Role of p53 and ATM in photodynamic therapy-induced apoptosis

Response of MCF-7 Breast Cancer Cells Overexpressed with P-Glycoprotein to Apoptotic Induction after Photodynamic Therapy

Multidrug resistance (MDR) has posed a significant threat to cancer treatment and has led to the emergence of a new therapeutic regime of photodynamic therapy (PDT) to curb the menace. The PDT modality employs a photosensitiser (PS), excited at a specific wavelength of light to kill cancer cells. In the present study, we used a zinc phthalocyanine tetrasulfonic acid PS to mediate the photodynamic killing of MCF-7 cells overexpressed with P-glycoprotein (P-gp) and investigate the response to cell death induction. After photodynamic treatment, MCF-7 cells undergo cell death, and indicators like Annexin V/PI staining, DNA fragmentation, and measurement of apoptotic protein expression were investigated. Results showed increased externalisation of phosphatidylserine protein, measured as a percentage in flow cytometry indicative of apoptotic induction. This expression was significant (p < 0.006) for the untreated control cells, and there was no detection of DNA fragments after a laser fluence of 20 J/cm². In addition, a statistically significant difference (p < 0.05) was seen in caspase 8 activity and Bax protein expression. These findings were indicative of apoptotic induction and thus seem to represent the extrinsic apoptotic pathway. This study shows the role of PDT in the treatment of a resistant phenotype breast cancer.

Immunohistochemical detection of p53 and pp53 Ser392 in canine hemangiomas and hemangiosarcomas located in the skin

Background

p53 protein is essential for the regulation of cell proliferation. Aberrant accumulation of it usually occurs in cutaneous malignancies. Mutant p53 is detected by immunohistochemistry because it is more stable than the wild-type p53. However, post-translational modifications of p53 in response to ultraviolet radiation are important mechanisms of wild-type p53 stabilization, leading to positive staining in the absence of mutation. The aims were: 1) to analyze the immunohistochemical expression of p53 and phospho-p53 Serine³⁹² in canine skin endothelial tumours; and 2) to determine if any relationship exists between p53 and phospho-p53 Serine³⁹² overexpression and cell proliferation.

Results

p53 and phospho-p53 Serine³⁹² immunolabeling was examined in 40 canine cutaneous endothelial tumours (13 hemangiomas and 27 hemangiosarcomas). Their expression was associated with tumour size, hemangiosarcoma stage (dermal versus hypodermal), histological diagnosis and proliferative activity (mitotic count and Ki-67 index). Statistical analysis revealed a significant increase of p53 immunoreactivity in hemangiosarcomas (median, 74.61%; interquartile range [IQR], 66.97–82.98%) versus hemangiomas (median, 0%; IQR, 0–20.91%) (p < .001) and in well-differentiated hemangiosarcomas (median, 82.40%; IQR, 66.49–83.17%) versus hemangiomas (p = .002). Phospho-p53 Serine³⁹² immunoreactivity was significantly higher in hemangiosarcomas (median, 53.80%; IQR, 0–69.50%) than in hemangiomas (median, 0%; IQR, 0.0%) (p < .001). Positive correlation of the overexpression of p53 and phospho-p53 Serine³⁹² with mitotic count and Ki-67 index was found in the cutaneous vascular tumours (p < .001). The Ki-67 index of the hemangiomas (median, 0.50%; IQR, 0–2.80%) was significantly lower than that of the hemangiosarcomas (median, 34.85%; IQR, 23.88–42.33%) (p < .001), and that specifically of well-differentiated hemangiosarcomas (median, 24.60%; IQR, 15.45–39.35%) (p = .001). Immunolabeling of 18 visceral hemangiosarcomas showed that the p53 (median, 41.59%; IQR, 26.89–64.87%) and phospho-p53 Serine392 (median, 0%; IQR, 0–22.53%) indexes were significantly lower than those of skin (p = .001; p = .006, respectively).

Conclusions

The p53 and phospho-p53 Serine³⁹²overexpression together with high proliferative activity in hemangiosarcomas versus hemangiomas indicated that p53 might play a role in the acquisition of malignant phenotypes in cutaneous endothelial neoplasms in dogs. The Ki-67 index may be useful in distinguishing canine well-differentiated hemangiosarcomas from hemangiomas.

Wild-type and mutant p53 differentially modulate miR-124/iASPP feedback following pohotodynamic therapy in human colon cancer cell line

Colorectal cancer (CRC) is a most common digestive system malignant tumor. p53 mutation has essential role in cancers and is frequently observed in CRC and presents a huge challenge. p53 mutation has been reported to attenuate the inhibitory effect of photofrin-based photodynamic therapy (PDT). p53 mutation-induced gain of function brings up the dysfunction of carcinogenic factors, including miRNAs. Our research found that PDT suppressed CRC cell viability, reduced the tumor size and prolonged the survival time, all of which could be attenuated by p53 mutation or deletion. After p53 mutation or deletion, several miRNA expression levels were downregulated, among which miR-124 was the most strongly downregulated, whereas iASPP expression was upregulated. p53 binds to the promoter of miR-124 to promote its expression and then inhibited iASPP expression, so as to amplify the inhibitory effect of PDT on wild-type p53 cells. In p53-mutant or -deleted cells, this binding no longer worked to promote miR-124 expression, and iASPP expression increased, finally resulted in promoted CRC cell viability upon PDT. The interactive modulation among miR and iASPP in p53-mutant or -deleted cells may serve as a crucial pathway, which mediates therapy resistance when p53 is mutated or deleted, in the process of PDT treatment of CRC.

MTT assay for cell viability: Intracellular localization of the formazan product is in lipid droplets

Although MTT is widely used to assess cytotoxicity and cell viability, the precise localization of its reduced formazan product is still unclear. In the present study the localization of MTT formazan was studied by direct microscopic observation of living HeLa cells and by colocalization analysis with organelle-selective fluorescent probes. MTT formazan granules did not colocalize with mitochondria as revealed by rhodamine 123 labeling or autofluorescence. Likewise, no colocalization was observed between MTT formazan granules and lysosomes labeled by neutral red. Taking into account the lipophilic character and lipid solubility of MTT formazan, an evaluation of the MTT reaction was performed after treatment of cells with sunflower oil emulsions to induce a massive occurrence of lipid droplets. Under this condition, lipid droplets revealed a large amount of MTT formazan deposits. Kinetic studies on the viability of MTT-treated cells showed no harmful effects at short times. Quantitative structure-activity relations (QSAR) models were used to predict and explain the localization of both the MTT tetrazolium salt and its formazan product. These predictions were in agreement with experimental observations on the accumulation of MTT formazan product in lipid droplets.

Temoporfin (Foscan®, 5,10,15,20-tetra(m-hydroxyphenyl)chlorin)--a second-generation photosensitizer

This review traces the development and study of the second-generation photosensitizer 5,10,15,20-tetra(m-hydroxyphenyl)chlorin through to its acceptance and clinical use in modern photodynamic (cancer) therapy. The literature has been covered up to early 2011.

TP53 regulates human AlkB homologue 2 expression in glioma resistance to Photofrin-mediated photodynamic therapy

BACKGROUND

Photodynamic therapy (PDT) is a promising adjuvant therapy in cancer treatment. However, cancers resistant to PDT, mediated through the efflux of photosensitisers by means of P-glycoprotein or ATP-binding cassette transporter proteins, have been reported. The DNA repair has also been suggested to be responsible for PDT resistance, but little is known about the repair pathways and mechanisms involved. Therefore, this study aimed to investigate the possible function of six major DNA repair mechanisms in glioma cells resistant to Photofrin-mediated PDT (Ph-PDT).

METHODS

The U87 glioma cells relatively resistant to Ph-PDT were obtained by recovering the viable cells 3 h after PDT treatment. The mRNA and protein expression levels of DNA repair genes were evaluated by quantitative real-time reverse transcription-polymerase chain reaction and western blotting, respectively. Small-interfering RNA and chromatin-immunoprecipitation assays were used to further examine the relationship between AlkB, an alkylation repair homologue 2 (Escherichia coli) (ALKBH2) and Ph-PDT responsiveness, and transcription factors involved in ALKBH2 transcription.

RESULTS

The ALKBH2 of DNA damage reversal was significantly increased at both mRNA and protein levels from 30 min to 48 h post-treatment with Ph-PDT. Conversely, down-regulating ALKBH2 expression enhances Ph-PDT efficiency. Furthermore, our data clearly show for the first time that tumour protein (TP53) is directly involved by binding to the promoter of ALKBH2 in mediating Ph-PDT resistance.

CONCLUSION

C The DNA damage reversal mechanisms may have important functions in Ph-PDT resistance through the activation of ALKBH2 by TP53.

Endoscopic therapy of dysplasia and early-stage cancers of the esophagus

Endoscopic treatments have become a viable alternative for some patients with early-stage esophageal neoplasia. Although esophagectomy remains the standard of care for high-grade dysplasia and superficial cancers, surgical morbidity and mortality may deter patients who are medically unfit or reluctant to undergo surgery. Photodynamic therapy (PDT) and endoscopic mucosal resection (EMR) are the best-studied nonsurgical approaches at present. PDT has been reported to eradicate high-grade dysplasia (HGD) and early Barrett's cancers at rates ranging from 75% to 100% and 17% to 100%, respectively, and a recent randomized controlled trial confirmed that PDT may prevent progression of HGD to cancer. Complete remission rates greater than 90% have also been reported with EMR and other mucosa-ablating interventions, although recurrence rates necessitate close endoscopic surveillance and retreatment in some patients. In addition to PDT and EMR, several emerging endoscopic treatment options for superficial esophageal neoplasia may provide attractive alternatives to surgery.

Protoporphyrin IX Interacts with Wild-type p53 Protein in Vitro and Induces Cell Death of Human Colon Cancer Cells in a p53-dependent and -independent Manner

Photodynamic therapy (PDT) of cancer is an alternative treatment for tumors resistant to chemo- and radiotherapy. It induces cancer cell death mainly through generation of reactive oxygen species by a laser light-activated photosensitizer. It has been suggested that the p53 tumor suppressor protein sensitizes some human cancer cells to PDT. However, there is still no direct evidence for this. We have demonstrated here for the first time that the photosensitizer protoporphyrin IX (PpIX) binds to p53 and disrupts the interaction between p53 tumor suppressor protein and its negative regulator HDM2 in vitro and in cells. Moreover, HCT116 colon cancer cells exhibited a p53-dependent sensitivity to PpIX in a dose-dependent manner, as was demonstrated using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay and fluorescence-activated cell sorter (FACS) analysis of cell cycle profiles. We have also observed induction of p53 target pro-apoptotic genes, e.g. puma (p53-up-regulated modulator of apoptosis), and bak in PpIX-treated cells. In addition, p53-independent growth suppression by PpIX was detected in p53-negative cells. PDT treatment (2 J/cm2) of HCT116 cells induced p53-dependent activation of pro-apoptotic gene expression followed by growth suppression and induction of apoptosis.

Differential effects of 5-aminolaevulinic acid photodynamic therapy and psoralen + ultraviolet A therapy on p53 phosphorylation in normal human skin in vivo

BACKGROUND

Phosphorylation of the tumour suppressor p53 by the CK2/FACT pathway plays a central role in suppressing ultraviolet (UV)-induced skin cancer in animal models. Although p53 protein stabilization is induced after solar-simulated irradiation of human skin in vivo, p53 phosphorylation has not been defined.

OBJECTIVES

To investigate the effects of clinically effective treatments for skin diseases including psoralen + UVA (PUVA) and photodynamic therapy (PDT) on p53 phosphorylation to determine whether the tumour-suppressing p53 kinase pathways are activated upon use of these therapies.

METHODS

We used antibodies to the ATM/ATR and CK2/FACT phosphorylation sites on p53.

RESULTS

We found that p53 activation was induced selectively by PUVA treatment, while 8-oxo-7,8-dihydroguanine DNA damage was induced selectively by 5-aminolaevulinic acid (ALA)-PDT treatment. Importantly, PUVA treatment resulted in p53 kinase activation, as defined by p53 modification at AT (serine-15) and CK2/FACT (serine-392) sites within the proliferative compartment.

CONCLUSIONS

These data demonstrate that PUVA provokes accumulation and phosphorylation of p53 by AT and CK2/FACT within critical proliferative focal points (as determined by p63 colocalization studies) where DNA damage may lead to tumorigenesis. PDT is mechanistically distinct in that there is a lower level of induction of p53 expression with no evidence of AT- or CK2/FACT-mediated phosphorylation. This suggests that the type of DNA damage created by the reactive oxygen species generated by ALA-PDT does not induce the p53 pathway classically required for the repair of DNA photoadducts induced by UV.

p53 Status does not affect photodynamic cell killing induced by hypericin

PURPOSE

Given that p53 is a tumor suppressor that plays a central role in the cellular response to DNA damage and that more than 50% of all cancers have mutated p53, the wider utility of photodynamic therapy (PDT) in the treatment of cancer will depend on an understanding of whether p53 status modulates response to PDT. In this study, we investigated the photosensitivity of isogenic cell lines that differ only in their p53 status to PDT using hypericin as the photosensitizer.

METHODS

Acute (MTT) and chronic (clonogenic) cytotoxic assays were performed on two osteosarcoma cell-lines (U2OS and U2OS+p53DD) that are isogenic except that the latter expresses dominant negative p53. The inducible expression of p53 was determined on western blots. Uptake of hypericin, cell cycle profile analysis, measurement of membrane phosphatidylserine externalization and changes in mitochondrial membrane potential were investigated using flow cytometry.

RESULTS

Hypericin uptake was observed to be equivalent in U2OS and U2OS+p53DD cells. There were no significant differences in cell killing between these cell-lines in both the MTT and clonogenic assays (IC(50) of 0.4 microg/ml from MTT assay). p53 expression did not increase up to 24 h after PDT treatment in both cell lines. There were also no significant differences in the cell-cycle arrest profiles and timing of onset of apoptosis.

CONCLUSIONS

Taken together, these results suggest that the status of p53 may not be important in PDT-mediated cell killing or induction of apoptosis. By extension, these results imply that PDT may be used with equal efficacy for the treatment of p53-positive and -negative tumors.