**Abstract**

Arginine is well known semi-essential amino acid used in protein biosynthesis through several metabolic pathways. It is majorly obtained from nutrients sources and synthesized by the urea cycle in the body using citrulline. Arginine found to be involved in several mechanisms including; hormone synthesis, cell division, activation of the immune system, ammonia disposal and wound healing and also in the production of nitric oxide (NO) and polyamines. During cancer persistence, the biosynthesis of arginine is not sufficient to compensate for their higher nutritional requirements but extracellular availability of arginine is also required. Therefore, the consequences of arginine deprivation may represent a novel targeting therapy to cure cancer. The impact of different arginine deprivation agents and their mechanism of action always found to be correlated with NO and polyamine levels. Arginine deprivation strategy to hamper the proliferation of cancerous cells and their migration is represented as a new approach to cure cancer by inhibiting the argininosuccinate synthetase1 (ASS1) expression and NO and polyamines production. ASS1 is the first key enzyme that converts citrulline to arginine and numerous tumors such as hepatocellular carcinoma, melanoma, mesotheliomas and renal cancer do not express ASS1 and main focused enzyme for cancer treatment. Degradation of arginine by the enzyme arginine deiminase (ADI) specifically triggers the arginine elimination and inhibition of cancer migration. Though, ADI is a microbial enzyme but has a high affinity to arginine and converts arginine into citrulline and NH3. This produced citrulline can be recycled back to arginine in normal cells where ASS1 expression is very high in comparison to ASS1-negative tumor cells. A modified form of ADI with pegylate (ADI-PEG20) has been formulated which showed both in-vivo and in-vitro activity against hepatocellular carcinoma and melanoma by inducing apoptosis. In this chapter, we have majorly discussed arginine production with different pathways and how its degradation into other metabolic active compounds involved in cancer treatment. Moreover, how arginine deprivation is directly taking part in the inhibition of cancer cell proliferation and its migration.

**Keywords:** arginine, metabolic pathways, arginine deprivation, cancer therapy

## **1. Introduction**

Arginine is essential for microbes and semi-essential for eukaryotes which play numerous crucial roles in cellular metabolism. The impact of arginine always considered as a nonessential amino acid because a cell can synthesize arginine its

own as per the requirement. But, during its limitation in the cells, it is necessary to acquire arginine from outside environment and this condition denoted arginine as a conditionally essential amino acid. Majorly, arginine is produced by two ways; from food sources and biosynthesized through urea cycle in the kidney [1]. The biosynthesis of arginine represented the conversion of citrulline to arginine by the enzymes arginosuccinate synthetase1 (ASS1) and arginosuccinate lyase (ASL). The role of enzyme ASS1 is the conversion of citrulline and aspartic acid to arginosuccinate, which then directly converted to arginine and fumaric acid by the enzyme ASL [2]. In case of bacteria, ornithine also indicated as a substrate to synthesize arginine by the enzyme ornithine transcarbamylase (OCT) [3]. Arginine is a precursor molecule for the formation of amino acids such as proline, glutamate and arginine itself and several other components like succinate, nitrate, nitrite, nitric oxide (NO), ammonia and CO2. It acts as an intermediate in urea cycle and precursor molecules for polyamine, creatine and proteins biosynthesis [4]. Arginine becomes necessary for growth and promotes wound healing by stimulating the release of growth hormones such as insulin-like growth factor-1, insulin and prolactin and also has several immunomodulatory effects such as stimulation of T cells, natural killer cell and enhances pro-inflammatory cytokine levels [5]. Thus, arginine deprived cancer cells can be rescued by activating immunity and increasing the flux of arginine through urea cycle [6]. When a cell is under stress or need to proliferate like tumor cell, then the requirement of cellular components such as citrulline, nitric oxide and polyamine levels get increase. Therefore arginine synthesis and degradation tremendously increase in cancer cells [7]. Arginine depletion is one of the most accepted way to cure tumor cells which are auxotrophic (dependent on uptake of extracellular arginine) to arginine. Some tumor cells adapted with downregulated arginine metabolizing enzymes for inhibiting the production of arginine from the substrates and become arginine auxotrophic [8]. Therefore, during cancer some nonessential amino acids turned in to the essential and cancer cell becomes auxotrophic for these [9]. As we all know that cancerous cells are associated with very high survival rates, therefore, some significant improvements are required for early detection and treatment of cancer. The idea for cancer treatment open the door for some most advanced approaches including; hormone therapy, stem cell therapy, immunotherapy and amino acid deprivation therapy [6, 10, 11]. One of the most capable amino acid deprivation therapy is arginine deprivation where arginine-depleting agents are the main focused and depletion of arginine harms the ability of cancer cell metastasize. The mechanisms of arginine impairment are still not clear hence, in this chapter we will try to give a brief discussion about the different biosynthesis and catabolic pathways of arginine. How arginine deprivation can be focused for cancer therapy for both arginine auxotrophic and non-auxotrophic cancerous cells with different mechanism of actions. Moreover, we will discuss the impact of arginine deprivation in cell migration through different intermediates production such as polyamines and NO.

### **2. Arginine biosynthesis pathways**

Arginine is synthesized from citrulline by the key enzymes ASS1and ASL of the urea cycle which also called ornithine cycle and then released into the bloodstream (**Figure 1a**). In large animals, citrulline is produced majorly from NH3, CO2 and ornithine by the enzymes OTC and carbamylphosphate synthetase I (CPS1) in the small intestine. Citrulline is also recycled to arginine when both argininosuccinate ASS1and ASL are present in the same cell and take part in to the citrulline-nitric oxide cycle [12]. In contrast arginase and nitric oxide synthetase use arginine as a

**155**

**Figure 1.**

*biosynthesis form glutamine.*

*Arginine Metabolism: An Enlightening Therapeutic Attribute for Cancer Treatment*

common substrate and always compete for this substrate [13]. Arginine biosynthesis exhibits diverse pattern of gene organization in bacteria, mammals and plants and uses different set of enzymes which catalyze reactions for the formation of a key intermediate "ornithine". Additionally, glutamate is also utilized as the precursor for ornithine synthesis using some intermediates of the urea cycle [13, 14]. Extracellular arginine is also a source for ornithine synthesis in cells by enzyme arginase 1 [12]. In bacteria and plants, ornithine is synthesized from glutamate in five enzymatic steps initiated by the acetylation of glutamate by N-acetylglutamate synthase and called N-acetylglutamate synthase pathway (**Figure 1b**) [15]. Here, first ornithine is converted to citrulline by ornithine carbamoyltransferase.

*(a) Arginine biosynthesis from glutamine and arginine itself in the urea cycle. (b) Key steps of the arginine* 

*DOI: http://dx.doi.org/10.5772/intechopen.97254*

*Arginine Metabolism: An Enlightening Therapeutic Attribute for Cancer Treatment DOI: http://dx.doi.org/10.5772/intechopen.97254*

common substrate and always compete for this substrate [13]. Arginine biosynthesis exhibits diverse pattern of gene organization in bacteria, mammals and plants and uses different set of enzymes which catalyze reactions for the formation of a key intermediate "ornithine". Additionally, glutamate is also utilized as the precursor for ornithine synthesis using some intermediates of the urea cycle [13, 14]. Extracellular arginine is also a source for ornithine synthesis in cells by enzyme arginase 1 [12]. In bacteria and plants, ornithine is synthesized from glutamate in five enzymatic steps initiated by the acetylation of glutamate by N-acetylglutamate synthase and called N-acetylglutamate synthase pathway (**Figure 1b**) [15]. Here, first ornithine is converted to citrulline by ornithine carbamoyltransferase.

**Figure 1.**

*(a) Arginine biosynthesis from glutamine and arginine itself in the urea cycle. (b) Key steps of the arginine biosynthesis form glutamine.*

*Bioactive Compounds - Biosynthesis, Characterization and Applications*

intermediates production such as polyamines and NO.

Arginine is synthesized from citrulline by the key enzymes ASS1and ASL of the urea cycle which also called ornithine cycle and then released into the bloodstream (**Figure 1a**). In large animals, citrulline is produced majorly from NH3, CO2 and ornithine by the enzymes OTC and carbamylphosphate synthetase I (CPS1) in the small intestine. Citrulline is also recycled to arginine when both argininosuccinate ASS1and ASL are present in the same cell and take part in to the citrulline-nitric oxide cycle [12]. In contrast arginase and nitric oxide synthetase use arginine as a

**2. Arginine biosynthesis pathways**

own as per the requirement. But, during its limitation in the cells, it is necessary to acquire arginine from outside environment and this condition denoted arginine as a conditionally essential amino acid. Majorly, arginine is produced by two ways; from food sources and biosynthesized through urea cycle in the kidney [1]. The biosynthesis of arginine represented the conversion of citrulline to arginine by the enzymes arginosuccinate synthetase1 (ASS1) and arginosuccinate lyase (ASL). The role of enzyme ASS1 is the conversion of citrulline and aspartic acid to arginosuccinate, which then directly converted to arginine and fumaric acid by the enzyme ASL [2]. In case of bacteria, ornithine also indicated as a substrate to synthesize arginine by the enzyme ornithine transcarbamylase (OCT) [3]. Arginine is a precursor molecule for the formation of amino acids such as proline, glutamate and arginine itself and several other components like succinate, nitrate, nitrite, nitric oxide (NO), ammonia and CO2. It acts as an intermediate in urea cycle and precursor molecules for polyamine, creatine and proteins biosynthesis [4]. Arginine becomes necessary for growth and promotes wound healing by stimulating the release of growth hormones such as insulin-like growth factor-1, insulin and prolactin and also has several immunomodulatory effects such as stimulation of T cells, natural killer cell and enhances pro-inflammatory cytokine levels [5]. Thus, arginine deprived cancer cells can be rescued by activating immunity and increasing the flux of arginine through urea cycle [6]. When a cell is under stress or need to proliferate like tumor cell, then the requirement of cellular components such as citrulline, nitric oxide and polyamine levels get increase. Therefore arginine synthesis and degradation tremendously increase in cancer cells [7]. Arginine depletion is one of the most accepted way to cure tumor cells which are auxotrophic (dependent on uptake of extracellular arginine) to arginine. Some tumor cells adapted with downregulated arginine metabolizing enzymes for inhibiting the production of arginine from the substrates and become arginine auxotrophic [8]. Therefore, during cancer some nonessential amino acids turned in to the essential and cancer cell becomes auxotrophic for these [9]. As we all know that cancerous cells are associated with very high survival rates, therefore, some significant improvements are required for early detection and treatment of cancer. The idea for cancer treatment open the door for some most advanced approaches including; hormone therapy, stem cell therapy, immunotherapy and amino acid deprivation therapy [6, 10, 11]. One of the most capable amino acid deprivation therapy is arginine deprivation where arginine-depleting agents are the main focused and depletion of arginine harms the ability of cancer cell metastasize. The mechanisms of arginine impairment are still not clear hence, in this chapter we will try to give a brief discussion about the different biosynthesis and catabolic pathways of arginine. How arginine deprivation can be focused for cancer therapy for both arginine auxotrophic and non-auxotrophic cancerous cells with different mechanism of actions. Moreover, we will discuss the impact of arginine deprivation in cell migration through different

**154**

Enzyme ASS1 catalyzes the conversion of citrulline to aspartate and argininosuccinate which is further converted into arginine and fumarate by ASL [16, 17]. Ornithine can also be converted back to citrulline by arginine deiminase (ADI) pathway in bacteria [18] and by arginase1 pathway in mammals [19]. In both the cases citrulline is recycled back to arginine by ASS enzyme [15]. The ability to generate arginine from citrulline depends on the activity of ASS and ASL [20]. These two enzymes are tightly coupled for sensitivity of cells to arginine deprivation and their activity depends on their ability to regenerate arginine from the alternative sources [21].
