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Characterization of the mechanisms by which Carbonic Anhydrase IX facilitates tumour growth and metastasis Vallejo Espi, Maria de Lourdes

Abstract

The presence of hypoxic microenvironments in solid tumours is a marker of poor prognosis in numerous cancer types, including breast cancer; the second leading cause of cancer-related death. Hypoxia results in an adaptive response in tumour cells through the activation of the transcription factor Hypoxia Inducible Factor-1α (HIF-1α), which stimulates the expression of a large number of genes that contribute to tumour progression. One of the most prominently activated genes is Carbonic Anhydrase IX (CAIX), which facilitates the acidification of the extracellular space and cell invasion by producing protons. Moreover, it assists in keeping the intracellular space neutral through the generation of bicarbonate, which is shuttled into the cytoplasm by bicarbonate transporters, ultimately favouring cell survival. CAIX facilitates breast tumour growth and metastasis; however the exact mechanism remains unknown. The overexpression of CAIX in hypoxic solid tumours, its limited expression in normal tissue and the presence of an extracellular catalytic domain makes this protein an excellent therapeutic target. The intent of this thesis was to unveil the mechanisms by which CAIX facilitates tumour progression, and to characterize novel small molecule inhibitors and antibodies targeting CAIX. It was found that the intracellular (IC) domain of CAIX regulates its catalytic activity, which is required for cell survival, cell invasion and metastasis. The extracellular proteoglycan-like (PG-like) domain of CAIX does not regulate CAIX catalytic activity; however it does modulate cell migration, invasion and metastasis. I identified a role of CAIX in promoting tumour cell invasion through interaction with membrane-bound matrix metalloprotease-14 (MMP-14) and localization in invadopodia. The IC domain of CAIX mediates this interaction and CAIX enzymatic activity appears to regulate the ability of MMP-14 to degrade type I collagen during cell invasion. From the pool of anti-CAIX inhibitors and antibodies characterized in this thesis, the inhibitor U-104 was excellent at blocking CAIX enzymatic activity and has entered phase I clinical trials. Likewise, anti-CAIX antibody MM-26 blocked 50% of CAIX activity and induced cell death in vitro. The work described here provides new insight into the mechanism of CAIX-mediated tumour invasion and metastasis and has identified two new therapeutic strategies for targeting CAIX.

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Attribution-NonCommercial-NoDerivs 2.5 Canada

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