Impact of UVR Exposure Pattern on Squamous Cell Carcinoma-A Dose-Delivery and Dose-Response Study in Pigmented Hairless Mice

Changes in mouse epidermal DNA methylation during development of squamous cell carcinoma in response to UVR

Squamous cell carcinoma (SCC) is a common skin cancer, often caused by exposure to ultraviolet radiation (UVR). Recent studies have shown that changes in DNA methylation play a crucial role in the development of cancers. However, methylation patterns of SCC are not well characterised. Identifying biomarkers for the risk of developing SCC could be helpful for early detection and diagnosis and can potentially improve treatment and prevention strategies. This study aimed to investigate methylation changes in the epidermis of mice exposed to UVR for 24 weeks. We examined the DNA methylation levels of 260 199 CpGs using the Illumina Infinium Mouse Methylation BeadChip and studied the epidermis of UVR-exposed and unexposed mice every 4 weeks for 24 weeks (n = 39). We identified CpGs with large differences in methylation levels (β-values) between UVR-exposed and unexposed mice. We also observed differences in the epigenetic age of these mice. We identified CpGs in Rev, Ipmk, Rad51b, Fgfr2, Fgfr3 and Ctnnb1 that may serve as potential biomarkers for SCC risk and could be helpful for the early detection and prevention of SCC. Further investigations are necessary to determine the biological functions and clinical significance of these CpGs.

Incidence of Nonmelanoma Skin Cancers in Alberta, Canada, From 2007 to 2018

BACKGROUND

Nonmelanoma skin cancer (NMSC) is the most common malignancy affecting Caucasian populations and has been seeing steady increases in incidence globally for decades. Our previous study (from Alberta, Canada) had shown a plateau in the incidence rates for NMSC. This contrasts with data from other regions within Canada and throughout the world that indicated a continued increase in incidence rates of NMSCs.

OBJECTIVES

The objective of this study was to provide an update on the trends in incidence of NMSC in Alberta, Canada, from 2007 to 2018.

METHODS

A retrospective analysis of patients from Alberta diagnosed with NMSC from 2007 to 2018 inclusive was conducted with data retrieved from Alberta Cancer Registry. Sex-, age-, anatomical location-, NMSC subtype-, stage-specific incidence rates and trends were examined.

RESULTS

From 2007 to 2018, overall incidence rates of NMSC increased by 36%. Invasive squamous cell carcinoma (SCC) and in situ SCC demonstrated the most significant increase, invasive SCC [annual percentage change (APC) 3.48, P = .014] and in situ SCC (APC 5.61, P = .0001). In addition, we were able to determine that females had the most significant increases in NMSC incidence rates from 2007 to 2018 particularly invasive SCC (APC 3.03, P = <.0001) and in situ SCC (APC 5.08, P = <.0001).

CONCLUSIONS

After initial levelling of NMSC incidence in Alberta in the early part of 21st century, the incidence of NMSC continues to increase over the past decade. The reasons for this change are not clear and likely multifactorial.

Oral phytochemicals as photoprotectants in UVR exposed hairless mice: A study of hesperidin methyl chalcone, phloroglucinol, and syringic acid

Ultraviolet radiation is the primary risk factor for keratinocyte carcinoma. Because of increasing incidence rates, new methods of photoprotection must be explored. Oral supplementation with photoprotective compounds presents a promising alternative. Phytochemical compounds like hesperidin methyl chalcone, phloroglucinol, and syringic acid are particularly of interest because of their antioxidant properties. Our primary outcome was to evaluate the effects of oral phytochemicals on photocarcinogenesis with time until tumour onset as the primary endpoint. A total of 125 hairless C3.Cg-Hrhr/TifBom Tac mice were randomised to receive tap water supplemented with either 100 mg/kg hesperidin methyl chalcone, phloroglucinol, or syringic acid, 600 mg/kg nicotinamide as a positive control, or no supplementation. The mice were irradiated with 3.5 standard erythema doses thrice weekly to induce photocarcinogenesis. Supplementation with the phytochemicals phloroglucinol and syringic acid and nicotinamide delayed tumour onset from a median of 140 days to 151 (p = 0.036), 157 days (p = 0.02), and 178 (p = 2.7·10-5), respectively. Phloroglucinol and nicotinamide supplementation reduced tumour number. Nicotinamide increased UV-induced pigmentation and reduced oedema formation, while phloroglucinol supplementation reduced epidermal thickness. These results indicate that oral supplementation with phloroglucinol and syringic acid protects against photocarcinogenesis in hairless mice, but not to the same extent as nicotinamide.

Skin Cancer Prevention across the G7, Australia and New Zealand: A Review of Legislation and Guidelines

Incidence rates of melanoma and keratinocyte skin cancers have been on the rise globally in recent decades. While there has been a select focus on personal sun protection awareness, to our knowledge, there is a paucity of legislation in place to help support citizens' efforts to protect themselves from the harmful effects of ultraviolet radiation (UVR). Given this, we conducted a comprehensive review of legislation and guidelines pertaining to a variety of sun protection-related topics in countries of the Group of Seven (G7), Australia and New Zealand. Australia was the only country to have banned tanning beds for individuals of all ages, while other select countries have instituted bans for minors. In workplace policy, there is very little recognition of the danger of occupational UVR exposure in outdoor workers, and thus very few protective measures are in place. With regard to sports and recreation, certain dermatological/professional associations have put forward recommendations, but no legislation was brought forward by government bodies outside of Australia and New Zealand. With regard to youth, while there are various guidelines and frameworks in place across several countries, adherence remains difficult in the absence of concrete legislation and standardization of procedures. Finally, only Australia and a few select jurisdictions in the United States have implemented sales tax exemptions for sunscreen products. In light of our findings, we have made several recommendations, which we anticipate will help reduce the rates of melanoma and keratinocyte cancers in years to come. However, minimizing UVR exposure is not without risk, and we, therefore, suggest the promotion of vitamin D supplementation in conjunction with sun protective practices to limit potential harm.

Few X-ray and PUVA treatments accelerate photocarcinogenesis in hairless mice

PUVA is a treatment that combines oral methoxypsoralen (8-MOP) with ultraviolet radiation A (UVA). It is used for severe psoriasis and the early stages of T-cell lymphoma. X-rays are an effective treatment for skin cancers. Both treatments are in higher doses used to treat skin malignancies and simultaneously increase the risk of keratinocyte cancer. The main objective of this study was to test whether a few PUVA or X-ray treatments could delay the development of ultraviolet radiation (UVR)-induced skin tumors in a well-established hairless mouse model. Three groups of immunocompetent mice (total, N = 75) were included in the study. All groups were UVR-exposed during the study period. In addition, one group was treated with PUVA and another group was treated with X-rays at days 45, 52, 90 and 97. A control group was treated with UVR only. We recorded when the first, second and third skin tumors were induced in each mouse. Skin tumors developed significantly earlier in both the PUVA and X-ray groups (median, 188 days) than in the control mice (median, 215 days; p < 0.001). Therefore, a few X-ray and PUVA treatments both significantly accelerated the development of skin tumors in hairless mice, compared to UVR controls. Neither treatment showed a delay of UVR-induced skin tumors and caution should be exercised before applying these treatments to sun-damaged skin.

A Skin Cancer Prophylaxis Study in Hairless Mice Using Methylene Blue, Riboflavin, and Methyl Aminolevulinate as Photosensitizing Agents in Photodynamic Therapy

The high incidence of sunlight-induced human skin cancers reveals a need for more effective photosensitizing agents. In this study, we compared the efficacy of prophylactic photodynamic therapy (PDT) when methylene blue (MB), riboflavin (RF), or methyl aminolevulinate (MAL) were used as photosensitizers. All mice in four groups of female C3.Cg/TifBomTac hairless immunocompetent mice (N = 100) were irradiated with three standard erythema doses of solar-simulated ultraviolet radiation (UVR) thrice weekly. Three groups received 2 × 2 prophylactic PDT treatments (days 45 + 52 and 90 + 97). The PDT treatments consisted of topical administration of 16% MAL, 20% MB, or 20% RF, and subsequent illumination that matched the photosensitizers’ absorption spectra. Control mice received no PDT. We recorded when the first, second, and third skin tumors developed. The pattern of tumor development after MB-PDT or RF-PDT was similar to that observed in irradiated control mice (p > 0.05). However, the median times until the first, second, and third skin tumors developed in mice given MAL-PDT were significantly delayed, compared with control mice (256, 265, and 272 vs. 215, 222, and 230 days, respectively; p < 0.001). Only MAL-PDT was an effective prophylactic treatment against UVR-induced skin tumors in hairless mice.

Tumor Clearance and Immune Cell Recruitment in UV-Induced Murine Squamous Cell Carcinoma Exposed to Ablative Fractional Laser and Imiquimod Treatment

BACKGROUND AND OBJECTIVES

Keratinocyte carcinoma (KC) is the most common cancer worldwide, and squamous cell carcinoma (SCC) is the second most frequent subtype. Ablative fractional laser (AFL)-assisted drug delivery significantly enhances the uptake of topically applied drugs. The objective of this study was to assess tumor response and perform a descriptive characterization of the local recruitment of immune cells and systemic immune mediator levels in an ultraviolet radiation (UVR)-induced murine SCC model after AFL treatment alone and combined with topical imiquimod.

STUDY DESIGN/MATERIALS AND METHODS

Immunocompetent hairless mice (C3·Cg/TifBomTac, n = 74) were irradiated with solar-simulated UVR until 3-mm SCCs developed. The mice were divided into four interventional groups: AFL alone, AFL + imiquimod, imiquimod alone, and untreated SCC controls. AFL was given as a single treatment, whereas imiquimod was applied daily until the mice were euthanized on Days 0, 2, 7, or 14. SCCs were photographed and measured (mm) to assess the therapeutic response. Skin samples were processed for histopathological and immunohistochemical analyses, as well as for flow cytometry. Cytokine expression changes in sera were analyzed using ELISpot cytokine arrays.

RESULTS

Treatment of mouse SCCs with AFL + imiquimod induced the most robust immune cell infiltration and the greatest proportion of tumor clearance compared to other interventions. Early innate immune cell infiltration was induced by AFL + imiquimod treatment as the number of neutrophils and macrophages had increased fourfold within 2 days of treatment initiation compared with untreated SCC control mice (P < 0.05). AFL treatment alone had a more limited effect, with a fourfold increase in neutrophils (P < 0.05) but no significant increase in the number of macrophages. Correspondingly, treatment with AFL + imiquimod had the greatest effects on the adaptive immune cell recruitment: CD4⁺ T-helper cells increased threefold at Day 7 compared with untreated SCCs (P = 0.0001) and, notably, cytotoxic CD8⁺ T cells increased 14-fold at Day 14 (P = 0.0112). In addition, FOXP3⁺ regulatory T cells (Tregs) increased 14-fold at Day 7 (P = 0.0026), suggesting the resolution of the inflammatory infiltration. AFL treatment alone induced a moderate immune cell infiltration (a twofold increase in CD4⁺ T-helper cells, P = 0.0200; a threefold increase in CD8⁺ T cells, P = 0.0100; and a 14-fold increase in FOXP3⁺ Tregs at Day 14, P = 0.0021), whereas imiquimod alone did not significantly increase cell counts. AFL + imiquimod treatment increased CXCL12 serum levels threefold at Day 14 (P = 0.0200).

CONCLUSION

AFL treatment alone and in combination with imiquimod induces substantial tumor clearance associated with local recruitment of innate and adaptive immune cells in UVR-induced murine SCCs. These results may provide a basis for new immunotherapeutic approaches to KC treatment.