In recent years, our understanding of the importance of microorganisms on and within our bodies has been revolutionized by the ability to characterize entire microbial communities. No more so is this true than in cases of disease. Community studies have revealed strong associations between microbial populations and disease states where such concomitance was previously absent from aetiology: including in cancers. The study of viruses, in particular, has benefited from the development of new community profiling techniques and we are now realising that their prominence within our physiology is nearly as broad as the diversity of the organisms themselves. Here, we examine the relationship between viruses and colorectal cancer (CRC), the leading cause of gastrointestinal cancer-related death worldwide. In CRC, viruses have been suggested to be involved in oncogenesis both directly, through infection of our cells, and indirectly, through modulating the composition of bacterial communities. Interestingly though, these characteristics have also led to their examination from another perspective—as options for treatment. Advances in our understanding of molecular and viral biology have caused many to look at viruses as potential modular biotherapeutics, where deleterious characteristics can be tamed and desirable characteristics exploited. In this article, we will explore both of these perspectives, covering how viral infections and involvement in microbiome dynamics may contribute to CRC, and examine ways in which viruses themselves could be harnessed to treat the very condition their contemporaries may have had a hand in creating.
Background: Colorectal cancer is the second leading cause of cancer deaths in the US. Genetic predisposition occurs in ∼30% of cases, suggesting that treatments with the ability to decrease lesion formation could significantly improve disease-free survival in potential patients with a strong family history. Genetically-engineered bacterial minicells (MC) are noninfectious, nano-sized bacterial particles derived from E. coli that can display immunomodulatory and antitumor activity in animal models of cancer. The expression of Invasin on the MC surface targets them to cancer-associated integrin heterodimers exposed on malignant cells, where they deliver Perfringolysin O, a unique tumorlytic bacterial toxin, that destroys these cells. We hypothesize that these MC can reduce colon lesions in genetically predisposed animals and that they have potential to be developed as a ‘probiotic’ therapy for individuals at high risk to develop colorectal cancer. Methods: The TS4CRE mouse line expresses the Cre recombinase specifically in the distal ileum and colon under the control of the fatty acid binding protein-4 promoter. The Apcfl-468 mouse line has lox-P recombination sites flanking exons 11-12 of the Apc gene. Cross-breeding results in a deletion in one allele of the Apc gene in a tissue-specific manner, resulting in lesion formation by 14-18 weeks of age. Cross-bred mice were treated intra-rectally with 1.5×109 MC or PBS, once a week for 6 doses, at either 8-13 or 14-19 weeks of age and harvested at various times after treatment is complete to evaluate tumor number and size. Tumor and tumor adjacent tissue is evaluated for immune biomarkers using qPCR and immunohistochemistry studies. Mann-Whitney (two-tailed) tests are used to determine statistical significance. Results: MC treatment during lesion development (14-19 weeks of age) significantly decreases tumor number (p = 0.007) and size (p = 0.03) in mice harvested at 6 months of age as compared to controls. Similarly, in animals treated from 8-13 weeks of age, when lesions are absent or only in the earliest stages, a significant decrease in tumor number (p = 0.04) was observed. MC can reduce tumor load through direct killing of developing lesions but they also have the potential to modulate immune responses. Since immune/inflammatory mediators are known to significantly contribute to tumor progression in colorectal cancer, decreased tumors in MC treated mice could be the result, at least in part, of a change in the immune/inflammatory environment of the colon. Chloracetate Esterase (CAE) staining for inflammatory granulocytes and mast cells showed that numbers of CAE+ cells in tumors and normal adjacent tissue from MC treated mice (at 14-19 weeks of age) were significantly lower than PBS-treated controls (p = 0.02). Moreover we saw that cells expressing CD11b, a biomarker for inflammatory, myeloid-lineage cells, were also significantly decreased in MC treated mice (p = 0.01). In addition, using qPCR we have determined that both the CD8 and IFNγ biomarkers were significantly increased in the tumor tissue of MC treated mice (p = 0.03 for each) while perforin and Tbet were increased in the tumor-adjacent tissue in these same mice (p = 0.04 for each), when compared to controls. Conclusions: Taken together, these data strongly suggest that MC reduce colon tumor burden in genetically predisposed mice, most likely both by directly eliminating tumor cells and changing the immune environment of the lesions. The immunomodulatory effects appear to consist of both increased anti-tumor immunity and decreased inflammatory cell infiltration. Future studies will continue to access the actions of these MC and the possibility that they can be developed as a ‘probiotic’ therapeutic approach against colorectal cancer in genetically predisposed individuals. Citation Format: Mengxi Tian, Mohammad W. Khan, Shea Grenier, Shingo Tsuji, Matthew A. Giacalone, Kathleen L. McGuire. Bacterial minicells decrease tumor development and modulate immunity in a mouse mouse model of colon cancer [abstract]. In: Proceedings of the Second CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; 2016 Sept 25-28; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(11 Suppl):Abstract nr B017.
In pancreatic ductal adenocarcinoma (PDAC), glutamine is a critical nutrient that drives a wide array of metabolic and biosynthetic processes that support tumor growth. Despite this established dependency, the targeting of specific enzymes involved in glutamine metabolism is yet to yield any clinical benefit. Here, we have examined the therapeutic potential of 6-diazo-5-oxo-L-norleucine (DON), a glutamine antagonist that broadly inhibits glutamine metabolism. We found that DON treatment significantly blocks PDAC tumor growth and attenuates metastasis. Interestingly, we link the effectiveness of DON in PDAC to asparagine (Asn) metabolism. By inhibiting asparagine synthetase (ASNS), DON significantly reduces intracellular Asn production and Asn supplementation rescues the anti-proliferative effects of DON. We discern that PDAC cells upregulate expression of ASNS as a metabolic adaptation and that modulating ASNS levels can impact DON efficacy. Strikingly, in patient-derived organoids, DON responsiveness is inversely correlated with ASNS expression, a feature that is not observed for other metabolic enzymes targeted by DON. We find that treatment with L-asparaginase (ASNase), an enzyme that catabolizes free Asn, synergizes with DON to impact the viability of PDAC cells. Finally, we identify that a combination therapy of DON and ASNase has a significant impact on metastasis. These results shed light on the mechanisms that drive the effects of glutamine mimicry and point to the utility of co-targeting adaptive responses to control PDAC progression.
Background: Colorectal cancer (CRC) is the second leading cause of cancer-associated deaths in the US. Evidence from several studies suggests that the colonic immune environment can influence the risk of CRC. Bacterial minicells (MC) are spherical, non-viable nano-sized particles derived from genetically-engineered E. coli (Vaxiion Therapeutics, Inc). MC contain all of the components of parental bacteria they are derived from with the exception of the chromosome, making them non-infectious. MC used here have been engineered to display antitumor activity via integrin-specific cytotoxic effects but evidence suggests they also require a working immune system to be optimally effective in mouse models of cancer. For our colon cancer studies, we are using an immune-competent mouse model, FABP-CreXApcfl/+, which has a conditional deletion of exons 11-12 in one Adenomatous Polyposis Coli (Apc) allele in the epithelium of colon and distal ileum, due to the targeted expression of CRE, leading to colonic polyposis. Hypothesis: Since MC have been shown to have anti-cancer activity in multiple mouse models, but even more importantly because evidence suggests they are more effective in animals with a functional immune system, we hypothesize that MC can change the immune environment of the colon and delay/decrease the onset of colon cancer in our mouse model. Methods: We treated 14 week old FABP-CreXApcfl/+ mice with PBS or 1.5 x 109 MC in PBS intra-rectally once a week until 19 weeks of age (6 treatments total). Mice were then left untreated until 26 weeks of age, euthanized, and colons were collected to measure tumor number and size. Colonic tumor load was also compared to 24 week old untreated FABP-CreXApcfl/+ controls. RNA was isolated from tumor adjacent (TA), small tumor (≤4mm) and large tumor (>4 mm) tissue, converted to cDNA, and qPCR studies were performed. Hprt was used as a housekeeping gene control and fold-change target gene expression was reported in comparison to Hprt expression. Results: The mean number of colonic polyps in 26 week old mice that received MC-treatment during the 14th-19th week of age was significantly lower (2.4±1.5) in comparison with mice that received PBS only (9.3±1.4, p=0.03) or 24 week-old untreated controls (8.0±1.9, p=0.02). Moreover, MC-treatment significantly restricted the development of colonic polyps >4mm in size (0.6±0.2/mouse, i.e. 60% of mice had one large tumor each) in comparison to PBS-treated (3.7±0.8/mouse, p=0.03) and 24 week-old untreated (2.0±0.2/mouse, p=0.01) controls. Furthermore, as per qPCR studies, preliminary work suggests that MC promote the expression of TH1 and cytotoxic T cell-associated immune responses (CD8a, Tbet, Ifng, perforin) as well as the TH17 (Il17a) immune gene marker in the TA areas of the colon. We also found a decline in the expression of pro-inflammatory (il23, Il6), immunosuppressive (Il10, Foxp3) and immune cell recruitment (Cx3cl1) immune markers in the large tumors of MC-treated mice. Furthermore, our preliminary data suggest the presence of ‘low’ and ‘high’ responders in MC-treated mice. ‘Low responders’ have at least one large tumor at 26 weeks of age and lower correlation of TH1 and cytotoxic T cell-associated immune responses in comparison to ‘high responders’ which have an absence of large tumors and display multi-fold higher levels of TH1 and cytotoxic T cell-associated immune responses in comparison to PBS-treated controls. Conclusion: MC significantly delay the development of colonic polyps and our preliminary data suggest that the delay/decrease in tumorigenesis could be because of attenuation of pro-tumor inflammation as well as promotion of anti-tumor immunity in the colon. These studies also suggest our mouse model will be appropriate for the study of low and high responder anti-tumor immune phenotypes in mice, shedding light on what may be occurring in human CRC patients. Citation Format: Mohammad W. Khan, Shingo Tsuji, MengXi Tian, Nairika Meshgin, Shea Grenier, Matthew J. Giacalone, Kathleen L. McGuire. Immunity, the colonic environment, and colon cancer. [abstract]. In: Proceedings of the AACR Special Conference: Function of Tumor Microenvironment in Cancer Progression; 2016 Jan 7–10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2016;76(15 Suppl):Abstract nr A05.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.