Fluorescence-guided tumor surgery using a new RGD-based probe

Introduction – Despite many improvements in the treatment of cancer, surgery remains the most important curative option for solid tumors. Fluorescence-guided surgery is a promising strategy to improve surgical resection,... [ view full abstract ]

Introduction – Despite many improvements in the treatment of cancer, surgery remains the most important curative option for solid tumors. Fluorescence-guided surgery is a promising strategy to improve surgical resection, with the aim of reducing local recurrences and increasing survival rate. 

Integrins are an attractive biomarker for targeted imaging-guided surgery. α_vβ₃ Integrin is usually expressed at undetectable levels in most adult epithelia, but it is highly up-regulated in tumors and correlates positively with disease progression. 

To visualize α_vβ₃ integrin expression in real time during tumor resection, a new cyclic RGD-based peptidomimetic was conjugated with cyanine 5.5, a near-infrared (NIR) fluorophore. The in vitro, in vivo and ex vivo characterization of this conjugate, coded B26100, is presented here, to show its affinity for the target receptor and its capability to identify tumor mass and margins.

Methods - ELISA and Maximum Absorbance Shift techniques were used to measure the affinity of the probe for α_vβ₃ integrin and serum albumin respectively. Flow cytometry and cell assays were used to assess the interaction of the probe with tumor cells. Nude mice bearing tumors from U87-MG human glioblastoma and A431 human epidermoid carcinoma cells were chosen for in vivo optical imaging experiments, to evaluate the efficacy and biodistribution of the probe. The ability of B26100 in identifying tumor masses during surgery was tested on rat MAT-Ly-Lu tumor, an orthotopic prostatic model.

Results – B26100 exhibited high affinity to isolated α_vβ₃ integrin and moderate binding to serum albumin. The molecule was able to enter α_vβ₃-expressing cells, mainly by integrin-mediated internalization mechanism. In vivo optical imaging showed that the probe allows to visualize tumor masses, with low retention in healthy tissues and preferential accumulation in tumors that overexpress the target. During surgery, the molecule enabled the discrimination between MAT-Ly-Lu tumor and the surrounding healthy prostate, facilitating the complete removal of pathological tissue, while sparing the healthy one.

Discussion – B26100, a new fluorescent RGD-based molecule, can be used for sensitive outlining of tumor lesions in vivo. It is a promising optical imaging probe for fluorescence-guided surgery, identifying specifically tumor margins and enabling the precise tumor mass removal.