Chemoprevention of head and neck cancer

Soy protein extract (SPE) exhibits differential in vitro cell proliferation effects in oral cancer and normal cell lines

Prior research has demonstrated that specific isoflavones derived from soy may exhibit antitumor effects against many cancers, including oral cancer. Most of this prior research involved isolation and testing of individual soy components, such as genistein, daidzein, and glycitein, which exhibit cytotoxicity against cancerous cells but may also have residual cytotoxic effects on normal cells. Few studies have evaluated whole soy extract, containing a combination of these isoflavones, and other bioreactive compounds, which may function synergistically and more effectively against oral cancers. This study compared the antiproliferative effects of whole soy protein extract (SPE) on CAL 27 and SCC25 oral cancer cell lines in vitro. Administration of SPE significantly inhibited oral cancer growth and exerted these effects at lower concentrations compared with another class of flavonoids (proanthocyanidins) that were previously tested on these cell lines. This SPE-induced growth inhibition correlated with down-regulated mRNA expression in the oral cancer cell-cycle promoter ornithine decarboxylase (ODC), as well as upregulation of caspase-2 and caspase-8, initiators and effectors of apoptosis. These results suggest that SPE may represent a potential chemopreventive or chemotherapeutic option for oral cancer. Moreover, SPE may be more effective than other flavonoids currently used and may be effective at lower concentrations that approximate physiologic serum levels (0-2 μmol/l). This study may help to explain why diets rich in fruits, vegetables, and soy protein are associated with protection against development and progression of oral cancers, although further study is needed to develop specific public health recommendations for oral cancer treatment and prevention.

Proteasome regulation of ULBP1 transcription

Killer lymphocytes recognize stress-activated NKG2D ligands on tumors. We examined NKG2D ligand expression in head and neck squamous cell carcinoma (HNSCC) cells and other cell lines. HNSCC cells typically expressed MHC class I chain-related gene A (MICA), MICB, UL16-binding protein (ULBP)2, and ULBP3, but they were uniformly negative for cell surface ULBP1 and ULBP4. We then studied how cancer treatments affected NKG2D ligand expression. NKG2D ligand expression was not changed by most cancer-relevant treatments. However, bortezomib and other proteasome inhibitor drugs with distinct mechanisms of action dramatically and specifically up-regulated HNSCC ULBP1 mRNA and cell surface protein. Proteasome inhibition also increased RNA for ULBP1 and other NKG2D ligands in nontransformed human keratinocytes. Proteasome inhibitor drugs increased ULBP1 transcription by acting at a site in the 522-bp ULBP1 promoter. Although the DNA damage response pathways mediated by ATM (ataxia-telangiectasia, mutated) and ATR (ATM and Rad3-related) signaling had been reported to up-regulate NKG2D ligand expression, we found that ULBP1 up-regulation was not inhibited by caffeine and wortmannin, inhibitors of ATM/ATR signaling. ULBP1 expression in HNSCC cells was not increased by several ATM/ATR activating treatments, including bleomycin, cisplatin, aphidicolin, and hydroxyurea. Ionizing radiation caused ATM activation in HNSCC cells, but high-level ULBP1 expression was not induced by gamma radiation or UV radiation. Thus, ATM/ATR signaling was neither necessary nor sufficient for high-level ULBP1 expression in human HNSCC cell lines and could not account for the proteasome effect. The selective induction of ULBP1 expression by proteasome inhibitor drugs, along with variable NKG2D ligand expression by human tumor cells, indicates that NKG2D ligand genes are independently regulated.

Molecular mechanisms of the chemopreventive effects of resveratrol and its analogs in carcinogenesis

Resveratrol (3,4',5-trihydroxy-trans-stilbene), a phytoalexin found in grape skins, peanuts, and red wine, has been reported to exhibit a wide range of biological and pharmacological properties. It has been speculated that dietary resveratrol could be an explanation for the so-called 'French paradox' as it may act as an antioxidant, promote nitric oxide production, inhibit platelet aggregation, and increase high-density lipoprotein cholesterol, and thereby serve as a cardioprotective agent. Recently, it has been demonstrated that resveratrol can function as a cancer chemopreventive agent, and there has been a great deal of experimental effort directed toward defining this effect. It has been shown that resveratrol and some of its analogs interfere with signal transduction pathways, modulate cell cycle-regulating proteins, and is a potent inducer of apoptosis in multiple carcinoma cell lines. This review summarizes the recent advances that have provided new insights into the molecular mechanisms underlying the promising properties of resveratrol.