Vol.:(0123456789) 1 3 Clinical & Experimental Metastasis https://doi.org/10.1007/s10585-018-9941-7 RESEARCH PAPER Long-chain omega-3 polyunsaturated fatty acids decrease mammary tumor growth, multiorgan metastasis and enhance survival Saraswoti Khadge 1  · Geofrey M. Thiele 1,3,4  · John Graham Sharp 2  · Timothy R. McGuire 5  · Lynell W. Klassen 3,4  · Paul N. Black 6  · Concetta C. DiRusso 6  · Leah Cook 1  · James E. Talmadge 1,3 Received: 2 August 2018 / Accepted: 4 October 2018 © Springer Nature B.V. 2018 Abstract Epidemiological studies show a reduced risk of breast cancer (BC) in women consuming high levels of long-chain (LC) omega-3 (ω-3) fatty acids (FAs) compared with women who consumed low levels. However, the regulatory and mechanistic roles of dietary ω-6 and LC-ω-3 FAs on tumor progression, metastasis and survival are poorly understood. Female BALB/c mice (10-week old) were pair-fed with a diet containing ω-3 or an isocaloric, isolipidic ω-6 diet for 16 weeks prior to the orthotopic implantation of 4T1 mammary tumor cells. Major outcomes studied included: mammary tumor growth, survival analysis, and metastases analyses in multiple organs including pulmonary, hepatic, bone, cardiac, renal, ovarian, and con- tralateral MG (CMG). The dietary regulation of the tumor microenvironment was evaluated in mice autopsied on day-35 post tumor injection. In mice fed the ω-3 containing diet, there was a signifcant delay in tumor initiation and prolonged survival relative to the ω-6 diet-fed group. The tumor size on day 35 post tumor injection in the ω-3 group was 50% smaller and the frequencies of pulmonary and bone metastases were signifcantly lower relative to the ω-6 group. Similarly, the incidence/ frequencies and/or size of cardiac, renal, ovarian metastases were signifcantly lower in mice fed the ω-3 diet. The analyses of the tumor microenvironment showed that tumors in the ω-3 group had signifcantly lower numbers of proliferating tumor cells (Ki67 + )/high power feld (HPF), and higher numbers of apoptotic tumor cells (TUNEL + )/HPF, lower neo-vascularization (CD31 + vessels/HPF), infltration by neutrophil elastase + cells, and macrophages (F4/80 + ) relative to the tumors from the ω-6 group. Further, in tumors from the ω-3 diet-fed mice, T-cell infltration was 102% higher resulting in a neutrophil to T-lymphocyte ratio (NLR) that was 76% lower (p < 0.05). Direct correlations were observed between NLR with tumor size and T-cell infltration with the number of apoptotic tumor cells. qRT-PCR analysis revealed that tumor IL10 mRNA levels were signifcantly higher (six-fold) in the tumors from mice fed the ω-3 diet and inversely correlated with the tumor size. Our data suggest that dietary LC-ω-3FAs modulates the mammary tumor microenvironment slowing tumor growth, and reducing metastases to both common and less preferential organs resulting in prolonged survival. The surrogate analyses undertaken support a mechanism of action by dietary LC-ω-3FAs that includes, but is not limited to decreased infltration by myeloid cells (neutrophils and macrophages), an increase in CD3 + lymphocyte infltration and IL10 associated anti-infammatory activity. Keywords PUFA · Omega-3 · Mammary tumor · Metastasis · Survival Abbreviations AA Arachidonic acid BC Breast cancer Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10585-018-9941-7) contains supplementary material, which is available to authorized users. * James E. Talmadge jtalmadg@unmc.edu 1 Department of Pathology and Microbiology, University of Nebraska Medical Center, Omaha, NE 68198-6495, USA 2 Department of Genetics, Cell Biology and Anatomy, University of Nebraska Medical Center, Omaha, NE, USA 3 Department of Internal Medicine, University of Nebraska Medical Center, Omaha, NE 68198-6495, USA 4 Veteran Afairs Nebraska-Western Iowa Health Care System, Omaha, NE, USA 5 Department of Pharmacy Practice, University of Nebraska Medical Center, Omaha, NE, USA 6 Department of Biochemistry, University of Nebraska-Lincoln, Lincoln, NE, USA