Atypical nevi are the most important clinical risk factor for melanoma and may serve as non-obligate biologic intermediates in melanoma tumorigenesis, making them useful for early-phase candidate chemoprevention trials. Our phase IIa randomized, placebo controlled trial demonstrated that sulindac and sulindac metabolites were bioavailable in the skin, specifically in BN following oral administration. Sulindac sulfone, a pro-apoptotic metabolite, reached the target tissue at concentrations similar to the respective plasma concentrations. The nevus distribution of sulindac sulfide, the metabolite responsible for cyclooxygenase inhibition, was limited. Eight weeks of sulindac intervention did not result in significant changes in VEGF expression, but it resulted in a marginal modulation of a marker of apoptosis, cleaved caspase 3, in the melanocytic junctional component in dysplastic nevi. This borderline effect could be due to small sample size (with only 20 subjects in the sulindac arm and 21 in the placebo arm with evaluable dysplastic nevi data) or relatively short duration of the intervention. However, this finding should be explored further since possible induction of apoptosis with sulindac intervention would be consistent with the observed identification of high concentrations of sulindac sulfone in the nevi.
Prior studies have evaluated the effect of topical tretinoin (retinoic acid analog) on AN as a surrogate marker for the chemoprevention of melanoma.24-27
Although some of these studies demonstrated significant histologic change toward benignity, the endpoint of evaluating degree of histological dysplasia was complication by the resulting inflammatory response from topical application of retinoid to a large segment of the back where the study nevi where located. In addition, a small pilot study examined the effect of topical imiquimod on AN.28
There were no obvious clinical changes in the size and morphology of the study nevi after 16 weeks of imiquimod 5% cream applied 3 times per week. Histologically, 4 of 14 treated nevi showed a significant reduction of junctional and intraepidermal melanocytes suggestive of partial regression, compared with untreated nevi.
Despite potential activity, topical application of melanoma preventive agents imposes a number of limitations. Most importantly, while there are certain anatomical sites that are known to be at higher risk of developing melanoma according gender and sub-type of melanoma, most melanomas arise de novo and not from precursor nevi (common, congenital, or dysplastic), and so targeting selected nevi on the skin may prove to be less effective for melanoma prevention compared with a systemic approach.
Prior studies have evaluated oral isotretinoin 25
and beta-carotene 29
in patients with dysplastic nevi but failed to demonstrate activity. We conducted the current study to evaluate the potential activity of NSAIDs for melanoma prevention because recent epidemiological studies suggest that regular use of NSAIDs, particularly aspirin reduces the risk of melanoma.13-17
We elected to study sulindac because it demonstrates a broad spectrum of anti-cancer activity and well-documented safety. Given the long prescription history of this agent, adverse reactions can be minimized with knowledge of the established predisposing risk factors, including but not limited to history of adverse reaction to any NSAID and active GI disease.
The anti-inflammatory activity of sulindac is believed to be mostly through inhibition of prostaglandin synthesis by the sulfide metabolite.30, 31
Sulindac sulfone possesses minimal activity toward cyclooxygenase; however, it has been shown to be a pro-apoptotic compound. In melanoma cell lines, both sulindac metabolites are effective in reducing the number of viable cells. 32
The decrease in cell viability is accompanied by an induction of apoptosis, measured by morphological changes and fragmented DNA in cell lysates.32
Because of their long half-lives and high lipophilicity, 32
sulindac metabolites may distribute to the skin to a greater extent than other NSAIDs and as so may be better candidates for skin cancer prevention. In preclinical studies, oral administration of sulindac at physiological concentrations has shown biological activities in the skin.18-20
As we demonstrated, sulindac metabolites are bioavailable in the skin after oral sulindac administration, with sulindac sulfone showing favorable nevi distribution which correlated with the observed changes in the apoptotic marker.
Reduced VEGF production and gene activation are among the proposed mechanisms of NSAID-induced inhibition of angiogenesis. 34,35
Melanoma cells have been shown to strongly express VEGF (or VEGF-A), whereas benign melanocytic nevi and melanocytes are largely thought not to express VEGF.36-40
Expression of other VEGF family members has also been described in melanoma.41,42
Our research group previously showed that VEGF expression in melanocytic cells was low or absent in BN, increased significantly in dysplastic nevi, and was further increased in primary melanoma.43
Collectively, these studies suggest that angiogenesis may be an early event of melanocytic lesion progression and could be a useful target for melanoma prevention. In our study, VEGF expression was not modulated with eight weeks of sulindac intervention. Further studies are needed to determine whether a longer duration of NSAIDs intervention would affect these findings.
An important outcome of our study relates to the feasibility of conducting this type of intervention in individuals at risk for melanoma. We were able to recruit the target cohort of 50 subjects within 16 months from 2 geographically distinct study sites. In addition, the introduction of dermoscopy-based algorithms for selection of study AN appears to effectively improve the clinical-pathological correlation. A pattern analysis-based algorithm was utilized to enhance the sensitivity of selecting AN while the ABCDE clinical algorithm was implemented with the objective of excluding concerning melanocytic lesions. Overall, 73.4% of AN were histologically classified as dysplastic, which demonstrates high clinical-pathological correlation when compared to other studies.44
Potential limitations of the study are the small sample size and short intervention duration for assessing tissue biomarker and pathological changes, as the study was designed and powered for the primary endpoint. The identification of optimal and reproducible biomarkers to assess the effect on sulindac and other NSAIDs in melanocytic nevi requires further evaluation. An important consideration for future studies will be to clinically target AN that represent a compound melanocytic process in order to increase the likelihood of identifying a junctional and dermal component for the evaluation of biomarkers. In addition, more subjects in the sulindac arm had a prior history of melanoma which may affect the tissue biomarker expression. While we did not find a significant difference in baseline tissue biomarker expression in subjects with or without prior melanoma (data not shown), stratification based on prior melanoma history may still be an important consideration for future clinical trial design.
We conclude that sulindac and sulindac metabolites can reach measurable levels in melanocytic nevi after oral sulindac administration, with sulindac sulfone, a pro-apoptotic compound, showing favorable nevi distribution. Eight weeks of sulindac intervention demonstrated a marginal effect in the expression of a marker of apoptosis in dysplastic nevi and did not result in significant changes in VEGF expression. The study findings support the further evaluation of sulindac as a chemopreventive agent for melanoma.