Leukoplakia is associated with increased risk of oral cancer and is considered a premalignant lesion. Retinoids, particularly 13-cis retinoic acid, can frequently reverse leukoplakia. However, these drugs have considerable toxicity and are not suitable for large-scale use in the prevention of oral cancer. Beta-carotene is a naturally occurring, nontoxic carotenoid with biologic properties that suggest that it might be efficacious against oral leukoplakia. In 1986, we began a randomized study of 13-cis retinoic acid (1 mg/kg/d) versus beta-carotene (30 mg/d) in leukoplakia. However, owing to the marked differences in toxicity between the two compounds outlined in the consent form, 11 of the initial 16 eligible patients refused to participate unless they were "guaranteed" beta-carotene. Therefore, the study design was changed to a phase II trial of beta-carotene in which the compound was given daily for 3 months. Responding patients were continued for another 3 months of treatment. All lesions were examined histologically at entry. Responses were monitored by bidimensional measurements and photography done at entry, then monthly while on treatment and at study completion. Twenty-four evaluable patients were treated, and 17 had major responses (two complete, 15 partial), a response rate of 71% (95% confidence limits, 53% to 89%). There was no significant toxicity requiring drug discontinuation or dose reduction. These results indicate that beta-carotene has substantial activity in oral premalignancy. Because of its lack of toxicity, it is an excellent candidate for a preventive agent for oral cancer.

The differential expression of protein kinase C genes in normal human neonatal melanocytes and metastatic melanomas In contrast, PKC a and e RNA transcripts were detected in melanocytes cultivated in medium without serum and TPA, but were repressed in melanocytes cultivated in medium with serum and TPA. Only PKC a and e RNA transcripts were detected in the melanoma cell strains and the PKC RNA transcript expression levels varied among the five metastatic melanomas. In four metastatic melanoma cell strains, PKC a and e RNA transcript expression levels were repressed by serum, but in one melanoma cell strain, PKC a and e RNA transcript expression levels were induced by serum. Protein kinase C y RNA transcripts were not detected in either the melanocytes or melanoma cell strains. These data suggest an alteration of PKC isotype gene expression in the progression of primary melanocytes to metastatic melanoma. The absence of the PKC /3 RNA transcripts and altered expression of PKC a and e isotypes in particular may be a feature in the transformation of human primary melanocytes.

Epidemiologic studies implicate ultraviolet radiation (sunlight) as an etiologic agent for the pathogenesis of melanoma. However, the experimental evidence is less convincing. We present information from recent experimental findings that elevation of reactive oxygen species follows from melanin serving as a redox generator, and that this may play an important role in the etiology and pathogenesis of cutaneous melanoma. These observations offer a new paradigm for the development of preventive (and therapeutic) approaches to this disease.

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The p66shc protein governs oxidant stress and mammalian lifespan. Here, we identify melanoma inhibitory activity (MIA), a protein secreted by melanoma cells, as a novel binding partner and antagonist of p66shc. The N-terminal collagen homology-2 (CH2) domain of p66shc binds to the Src Homology-3 (SH3)-like domain of MIA in vitro. In cells, ectopically expressed MIA and p66shc colocalize and co-precipitate. MIA also co-precipitates with the CH2 domain of p66shc in vivo. MIA expression in vivo suppresses p66shc-stimulated increase in endogenous hydrogen peroxide (H 2 O 2 ), and inhibits basal and H 2 O 2 -induced phosphorylation of p66shc on serine 36 and H 2 O 2 -induced death. In human melanoma cells expressing MIA, endogenous MIA and p66shc co-precipitate. Downregulation of MIA in melanoma cells increases basal and ultraviolet radiation (UVR)-induced phosphorylation of p66shc on serine 36, augments endogenous H 2 O 2 levels, and increases their susceptibility to UVR-induced death. These findings show that MIA binds to p66shc, and suggest that this interaction antagonizes phosphorylation and function of p66shc. P66shc belongs to the shcA family of adapter proteins, and plays a crucial part in governing mammalian lifespan, the only protein thus far shown to do so. In this regard, p66shc-null mice live 30% longer than their wildtype littermates, and are resistant to oxidant stimuli.1 In response to such stimuli, p66shc is phosphorylated on serine 36, a residue that is not present in other shcA proteins.2 The phosphorylation of p66shc on serine 36 is essential to its function as a governor of cellular reactive oxygen species levels. 3P66shc governs reactive oxygen species levels by regulating mitochondrial oxidative capacity. 4 Recently, we have reported another mechanism through which p66shc increases oxidant stress: by stimulating the activity of the guanine nucleotide exchange factor son of sevenless-1 toward the rac1 GTPase.5 This mechanism employs interaction between specific proline residues in the unique N-terminal collagen homology-2 (CH2) domain of p66shc to the src homology-3 (SH3) domains of growth factor receptor bound-2 (Grb2). The ability of the proline-rich CH2 domain to bind to SH3 domains of grb2 raised the possibility of other SH3-containing proteins as binding partners of p66shc.Melanoma Inhibitory Activity (MIA) is a protein that plays a key role in the progression and metastasis of malignant melanoma. Its name, a misnomer, is derived from its initial characterization as a protein secreted by a human melanoma cell line that inhibited attachment and growth of melanoma cells in culture. 6 Subsequently, MIA was shown to bind to specific extracellular matrix proteins, thereby masking the binding sites of integrins to these proteins, 7 as well as directly binding to specific integrins.8 MIA promotes melanoma metastasis and invasion in vivo, 9 partly through these means. MIA is primarily expressed in malignant melanoma cells, though emerging evidence indicates that other cell types, especially chondro...