Cajanol: The role of phytoestrogen in cancer cells

Cajanol (5-hydroxy-3-(4-hydroxy-2-methoxyphenyl)-7-methoxychroman-4-one) is an isoflavanone from Pigeonpea (Cajanus cajan)roots. It is the most active phytoalexin in pigeon pea, with a chemical struture of C17H16O6. Cajanol belongs to the group of isoflavonoids with methoxy group C7 of the isoflavonoid backbone.

Benefits of cajanol in cancer cell inhibition

Cajanol is beneficial to the body. It has been proved to exert anti-tumor and anti-carcinogenesis to cancer cells. It is also a strong antibacterial compounds against both gram negative and gram positive bacteria.

Mechanism of action of Cajanol

There are several biochemical pathways by which Cajanol exert its action against cancer cells and bacteria. In this article, you will learn the mechanism of action of Cajanol against several cancer cell lines. You will also learn about the inhibitory action of Cajanol against both gram negative and gram positive bacteria.

Cajanol in breast cancer

In human breast cancer experiments, cajanol has been shown to inhibit MCF-7 cells. MCF-7 is a human breast cancer cell line with estrogen, progesterone and glucocorticoid receptors. It is said to be derived from the pleural effusion of a 69 years old Caucasian metastatic breast cancer (adenocarcinoma) in 1970 by Dr Soule of the Michigan Cancer Foundation, Detroit, MI.

Cajanol is similar to mammalian estrogens. It exerts its inhibitory role in E2-induced MCF-7 proliferation by interacting directly with estrogen receptors. Cajanol also have the ability to arrest the cell cycle in the G2/M phase and have also induced apoptosis via a reactive oxygen species (ROS)-mediated mitochondria- dependent pathway.

In Prostate cancer

Prostate cancer is the leading cause of cancer related deaths in men. It develops mainly in men of age 65 or older. It is rare among men of age below 40, and is commonly referred to as hormone-dependent cancer, because sex steroid hormones control the initiation and progression of prostate cancer.

Estrogen plays important role in prostate cancer pathogenesis. According a study on aromatase knockout mice, which cannot metabolize androgens to estrogens, high testosterone levels led prostatic hyperplasia. In contrast, high estrogen and low testosterone levels induce inflammatory events and premalignant lesions. As a man grows older, the production of testosterone decreases which estrogen level remains constant. This leads to a high estradiol/testosterone ratio, and thus leads to premalignant lesions.

E2 is the human endogenous estrogen and known to be the most active estrogen receptor agonist. To inhibit the proliferation of prostate cancer, the phytoestrogen competes effectively with E2 for the receptor sites, thus inhibiting E2-induced proliferation of PC-3 prostate cancer cells.

Cajanol modulates PC-3 cell proliferation via ERα-associated PI3K signal-regulated pathways. By interfering with ERα-associated PI3K pathway, cajanol inhibited the survival and proliferation of estrogen-responsive cells following a process that could be independent of the nuclear functions of the ERα. This is followed by the activation of effectors GSK3 and cyclin D1, and then, these cascade reactions results in cell cycle arrest and the final apoptosis.

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Luo M, Liu X, Zu YG, et al. 2010. Cajanol, a novel anticancer agentfrom Pigeonpea [Cajanus cajan (L.) Millsp.] roots, induces apop-tosis in human breast cancer cells through a ROS-mediatedmitochondrial pathway. Chem Biol Interact 188: 151–160.

Liang, Lu & Gao, Chang & Luo, Meng & Zhao, Chunjian & Wang, Yi & gu, Chengbo & Jinghua, Yu & Fu, Yujie. (2013). The Phytoestrogenic Compound Cajanol from Pigeonpea Roots is Associated with the Activation of Estrogen Receptor α-dependent Signaling Pathway in Human Prostate Cancer Cells. Phytotherapy research : PTR. 27. 10.1002/ptr.4937.

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Molecular Mechanism of Malaria Parasite Infection

Malaria is a life-threatening disease that is caused by Plasmodium parasites. It is transmitted to individuals through the bite of an infected female anopheles mosquito. Malaria is a tropical disease that is prevalent in Sub-Saharan African populations.

There are five species of plasmodium parasites, which affect humans. They are:

  • Plasmodium falciparum
  • Plasmodium vivax
  • Plasmodium malariae
  • Plasmodium ovale

Among the five species of plasmodium parasite, Plasmodium falciparum causes the most severe and life-threatening malaria, while Plasmodium vivax is the most widely distributed, representing 53% of malaria incidences.


Symptoms of Malaria

The signs and symptoms if malaria may include:

  • Fever
  • Headache
  • Chills
  • Vomiting and diarrhea
  • Nausea
  • Tiredness
  • Muscular pain


How Is Malaria Parasite Transmitted?

Malaria parasite can only be transmitted when an infective female anopheles mosquito bites and feeds on the blood of and person. At first, the female anopheles mosquito bites and feeds on the blood of an infective person, thereby taking along the blood plasmodium sporozoites. When the mosquito bites another individual, it injects the plasmodium sporozoites into the blood circulation, from it they move to the liver of the newly infected person.

When the sporozoites get to the liver cells they rapidly bind and invade the liver cells and undergo rapid multiplication. This leads to the release of infective merozoites which invade red blood cells and destroy them.


Life Cycle of Plasmodium Falciparum

The life cycle of malaria parasites involves two hosts which are the female anopheles mosquito and human hosts. In humans, the parasite grows and multiply in the liver cells and then in the red blood cells, where successive broods of parasites grow and destroy the cells, releasing the merozoites, which continue to the cycle by invading other red blood cells.


Stages of Life Cycle of Plasmodium Falciparum

As seen above, malaria parasite passes through several stages in its life cycle. We shall look at the major stages which are the human stages and the mosquito stages of the life cycle of plasmodium falciparum.


The human stage (Exo-erythrocytic schizogony)

In the liver, the sporozoites infect the liver cells and mature into Schizonts, which rupture and release the Merozoites. In plasmodium vivax, and plasmodium ovale a dormant stage called hypnozoites can persist in the liver, if untreated, and cause relapses by invading the bloodstream weeks or months later.


Human Blood Stage (Erythrocytic Schizogony)

In this stage, the merozoites released infect red blood cells and form a ring-stage, trophozoites. The trophozoites differentiate into sexual erythrocytic stage called gametocytes.

The blood stage parasites are responsible for the clinical manifestations of the disease.


Mosquito stage (Sporogonic cycle)

During blood meal, the female anopheles mosquito ingests the male and female gametocytes. The male gametocyte is called microgametocyte while the female gametocyte is called macrogametocyte.

In the mosquito’s stomach, the microgametes penetrate the macrogametes to form the zygotes. The zygotes then become motile and elongated, and are called Ookinetes. The ookinetes invade the mid gut of wall of the mosquito, where they develop into Oocysts. The Oocysts grow, rupture and release sporozoites. These then make their way to the mosquito’s salivary glands.

When the mosquito bites and feeds on another person’s blood, the sporozoites are inoculated, thereby repeating the life cycle of malaria.


Molecular Mechanism of Plasmodium Falciparum Erythrocyte Invasion

The entry of parasite into the erythrocytes is the key to establishing blood stage infection and thus, central to both acute and severe malaria. When the merozoites invades the red blood cells, it changes its orientation until its apical end containing specialized secretory organelles called micronemes, rhoptries and base granules is pointed at the erythrocyte.

The binding and invasion of erythrocytes are carried out by two proteins of the apical secretory organelles. These proteins are the reticulocyte-binding protein homologous (RHs) and erythrocyte-binding-like proteins (EBLs).

In EBLs, a dufy-binding-like (DBL) domain mediates specific binding to different host cell receptors, including glycophorins A, B, and C as well as duffy blood antigen. But in RHs, complement receptor 1 (CR1) and basigin are the receptors for PfRH4 and PfRH5 respectively.

Whereas RHs have early role in host sensing, EBLs play a direct role in junction formation. This suggests that RH sensing and subsequent interaction with a suitable host erythrocyte sends a signal to the merozoite that triggers the subsequent steps of invasion.


PfRH1 interaction with its receptor on erythrocyte surface initiates invasion of parasite.

The complex invasion process of merozoite erythrocyte invasion begins with the interaction of a relatively small amount of PfRH1 with its receptor on the erythrocyte surface. This interaction leads to a signaling cascade that leads to the release of intracellular Ca2+ stores, followed by triggering of microneme and rhoptry discharge and junction formation.

PfRH1 is located at the Rhoptry duct. Whereas its role in parasite invasion is known, its receptor on erythrocyte is unknown. PfRH1 is sialic acid-dependent and binds to its receptor in a protease sensitive manner.

EBA-175 binding and parasite invasion of red blood cells

EBA-175 is located on the microneme and is responsible for the binding and invasion of merozoites to erythrocytes. Unlike PfRH1, EBA-175 receptor is known; it binds to the glycophorin A (GpA). GpA is the major glycoprotein found on human erythrocytes and is heavily sialylated. It is a 131 amino acid transmembrane dimer. Each monomer spans the membrane once exposing its N terminus extracellularly. The EBA-175/GpA is the dorminant chymotrypsin-resistant invasion pathway.





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CaMKII (Calcium/calmodulin-dependent protein kinase II) is one of the most important regulators of calcium signaling. It is a ubiquitous mediator of Ca2+-linked signaling that phosphorylates a wide range of substrates to co-ordinate and regulate Ca2+-mediated alterations in cellular functions. CaMKII is a multifunctional serine/threonine kinase, which plays a critical role in the survival, proliferation, invasion, and differentiation of various cancer cells by activating multiple signaling pathways, such as the extracellular signal-regulated kinase (ERK), protein kinase B (AKT), the signal transducer and activator of transcription 3 (STAT3), and Wnt/β-catenin signaling pathways. It also plays a critical role in the survival, proliferation, and maintenance of cancer stem cells. According to research findings, the ϒ isoform of CaMKII (CaMKIIϒ) is required for the maintenance of stem-like and tumorigenic properties in the blood, lung, liver and prostate cancer cells. Each CaMKII monomer consists of three subunits: a catalytic, a regulatory and an association one that is responsible the assembly into the holoenzyme.

CaMKIIϒ acts as a major molecular switch for regulating the NF-kB, Wnt/β-Catenin, Notch, STAT3, and AKT signaling pathways, which are essential for cancer stem-like features in these cancer cells. The CaMKIIϒ inhibitor, berbamine, supresses leukemia stem cells and liver cancer-initiating cells by inhibiting the activity of CaMKIIϒ. In a recent research, Hydrazinobenzoylcurcumin (HBC), a synthetic derivative of curcumin and a Ca2+/CaM antogonist, inhibited not only the self-renewal capacity but also the metastatic potential of GSCs by blocking the CaM/CaMKII/c-Met signaling pathway.

A selective CaMKII inhibitor, KN93, also inhibited the growth of GSCs and the expression of GSC stemless markers. Additionally, CaMKIIγ knockdown decreased the stem-like features of GBM cells. Therefore, CaMKII has attracted attention as an emerging target for eliminating cancer stem cells.

The transmission of information by the kinase from extracellular stimuli and the intracellular Ca2+ rise is not passive. Rather, its multimeric structure and autoregulation enable this enzyme to participate actively in the sensitivity, timing and location of its action.

CaMKII can: (i) be activated in a Ca2+-spike frequency-dependent manner; (ii) become independent of its initial Ca2+}CaM activators; and (iii) undergo a ‘molecular switch-like’ behaviour, which is crucial for certain forms of learning and memory


CaMKII activation and inhibition

Activity of each Calcium/calmodulin-dependent protein kinase II subunit is stimulated individually by direct binding of Ca2+/CaM to their regulatory domains. Autophosphorylation at Threo286 within the regulatory domain transforms CaMKII from one of the lowest to one of the highest affinity CaM binders within the cell. This autophosphorylation also generates autonomous (Ca2+-independent) kinase activity.

The autoregulatory domain of Calcium/calmodulin-dependent protein kinase II ensures, via a pseudosubstrate type of interaction, that the basal kinetic acivity levels remain 100-1000 fold below the maximal Ca2+/CaM-stimulated values. In this mode of inhibition, the autoinhibitory domain has residues that mimic aprotein substrate or nucleotide to interact with the catalytic domain, thereby blocking access to the substrate-binding pockets. However, a binding of an allosteric activator alters the conformation of the autoinhibitory domain and decreases its inhibitory potency; thereby permitting substrates’ access to the catalytic site.

Like all known Ca2+/caMKs, the autoregulatory domain of CaMKII is N-terminal and contiguous with the CaM-binding domain.


CaMKII Structure and Mechanism of activation 

Each of the subunits that comprise CaMKII multimeric enzyme has a conserved structure among the different isoforms; an amino terminal catalytic domain, followed by a regulatory domain that contains a self-inhibitory region and a variable sequence and finally an associative domain in the Carboxy-terminal end, which allows assembly between the different subunits.

The entry of calcium into the cell leads to the formation of the Ca2+/CaM complex, which binds approximately 3-4 calcium ions per CaM in a cooperative form. This complex binds to the regulatory region of CaMKII and produces a conformational change, which not only leads to the phosphorylation of its subunits, but also to an inter-subunits, intra-holoenzyme autophosphorylation at threonine 286 in the alpha isoform and threonine 287 in the β, d and ϒ isoforms.

Autophosphorylation on these sites prevent the enzyme from reverting to its inactive conformation and decreases the dissociation rate of the bound CaM.


Ca2+/CaM-independent activation

Without requirement of any Ca2+ or CaM, Calcium/calmodulin-dependent protein kinase II can be directly activated by gangliosides, especially GTIb, Zn2+ or α-actinin. Α-actinin selectively stimulates phoshorylation of CaMKII substrates that leads to the T-site; however, this activation by α-actinin is not as effective as Ca2+/CaM complex.

Since α-actinin competes with Ca2+/CaM for binding to CaMKII, its net effect in the presence of Ca2+/CaM is inhibitory for all substrates in addition to participation in mechanisms of substrate selection.


Negative regulation of CaMKII activity

Calcium/Camodulin-dependent protein kinase can be negatively regulated by α-actinin, by the inhibitory protein CaM-KII or by Threo305/306 autophosphorylation.

Binding of CaM-KIINα or β isoforms to CaMKII involves the T-site of the kinase and thus, prior displacement of the CaMKII regulatory domain is required. However, in contrast to GluN2B, CaM-KIIN binding completely blocks substrate access. CaM-KIIN can be regulated by its expression level, and possibly by phosphorylation.


Negative regulation by Threo305/306

Threo305/306 phosphorylation inhibits CaM-binding and, vice versa, CaM-binding inhibits Threo305/306 phophorylation. As a result, efficient Threo305/306 autophosphorylation requires autonomous CaMKII with no bound CaM. Hence, dissociation of CaM from Threo286-phosphorylated CaMKII triggers Threo305/306 autophosphorylation. The resulting state of the kinase would be autonomous but without the ability to be further stimulated.


CaMKII and Oxidation

It has been shown that CaMKII is activated by both angiotensinII (AngII) and endothelin-1(ET1) through a primary oxidation-dependent pathway. Oxidation of Methionine281/282 (M281/282) of CaMKII was shown to activate the kinase, thus underscoring the potential of oxidative stress to affect both pathologic and physiologic pathways in excitable cells, such as the cardiomyocyte.

Upon Ca2+/CaM binding at the regulatory CaMKII domain, oxidation of M281/282 leads to activation of the enzyme. Metheonine oxidation inhibits re-association between regulatory and catalytic subunits of CaMKII and thus enables perpetuation of its activity.


Bipolar disorder (BD) is a psychiatric illness associated with high morbidity, mortality and suicidal rate. It has neuroprogressive course and a high rate of treatment resistance. Bipolar disorder is a burdensome and recurrent psychiatric condition that affects more than 1% of the population, and has the highest risk of suicide among all psychiatric disorders. Research has shown that most patients experience depression for a significant part their lives.

The treatment failure rates of bipolar depression are higher than those of major depression disorder (MDD). A longer duration of bipolar disorder leads to neuroprogression which involves structural brain changes and neuropsychological deficits. Currently, there is an unmet options for both short- and long-term treatment options for patients with refractory bipolar depression.


TRBD is the health condition in which there is a lack of response to treatment to at least two previously established treatments for bipolar depression. Despite the importance of TRBD, only a small number of recognized treatment options are available. A few trials have indicated a role for electroconvulsive therapy and repetitive transcranial magnetic stimulation.

While recent network meta-analysis have shown consistent evidence for use of multiple pharmacotherapies in non-TRBD, there is more limited evidence for use of medication based treatments in TRBD.


Ketamine appears to have rapid anti-depressive and anti-suicidal effects. The robust anti-depressant and anti-suicidal effects of ketamine in treatment-resistant patients, as well as its unique mechanism of action, may point o ketamine as an interesting treatment option for BD. Research has reported a rapid and consistent effects of ketamine on BD patients, which included the improvement of mood level and stability, cognition and sleep. A recent study suggests that using ketamine to treat resistant depression has a rapid effect in reducing agitation, irritation and anxiety and suicidal ideation.