Near-IR photodynamic therapy approach effectively targets prostate cancer

The efficacy and optimal dose for targeted photodynamic therapy to treat prostate cancer before and during surgery has been shown.

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Researchers at Radboud University (Nijmegen, Netherlands) and the Clinic for Nuclear Medicine at University Hospital (Essen, Germany) have demonstrated the efficacy and optimal dose for targeted photodynamic therapy to treat prostate cancer before and during surgery.

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Prostate-specific membrane antigen (PSMA) was targeted with an anti-PSMA antibody radiolabeled with the tracer indium-111 (111In) and coupled with specialized photosensitizers that cause cell destruction upon exposure to near-infrared (near-IR) light. The combined formula is 111In-DTPA-D2B-IRDye700DX.

"Coupling the photosensitizer to an imaging agent that targets PSMA on the tumor surface makes it possible to selectively and effectively destroy prostate tumor remnants and micrometastases while surrounding healthy tissues remain unaffected," says Susanne Lütje, MD, Ph.D., lead author of the study from the Department of Radiology and Nuclear Medicine at Radboud University Medical Center and the Clinic for Nuclear Medicine at University Hospital.

This technique optimizes prostate cancer care by allowing visualization of tumors prior to surgery by providing real-time guidance to surgeons in the operating room, and by priming tumors for photodynamic therapy when surgery isn't enough or risks damage to sensitive structures.

A gamma probe is used to detect PSMA-expressing tumor cells. Photosensitizers can then be activated with light in the near-IR, which causes them to emit fluorescence, or oxygen radicals, that damage PSMA over-expressing tumor tissues.

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This is a characterization of an In-111-labeled anti-PSMA antibody-photosensitizer conjugate for targeted photodynamic therapy of PSMA-expressing tumors. (Image credit: Department of Radiology and Nuclear Medicine at Radboud University Medical Center and the Clinic for Nuclear Medicine at University Hospital)

Study results showed effective localization of the drug at the site of tumors, as well as effective imaging and photodynamic therapy via near-IR exposure in mice. Further study in humans is needed before this procedure could be made available for prostate cancer patients.

"In the future, this novel approach to prostate cancer could significantly improve the effectiveness of treatment, reduce recurrent disease and ultimately prolong survival and protect quality of life for patients," Lütje says.

The researchers presented the work during the 2017 Annual Meeting of the Society of Nuclear Medicine and Molecular Imaging (SNMMI), held June 10-14, 2017, in Denver, CO.

Full details of the work appear in the Journal of Nuclear Medicine.

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