Photocarcinogenesis of topical tazarotene and isotretinoin alone and in combination with valproic acid in hairless mice

Keratinocyte Carcinoma and Photoprevention: The Protective Actions of Repurposed Pharmaceuticals, Phytochemicals and Vitamins

Simple Summary

Keratinocyte carcinoma is the most common type of cancer. Sun exposure and ultraviolet radiation are significant contributors to the development of carcinogenesis, mediated by DNA damage, increased oxidative stress, inflammation, immunosuppression and dysregulated signal transduction. Photoprevention involves using different compounds to delay or prevent ultraviolet radiation-induced skin cancer. In this review, we look at new avenues for systemic photoprevention that are based on pharmaceuticals, plant-derived phytochemicals and vitamins. We also investigate the mechanisms underlying these strategies for preventing the onset of carcinogenesis.

Abstract

Ultraviolet radiation (UVR) arising from sun exposure represents a major risk factor in the development of keratinocyte carcinomas (KCs). UVR exposure induces dysregulated signal transduction, oxidative stress, inflammation, immunosuppression and DNA damage, all of which promote the induction and development of photocarcinogenesis. Because the incidence of KCs is increasing, better prevention strategies are necessary. In the concept of photoprevention, protective compounds are administered either topically or systemically to prevent the effects of UVR and the development of skin cancer. In this review, we provide descriptions of the pathways underlying photocarcinogenesis and an overview of selected photoprotective compounds, such as repurposed pharmaceuticals, plant-derived phytochemicals and vitamins. We discuss the protective potential of these compounds and their effects in pre-clinical and human trials, summarising the mechanisms of action involved in preventing photocarcinogenesis.

[UV phototherapy : UV phototherapy and photodiagnostics-a practical overview]

UV phototherapy is an essential and efficient therapeutic option in the treatment of dermatological diseases. It is an integral part of multiple guidelines and maintains its high clinical significance despite the development of new therapeutic options for systemic treatment. Due to the difficult revenue situation, the market for ready-to-use products of psoralen and UV therapy devices is constantly changing.

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

Cumulative lifetime ultraviolet radiation (UVR) is an important factor in the development of squamous cell carcinoma. This study examines the impact of UVR exposure pattern on tumor development. Hairless C3.Cg/TifBomTac immunocompetent pigmented mice (n = 351) were irradiated with 12 standard erythema doses (SED)/week, given as 2 SED ×6, 3 SED ×4, 4 SED ×3, or 6 SED ×2 (dose-delivery study) or 0, 0.6, 1.2, 2, 3 or 4 SED ×3/week (dose-response study). All mice were irradiated until development of 3 tumors of 4 mm each. Pigmentation was measured once monthly. In the dose-delivery study, the median time until tumor development was independent of dose fractions. In the dose-response study, higher UVR doses resulted in faster tumor appearance. When the weekly UVR dose was decreased from 12 to 6 SED, the cumulative UVR dose needed for tumor development was reduced by 40%. In conclusion, delivery schedules of a fixed weekly UVR dose did not affect tumor development. When using different weekly UVR doses, longer time to tumor development was observed using lower UVR doses. Lower weekly UVR doses however resulted in lower cumulative UVR doses to induce tumors in hairless pigmented mice.

Topical nutlin-3a does not decrease photocarcinogenesis induced by simulated solar radiation in hairless mice

BACKGROUND

Nutlin-3a increases p53 levels after UVB radiation, which could result in a decrease in DNA damage and thus lead to a lower risk of non-melanoma skin cancer. Especially, organ transplant recipients might derive benefit from such a topical formulation with an active ingredient to prevent DNA damage.

PURPOSE

To investigate whether topical nutlin-3a can decrease photocarcinogenesis induced by simulated solar radiation.

METHODS

72 hairless C3.Cg/TifBomTac mice were treated 3 days/week topically with 100 μl nutlin-3a (9 mM) [Groups 1 and 3 (120 days)) or 100 μl vehicle (Group 2). Three hours later, all mice were exposed to simulated solar radiation (a radiometric equivalent of three standard erythema dose units).

RESULTS

The median time to tumours did not differ between the mice treated with nutlin-3a and with the vehicle. The median time to the first and second tumours did not differ between 'nutlin-3a-120 days' and vehicle-treated mice, but there was a small significant difference in the median time to the third tumour (211 vs. 196 days, P = 0.043). However, after Bonferroni correction, there was no difference at all.

CONCLUSION

Nutlin-3a had no reductive effect on photocarcinogenesis and we do not believe in nutlin-3a as a potential drug against DNA damage in a topical formulation for organ transplant patients.

Neonatal mice do not have increased sensitivity to induction of squamous cell carcinomas

BACKGROUND

Squamous cell carcinoma (SCC) is linked with the lifelong cumulative effect of ultraviolet radiation (UVR). In contrast, epidemiological data have shown that sunburn in childhood is a stronger risk factor for cutaneous malignant melanoma than continuous UVR, indicating a higher carcinogenic sensitivity early in life.

METHODS

We investigated how a high neonatal dose of UVR affects the development of SCC in mice irradiated later in life. We used simulated solar radiation (sun) and solarium radiation (solarium). Ninety-nine C3.Cg/TifBomTac-immunocompetent hairless mice received 0, 25 or 35 standard erythema doses (SED) UVR when they were 4 days old followed by 4 SED sun or 4 SED solarium three times/weekly from 9 weeks of age.

RESULTS

Tumours developed faster in mice treated with 35 SED UVR + 4 SED sun compared with 4 SED sun, but no change was observed in the cumulative dose required to achieve tumours. Tumours also developed faster in mice treated with 35 SED UVR + 4 SED solarium compared with 4 SED solarium, and a difference was also observed in the cumulative dose required to achieve tumours. If the Skin Cancer Utrecht-Philadelphia-murine spectrum was used to weigh the delivered irradiance instead of the International Commission on Illumination erythema action spectrum, tumours developed after the same accumulated dose.

CONCLUSION

In conclusion, this study does not indicate increased sensitivity to induction of SCC early in life.

Oral epithelial dysplasia and squamous cell carcinoma following allogeneic hematopoietic stem cell transplantation: clinical presentation and treatment outcomes

Background

Late complications of allogeneic hematopoietic stem cell transplantation (HSCT) include a risk of secondary malignancies, including oral cancers. Optimization of best clinical practices for early diagnosis and treatment of oral premalignant or malignant lesions requires an assessment of potential predisposing risk factors as well as treatment outcomes.

Methods

The medical records of patients who developed oral epithelial dysplasia (OED) and oral squamous cell carcinoma (OSCC) following allogeneic HSCT were reviewed. Data on demographics, HSCT course, chronic graft-versus-host disease (cGVHD), smoking and alcohol consumption, oral lesion characteristics, mode of therapy and clinical outcome were recorded; landmark survival was calculated.

Results

Twenty-six patients with OED (n = 8) and OSCC (n = 18) were identified with a median follow-up of 26.5 and 21.5 months, respectively. Premalignant and malignant oral lesions were diagnosed at a median time of 2.5 and 8 years after HSCT, respectively. Chronic GVHD was present in 96% of patients and of these, 96% had oral involvement. Multifocal oral cancer was found in 28% of cases, and localized recurrence was observed in 44% of cases. Five-year overall survival was 75% and 70% for OED and OSCC, respectively.

Conclusions

These results suggest that oral cGVHD may be considered a potential risk factor for the development of OSCC following allogeneic HSCT. The observation that oral cancers were frequently multifocal and recurred locally supports the concept of field cancerization and suggests that these cancers may be more aggressive compared with the non-HSCT population. Vigilant follow-up and coordination of care between hematologists and oral health specialists are critical to minimize morbidity and mortality.

High death rate in mice treated topically with diclofenac

Recently, 3% diclofenacnatrium gel (diclofenac) was introduced for the treatment of actinic keratoses. Data on photocarcinogenesis of topical diclofenac are limited, and we wished to investigate whether topical diclofenac can accelerate photocarcinogenesis using simulated solar radiation (SSR). Diclofenac was applied topically on the backs of hairless, female, C3.Cg/TifBomTac immunocompetent mice three times weekly followed by ultraviolet radiation (2, 3, or 4 Standard Erythema Dose) until death. There was a significant difference in survival between diclofenac-treated groups and control groups (P<0.0001). Physical examination of the diclofenac-treated mice showed peptic ulcers, oesophageal ulcers and gastrointestinal bleeding. To be sure that these side effects were not caused by topical absorption without oral ingestion, one group of mice was wearing Elizabethan collars and was single housed. Nevertheless, these mice also had gastrointestinal side effects. We terminated the experiment after 151 days when only a few mice remained in the diclofenac-treated groups and most had symptoms of discomfort and weight loss. No tumors developed as a result of the early termination.

Photosensitizing medication use and risk of skin cancer

BACKGROUND

Many commonly used medications, including both medications for long-term (daily) use and short-term use (treatment courses of finite duration), have photosensitizing properties. Whether use of these medications affects skin cancer risk, however, is unclear.

METHODS

Using a cohort of all Danish residents ≥15 years old in 1995 to 2006 (n = 4,761,749) and information from Danish national registers, we examined associations between use of photosensitizing medications and risk of basal cell carcinoma, cutaneous malignant melanoma, Merkel cell carcinoma, and squamous cell carcinoma.

RESULTS

Users of only 2 of 19 medications for long-term use (methyldopa and furosemide) had both a ≥20% increased risk of skin cancer (compared with nonusers) and an increase in risk with increasing duration of use; these effects were limited to basal cell carcinoma and squamous cell carcinoma, respectively. In contrast, 8 of 10 medications for short-term use were associated with both a ≥20% increased risk of skin cancer and an increase in risk with increasing use for at least one of the four cancers.

CONCLUSION

We found little evidence of an increased risk of skin cancer among users of photosensitizing medications for long-term daily use, but could not rule out the possibility that users of some photosensitizing medications for short-term use may have an increased risk of skin cancer.

IMPACT

Previous studies have been limited to specific medication types (e.g., antidiuretics). Our study examined the effect of a wide range of photosensitizing medications on skin cancer risk and suggests that future work should focus on photosensitizing medications for short-term use.

Reduced ultraviolet irradiation delays subsequent squamous cell carcinomas in hairless mice

BACKGROUND

Ultraviolet (UV) radiation induces non-melanoma skin cancer (NMSC), and UV prophylaxis is essential to prevent skin cancer. It is unclear whether patients diagnosed with squamous cell carcinomas (SCC) may benefit from reduced UV exposures in terms of delaying the development of new tumors. The objective was to evaluate the significance of discontinued or reduced UV exposure for the development of subsequent skin tumors.

METHODS

Seven groups of mice (n = 175) were irradiated with UV doses of 2 and 4 standard erythema doses (SED) that were continued, reduced or discontinued at the time of appearance of the first skin tumor.

RESULTS

The development of new tumors was delayed, corresponding to the degree of reductions in UV dose in an inversely linear manner. Discontinuation of UV doses delayed the median times to the second tumor by 24 days (2 SED, P = 0.0549) and 33.5 days (4 SED, P < 0.0001), and when reduced to 1 SED, the median delays were 18 days (2 SED, P = 0.0469) and 33 days (4 SED, P < 0.0001). The median delay to the third tumor was after UV reduction 47 days (4 SED, P < 0.0001) and 35 days (2 SED, P = 0.151), and after UV discontinuation 49 days (4 SED, P < 0.0001) and 44 days (2 SED, P = 0.111).

CONCLUSION

This suggests that patients with SCC may benefit from reduced UV exposure.

Calcineurin inhibitors for the treatment of atopic dermatitis

BACKGROUND

Atopic dermatitis (AD) is a chronic disease characterized by periods of remission and relapse. Therapeutic objectives for AD should be to quickly reduce disease symptoms by targeting pathophysiological pathways, and to provide long-term management by reducing recurrences.

OBJECTIVE

Calcineurin inhibitors currently appear to be one of the most promising alternative systemic and topical compounds to treat AD. This review focuses on new developments of topical calcineurin inhibitors, therapeutic regimens including long-term management, and prophylaxis of AD.

METHODS

The published clinical studies that present data on treatment of AD with calcineurin inhibitors were assessed.

RESULTS/CONCLUSION

Topical calcineurin inhibitors such as tacrolimus and pimecrolimus provide an effective treatment for AD. They are useful for long-term management and prophylaxis of AD. Safety concerns with regard to increased risk for lymphomas or skin cancer could not be confirmed but will remain under careful observation.