Isolation and characterization of PDT-resistant cancer cells.

Even though the efficacy of photodynamic therapy (PDT) for treating premalignant and malignant lesions has been demonstrated, resistant tumor cells to this therapy occasionally appear. Here, we describe the published methods to isolate resistant cancer cells to PDT and propose new procedures that may be used, as laboratory models allow a better understanding of resistance mechanisms. For this purpose, the treatment conditions, the photosensitizer (PS) or pro-drug, the cell line and the final selection - clonal of total population - must be taken into account. In general, high and repeated treatment doses are used. The resistant cell population characterization may include cell morphology, response to PDT, expression of death proteins or survival related genes and cell proliferation analysis. In addition, in vivo models such as the resistant cell transplantation to mice, allow evaluating tumorigenicity and aggressiveness, leading to the determination of the in vivo resistance. Summarizing, in order to improve clinical results, cellular models can help understand PDT-resistance mechanisms in vivo and in vitro.

Combined Treatments with Photodynamic Therapy for Non-Melanoma Skin Cancer.

Non-melanoma skin cancer (NMSC) is the most common form of cancer in the Caucasian population. Among NMSC types, basal cell carcinoma (BCC) has the highest incidence and squamous cell carcinoma (SCC) is less common although it can metastasize, accounting for the majority of NMSC-related deaths. Treatment options for NMSC include both surgical and non-surgical modalities. Even though surgical approaches are most commonly used to treat these lesions, Photodynamic Therapy (PDT) has the advantage of being a non-invasive option, and capable of field treatment, providing optimum cosmetic outcomes. Numerous clinical research studies have shown the efficacy of PDT for treating pre-malignant and malignant NMSC. However, resistant or recurrent tumors appear and sometimes become more aggressive. In this sense, the enhancement of PDT effectiveness by combining it with other therapeutic modalities has become an interesting field in NMSC research. Depending on the characteristics and the type of tumor, PDT can be applied in combination with immunomodulatory (Imiquimod) and chemotherapeutic (5-fluorouracil, methotrexate, diclofenac, or ingenol mebutate) agents, inhibitors of some molecules implicated in the carcinogenic process (COX2 or MAPK), surgical techniques, or even radiotherapy. These new strategies open the way to a wider improvement of the prevention and eradication of skin cancer.

Comparative study of the clinical, histological, and biological characteristics of squamous cell carcinomas in areas previously treated with photodynamic therapy.

Although photodynamic therapy (PDT) is an effective treatment option for non-melanoma skin cancer, the development of aggressive tumours in PDT-treated areas has been described. To evaluate the clinical, histological, and biological characteristics of squamous cell carcinomas (SCCs) in areas previously treated with PDT vs those arising in areas never treated with this therapeutic modality. A retrospective observational study was designed. We collected all cases of invasive SCCs in areas previously treated with PDT. The control group consisted of an equivalent number of SCCs randomly selected from the database of our pathology department. Expression of specific markers implicated in SCC progression, including p53, Ki67, COX-2, cyclin D1, E-cadherin, EGFR, survivin, and pERK, was analysed. A total of 699 patients were treated with PDT for non-melanoma skin cancer during the course of the study. Ten invasive SCCs arising in areas previously treated with methylaminolevulinate-PDT were diagnosed in six patients. The control group consisted of 10 invasive SCCs from 10 patients never treated with PDT. In the PDT group, the mean tumour size was significantly lower and the absence of ulceration was more frequent than in the control group (p<0.024 and p = 0.035, respectively). A diffuse survivin staining pattern was observed in 90% of tumours in the PDT group versus 50% in the comparative group (p = 0.141). The number of SCCs arising in areas previously treated with PDT was very low and did not differ significantly from that of SCCs developing in non-PDT-treated areas.

Cellular intrinsic factors involved in the resistance of squamous cell carcinoma to photodynamic therapy.

Photodynamic therapy (PDT) is widely used to treat non-melanoma skin cancer. However, some patients affected with squamous cell carcinoma (SCC) do not respond adequately to PDT with methyl-δ-aminolevulinic acid (MAL-PDT) and the tumors acquire an infiltrative phenotype and became histologically more aggressive, less differentiated, and more fibroblastic. To search for potential factors implicated in SCC resistance to PDT, we have used the SCC-13 cell line (parental) and resistant SCC-13 cells obtained by repeated MAL-PDT treatments (5th and 10th PDT-resistant generations). Xenografts assays in immunodeficient mice showed that the tumors generated by resistant cells were bigger than those induced by parental cells. Comparative genomic hybridization array (aCGH) showed that the three cell types presented amplicons in 3p12.1 CADM2, 7p11.2 EFGR, and 11q13.3 CCND1 genes. The 5th and 10th PDT-resistant cells showed an amplicon in 5q11.2 MAP3K1, which was not present in parental cells. The changes detected by aCGH on CCND1, EFGR, and MAP3K1 were confirmed in extracts of SCC-13 cells by reverse-transcriptase PCR and by western blot, and by immunohistochemistry in human biopsies from persistent tumors after MAL-PDT. Our data suggest that genomic imbalances related to CCND1, EFGR, and particularly MAP3K1 seem to be involved in the development of the resistance of SCC to PDT.