Alpha fetoprotein was reported in 1963 by Yuri S. Tatarinov as a specific antigen for human liver carcinoma (HCC). Peptide fragments of alpha fetoprotein have the potential to create a new type of anti-cancer agent, including the EBR peptide fragment derived from this protein, which has the ability to bind to estradiol and thus can inhibit the estradiol dependent growth of hormone-dependent cancer cells [21]. The chimeric EBR peptide derived from human and rat alpha fetoprotein (HM-I) has the ability to bind to estradiol far more than human EBR, which was determined in 1995 by Shahbazzadeh [22]. The above results indicate that the concentration of 10− 9 M of estradiol causes more growth of cells in the positive control than the negative control groups. By comparing this result with the results of previous studies, it can be understood that the concentration of 10− 9 M of estradiol which is equivalent to 1 nM has the ability to stimulate the growth of estradiol recipient cells compared to cells in the negative group [14].
The results showed that the concentration of 10− 8 M of the chimeric peptide HM-I with binding to estradiol reduces the growth of cells in the treatment group compared to the cells in the control group. However, comparing the negative control group with the treated one, which is the only effect of the peptide in the absence of estradiol, showed that HM-I singly has no anti-cancer effect on the ZR-75-1 cancer line. In 2008, Sierralta and colleagues worked on an alpha-fetoprotein (Cp) derivative of the 9-esophageal ring. This peptide inhibits the growth of MCF7 and ZR-75-1 cell lines by binding to estradiol while showed no inhibitory effect on estrogen receptor-free breast cancer, MDA-MB231 [23]. But so far no research has been done on the chimeric EBR fragment created of HM-I. The rat EBR binds to estradiol with a higher affinity than human one, and this chimerization promotes the binding of HM-I to estradiol [22]. It should also be noted that in this study, altered metabolic pathways in breast cancer cell of ZR-75-1 class in the presence of estradiol as well as in the presence of estradiol and chimeric peptide were investigated and thus showed the mechanism of action of estradiol in inducing cell growth and also the inhibition of cell growth in the simultaneous presence of estradiol and peptide.
Altered metabolites of ZR-75-1 cells in a culture containing estradiol include glucose, 17α-estradiol, 16alpha-hydroxyestrone, biotin, leucine, tryptophan, arginine, NADPH, pantothenic acid, glutamic acid and lipids (Table 1). Glucose is one of the modified metabolites, and tumor cells use the anaerobic glycolysis pathway (ATP) to produce energy (ATP) faster, which is known as the Warberg effect which produces energy faster than glucose and creates an acidic environment (lactic acid) to protect cancer cells [24]. And because it produces less ATP per glucose molecule, it increases the uptake of glucose by increasing the expression of glucose transporters, including Na+ -dependent glucose transporters (SGLTs) and facilitating glucose transporters (GLUTs) in this cell line [25]. Giuseppe Tripod and colleagues used vitamins, including biotin, as carriers of anti-cancer drugs, arguing that cancer cells needed more vitamins such as biotin to divide and multiply rapidly and biotin can increase the growth of cancer cells, thus being able to act as a suitable vector for anti-cancer drug [26]. Estradiol is one of the compounds that were added to the culture medium of cancer cells at the time of culture and enters the cell through estrogen receptors. The compounds estradiol, estrone and estriol are the main types of estrogen. These compounds of estrogen and the estrogen receptor and estrogen-related metabolites such as 16 alpha-OH can be associated with cancer risk [27].
NADPH is another modified metabolite in this project. It is an essential source of electrons for the synthesis of steroids, amino acids and fatty acids that enhance the rapid growth of tumor cells. It provides the electrons needed for iron-sulfur protein (Fe/S) fusion, which participates in the synthesis of unnecessary amino acids and the formation of lipoic acid, modifications in the tRNA molecule, replication of the DNA molecule and its repair, as well as telomere protection. The enzyme dihydrofolate reductase (DHFR) catalyzes the reduction reaction of conversion of dihydrofolate to tetrahydrofolate (THF) in folate metabolism using NADPH which is required for the biosynthesis of some amino acids, methionine, thymidylate and purines [28]. As the lipids are involved in rapid and uncontrolled proliferation of cancer cells, loss of molecular adhesion and the ability to communicate with other cells, failure to repair DNA damage and ultimately, the ability to tolerate apoptosis by active lipid metabolism in cancer cells [29].
Other altered metabolites are leucine and tryptophan amino acids, in which tryptophan stops the cell cycle in the G1 phase and the proliferation of T lymphocytes. By activating the non-depressible kinase GCN2 pathway, it produces a modulated stress response that ultimately provides the energy responsible for T cells and formation apoptosis. kynorene (Kyn) and downstream metabolites of tryptophan can activate the aryl hydrocarbon receptor (AHR). These metabolites also involved in Treg detection and T lymphocytes and natural killer cells (NK) inhibited by them [30]. Leucine is an essential, branched-chain amino acid that acts as a signaling molecule in the mTOR signaling pathway. Leucine is the most important amino acid involved in protein synthesis, however, if cancer cells do not have access to this amino acid, it does not have a significant effect on these cells [31]. Pantothenic acid and glutamic acid are other metabolites that have undergone changes in these cancer cells that can play an important role in the growth and proliferation of these cells.
Progressive lipid metabolism and mitochondria, mitochondrial leucine metabolism and citric acid cycle can be mentioned as important reactions that the presence of pantothenic acid (vitamin B5) as a precursor of coenzyme A (CoA). Pantothenic acid acts as a coagulant and acyl- carrier protein and has a protective role against oxygen species [30]. Changes in the path of glutamine metabolism can be seen in many cancers. Mitochondrial glutaminase catalyzes the conversion of glutamine to glutamate and increases the amount of this enzyme in cancers. Glutamine provides the nitrogen needed to synthesize nucleotides and hexamine, and some unnecessary amino acids are synthesized in the presence of glutamine as the nitrogen donor [32].
In our study, altered metabolic pathways in the presence of estradiol as well as the concomitant presence of estradiol and chimeric peptide include: the aminoacyl-tRNA biosynthesis pathways, glycolysis and gluconeogenesis, galactose metabolism, biotin metabolism, arginine biosynthesis, alanine aspartate and glutamate metabolism, glutathione metabolism, arginine-proline metabolism, and tryptophan metabolism. They are consistent with previous studies of Yang et al., 2020, working on altered metabolic pathways in breast cancer cells in another study by using 1HNMR metabolomics showing the metabolic pathways of amino acids and aminoacyl-tRNA [33]. Aru Singh and colleagues in 2017 worked on the metabolic pathways of breast cancer that showing the alanine aspartate and glutamate metabolism, glycolysis and gluconeogenesis pathways are altered which is consistent with our study [34].
In cancer cells, there is a link between increased cell growth rate and proliferation, metabolism and protein synthesis. T-RNA expression is higher in cancer cells than in normal cells, this increase in expression is often associated with high expression of TFΙΙΙ factor compounds. Microarray performed in 2009 by Pavon-Eternod et al. was able to measure the levels of tRNA molecules in 3 categories of normal breast epithelial cell groups and 6 categories of breast cancer cells and reported high expression of all types of tRNA in breast cancer cells. Arginine biosynthesis is another altered metabolic pathway [34]. The glycolysis and gluconeogenesis pathways are other altered in breast cancers are consistent with the results of our research and increase glycolysis and decrease gluconeogenesis to produce more energy are indicators of cancer cells [34]. UDP-galactose, the active form of galactose, is a galactosyl donor for the biosynthesis of glycoproteins and glycolipids, indicating that galactose metabolism is required for many cancer cell functions, such as cell-cell detection, metastasis, and receptor-modulated signaling. In fact, it can be said that carbohydrate metabolism affects the growth of cancer cells [36].
L-Arginine is an essential amino acid for cancer cell growth and is obtained by biosynthesis or by adsorption from culture medium in vitro. Arginine enters the cell through cationic amino acid transporters (CATs), and the enzymes arginine synthase and nitric oxide synthase use this amino acid to produce ornithine and nitric oxide (NO) compounds. Both of these compounds are needed for cell proliferation, including cancer cells [37]. The glutathione metabolism pathway is seen in our study, and the antioxidant glutathione can act on the drug metabolites, thus protecting cancer cells from drug poisoning [38].
The metabolic pathways was observed in the treated and positive control groups and negative control along with the positive control group that are quite similar to each other. This is due to the fact that the peptide blocks estrogen but does not affect cancer cells at all, hence its response is due to the presence and absence of estrogen and not the peptide.