Ketone body utilization drives tumor growth and metastasis

We have previously proposed that catabolic fibroblasts generate mitochondrial fuels (such as ketone bodies) to promote the anabolic growth of human cancer cells and their metastasic dissemination. We have termed this new paradigm “two-compartment tumor metabolism.” Here, we further tested this hypothesis by using a genetic approach. For this purpose, we generated hTERT-immortalized fibroblasts overexpressing the rate-limiting enzymes that promote ketone body production, namely BDH1 and HMGCS2. Similarly, we generated MDA-MB-231 human breast cancer cells overexpressing the key enzyme(s) that allow ketone body re-utilization, OXCT1/2 and ACAT1/2. Interestingly, our results directly show that ketogenic fibroblasts are catabolic and undergo autophagy, with a loss of caveolin-1 (Cav-1) protein expression. Moreover, ketogenic fibroblasts increase the mitochondrial mass and growth of adjacent breast cancer cells. However, most importantly, ketogenic fibroblasts also effectively promote tumor growth, without a significant increase in tumor angiogenesis. Finally, MDA-MB-231 cells overexpressing the enzyme(s) required for ketone re-utilization show dramatic increases in tumor growth and metastatic capacity. Our data provide the necessary genetic evidence that ketone body production and re-utilization drive tumor progression and metastasis. As such, ketone inhibitors should be designed as novel therapeutics to effectively treat advanced cancer patients, with tumor recurrence and metastatic disease. In summary, ketone bodies behave as onco-metabolites, and we directly show that the enzymes HMGCS2, ACAT1/2 and OXCT1/2 are bona fide metabolic oncogenes.     

Ketone bodies and two-compartment tumor metabolism: Stromal ketone production fuels mitochondrial biogenesis in epithelial cancer cells

We have previously suggested that ketone body metabolism is critical for tumor progression and metastasis. Here, using a co-culture system employing human breast cancer cells (MCF7) and hTERT-immortalized fibroblasts, we provide new evidence to directly support this hypothesis. More specifically, we show that the enzymes required for ketone body production are highly upregulated within cancer-associated fibroblasts. This appears to be mechanistically controlled by the stromal expression of caveolin-1 (Cav-1) and/or serum starvation. In addition, treatment with ketone bodies (such as 3-hydroxy-butyrate, and/or butanediol) is sufficient to drive mitochondrial biogenesis in human breast cancer cells. This observation was also validated by unbiased proteomic analysis. Interestingly, an MCT1 inhibitor was sufficient to block the onset of mitochondrial biogenesis in human breast cancer cells, suggesting a possible avenue for anticancer therapy. Finally, using human breast cancer tumor samples, we directly confirmed that the enzymes associated with ketone body production (HMGCS2, HMGCL and BDH1) were preferentially expressed in the tumor stroma. Conversely, enzymes associated with ketone re-utilization (ACAT1) and mitochondrial biogenesis (HSP60) were selectively associated with the epithelial tumor cell compartment. Our current findings are consistent with the “two-compartment tumor metabolism” model. Furthermore, they suggest that we should target ketone body metabolism as a new area for drug discovery, for the prevention and treatment of human cancers.     

Ketone bodies and two-compartment tumor metabolism: Stromal ketone production fuels mitochondrial biogenesis in epithelial cancer cells

We have previously suggested that ketone body metabolism is critical for tumor progression and metastasis. Here, using a co-culture system employing human breast cancer cells (MCF7) and hTERT-immortalized fibroblasts, we provide new evidence to directly support this hypothesis. More specifically, we show that the enzymes required for ketone body production are highly upregulated within cancer-associated fibroblasts. This appears to be mechanistically controlled by the stromal expression of caveolin-1 (Cav-1) and/or serum starvation. In addition, treatment with ketone bodies (such as 3-hydroxy-butyrate, and/or butanediol) is sufficient to drive mitochondrial biogenesis in human breast cancer cells. This observation was also validated by unbiased proteomic analysis. Interestingly, an MCT1 inhibitor was sufficient to block the onset of mitochondrial biogenesis in human breast cancer cells, suggesting a possible avenue for anticancer therapy. Finally, using human breast cancer tumor samples, we directly confirmed that the enzymes associated with ketone body production (HMGCS2, HMGCL and BDH1) were preferentially expressed in the tumor stroma. Conversely, enzymes associated with ketone re-utilization (ACAT1) and mitochondrial biogenesis (HSP60) were selectively associated with the epithelial tumor cell compartment. Our current findings are consistent with the “two-compartment tumor metabolism” model. Furthermore, they suggest that we should target ketone body metabolism as a new area for drug discovery, for the prevention and treatment of human cancers.     

Olfactomedin 4 suppresses tumor growth and metastasis of mouse melanoma cells through downregulation of integrin and MMP genes

Olfactomedin 4 (OLFM4) is highly expressed in gastrointestinal cancers and has an anti-apoptotic function. The roles of OLFM4 in tumor growth and metastasis and how it functions in these processes remain elusive. We investigated the function of OLFM4 in tumor growth and metastasis using B16F10 mouse melanoma cells as an experimental system. Our results showed that OLFM4 had no positive effect on cell viability or cell cycle progression in B16F10 cells. However, it significantly suppressed the tumorigenicity of B16F10 cells, i.e., intradermal primary tumor growth and lung metastasis. OLFM4 also suppressed the migration and invasion of B16F10 cells in vitro. For further insight into the mechanisms underlying OLFM4-mediated suppression of tumor progression, we examined the effect of OLFM4 on the expression of integrin and matrix metalloproteinase (MMP), both of which are involved in tumor progression. Overexpression of OLFM4 clearly reduced the expression levels of integrin α1, integrin α4, integrin α5, integrin α6, and MMP9. Moreover, forced expression of MMP9 attenuated the inhibitory activity of OLFM4 on migration and invasiveness. Our findings provide the experimental evidence that OLFM4 may function as a tumor suppressor and an anti-metastatic gene during tumor progression.     

肿瘤转移抑制基因BRMS1的表达分析及机制研究进展

乳腺癌转移抑制基因1(BRMS1)是一个有活性的肿瘤转移抑制基因,参与抑制乳腺癌、黑素瘤、鼻咽癌、非小细胞肺癌、卵巢癌等恶性肿瘤的转移。BRMS1编码蛋白主要通过转录调控转移相关靶基因,参与调节细胞凋亡、细胞通讯、肿瘤血管新生等多种细胞事件。从BRMS1基因的分子结构、表达调控、生物学功能以及转移抑制机理等方面对BRMS1的研究进展做简要回顾。     

Functional mechanism of Ginsenosides on tumor growth and metastasis

Ginsengs, has long been used as one medicinal herb in China for more than two thousand years. Many studies have shown that ginsengs have preventive and therapeutic roles for cancer, and play a good complementary role in cancer treatment. Ginsenosides, as most important constituents of ginseng, have been extensively investigated and emphasized in cancer chemoprevention and therapeutics. However, the functional mechanism of Ginsenosides on cancer is not well known. This review will focus on introducing the functional mechanisms of ginsenosides and their metabolites, which regulate signaling pathways related with tumor growth and metastasis. Ginsenosides inhibit tumor growth via upregulating tumor apoptosis, inducing tumor cell differentiation and targeting cancer stem cells. In addition, Ginsenosides regulate tumor microenvironment via suppressing tumor angiogenesis-related proteins and pathways. Structural modification of ginsenosides and their administration alone or combinations with other Chinese medicines or chemical medicines have recently been developed to be a new therapeutic strategy for cancer.     

Copper and zinc metabolism with solid tumor growth

The variation in copper and zinc metabolism with tumor growth appears to relate directly to progression or regression of the disease. Historically, elevations in serum copper have been used as clinical indicators in hematological neoplasms since the early 1960s. More recently, we have monitored breast, colo-rectal, and lung cancer patients for a six-month period through courses of cytotoxic chemotherapy to determine copper and zinc changes with tumor growth. Groups were divided into responders and nonresponders blind to their serum copper and zinc levels. Trends in elevated serum copper with active disease have shown similar trends in decreasing values with effective therapy, but normalization was at a slower rate. Serum zinc levels in the same patients were markedly below normal and did not increase in the study period. The clinical significance or elevated serum copper and depressed serum zinc is discussed and the potential relationship between the two elements is explored. A solid tumor-bearing rat model, mammary adenocarcinoma R 3230 AC, has detailed more of the changes in copper and zinc metabolism with solid tumor growth. Serum copper and zinc varied with tumor mass, as in clinical studies. Liver values of the two essential metals did not change significantly, but liver-related copper-containing enzymes showed marked variations. Ceruloplasmin in serum increased with increasing tumor mass, as would be expected with the increased serum copper levels. Cytochrome c oxidase activity in liver homogenates from tumor-bearing animals was significantly depressed.     

The tumor microenvironment: An irreplaceable element of tumor budding and epithelial-mesenchymal transition-mediated cancer metastasis

Tumor budding occurs at the invasive front of cancer; the tumor cells involved have metastatic and stemness features, indicating a poor prognosis. Tumor budding is partly responsible for cancer metastasis, and its initiation is based on the epithelial-mesenchymal transition (EMT) process. The EMT process involves the conversion of epithelial cells into migratory and invasive cells, and is a profound event in tumorigenesis. The EMT, associated with the formation of cancer stem cells (CSCs) and resistance to therapy, results from a combination of gene mutation, epigenetic regulation, and microenvironmental control. Tumor budding can be taken to represent the EMT in vivo. The EMT process is under the influence of the tumor microenvironment as well as tumor cells themselves. Here, we demonstrate that the tumor microenvironment dominates EMT development and impacts cancer metastasis, as well as promotes CSC formation and mediates drug resistance. In this review, we mainly discuss components of the microenvironment, such as the extracellular matrix (ECM), inflammatory cytokines, metabolic products, and hypoxia, that are involved in and impact on the acquisition of tumor-cell motility and dissemination, the EMT, metastatic tumor-cell formation, tumor budding and CSCs, and cancer metastasis, including subsequent chemo-resistance. From our point of view, the tumor microenvironment now constitutes a promising target for cancer therapy.     

Mitochondrial dysfunction in breast cancer cells prevents tumor growth

Metformin is a well-established diabetes drug that prevents the onset of most types of human cancers in diabetic patients, especially by targeting cancer stem cells. Metformin exerts its protective effects by functioning as a weak “mitochondrial poison,” as it acts as a complex I inhibitor and prevents oxidative mitochondrial metabolism (OXPHOS). Thus, mitochondrial metabolism must play an essential role in promoting tumor growth. To determine the functional role of “mitochondrial health” in breast cancer pathogenesis, here we used mitochondrial uncoupling proteins (UCPs) to genetically induce mitochondrial dysfunction in either human breast cancer cells (MDA-MB-231) or cancer-associated fibroblasts (hTERT-BJ1 cells). Our results directly show that all three UCP family members (UCP-1/2/3) induce autophagy and mitochondrial dysfunction in human breast cancer cells, which results in significant reductions in tumor growth. Conversely, induction of mitochondrial dysfunction in cancer-associated fibroblasts has just the opposite effect. More specifically, overexpression of UCP-1 in stromal fibroblasts increases β-oxidation, ketone body production and the release of ATP-rich vesicles, which “fuels” tumor growth by providing high-energy nutrients in a paracrine fashion to epithelial cancer cells. Hence, the effects of mitochondrial dysfunction are truly compartment-specific. Thus, we conclude that the beneficial anticancer effects of mitochondrial inhibitors (such as metformin) may be attributed to the induction of mitochondrial dysfunction in the epithelial cancer cell compartment. Our studies identify cancer cell mitochondria as a clear target for drug discovery and for novel therapeutic interventions.     

不同接种量荧光素酶标记小鼠乳腺癌细胞4T1在小鼠体内生长及肺转移的比较

目的 采用活体成像技术比较四种剂量荧光素酶标记肿瘤细胞在小鼠体内生长及肺转移情况,为光学标记肿瘤模型的药物筛选或机制研究提供参考资料.方法 以荧光素酶作为报告基因导人小鼠乳腺癌细胞4T1中,经G418筛选获得稳定表达荧光素酶的细胞克隆并扩大培养.标记细胞稀释成1×107细胞/mL,2×107细胞/mL,5×107细胞/mL和1×108细胞/mL四种剂量,取0.1 mL接种子BALB/c小鼠右侧第二对乳腺脂肪垫内,制作小鼠原位乳腺癌模型,比较肿瘤细胞在小鼠体内生长及肺转移情况.结果获得稳定表达荧光素酶基因的细胞克隆,在致瘤性方面和亲代细胞无明显差别,四种剂量细胞接种BALB/c小鼠后,均有肿瘤生长,接种第28天时,四种剂量接种的原位移植瘤大小没有明显差别,但接种两个高剂量肿瘤细胞的小鼠组各有2只小鼠死亡;接种后31 d,发现四种剂量接种的原位移植瘤均发生不同程度的转移,随着观察天数的增加,转移程度逐渐严重,接种后42 d,小鼠陆续发生死亡.结论 根据转移和死亡情况,确定接种1×106个细胞/只不仅肺转移明显,而且存活时间一般超过45 d,比高剂量接种存活时间长,为最佳肺转移剂量.     

Role of proteins of the macroglobulin family in regulation of tumor growth

Proteins of the macroglobulin family are an ancient and evolutionarily conservative link of the immune system, which is actively involved in both inhibition of tumor growth cells and proliferation of tumor cells. Two basically different binding sites and a great conformational plasticity of all representatives of the macroglobulin family, as well as the presence of two to four representatives of the family in the blood of most species allow them to transport diverse substances and exert various regulatory influences on both the tumor and the entire organism. For example, the capacity of macroglobulins for binding hydrolases makes it possible to inhibit enzyme mediated tumor invasion. At the same time, an excess of macroglobulin/hydrolase complexes can activate apoptosis. The tumor is able of using macroglobulins, especially pregnancy-associated proteins, for its own protection. Specifically, pregnancy-associated α₂-glycoprotein, which is actively produced by human tumor cells, blocks the his to compatibility complex antigens. On the contrary, the capacity of binding zinc stimulates the thymulin-dependent activation of natural killer cells. Nevertheless, the actively growing tumor expresses many receptors to macroglobulins, which are the main carriers of some cytokines and growth factors essential for proliferation.     

Osteopontin contributes to hepatocyte growth factor-induced tumor growth and metastasis formation

The cytokine hepatocyte growth factor (HGF)/scatter factor-1 and its cognate receptor, Met, are involved in the etiology and progression of many types of cancer. Despite recent advances in understanding the signal transduction pathways activated by HGF, the mechanism by which HGF exerts its tumorigenic effect is not well understood. To identify proteins that may be involved in mediating HGF-induced cell motility, invasiveness, and tumorigenesis, we used two separate differential display screening methods to identify changes in gene expression that are initiated by HGF in an epithelial cell culture system. Among several known and unknown genes whose expression was modified, osteopontin (OPN), a protein previously associated with tumorigenesis, was found to be upregulated within 6 h following HGF stimulation. OPN expression was dependent on activation of the PI-3 kinase pathway. Autocrine secretion of HGF resulted in sustained expression of OPN. Downregulation of opn expression by stable antisense transfection attenuated OPN expression and repressed HGF-induced invasiveness in vitro and decreased HGF-mediated tumor growth and metastasis formation in vivo. Constitutive expression of OPN in itself exerted partial invasiveness in vitro, but its expression itself was not sufficient to initiate tumor growth or metastasis formation in vivo. Thus, together with other molecules, OPN activity contributes to HGF-induced tumor growth and invasiveness.     

Urokinase-type plasminogen activator receptor signaling is critical in nasopharyngeal carcinoma cell growth and metastasis

Nasopharyngeal carcinoma (NPC) is one of the most common malignancies in southern China and Southeast Asia, with the highest metastasis rate among head and neck cancers. The mechanisms underlying NPC progression remain poorly understood. Genome-wide expression profiling on 18 NPC vs. 18 noncancerous nasopharyngeal tissues together with GeneGo pathway analysis and expression verification in NPC cells and tissues revealed a potential role of urokinase-type plasminogen activator receptor (uPAR) in NPC progression, which has not been investigated in NPC. We then observed that uPAR expression is increased in poorly differentiated, highly metastatic NPC cells compared with lowly metastatic cells or differentiated NPC cells. In vitro studies demonstrated that uPAR regulates NPC cell growth, colony formation, migration, and invasion and promotes the epithelial–mesenchymal transition (EMT). Additional tumor xenograft and spontaneous metastasis experiments revealed that uPAR promotes NPC cell growth and metastasis in vivo. The JAK–STAT pathway is involved in uPAR-regulated signaling in NPC cells as determined by immunoblotting. Moreover, uPAR-mediated growth and motility is partially abolished upon treatment with the Jak1/Jak2 inhibitor INCB018424. We suppressed uPA expression in uPAR-overexpressing NPC cells and found that uPAR-mediated cellular growth and motility is not exclusively dependent on uPA. In summary, uPAR is a significant regulator of NPC progression and could serve as a promising therapeutic target.