N-cadherin: Regulation, Role and Therapeutic Targeting in Multiple Myeloma

Multiple myeloma (MM) is a largely incurable haematological malignancy characterised by the clonal proliferation of neoplastic immunoglobulin-producing plasma cells (PCs) within the bone marrow (BM). Previous studies from our laboratory, and those of others, have shown that gene and protein expression of the homophilic cellcell adhesion and signalling molecule, N-cadherin, is up-regulated in PCs in approximately 50% of newly-diagnosed MM patients. Notably, increased expression of N-cadherin is associated with inferior prognosis in these patients. In this thesis, bioinformatic and in vitro analyses were performed to determine the mechanisms responsible for the up-regulation of N-cadherin expression in MM. The histone methyltransferase MMSET, universally dysregulated in the 10-15% of MM patients which harbour the chromosomal translocation t(4;14), was a positive regulator of CDH2 expression in human MM cell lines, suggesting it is a key driver of in N-cadherin expression in t(4;14)+ MM. Several additional candidate molecules and pathways (e.g. miR-190 and IL-6/JAK2/STAT3 signalling) were also identified which may represent previously unknown, MMSET-independent regulators of N-cadherin expression in t(4;14)- MM. The development, progression and relapse of MM is underpinned by the trafficking, or dissemination, of MM PCs from one tumour site to distant BM sites via the circulation. Previous studies suggest that inhibition of MM PC adhesion to the endothelium may represent a potential therapeutic modality to prevent the extravasation and dissemination of MM PCs. In this thesis, pre-treatment of C57Bl/KaLwRij mice with the cyclic pentapeptide N-cadherin antagonist ADH-1 inhibited tumour development following intravenous injection of 5TGM1 MM PCs. This effect was not seen in mice treated with ADH-1 after tumour establishment, suggesting that Ncadherin plays a role in the extravasation and BM homing of MM PCs. In support of this, N-cadherin was found to mediate the adhesion of MM PCs to endothelial cells (ECs), which represents a key step in the extravasation of circulating MM PCs. These studies suggest that ADH-1 may be clinically useful in the prevention of MM PC dissemination, thereby delaying disease progression and relapse. In addition to its role in MM pathogenesis, N-cadherin is critical in the regulation of vascular integrity and permeability. Recently, studies have shown that perturbation of N-cadherin function disrupts established EC-EC and EC-mural cell junctions resulting in increased permeability of the EC barrier to macromolecules in vitro and in vivo. This thesis describes the identification of a small molecule peptidomimetic of ADH-1, LCRF-0006, as a novel vascular disrupting agent which enhances vascular permeability in vitro and in vivo, and synergistically increases the efficacy of the anti-MM agent bortezomib in C57Bl/KaLwRij mice with established MM disease. To this end, LCRF-0006 may be clinically useful in increasing the depth of MM tumour response to bortezomib, which is currently used in MM patients as induction therapy, maintenance therapy, and in the relapse setting. In addition, we speculate that the potential ability of LCRF-0006 to augment the enhanced permeability and retention (EPR) effect could be utilised to increase the delivery, and therefore anticancer efficacy, of various therapeutic agents in MM and other cancers in the clinical setting.Thesis (Ph.D.) -- University of Adelaide, Adelaide Medical School, 201