Nitric oxide signalling in cancer: Functional, therapeutic, and diagnostic insights

Breast and prostate cancer are the most commonly diagnosed cancers in Irish women and men respectively. Expression of inducible nitric oxide synthase (iNOS) in these tumours is associated with more aggressive disease and poor prognosis. Nitric oxide (NO) signalling is characterised by its dichotomous nature with high and low levels having contrasting effects. This study investigates the impact of endogenous NO (from iNOS) and a range of NO concentrations (via the NO donor DETA/NO) on proliferation, migration, invasion and response to therapeutics in both triple negative and HER2-amplified breast cancer. Endogenously produced NO was not found to have any significant effects on proliferation or cell motility, while DETA/NO had concentration and time dependent effects. Low DETA/NO stimulated cell proliferation and enhanced chemoresistance. High DETA/NO induced a transient stimulation of proliferation prior to triggering cell cycle arrest. This limited the efficacy of chemotherapeutic agents but ultimately resulted in reduced cell viability compared to chemotherapy alone indicating a potential for combination therapy. NO can exert its effects via activation of soluble guanylyl cyclase or s-nitrosation of proteins. Its effects on proliferation and chemoresistance were found to be via protein s-nitrosation as a soluble guanylyl cyclase inhibitor had no effect. Known drivers of proliferation EGFR and HER2 showed increased s-nitrosation following treatment with DETA/NO, but demonstrated high baseline s-nitrosation indicating the importance of nitrosative signalling. Pharmacological inhibition of EGFR and HER2 did not impact the effects of DETA/NO on proliferation. However, this study uncovered other novel s-nitroso-proteins that may play a role. Furthermore, iNOS was investigated as a potential liquid biopsy biomarker for prostate cancer diagnosis. High iNOS mRNA expression in the PBMC fraction of whole blood increased the predictive power of several other biomarkers investigated including EpCAM and HERV-K transcripts. This highlights the need for further research into the impact of NO signalling on the progression of cancer and other disease states particularly as it can be modulated therapeutically through NOS inhibitors or NO donors.

Funder

University of Galway
Research Ireland
European Commission

Publisher

University of Galway

Rights

CC BY-NC-ND

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Collections

University of Galway Theses (PhD Theses)