Bimodal PSMA ligand for targeted photodynamic therapy and intra-operative tumor detection of prostate cancer

Introduction: Incomplete resection of prostate cancer (PCa) and its metastases may lead to disease recurrence and consequently poor patient outcome. To obtain complete removal of tumor tissue during surgery, prostate specific membrane antigen (PSMA) targeting bimodal ligands containing both a radiolabel (¹¹¹In) and a photosensitizer (IRDye700DX) can be used for radioguided tumor detection, IRDye700DX mediated fluorescence imaging and tumor-targeted photodynamic therapy (tPDT). IRDye700DX-based tPDT is a selective cancer treatment that induces cell death upon exposure to near-infrared (NIR) light. The aim of our study was to develop and to evaluate a novel bimodal [¹¹¹In]In-DOTAGA-IRDye700DX-labeled PSMA-targeting agent (PSMA-N064) for intra-operative detection and photodynamic therapy of PSMA-positive tumor lesions.

Methods: The glutamate-urea-lysine-based PSMA ligand was synthesized and via a linker conjugated with IRDye700DX, DOTAGA, and labeled with ¹¹¹In. Cell viability of PSMA-transfected LS174T and PSMA-negative wild-type LS174T cells was analyzed after ¹¹¹In-PSMA-N064-mediated tPDT using 100-300 J/cm² NIR light irradiation (3-10 min). To determine the optimal dose and timing for in vivo imaging and tPDT, BALB/c nude mice with s.c. LS174T-PSMA-positive and -negative tumors were injected with ¹¹¹In-PSMA-N064 (0.1-3 nmol, 10 MBq/mouse). Tumor uptake and whole body distribution was evaluated 1, 2, 4 and 24 h p.i. using µSPECT/CT, NIR fluorescence imaging and ex vivo biodistribution studies. Additionally, co-localization studies were performed comparing ¹¹¹In autoradiography, IRDye700DX fluorescence imaging and PSMA expression.

Results: Viability of PSMA-N064 tPDT-treated LS174T-PSMA cells was significantly reduced with 87.6% ± 5.8% compared to PSMA-negative LS174T cells (33 nM, 300 J/cm², P<0.001). In addition, a dose-dependent PSMA-specific loss of viability was observed after 100 J/cm² NIR irradiation, ranging from 74% ± 10.7% (3 nM) to 17.3% ± 7.3% (30 nM). In vivo, the highest tumor uptake in s.c. LS174T-PSMA tumors was measured 2 h p.i. at a dose of 0.3 nmol/mouse. Tumors were clearly visualized using both µSPECT/CT and NIR fluorescence imaging and uptake in the PSMA-positive tumors (12.6 ± 1.8 %ID/g) was significantly higher than uptake in PSMA-negative LS174T tumors (0.4 ± 0.2 %ID/g, P<0.001). Moreover, co-localization of the radiosignal, fluorescent signal and expression of PSMA as determined immunohistochemically was observed.

Conclusions: We demonstrated the feasibility of PSMA-targeted PDT of the newly developed ¹¹¹In-PSMA-N064. Furthermore, we observed a highly efficient and PSMA-specific uptake of the bimodal ligand in vivo. In the future, this ligand may be used for intra-operative tumor detection and photodynamic therapy to improve the surgical outcome of PCa patients. Acknowledgment: This work was supported by EKFS (2016-A64) and the Dutch Cancer Society (NKB-KWF 10443/2016-1).

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