Time-restricted feeding and breast cancer

There is abundant evidence that obesity confers increased risk for at least 13 forms of cancer. The incidence of breast, colon, and liver cancer are all increased in obese populations, and the epidemiologic evidence for the obesity-breast cancer connection is particularly strong. One in eight women will be diagnosed with breast cancer during their lifetime. Breast cancer incidence increases approximately 10-fold for women over the of age 60, compared to age 50 or younger. This increase in breast cancer risk is associated with an increase in obesity. Indeed, obesity increases the risk of triple-negative breast cancer in premenopausal women and estrogen receptor positive breast cancer in postmenopausal women. A rarer form of inflammatory breast cancer is dramatically increased (up to 5-fold) in both groups. More importantly, obesity shortens disease-free survival in both pre- and postmenopausal women. Patient mortality in breast cancer is primarily caused by distant metastases. Obesity at the time of diagnosis is associated with increased risk of distant metastasis and mortality. Studies in rodents have confirmed these relationships, showing that dietary-induced obesity and high-fat diets lead to increased incidence and growth of tumors in oncogene and carcinogen-induced breast cancers. Despite this body of correlative evidence, the mechanisms of obesity-induced breast cancer risk remain poorly understood. One possibility is that the obesity causes insulin resistance in the liver and compensatory elevation in circulating insulin to control glucose levels. At the same time, other tissues, including tumors, may not be insulin resistant and so are exposed to increased insulin signaling. Indeed, we have shown that reducing insulin resistance by treating with omega-3 fatty acids reduces breast cancer growth in mice. We have also shown that time-restricted feeding (TRF) versus unrestricted feeding of a high-fat diet improves insulin resistance despite sustained obesity and equal caloric intake. Furthermore, we showed that TRF inhibited obesity-driven breast tumor growth and corrected tumor circadian rhythms, and that the TRF impact on tumor growth was mediated by reducing insulin levels. A number of important questions remain unanswered. Firstly, how does insulin drive tumor growth? Is it a direct effect on the tumor cell, or on the microenvironment? Secondly, does correction of the circadian rhythms in the tumor cell by TRF contribute to the reduced tumor growth? Thirdly, how do nutrients and insulin entrain the circadian clock in tumors? Due to the link between obesity, insulin resistance and breast cancer in pre- and postmenopausal women, and the translational potential of time-restricted feeding, we will investigate the effect of deleting the insulin receptor, mTORC1 signaling, or components of the circadian clock in tumor cells to test whether loss of these signals alters tumor growth in vivo and the response to TRF. We will also test whether TRF enhances chemotherapy to inhibit tumor growth. Accumulating evidence from TRF-related clinical studies support the translational relevance of our proposal. Translational, mechanistic findings from these studies will impact on breast cancer prevention and therapy.