Photodynamic therapy with the phthalocyanine photosensitizer Pc 4 of SW480 human colon cancer xenografts in athymic mice.
Photodynamic therapy (PDT) using the silicon phthalocyanine photosensitizer Pc 4 [HOSiPcOSi(CH3)2(CH2)3N-(CH3)2] is an oxidative stress associated with induction of apoptosis in various cell types. We assessed the effectiveness of Pc 4-PDT on SW480 colon cancer xenografts grown in athymic nude mice. Animals bearing xenografts were treated with 1 mg/kg body weight Pc 4 and 48 h later were irradiated with 150 J/cm2 672-nm light from a diode laser delivered at 150 mW/cm2. Biochemical studies were performed in xenografts resected at various time points up to 26 h after Pc 4-PDT treatment, whereas tumor size was evaluated over a 4-week period in parallel experiments. In the tumors resected for biochemical studies, apoptosis was visualized by activation of caspase-9 and caspase-3 and a gradual increase in the cleavage of the nuclear enzyme poly(ADP-ribose) polymerase (PARP) to a maximum of approximately 60% of the total PARP present at approximately 26 h. At that time all Pc 4-PDT-treated tumors had regressed significantly. Two signaling responses that have previously been shown to be associated with Pc 4-PDT-induced apoptosis in cultured cells, p38 mitogen-activated protein kinase and p21/WAF1/Cip1, were examined. A marked increase in phosphorylation of p38 was observed within 1 h after Pc 4-PDT without changes in levels of the p38 protein. Levels of p21 were not altered in the xenografts in correspondence with the presence of mutant p53 in SW480 cells. Evaluation of tumor size showed that tumor growth resumed after a delay of 9-15 days. Our results suggest that: (a) Pc 4-PDT is effective in the treatment of SW480 human colon cancer xenografts independent of p53 status; (b) PARP cleavage may be mediated by caspase-9 and caspase-3 activation in the Pc 4-PDT-treated tumors; and (c) p38 phosphorylation may be a trigger of apoptosis in response to PDT in vivo in this tumor model.
Whitacre
C M
CM
Department of Medicine, Case Western Reserve University School of Medicine, Cleveland, Ohio 44106-4937, USA. cxw34@po.cwru.edu
Feyes
D K
DK
Satoh
T
T
Grossmann
J
J
Mulvihill
J W
JW
Mukhtar
H
H
Oleinick
N L
NL
D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D002455:Cell Division / Q000187:drug effects; D003110:Colonic Neoplasms / Q000188:drug therapy* / Q000473:pathology; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000187:drug effects / Q000378:metabolism; D005260:Female; D006801:Humans; D007211:Indoles / Q000627:therapeutic use*; D051379:Mice; D008819:Mice, Nude; D020928:Mitogen-Activated Protein Kinases / Q000187:drug effects / Q000378:metabolism; D009368:Neoplasm Transplantation; D017646:Organosilicon Compounds / Q000627:therapeutic use*; D010766:Phosphorylation / Q000187:drug effects; D010778:Photochemotherapy; D017319:Photosensitizing Agents / Q000627:therapeutic use*; D012821:Silanes; D014183:Transplantation, Heterologous; D014407:Tumor Cells, Cultured; D048051:p38 Mitogen-Activated Protein Kinases
C493956:CDKN1A protein, human; C493957:Cdkn1a protein, mouse; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D007211:Indoles; D017646:Organosilicon Compounds; D017319:Photosensitizing Agents; D012821:Silanes; C082854:silicon phthalocyanine; C052464:bis(tri-n-hexylsiloxy)(2,3-naphthalocyaninato)silicon; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases