A targeted near-infrared nanoprobe for deep-tissue penetration and imaging of prostate cancer

Fluorescent guided surgery (FGS) has been highlighted as a potential to increase precision of diseased tissue whilst minimising the removal of surrounding healthy tissue, particularly relevant for increasingly prevalent prostate cancer (PCa). There remain challenges in the design of imaging probes presenting high selectivity for tumour tissue, clear visualization and minimal toxicity. Here we report the design and development of a novel NIR-nanoprobe and evaluate its potential in penetration inside PCa tumour tissues. Prostate-specific membrane antigen (PSMA) receptor-targeted near infrared emitting quantum dots (PSMA-NIR-QDot) are demonstrated as deep tissue imaging agents for intraoperative navigation during surgery and improving detection specificity for PCa. Probes were designed and synthesized by conjugating functionalized amino-PEG QDots through a heterobifunctional linker to a DUPA targeted polypeptide construct. Nanoprobes were evaluated in vitro in PSMA+ PCa cell lines for specificity and affinity determined by flow cytometric analysis. The penetration efficacy was tested further on large PCa 3D tumour spheroids (dia ~ 1.2 mm, width ~ 250 µm) by deep tissue multiphoton imaging. The PSMA-NIR-Qdot was found to be an efficient deep tissue penetrating intra-operative guided surgical tool with high affinity (KD = 15 nM) and penetrative capacity. The results have been demonstrated in vitro in 2D and 3D tissue models, mimicking cancer lesions in vivo. The presented deep-tissue imaging NIR nanoprobes target prostatic lesions that (i) bind to PSMA+ tumour with sub-nanomolar affinity and high specificity, (ii) show excellent safety profile in primary cell lines in vitro, and (iii) show high penetrative capacity in 3D prostate tumour model (~ 250 µm tissue depth). These probes may potentially offer vastly improved surgical accuracy for diseased tissue removal.