A mixture of amino acids and other small molecules present in the serum suppresses the growth of murine and human tumors in vivo

Active mixture of serum-circulating small molecules selectively inhibits proliferation and triggers apoptosis in cancer cells via induction of ER stress

Genetic and epigenetic regulation as well as immune surveillance are known defense mechanisms to protect organisms from developing cancer. Based on experimental evidence, we proposed that small metabolically active molecules accumulating in cancer cells may play a role in an alternative antitumor surveillance system. Previously, we reported that treatment with a mixture of experimentally selected small molecules, usually found in the serum (defined 'active mixture', AM), selectively induces apoptosis in cancer cells and significantly inhibits tumor formation in vivo. In this study, we show that the AM elicits gene expression changes characteristic of endoplasmic reticulum (ER) stress in HeLa, MCF-7, PC-3 and Caco-2 cancer cells, but not in primary human renal epithelial cells. The activation of the ER stress pathway was confirmed by the upregulation of ATF3, ATF4, CHAC1, DDIT3 and GDF15 proteins. Mechanistically, our investigation revealed that eIF2α, PERK and IRE1α are phosphorylated upon treatment with the AM, linking the induction of ER stress to the antiproliferative and proapoptotic effects of the AM previously demonstrated. Inhibition of ER stress in combination with BBC3 and PMAIP1 knockdown completely abrogated the effect of the AM. Moreover, we also demonstrated that the AM induces mIR-3189-3p, which in turn enhances the expression of ATF3 and DDIT3, thus representing a possible new feedback mechanism in the regulation of ATF3 and DDIT3 during ER stress. Our results highlight small molecules as attractive anticancer agents and warrant further evaluation of the AM in cancer therapy, either alone or in combination with other ER stress inducing agents.

Identification of Further Components of an Anticancer Defense System Composed of Small Molecules Present in the Serum

BACKGROUND

Earlier we assumed that small molecules selectively accumulated in cancer cells might have a role in a defense system capable of killing cancer cells. We reported earlier that an experimentally selected mixture of substances present in the serum ("active mixture," AM) shows a selective toxic effect in vitro and in vivo on various cancer cells. In this study we investigated additional compounds found in the serum to further expand our knowledge of this defense system.

MATERIALS AND METHODS

The cell proliferation was detected by WST-1 assay. The mRNA level of the examined genes was measured by quantitative real-time polymerase chain reaction.

RESULTS

We identified 34 additional compounds (l-amino acid metabolites, phenolic acids, d-amino acids, keto acids, etc.), which when applied in a per se nontoxic concentration are able to enhance the effect of AM. The combination of the mixture of these newly identified substances (new mixture, NM) with AM produced a significantly higher cancer cell growth inhibitory effect than NM or AM applied alone on HeLa, MCF-7, PC-3, Caco-2, HepG2, and 4T1 cancer cell lines, and more efficiently induced the expression of certain proapoptotic genes in HeLa cells. Any given combinations of the individual compounds of AM and NM always produced an increased effect compared with AM alone.

CONCLUSIONS

The newly identified compounds significantly enhance the anticancer effect of AM. The components of AM and NM together may form part of a defense system capable of killing cancer cells and are worthy of further investigation.

Parsing the life-shortening effects of dietary protein: effects of individual amino acids

High-protein diets shorten lifespan in many organisms. Is it because protein digestion is energetically costly or because the final products (the amino acids) are harmful? To answer this question while circumventing the life-history trade-off between reproduction and longevity, we fed sterile ant workers on diets based on whole proteins or free amino acids. We found that (i) free amino acids shortened lifespan even more than proteins; (ii) the higher the amino acid-to-carbohydrate ratio, the shorter ants lived and the lower their lipid reserves; (iii) for the same amino acid-to-carbohydrate ratio, ants eating free amino acids had more lipid reserves than those eating whole proteins; and (iv) on whole protein diets, ants seem to regulate food intake by prioritizing sugar, while on free amino acid diets, they seem to prioritize amino acids. To test the effect of the amino acid profile, we tested diets containing proportions of each amino acid that matched the ant's exome; surprisingly, longevity was unaffected by this change. We further tested diets with all amino acids under-represented except one, finding that methionine, serine, threonine and phenylalanine are especially harmful. All together, our results show certain amino acids are key elements behind the high-protein diet reduction in lifespan.

Soy-Based Multiple Amino Acid Oral Supplementation Increases the Anti-Sarcoma Effect of Cyclophosphamide

The use of a mixture of amino acids caused a selective apoptosis induction against a variety of tumor cell lines, reduced the adverse effects of anti-cancer drugs and increased the sensitivity of tumor cells to chemotherapeutic agents. We evaluated the effects and underlying mechanisms of soy-derived multiple amino acids' oral supplementation on the therapeutic efficacy of low-dose cyclophosphamide (CTX) and on tumor growth, apoptosis, and autophagy in severe combined immunodeficiency (SCID) mice that were injected with sarcoma-180 (S-180) cells. 3-methyladenine or siRNA knockdown of Atg5 was used to evaluate its effect on sarcoma growth. A comparison of mice with implanted sarcoma cells, CTX, and oral saline and mice with implanted sarcoma cells, CTX, and an oral soy-derived multiple amino acid supplement indicated that the soy-derived multiple amino acid supplement significantly decreased overall sarcoma growth, increased the Bax/Bcl-2 ratio, caspase 3 expression, and apoptosis, and depressed LC3 II-mediated autophagy. Treatment with 3-methyladenine or Atg5 siRNA elicited similar responses as CTX plus soy-derived multiple amino acid in downregulating autophagy and upregulating apoptosis. A low dose of CTX combined with an oral soy-derived multiple amino acid supplement had a potent anti-tumor effect mediated through downregulation of autophagy and upregulation of apoptosis.

Safety, tolerability, and effect on quality of life of a mixture of amino acids and other small molecules in cancer patients

We performed two clinical studies to evaluate the safety, tolerability, and effect on quality of life of a product containing a mixture of amino acids, vitamins, and other small molecules. In the first one period, open-label, multiple-dose study, the safety and tolerability of a 1-week administration was evaluated in 24 healthy volunteers. In the second one period, open-label, multiple-dose, single-arm study, we investigated the safety, tolerability, and effect on quality of life of a 4-week administration in 50 cancer patients. The safety assessment included the monitoring of adverse events, changes in physical status, and clinical laboratory tests. Changes in quality of life were measured with the European Organization for Research and Treatment of Cancer Quality of Life Questionnaire Core 30 version 3.0 (EORTC QLQ-C30). We have found that administration of the investigated product is safe and well tolerated in healthy individuals and in cancer patients. Administration of the product to cancer patients significantly improved their quality of life (EORTC QLQ-C30 global health status score: baseline: 24.17 ± 9.2; end of treatment: 47.08 ± 14.56, p<0.001). To evaluate the anticancer activity of the investigated product in humans, a randomized, blinded, combination clinical trial should be conducted.

Tumor-dependent increase of serum amino acid levels in breast cancer patients has diagnostic potential and correlates with molecular tumor subtypes

Background

Malignancies induce changes in the levels of serum amino acids (AA), which may offer diagnostic potential. Furthermore, changes in AA levels are associated with immune cell function. In this study, serum AA levels were studied in breast cancer patients versus patients with benign breast lesions.

Methods

In a prospective study, serum levels of 15 AA were measured by high performance liquid chromatography before and after surgery in 41 breast cancer patients (BrCA) and nine patients with benign breast lesions (healthy donors, HD). Results were analyzed in relation to clinical tumor data and tested against immunological flow cytometry data. Principal component analysis was performed and the accuracy of AA levels as a potential diagnostic tool was tested.

Results

Pre- but not postoperative serum AA levels were increased in BrCA in eight out of 15 AA compared with HD. Serum AA levels were highest in the most aggressive (basal-like) as compared with the least aggressive tumor subtype (luminal A). A principal component (PC1) of all measured AA correlated with a mainly pro-inflammatory immune profile, while a second one (PC2, selectively considering AA preoperatively differing between HD and BrCA) could predict health state with an area under the curve of 0.870.

Conclusions

Breast cancer shows a tumor-dependent impact on serum AA levels, which varies with intrinsic tumor subtypes and is associated with a pro-inflammatory state. Serum AA levels need further evaluation as a potential diagnostic tool.

Effects of vitamin B6 metabolism on oncogenesis, tumor progression and therapeutic responses

Pyridoxal-5'-phosphate (PLP), the bioactive form of vitamin B6, reportedly functions as a prosthetic group for >4% of classified enzymatic activities of the cell. It is therefore not surprising that alterations of vitamin B6 metabolism have been associated with multiple human diseases. As a striking example, mutations in the gene coding for antiquitin, an evolutionary old aldehyde dehydrogenase, result in pyridoxine-dependent seizures, owing to the accumulation of a metabolic intermediate that inactivates PLP. In addition, PLP is required for the catabolism of homocysteine by transsulfuration. Hence, reduced circulating levels of B6 vitamers (including PLP as well as its major precursor pyridoxine) are frequently paralleled by hyperhomocysteinemia, a condition that has been associated with an increased risk for multiple cardiovascular diseases. During the past 30 years, an intense wave of clinical investigation has attempted to dissect the putative links between vitamin B6 and cancer. Thus, high circulating levels of vitamin B6, as such or as they reflected reduced amounts of circulating homocysteine, have been associated with improved disease outcome in patients bearing a wide range of hematological and solid neoplasms. More recently, the proficiency of vitamin B6 metabolism has been shown to modulate the adaptive response of tumor cells to a plethora of physical and chemical stress conditions. Moreover, elevated levels of pyridoxal kinase (PDXK), the enzyme that converts pyridoxine and other vitamin B6 precursors into PLP, have been shown to constitute a good, therapy-independent prognostic marker in patients affected by non-small cell lung carcinoma (NSCLC). Here, we will discuss the clinical relevance of vitamin B6 metabolism as a prognostic factor in cancer patients.