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Microorganisms living at many sites in the human body compose a complex and dynamic community. Accumulating evidence suggests a significant role for microorganisms in cancer, and therapies that incorporate bacteria have been tried in various types of cancer. We previously demonstrated that cupredoxin azurin secreted by the opportunistic pathogen Pseudomonas aeruginosa, enters human cancer cells and induces apoptotic death 1-4 . However, the physiological interactions between P. aeruginosa and humans and their role in tumor homeostasis are largely unknown. Here, we show that P. aeruginosa upregulated azurin secretion in response to increasing numbers of and proximity to cancer cells. Conversely, cancer cells upregulated aldolase A secretion in response to increasing proximity to P. aeruginosa, which also correlated with enhanced P. aeruginosa adherence to cancer cells. Additionally, we show that cancer patients had detectable P. aeruginosa and azurin in their tumors and exhibited increased overall survival when they did, and that azurin administration reduced tumor growth in transgenic mice. Our results suggest host-bacterial symbiotic mutualism acting as a diverse adjunct to the host defense system via inter-kingdom communication mediated by the evolutionarily conserved proteins azurin and human aldolase A. This improved understanding of the symbiotic relationship of bacteria with humans indicates the potential contribution to tumor homeostasis., (© 2023. The Author(s).)

Azurin and Laz (lipidated azurin) are 2 bacterial proteins with anticancer, anti-viral and anti-parasitic activities. Azurin, isolated from the bacterium Pseudomonas aeruginosa, termed Paz, demonstrates anticancer activity against a range of cancers but not against brain tumors. In contrast, Laz is produced by members of Gonococci/Meningococci, including Neisseria meningitides which can cross the blood-brain barrier to infect brain meninges. It has been previously reported that Laz has an additional 39 amino acid moiety, called an H.8 epitope, in the N-terminal part of the azurin moiety that allows Laz to cross the entry barrier to brain tumors such as glioblastomas. Exactly, how the H.8 epitope helps the azurin moiety of Laz to cross the entry barriers to attack glioblastoma cells is unknown. In this paper, we describe the structural features of the H.8 moiety in Laz using X-ray crystallography and demonstrate that while the azurin moiety of Laz adopts a β-sandwich fold with 2 β-sheets arranged in the Greek key motif, the H.8 epitope was present as a disordered structure outside the Greek key motif. Structures of Paz and H.8 epitope-deficient Laz are well superimposed. The structural flexibility of the H.8 motif in Laz explains the extracellular location of Laz in Neisseria where it can bind the key components of brain tumor cells to disrupt their tight junctions and allow entry of Laz inside the tumors to exert cytotoxicity.

Pathogenic microorganisms, particularly pathogenic bacteria that cause debilitating diseases, are considered a threat for human health and well-being. Infectious diseases are rampant, particularly in developing countries. However, there are many other deadly diseases, such as cancer, diabetes, cardiac malfunction, etc., that account for significant loss of life and trauma in our society. In this article, I try to describe the role certain bacterial pathogens with long term residence in the human body can play in providing us with our next generation anticancer and other drugs, demonstrating that a certain amount of good can come out of such bacterial pathogens as well.

Azurin, a member of the cupredoxin family of copper containing redox proteins, preferentially penetrates human cancer cells and exerts cytostatic and cytotoxic (apoptotic) effects with no apparent activity on normal cells. Amino acids 50 to 77 (p28) of azurin seem responsible for cellular penetration and at least part of the antiproliferative, proapoptotic activity of azurin against a number of solid tumor cell lines. We show by confocal microscopy and fluorescence-activated cell sorting that amino acids 50 to 67 (p18) are a minimal motif (protein transduction domain) responsible for the preferential entry of azurin into human cancer cells. A combination of inhibitors that interfere with discrete steps of the endocytotic process and antibodies for caveolae and Golgi-mediated transport revealed that these amphipathic, alpha-helical peptides are unique. Unlike the cationic cell-penetrating peptides, alpha-helical antennapedia-like, or VP22 type peptides, p18 and p28 are not bound by cell membrane glycosaminoglycans and preferentially penetrate cancer cells via endocytotic, caveosome-directed, and caveosome-independent pathways. Once internalized, p28, but not p18, inhibits cancer cell proliferation initially through a cytostatic mechanism. These observations suggest the azurin fragments, p18 and p28, account for the preferential entry of azurin into human cancer cells and a significant amount of the antiproliferative activity of azurin on human cancer cells, respectively.

Some pathogenic bacteria produce factors that have evolved a capacity to neutralize competing microbes. The cupredoxin family protein azurin, produced by Pseudomonas aeruginosa, exhibits a remarkable ability to impede invasion of a number of diverse intracellular pathogens, including the human AIDS virus human immunodeficiency virus type 1 and the protozoan parasite Plasmodium falciparum (which causes malaria). Here we report that azurin and an azurin-like protein (Laz) from gonococci/meningococci have activity against Toxoplasma, an apicomplexan parasite that causes opportunistic infection in immunocompromised individuals. We demonstrate that the mechanism of action for Laz involves interfering with the ability of Toxoplasma to adhere to host cells. Computer structural analysis reveals that azurin shares structural features with the predominant surface antigen SAG1, which is known to play an important role in parasite attachment. Interestingly, azurin also has structural similarities to a monoclonal antibody to SAG1. Surface plasmon resonance binding studies validate that SAG1 interacts strongly with Laz and, to lesser extent, azurin. Moreover, Toxoplasma mutants lacking SAG1 are not as susceptible to the growth-inhibitory effects of Laz. Collectively, our data show that Toxoplasma adhesion can be significantly impaired by Laz, and to some extent by azurin, via interactions with SAG1. These observations indicate that Laz can serve as an important tool in the study of host-pathogen interactions and is worthy of further study for development into potential therapeutic agents.

Azurin is a member of a family of metalloproteins called cupredoxins. Although previously thought to be involved in electron transfer, azurin has recently been shown to preferentially enter cancer cells than normal cells and induce apoptosis in such cells. Azurin also demonstrates structural similarity to a ligand known as ephrinB2, which binds its cognate receptor tyrosine kinase EphB2 to initiate cell signaling. Eph/ephrin signaling is known to be involved in cancer progression. We now demonstrate that azurin binds to the EphB2-Fc receptor with high affinity. We have localized a C-terminal domain of azurin (Azu 96-113) that exhibits structural similarity to ephrinB2 at the G-H loop region known to be involved in receptor binding. A synthetic peptide (Azu 96-113) as well as a GST fusion derivative GST-Azu 88-113 interferes with the growth of various human cancer cells. In a prostate cancer cell line DU145 lacking functional EphB2, azurin or its GST-fusion derivatives had little cytotoxic effect. However, in DU145 cells expressing functional EphB2, azurin and GST-Azu 88-113 demonstrated significant cytotoxicity, whereas ephrinB2 promoted cell growth. Azurin inhibited the ephrinB2-mediated autophosphorlyation of the EphB2 tyrosine residue, thus interfering in upstream cell signaling and contributing to cancer cell growth inhibition.

Bacterial proteins such as azurin and Laz have recently been shown to enter preferentially to cancer cells and kill them by multiple mechanisms. Historically, bacterial DNA, particularly the unmethylated CpG dinucleotides, have been shown to trigger activation of specific Toll-like receptors (TLRs) in immune cells, leading to various cytokine and chemokine production that allows cancer cell death and their regression. However, the enhanced release of specific protein or extrachromosomal DNA by bacteria in response to exposure to cancer cells has not been previously demonstrated. In this review, we discuss how an opportunistic, extracellular pathogenic bacterium, Pseudomonas aeruginosa, senses the presence of cancer cells and releases a specific protein or extrachromosomal DNA with antitumor activity for inhibition of cancer cell growth.

Azurin, a member of a family of copper-containing proteins involved in electron transfer called cupredoxins, demonstrates structural features similar to the variable domains of the immunoglobulin superfamily members. An azurin-like protein called Laz with an additional N-terminal 39 amino acid peptide known as H.8 epitope is present on the surface of gonnococci and meningococci. We demonstrate that azurin, Laz and H.8-azurin can bind to the C-terminal cleavage product MSP1-19 of merozoite surface protein 1 (MSP1) of the malarial parasite Plasmodium falciparum and significantly reduce parasitemia. Azurin and Laz also bound strongly to HIV-1 gp120. Interestingly, azurin could not only bind to gp120 but also to the dendritic cell-specific adhesion receptor DC-SIGN, mimicking the functionality of the intercellular adhesion molecule ICAM-3 with which it also binds avidly. Furthermore, these three proteins significantly suppressed HIV-1 growth in peripheral blood mononuclear cells and such suppression appeared to be occurring at an entry stage in the infection process. The presence of both antimalarial and antiretroviral activity in azurin, H.8-azurin and Laz makes these proteins, or peptides derived from them, potential therapeutic agents in the treatment of malaria, HIV-1 infections or coinfections with both P. falciparum and HIV-1.

Azurin is a periplasmic 128 amino acid protein in Pseudomonas aeruginosa, termed Paz, which has been shown to enter preferentially and induce apoptosis in cancer cells such as human melanoma or breast cancer. Its effectiveness against brain tumors such as glioblastomas has not been studied. The meningitis-causing bacterium Neisseria meningitidis also harbors an azurin-like protein. Unlike all other known azurins, Neisserial azurin, termed Laz, is surface-exposed and has in its N-terminal region a 39 amino acid epitope called H.8. Upstream of this H.8 moiety is a lipobox that results in the truncation of the protein at the N-terminal cysteine residue with modification by a lipid group. No function of Laz is known. We demonstrate that while Paz is deficient in entering glioblastoma cells and exhibits low cytotoxicity, Laz is much more proficient in entering glioblastoma cells and shows a higher level of cytotoxicity. When the Neisserial H.8 moiety containing the lipobox is fused in frame with Paz either in its N-terminal (H.8-Paz) or in its C-terminal (Paz-H.8), both had high cytotoxicity for glioblastoma cells and a higher level of internalization. When expressed in E. coli, H.8-Paz was much more exposed on the surface than Paz-H.8. The replacement of the Laz N-terminal cysteine residue involved in acylation with an alanine residue abolished the surface display, but had no effect on cytotoxicity or entry in glioblastoma cells, suggesting a role of the H.8 moiety, but not its lipidation, in disrupting the entry barrier in brain tumor cells.

Azurin is a member of a group of copper-containing redox proteins called cupredoxins. Different cupredoxins are produced by different aerobic bacteria as agents of electron transfer. Recently, we demonstrated that azurin enters into J774 and several types of cancer cells leading to the induction of apoptosis. We now demonstrate that azurin is internalized in J774 or cancer cells in a temperature-dependent manner. Azurin shows preferential entry into cancer compared with normal cells. An 28-amino-acid fragment of azurin fused to glutathione S-transferase (GST) or the green fluorescent protein (GFP), which are incapable of entering mammalian cells by themselves, can be internalized in J774 or human melanoma or breast cancer cells at 37 degrees C, but not at 4 degrees C. Competition experiments as well as studies with inhibitors such as cytochalasin D suggest that azurin may enter cells, at least in part, by a receptor-mediated endocytic process. The 28-amino-acid peptide therefore acts as a potential protein transduction domain (PTD), and can be used as a vehicle to transport cargo proteins such as GST and GST-GFP fusion proteins. Another member of the cupredoxin family, rusticyanin, that has also been shown to enter J774 and human cancer cells and exert cytotoxicity, does not demonstrate preferential entry for cancer cells and lacks the structural features characteristic of the azurin PTD.

During acid mine drainage, Acidithiobacillus ferrooxidans, a nonpathogenic, acidophilic, lithotrophic bacterium, utilizes rusticyanin to transfer electrons for the oxidation of Fe(2+) to Fe(3+) for deriving its energy. No other function of rusticyanin is known. We demonstrate that purified rusticyanin enters mammalian cells inducing either inhibition of cell cycle progression or caspase-8 mediated apoptosis. Treatment of human melanoma cells with rusticyanin allowed significant generation of reactive oxygen species and active caspase-8, leading to cell death. The ability of rusticyanin to modulate mammalian cell death might be relevant to a role of this cupredoxin in protecting At. ferrooxidans from eukaryotic predators in the environment.

Recent evidence indicates that bacterial redox proteins such as cupredoxins and cytochromes, that are normally involved in electron transfer during respiration, can enter mammalian cells and induce either apoptosis or inhibition of cell cycle progression. Such proteins have also been shown to demonstrate a good deal of specificity for entry and induction of cytotoxic effects in cancer cells, allowing both in vitro cell death and in vivo inhibition of cancer progression. An alteration in the hydrophobicity of the bacterial redox proteins can lead to a switch from apoptosis to growth arrest and vice versa through modulation of the intracellular levels of tumor suppressors. The preferential entry and cytotoxicity of these redox proteins in cancer cells raises interesting questions about the presence of other bacterial proteins that may affect cell cycle at the G(2)/M phase, thereby potentially arresting cancer growth. The intracellular localization of the bacterial redox proteins in nonpathogenic soil bacteria similarly raises questions about their possible role in allowing various nonpathogenic soil bacteria to defend themselves from environmental predators by inducing cytotoxicity when engulfed in large numbers. A new role of the redox proteins in soil bacteria in maintaining an ecological balance among the predators and preys is proposed.

The tumor suppressor protein p53 is known to induce either apoptosis or growth arrest depending on cellular background. We have previously reported that a bacterial redox protein azurin induces apoptosis in J774 cell line-derived macrophages whereas a site-directed mutant M44KM64E azurin shows very little cytotoxicity and fails to induce apoptosis in J774 cells. We now report that purified M44KM64E mutant azurin protein can enter both J774 cells as well as the human breast cancer MCF-7 cells. Entry of M44KM64E mutant azurin in J774 cells causes strong inhibition of cell-cycle progression at the G1 to S phase and a higher level of transcription of the p21 gene. Corresponding to high p21 levels, the levels of cyclins and cyclin-dependent kinases were greatly lowered in M44KM64E mutant azurin-treated J774 cells. Interestingly, M44KM64E mutant azurin protein failed to elicit inhibition of cell-cycle progression in MCF-7 cells, presumably because of mutation at the retinoblastoma tumor suppressor protein that allows functional E2F formation in MCF-7 cells even in the presence of high intracellular p21 level. Thus, the WT azurin induces apoptosis but little inhibition of cell-cycle progression whereas the M44KM64E mutant azurin is deficient in the induction of apoptosis but mediates strong inhibition of cell-cycle progression, demonstrating the role of a single bacterial protein and its hydrophobic patch in modulating two important functions of p53.

Azurin, a copper-containing redox protein released by the pathogenic bacterium Pseudomonas aeruginosa, is highly cytotoxic to the human breast cancer cell line MCF-7, but is less cytotoxic toward p53-negative (MDA-MB-157) or nonfunctional p53 cell lines like MDD2 and MDA-MB-231. The purpose of this study was to investigate the underlying mechanism of the action of bacterial cupredoxin azurin in the regression of breast cancer and its potential chemotherapeutic efficacy. Azurin enters into the cytosol of MCF-7 cells and travels to the nucleus, enhancing the intracellular levels of p53 and Bax, thereby triggering the release of mitochondrial cytochrome c into the cytosol. This process activates the caspase cascade (including caspase-9 and caspase-7), thereby initiating the apoptotic process. Our results indicate that azurin-induced cell death stimuli are amplified in the presence of p53. In vivo injection of azurin in immunodeficient mice harboring xenografted human breast cancer cells in the mammary fat pad leads to statistically significant regression (85%, P = 0.0179, Kruskal-Wallis Test) of the tumor. In conclusion, azurin blocks breast cancer cell proliferation and induces apoptosis through the mitochondrial pathway both in vitro and in vivo, thereby suggesting a potential chemotherapeutic application of this bacterial cupredoxin for the treatment of breast cancer.

The use of live bacteria in the treatment of cancer has a long and interesting history. We report the use of a purified bacterial redox protein, azurin, that enters human cancer (melanoma UISO-Mel-2) cells and induces apoptosis. The induction of apoptosis occurs readily in melanoma cells harboring a functional tumor suppressor protein p53, but much less efficiently in p53-null mutant melanoma (UISO-Mel-6) cells. A redox-negative mutant form of azurin (M44K/M64E) demonstrates much less cytotoxicity to the UISO-Mel-2 cells than the wild-type protein. Azurin has been shown to be internalized in UISO-Mel-2 cells and is localized predominantly in the cytosol and in the nuclear fraction. In the p53-null UISO-Mel-6 cells, azurin is localized only in the cytosol. Thus, intracellular trafficking of azurin to the nucleus is p53-dependent. Azurin forms a complex with p53, thereby stabilizing it and raising its intracellular level in cytosolic, mitochondrial, and nuclear fractions. Corresponding to an increasing level of p53, an inducer of apoptosis, the level of Bax also increases in mitochondria, allowing significant release of mitochondrial cytochrome c into the cytosol, thus initiating the onset of apoptosis. The M44K/M64E mutant form of azurin, deficient in cytotoxicity, is also deficient in forming a complex with p53 and is less efficient in stabilizing p53 than wild-type azurin. Azurin has been shown to allow regression of human UISO-Mel-2 tumors xenotransplanted in nude mice and may potentially be used in cancer treatment.

Cancer is a complex disease with a network of multiple metabolic pathways that are interlinked to promote growth and resist immune surveillance. Such a network is efficiently maintained through acquisition of multiple mutations in the human genome that result in the escape from normal cellular growth regulation and formation of lumps of fast growing cells known as tumors. The varied pathways through which cancer cells grow and inhibit their own cell death have made it difficult to develop effective drugs either to prevent the emergence of tumors or to check their rapid growth. Current anticancer drugs are either small molecules or monoclonal antibodies that target and inhibit a key important step in cancer progression pathway, thereby significantly inhibiting their proliferation. No effective drug or vaccine exists to prevent cancer initiation and drug resistance and toxicity are major problems in cancer chemotherapy. This article describes recent attempts to develop bacterial proteins that are used as weapons by certain pathogenic bacteria with long term residence in human bodies to prevent invasion of their habitat by invaders such as cancers, viruses or parasites. In one instance, such a protein, termed azurin, has been shown not only to have entry specificity in cancer cells and prevent cancer cell growth by interfering in multiple pathways by which cancer cells grow, but also to prevent induction of pre-cancerous lesion formation triggered by a potent carcinogen. A 28 amino acid peptide derived from azurin, p28, also shows similar anticancer and cancer preventive activity. In phase I human clinical trials, chemically-synthesized p28 has shown very little toxicity but significant beneficial effects, including partial and sometimes complete regression of metastatic refractory solid tumors in 15 advanced stage (stage IV) cancer patients where no conventional drugs were working. A second such protein, termed ATP-01, very different from azurin and obtained from a different bacterium, has shown similar anticancer and anti-HIV/AIDS activity and a 30 amino acid peptide derived from it has anticancer activity similar to p28. It would be of great interest to test these two proteins, should they prove to be non-toxic and non-immunogenic in humans, and the peptides derived from them, for their efficacy in cancer therapy and prevention. Such efficacies can be tested, singly or in combination, in vulnerable people such as people with predisposition to cancer (women with BRCA1/2 mutations, for example) or in HIV/AIDS patients with Kaposi's sarcoma or other forms of cancer. [ABSTRACT FROM AUTHOR]

Abstract: Azurin and Laz are bacterial proteins that have been shown to exert anticancer effects against a variety of solid tumors. Their effects on liquid cancers have never been studied. We now show that they are also effective against liquid-borne cancers such as leukemia. Azurin and Laz can each enter in two leukemia cell lines but Laz exerts a greater cytotoxic effect on both K562 and HL60 cells, while having little effect on peripheral blood mononuclear cells, where they have very limited entry. In addition to Azurin and Laz, we have recently identified another protein, Pa-CARD, from Pseudomonas aeruginosa that carries a caspase recruiment domain (CARD)-like domain. This CARD domain polypeptide, called Pa-CARD, demonstrates cytotoxic activity against leukemia cells. In the leukemia cell lines, HL60 and K562, the anticancer activity of Laz and Pa-CARD is mediated through cell cycle arrest at the G2/M phase involving the Wee1 protein stabilization and the depletion of phosphorylated AKT-Ser-473, the active form of a serine/threonine kinase that is often dysregulated in many cancer types. [Copyright &y& Elsevier]