A Geneticist's View of Prostate Cancer: Prostate Cancer Treatment Considerations.

Prostate cancer remains a life-threatening disease of men. While early detection has been helpful to reduce the mortality rate, we currently do not have a desired therapy. In recent years, new strategies have been proposed to treat prostate cancers with poor prognosis by utilizing genetically modified bacteria, including Salmonella typhimurium that preferentially replicate within solid tumors (1000:1 and up to 10,000:1 compared to non-cancerous tissue) destroying cancer cells without causing septic shock that is typically associated with wild-type S. typhimurium infections. Furthermore, these bacteria have the potential to be utilized as drug delivery systems to more effectively target different subpopulations of prostate tumor cells. This chapter reviews progress in using genetically modified S. typhimurium for destruction of prostate tumors.

Whole-Genome Shotgun Sequences of Salmonella enterica Serovar Typhimurium Lilleengen Type Strains LT1, LT18, LT19, LT20, LT21, and LT22.

The Lilleengen type (LT) collection of Salmonella enterica serovar Typhimurium strains has served the scientific community as a group of model organisms for basic genetic and biochemical pathway research. Here, we report the whole-genome shotgun sequences of Salmonella enterica serovar Typhimurium strains LT1, LT18, LT19, LT20, LT21, and LT22.

Salmonella Bacterial Monotherapy Reduces Autochthonous Prostate Tumor Burden in the TRAMP Mouse Model.

Attenuated Salmonella typhimurium injected in the circulatory system of mammals selectively targets tumors. Using weekly intraperitoneal injections of attenuated Salmonella strain CRC2631, we tested for regression and/or inhibition of tumor development in the TRAMP prostate tumor mouse model, which utilizes SV40 early region expression for autochthonous formation of prostate tumors that progress into metastatic, poorly differentiated prostatic carcinomas in an immunocompetent murine model. Thirteen weekly intraperitoneal administrations of 105-107 CFU CRC2631 into 10 week old mice were well tolerated by the TRAMP model. Sacrifice and histological analysis of TRAMP prostates at 22 weeks indicated that Salmonella monotherapy at administrated levels decrease visible tumor size (>29%) but did not significantly inhibit previously described SV40 expression-driven TRAMP tumor progression to undifferentiated carcinomas when histologically examined. In conclusion, this work demonstrates baseline results for CRC2631 Salmonella monotherapy using the immunocompetent TRAMP prostate tumor model in preparation for study of combination therapies that resolve autochthonously generated TRAMP prostate tumors, further reduce tumor size, or inhibit prostate tumor progression.

Strains, Mechanism, and Perspective: Salmonella-Based Cancer Therapy.

Recently, investigation of bacterial-based tumor therapy has regained focus due to progress in molecular, cellular, and microbial biology. Many bacteria such as Salmonella, Listeria, Escherichia, and Clostridium have proved to have tumor targeting and in some cases even tumor-destroying phenotypes. Furthermore, bacterial clinical treatments for cancer have been improved by combination with other therapeutic methods such as chemotherapeutic drugs and radioactive agents. Synthetic biology techniques have also driven the development of new bacterial-based cancer therapies. However, basic questions about the mechanisms of bacterial-mediated tumor targeting and destruction are still being elucidated. In this review, we focus on three tumor-therapeutic Salmonella models, the most intensively studied bacterial genus in this field. One of these Salmonella models is our Salmonella enterica serovar Typhimurium LT2 derived strain CRC2631, engineered to minimize toxicity but maximize tumor-targeting and destruction effects. The other two are VNP20009 and A1-R. We compare the means by which these therapeutic candidate strain models were selected for study, their tumor targeting and tumor destruction phenotypes in vitro and in vivo, and what is currently known about the mechanisms by which they target and destroy tumors.

Direct attachment of nanoparticle cargo to Salmonella typhimurium membranes designed for combination bacteriotherapy against tumors.

Nanoparticle technology is an emerging approach to resolve difficult-to-manage internal diseases. It is highly regarded, in particular, for medical use in treatment of cancer due to the innate ability of certain nanoparticles to accumulate in the porous environment of tumors and to be toxic to cancer cells. However, the therapeutic success of nanoparticles is limited by the technical difficulty of fully penetrating and thus attacking the tumor. Additionally, while nanoparticles possess seeming-specificity due to the unique physiological properties of tumors themselves, it is difficult to tailor the delivery of nanoparticles or drugs in other models, such as use in cardiac disease, to the specific target. Thus, a need for delivery systems that will accurately and precisely bring nanoparticles carrying drug payloads to their intended sites currently exists. Our solution to this engineering challenge is to load such nanoparticles onto a biological "mailman" (a novel, nontoxic, therapeutic strain of Salmonella typhimurium engineered to preferentially and precisely seek out, penetrate, and hinder prostate cancer cells as the biological delivery system) that will deliver the therapeutics to a target site. In this chapter, we describe two methods that establish proof-of-concept for our cargo loading and delivery system by attaching nanoparticles to the Salmonella membrane. The first method (Subheading 1.1) describes association of sucrose-conjugated gold nanoparticles to the surface of Salmonella bacteria. The second method (Subheading 1.2) biotinylates the native Salmonella membrane to attach streptavidin-conjugated fluorophores as example nanoparticle cargo, with an alternative method (expression of membrane bound biotin target sites using autodisplay plasmid vectors) that increases the concentration of biotin on the membrane surface for streptavidin-conjugated nanoparticle attachment. By directly attaching the fluorophores to our bacterial vector through biocompatible, covalent, and stable bonds, the coupling of bacterial and nanoparticle therapeutic approaches should synergistically lead to improved tumor destruction.

Phenotypic evolution of therapeutic Salmonella enterica serovar Typhimurium after invasion of TRAMP mouse prostate tumor.

Salmonella has been of interest in cancer research due to its intrinsic ability to selectively target and colonize within tumors, leading to tumor cell death. Current research indicates promising use of Salmonella in regular administrations to remove tumors in mouse models while minimizing toxic side effects. However, selection of mutants during such long-term tumor colonization is a safety concern, and understanding selection of certain phenotypes within a tumor is an important consideration in predicting the long-term success of bacterium-based cancer treatment strategies. Thus, we have made an initial examination of selected phenotypes in a therapeutic Salmonella enterica serovar Typhimurium population developed from an archival wild-type LT2 strain and intraperitoneally injected into a 6-month-old TRAMP (transgenic adenocarcinoma of mouse prostate) mouse. We compared the original injected strain to isolates recovered from prostate tumors and those recovered from the spleen and liver of non-tumor-bearing TRAMP mice through phenotypic assessments of bacteriophage susceptibility, motility, growth rates, morphology, and metabolic activity. Tumor isolate traits, particularly the loss of wild-type motility and flagella, reflect the selective pressure of the tumor, while the maintenance of bacteriophage resistance indicates no active selection to remove this robust trait. We posit that the Salmonella population adopts certain strategies to minimize energy consumption and maximize survival and proliferation once within the tumor. We find these insights to be nonnegligible considerations in the development of cancer therapies involving bacteria and suggest further examinations into the evolution of therapeutic strains during passage through tumors. Importance: Salmonella is of interest in cancer research due to its intrinsic abilities to selectively target, colonize, and replicate within tumors, leading to tumor cell death. However, mutation of strains during long-term colonization within tumors is a safety concern, and understanding their evolution within a tumor is an important consideration in predicting the long-term success of bacterium-based cancer treatment strategies. Thus, we have made an initial examination of phenotypically diverse Salmonella colonies recovered from a therapeutic Salmonella strain that we developed and injected into prostate tumor-bearing mice. We compared the bacteriophage susceptibility, motility, growth rates, morphology, and metabolic activity of the original therapeutic strain to those of strains recovered from prostate tumors of tumor-bearing mice and the liver and spleen of non-tumor-bearing mice. Our results suggest that the Salmonella population adopts certain strategies to minimize energy consumption and maximize survival and proliferation once within the tumor, leading to phenotypic changes in the strain.

Metastatic prostate cancer cell-specific phage-like particles as a targeted gene-delivery system.

BACKGROUND: One of the cardinal requirements for effective therapeutic management of tumors is the selective delivery of cancer drugs to the right site by ligand-decorated nanomedicines. Screening of 2 × 109 clone landscape phage library provides a reliable avenue for generating protein ligands specific for tumor cells. It was shown that selective phage proteins derived from landscape phage libraries against breast and prostate cancer cells are able to navigate drug or siRNA loaded liposomes to corresponding cancer cells with minimal toxicity to non-neoplastic cells. In an alternative platform, glioma cell-specific phage proteins were used for assembling in vivo cancer-specific phage-like particles, named 'phagemid infective particles' as targeted gene-delivery vehicles. METHODS: To extend the panel of anticancer cell phages, we have screened a 2 × 109 clone landscape phage library f8/8 to select phage clones specific for metastatic prostate cancer cell PC-3M. The phage clones were characterized for their selective interaction with PC-3M cells using phage capture assay, immunofluorescence microscopy and electron microscopy. A prostate cancer selective phage was converted to phage-like particles harboring emerald green fluorescent protein. RESULTS: Phage clone EPTHSWAT (designated by the sequence of inserted peptide) was found to be most selective for PC-3M cells and was observed to internalize PC-3M cells as revealed by immunofluorescence microscopy and electron microscopy. Conversion of this phage to phage-like particles harboring emerald green fluorescent protein and the expression of emerald green fluorescent protein in the phage-like particles treated PC-3M cells showed potential of adoption of this phage-like particle in prostate cancer therapeutic gene delivery. CONCLUSION: Successful employment of phage-like particles expressing emerald green fluorescent protein genes targeted to prostate cancer cells PC-3M confirms a prospect of their use for targeted delivery of therapeutic genes to cancer cells.

mutL as a genetic switch of bacterial mutability: turned on or off through repeat copy number changes.

Bacterial adaptation to changing environments can be achieved through the acquisition of genetic novelty by accumulation of mutations and recombination of laterally transferred genes into the genome, but the mismatch repair (MMR) system strongly inhibits both these types of genetic changes. As mutation and recombination do occur in bacteria, it is of interest to understand how genetic novelty may be achieved in the presence of MMR. Previously, we observed associations of a defective MMR genotype, 6bpΔmutL, with greatly elevated bacterial mutability in Salmonella typhimurium. To validate these observations, we experimentally converted the mutL gene between the wild-type and 6bpΔmutL in S. typhimurium and inspected the bacterial mutability status. When 6bpΔmutL was converted to mutL, the originally highly mutable Salmonella strains regained genetic stability; when mutL was converted to 6bpΔmutL, the mutability was elevated 100-fold. Interestingly, mutL cells were found to grow out of 6bpΔmutL cells; the new mutL cells eventually replaced the original 6bpΔmutL population. As conversion between mutL and 6bpΔmutL may occur readily during DNA replication, it may represent a previously unrecognized mechanism to modulate bacterial mutability at the population level, allowing bacteria to respond rapidly to changing environments while minimizing the risks associated with persistent hypermutability.

Multiple genetic switches spontaneously modulating bacterial mutability.

BACKGROUND: All life forms need both high genetic stability to survive as species and a degree of mutability to evolve for adaptation, but little is known about how the organisms balance the two seemingly conflicting aspects of life: genetic stability and mutability. The DNA mismatch repair (MMR) system is essential for maintaining genetic stability and defects in MMR lead to high mutability. Evolution is driven by genetic novelty, such as point mutation and lateral gene transfer, both of which require genetic mutability. However, normally a functional MMR system would strongly inhibit such genomic changes. Our previous work indicated that MMR gene allele conversion between functional and non-functional states through copy number changes of small tandem repeats could occur spontaneously via slipped-strand mis-pairing during DNA replication and therefore may play a role of genetic switches to modulate the bacterial mutability at the population level. The open question was: when the conversion from functional to defective MMR is prohibited, will bacteria still be able to evolve by accepting laterally transferred DNA or accumulating mutations? RESULTS: To prohibit allele conversion, we "locked" the MMR genes through nucleotide replacements. We then scored changes in bacterial mutability and found that Salmonella strains with MMR locked at the functional state had significantly decreased mutability. To determine the generalizability of this kind of mutability 'switching' among a wider range of bacteria, we examined the distribution of tandem repeats within MMR genes in over 100 bacterial species and found that multiple genetic switches might exist in these bacteria and may spontaneously modulate bacterial mutability during evolution. CONCLUSIONS: MMR allele conversion through repeats-mediated slipped-strand mis-pairing may function as a spontaneous mechanism to switch between high genetic stability and mutability during bacterial evolution.

Genetic diversity among offspring from archived Salmonella enterica ssp. enterica serovar typhimurium (Demerec Collection): in search of survival strategies.

Extensive phenotypic and genomic diversity was detected among offspring of Salmonella enterica ssp. enterica serovar Typhimurium LT2 (nonmutator) and LT7 (mutator, mutL) strains after decades of storage in sealed nutrient agar stabs. In addition to numerous losses in carbon and nitrogen metabolism, the acquired new metabolites indicated that alternate pathways were established. Particularly striking was the array of phage types when this phenotype was expected to be a stable feature. Evidence is presented regarding the role of mutator gene mutL(-) in the establishment of diversity as well as the ability of cells to return to mutL(+) genetic stabilization. Mutations included deletions, duplications, frameshifts, inversions and transpositions. In competition tests, survivors were more fit than were wild type. Because survival strategies continue to intrigue microbiologists, observations are compared with those of others who have addressed related questions. A brief genealogy of the archived strains is also recorded.

Morphology of Salmonella Typhimurium typing phages of the Lilleengen set.

The Lilleengen scheme for typing Salmonella enterica serovar Typhimurium consists of 12 tailed phages. Ten phages are podoviruses and morphologically identical to Salmonella phage P22. Two phages are siphoviruses and identical to flagella-specific phage chi.

Competition among isolates of Salmonella enterica ssp. enterica serovar Typhimurium: role of prophage/phage in archived cultures.

Previously, we reported extensive diversity among survivors of Salmonella enterica ssp. enterica serovar Typhimurium that were stored for four decades in sealed agar stabs. Thus raising the question: was there selection for greater fitness among eventual survivors? To address this, we cocultured archived LT2 survivors with nonarchived (parental) LT2 strains in competition experiments. Selected archived strains outgrew a nonarchived LT2 sequenced strain. Although we initially assumed this was the result of mutations empowering greater nutritional utilization, we found phage selection was also involved. Phage fels-1 and fels-2 in supernatants were identified by primer/PCR as a putative selective force following single plaque isolations on a prophage-free strain and testing on appropriate hosts. In confirmatory experiments, instead of coculture in Luria-Bertani requiring antibiotic marker insertions, competing strains without markers were inoculated at opposite edges of motility plates. Not only did the archived LT2 population overgrow the nonarchived LT2 population, but also clear zones appeared at edges of encounters from which phage fels-1 and fels-2 (but not gifsy-1 nor gifsy-2) were recovered. However, in competitions of an archived strain with S. Typhimurium ATCC 14028, phage emerged that had a DNA base sequence segment of prophage ST64B but the sequence differed from the reported homologous segment in ST64B.

Salmonella-host cell interactions, changes in host cell architecture, and destruction of prostate tumor cells with genetically altered Salmonella.

Increasingly, genetically modified Salmonella are being explored as a novel treatment for cancer because Salmonella preferentially replicate within tumors and destroy cancer cells without causing the septic shock that is typically associated with wild-type S. typhimurium infections. However, the mechanisms by which genetically modified Salmonella strains preferentially invade cancer cells have not yet been addressed in cellular detail. Here we present data that show S. typhimurium strains VNP20009, LT2, and CRC1674 invasion of PC-3M prostate cancer cells. S. typhimurium-infected PC-3M human prostate cancer cells were analyzed with immunofluorescence microscopy and transmission electron microscopy (TEM) at various times after inoculation. We analyzed microfilaments, microtubules, and DNA with fluorescence and immunofluorescence microscopy. 3T3 Phi-Yellow-mitochondria mouse 3T3 cells were used to study the effects of Salmonella infestation on mitochondria distribution in live cells. Our TEM results show gradual destruction of mitochondria within the PC-3M prostate cancer cells with complete loss of cristae at 8 h after inoculation. The fluorescence intensity in YFP-mitochondria-transfected mouse 3T3 cells decreased, which indicates loss of mitochondria structure. Interestingly, the nucleus does not appear affected by Salmonella within 8 h. Our data demonstrate that genetically modified S. typhimurium destroy PC-3M prostate cancer cells, perhaps by preferential destruction of mitochondria.

Spontaneous conversion between mutL and 6 bpDeltamutL in Salmonella typhimurium LT7: association with genome diversification and possible roles in bacterial adaptation.

Previously, we reported the phenomenon of genome diversification in Salmonella typhimurium LT7, i.e., individual strains derived from LT7 kept changing the genome structure by inversions, translocations, duplications, and mutations. To elucidate the genetic basis, we sequenced selected genes of the mismatch repair (MMR) system for correlations between MMR defects and genome diversification. We chose S. typhimurium LT7 mutants 8111F2 and 9052D1 for mut gene sequence analyses and found that both mutants had a deletion of one of three tandem 6-bp repeats, GCTGGC GCTGGC GCTGGC, within mutL, which was designated 6 bpDeltamutL. mutS and mutH genes were unchanged in the mutants analyzed. Some sublines of 8111F2 and 9052D1 spontaneously stopped the genome diversification process at certain stages during single-colony restreaking passages, and in these strains the 6 bpDeltamutL genotype also became wild-type mutL. We conclude that conversion between mutL and 6 bpDeltamutL occurs spontaneously and that transient defects of mutL facilitate genome diversification without leading to the accumulation of multiple detrimental genetic changes. Spontaneous conversion between mutL and 6 bpDeltamutL may be an important mechanism used by bacteria to regulate genetic stability in adaptation to changing environments.

Development of Salmonella strains as cancer therapy agents and testing in tumor cell lines.

Despite significant progress in the development of new drugs and radiation, deaths due to cancer remain high. Many novel therapies are in clinical trials and offer better solutions, but more innovative approaches are needed to eradicate the various subpopulations that exist in solid tumors. Since 1997, the use of bacteria for cancer therapy has gained increased attention. Salmonella Typhimurium strains have been shown to have a remarkably high affinity for tumor cells. The use of bacterial strains to target tumors is a relatively new research method that has not yet reached the point of clinical success. The first step in assessing the effectiveness of bacterial tumor therapy will require strain development and preclinical comparisons of candidate strains, which is the focus of this chapter. Several investigators have developed strains of Salmonella with reduced toxicity and capacity to deliver anti-tumor agents. Although methods for obtaining safe therapeutic strains have been relatively successful, there is still need for further genetic engineering before successful clinical use in human patients. As described by Forbes et al. in 2003, the main stumbling block is that, while bacteria preferentially embed within tumor cells, they fail to spread within the tumor and finish the eradication process. Further engineering might focus on creating Salmonella that remove motility limitations, including increased affinity toward tumor-generated chemotactic attractants and induction of matrix-degrading enzymes.

Reduced hydroperoxidase (HPI and HPII) activity in the Deltafur mutant contributes to increased sensitivity to UVA radiation in Escherichia coli.

In Escherichia coli, Deltafur (ferric uptake regulator) mutants are hypersensitive to various oxidative agents, including UVA radiation (400-315 nm). Studies suggest that UVA radiation mediates its biological effects on bacteria via oxidative mechanisms that lead to reactive oxygen species, including the superoxide anion radical (O2.-), hydroxyl radical (HO.), hydrogen peroxide (H2O2) and singlet oxygen (1O2). There is accumulating evidence that Fur may play an important role in the defense against UVA radiation. In addition to regulating almost all genes directly involved in iron acquisition, Fur also regulates the expression of manganese and iron superoxide dismutase (MnSOD, FeSOD), key enzymes in the defense against oxygen toxicity in E. coli. In Deltafur mutants, there is a complete absence of FeSOD. Previous results suggest that the native iron chelating agent, enterobactin, which exists in increased levels in Deltafur mutants, is an endogenous chromophore for UVA, releasing Fe2+ into the cytoplasm to catalyze the production of highly reactive hydroxyl radicals. We now report that the hypersensitivity of Deltafur mutants to UVA irradiation is associated with reduced hydroperoxidase I (HPI) and hydroperoxidase II (HPII) activity, and is associated with a decrease in the transcription of katE and katG genes. The observed decrease in HPII activity in Deltafur mutants is also associated with reduced rpoS gene transcription. This study provides additional evidence that the Fur gene product, in addition to its known regulatory effect on the expression of SOD and iron uptake mechanisms, also regulates HPI and HPII activity levels in E. coli. An H2O2-inducible antioxidant defense system leading to an increase in HPI activity, is unaltered in Deltafur mutants.

Pigeon-associated strains of Salmonella enterica serovar Typhimurium phage type DT2 have genomic rearrangements at rRNA operons.

Strains from a subgroup of Salmonella enterica serovar Typhimurium frequently associated with pigeon infections were tested for genomic anomalies and virulence in mice. Some strains have a genomic inversion between rrn operons. Two prophages found in the common laboratory strain LT2 were absent. Pigeon-associated strains are still virulent in mice.