Environmental impact on carcinogenesis under BRCA1 haploinsufficiency.

Cancer is the primary cause of human mortality in Japan since 1981. Although numerous novel therapies have been developed and applied in clinics, the number of deaths from cancer is still increasing worldwide. It is time to consider the strategy of cancer prevention more seriously. Here we propose a hypothesis that cancer can be side effects of long time-use of iron and oxygen and that carcinogenesis is an evolution-like cellular events to obtain "iron addiction with ferroptosis-resistance" where genes and environment interact each other. Among the recognized genetic risk factors for carcinogenesis, we here focus on BRCA1 tumor suppressor gene and how environmental factors, including daily life exposure and diets, may impact toward carcinogenesis under BRCA1 haploinsufficiency. Although mice models of BRCA1 mutants have not been successful for decades in generating phenotype mimicking the human counterparts, a rat model of BRCA1 mutant was recently established that reasonably mimics the human phenotype. Two distinct categories of oxidative stress, one by radiation and one by iron-catalyzed Fenton reaction, promoted carcinogenesis in Brca1 rat mutants. Furthermore, mitochondrial damage followed by alteration of iron metabolism finally resulted in ferroptosis-resistance of target cells in carcinogenesis. These suggest a possibility that cancer prevention by active pharmacological intervention may be possible for BRCA1 mutants to increase the quality of their life rather than preventive mastectomy and/or oophorectomy.