochondrial gene expression, a process required both for mitochondrial function and mitochondrial biogenesis. We further demonstrate that inhibition of this newly defined MYC effector pathway causes robust and selective tumor cell apoptosis, via an acute, checkpoint-like mechanism linked to aberrant electron transport chain complex assembly and mitochondrial reactive oxygen species (ROS) production. Fortuitously, MYC-dependent tumor cell death can be induced by inhibiting the mitochondrial gene expression pathway using a variety of strategies, including treatment with FDA-approved antibiotics. In vivo studies using a mouse model of Burkitt's Lymphoma provide pre-clinical evidence that these antibiotics can successfully block progression of MYC-dependent tumors.

A pharmacogenetic approach to identify mutant forms of α-galactosidase A that respond to a pharmacological chaperone for Fabry disease.

Fabry disease is caused by mutations in the gene (GLA) that encodes α-galactosidase A (α-Gal A). The iminosugar AT1001 (GR181413A, migalastat hydrochloride, 1-deoxygalactonojirimycin) is a pharmacological chaperone that selectively binds and stabilizes α-Gal A, increasing total cellular levels and activity for some mutant forms (defined as "responsive"). In this study, we developed a cell-based assay in cultured HEK-293 cells to identify mutant forms of α-Gal A that are responsive to AT1001. Concentration-dependent increases in α-Gal A activity in response to AT1001 were shown for 49 (60%) of 81 mutant forms. The responses of α-Gal A mutant forms were generally consistent with the responses observed in male Fabry patient-derived lymphoblasts. Importantly, the HEK-293 cell responses of 19 α-Gal A mutant forms to a clinically achievable concentration of AT1001 (10 µM) were generally consistent with observed increases in α-Gal A activity in peripheral blood mononuclear cells from male Fabry patients orally administered AT1001 during Phase 2 clinical studies. This indicates that the cell-based responses can identify mutant forms of α-Gal A that are likely to respond to AT1001 in vivo. Thus, the HEK-293 cell-based assay may be a useful aid in the identification of Fabry patients with AT1001-responsive mutant forms.

Inhibition of pro-inflammatory cytokine generation by CTLA4-Ig in the skin and colon of mice adoptively transplanted with CD45RBhi CD4+ T cells correlates with suppression of psoriasis and colitis.

Transfer of CD45RBhi CD4 + naïve T cells into severe combined immunodeficient (SCID) mice induces colitis and skin lesions. Recipients treated with cyclosporin A (CsA), CTLA4-Ig, or vehicle were evaluated for weight loss, skin lesions, and cutaneous blood flow. Necropsy, histological, hematological and cytokine analyses were performed at the conclusion of the experiment to confirm the clinical findings. Vehicle-treated mice lost weight and had 100% incidence of skin lesions by 46-days. CsA-treated mice also lost weight, but only 3/8 mice developed mild, clinically evident skin lesions. In contrast, all CTLA4-Ig-treated mice gained weight and did not develop skin lesions. Increase in cutaneous blood flow correlated with the development of skin lesions. Granulocyte numbers, which were high or moderately high in the vehicle- or CsA-treated mice, respectively, remained as low in the CTLA4-Ig-treated group as in untreated mice. IFN-gamma, IL-1beta, and TNF-alpha levels in the gut and skin correlated with the extent of inflammation in both organs. Histology revealed that CTLA4-Ig but not CsA effectively prevented both autoimmune disorders. The ability of CTLA4-Ig to prevent both colitis and skin lesions suggests that CD28-dependent co-stimulation of T cells is critical for generation of pro-inflammatory cytokines and induction of clinical disease in such autoimmune disorders.