Physical Activity Plus Energy Restriction Prevents 4T1.2 Mammary Tumor Progression, MDSC Accumulation, and an Immunosuppressive Tumor Microenvironment

Abstract

Physical activity and the prevention of weight gain decrease breast cancer incidence and improve survival. Unraveling the biological mechanisms underlying these cancer prevention effects is difficult because activity and dietary restriction are often linked. The goal of this study was to determine whether physical activity (PA), preventing weight gain via energy restriction (ER), or the combination was most effective in delaying tumor growth, reducing metastatic progression, and improving survival in the 4T1.2 mammary tumor model. Furthermore, we determined whether any of these interventions prevented the expansion of protumor immunosuppressive cells and altered the tumor microenvironment (TME). Female BALB/c mice (n ¼ 7-20/group) were randomized to sedentary (SED) or PA wheel cages and fed ad libitum (AL) or 90% of control food intake (ER). After 8 weeks on the interventions, mice were inoculated with 5 Â 10 4 4T1.2 luc cells into the 4th mammary fat pad and continued on their respective intervention. PAþER significantly delayed primary tumor growth (final tumor volume, 0.193 AE 0.042 vs. 0.369 AE 0.049 cm 3 , P < 0.001), reduced metastatic burden in the lungs (0.72 AE 0.36 vs. 16.27 AE 6.98, P ¼ 0.054) and increased survival (median survival, 68 vs 40 days, P ¼ 0.043) compared with SEDþAL mice. PAþER also reduced the expression level of metastatic and immunosuppressive genes and resulted in favorable changes in immune cell infiltrates in the tumor. These data suggest that both PA and ER are needed to reduce tumor growth, delay metastatic progression, and improve survival, and that this protection is associated with changes in immune-mediated mechanisms.

Increased Adiposity Enhances the Accumulation of MDSCs in the Tumor Microenvironment and Adipose Tissue of Pancreatic Tumor-Bearing Mice and in Immune Organs of Tumor-Free Hosts

“…Spleens, tumor-draining lymph nodes (TDLN), and tumors were harvested, and single-cell suspensions were prepared as previously described [6,40]. Cell counts and viability were determined via trypan blue exclusion (Corning; Tewksbury, MA, USA).…”

“…Single cell suspensions of splenocytes, TDLN, and tumor-infiltrating immune cells were washed twice in PBS containing 0.01% bovine serum albumin at 4 • C. Cells were incubated with Fc block (Biolegend; San Diego, CA, USA) and stained with saturating concentrations of conjugated antibodies, listedin Supplemental Table S2, as previously described [6,40]. Lymphoid and myeloid cells were gated on forward vs. side scatter, and a total of 30,000 events were acquired.…”

“…Obesity increases the risk of cancer at 13 sites, including breast, colon, and pancreas, among others [2,3]. Obesity is also associated with accelerated tumor progression, poorer response to treatment, and increased cancer-related mortality in multiple cancer types including pancreatic and breast cancer [4][5][6]. In addition to the well-established relationship between obesity in adulthood and poorer cancer outcomes, being overweight or obese during early life may also increase subsequent mortality risk for certain cancer types, including pancreatic cancer [7].…”

Physical Activity and Breast Cancer Prevention: Possible Role of Immune Mediators

“…Nineteen studies investigated the effect of PA interventions on cancer immune outcomes using preclinical breast cancer models ( Table 1 ). Transplantable tumor models were used in 14 studies ( 31 , 32 , 34 , 35 , 44 – 50 , 53 – 55 ), among which six used the 4T1 (or its subclone 4T1.2) TNBC murine mammary tumor model ( 32 , 34 , 35 , 44 , 48 , 54 ). Carcinogen-induced ( n = 3) ( 33 , 56 , 57 ) and genetically-engineered/spontaneous ( n = 2) ( 51 , 52 ) mammary tumor models were also used.…”

Resisting Resistance to Immune Checkpoint Therapy: A Systematic Review

“…Caloric restriction improves immunosurveillance [ 250 ] and protects against T-cell senescence [ 251 ] via the suppression of insulin-like growth factor 1 and IL-6 [ 252 ], as well as decreased mTOR signaling [ 253 ] and a decreased anti-OX40 immunotherapy response [ 254 ]. Mouse models showed improved immune cell–adipose tissue signaling after CR, with better glucose tolerance and greater fat loss [ 255 ].…”