Engineering PSMA-targeted exosome-like vesicles to target prostate cancer metastasis

Abstract

Prostate cancer (PC) is the second most common type of cancer in men worldwide. A range of effective anti-cancer drugs have been used to treat advanced PC however, their systemic toxicity has limited their clinical use. Therefore, there is an unmet need to develop novel selective drug delivery strategies to deliver cancer therapeutics to PC tissues. Two most common selective targeting approaches to treat PC are through the prostate-specific membrane antigen (PSMA) and prostate- specific antigen (PSA). PSMA is overexpressed in PC cells and various targeting ligands have been discovered to bind to PSMA and serve as a tool for active targeting. On the other hand, PSA-cleavable peptides have been conjugated to various cytotoxic drugs which are activated in the presence of enzymatically active PSA at the tumour site. To combine these two PC targeting approaches, a suitable drug delivery system has to be used to incorporate the PSMA targeting ligand on the surface and encapsulate the PSA-cleavable prodrug inside.  
 
Among a wide range of synthetic drug delivery systems, exosomes are nanosized, naturally secreted membrane vesicles that carry proteins and RNAs for intercellular communication. They can also deliver loaded chemotherapeutics across the plasma membrane and delay premature drug transformation and elimination. Besides that, exosomes have shown an intrinsic homing ability to a wide range of cells. Although they showed great potential as drug delivery systems, their main disadvantage is low yield after cell culture isolation and poor drug loading. Therefore, an alternative approach has been described to engineer exosome-like vesicles (ELVs) from U937 monocytes with intrinsic homing ability, good yield, and improved drug loading efficiency.  
 
In the present thesis, we aim to engineer PSMA- targeted exosome-like vesicles (ELVs) that will actively target advanced PC and improve the delivery and therapeutic efficacy of encapsulated doxorubicin-PSA (Dox-PSA) prodrug.
 
Therefore, a stably transfected PSMA-peptide expressing monocyte U937 cell line was established. PSMA-targeted ELVs were prepared by serial extrusion of the transfected U937 monocytes. The engineered ELVs were nanosized, produced at a high yield, and displayed the anti-PSMA peptide, exosomal markers and monocytes proteins on their surface. As anticipated, PSMA-ELVs showed increased cellular internalization in PSMA positive PC cell lines, compared to unmodified ELVs. Most importantly, higher tumour accumulation was observed in solid PSMA-expressing tumour, following intravenous administration, confirming their targeting ability in vivo.  
 
In the second part of the thesis, we successfully engineered Dox-PSA-loaded, PSMA-targeted ELVs called hybrids, where we increased the drug loading efficacy by fusion of the U937 cell membranes with commercial lipids. The hybrids were also characterized and their PSMA targeting ability was confirmed in vitro and in vivo. Furthermore, the therapeutic efficacy of encapsulated prodrug was also studied in vitro and in vivo on both solid and metastatic PC.

This is the first study that shows the engineering of PSMA-targeted ELVs by expressing the targeting peptide on the ELVs surface. Also, the formulation of the PSMA-Hybrids loaded with Dox-PSA prodrug was developed for the first time. We have shown that the active PSMA targeting increased the internalisation of the hybrids in the tumour tissues and improved the therapeutic efficacy of Dox-PSA prodrug. Further studies are necessary to conclude on the therapeutic efficacy in metastatic PC model.

Thesis is embargoed until 31 December 2024.

Date of Award	Dec 2022
Original language	English
Awarding Institution	Queen's University Belfast
Sponsors	Rosetrees Trust
Supervisor	Wafa Al-Jamal (Supervisor) & James Burrows (Supervisor)