Combination of photodynamic therapy with aspirin in human-derived lung adenocarcinoma cells affects proteasome activity and induces apoptosis.
OBJECTIVE
Photodynamic treatment (PDT) of human lung carcinoma cells A549 (p53(+/+)) and H1299 (p53(-/-)) induces fast but transient stalling of proteasome activity. We have explored the possibility of prolonging this effect by combining PDT with drugs capable of sustaining the stall, and promote apoptosis of surviving cells. We show that aspirin can be used to accomplish this.


METHODS
Cells were irradiated at doses ranging from 0.54 to 1.10 J cm(-2), and subsequently were incubated with aspirin at either high (10 and 5 mm) or low concentration (2.5 and 1.5 mm). Photofrin concentration and incubation time were constant (2.5 μg/ml and 16 h). Under these conditions, we analysed cell viability, colony-forming efficiency, cycle profile, expression patterns of specific proteins and ubiquitination state, after individual or combined administration.


RESULTS
Treatment with either PDT or aspirin, rapidly induced proteasome malfunction and accumulation of cells in G(2)M, but did not induce apoptosis. However, when aspirin was added to cells (even at low concentrations) after PDT, the proteasome block was sustained. Moreover, significant cytotoxic effects, including apoptosis, were observed along with cytostatic effects (G(2)M accumulation/decreased colony formation).


CONCLUSIONS
Combination of PDT and low-toxicity drugs (such as aspirin) resulted in protracted inhibition of proteasome activity and induced apoptosis even in apoptosis-resistant cancer cells.
Chiaviello
A
A
Department of Molecular and Cellular Biology and Pathology L. Califano, University of Naples Federico II, Naples, Italy.
Paciello
I
I
Postiglione
I
I
Crescenzi
E
E
Palumbo
G
G
D017209:Apoptosis / Q000187:drug effects*; D001241:Aspirin / Q000494:pharmacology / Q000627:therapeutic use*; D002289:Carcinoma, Non-Small-Cell Lung / Q000188:drug therapy*; D002453:Cell Cycle / Q000187:drug effects; D045744:Cell Line, Tumor; D006801:Humans; D008175:Lung Neoplasms / Q000188:drug therapy*; D010778:Photochemotherapy / Q000379:methods*; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*
D046988:Proteasome Endopeptidase Complex; D001241:Aspirin