Sensitivity of cancer cells to truncated diphtheria toxin

Bacterial Therapy of Cancer: A Way to the Dustbin of History or to the Medicine of the Future?

Bacteria are the constant companions of the human body throughout its life and even after its death. The history of a human disease such as cancer and the history of microorganisms, particularly bacteria, are believed to closely intertwined. This review was conceived to highlight the attempts of scientists from ancient times to the present day to discover the relationship between bacteria and the emergence or development of tumors in the human body. Challenges and achievements of 21st century science in forcing bacteria to serve for cancer treatment are considered. The future possibilities of bacterial cancer therapy, including the creation of bacterial microrobots, or "bacteriobots", are also discussed.

A recombinant affitoxin derived from a HER3 affibody and diphteria-toxin has potent and selective antitumor activity

High expression of receptor tyrosine-protein kinase erbB-3 (HER3) has been found in several malignancies such as breast cancer. In this study, we designed, produced and evaluated a new affitoxin consisting of a truncated form of diphtheria toxin and a HER3-binding affibody domains. The new affitoxin was expressed in Escherichia coli and purified by affinity chromatography. We evaluated the suitability of affitoxin to kill HER3 positive breast cancer cells with MTT and apoptosis assays. The protein synthesis inhibition was also evaluated. The IC50 value in HER3 negative cells is about 10 times more than HER3 positive cells in new design of affitoxin. The specificity of affitoxin for binding to HER3 positive cells was also investigated with binding assay with flow cytometry. The results show that, the new affitoxin is an anti-cancer molecule with specific binding to HER3 positive cells and may open a new window for the treatment of HER3-positive cancers.

Do Bacteria Provide an Alternative to Cancer Treatment and What Role Does Lactic Acid Bacteria Play?

Cancer is one of the leading causes of mortality and morbidity worldwide. According to 2022 statistics from the World Health Organization (WHO), close to 10 million deaths have been reported in 2020 and it is estimated that the number of cancer cases world-wide could increase to 21.6 million by 2030. Breast, lung, thyroid, pancreatic, liver, prostate, bladder, kidney, pelvis, colon, and rectum cancers are the most prevalent. Each year, approximately 400,000 children develop cancer. Treatment between countries vary, but usually includes either surgery, radiotherapy, or chemotherapy. Modern treatments such as hormone-, immuno- and antibody-based therapies are becoming increasingly popular. Several recent reports have been published on toxins, antibiotics, bacteriocins, non-ribosomal peptides, polyketides, phenylpropanoids, phenylflavonoids, purine nucleosides, short chain fatty acids (SCFAs) and enzymes with anticancer properties. Most of these molecules target cancer cells in a selective manner, either directly or indirectly through specific pathways. This review discusses the role of bacteria, including lactic acid bacteria, and their metabolites in the treatment of cancer.

Bugs as drugs: neglected but a promising future therapeutic strategy in cancer

Effective cancer treatment is an urgent need due to the rising incidence of cancer. One of the most promising future strategies in cancer treatment is using microorganisms as cancer indicators, prophylactic agents, immune activators, vaccines or vectors in antitumor therapy. The success of bacteria-mediated chemotherapy will be dependent on the balance of therapeutic benefit and the control of bacterial infection in the body. Additionally, protozoans and viruses have the potential to be used in cancer therapy. This review summarizes how these microorganisms interact with tumor microenvironments and the challenges of a 'bugs as drugs' approach in cancer therapy. Several standpoints are discussed, such as bacteria as vectors for gene therapy that shuttle therapeutic compounds into tumor tissues, their intrinsic antitumor activities and their combination with chemotherapy or radiotherapy. Bug-based cancer therapy is a two-edged sword and we need to find the opportunities by overcoming the challenges.

In vivo solid tumor targeting with recombinant VEGF-diphtheria immunotoxin

Objectives

A variety of signaling molecules have been identified that play a role in angiogenesis, of prime importance, vascular endothelial growth factor (VEGF) and its resceptor (VEGFR), which is highly expressed in most human solid tumors. Targeting VEGF or/and VEGFR with immunotoxin may be a promising approach to directly affect cancer cells. Immunotoxins are for targeted treatment comprising two functional moieties, an antibody that binds to target cells along with toxin that kills molecules.

Materials and Methods

In this study, an immunotoxin comprising domain of diphtheria toxin subunit A (DT386) genetically fused to mouse VEGF (mVEGF-DT) was developed. The second construct, which contains the DT386 domain, was made to investigate the action of the DT386 domain on tumor cells. Both gene constructs were cloned, expressed, and were further purified. The biological activity of mVEGF-DT and DT386 proteins was assessed on the TC1 cell line bearing mouse model. Proteins were injected intra-tumoral in mice, in separate groups.

Results

Tumors in the mVEGF-DT group started to dwindle after six injections, but tumor size in both control groups (DT386 and PBS), continued to grow.

Conclusion

Successful targeting of solid tumor cells by mVEGF-DT immunotoxin demonstrates the therapeutic potential utility of these conjugates for tumor targeting.

Bacterial-Based Cancer Therapy (BBCT): Recent Advances, Current Challenges, and Future Prospects for Cancer Immunotherapy

Currently approximately 10 million people die each year due to cancer, and cancer is the cause of every sixth death worldwide. Tremendous efforts and progress have been made towards finding a cure for cancer. However, numerous challenges have been faced due to adverse effects of chemotherapy, radiotherapy, and alternative cancer therapies, including toxicity to non-cancerous cells, the inability of drugs to reach deep tumor tissue, and the persistent problem of increasing drug resistance in tumor cells. These challenges have increased the demand for the development of alternative approaches with greater selectivity and effectiveness against tumor cells. Cancer immunotherapy has made significant advancements towards eliminating cancer. Our understanding of cancer-directed immune responses and the mechanisms through which immune cells invade tumors have extensively helped us in the development of new therapies. Among immunotherapies, the application of bacteria and bacterial-based products has promising potential to be used as treatments that combat cancer. Bacterial targeting of tumors has been developed as a unique therapeutic option that meets the ongoing challenges of cancer treatment. In comparison with other cancer therapeutics, bacterial-based therapies have capabilities for suppressing cancer. Bacteria are known to accumulate and proliferate in the tumor microenvironment and initiate antitumor immune responses. We are currently well-informed regarding various methods by which bacteria can be manipulated by simple genetic engineering or synthetic bioengineering to induce the production of anti-cancer drugs. Further, bacterial-based cancer therapy (BBCT) can be either used as a monotherapy or in combination with other anticancer therapies for better clinical outcomes. Here, we review recent advances, current challenges, and prospects of bacteria and bacterial products in the development of BBCTs.

Design of a Cytotoxic Neuroblastoma-Targeting Agent Using an Enzyme Acting on Polysialic Acid Fused to a Toxin

Polysialic acid, an abundant cell surface component of the developing nervous system, which declines rapidly postnatally to virtual absence in the majority of adult tissues, is highly expressed in some malignant tumors including neuroblastoma. We found that the binding of a noncatalytic endosialidase to polysialic acid causes internalization of the complex from the surface of neuroblastoma kSK-N-SH cells, a subline of SK-N-SH, and leads to a complete relocalization of polysialic acid to the intracellular compartment. The binding and uptake of the endosialidase is polysialic acid-dependent as it is inhibited by free excess ligand or removal of polysialic acid by active endosialidase, and does not happen if catalytic endosialidase is used in place of inactive endosialidase. A fusion protein composed of the noncatalytic endosialidase and the cytotoxic portion of diphtheria toxin was prepared to investigate whether the cellular uptake observed could be used for the specific elimination of polysialic acid-containing cells. The conjugate toxin was found to be toxic to polysialic acid-positive kSK-N-SH with an IC₅₀ of 1.0 nmol/L. Replacing the noncatalytic endosialidase with active endosialidase decreased the activity to the level of nonconjugated toxin. Normal nonmalignant cells were selectively resistant to the toxin conjugate. The results demonstrate that noncatalytic endosialidase induces a quantitative removal and cellular uptake of polysialic acid from the cell surface which, by conjugation with diphtheria toxin fragment, can be exploited for the selective elimination of polysialic acid-containing tumor cells.

The chorioallantoic membrane as a bio-barrier model for the evaluation of nanoscale drug delivery systems for tumour therapy

In 2010, the European Parliament and the European Union adopted a directive on the protection of animals used for scientific purposes. The directive aims to protect animals in scientific research, with the final goal of complete replacement of procedures on live animals for scientific and educational purposes as soon as it is scientifically viable. Furthermore, the directive announces the implementation of the 3Rs principle: "When choosing methods, the principles of replacement, reduction and refinement should be implemented through a strict hierarchy of the requirement to use alternative methods." The visibility, accessibility, and the rapid growth of the chorioallantoic membrane (CAM) offers a clear advantage for various manipulations and for the simulation of different Bio-Barriers according to the 3R principle. The extensive vascularisation on the CAM provides an excellent substrate for the cultivation of tumour cells or tumour xenografts which could be used for the therapeutic evaluation of nanoscale drug delivery systems. The tumour can be targeted either by topical application, intratumoural injection or i.v. injection. Different application sites and biological barriers can be examined within a single model.

Co-assembled Ca2+ Alginate-Sulfate Nanoparticles for Intracellular Plasmid DNA Delivery

Successful gene therapy requires the development of suitable carriers for the selective and efficient delivery of genes to specific target cells, with minimal toxicity. In this work, we present a non-viral vector for gene delivery composed of biocompatible materials, CaCl2, plasmid DNA and the semi-synthetic anionic biopolymer alginate sulfate (AlgS), which spontaneously co-assembled to form nanoparticles (NPs). The NPs were characterized with a slightly anionic surface charge (Zeta potential [ζ] = -14 mV), an average size of 270 nm, and their suspension was stable for several days with no aggregation. X-ray photoelectron spectroscopy (XPS) validated their ternary composition, and it elucidated the molecular interactions among Ca2+, the plasmid DNA, and the AlgS. Efficient cellular uptake (>80%), associated with potent GFP gene expression (22%-35%), was observed across multiple cell types: primary rat neonatal cardiac fibroblasts, human breast cancer cell line, and human hepatocellular carcinoma cells. The uptake mechanism of the NPs was studied using imaging flow cytometry and shown to be via active, clathrin-mediated endocytosis, as chemical inhibition of this pathway significantly reduced EGFP expression. The NPs were cytocompatible and did not activate the T lymphocytes in human peripheral blood mononuclear cells. Proof of concept for the efficacy of these NPs as a carrier in cancer gene therapy was demonstrated for Diphtheria Toxin Fragment A (DT-A), resulting in abrogation of protein synthesis and cell death in the human breast cancer cell line. Collectively, our results show that the developed AlgS-Ca2+-plasmid DNA (pDNA) NPs may be used as an effective non-viral carrier for pDNA.

Anti-cancer Potential of Captopril and Botulinum Toxin Type-A and Associated p53 Gene Apototic Stimulating Activity

Mutational inactivation of p53 is a key player in the development of human cancer. Thus, retrieving the tumor suppressor activity of p53 gene is considered a novel strategy in cancer therapy. Current study aimed to investigate the anti-cancer potentials of botulinum toxin type-A (BTX-A) and captopril as a trial to shed light on effective anti-cancer therapy with lower side effects. Cytotoxic effect of captopril and BTX-A was determined using MTT assay against colon (HCT116) and prostate cancer (DU145) cells compared to their effect on normal vero cells. Anti-proliferation assay and anti-metastatic effect were carried out using trypan blue exclusion method and wound scratch migration test, respectively. The ability of test drugs to induce apoptosis in cancer cells was examined using real time PCR. Recorded data revealed that captopril exhibited a statistically significant cytotoxicity (P < 0.05) to cancer cells (IC50 values of 1.5 and 1.2 mg/mL) with much lower toxicity to normal cells. At the same time, IC50 values post BTX-A treatment were 7.2 and 6.4 U/mL for HCT116 and DU145 cells, respectively without any toxicity to vero cells. Both drugs showed inhibitory potentials on cellular proliferation and the ability of cancer cells to migrate in scratched monolayers was obviously inhibited along with increasing their concentrations. P53 expression levels in captopril and BTX-A treated DU145 cells were elevated by 4 and 2.5 folds, respectively, while lower level of apoptosis induction in HCT116 cells was observed. Accordingly, BTX-A and captopril could present potential anti-cancer candidates through triggering cancer cells towards self-destruction.

Cellular Entry of the Diphtheria Toxin Does Not Require the Formation of the Open-Channel State by Its Translocation Domain

Cellular entry of diphtheria toxin is a multistage process involving receptor targeting, endocytosis, and translocation of the catalytic domain across the endosomal membrane into the cytosol. The latter is ensured by the translocation (T) domain of the toxin, capable of undergoing conformational refolding and membrane insertion in response to the acidification of the endosomal environment. While numerous now classical studies have demonstrated the formation of an ion-conducting conformation-the Open-Channel State (OCS)-as the final step of the refolding pathway, it remains unclear whether this channel constitutes an in vivo translocation pathway or is a byproduct of the translocation. To address this question, we measure functional activity of known OCS-blocking mutants with H-to-Q replacements of C-terminal histidines of the T-domain. We also test the ability of these mutants to translocate their own N-terminus across lipid bilayers of model vesicles. The results of both experiments indicate that translocation activity does not correlate with previously published OCS activity. Finally, we determined the topology of TH5 helix in membrane-inserted T-domain using W281 fluorescence and its depth-dependent quenching by brominated lipids. Our results indicate that while TH5 becomes a transbilayer helix in a wild-type protein, it fails to insert in the case of the OCS-blocking mutant H322Q. We conclude that the formation of the OCS is not necessary for the functional translocation by the T-domain, at least in the histidine-replacement mutants, suggesting that the OCS is unlikely to constitute a translocation pathway for the cellular entry of diphtheria toxin in vivo.

Optimization of the Expression of DT386-BR2 Fusion Protein in Escherichia coli using Response Surface Methodology

Background:

The aim of this study was to determine the best condition for the production of DT386-BR2 fusion protein, an immunotoxin consisting of catalytic and translocation domains of diphtheria toxin fused to BR2, a cancer specific cell penetrating peptide, for targeted eradication of cancer cells, in terms of the host, cultivation condition, and culture medium.

Materials and Methods:

Recombinant pET28a vector containing the codons optimized for the expression of the DT386-BR2 gene was transformed to different strains of Escherichia coli (E. coli BL21 DE3, E. coli Rosetta DE3 and E. coli Rosetta-gami 2 DE3), followed by the induction of expression using 1 mM IPTG. Then, the strain with the highest ability to produce recombinant protein was selected and used to determine the best expression condition using response surface methodology (RSM). Finally, the best culture medium was selected.

Results:

Densitometry analysis of sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the expressed fusion protein showed that E. coli Rosetta DE3 produced the highest amounts of the recombinant fusion protein when quantified by 1 mg/ml bovine serum albumin (178.07 μg/ml). Results of RSM also showed the best condition for the production of the recombinant fusion protein was induction with 1 mM IPTG for 2 h at 37°C. Finally, it was established that terrific broth could produce higher amounts of the fusion protein when compared to other culture media.

Conclusion:

In this study, we expressed the recombinant DT386-BR2 fusion protein in large amounts by optimizing the expression host, cultivation condition, and culture medium. This fusion protein will be subjected to purification and evaluation of its cytotoxic effects in future studies.

Expression and purification of truncated diphtheria toxin, DT386, in Escherichia coli: An attempt for production of a new vaccine against diphtheria

The aim of this study was to produce a recombinant protein consisting of the catalytic and translocation domains of diphtheria toxin for its later application as a vaccine candidate against Corynebacterium diphtheria. To achieve this goal, at first, the amino acid sequence of DT386 was used for prediction of T and B cell epitopes using on-line servers. The DT386 coding sequence was synthesized and subcloned into the NcoI and XhoI sites of pET28a plasmid and recombinant pET28a plasmid was used to transform Escherichia coli BL21 (DE3) host cells. Afterwards, recombinant cells were selected and subjected to induction of expression by 1 mM isopropyl β-D-1-thiogalactopyranoside, (IPTG). Expression of the desired protein was evaluated by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and Western blotting, and finally, the recombinant protein was purified using nickel affinity chromatography. The results of epitope prediction using on-line servers established the ability of DT386 for stimulation of immune system against diphtheria toxin. Restriction digestion of the recombinant plasmids using NcoI and XhoI enzymes confirmed the fidelity of cloning by producing a band of about 1200 bp. SDS-PAGE analysis following induction of expression and also purification step confirmed the expression of the desired protein by showing a band of about 45 kDa. In addition, Western blot analysis using anti-6X-His antibody confirmed the identity of the expected protein. In conclusion, in the present study we amplified and cloned the coding sequence of DT386 fragment, followed by its expression by E. coli BL21 (DE3) cells. Then, the expressed protein was purified and will be used for later studies of evaluation of its immunogenic properties.

Tunable Lipidoid-Telodendrimer Hybrid Nanoparticles for Intracellular Protein Delivery in Brain Tumor Treatment

A strategy to precisely engineer lipidoid-telodendrimer binary hybrid nanoparticles that offer enhanced cell membrane permeability for therapeutic proteins to reach the intracellular targets is established. The highly controllable biochemical and physical properties of the nanoparticles make them promising for protein-based brain cancer treatment with the assistance of convection-enhanced delivery.

Spontaneous regression of tumour and the role of microbial infection--possibilities for cancer treatment

This review deals with the role of microorganisms in spontaneous regression of a tumour. Spontaneous cancer regression is a phenomenon that has been described for many centuries. One of the most well known methods of inducing spontaneous regression of cancer is the application of Coley's toxin (heat-killed Streptococcus pyogenes and Serratia marcescens), which has been used for the successful treatment of sarcomas, carcinomas, lymphomas, myelomas and melanomas. In clinical practice, the use of Bacillus Calmette-Guérin vaccine for the treatment of superficial urinary bladder cancer is the most common instance of the application of microorganisms for the treatment of cancer. This review provides further information on other tested bacteria--Clostridium spp., Bifidobacterium spp., Lactobacillus spp. and Salmonella spp.--in this field of study. Among new age methods, bactofection, alternative gene therapy, combination bacteriolytic therapy and bacteria-directed enzyme prodrug therapy are some of the potential cancer treatment modalities that use microorganisms. We have also provided information about the interconnection among microorganisms, immune system response, and the possible mechanisms involved in the spontaneous regression of tumours.

Augmenting the Efficacy of Immunotoxins and Other Targeted Protein Toxins by Endosomal Escape Enhancers

The toxic moiety of almost all protein-based targeted toxins must enter the cytosol of the target cell to mediate its fatal effect. Although more than 500 targeted toxins have been investigated in the past decades, no antibody-targeted protein toxin has been approved for tumor therapeutic applications by the authorities to date. Missing efficacy can be attributed in many cases to insufficient endosomal escape and therefore subsequent lysosomal degradation of the endocytosed toxins. To overcome this drawback, many strategies have been described to weaken the membrane integrity of endosomes. This comprises the use of lysosomotropic amines, carboxylic ionophores, calcium channel antagonists, various cell-penetrating peptides of viral, bacterial, plant, animal, human and synthetic origin, other organic molecules and light-induced techniques. Although the efficacy of the targeted toxins was typically augmented in cell culture hundred or thousand fold, in exceptional cases more than million fold, the combination of several substances harbors new problems including additional side effects, loss of target specificity, difficulties to determine the therapeutic window and cell type-dependent variations. This review critically scrutinizes the chances and challenges of endosomal escape enhancers and their potential role in future developments.

DT(270-326) , a Truncated Diphtheria Toxin, Increases Blood-Tumor Barrier Permeability by Upregulating the Expression of Caveolin-1

AIM

The nontoxic mutant of diphtheria toxin (DT) has been demonstrated to act as a receptor-specific carrier protein to delivery drug into brain. Recent research showed that the truncated "receptorless" DT was still capable of being internalized into cells. This study investigated the effects and potential mechanisms of DT(270-326) , a truncated "receptorless" DT, on the permeability of the blood-tumor barrier (BTB).

METHODS

BTB and GECs were subjected to DT(270-326) treatment. HRP flux assays, immunofluorescent, co-immunoprecipitation, Western blot, CCK-8, and Flow cytometry analysis were used to evaluate the effects of DT(270-326) administration.

RESULTS

Our results revealed that 5 μM of DT(270-326) significantly increased the permeability of BTBin vitro, which reached its peak at 6 h. The permeability was reduced by pretreatment with filipinIII. DT(270-326) co-localized and interacted with caveolin-1 via its caveolin-binding motif. The mRNA and protein expression levels of caveolin-1 were identical with the changes of BTB permeability. The upregulated expression of caveolin-1 was associated with Src kinase-dependent tyrosine phosphorylation of caveolin-1, which subsequently induced phosphorylation and inactivation of the transcription factor Egr-1. The combination of DT(270-326) with doxorubicin significantly enhanced the loss of cell viability and apoptosis of U87 glioma cells in contrast to doxorubicin alone.

CONCLUSIONS

DT(270-326) might provide a novel strategy to increase the delivery of macromolecular therapeutic agents across the BTB.

Membrane translocation assay based on proteolytic cleavage: application to diphtheria toxin T domain

The function of diphtheria toxin translocation (T) domain is to transfer the catalytic domain across the endosomal membrane upon acidification. The goal of this study was to develop and apply an in vitro functional assay for T domain activity, suitable for investigation of structure-function relationships of translocation across lipid bilayers of various compositions. Traditionally, T domain activity in vitro is estimated by measuring either conductance in planar lipid bilayers or the release of fluorescent markers from lipid vesicles. While an in vivo cell death assay is the most relevant to physiological function, it cannot be applied to studying the effects of pH or membrane lipid composition on translocation. Here we suggest an assay based on cleavage of the N-terminal part of T domain upon translocation into protease-loaded vesicles. A series of control experiment was used to confirm that cleavage occurs inside the vesicle and not as the result of vesicle disruption. Translocation of the N-terminus of the T domain is shown to require the presence of a critical fraction of anionic lipids, which is consistent with our previous biophysical measurements of insertion. Application of the proposed assay to a series of T domain mutants correlated well with the results of cytotoxicity assay.

pH-triggered conformational switching along the membrane insertion pathway of the diphtheria toxin T-domain

The translocation (T)-domain plays a key role in the action of diphtheria toxin and is responsible for transferring the catalytic domain across the endosomal membrane into the cytosol in response to acidification. Deciphering the molecular mechanism of pH-dependent refolding and membrane insertion of the T-domain, which is considered to be a paradigm for cell entry of other bacterial toxins, reveals general physicochemical principles underlying membrane protein assembly and signaling on membrane interfaces. Structure-function studies along the T-domain insertion pathway have been affected by the presence of multiple conformations at the same time, which hinders the application of high-resolution structural techniques. Here, we review recent progress in structural, functional and thermodynamic studies of the T-domain archived using a combination of site-selective fluorescence labeling with an array of spectroscopic techniques and computer simulations. We also discuss the principles of conformational switching along the insertion pathway revealed by studies of a series of T-domain mutants with substitutions of histidine residues.

Pentapeptide commonality between Corynebacterium diphtheriae toxin and the Homo sapiens proteome

Cross-reactivity may affect diagnostic tests and cause harmful autoimmune reactions following immunotherapy. To predict potential cross-reactivity and search for safe immunotherapeutic approaches, we analyzed sequence identity between microbial antigens and the human proteome. Using diphtheria toxin (DT) as a model, we examined its patterns of identity with human proteins at the pentapeptide level. DT shares 503 pentapeptides with the human proteome, while only 31 pentapeptides are unique to the toxin. DT pentapeptide identity involves multiple/repeated matches in human proteins (a total of 4966 occurrences). Human proteins containing bacterial peptide matches include antigens linked to fundamental cellular functions, such as cell cycle control, proliferation, development and differentiation. The data presented in this article offer a rational basis for designing peptide-based vaccines that specifically target DT and thus eliminate the potential risk of cross-reactivity with human proteins. More generally, this study proposes a methodological approach for avoiding cross-reactivity in immune reactions.