Photodynamic Therapy Is an Effective Adjuvant Therapy for Image-Guided Surgery in Prostate Cancer

Abstract

Local and metastatic relapses of prostate cancer often occur following attempted curative resection of the primary tumor, and up to 66% of local recurrences are associated with positive margins. Therefore, technologies that can improve the visualization of tumor margins and adjuvant therapies to ablate remaining tumor tissues are needed during surgical resection of prostate adenocarcinoma. Photodynamic agents have the potential to combine both fluorescence for image-guided surgery (IGS) and photodynamic therapy (PDT) to resect and ablate cancer cells. The objective of this study was to determine the utility of a targeted PDT agent for IGS and adjuvant PDT. Using a previously developed prostate-specific membrane antigen (PSMA)-targeted PDT agent, PSMA-1-Pc413, we showed that PSMA-1-Pc413 selectively highlighted PSMA-expressing tumors, allowing IGS and more complete tumor resection compared with white light surgery. Subsequent PDT further reduced tumor recurrence and extended animal survival significantly. This approach also enabled identification of tumor cells in lymph nodes. In summary, this study presents a potential new treatment option for patients with prostate cancer undergoing surgery, which improves tumor visualization and discrimination during surgery, including identification of cancer in lymph nodes. SIGNIFICANCE: These findings present a photodynamic agent that can be used for both photodynamic therapy and image-guided surgery, allowing better visualization of tumor margins and elimination of residual tumor tissues.

Figure 1.

Experimental design and generation of ROS in vivo. A, Scheme of experimental design. B, Detection of ROS in vivo after PDT. Mice bearing PC3pip tumor received PSMA-1-Pc413 and 24 hours later were administered ROSstar800cw, which detects ROS. Both PSMA-1-Pc413 and ROSstar800cw fluorescence were measured before and after light irradiation. Fluorescent signal in the deep red channel was observed after PDT, indicating generation of ROS after PDT.

Figure 2.

In vivo fluorescence imaging of mice bearing orthotopic PC3pipGFP tumor. A, Representative images of whole mouse, primary tumor, and LNs. PSMA-1-Pc413 was able to detect both primary tumor and LN metastasis. White arrow, iliac LNs. Representative images are shown from five animals. B, Histologic analysis of resected primary tumor and LNs. Presence of tumor cells in LNs was confirmed by GFP signal (green), PSMA-1-Pc413 signal (red), and hematoxylin and eosin (H&E) staining. White asterisks (*), the rim of lymphocytes in LNs. Red arrows and dashed blue out lines indicate the residual lymphocyte islands in LN surrounded by tumor cells. Images in orange boxes are the enlarged microscopic images of the orange rectangles in column 1.

Figure 3.

Use of PSMA-1-Pc413 for IGS and PDT. A, Representative images of WLS mice under Maestro and Curadel imaging systems. Circles, surgical bed. B, Representative images of IGS+PDT mice under Maestro and Curadel imaging systems. Minimal amount of GFP and PSMA-1-Pc413 signals was observed in the wound with loss of PSMA-1-Pc413 signal due to photo activation. Circles, surgical bed. C, Quantification of GFP signals in the three experimental groups before surgery (left), after surgery (middle), and after IGS+PDT (right). Before surgery, similar GFP signal was observed in three experimental groups (left). After surgery, significantly lower GFP signal was observed in the IGS and IGS+PDT groups than in the WLS group (*, P < 0.05; middle). Values are mean±SD (n = 5 animals for WLS and IGS; n = 8 for IGS+PDT). D, Quantification of PSMA-1-Pc413 signals in the experimental groups before surgery (left), after surgery (middle), and after IGS+PDT (right). After surgery, a significant difference was observed between IGS/IGS+PDT and WLS group (middle; *, P < 0.05). Within the IGS+PDT group, PDT further reduced PSMA-1-Pc413 signal significantly as compared with after IGS alone (right). Values are mean ± SD (n = 5 for WLS and IGS, n = 8 for IGS+PDT).

Figure 4.

Combination of IGS and PDT delayed tumor recurrence and extended animal survival. A, Representative postsurgery monitoring images of mice from WLS, IGS, and IGS+PDT groups measured using Maestro GFP channel. See Supplementary Fig. S6 for quantification of GFP signals. B, Tumor recurrence curves of mice from three experimental groups (n = animal numbers). IGS did not significantly delay tumor recurrence as compared with WLS (P = 0.2222). The tumor recurrence was significantly delayed by IGS+PDT. *, P = 0.0008, IGS+PDT vs. WLS; #, P = 0.00084, IGS+PDT vs. IGS. C, Kaplan–Meier survival curves of mice from the three experimental groups. IGS extended the animal survival significantly as compared with WLS (◆, P = 0.0317). The survival was further prolonged by PDT. *, P = 0.0008, IGS+PDT vs. WLS; #, P = 0.0008 IGS+PDT vs. IGS.