BRCA1 mRNA levels following a 4–6-week intervention with oral 3,3′-diindolylmethane

The inheritance of a deleterious mutation in the breast cancer susceptibility gene, BRCA1, confers high lifetime risks of developing breast and ovarian cancer, estimated at 80 and 40%, respectively (Ford et al, 1994; The Breast Cancer Linkage Consortium, 1999; Robson, 2002; Thompson and Easton, 2002; Antoniou et al, 2003; Chen and Parmigiani, 2007). Women with BRCA-associated breast cancers are often diagnosed at a young age (Narod, 2010), and have elevated risks of developing contralateral (Metcalfe et al, 2011a) and ipsilateral breast cancer (Metcalfe et al, 2011b). BRCA1-associated breast cancers exhibit features of an aggressive phenotype (for example, triple negative; Da Silva and Lakhani, 2010). Genetic testing permits the identification of high-risk women before cancer; however, prevention is limited to prophylactic surgery and chemoprevention with tamoxifen (Narod, 2010; Finch et al, 2014). The incomplete penetrance associated with a BRCA mutation suggests that non-genetic modifiers may have an important role (Narod et al, 1993; Foulkes et al, 2002; Antoniou et al, 2003; King et al, 2003). Various reproductive factors have been shown to influence the risk (Jernstrom et al, 2004; Kotsopoulos et al, 2005a); however, the role for dietary and lifestyle factors is less clear (Kotsopoulos and Narod, 2005). There is some evidence that caffeine (Nkondjock et al, 2006), selenium (Kowalska et al, 2005; Kotsopoulos et al, 2010) and weight loss in early adult life (Kotsopoulos et al, 2005b) protect against BRCA1-related breast cancer. In addition, we have recently reported possible relationships between plasma iron and antimony levels and BRCA1-associated breast cancer (Kotsopoulos et al, 2012). Cancer risk reduction options that are nonsurgical and modifiable are needed. When identifying possible lifestyle interventions that may help in the prevention of breast cancer, it is important to consider that the mechanism underlying the predisposition is likely to be different in BRCA1 mutation carriers from that of women in the general population (Salmena and Narod, 2012). BRCA1 helps maintain genomic integrity through participating in the cellular response to DNA damage, specifically in the repair of double-stranded DNA breaks (Scott, 2004). Haploinsufficiency refers to a state in which an individual has only one functional copy of a gene due to mutation or gene loss, and thus may produce an insufficient amount of protein (Berger and Pandolfi, 2011; Berger et al, 2011; Konishi et al, 2011). Although limited, there is evidence to support that the predisposition to breast cancer among BRCA1 mutation carriers is due to haploinsufficiency associated with heterozygosity, which increases genomic instability and accelerates the mutation rate of other critical genes, including the second copy of BRCA1 (Konishi et al, 2011; Salmena and Narod, 2012). Thus, factors that might increase the cellular expression of the normal copy of the gene and thereby help normalise protein levels may mitigate against the effect of the mutation. One dietary supplement that is thought to have potential for preventing cancer in BRCA1 mutation carriers is 3,3′-diindolylmethane (DIM), a phytochemical derived from cruciferous vegetables (Higdon et al, 2007). DIM has been found to have various cancer-protective effects, particularly for hormone-dependent cancers such as that of the breast (Higdon et al, 2007). In vitro administration of a relatively low dose of the phytochemical DIM (and its precursor indole-3-carbinol (I3C)) can significantly upregulate both the BRCA1 and BRCA2 mRNA and the protein expression in breast and prostate cancer cells (Meng et al, 2000a, 2000b, 2000c; Fan et al, 2006, 2009). If haploinsufficiency predisposes mutation carriers to cancer development, ultimately, the ability to upregulate BRCA1 expression in female BRCA1 heterozygotes may translate into a reduced cancer risk. To date, no studies have evaluated whether or not oral administration of I3C or DIM enhances the expression of normal BRCA1 mRNA or protein in vivo. We conducted a 4–6-week dietary intervention trial to evaluate the ability of DIM, a stable metabolite of I3C, to upregulate BRCA1 mRNA expression in women with a BRCA1 mutation.