The effects of varying dietary carbohydrate and fat content on survival in a murine LNCaP prostate cancer xenograft model

Abstract

Purpose: Numerous dietary factors elevate serum levels of insulin and insulin-like growth factor I (IGF-I), both potent prostate cancer mitogens. We tested whether varying dietary carbohydrate and fat, without energy restriction relative to comparison diets, would slow tumor growth and reduce serum insulin, IGF-I, and other molecular mediators of prostate cancer in a xenograft model.

Experimental design: Individually caged male severe combined immunodeficient mice (n = 130) were randomly assigned to one of three diets (described as percent total calories): very high-fat/no-carbohydrate ketogenic diet (NCKD: 83% fat, 0% carbohydrate, 17% protein), low-fat/high-carbohydrate diet (LFD: 12% fat, 71% carbohydrate, 17% protein), or high-fat/moderate-carbohydrate diet (MCD: 40% fat, 43% carbohydrate, 17% protein). Mice were fed to maintain similar average body weights among groups. Following a preliminary feeding period, mice were injected with 1 x 10(6) LNCaP cells (day 0) and sacrificed when tumors were >or=1,000 mm(3).

Results: Two days before tumor injection, median NCKD body weight was 2.4 g (10%) and 2.1 g (8%) greater than the LFD and MCD groups, respectively (P < 0.0001). Diet was significantly associated with overall survival (log-rank P = 0.004). Relative to MCD, survival was significantly prolonged for the LFD (hazard ratio, 0.49; 95% confidence interval, 0.29-0.79; P = 0.004) and NCKD groups (hazard ratio, 0.59; 95% confidence interval, 0.37-0.93; P = 0.02). Median serum insulin, IGF-I, IGF-I/IGF binding protein-1 ratio, and IGF-I/IGF binding protein-3 ratio were significantly reduced in NCKD relative to MCD mice. Phospho-AKT/total AKT ratio and pathways associated with antiapoptosis, inflammation, insulin resistance, and obesity were also significantly reduced in NCKD relative to MCD tumors.

Conclusions: These results support further preclinical exploration of carbohydrate restriction in prostate cancer and possibly warrant pilot or feasibility testing in humans.

Fig. 1

Mouse energy intake and body weights. One hundred thirty 8-wk-old male SCID mice were fed a LFD, MCD, or NCKD for 42 d and then injected s.c. in the flank with 1 × 10⁶ LNCaP tumor cells in 0.1 mL of Matrigel. Mice were weighed twice per week from the start of the experiment. Values are expressed as the median of each group. A, energy intake was measured for each mouse thrice per week by subtracting the weight of uneaten food from the weight of the food placed into the feeding receptacles at the start of each feeding period. B, mice were weighed twice per week from the start of the experiment. Values are expressed as the median of each group.

Fig. 2

A, LNCaP xenograft tumor growth in SCID mice. Mice were injected s.c. on day 0 in the flank with 1 × 10⁶ LNCaP tumor cells in 0.1 mL of Matrigel. Once the tumors became palpable, tumor volume was measured twice per week. Values are expressed as the median of each group. Curves only extend up to the point at which ≥50% of the mice in the respective group had been sacrificed, and therefore median tumor volume is not meaningful. B, Kaplan-Meier survival plot of overall mouse survival by diet group on days 45 and 92.

Fig. 3

Box-plot expression of fasting serum hormone concentrations at the time of sacrifice across all dietary groups. A, insulin; B, IGF-I; C, IGFBP-3; D, ratio of IGF-I/IGFBP-3. Upper and lower box borders represent 25th and 75th percentile values, respectively. Horizontal line within the box represents the median value. Upper and lower whiskers correspond to 95th and 5th percentile values, respectively.

Fig. 4

Box-plot expression of fasting serum hormone concentrations at the time of sacrifice across all dietary groups. A, IGFBP-1; B, ratio of IGF-I/IGFBP-1; C, IGFBP-2. Upper and lower box borders represent 25th and 75th percentile values, respectively. Horizontal line within the box represents the median value. Upper and lower whiskers correspond to 95th and 5th percentile values, respectively.

Fig. 5

Western blot analysis of p-AKT, t-AKT, and β-actin in pooled tumor lysates for each diet group (n = 5 per group). Total AKT levels reflect phosphorylated and unphosphorylated forms, whereas p-AKT reflects levels of the Ser⁴⁷³ phosphoform. β-Actin was used as an internal control for protein loading and transfer.