Abstract 1370: Characterizing the molecular activity of isothiocyanate analogues of sulforaphane: Will a longer carbon chain yield better protection against UVB-induced non-melanoma skin cancer

Abstract

Abstract Sulforaphane (SFN, chemical name 1-isothiocyanato-4-(methylsulfinyl)-butane) is a natural product found in cruciferous vegetables such as broccoli. Although SFN is known to inhibit several models of cancer, including skin cancer, the molecular mechanisms of this inhibition remain unclear. This is partially due to the myriad of activities that SFN is known to exert in the cell. One of the transcription factors known to play a key role in UV-induced non-melanoma skin cancer (NMSC) is Activator Protein-1 (AP-1). We have recently found that SFN blocks AP-1 activity in HaCaT keratinocytes and mouse skin due to a specific interaction with a cysteine required for DNA binding by AP-1 family members (Cancer Res 2009; 69: (17)). We have since investigated whether structurally-related analogues of SFN could also act as efficient inhibitors of AP-1 activity in keratinocytes. We have compared the activity of three SFN analogues whose only structural difference from SFN is the length of the carbon chain between the isothiocyanato and sulfinyl groups. They are 1-Isothiocyanato-7-(methylsulfinyl)-heptane (Iso-7, found in watercress), 1-Isothiocyanato-8-(methylsulfinyl)-octane (Iso-8, also found in watercress) and 1-Isothiocyanato-9-(methylsulfinyl)-nonane (Iso-9, found in shepard's purse seed). AP-1 luciferase assays in HaCaT cells indicate that all three analogues significantly inhibit UVB-induced AP-1 activity. Iso-7 treatment resulted in an even greater inhibition of AP-1 luciferase than SFN, although Iso-8 and Iso-9 were both less effective than SFN. In addition, there has recently been considerable interest regarding the ability of SFN to act as a histone deacetylase (HDAC) inhibitor. However, there is no evidence in the literature with respect to SFN acting as an HDAC inhibitor in keratinocytes. A commercial HDAC inhibitor (HDAC inhibitor III, Calbiochem) was thus tested for its affect on AP-1 luciferase in keratinocytes alongside SFN. This commercial HDAC inhibitor failed to inhibit AP-1 activity after UVB at low doses (100nM), and instead strongly activated AP-1 activity at higher doses (500nM and above), opposite of the SFN response. Western blots also indicate that while the commercial HDAC inhibitor strongly induces acetylation of histone H4 in keratinocytes, SFN and its analogues do not. Together, these results indicate that HDAC inhibition may not play a strong role in the chemopreventive action of SFN in UV-exposed keratinocytes, and that SFN analogues, especially Iso-7, deserve further scrutiny as potentially powerful natural products for chemoprevention of NMSC via AP-1 inhibition. This work was supported in part by the following grants: 5K07CA132956, 3K07CA132956-02S1, P01 CA27502 and P30 CA23074. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1370. doi:10.1158/1538-7445.AM2011-1370