In vitro evaluation of calphostin C as a novel agent for photodynamic therapy of bladder cancer.
OBJECTIVE
Calphostin C, a highly specific protein kinase C inhibitor, induces apoptosis in the presence of visible light. We report the photoactivatable cytotoxicity of calphostin C in a series of well-characterized human bladder cancer cell lines: RT4, UM-UC-3, and 5637.


METHODS
The human bladder cancer cell lines RT4, UM-UC-3, and 5637 were chosen on the basis of their p53, pRb and 9p21 deletion status. Using standard tissue culture techniques, the cytotoxicity of 10 to 100 nM calphostin C in combination with increasing exposures of visible light was examined. Controls consisted of cells treated with calphostin C without visible light and cells exposed to visible light without calphostin C treatment. Cell viability was determined by MTT assay. The induction of apoptosis by activated calphostin C was determined by 4,6-diamidino-2-phenylindole (DAPI) staining/fluorescence microscopy of nuclei.


RESULTS
In the absence of light, calphostin C did not demonstrate a cytotoxic effect on any of the cell lines tested. Increasing the duration of light exposure resulted in a concomitant decrease in cell viability. Significant cell death was seen with calphostin C concentrations as low as 10 nM. These studies also demonstrated that calphostin C induced apoptosis by a mechanism independent of p53 and pRb status and the presence or absence of 9p21 deletions.


CONCLUSIONS
We demonstrated the ability of activated calphostin C to induce apoptosis in a light-dependent and concentration-dependent fashion in a bladder cancer model system. Activated calphostin C cytotoxicity is independent of tumor genetic background and the status of p53 and pRb. Further development of calphostin C as a photosensitizer for photodynamic therapy of superficial bladder cancer may be warranted.
Beck
T P
TP
Department of Surgery, University of Chicago Pritzker School of Medicine, Illinois 60637, USA.
Kirsh
E J
EJ
Chmura
S J
SJ
Kovar
D A
DA
Chung
T
T
Rinker-Schaeffer
C W
CW
Stadler
W M
WM
D000903:Antibiotics, Antineoplastic / Q000627:therapeutic use*; D016923:Cell Death / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D006801:Humans; D009281:Naphthalenes / Q000627:therapeutic use*; D010778:Photochemotherapy; D011493:Protein Kinase C / Q000037:antagonists & inhibitors*; D014407:Tumor Cells, Cultured; D001749:Urinary Bladder Neoplasms / Q000188:drug therapy*
D000903:Antibiotics, Antineoplastic; D009281:Naphthalenes; D011493:Protein Kinase C; C058819:calphostin C