Phosphoinositide-binding molecules as potential multifunctional anticancer, anti-infective and immunomodulatory therapeutics

Submission note: A thesis submitted in total fulfilment of the requirements for the degree of Doctor of Philosophy to the Department of Biochemistry and Genetics, School of Molecular Sciences, College of Science, Health and Engineering, La Trobe University, Bundoora, Victoria.

Multidrug resistance and adverse off-target toxicity of current therapeutics have urgently called for less toxic, more effective and multifaceted therapeutics with new modes of action. Furthermore, owing to the emerging pathological association between cancer and microbial infection, there is also expectation for combinatorial anticancer and antiinfective agents, especially for patients suffering infective agent-induced malignancies or immunocompromised anticancer treatments. As phosphoinositides (PIPs), which are minor, yet functionally important, cellular lipids, and their metabolising enzymes crucially control multiple stages of malignant transformation and microbial infection, they offer invaluable opportunities for therapeutic targeting. Based on previous findings on a novel PIP-binding motif present in antifungal solanaceous plant defensins and on PIP-binding aminoglycosidic antibiotics, this thesis aimed to: (i) identify candidates that bind PIPs, particularly phosphatidylinositol 4,5- bisphopsphate [PI(4,5)P2], and display antimicrobial as well as anticancer activity through aminoglycoside testing, computational search for plant defensin-like or HBD-2-like cationic patterns, and PI(4,5)P2 bead pull-down using human hematological samples; (ii) investigate the role of PIPs and elucidate molecular mechanisms underlying the anticancer properties of a potential candidate, and (iii) determine the immunological effects, particularly ones governed by PI(4,5)P2 signalling, of the selected candidate. The study revealed an arsenal of potential PI(4,5)P2-binding proteins with speculative anticancer an antimicrobial activities. It also provides mechanistic and structural insights to lipid/PI(4,5)P2 targeting on mammalian plasma membranes, particularly in PI(4,5)P2- mediated cancer cell permeabilisation. Furthermore, it enriches the knowledge of PI(4,5)P2 and its signalling in immune response. Together, the knowledge acquired from this study would ultimately contribute to the exploration of PIP-binding molecules with anticancer, antimicrobial and immunomodulatory effects as a new generation of multifaceted therapeutics.

This thesis was a recipient of the Nancy Millis Award for theses of exceptional merit.