Studies of ionic mechanisms associated with human cancers

Abstract

The general aim of this thesis was to undertake a series of inter-related studies with a view to improving our understanding of the role of ion channel expression and its regulation in cancer cells with strong metastatic potential. The emphasis was on neonatal Nav1.5 (nNav1.5) subtype of voltage-gated sodium channel (VGSC). Chapter 1 (General Introduction) gives an account of the relevant literature and states the main aims of the studies. Chapter 2 details the Materials and Methods, ranging from quantitative molecular biology to in vitro assays of metastatic cell behaviour. Chapter 3 presents experiments on regulation of VGSCs by insulin and insulin-like growth factor1 (IGF1) in strongly metastatic human breast cancer (BCa) MDA-MB- 231 cells. The central strategy was to treat insulin and IGF1 as an integrated signalling system (”IIS”) and suppress it using pharmacological inhibitors and RNAi. Inhibiting IIS signalling suppressed metastatic cell behaviours (MCBs) and decreased nNav1.5 expression and activity. Chapter 4 describes studies on mRNA expression of a variety of cancer-associated ion channels (CAICs) in peripheral blood of normal human subjects with a view to laying the foundations for subsequent patient-based studies. The following 8 CAICs were studied: nNav1.5, VGSC-β1, VGSC-β1b, Kv1.3, Kv10.1, Kv11.1, KCa3.1 and TRPM8. Several differences were noted between healthy cases and cancer patients. In particular, nNav1.5 and Kv1.3 mRNA expressions were up- and down-regulated, respectively. Chapter 5 shows that the anti-diabetic drug Metformin suppressed Matrigel invasion and nNav1.5 mRNA expression in MDA-MB-231 cells. Chapter 6 involves studies on the strongly metastatic human colorectal cancer (CRCa) SW-620 cells, which were found to express nNav1.5 mRNA and protein. Silencing nNav1.5 expression had a significant inhibitory effect on Matrigel invasion. The thesis ends with a General Discussion and Conclusion chapter, integrating the findings in the context of the field at large and pointing to future directions.