Cry1A Proteins are Cytotoxic to HeLa but not to SiHa Cervical Cancer Cells

Cry1Ac Protoxin Confers Antitumor Adjuvant Effect in a Triple-Negative Breast Cancer Mouse Model by Improving Tumor Immunity

The Cry1Ac protoxin from Bacillus thuringiensis is a systemic and mucosal adjuvant, able to confer protective immunity in different infection murine models and induce both Th1 and TCD8+ cytotoxic lymphocyte responses, which are required to induce antitumor immunity. The Cry1Ac toxin, despite having not being characterized as an adjuvant, has also proved to be immunogenic and able to activate macrophages. Here, we investigated the potential antitumor adjuvant effect conferred by the Cry1Ac protoxin and Cry1Ac toxin in a triple negative breast cancer (TNBC) murine model. First, we evaluated the ability of Cry1Ac proteins to improve dendritic cell (DC) activation and cellular response through intraperitoneal (i.p.) coadministration with the 4T1 cellular lysate. Mice coadministered with the Cry1Ac protoxin showed an increase in the number and activation of CD11c+MHCII- and CD11c+MHCII+^low in the peritoneal cavity and an increase in DC activation (CD11c+MHCII+) in the spleen. Cry1Ac protoxin increased the proliferation of TCD4+ and TCD8+ lymphocytes in the spleen and mesenteric lymph nodes (MLN), while the Cry1Ac toxin only increased the proliferation of TCD4+ and TCD8+ in the MLN. Remarkably, when tested in the in vivo TNBC mouse model, prophylactic immunizations with 4T1 lysates plus the Cry1Ac protoxin protected mice from developing tumors. The antitumor effect conferred by the Cry1Ac protoxin also increased specific cytotoxic T cell responses, and prevented the typical tumor-related decrease of T cells (TCD3+ and TCD4+) as well the increase of myeloid-derived suppressor cells (MDSC) in spleen. Also in the tumor microenvironment of mice coadministered twice with Cry1Ac protoxin immunological improvements were found such as reductions in immunosupressive populations (T regulatory lymphocytes and MDSC) along with increases in macrophages upregulating CD86. These results show a differential antitumor adjuvant capability of Cry1Ac proteins, highlighting the ability of Cry1Ac protoxin to enhance local and systemic tumor immunity in TNBC. Finally, using a therapeutic approach, we evaluated the coadministration of Cry1Ac protoxin with doxorubicin. A significant reduction in tumor volume and lung metastasis was found, with increased intratumoral levels of tumor necrosis factor-α and IL-6 with respect to the vehicle group, further supporting its antitumor applicability.

The Cytocidal Spectrum of Bacillus thuringiensis Toxins: From Insects to Human Cancer Cells

Bacillus thuringiensis (Bt) is a ubiquitous bacterium in soils, insect cadavers, phylloplane, water, and stored grain, that produces several proteins, each one toxic to different biological targets such as insects, nematodes, mites, protozoa, and mammalian cells. Most Bt toxins identify their particular target through the recognition of specific cell membrane receptors. Cry proteins are the best-known toxins from Bt and a great amount of research has been published. Cry are cytotoxic to insect larvae that affect important crops recognizing specific cell membrane receptors such as cadherin, aminopeptidase-N, and alkaline phosphatase. Furthermore, some Cry toxins such as Cry4A, Cry4B, and Cry11A act synergistically with Cyt toxins against dipteran larvae vectors of human disease. Research developed with Cry proteins revealed that these toxins also could kill human cancer cells through the interaction with specific receptors. Parasporins are a small group of patented toxins that may or may not have insecticidal activity. These proteins could kill a wide variety of mammalian cancer cells by recognizing specific membrane receptors, just like Cry toxins do. Surface layer proteins (SLP), unlike the other proteins produced by Bt, are also produced by most bacteria and archaebacteria. It was recently demonstrated that SLP produced by Bt could interact with membrane receptors of insect and human cancer cells to kill them. Cyt toxins have a structure that is mostly unrelated to Cry toxins; thereby, other mechanisms of action have been reported to them. These toxins affect mainly mosquitoes that are vectors of human diseases like Anopheles spp (malaria), Aedes spp (dengue, zika, and chikungunya), and Culex spp (Nile fever and Rift Valley fever), respectively. In addition to the Cry, Cyt, and parasporins toxins produced during spore formation as inclusion bodies, Bt strains also produce Vip (Vegetative insecticidal toxins) and Sip (Secreted insecticidal proteins) toxins with insecticidal activity during their vegetative growth phase.

Chitinases of Bacillus thuringiensis: Phylogeny, Modular Structure, and Applied Potentials

The most important bioinsecticide used worldwide is Bacillus thuringiensis and its hallmark is a rich variety of insecticidal Cry protein, many of which have been genetically engineered for expression in transgenic crops. Over the past 20 years, the discovery of other insecticidal proteins and metabolites synthesized by B. thuringiensis, including chitinases, antimicrobial peptides, vegetative insecticidal proteins (VIP), and siderophores, has expanded the applied value of this bacterium for use as an antibacterial, fungicidal, and nematicidal resource. These properties allow us to view B. thuringiensis not only as an entity for the production of a particular metabolite, but also as a multifaceted microbial factory. In particular, chitinases of B. thuringiensis are secreted enzymes that hydrolyze chitin, an abundant molecule in the biosphere, second only to cellulose. The observation that chitinases increase the insecticidal activity of Cry proteins has stimulated further study of these enzymes produced by B. thuringiensis. Here, we provide a review of a subset of our knowledge of B. thuringiensis chitinases as it relates to their phylogenetic relationships, regulation of expression, biotechnological potential for controlling entomopathogens, fungi, and nematodes, and their use in generating chitin-derived oligosaccharides (ChOGs) that possess antibacterial activities against a number of clinically significant bacterial pathogens. Recent advances in the structural organization of these enzymes are also discussed, as are our perspective for future studies.