Inhibition of Neuroblastoma Tumor Growth by Ketogenic Diet and/or Calorie Restriction in a CD1-Nu Mouse Model

INTRODUCTION

Neuroblastoma is a malignant pediatric cancer derived from neural crest cells. It is characterized by a generalized reduction of mitochondrial oxidative phosphorylation. The goal of the present study was to investigate the effects of calorie restriction and ketogenic diet on neuroblastoma tumor growth and monitor potential adaptive mechanisms of the cancer's oxidative phosphorylation system.

METHODS

Xenografts were established in CD-1 nude mice by subcutaneous injection of two neuroblastoma cell lines having distinct genetic characteristics and therapeutic sensitivity [SH-SY5Y and SK-N-BE(2)]. Mice were randomized to four treatment groups receiving standard diet, calorie-restricted standard diet, long chain fatty acid based ketogenic diet or calorie-restricted ketogenic diet. Tumor growth, survival, metabolic parameters and weight of the mice were monitored. Cancer tissue was evaluated for diet-induced changes of proliferation indices and multiple oxidative phosphorylation system parameters (respiratory chain enzyme activities, western blot analysis, immunohistochemistry and mitochondrial DNA content).

RESULTS

Ketogenic diet and/or calorie restriction significantly reduced tumor growth and prolonged survival in the xenograft model. Neuroblastoma growth reduction correlated with decreased blood glucose concentrations and was characterized by a significant decrease in Ki-67 and phospho-histone H3 levels in the diet groups with low tumor growth. As in human tumor tissue, neuroblastoma xenografts showed distinctly low mitochondrial complex II activity in combination with a generalized low level of mitochondrial oxidative phosphorylation, validating the tumor model. Neuroblastoma showed no ability to adapt its mitochondrial oxidative phosphorylation activity to the change in nutrient supply induced by dietary intervention.

CONCLUSIONS

Our data suggest that targeting the metabolic characteristics of neuroblastoma could open a new front in supporting standard therapy regimens. Therefore, we propose that a ketogenic diet and/or calorie restriction should be further evaluated as a possible adjuvant therapy for patients undergoing treatment for neuroblastoma.

Effects of glucose on neuroblastoma in vitro and in vivo

Because neuroblastoma cells in vitro are sensitive to changes in glucose levels in growth media, the effects of glucose levels and dietary carbohydrate on the sensitivity of neuroblastoma cells to chemotherapy were studied. In vitro, 20 microM bromoacetylcholine, 3mM 1,3-diaminopropane, and 5 mM 5-fluorouracil were added to the growth medium of strain N2a neuroblastoma cells cultured in Dulbecco's modified Eagle medium with high glucose (4.5 g/L, HG), normal glucose (1.0 g/L, NG), or low glucose (0.1 g/L, LG). Diaminopropane and 5-fluorouracil had some cytotoxic effect on cells in all media. Bromoacetylcholine killed cells in all media, but at a concentration of 20 microM was most effective in LG medium. Mice (A/Jax) were inoculated with neuroblastoma cells for in vivo studies. Mice could not tolerate a carbohydrate-free diet, while a high-carbohydrate diet caused no change in survival time. When mice on a high carbohydrate diet were treated with cyclophosphamide (100 mg/kg, ip) or 5-fluorouracil (125 mg/kg, ip) they died faster than drug-treated mice on a normal diet. Oral chlorpropamide or cimetidine did not prolong survival time. Analysis of blood glucose levels showed neuroblastoma significantly lowered blood glucose levels (p less than 0.05), while chlorpropamide had no significant effect. It is proposed that manipulation of plasma glucose to lower levels will not be effective in enhancing the chemotherapy of neuroblastoma.

Neuroblastoma and nutritional support: influence on the host-tumor relationship

The nutritional sequelae of neuroblastoma are secondary to tumor burden, tumor-host influenced metabolism, and antitumor operative, pharmacologic, and radiation therapy. Nutritional support and its influence on the outcome of clinical cancer is confusing; but in a defined murine system, we hypothesized that whether or not nutritional repletion favors the host-tumor relationship is dependent on a nutritional augmentation of host antitumor immunity. C1300 murine neuroblastoma (NB) elicits a host antitumor immune response as determined by in vivo and in vitro testing; but the TBJ clone of the same tumor is nonimmunogenic. After receiving two weeks of either regular 24% protein or protein restricted 2.5% protein chow, normal and malnourished mice received either C1300-NB or TBJ-NB and were serially followed to animal death. The median survival time (MST) of TBJ recipients was shorter in this more aggressive tumor, but the MST of 27.5 days was equal for normal and malnourished mice. Contrasting with these data were an MST of 38 days for malnourished C1300 NB recipients and an MST of 64.5 days for normally nourished C1300 NB recipients, values that are significantly different (P less than 0.02). These data suggest that nutritional support influencing host antitumor immunity may be of benefit only in that circumstance where the tumor elicits an antitumor immune response.