Photodynamic Therapy Being Developed To Target Prostate Cancer Interview with:
Dr. Susanne Lütje
Ärztlicher Dienst
Universitätsklinikum Essen (AöR)
Klinik für Nuklearmedizin
Essen Germany What is the background for this study? What are the main findings?

Response: Prostate cancer (PCa) is the most common cancer in men and accounts for a significant amount of morbidity and mortality. At present, the curative treatment option of choice for localized stages of PCa is radical prostatectomy, which may include extended lymph node dissection. Unfortunately, surgical procedures can be accompanied by complications such as urinary incontinence. Most importantly, small tumor deposits may not be seen by the surgeon during surgery and could ultimately lead to disease recurrence. To overcome these issues, new and innovative treatments are needed. The prostate-specific membrane antigen (PSMA) is a surface protein that is overexpressed in prostate cancer and can be used as a target to guide new therapies.

Photodynamic therapy (PDT) is an ablative procedure in which tumor cells can be destroyed effectively by irradiation of light of a specific wavelength, which activates previously administered photosensitizers. The photosensitizers can respond by emitting fluorescence or emitting oxygen radicals which can cause cellular damage. Coupling the photosensitizer to an agent that targets PSMA on the tumor surface offers the possibility to selectively and effectively destroy prostate tumor remnants and micrometastases, while surrounding healthy tissues remain unaffected.

In our study, the PSMA targeting antibody D2B was coupled to the photosensitizer IRDye700DX and radiolabeled with 111In. In a mouse model, this multi-modality agent was used to preoperatively visualize tumor lesions with SPECT/CT to allow rough localization of the tumors. During surgery, the fluorescent signal originating from the photosensitizer facilitates visualization of tumors and residual tumor tissue, so the surgeon can be guided towards accurate resection of the entire tumors and metastases. In addition, the PSMA-targeted PDT can be applied to destroy small tumor deposits in cases where close proximity of the tumors. What should clinicians and patients take away from your report?

Response: In future, this new treatment modality could fit perfectly in and expand the field of nuclear medicine and molecular imaging. This multi-modality approach might have the potential to complement the current applications for PSMA ligands in radionuclide imaging and therapy of  prostate cancer and offers the possibility to bridge the gap between nuclear medicine/molecular imaging and urological surgery. What recommendations do you have for future research as a result of this study?

Response: In future, this targeted multi-modality approach could majorly improve oncological surgery as resection of malignant tissues might become less invasive. During traditional approaches, complete removal of the entire tumor tissue can be extremely challenging, especially when surrounding healthy tissues preclude wide excision. The new approach has the advantage that tumors can be visualized before surgery to get an impression on how many tumors need to be resected. During surgery, guidance by a gamma-probe and by fluorescent signals could guide the surgeon towards selective and tissue sparing resection. In areas, where resection is not possible, PDT can be applied to even destroy these remaining tumor deposits.

In future, this multi-modality approach may decrease the number of patients that will develop recurrent disease. Ultimately, this can result in improved treatment outcome, prolonged survival, and improved quality of life. Thank you for your contribution to the community.

Citation:  SNMMI abstract: (Society of Nuclear Medicine 2017)

Characterization of an In-111-labeled anti-PSMA antibody-photosensitizer conjugate for targeted photodynamic therapy of PSMA-expressing tumors

Note: Content is Not intended as medical advice. Please consult your health care provider regarding your specific medical condition and questions.

Note: Content is Not intended as medical advice. Please consult your health care provider regarding your specific medical condition and questions.