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

Enhancing 5-ALA-PDT efficacy against resistant tumor cells: Strategies and advances

As a precursor of protoporphyrin IX (PpIX), an endogenous pro-apoptotic and fluorescent molecule, 5-Aminolevulinic acid (5-ALA) has gained substantial attention for its potential in fluorescence-guided surgery as well as photodynamic therapy (PDT). Moreover, 5-ALA-PDT has been suggested as a promising chemo-radio sensitization therapy for various cancers. However, insufficient 5-ALA-induced PpIX fluorescence and the induction of multiple resistance mechanisms may hinder the 5-ALA-PDT clinical outcome. Reduced efficacy and resistance to 5-ALA-PDT can result from genomic alterations, tumor heterogeneity, hypoxia, activation of pathways related to cell surveillance, production of nitric oxide, and most importantly, deregulated 5-ALA transporter proteins and heme biosynthesis enzymes. Understanding the resistance regulatory mechanisms of 5-ALA-PDT may allow the development of effective personalized cancer therapy. Here, we described the mechanisms underlying resistance to 5-ALA-PTD across various tumor types and explored potential strategies to overcome this resistance. Furthermore, we discussed future approaches that may enhance the efficacy of treatments using 5-ALA-PDT.

Comparative response to PDT with methyl-aminolevulinate and temoporfin in cutaneous and oral squamous cell carcinoma cells

Cutaneous and Head and Neck squamous cell carcinoma (CSCC, HNSCC) are among the most prevalent cancers. Both types of cancer can be treated with photodynamic therapy (PDT) by using the photosensitizer Temoporfin in HNSCC and the prodrug methyl-aminolevulinate (MAL) in CSCC. However, PDT is not always effective. Therefore, it is mandatory to correctly approach the therapy according to the characteristics of the tumour cells. For this reason, we have used cell lines of CSCC (A431 and SCC13) and HNSCC (HN5 and SCC9). The results obtained indicated that the better response to MAL-PDT was related to its localization in the plasma membrane (A431 and HN5 cells). However, with Temoporfin all cell lines showed lysosome localization, even the most sensitive ones (HN5). The expression of mesenchymal markers and migratory capacity was greater in HNSCC lines compared to CSCC, but no correlation with PDT response was observed. The translocation to the nucleus of β-catenin and GSK3β and the activation of NF-κβ is related to the poor response to PDT in the HNSCC lines. Therefore, we propose that intracellular localization of GSK3β could be a good marker of response to PDT in HNSCC. Although the molecular mechanism of response to PDT needs further elucidation, this work shows that the most MAL-resistant line of CSCC is more sensitive to Temoporfin.

Treatment of nonmelanoma skin cancer with pro-differentiation agents and photodynamic therapy: Preclinical and clinical studies (Review)

Photodynamic therapy (PDT) is a nonscarring cancer treatment in which a pro-drug (5-aminolevulinic acid, ALA) is applied, converted into a photosensitizer (protoporphyrin IX, PpIX) which is then activated by visible light. ALA-PDT is now popular for treating nonmelanoma skin cancer (NMSC), but can be ineffective for larger skin tumors, mainly due to inadequate production of PpIX. Work over the past two decades has shown that differentiation-promoting agents, including methotrexate (MTX), 5-fluorouracil (5FU) and vitamin D (Vit D) can be combined with ALA-PDT as neoadjuvants to promote tumor-specific accumulation of PpIX, enhance tumor-selective cell death, and improve therapeutic outcome. In this review, we provide a historical perspective of how the combinations of differentiation-promoting agents with PDT (cPDT) evolved, including Initial discoveries, biochemical and molecular mechanisms, and clinical translation for the treatment of NMSCs. For added context, we also compare the differentiation-promoting neoadjuvants with some other clinical PDT combinations such as surgery, laser ablation, iron-chelating agents (CP94), and immunomodulators that do not induce differentiation. Although this review focuses mainly on the application of cPDT for NMSCs, the concepts and findings described here may be more broadly applicable towards improving the therapeutic outcomes of PDT treatment for other types of cancers.

The Potential of Antibody Technology and Silver Nanoparticles for Enhancing Photodynamic Therapy for Melanoma

Melanoma is highly aggressive and is known to be efficient at resisting drug-induced apoptotic signals. Resection is currently the gold standard for melanoma management, but it only offers local control of the early stage of the disease. Metastatic melanoma is prone to recurrence, and has a poor prognosis and treatment response. Thus, the need for advanced theranostic alternatives is evident. Photodynamic therapy has been increasingly studied for melanoma treatment; however, it relies on passive drug accumulation, leading to off-target effects. Nanoparticles enhance drug biodistribution, uptake and intra-tumoural concentration and can be functionalised with monoclonal antibodies that offer selective biorecognition. Antibody–drug conjugates reduce passive drug accumulation and off-target effects. Nonetheless, one limitation of monoclonal antibodies and antibody–drug conjugates is their lack of versatility, given cancer’s heterogeneity. Monoclonal antibodies suffer several additional limitations that make recombinant antibody fragments more desirable. SNAP-tag is a modified version of the human DNA-repair enzyme, O6-alkylguanine-DNA alkyltransferase. It reacts in an autocatalytic and covalent manner with benzylguanine-modified substrates, providing a simple protein labelling system. SNAP-tag can be genetically fused with antibody fragments, creating fusion proteins that can be easily labelled with benzylguanine-modified payloads for site-directed delivery. This review aims to highlight the benefits and limitations of the abovementioned approaches and to outline how their combination could enhance photodynamic therapy for melanoma.

Identification and validation of four photodynamic therapy related genes inhibiting MAPK and inducing cell cycle alteration in squamous cell carcinoma

Introduction

Cutaneous squamous cell carcinoma (cSCC) is the second most common skin cancer, and photodynamic therapy (PDT) is a promising modality against cSCC. This study investigated the impact of PDT on the MAPK pathway and cell cycle alternation of cSCC as well as the related molecular mechanisms.

Method

Expressing mRNA profile data sets GSE98767, GSE45216, and GSE84758 were acquired from the GEO database. The functions of differently expressed genes (DEGs) were enriched by Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis. Least absolute shrinkage and selection operator (Lasso) analysis were used to establish a diagnosis model based on GSE98767. A correlation analysis and a protein–protein interaction (PPI) network were used to evaluate the relationship between cSCC-PDT-related genes and the MAPK pathway. Single-sample gene set enrichment analysis (ssGSEA) was performed on GSE98767 to estimate MAPK activation and cell cycle activity. Finally, the effect of MAPK activation on the cell cycle was explored in vitro.

Result

Four cSCC-PDT-related genes, DUSP6, EFNB2, DNAJB1, and CCNL1, were identified as diagnostic markers of cSCC, which were upregulated in cSCC or LC50 PDT-protocol treatment and negatively correlated with the MAPK promoter. Despite having a smaller MAPK activation score, cSCC showed higher cell cycle activity. The PDT treatment suppressed the G1 to G2/M phase in JNK overexpressed A431 cells.

Conclusion

CCNL1, DNAJB1, DUSP6, and EFNB2 were identified as potential PDT target genes in cSCC treatment, whose potential therapeutic mechanism was inhibiting the MAPK pathway and inducing cell cycle alternation.

Halofuginone enhances the anti-tumor effect of ALA-PDT by suppressing NRF2 signaling in cSCC

BACKGROUND

5-aminolevulinic acid-mediated PDT (ALA-PDT) has been used in a variety of skin diseases including cSCC (cutaneous squamous cell carcinoma). Halofuginone (HL) is a less-toxic febrifugine derivative and has inhibitory effects on a variety of cancer cells. For now, there are no published study focusing on the combination use of ALA-PDT with HL to improve clinical efficacy of cSCC.

OBJECTIVE

In this study, we will examine the effectiveness of combined treatment of ALA-PDT and HL in cSCC as well as its underlying mechanism.

METHODS

The human epidermoid carcinoma cell line SCL-1 was treated with ALA-PDT or/ and HL, and cell viability, cell migration, ROS production, apoptosis were evaluated by CCK-8, colony formation, scratch assay, DCFH-DA probe, flow cytometry, respectively. The protein expression of NRF2 signaling was examined by western blot.

RESULTS

HL strengthened ALA-PDT's inhibition of SCL-1 cell viability, migration, as well as NRF2 related β-catenin, p-Erk1/2, p-Akt and p-S6K1 expression. Overexpression of NRF2 conferred resistance to co-treatment's effects on c-Myc, Cyclin D1, Bcl-2, as well as cell proliferation. HL also strengthened ALA-PDT's inhibition of tumor volume in cSCC mouse model and elevated ROS generation of ALA-PDT.

CONCLUSION

HL enhances the anti-tumor effect of ALA-PDT in vitro and in vivo. HL has the potential to enhance the anti-tumor effect of ALA-PDT in cSCC via inhibiting NRF2 signaling.

Modified 5-aminolevulinic acid photodynamic therapy reduces pain and improves therapeutic effects in cutaneous squamous cell carcinoma mouse model

BACKGROUND AND OBJECTIVES

Conventional ALA-PDT (C-PDT) has limited efficacy in cutaneous squamous cell carcinoma (cSCC), and there is obvious pain during treatment, which limits its clinical application. We sought to modify photodynamic therapy into a more painless and effective treatment.

METHODS

We modified C-PDT by reducing the incubation time of the pro-sensitizer and increasing the light dose; we named this method modified ALA-PDT (M-PDT). We compared the pain response and curative effect between C-PDT and M-PDT in cSCC mouse models. Pain-related proteins were examined by western blot analysis and immunohistochemistry. Tumor progression-associated signaling pathways were analyzed by RNA-seq and western blot analysis. Reactive oxygen species (ROS) generation was measured with a ROS test kit and Microplate reader.

RESULTS

M-PDT greatly reduced pain during treatment. Interestingly, when the cSCC tumor volume increased to 150-200 mm³ , M-PDT almost completely eliminated the tumors, while C-PDT did not. The better curative effect of M-PDT might be due to the stronger suppression of the Stat3, Erk1/2, and mTOR signaling pathways. Moreover, flow cytometry demonstrated that M-PDT could recruit CD8⁺ T cells to inhibit cSCC progression. Further investigation determined that the different mechanisms of C-PDT and M-PDT were related to more ROS generation induced by M-PDT.

CONCLUSIONS

Our results suggest that M-PDT, which is more painless and effective than C-PDT, is expected to provide a solution for the treatment of cSCC.

PD-L1 blockade potentiates the antitumor effects of ALA-PDT and optimizes the tumor microenvironment in cutaneous squamous cell carcinoma

Immune checkpoint blockade (ICB) is a powerful oncologic treatment modality for a wide variety of human malignancies, but the patient response rate to this treatment remains low, especially in patients with cutaneous squamous cell carcinoma (cSCC). 5-Aminoleuvulinic acid-photodynamic therapy (ALA-PDT) is widely used to treat cancerous and precancerous skin diseases, but the value of ALA-PDT in the treatment of invasive cSCC is debatable. Our previous studies have shown that ALA-PDT can induce antitumor immune responses by promoting the immunogenic death of tumor cells. However, it is unclear whether ALA-PDT exerts synergistic effects with ICB in cSCC. Here, we report that PD-L1 blockade potentiates the antitumor effects of ALA-PDT both on primary and distant tumors, and optimizes the tumor microenvironment in cSCC. In this study, we first detected PD-L1 expression in patients with different grades of cSCC. Then we found the combination of anti-PD-L1 monoclonal antibody (mAb) and ALA-PDT killed tumor cells by apoptosis- and/or ferroptosis-mediated immunogenic cell death (ICD) and stimulated systemic immune response, as well as building the immunological memory response to prevent tumor recurrence. Furthermore, we found that combination therapy can be used to recruit tertiary lymphoid structure (TLS)-like intratumoral lymphoid aggregates, which may promote tumor-infiltrating lymphocyte (TIL)-mediated antitumor immunity. In summary, our work demonstrates that ICB treatment with an anti-PD-L1 antibody is a promising strategy that may potentiate the antitumor effects of ALA-PDT in cSCC.

Overcoming barriers in photodynamic therapy harnessing nano-formulation strategies

Photodynamic therapy (PDT) has been extensively investigated for decades for tumor treatment because of its non-invasiveness, spatiotemporal selectivity, lower side-effects, and immune activation ability. It can be a promising treatment modality in several medical fields, including oncology, immunology, urology, dermatology, ophthalmology, cardiology, pneumology, and dentistry. Nevertheless, the clinical application of PDT is largely restricted by the drawbacks of traditional photosensitizers, limited tissue penetrability of light, inefficient induction of tumor cell death, tumor resistance to the therapy, and the severe pain induced by the therapy. Recently, various photosensitizer formulations and therapy strategies have been developed to overcome these barriers. Significantly, the introduction of nanomaterials in PDT, as carriers or photosensitizers, may overcome the drawbacks of traditional photosensitizers. Based on this, nanocomposites excited by various light sources are applied in the PDT of deep-seated tumors. Modulation of cell death pathways with co-delivered reagents promotes PDT induced tumor cell death. Relief of tumor resistance to PDT with combined therapy strategies further promotes tumor inhibition. Also, the optimization of photosensitizer formulations and therapy procedures reduces pain in PDT. Here, a systematic summary of recent advances in the fabrication of photosensitizers and the design of therapy strategies to overcome barriers in PDT is presented. Several aspects important for the clinical application of PDT in cancer treatment are also discussed.

Comparative histological and immunohistochemical changes in recurrent nodular basal cell carcinoma after photodynamic therapy

Photodynamic therapy (PDT) is an established nonsurgical treatment for nodular basal cell carcinoma (nBCC). This study compares the clinical, histopathological, and immunohistochemical findings in recurrent nBCC after PDT versus pre-treatment (primary) nBCC. This retrospective study analyzed nodular BCCs treated with methyl aminolevulinate (MAL)-PDT at the Department of Dermatology, San Jorge Hospital (Huesca, Spain), between 2006 and 2015. Only cases in which both the primary and the recurring tumor were histologically confirmed were included in the analysis. Data on clinical, histological, and immunohistochemical variables were collected. The analysis included a total of 15 nBCCs resistant to 2 sessions of MAL-PDT: 11 (73.3%) were persistent BCCs (cure not achieved within 3 months of treatment) and 4 (26.7%) recurred in the first 2 years of follow-up. Subsequent biopsies of the 11 persistent nBCCs revealed that 9 (81.8%) retained the same histological type while the other 2 (18.2%) had another histological variant (micronodular and metatypical). Biopsy of the 4 recurring nBCCs revealed a persistent nodular subtype in all cases. MAL-PDT resulted in no changes in p53, survivin or β-catenin expression, and trend toward increased EGFR immunostaining. Histology revealed a trend toward a dense stroma without ulceration in recurrent nBCC after PDT. Trend toward increased EGFR immunostaining, and no changes in survivin (which remained negative or mildly positive) or β-catenin, (which remained moderately or our findings indicate that MAL-PDT does not induce histological or immunohistochemical changes that increase tumor aggressiveness.

Isolation and initial characterization of human glioblastoma cells resistant to photodynamic therapy

Glioblastoma is the most severe form of brain cancer. Despite multimodal therapy combining surgery, radiotherapy and chemotherapy, prognosis of patients is dismal. It has been observed that the surgical resection guided by photosensitizer fluorescence followed by photodynamic therapy (PDT) prolongs the average survival in patients with glioblastoma. The main problem with all oncological treatments, including PDT, is the presence of resistant cells. The objective of this study was to isolate and perform an initial characterization of human glioblastoma cells resistant to PDT employing methyl-5-aminolevulinic acid. We obtained resistant cells from the T98 G cell line. Resistant populations accumulated less photosensitizer, formed spheroids of higher number of cells, had higher tumorigenic capacity, and expressed higher mRNA levels of fibroblastic growth factor receptor (FGFR), epidermal growth factor receptor (EGFR) and β-platelet-derived growth factor receptor (βPDGFR) than parental cells. The studies of glioblastoma resistance to PDT would help to better understand the causes of tumor recurrence after PDT and to develop new therapeutic proposals in this field of oncology.

European Dermatology Forum guidelines on topical photodynamic therapy 2019 Part 1: treatment delivery and established indications - actinic keratoses, Bowen's disease and basal cell carcinomas

Topical photodynamic therapy (PDT) is a widely approved therapy for actinic keratoses, Bowen's disease (squamous cell carcinoma in situ), superficial and certain thin basal cell carcinomas. Recurrence rates when standard treatment protocols are used are typically equivalent to existing therapies, although inferior to surgery for nodular basal cell carcinoma. PDT can be used both as lesional and field therapies and has the potential to delay/reduce the development of new lesions. A protocol using daylight to treat actinic keratoses is widely practised, with conventional PDT using a red light after typically a 3-h period of occlusion employed for other superficial skin cancer indications as well as for actinic keratoses when daylight therapy is not feasible. PDT is a well-tolerated therapy although discomfort associated with conventional protocol may require pain-reduction measures. PDT using daylight is associated with no or minimal pain and preferred by patient. There is an emerging literature on enhancing conventional PDT protocols or combined PDT with another treatment to increase response rates. This guideline, published over two parts, considers all current approved and emerging indications for the use of topical PDT in dermatology, prepared by the PDT subgroup of the European Dermatology Forum guidelines committee. It presents consensual expert recommendations reflecting current published evidence.

Biomarkers of basal cell carcinoma resistance to methyl-aminolevulinate photodynamic therapy

Background

Methyl-aminolevulinate photodynamic therapy (MAL-PDT) is an excellent option for the treatment of basal cell carcinoma (BCC). However, up to 25% of cases are resistant to this treatment modality.

Objective

The aim of this study was to identify potential biomarkers of BCC response to MAL-PDT.

Material and methods

Clinical, histological, and immunohistochemical (p53, Ki-67, CD-31, COX2, β-catenin, EGFR, and survivin) variables were analyzed in a retrospective study of consecutive BCC patients treated with MAL-PDT at the San Jorge Hospital, Huesca, Spain between January 2006 and December 2015. To deepen on these markers, the effects on p53 and cyclin D1 expression, in vitro response to MAL-PDT of 2 murine BCC cell lines (ASZ and BSZ), was also evaluated.

Results

The retrospective study examined the response to MAL-PDT of 390 BCCs from 182 patients. The overall clinical response rate was 82.8%, with a mean follow-up time of 35.96 months (SD = 23.46). Immunohistochemistry revealed positive p53 in 84.6% of responders but only 15.4% of nonresponsive tumors (p = 0.011). Tumors with increased peripheral palisading of basal cell islands to immunostaining β-catenin responded poorly to PDT (p = 0.01). In line with our findings in patients, in vitro studies revealed a better response to PDT in the p53-positive ASZ cell line than the p53-negative BSZ cell line (p<0.01).

Multivariate analysis revealed that the following variables were significantly associated with response to PDT: age, nBCC, presence of peritumoral inflammatory infiltrate, and p53 immunopositivity. Patients with positive p53 immunostaining were 68.54 times more likely to achieve cure than p53-negative patients (CI95% 2.94–159.8)

Conclusion

Our finding suggest that certain clinicopathological and immunohistochemical variables, particularly p53 expression, may serve as indicators of BCC response to MAL-PDT, and thus facilitate the selection of patients who are most likely to benefit from this therapy.

Characterisation of resistance mechanisms developed by basal cell carcinoma cells in response to repeated cycles of Photodynamic Therapy

Photodynamic Therapy (PDT) with methyl-aminolevulinate acid (MAL-PDT) is being used for the treatment of Basal cell carcinoma (BCC), but recurrences have been reported. In this work, we have evaluated resistance mechanisms to MAL-PDT developed by three BCC cell lines (ASZ, BSZ and CSZ), derived from mice on a ptch+/- background and with or without p53 expression, subjected to 10 cycles of PDT (10thG). The resistant populations showed mesenchymal-like structure and diminished proliferative capacity and size compared to the parental (P) cells. The resistance was dependent on the production of the endogenous photosensitiser protoporphyrin IX in the CSZ cell line and on its cellular localisation in ASZ and BSZ cells. Moreover, resistant cells expressing the p53 gene presented lower proliferation rate and increased expression levels of N-cadherin and Gsk3β (a component of the Wnt/β-catenin pathway) than P cells. In contrast, 10thG cells lacking the p53 gene showed lower levels of expression of Gsk3β in the cytoplasm and of E-cadherin and β-catenin in the membrane. In addition, resistant cells presented higher tumorigenic ability in immunosuppressed mice. Altogether, these results shed light on resistance mechanisms of BCC to PDT and may help to improve the use of this therapeutic approach.

Unveiling Ga(III) phthalocyanine-a different photosensitizer in neuroblastoma cellular model

Phthalocyanines (Pc) and their metallated derivatives are strongly considered for photodynamic therapy (PDT) possessing unique properties as possible new photosensitizers (PS). We have used toxicological assessments, real-time monitoring of cellular impedance, and imagistic measurements for assessing the in vitro dark toxicity and PDT efficacy of Ga(III)-Pc in SHSy5Y neuroblastoma cells. We have established the non-toxic concentration range of Ga(III)-Pc, a compound which shows a high intracellular accumulation, with perinuclear distribution in confocal microscopy. By choosing Ga(III)Pc non-toxic dose, we performed in vitro experimental PDT hampering cellular proliferation. Our proposed Ga(III)-Pc could complete a future PS panel for neuroblastoma alternate therapy.

Present and future perspectives of photodynamic therapy for cutaneous squamous cell carcinoma

Cutaneous squamous cell carcinoma (SCC) is the second most common skin cancer. Surgery remains the main stay of treatment, but some patients are not eligible for surgery and, more importantly, lesions at critical sites need nonsurgical approaches for tissue preservation. In this context, photodynamic therapy (PDT) has been extensively studied as noninvasive or minimally invasive treatment, and studies have shown promising results in terms of safety, efficacy, and cosmetic outcome. Also, studies have proposed different mechanism for its efficacy. However, human studies demonstrating its efficacy are limited in terms of sample size and tumor depth of invasion. Good results are mainly seen in case reports of microinvasive SCC, which is defined as SCC limited to papillary dermis. This inadequacy is due to inadequate penetration of topically applied photosensitizers through keratinized tumor surfaces. To overcome these hurdles, pretreatment with lasers or microneedles and encapsulation of photosensitizers into nanoparticles have been tried. Hence, the present article will discuss studies that have demonstrated the efficacy and safety of PDT for cutaneous SCC, studies that have postulated the mechanism of action of PDT, agents that have been used as PDT enhancers, and finally, the recent use of adjuvant therapy in combination with PDT.

Thermal photodynamic therapy increases apoptosis and reactive oxygen species generation in cutaneous and mucosal squamous cell carcinoma cells

Thermal photodynamic therapy (PDT) is an emerging modality to optimize treatment of pre-cancerous squamous cell carcinoma (SCC) lesions, known as actinic keratoses. Thermal PDT involves heating the tissue, skin, or mucosa above normal skin temperature during 5-aminolevulinic (5-ALA) incubation and irradiating with blue light, which leads to cell apoptosis and reactive oxygen species (ROS) generation. To our knowledge, thermal PDT has not been studied for the treatment of cutaneous or mucosal SCC. We incubated two SCC cell lines with 5-ALA for 30 minutes at temperatures between 21 °C and 42 °C and then irradiated cells with 1000 seconds of blue light. We measured changes in apoptosis, necrosis, and ROS. At 36 °C, there was a dose-dependent increase in apoptosis and ROS generation. Thermal incubation of 5-ALA at 39° and 42 °C followed by blue light increased cell apoptosis and ROS generation compared to untreated control samples incubated at the same temperatures. Thermal PDT may represent a new treatment option for cutaneous and mucosal SCC cancer. Thermal PDT is associated with an increase in SCC cellular apoptosis and is associated with an upregulation in ROS. Clinical trials are required to determine optimal thermal PDT treatment parameters and efficacy for cutaneous and mucosal SCC.

An In Vitro Approach to Photodynamic Therapy

Photodynamic therapy (PDT) is a medical procedure that involves incubation of an exogenously applied photosensitizer (PS) followed by visible light photoactivation to induce cell apoptosis. The Federal Drug Administration has approved PDT for the treatment of actinic keratosis, and clinical guidelines recommend PDT as a treatment for certain non-melanoma skin cancers and acne vulgaris. PDT is an advantageous therapeutic modality as it is low cost, non-invasive, and associated with minimal adverse events and scaring. In the first step of PDT, a PS is applied and allowed to accumulate intracellularly. Subsequent light irradiation induces reactive oxygen species formation, which may ultimately lead to cell apoptosis, membrane disruption, mitochondrial damage, immune modulation, keratinocyte proliferation, and collagen turnover. Herein, we present an in vitro method to study PDT in an adherent cell line. This treatment protocol is designed to simulate PDT and may be adjusted to studying the use of PDT with various cell lines, photosensitizers, incubation temperatures, or photoactivation wavelengths. Squamous cell carcinoma cells were incubated with 0, 0.5, 1.0, and 2 mM 5-aminolevulinic acid (5-ALA) for 30 min and photoactivated with 417 nm blue light for 1,000 s. The primary outcome measure was apoptosis and necrosis, as measured by annexin-V and 7-aminoactinomycin D flow cytometry. There was a dose-dependent increase in cell apoptosis following thirty-minute incubation of 5-ALA. To achieve high inter-test validity, it is important to maintain consistent incubation and light parameters when performing in vitro PDT experiments. PDT is a useful clinical procedure and in vitro research may allow for the development of novel PSs, optimization of protocols, and new indications for PDT.

The influence of different illumination parameters on protoporphyrin IX induced cell death in squamous cell carcinoma cells

BACKGROUND

Topical photodynamic therapy (PDT) is a highly effective therapy especially for extended cancerized fields of the skin. Whenever extended fields are treated pain management is advisable. Light source mediated pain management can be performed by reducing fluence rates, as long as this does not compromise efficacy.

METHODS

Two squamous cell carcinoma cell lines (A431 and SCC-13) were subjected to in vitro PDT using two different ALA concentrations and synthesis intervals and protoporphyrin IX (PpIX) synthesis was assessed. Two total light doses (6 J/cm² and 37 J/cm²) were applied at three different fluence rates and cell viability was measured using the MTS-test.

RESULTS

Both cell lines synthetized PpIX at different kinetics. A431 cells produced a maximum 28.6 nmol/l PpIX, while SCC-13 reached only a production of 8.7 nmol/l. Illumination reduced cell viability depending on PpIX content and light dose. When a lower light dose (6 J/cm²) was applied, only the combination with the highest PpIX content was effective in A431 cells and no effect could be detected in SCC-13 cells. With a light dose of 37 J/cm², lower PpIX amounts became effective in A431 and cell death could be induced in SCC-13 cells. Light fluence rate had no differential effect in this setup.

CONCLUSIONS

In both, A431 and SCC-13 cells, total light dose is a key factor for photodynamic efficacy. Additionally, our results hint towards a threshold concentration of PpIX upon which a drastic loss of viability occurs. Light fluence rate in the analyzed range is not a limiting factor of photodynamic cytotoxicity. This may allow for the clinical implementation of low fluence rate protocols for pain management without compromising efficacy.

Early and Late Onset Side Effects of Photodynamic Therapy

Photodynamic Therapy (PDT) is a non-invasive treatment successfully used for neoplastic, inflammatory and infectious skin diseases. One of its strengths is represented by the high safety profile, even in elderly and/or immuno-depressed subjects. PDT, however, may induce early and late onset side effects. Erythema, pain, burns, edema, itching, desquamation, and pustular formation, often in association with each other, are frequently observed in course of exposure to the light source and in the hours/days immediately after the therapy. In particular, pain is a clinically relevant short-term complication that also reduces long-term patient satisfaction. Rare complications are urticaria, contact dermatitis at the site of application of the photosensitizer, and erosive pustular dermatosis. Debated is the relationship between PDT and carcinogenesis: the eruptive appearance of squamous cell carcinoma (SCC) in previously treated areas has been correlated to a condition of local and/or systemic immunosuppression or to the selection of PDT-resistant SCC. Here we review the literature, with particular emphasis to the pathogenic hypotheses underlying these observations.

Establishment and characterization of human osteosarcoma cells resistant to pyropheophorbide-α methyl ester-mediated photodynamic therapy

The present study was performed to establish and characterize new human osteosarcoma cell lines resistant to pyropheophorbide-α methyl ester-mediated photodynamic therapy (MPPa-PDT). MPPa-PDT-resistant cells are isolated from the human osteosarcoma MG63 and HOS cell lines and two resistant populations were finally acquired, including MG63/PDT and HOS/PDT. Cell Counting Kit-8 (CCK-8) assay was used to determine the MPPa-PDT, cisplatin (CDDP) resistance and proliferation of MG63, MG63/PDT, HOS and HOS/PDT cells. The intracellular ROS were analyzed using DCFH-DA staining. The colony formation, invasion and migration of parental and resistant cells were compared. FCM was employed to examine the cell cycle distribution, the apoptosis rate and the proportion of CD133⁺ cells. The fluorescence intensity of intracellular MPPa was observed by fluorescence microscopy and quantified using microplate reader. The protein levels were assessed by western blotting (WB). Compared with two parental cells, MG63/PDT and HOS/PDT were 1.67- and 1.61-fold resistant to MPPa-PDT, respectively, and also exhibited the resistance to CDDP. FCM assays confirmed that both MG63/PDT and HOS/PDT cells treated with MPPa-PDT displayed a significantly lower apoptosis rate in comparison with their corresponding parental cells. The expression of apoptosis-related proteins (i.e. cleaved-caspase 3 and cleaved-PARP), intracellular ROS and the antioxidant proteins (HO-1 and SOD1) in MG63/PDT and HOS/PDT cells was also lower than that in parental cells. Both MG63/PDT and HOS/PDT cells exhibited changes in proliferation, photosensitizer absorption, colony formation, invasion, migration and the cell cycle distribution as compared to MG63 and HOS cells, respectively. Compared to MG63 and HOS cells, both resistant cell lines had a higher expression of CD133, survivin, Bcl-xL, Bcl-2, MRP1, MDR1 and ABCG2, but a lower expression of Bax. The present study successfully established two resistant human osteosarcoma cell lines which are valuable to explore the resistance-related mechanisms and the approaches to overcome resistance.

Photodynamic Therapy and Non-Melanoma Skin Cancer

Non-melanoma skin cancer (NMSC) is the most common malignancy among the Caucasian population. Photodynamic therapy (PDT) is gaining popularity for the treatment of basal cell carcinoma (BCC), Bowen's disease (BD) and actinic keratosis (AK). A topical or systemic exogenous photosensitiser, results in selective uptake by malignant cells. Protoporphyrin IX (PpIX) is produced then activated by the introduction of a light source. Daylight-mediated MAL (methyl aminolaevulinate) PDT for AKs has the advantage of decreased pain and better patient tolerance. PDT is an effective treatment for superficial BCC, BD and both individual and field treatment of AKs. Excellent cosmesis can be achieved with high patient satisfaction. Variable results have been reported for nodular BCC, with improved outcomes following pretreatment and repeated PDT cycles. The more aggressive basisquamous, morphoeic infiltrating subtypes of BCC and invasive squamous cell carcinoma (SCC) are not suitable for PDT. Prevention of "field cancerization" in organ transplant recipients on long-term immunosuppression and patients with Gorlin syndrome (naevoid basal cell carcinoma syndrome) is a promising development. The optimisation of PDT techniques with improved photosensitiser delivery to target tissues, new generation photosensitisers and novel light sources may expand the future role of PDT in NMSC management.

A photodynamic bifunctional conjugate for prostate cancer: an in vitro mechanistic study

Photodynamic therapy (PDT) has drawn considerable attention for its efficacy against certain types of cancers. It shows however limits in the case of deep cancers, favoring tumor recurrence under suboptimal conditions. More insight into the molecular mechanisms of PDT-induced cytotoxicity and cytoprotection is essential to extend and strengthen this therapeutic modality. As PDT induces iNOS/NO in both tumor and microenvironment, we examined the role of nitric oxide (NO) in cytotoxicity and cytoprotection. Our findings show that NO mediates its cellular effects by acting on the NF-κB/YY1/RKIP loop, which controls cell growth and apoptosis. The cytoprotective effect of PDT-induced NO is observed at low NO levels, which activate the pro-survival/anti-apoptotic NF-κB and YY1, while inhibiting the anti-survival/pro-apoptotic and metastasis suppressor RKIP. In contrast, high PDT-induced NO levels inhibit NF-κB and YY1 and induce RKIP, resulting in significant anti-tumor activity. These findings reveal a critical role played by NO in PDT and suggest that the use of bifunctional PDT agents composed of a photosensitizer and a NO-donor could enhance the photo-treatment effect. A successful application of NO in anticancer therapy requires control of its concentration in the target tissue. To address this issue we propose as PDT agent, a bimolecular conjugate called DR2, composed of a photosensitizer (Pheophorbide a) and a non-steroidal anti-androgen molecule capable of releasing NO under the exclusive control of light. The mechanism of action of DR2 in prostate cancer cells is reported and discussed.

Molecular mechanisms of OLIG2 transcription factor in brain cancer

Oligodendrocyte lineage transcription factor 2 (OLIG2) plays a pivotal role in glioma development. Here we conducted a comprehensive study of the critical gene regulatory networks involving OLIG2. These include the networks responsible for OLIG2 expression, its translocation to nucleus, cell cycle, epigenetic regulation, and Rho-pathway interactions. We described positive feedback loops including OLIG2: loops of epigenetic regulation and loops involving receptor tyrosine kinases. These loops may be responsible for the prolonged oncogenic activity of OLIG2. The proposed schemes for epigenetic regulation of the gene networks involving OLIG2 are confirmed by patient survival (Kaplan-Meier) curves based on the cancer genome atlas (TCGA) datasets. Finally, we elucidate the Coherent-Gene Modules (CGMs) networks-framework of OLIG2 involvement in cancer. We showed that genes interacting with OLIG2 formed eight CGMs having a set of intermodular connections. We showed also that among the genes involved in these modules the most connected hub is EGFR, then, on lower level, HSP90 and CALM1, followed by three lower levels including epigenetic genes KDM1A and NCOR1. The genes on the six upper levels of the hierarchy are involved in interconnections of all eight CGMs and organize functionally defined gene-signaling subnetworks having specific functions. For example, CGM1 is involved in epigenetic control. CGM2 is significantly related to cell proliferation and differentiation. CGM3 includes a number of interconnected helix-loop-helix transcription factors (bHLH) including OLIG2. Many of these TFs are partially controlled by OLIG2. The CGM4 is involved in PDGF-related: angiogenesis, tumor cell proliferation and differentiation. These analyses provide testable hypotheses and approaches to inhibit OLIG2 pathway and relevant feed-forward and feedback loops to be interrogated. This broad approach can be applied to other TFs.

Reversal of the Migratory and Invasive Phenotype of Ras-Transfected Mammary Cells by Photodynamic Therapy Treatment

Photodynamic therapy (PDT) is a non-thermal technique for inducing tumor damage following administration of a light-activated photosensitizing drug (PS). In a previous work we found that PDT induces cytoskeleton changes in HB4a-Ras cells (human mammary breast carcinoma HB4a cells transfected with the RAS oncogene). In the present work we have studied the migratory and invasive features and the expression of proteins related to these processes on HB4a-Ras cells after three successive cycles of PDT using different PSs: 5-aminolevulinic acid (ALA), Verteporfin (Verte), m-tetrahydroxyphenylchlorin (m-THPC), and Merocyanine 540 (MC). A slight (1.25- to 2-fold) degree of resistance was acquired in cell populations subjected to the three successive PDT treatments. However, complete cell killing was achieved after a light dose increase. Regardless of the PS employed, all the PDT-treated populations had shorter stress fibres than the untreated control HB4a-Ras cells, and the number of dorsal stress fibres was decreased in the PDT-treated populations. E-Cadherin distribution, which was already aberrant in HB4a-Ras cells, became even more diffuse in the PDT-treated populations, though its expression was increased in some of them. The strong migratory and invasive ability of HB4a-Ras cells in vitro was impaired in all the PDT-treated populations, with a behavior that was similar to the parental non-tumoral HB4a cells. MMP-2 and -9 metalloproteinase activities were also impaired in the PDT-treated populations. The evidence presented herein suggests that the cells surviving PDT would be less metastatic than the initial population. These findings encourage the use of PDT in combination with other treatments such as intraoperative or post-surgery therapeutic procedures. J. Cell. Biochem. 118: 464-477, 2017. © 2016 Wiley Periodicals, Inc.

Resistance of Nonmelanoma Skin Cancer to Nonsurgical Treatments. Part II: Photodynamic Therapy, Vismodegib, Cetuximab, Intralesional Methotrexate, and Radiotherapy

A wide range of treatments is now available for nonmelanoma skin cancer, including 5-fluorouracil, ingenol mebutate, imiquimod, diclofenac, photodynamic therapy, methotrexate, cetuximab, vismodegib, and radiotherapy. All are associated with high clinical and histologic response rates. However, some tumors do not respond due to resistance, which may be primary or acquired. Study of the resistance processes is a broad area of research that aims to increase our understanding of the nature of each tumor and the biologic features that make it resistant, as well as to facilitate the design of new therapies directed against these tumors. In this second article, having covered the topical treatments of nonmelanoma skin cancer, we review resistance to other nonsurgical treatments, such as monoclonal antibodies against basal and squamous cell carcinomas, intralesional chemotherapy, photodynamic therapy, and radiotherapy.

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.

The role of photodynamic therapy in overcoming cancer drug resistance

Many modalities of cancer therapy induce mechanisms of treatment resistance and escape pathways during chronic treatments, including photodynamic therapy (PDT). It is conceivable that resistance induced by one treatment might be overcome by another treatment. Emerging evidence suggests that the unique mechanisms of tumor cell and microenvironment damage produced by PDT could be utilized to overcome cancer drug resistance, to mitigate the compensatory induction of survival pathways and even to re-sensitize resistant cells to standard therapies. Approaches that capture the unique features of PDT, therefore, offer promising factors for increasing the efficacy of a broad range of therapeutic modalities. Here, we highlight key preclinical findings utilizing PDT to overcome classical drug resistance or escape pathways and thus enhance the efficacy of many pharmaceuticals, possibly explaining the clinical observations of the PDT response to otherwise treatment-resistant diseases. With the development of nanotechnology, it is possible that light activation may be used not only to damage and sensitize tumors but also to enable controlled drug release to inhibit escape pathways that may lead to resistance or cell proliferation.

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.

Upregulation of ATG3 contributes to autophagy induced by the detachment of intestinal epithelial cells from the extracellular matrix, but promotes autophagy-independent apoptosis of the attached cells

Detachment of nonmalignant intestinal epithelial cells from the extracellular matrix (ECM) triggers their growth arrest and, ultimately, apoptosis. In contrast, colorectal cancer cells can grow without attachment to the ECM. This ability is critical for their malignant potential. We found previously that detachment-induced growth arrest of nonmalignant intestinal epithelial cells is driven by their detachment-triggered autophagy, and that RAS, a major oncogene, promotes growth of detached cells by blocking such autophagy. In an effort to identify the mechanisms of detachment-induced autophagy and growth arrest of nonmalignant cells we found here that detachment of these cells causes upregulation of ATG3 and that ATG3 upregulation contributes to autophagy and growth arrest of detached cells. We also observed that when ATG3 expression is artificially increased in the attached cells, ATG3 promotes neither autophagy nor growth arrest but triggers their apoptosis. ATG3 upregulation likely promotes autophagy of the detached but not that of the attached cells because detachment-dependent autophagy requires other detachment-induced events, such as the upregulation of ATG7. We further observed that those few adherent cells that do not die by apoptosis induced by ATG3 become resistant to apoptosis caused by cell detachment, a property that is critical for the ability of normal epithelial cells to become malignant. We conclude that cell-ECM adhesion can switch ATG3 functions: when upregulated in detached cells in the context of other autophagy-promoting events, ATG3 contributes to autophagy. However, when overexpressed in the adherent cells, in the circumstances not favoring autophagy, ATG3 triggers apoptosis.