Dietary modification such as caloric restriction (CR) has been shown to decrease tumor initiation and progression. We sought to determine if nutrient restriction could be used as a novel therapeutic intervention to enhance cytotoxic therapies such as radiation (IR) and alter the molecular profile of triple-negative breast cancer (TNBC), which displays a poor prognosis. In two murine models of TNBC, significant tumor regression is noted with IR or diet modification, and a greater regression is observed combining diet modification with IR. Two methods of diet modification were compared, and it was found that a daily 30% reduction in total calories provided more significant tumor regression than alternate day feeding. At the molecular level, tumors treated with CR and IR showed less proliferation and more apoptosis. cDNA array analysis demonstrated the IGF-1R pathway plays a key role in achieving this physiologic response, and multiple members of the IGF-1R pathway including IGF-1R, IRS, PIK3ca and mTOR were found to be downregulated. The innovative use of CR as a novel therapeutic option has the potential to change the biology of tumors and enhance the opportunity for clinical benefit in the treatment of patients with TNBC.

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As the link between obesity and metabolic syndrome and cancer becomes clearer, the need to determine the optimal way to incorporate dietary manipulation in the treatment of cancer patients becomes increasingly important. Metabolic-based therapies, such as caloric restriction, intermittent fasting and a ketogenic diet, have the ability to decrease the incidence of spontaneous tumors and slow the growth of primary tumors, and may have an effect on distant metastases in animal models. Despite the abundance of preclinical data demonstrating the benefit of dietary modification for cancer, to date there are few clinical trials targeting diet as an intervention for cancer patients. We hypothesize that this may be due, in part, to the fact that several different types of diet modification exist with no clear recommendations regarding the optimal method. This article will delineate three commonly used methods of dietary manipulation to assess the potential of each as a regimen for cancer therapy.

CR decreased metastatic burden and therefore may complement cytotoxic therapies being used in the clinical setting for metastatic disease. Downregulation of the IGF-1R pathway, is in part responsible for this response and modulating IGF-1R directly resulted in similar improved progression-free survival. The novel use of CR has the potential to enhance clinical outcomes for patients with metastatic breast cancer.

Arp2/3 complex is an actin polymerization nucleator and localized in the leading protrusions of migrating cells. It has been unclear how this complex is targeted to the protrusions and whether its localization is functionally important. We previously demonstrated that mRNAs encoding for the subunits of the complex were localized in the protrusions of fibroblasts, suggesting a mechanism to target the complex to the protrusions. We here present data demonstrating the importance of Arp2/3 complex mRNA localization in directional cell migration. Using a novel mechanism by which Dia1 mRNA is targeted to the perinuclear endoplasmic reticulum, we re-directed the mRNA encoding Arp2, a subunit of the Arp2/3 complex, to the perinuclear region in fibroblasts. Knockdown of Arp2 alone caused dramatic reduction of the complex and resulted in narrow protrusions, increased random cell migration speed and loss of directionality. Rescue with a protrusion-localizing Arp2 mRNA restored normal cell migration behavior, whereas rescue with a mis-localizing Arp2 mRNA failed to restore speed and directionality. These results demonstrate that localization of Arp2/3 complex mRNAs in the leading protrusions is functionally important for directional cell migration.

Triple negative breast cancer (TNBC) is a heterogeneous disease that has no available targeted therapies. Previously, we have shown that caloric restriction (CR) can augment the effects of radiation therapy in a TNBC mouse model. To build upon this, we now present data regarding the combination of chemotherapy and CR in the same 4T1 model. Chemotherapy can induce inflammation that breeds resistance to therapy. We propose CR as a mechanism to decrease chemotherapy-induced inflammation and increase efficacy of therapy. 12-week old Balb/c mice were orthotopically injected with a syngeneic triple negative breast cancer cell line (4T1) and were treated in one of six cohorts: ad lib fed (AL), 30% reduction in calorie intake (CR), cisplatin or docetaxol alone or a combination CR+cisplatin/docetaxol. Mice in the cohorts receiving chemotherapy+CR had longer overall survival (12 ± 2 days) as compared to the AL group. These mice also demonstrated less lung metastases at the final time point of in vivo imaging. In addition, downregulation of the IGF-1R and IRS signaling pathways were noted most significantly in those mice receiving combination therapy. Lastly, serum from these mice demonstrated an increase in inflammatory cytokines TNF-α and IL-1β in response to chemotherapy alone. This increase was dampened by the addition of CR. Taken together, these data suggest that while chemotherapy is effective in TNBC, it can cause inflammation, which can be a driver of resistance to therapy. This chemotherapy-induced inflammation can be reversed with the use of CR as a nontoxic adjunct to treatment.

Caloric restriction (CR) has been shown to cause tumor regression in models of triple-negative breast cancer (TNBC), and the regression is augmented when coupled with ionizing radiation (IR). In this study, we sought to determine if the molecular interaction between CR and IR could be mediated by microRNA (miR). miR arrays revealed 3 miRs in the miR-17~92 cluster as most significantly down regulated when CR is combined with IR. In vivo, CR and IR down regulated miR-17/20 in 2 TNBC models. To elucidate the mechanism by which this cluster regulates the response to CR, cDNA arrays were performed and the top 5 statistically significant gene ontology terms with high fold changes were all associated with extracellular matrix (ECM) and metastases. In silico analysis revealed 4 potential targets of the miR-17~92 cluster related to ECM: collagen 4 alpha 3, laminin alpha 3, and metallopeptidase inhibitors 2 and 3, which were confirmed by luciferase assays. The overexpression or silencing of miR-17/20a demonstrated that those miRs directly affected the ECM proteins. Furthermore, we found that CR-mediated inhibition of miR-17/20a can regulate the expression of ECM proteins. Functionally, we demonstrate that CR decreases the metastatic potential of cells which further demonstrates the importance of the ECM. In conclusion, CR can be used as a potential treatment for cancer because it may alter many molecular targets concurrently and decrease metastatic potential for TNBC.

Our data demonstrate an inverse relationship with miR-34a and c-Met; the upregulation of miR-34a in RIF causes inhibition of c-Met production. miRs may play a role in RIF; in particular, miR-34a should be investigated as a potential target to prevent or treat this devastating side effect of irradiation.