Polyamines and nonmelanoma skin cancer

Carcinogenesis studies in mice with genetically engineered alterations in polyamine metabolism

Polyamines are intimately linked to essential cellular processes that are required for cell growth and -proliferation, and abundant evidence links polyamine metabolism to tumor susceptibility and progression. Intensive efforts over the past 2 decades have yielded numerous mouse models of cancer that utilize genetic manipulations to recapitulate the molecular alterations and cellular interactions that characterize human cancers. These models provide the ideal genetic context to examine the impact of altered polyamine content on tumor biology, with the goal of applying the knowledge acquired in mice to the prevention and treatment of human cancer. Transgenic and knockout mouse technologies allow the investigator to enhance or delete, respectively, the expression of a given polyamine metabolic enzyme or regulatory protein, and advanced models facilitate both temporal and spatial control of gene expression in the mouse. These methods can be utilized to modulate total polyamine content or relative polyamine ratios in specific cell populations in vivo and evaluate the impact of this manipulation on tumor appearance and progression. This chapter provides resources to identify existing mouse strains that exhibit increased susceptibility to tumor development as well as strains that were engineered for increased or decreased expression of polyamine regulatory proteins. A conceptual framework is then presented to combine these resources in order to successfully complete a carcinogenesis study in mice with altered polyamine metabolism.

Pathogenesis of nonmelanoma skin cancers in organ transplant recipients

Nonmelanoma skin cancer (NMSC) is the most common human cancer, with an incidence of more than 1.2 million per year in the USA. The risk for the development of NMSCs increases by approximately 10-250 fold in chronically immune suppressed organ transplant recipients (OTRs). Solar UVB is the most common etiologic factor in the development of this neoplasm, both in immune competent and immune suppressed populations. This review provides a description of NMSC in OTRs. It also provides an account of the various immunologic and non-immune-dependent mechanisms involved in the pathogenesis and progression of NMSCs in OTRs. Finally, this review addresses possible strategies for the prevention of this cancer, particularly focusing on the aspects that may be incorporated to prevent negative effects of chemopreventive chemicals on graft survival.

New agents for prevention of ultraviolet-induced nonmelanoma skin cancer

With the incidence of nonmelanoma skin cancer on the rise, current prevention methods, such as the use of sunscreens, have yet to prove adequate to reverse this trend. There has been considerable interest in identifying compounds that will inhibit or reverse the biochemical changes required for skin cancers to develop, either by pharmacologic intervention or by dietary manipulation. By targeting different pathways identified as important in the pathogenesis of nonmelanoma skin cancers, a combination approach with multiple agents or the addition of chemopreventative agents to topical sunscreens may offer the potential for novel and synergistic therapies in treating nonmelanoma skin cancer.

Oral feeding of pomegranate fruit extract inhibits early biomarkers of UVB radiation-induced carcinogenesis in SKH-1 hairless mouse epidermis

Pomegranate from the plant Punica granatum L. possesses strong antioxidant and anti-inflammatory properties. Recently, we have demonstrated that treatment of normal human epidermal keratinocytes with pomegranate fruit extract (PFE) inhibited UVB-mediated activation of nuclear factor kappa B (NF-κB) and mitogen activated protein kinases pathways. Here, we evaluated the effect of PFE on early biomarkers of photocarcinogenesis employing SKH-1 hairless mice. PFE was provided in drinking water (0.2%, wt/vol) to SKH-1 hairless mice for 14 days before a single UVB (180 mJ cm(-2)) irradiation. We found that oral feeding of PFE inhibited UVB-induced: (1) skin edema; (2) hyperplasia; (3) infiltration of leukocytes; (4) lipid peroxidation; (5) hydrogen peroxide generation; (6) ornithine decarboxylase (ODC) activity; and (7) ODC, cyclooxygenase-2 and proliferating cell nuclear antigen protein expression. Oral feeding of PFE enhanced repair of UVB-mediated formation of cyclobutane pyrimidine dimers (CPDs) and 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG). Importantly, PFE treatment further enhanced UVB-mediated increase in tumor suppressor p53 and cyclin kinase inhibitor p21. Furthermore, oral feeding of PFE inhibited UVB-mediated: (1) nuclear translocation of NF-κB; (2) activation of IKKα; and (3) phosphorylation and degradation of IκBα. Taken together, we provide evidence that oral feeding of PFE to mice affords substantial protection from the adverse effects of UVB radiation via modulation in early biomarkers of photocarcinogenesis and provide suggestion for its photochemopreventive potential.

Novel investigational drugs for basal cell carcinoma

IMPORTANCE OF THE FIELD

In the United States, the annual incidence of basal cell carcinoma (BCC) is close to 1 million. Ultraviolet radiation exposure is the main risk factor; however, the availability of ever more potent sunscreens and education have not prevented the rise in BCC incidence. Therefore, concerted effects to identify novel preventive and therapeutic strategies are necessary.

AREAS COVERED IN THIS REVIEW

This article summarizes our current understanding of the etiology and molecular mechanisms of BCC tumorigenesis and discusses the preclinical and clinical studies to identify agents with anti-BCC efficacy.

WHAT THE READER WILL GAIN

The discovery that hyperactive Hh pathway signaling causes several cancers, including BCC, has spawned the development of many pharmacologic inhibitors of Hh signaling. Early clinical testing of the most advanced, GDC-0449, demonstrated impressive efficacy in patients with advanced BCC. Other promising anti-BCC chemopreventive strategies include drugs that are already FDA-approved for treating other diseases.

TAKE HOME MESSAGE

Preclinical and clinical trials with pre-existing FDA-approved drugs suggest novel uses for BCC chemoprevention and treatment. Also, new chemical entities that inhibit the Hh pathway show promise, and in combination with other drugs may provide a nonsurgical cure for this most common cancer.

Cytoplasmic accumulation of the RNA-binding protein HuR stabilizes the ornithine decarboxylase transcript in a murine nonmelanoma skin cancer model

Ornithine decarboxylase (ODC) is the first and usually rate-limiting enzyme in the polyamine biosynthetic pathway. Under normal physiological conditions, polyamine content and ODC enzyme activity are highly regulated. However, the induction of ODC activity is an early step in neoplastic transformation. The studies described here use normal mouse keratinocytes (C5N cells), and spindle carcinoma cells (A5 cells) to explore the regulation of ODC in nonmelanoma skin cancer development. Previous results have shown that induction of ODC activity is both necessary and sufficient for the promotion of skin tumors. We see a marked increase in ODC enzyme activity in A5 cells compared with C5N keratinocytes, which correlates with a 4-fold stabilization of ODC mRNA. These data suggest that ODC is post-transcriptionally regulated in skin tumor development. Thus, we sought to investigate whether the ODC transcript interacts with the RNA-binding protein HuR, which is known to bind to and stabilize its target mRNAs. We show that HuR is able to bind to the ODC 3'-UTR in A5 cells but not in C5N cells. Immunofluorescence results reveal that HuR is present in both the nucleus and cytoplasm of A5 cells, whereas C5N cells exhibit strictly nuclear localization of HuR. Knockdown experiments in A5 cells showed that when HuR is depleted, ODC RNA becomes less stable, and ODC enzyme activity decreases. Together, these data support the hypothesis that HuR plays a causative role in ODC up-regulation during nonmelanoma skin cancer development by binding to and stabilizing the ODC transcript.

Polyamines and hair: a couple in search of perfection

Polyamines (spermidine, putrescine and spermine) are multifunctional cationic amines that are indispensable for cellular proliferation; of key significance in the growth of rapidly regenerating tissues and tumors. Given that the hair follicle (HF) is one of the most highly proliferative organs in mammalian biology, it is not surprising that polyamines are crucial to HF growth. Indeed, growing (anagen) HFs show the highest activity of ornithine decarboxylase (ODC), the rate-limiting enzyme of polyamine biosynthesis, while inhibition of ODC, using eflornithine, results in a decreased rate of excessive facial hair growth in vivo and inhibits human scalp hair growth in organ culture. In sheep, manipulation of dietary intake of polyamines also results in altered wool growth. Polyamine-containing nutraceuticals have therefore been proposed as promoters of human hair growth. Recent progress in polyamine research, coupled with renewed interest in the role of polyamines in skin biology, encourages one to revisit their potential roles in HF biology and highlights the need for a systematic evaluation of their mechanisms of action and clinical applications in the treatment of hair disorders. The present viewpoint essay outlines the key frontiers in polyamine-related hair research and defines the major open questions. Moreover, it argues that a renaissance in polyamine research in hair biology, well beyond the inhibition of ODC activity in hirsutism therapy, is important for the development of novel therapeutic strategies for the manipulation of human hair growth. Such targets could include the manipulation of polyamine biosynthesis and the topical administration of selected polyamines, such as spermidine.

Targeting ornithine decarboxylase for the prevention of nonmelanoma skin cancer in humans

Bailey et al. report in this issue of the journal (beginning on page 35) one of the first successful trials of basal cell carcinoma (BCC) prevention. Oral alpha-difluoromethyl-dl-ornithine (DFMO) reduced new BCCs in patients with a prior history of nonmelanoma skin cancer. DFMO is an inhibitor of ornithine decarboxylase, a key enzyme in the polyamine biosynthetic pathway. This perspective on Bailey et al. discusses our knowledge of the contribution of polyamines to BCC pathogenesis, how this knowledge advanced the development of a new method to prevent BCCs, and prospects for future studies of DFMO in BCC prevention.

L-methioninase production by Aspergillus flavipes under solid-state fermentation

Solid-state fermentation was carried out for the production of extra-cellular L-methioninase by Aspergillus flavipes (Bain and Sart.) using nine agro-industrial residues, namely wheat bran, rice bran, wheat flour, coconut seeds, cotton seeds, ground nut cake, lentil hulls, soya beans and chicken feathers. Chicken feathers were selected as solid substrate for L-methioninase production by A. flavipes. The maximum L-methioninase productivity (71.0 U/mg protein) and growth (11 mg protein/ml) of A. flavipes was obtained using alkali pretreated chicken feathers of 50% initial moisture content as substrate supplemented with D-glucose (1.0% w/v) and L-methionine (0.2% w/v). External supplementation of the fermentation medium with various vitamin sources has no overinductive effect on L-methioninase biosynthesis. The partially purified A. flavipes L-methioninase preparation showed highest activity (181 U/ml) at pH 8.0 with stability over a pH range (pH 6-8) for 2 h. L-methioninase activity was increased by preincubation of the enzyme for 2 h with Co(2+), Mn(2+), Cu(2+) and Mg(2+) and strongly inhibited by the presence of EDTA, NaN(3), Li(2+), Cd(2+), DMSO and 2-mercaptoethanol. The enzyme preparation has a broad substrate spectrum showing a higher affinity to deaminate L-glycine, N -acetylglucosamine and glutamic acid, in addition to their proteolytic activity against bovine serum albumin, casein, gelatin and keratin. The partially purified enzyme was found to be glyco-metalloproteinic in nature as concluded from the analytical and spectroscopic profiles of the enzyme preparation. The demethiolating activity of the enzyme was also visualized chromogenially.