Biomedical subjects

Andrew M James

Publications and source records attributed to Andrew M James.

3 recordsLinked to original sources

PubMed2026

Tumor-derived antioxidants suppress immunity by depriving T cells of reactive oxygen species.

Reactive oxygen species (ROS) promote genomic instability and fuel oncogenic signaling in cancer, but antioxidant therapies have so far failed to improve, or worsen, cancer outcomes. Emerging data suggest that T cells depend on ROS for signal transduction. In this study, we show that tumors exploit this dependency, releasing antioxidant enzymes into the tumor environment to suppress T cell-mediated antitumor immunity. The interstitial fluid of tumors possesses potent antioxidant activity, associated with enrichment of the antioxidant enzyme peroxiredoxin 1 (PRDX1). Extracellular PRDX1 deprives T cells of ROS, preventing oxidative inactivation of phosphatases required for T cell receptor-driven kinase signaling and effector function. Prdx1 is up-regulated upon cancer immunoediting, and loss of PRDX1 within tumors enhances antitumor immunity and immunotherapy responses. These findings define a redox-dependent mechanism of tumor immunosuppression that is potentially amenable to therapeutic intervention.

Animals↗

PubMed2003

Specific targeting of a DNA-alkylating reagent to mitochondria. Synthesis and characterization of [4-((11aS)-7-methoxy-1,2,3,11a-tetrahydro-5H-pyrrolo[2,1-c][1,4]benzodiazepin-5-on-8-oxy)butyl]-triphenylphosphonium iodide.

The selective manipulation of the expression and replication of mitochondrial DNA (mtDNA) within mammalian cells has proven difficult. In progressing towards this goal we synthesized a novel mitochondria-targeted DNA-alkylating reagent. The active alkylating moiety [(11aS)-8-hydroxy-7-methoxy-1,2,3,11a-tetrahydro-5H-pyrrolo[2,1-c][1,4]benzodiazepin-5-one (DC-81)], irreversibly alkylates guanine bases in DNA (with a preference for AGA triplets), preventing its expression and replication. To target this compound to mitochondria it was covalently coupled to the lipophilic triphenylphosphonium (TPP) cation to form a derivative referred to as mitoDC-81. Incorporation of this lipophilic cation led to the rapid uptake of mitoDC-81 by mitochondria, driven by the large membrane potential across the inner membrane. This compound efficiently alkylated isolated supercoiled, relaxed-circular or linear plasmid DNA and isolated mtDNA. However mitoDC-81 did not alkylate mtDNA within isolated mitochondria or cells, even though it accessed the mitochondrial matrix at concentrations up to 100-fold higher than those required to alkylate isolated DNA. This surprising finding suggests that mtDNA within intact mitochondria may not be accessible to this class of alkylating reagent. This inability to alkylate mtDNA in situ has significant implications for the design of therapies for mtDNA diseases and for studies on the packaging, expression and turnover of mtDNA in general.

Alkylating Agents↗

PubMed2002

How mitochondrial damage affects cell function.

The pathophysiology of mitochondrial DNA (mtDNA) diseases is caused by increased cell death and dysfunction due to the accumulation of mutations to mtDNA. While the disruption of oxidative phosphorylation is central to mtDNA diseases, many other factors, such as Ca(2+) dyshomeostasis, increased oxidative stress and defective turnover of mitochondrial proteins, may also contribute. The relative importance of these processes in causing cell dysfunction and death is uncertain. It is also unclear whether these damaging processes lead to the disease phenotype through affecting cell function, increasing cell death or a combination of both. These uncertainties limit our understanding of mtDNA disease pathophysiology and our ability to develop rational therapies. Here, we outline how the accumulation of mtDNA mutations can lead to cell dysfunction by altering oxidative phosphorylation, Ca(2+) homeostasis, oxidative stress and protein turnover and discuss how these processes affect cell function and susceptibility to cell death. A better understanding of these processes will eventually clarify why particular mtDNA mutations cause defined syndromes in some cases but not in others and why the same mutation can lead to different phenotypes.

Animals↗