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Updated: Jun 26, 2026
An In Vitro Approach to Photodynamic Therapy
Published on: August 17, 2018
In vitro targeted photodynamic therapy with a pyropheophorbide--a conjugated inhibitor of prostate-specific membrane
Tiancheng Liu1, Lisa Y Wu, Joseph K Choi
1Department of Chemistry, Washington State University, Pullman, WA 99164-4630, USA.
Background:
The lack of specific delivery of photosensitizers (PSs), represents a significant limitation of photodynamic therapy (PDT) of cancer. The biomarker prostate-specific membrane antigen (PSMA) has attracted considerable attention as a target for imaging and therapeutic applications for prostate cancer. Although recent efforts have been made to conjugate inhibitors of PSMA with imaging agents, there have been no reports on PS-conjugated PSMA inhibitors for targeted PDT of prostate cancer. The present study focuses on the use of a PSMA inhibitor-conjugate of pyropheophorbide-a (Ppa-conjugate 2) for targeted PDT to achieve apoptosis in PSMA+ LNCaP cells.
Methods:
Confocal laser scanning microscopy with a combination of nuclear staining and immunofluorescence methods were employed to monitor the specific imaging and PDT-mediated apoptotic effects on PSMA-positive LNCaP and PSMA-negative (PC-3) cells.
Results:
Our results demonstrated that PDT-mediated effects by Ppa-conjugate 2 were specific to LNCaP cells, but not PC-3 cells. Cell permeability was detected as early as 2 hr by HOE33342/PI double staining, becoming more intense by 4 hr. Evidence for the apoptotic caspase cascade being activated was based on the appearance of poly-ADP-ribose polymerase (PARP) p85 fragment. Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay detected DNA fragmentation 16 hr post-PDT, confirming apoptotic events.
Conclusions:
Cell permeability by HOE33342/PI double staining as well as PARP p85 fragment and TUNEL assays confirm cellular apoptosis in PSMA+ cells when treated with PS-inhibitor conjugate 2 and subsequently irradiated. It is expected that the PSMA targeting small-molecule of this conjugate can serve as a delivery vehicle for PDT and other therapeutic applications for prostate cancer.
Insights
Targeted photodynamic therapy (PDT) using a prostate-specific membrane antigen (PSMA) inhibitor conjugate effectively induced apoptosis in PSMA-positive prostate cancer cells, demonstrating specificity and potential for cancer treatment.
Area of Science:
- Oncology
- Biochemistry
- Nanomedicine
Background:
- Photodynamic therapy (PDT) for cancer is limited by non-specific photosensitizer delivery.
- Prostate-specific membrane antigen (PSMA) is a promising target for prostate cancer imaging and therapy.
- Targeted PDT for prostate cancer using PSMA inhibitor conjugates has not been previously reported.
Purpose of the Study:
- To evaluate a novel PSMA inhibitor-conjugate of pyropheophorbide-a (Ppa-conjugate 2) for targeted PDT in prostate cancer.
- To assess the efficacy of Ppa-conjugate 2 in inducing apoptosis in PSMA-positive (LNCaP) versus PSMA-negative (PC-3) prostate cancer cells.
Main Methods:
- Confocal laser scanning microscopy was used for imaging and monitoring PDT effects.
- Immunofluorescence and nuclear staining (HOE33342/PI) assessed cell permeability and apoptosis.
- Western blotting for PARP cleavage and TUNEL assay detected DNA fragmentation.
Main Results:
- Ppa-conjugate 2 demonstrated specific PDT-mediated effects on PSMA-positive LNCaP cells, with no significant effect on PC-3 cells.
- Early cell permeability was observed within 2-4 hours post-treatment.
- Apoptosis was confirmed by PARP p85 fragment detection and DNA fragmentation via TUNEL assay.
Conclusions:
- The PSMA inhibitor conjugate (Ppa-conjugate 2) effectively induces apoptosis in PSMA-positive prostate cancer cells via targeted PDT.
- The conjugate shows promise as a targeted delivery vehicle for PDT and other therapies in prostate cancer treatment.
- The study validates the use of PSMA as a target for developing specific and effective prostate cancer therapies.
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