Cutaneous melanoma: pathogenesis and rationale for chemoprevention

Aetiology and Pathogenesis of Cutaneous Melanoma: Current Concepts and Advances

Melanoma develops from malignant transformations of the pigment-producing melanocytes. If located in the basal layer of the skin epidermis, melanoma is referred to as cutaneous, which is more frequent. However, as melanocytes are be found in the eyes, ears, gastrointestinal tract, genitalia, urinary system, and meninges, cases of mucosal melanoma or other types (e.g., ocular) may occur. The incidence and morbidity of cutaneous melanoma (cM) are constantly increasing worldwide. Australia and New Zealand are world leaders in this regard with a morbidity rate of 54/100,000 and a mortality rate of 5.6/100,000 for 2015. The aim of this review is to consolidate and present the data related to the aetiology and pathogenesis of cutaneous melanoma, thus rendering them easier to understand. In this article we will discuss these problems and the possible impacts on treatment for this disease.

Chemoprevention of Melanoma: Theoretical and Practical Considerations

BACKGROUND

Chemoprevention refers to the use of agents to reverse, suppress, or prevent carcinogenic progression of cancer. The use of chemoprevention is an unexplored strategy in melanoma prevention.

METHODS

A retrospective review of the literature was undertaken regarding the important elements in evaluating chemoprevention as a strategy in melanoma.

RESULTS

Several considerations need to be addressed before a chemoprevention agent can be moved to a large randomized trial. Statins have both experimental and epidemiologic evidence to support their further development as candidate chemopreventive agents, but the evidence is insufficient to justify large-scale phase III studies. A strong scientific rationale, a systematic approach to chemoprevention agent development with rigorous chemoprevention designs, and careful selection of surrogate endpoint biomarkers are critical issues in developing a chemoprevention strategy.

CONCLUSIONS

Addressing these relevant considerations will allow for the development of chemoprevention in melanoma.

Nanotechnology-Based Drug Delivery Systems for Melanoma Antitumoral Therapy: A Review

Melanoma (MEL) is a less common type of skin cancer, but it is more aggressive with a high mortality rate. The World Cancer Research Fund International (GLOBOCAN 2012) estimates that there were 230,000 new cases of MEL in the world in 2012. Conventional MEL treatment includes surgery and chemotherapy, but many of the chemotherapeutic agents used present undesirable properties. Drug delivery systems are an alternative strategy by which to carry antineoplastic agents. Encapsulated drugs are advantageous due to such properties as high stability, better bioavailability, controlled drug release, a long blood circulation time, selective organ or tissue distribution, a lower total required dose, and minimal toxic side effects. This review of scientific research supports applying a nanotechnology-based drug delivery system for MEL therapy.

Targeting events in melanoma carcinogenesis for the prevention of melanoma

Melanoma is one of the few tumors that have increased in incidence over the last few decades. Strategies devoted solely to protecting against ultraviolet radiation have, at best, had a modest impact on the development of melanoma. Chemoprevention is an under-explored approach that could significantly decrease the morbidity and mortality from this deadly cancer. However, the scientific and logistical challenges of performing clinical studies in chemoprevention require innovative approaches to prove the effectiveness of putative preventive agents. There are several pharmacological and nutriceutical agents that are mechanistically linked to events in melanoma carcinogenesis that are candidates for advanced human studies. We will review the data for several promising agents, including statins, curcumin, resveratrol, silymarin and green tea, and discuss some importance issues and concepts that should be considered in any melanoma chemoprevention strategy.

Chemoprevention of skin melanoma: facts and myths

Melanoma is the most dangerous type of skin cancer. Despite the rise of public awareness, the incidence rate among the white population has been rising constantly for several decades. Systematic improvement in knowledge about the biology of pigment cells and molecular mechanisms of their neoplastic transformation has enhanced the possibility of melanoma chemoprevention. Hence, chemopreventive agents that prevent, inhibit, or reverse melanoma development are being investigated intensively. Among synthetic compounds, especially well studied are lipid-lowering drugs and cyclooxygenase inhibitors. Substances found in everyday diet, such as genistein, apigenin, quercetin, resveratrol, and curcumin may also have potential chemopreventive qualities. However, studies examining the chemopreventive activity of these compounds have shown widely varying results. Early reports on the possible chemopreventive activity of statins and fibrates were not proved by the results of randomized clinical trials. Similarly, case-control studies examining the influence of NSAIDs on the risk of melanoma do not confirm the antitumor activity of cyclooxygenase inhibitors. Further clinical trials involving carefully selected target populations as well as the identification of specific biomarkers of prognostic and predictive value seem to be essential for the evaluation of the chemopreventive activity of the studied substances.

Chemoprevention of melanoma

Despite advances in drug discovery programs and molecular approaches for identifying drug targets, incidence and mortality rates due to melanoma continue to rise at an alarming rate. Existing preventive strategies generally involve mole screening followed by surgical removal of the benign nevi and abnormal moles. However, due to lack of effective programs for screening and disease recurrence after surgical resection, there is a need for better chemopreventive agents. Although sunscreens have been used extensively for protecting from UV-induced melanomas, results of correlative population-based studies are controversial, with certain studies suggest increased skin cancer risk in sunscreen users. Therefore, these studies require further authentication to conclusively confirm the chemoprotective efficacy of sunscreens. This chapter reviews the current understanding regarding melanoma chemoprevention and the various strategies used to accomplish this objective.

Melanoma chemoprevention in skin reconstructs and mouse xenografts using isoselenocyanate-4

Melanoma incidence and mortality rates continue to increase despite the use of sunscreen as well as screening programs for early surgical excision of premalignant lesions. The steady increase in melanoma incidence suggests that additional preventive approaches are needed to augment these existing strategies. One unexplored area involves targeting genes whose deregulation promotes disease development to prevent melanoma. The Akt3 signaling pathway is one key signaling cascade that plays a central role by deregulating apoptosis to promote development of approximately 70% of melanomas. Isoselenocyanate-4 (ISC-4), derived from isothiocyanates by increasing the alkyl chain length and replacing sulfur with selenium, has been developed to target this important signaling pathway in melanomas; however, its chemopreventive potential is unknown. In this study, the chemopreventive efficacy of topical ISC-4 was evaluated in a laboratory-generated human skin melanoma model containing early melanocytic lesion or advanced stage melanoma cell lines and in animals containing invasive xenografted human melanoma. Repeated topical application of ISC-4 reduced tumor cell expansion in the skin model by 80% to 90% and decreased tumor development in animals by approximately 80%. Histologic examination of ISC-4-treated skin showed no obvious damage to skin cells or skin morphology, and treated animals did not exhibit markers indicative of major organ-related toxicity. Mechanistically, ISC-4 prevented melanoma by decreasing Akt3 signaling that lead to a 3-fold increase in apoptosis rates. Thus, topical ISC-4 can delay or slow down melanocytic lesion or melanoma development in preclinical models and could impact melanoma incidence rates if similar results are observed in humans.

Inhibitory effects of fusarochromanone on melanoma growth

Fusarochromanone is a toxic metabolite produced by Fusarium equiseti, a fungus present in decaying cereal plants in northern latitudes; it has been detected in various food grains. Fusarochromanone has been shown to have both stimulatory and inhibitory effects on various mammalian cells, depending on the concentration used. Whether these cytotoxic effects can be used in the clinical treatment of tumors remains to be established. Here, we evaluated the effects of fusarochromanone on the growth of human melanoma cells both in vitro and in vivo. In vitro, low concentrations (0.1-1 nmol/l) of fusarochromanone were found to be cytotoxic to many melanoma cell lines. In contrast, growth of normal melanocytes was inhibited only at much higher fusarochromanone concentrations (100-200 nmol/l). In vivo, the growth of melanoma cells implanted subcutaneously in immuno-compromised mice was significantly (P<0.05) reduced by daily administration of fusarochromanone. Immunohistological analyses indicated a significant (P<0.05) increase in the expression of active caspase-3 in tumor masses of mice treated with fusarochromanone, compared with controls. Together, these observations show that fusarochromanone increased apoptosis of tumor cells and reduced tumor growth in vivo. Therefore, the effects of fusarochromanone warrant further investigation as an adjuvant molecule to prevent growth and recurrence of melanomas.

Melanoma chemoprevention

BACKGROUND

Despite efforts to promote sun protection behaviors, melanoma incidence continues to increase. The prognosis of advanced melanoma remains extremely poor in spite of treatment advances, emphasizing the importance of exploring additional preventive measures.

OBJECTIVE

We sought to summarize the results of published research on candidate chemoprevention agents for melanoma.

METHODS

We conducted a narrative review of the literature.

RESULTS

Investigation into a possible role in melanoma chemoprevention continues for multiple agents, including sunscreen, lipid-lowering medications, nonsteroidal anti-inflammatory drugs, dietary nutrients, immunomodulators, and other drugs, including retinoids, difluoromethylornithine, and T4 endonuclease V.

LIMITATIONS

Systematic review of the literature was not performed.

CONCLUSION

Because no agent yet emerges as a clear choice for effective melanoma chemoprevention, sun avoidance and sun protection remain the mainstay of melanoma prevention for persons at high risk.

Identifying Individuals at High Risk of Melanoma: A Practical Predictor of Absolute Risk

Purpose

We developed a model to estimate the 5-year absolute risk of melanoma to efficiently identify individuals at increased risk of melanoma for potential interventions.

Patients and Methods

We used data from a case-control study with 718 non-Hispanic white patients with invasive cutaneous melanoma from melanoma clinics in Philadelphia, PA and San Francisco, CA; matched controls were 945 patients from outpatient clinics with similar catchment areas. All participants underwent extensive interviews and skin examinations. We selected easily obtained clinical characteristics and responses to simple questions for study in order to develop sex-specific relative risk models. These models were combined with incidence and mortality rates by United States geographic areas to develop estimates of the absolute risk of developing melanoma within 5 years.

Results

Relative risk models yielded an attributable risk of 86% for men and 89% for women, using at most seven variables. Attributable risks did not vary by age, ultraviolet B flux or hours outdoors. The absolute individual risks varied widely, depending on age, other host characteristics, and geographic area. Individual absolute risk can be estimated using a program available online.

Conclusion

Our procedures allow for estimating the absolute risk of developing melanoma to assist in the identification of patients at high risk. Such high-risk individuals could undergo interventions including a complete skin examination, counseling to avoid sun exposures, regular self and professional surveillance, or participation in prevention trials. It is important to emphasize that these projections are not intended to identify current melanoma cases.

Epidemiology and prevention of cutaneous melanoma

Melanoma incidence has continued to increase in all white populations, and mortality from melanoma remains high in older men worldwide. In Australia, Europe, and the United States, a substantial number of thick melanomas in older men are of the nodular subtype, a subtype lacking asymmetry or color change. Educating the public and professionals about the significance of evolving pigmented lesions as emphasized in the revised ABCDE of pigmented lesions is relevant. Targeting screening efforts toward older men will be necessary to decrease worldwide melanoma mortality. Among prevention strategies, emphasizing multiple methods of sun protection in early childhood, adolescence, and adulthood is needed to decrease sunburn rates. Chemoprevention research in melanoma should become a research priority to complement ongoing prevention strategies.

What about chemoprevention for melanoma?

PURPOSE OF REVIEW

This paper aims to critically review the potential for a chemoprevention strategy in melanoma, and to discuss new data on candidate chemoprevention agents, as chemoprevention has been suggested as an unexplored approach in melanoma.

RECENT FINDINGS

A strong scientific rationale, established long-term safety of candidate agents, and a systematic step-wise approach to chemoprevention agent development are all critical for melanoma chemoprevention research. Among potential agents, the lipid-lowering drugs, the statins, satisfy these prerequisites.

SUMMARY

Chemoprevention of cutaneous melanoma can become a valid strategy complementing current prevention approaches, as long as these important prerequisites are taken into consideration.