Cancer is a group of diseases characterize by abnormal cell growths that can invade or spread to other parts of the body. Cancer can also be defined by uncontrolled cell proliferation. Cancer is one of the leading causes of death worldwide and the number of cancer patients is steadily increasing. There are over 100 different types of cancer known to affect humans, each classified according to the type of cell it was originally affected in. It was estimated that by 2030, 26 million new cancer cases and 17 million cancer deaths are expected each year [1]. Cancer hallmarks include maintaining proliferative signaling, evading growth inhibitors, defending against cell death, achieving replicative immortality, inducing angiogenesis, and activating invasion and metastasis to support human tumorigenesis. These processes are regulated by complex genetic circuits, often involving growth factor signaling, and cancer-associated proliferation can be either independent of this circuit or of the same growth-promoting signals that drive normal proliferation. Dependent on aberrant activation many normal processes also involve rapid cell proliferation, such as embryonic development, the immune response to infection, wound repair, and cell turnover in tissues such as the intestine [2]. The latter is a process regulated by a complex genetic circuit that often involves growth factor signaling, whereas cancer-associated proliferation is independent of this circuit or aberrant in the same growth signals that drive normal growth. The challenge in cancer therapy is to be able to target abnormal growth while suppressing normal growth. This requires a thorough understanding of both the normal and malignant mechanisms that drive cell growth and proliferation.
Pyruvate kinase muscle isoenzyme 2 (PKM2) is found primarily in the cytosol and catalyzes the irreversible transphosphorylation between phosphoenolpyruvate (PEP) and ADP to release pyruvate as the final step in glycolysis. It functions as an evolutionarily conserved glycolytic enzyme that produces ATP. Glycolysis is the key process of glucose breakdown, where glucose is broken down into two pyruvates. PKM2 acts as a protein kinase, regulates gene transcription in the nucleus [3], it reprograms oxidative phosphorylation to aerobic glycolysis, and promotes intra mitochondrial tumor cell proliferation and migration [4]. In addition, PKM2 has been found in the extracellular fluid of patients with gastrointestinal, pancreatic adenocarcinoma, lung, ovarian, and renal cell carcinomas [5]. Pyruvate kinase can exist as a tetramer or dimer (Fig. 1). The tetrameric structure is the active form with high binding affinity for PEP, while the dimeric form has low binding affinity for PEP and low activity. PKM1 constitutively oligomerizes into tetramers under physiological conditions, whereas PKM2 can exist as dimers or tetramers depending on the appropriate regulator. PKM1 and PKM2 undergo differential allosteric regulation and covalent modification [6]. The glycolytic intermediate fructose-1, 6-bisphosphate (FBP) preferentially binds to PKM2 rather than PKM1, thus increasing the affinity of PKM2 for PEP [7]. Besides FBP, many other metabolites, amino acids and small molecules are involved in regulating PKM2 activity [8]. Binding of small-molecule PKM2 activators to PKM2 promotes tetramer formation, thereby constitutively activating PKM2 and suppressing tumorigenesis. Post-translational modifications of PKM2, such as phosphorylation, acetylation, or oxidation, promote low activity of dimeric PKM2 [9]. Therefore, the activity of pyruvate kinase can be regulated by altering its conformation. The constitutive activity of tetramers like PKM1 allows them to function as pyruvate kinase in the cytosol, promoting the glycolytic process and energy production, whereas the less active dimeric PKM2 is involved in the accumulation of glycolytic intermediates and Promotes subsequent biosynthesis in tumor cells [10]. Importantly, PKM2 dimers are imported into the cell nucleus and function as protein kinases. Evidence supports a possible role of PKM2 in tumorigenesis. As an embryonic isoform, PKM2 is reactivated in tumors and overexpressed in several cancer types [11]. Deletion of PKM2 in normal cells leads to expression of PKM1 and induces growth arrest by impairing nucleotide production and subsequent DNA synthesis. Switching from PKM1 to PKM2 has been demonstrated in various cancer types, and reverse isoform switching from PKM2 to PKM1 inhibits aerobic glycolysis and reduces tumorigenesis in a nude mouse xenograft model [6].
Anti-apoptotic myeloid leukemia 1 (MCL-1) is an anti-apoptotic member of the BCL-2 family. Critical to cytochrome c release from mitochondria and subsequent caspase activation is the complex interplay of both pro- and anti-apoptotic proteins of the Bcl-2 family. There are several pro- and anti-apoptotic family members that can physically bind to each other, and the relative proportions of pro- and anti-apoptotic family members ultimately determine cell fate in terms of survival or death [12]. When an organism is exposed to certain stimuli that disrupt this balance, cell proliferation can overtake apoptosis and even lead to tumorigenesis. The intrinsic (or mitochondrial) pathway of apoptosis and the extrinsic pathway of apoptosis are the two apoptotic pathways. The ability to dampen cell death signaling pathways, such as mitochondrial apoptosis, is a hallmark of many cancers, including B-cell non-Hodgkin's lymphoma (B-NHL). Activation of mitochondrial apoptosis is tightly regulated by members of the B-cell leukemia/lymphoma-2 (BCL2) family of proteins through homotypic and heterotypic interactions [13]. The BCL-2 family of proteins share one or four homologous BCL-2 domains (BH 1–4) and are divided into three subgroups (Fig. 2). These BCL-2 family proteins regulate mitochondrial membrane integrity through complex interactions. MCL-1 inhibits mitochondrial outer membrane (MOMP) permeabilization and release of cytochrome C from mitochondria. MCL-1 is needed for the survival of many cells in the nervous system, T/B lymphocytes, and cardiomyocytes [12]. The extrinsic pathway is facilitated through death receptor activation. This activates the initiator caspases 8 and 10, which can directly trigger downstream executive caspases, such as caspases 3 and 7, to fully commit to apoptosis. In addition, caspase-8 and caspase-10 activate Bid, which activates Bak and Bax to induce MOMP. MOMP is a link between extrinsic and intrinsic signaling pathways [14].
Overexpression of the MCL-1 protein, or amplification of the MCL-1 gene, protects cancer cells from apoptosis and reduces their sensitivity to commonly used anticancer agents. This has been shown to be a mechanism of resistance to multiple cancer therapies, including radiotherapy., chemotherapy, and the BH3 mimetic targeting BCL-2/BCLXL. Therefore, MCL-1 is a highly promising target for tumor therapy [12].
Today, despite considerable efforts, cancer is still an active killer worldwide. The most common and effective methods of cancer treatment are surgery, chemotherapy, and radiation therapy [16]. However, these treatments have many limitations and drawbacks. Most cancer patients are diagnosed too late for surgery due to misdiagnosis and other factors. Chemotherapy and radiation therapy have serious side effects and complications such as fatigue, pain, diarrhea, nausea, vomiting, and hair loss. In addition, chemotherapy and radiation therapy can gradually make cancer cells more resistant to treatment. Therefore, there is a constant need to develop new, effective and affordable anticancer agents. Medicinal plants have become a popular alternative to cancer treatment in many countries around the world. Momordicoside is one of several related cucurbitan triterpenoid glycosides that can be extracted from bitter melon vine (Mormordica charantia), an important grape for medicinal purposes. Also various traditional medicines to treat bronchitis, gonorrhea, rheumatism, blood diseases, cholera, anemia, ulcers, diarrhea, gout, colic, helminths, dysentery, liver and spleen diseases, cancer, diabetes, etc. The main constituents of this plant include proteins, triterpenes, alkaloids, steroids, inorganic compounds, lipids, and antidiabetic, anticancer and antitumor, antibacterial, anthelmintic, antimalarial, antiulcer and immunomodulatory.