In vitro targeted photodynamic therapy with a pyropheophorbide--a conjugated inhibitor of prostate-specific membrane antigen.
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.
Liu
Tiancheng
T
Department of Chemistry, Washington State University, Pullman, WA 99164-4630, USA.
Wu
Lisa Y
LY
Choi
Joseph K
JK
Berkman
Clifford E
CE
D017209:Apoptosis / Q000187:drug effects; D045744:Cell Line, Tumor; D002734:Chlorophyll / Q000031:analogs & derivatives* / Q000627:therapeutic use; D053938:DNA Fragmentation; D004273:DNA, Neoplasm / Q000187:drug effects; D006801:Humans; D008297:Male; D010778:Photochemotherapy / Q000379:methods*; D017430:Prostate-Specific Antigen / Q000037:antagonists & inhibitors*; D011471:Prostatic Neoplasms / Q000188:drug therapy*
D004273:DNA, Neoplasm; D002734:Chlorophyll; C040298:pyropheophorbide a; D017430:Prostate-Specific Antigen