The ketogenic diet (KD), a high-fat low-carbohydrate diet, has shown some efficacy in the treatment of certain types of tumors such as brain tumors and neuroblastoma. These tumors are characterized by the Warburg effect. Because renal cell carcinoma (RCC) presents similar energetic features as neuroblastoma, KD might also be effective in the treatment of RCC. To test this, we established xenografts with RCC 786-O cells in CD-1 nu/nu mice and then randomized them to a control diet or to KDs with different triglyceride contents. Although the KDs tended to reduce tumor growth, mouse survival was dramatically reduced due to massive weight loss. A possible explanation comes from observations of human RCC patients, who often experience secondary non-metastatic hepatic dysfunction due to secretion of high levels of inflammatory cytokines by the RCCs. Measurement of the mRNA levels of tumor necrosis factor alpha (TNFα) and interleukin-6 revealed high expression in the RCC xenografts compared to the original 786-O cells. The expression of TNFα, interleukin-6 and C-reactive protein were all increased in the livers of tumor-bearing mice, and KD significantly boosted their expression. KDs did not cause weight loss or liver inflammation in healthy mice, suggesting that KDs are per se safe, but might be contraindicated in the treatment of RCC patients presenting with Stauffer’s syndrome, because they potentially worsen the associated hepatic dysfunction.
Kidney cancer is one of the 10 most prevalent cancers in Western countries, accounting for approximately 2–3% of adult malignancies, and renal cell carcinoma (RCC) comprises approximately 90% of all kidney cancers [1, 2]. In patients with organ-confined disease, surgical resection is the standard therapy and has excellent outcomes . Other current treatments, such as vascular endothelial growth factor (VEGF), platelet-derived growth factor (PDGF), and mammalian target of rapamycin (mTOR) antibodies and inhibitors, have been shown to increase progression-free survival, but the response is rather transient . Moreover, RCC is often diagnosed at a late stage, when curative treatment is not possible. Indeed, metastatic RCC is highly resistant to treatment, with outcomes that are generally poor and a median survival after diagnosis of less than one year [1, 5].
Many tumor cells display a special metabolic signature characterized by high glucose uptake and aerobic glycolysis which, even in the presence of sufficient amounts of oxygen, prevents pyruvate from being metabolized by the respiration of mitochondria, namely oxidative phosphorylation (OXPHOS) [6–9]. This metabolic switch is known as the Warburg effect [10, 11]. In most cases this shift in metabolism is accompanied by a general down-regulation of OXPHOS activity [12–15], or it may involve deficiency of two or three of the OXPHOS complexes [16, 17], or a single defect of one of the OXPHOS subunits [18–20].
RCC also exhibits the Warburg effect. Indeed, in RCC, an increase in glycolytic proteins and depletion of several mitochondrial enzymes has been observed [12, 21]. Moreover, the more aggressive types of RCC are characterized by stabilization of hypoxia-inducible factor (HIF), even in normoxia, due to loss of function of the von Hippel-Lindau (VHL) gene. HIF also contributes to up-regulation of many glycolytic enzymes and suppression of mitochondrial glucose oxidation [4, 22].
The ketogenic diet (KD) is high in fat and low in carbohydrates and protein, and it mimics starvation or prolonged exercise without restricting energy intake. It is characterized by increased ketone body levels (e.g. acetoacetate and β-hydroxybutyrate) and reduced glucose levels in the blood. Because tumor cells highly depend on glucose for energy production, limiting the glucose supply by means of KD could have anti-tumor effects. Moreover, KD has been reported to foster immunity, reduce both inflammation and angiogenesis, and increase apoptosis [23–25]. Finally, KD has shown good potential in enhancing the sensitivity of cancer cells to chemotherapy and in protecting normal cells from radiotherapy. Thus, KD allows cancer treatment with lower doses of chemotherapeutic agents, which might also improve patient compliance [6, 26, 27].
KD was recently shown to be particularly effective in the treatment of brain tumors such as malignant glioma [25, 28], and was applied in several clinical studies as an adjuvant therapy for glioblastoma, astrocytoma, tumors of the gastrointestinal tract, and other advanced metastatic types of cancers [28–32]. In most cases the patients showed a stable disease or general clinical improvement, with increased progression-free survival. In a single case, there was tumor recurrence after KD suspension .
In preclinical studies, KD produced excellent results as an adjuvant therapy in the treatment of neuroblastoma in a murine xenograft model [6, 33]. Neuroblastoma and RCC share a similar metabolic signature, with reduced mitochondrial DNA content and a general reduction of OXPHOS activity [9, 12]. There is evidence that medium-chain triglycerides (MCTs) based KD’s are as effective in the dietary management of intractable epilepsy as those based on long-chain triglycerides (LCTs) , and MCT is included in KD’s as it is more rapidly metabolized and less likely to be stored in adipose tissue compared to LCTs [35, 36]. Based on these premises, we postulated that RCC patients might also benefit from KD therapy. Thus, to elucidate if KD can be used as a potential adjuvant in the treatment of RCC, we created xenografts of human RCC in immunodeficient mice and randomized the mice to a control diet group and to three KD groups with or without MCT enrichment.
Human RCC xenografts have similar respiratory features as human RCC
To ensure that human RCC xenografts of 786-O cells have similar respiratory features as human RCC, we carried out immunohistochemical (IHC) staining of the 5 OXPHOS complexes and porin (a marker of mitochondrial mass) on RCC 786-O xenograft tissue sections. The xenografts exhibited normal mitochondrial mass but significantly lower levels of OXPHOS complexes I–IV compared to normal kidney (Figure 1), consistent with previously published data on respiratory impairment in human RCC samples . These results thus confirmed a general reduction of aerobic mitochondrial metabolism in the RCC 786-O xenograft model.