Solid tumors provide niche-specific conditions that lead to preferential growth of Salmonella

Therapeutic attenuated strains of Salmonella Typhimurium target and eradicate tumors in mouse models. However, the mechanism of S. Typhimurium for tumor targeting is still poorly understood. We performed a high-throughput screening of single-gene deletion mutants of S. Typhimurium in an orthotopic, syngeneic murine mammary model of breast cancer. The mutants under selection in this system were classified into functional categories to identify bacterial processes involved in Salmonella accumulation within tumors. Niche-specific genes involved in preferential tumor colonization were identified and exemplars were confirmed by competitive infection assays. Our results show that the chemotaxis gene cheY and the motility genes motAB confer an advantage for colonization of Salmonella within orthotopic syngeneic breast tumors. In addition, eutC, a gene belonging to the ethanolamine metabolic pathway, also confers an advantage for Salmonella within tumors, perhaps by exploiting either ethanolamine or an alternative nutrient in the inflamed tumor environment.

Application of arteether-loaded polyurethane nanomicelles to induce immune response in breast cancer model

To concentrate a potent anticancer drug (Arteether) in tumor microenvironment, we encapsulated it in biodegradable and pH sensitive polyurethane (PU) nanomicelles (NMs). The nanocomplex was characterized by Fourier transform infrared (FTIR), dynamic light scattering (DLS). The loading capacity and release profile in pH of 5.4 and 7.4 were considered. The cytotoxicity effect was evaluated in vitro and in vivo settings. The level of IFN-γ and IL-4 cytokines of mice splenocytes were assessed by enzyme-linked immunosorbent assay (ELISA). The nanocomplex showed negative zeta charge of -26.2 mV, size of 42.30 nm and high loading capacity (92%). Release profile showed a faster rate of drug liberation at pH 5.4 as compared to that of pH 7.4. It indicated significant inhibitory effect on the growth of 4T1 cell line and increased IFN-γ level.

Endostatin inhibits the growth and migration of 4T1 mouse breast cancer cells by skewing macrophage polarity toward the M1 phenotype

The phenotypic diversity of tumor-associated macrophages (TAMs) increases with tumor development. One of the hallmarks of malignancy is the polarization of TAMs from a pro-immune (M1) phenotype to an immunosuppressive (M2) phenotype. However, the molecular basis of this process is still unclear. Endostatin is a powerful inhibitor of angiogenesis capable of suppressing tumor growth and metastasis. Here, we demonstrate that endostatin induces RAW264.7 cell polarization toward the M1 phenotype in vitro. Endostatin has no effect on TAM numbers in vivo, but results in an increased proportion of F4/80(+)Nos2(+) cells and a decreased proportion of F4/80(+)CD206(+) cells. Overexpression of endostatin in RAW264.7 cells resulted in a decrease in the phosphorylation of STAT3, an increase in expression of vascular endothelial growth factor A and placental growth factor, and an increase in the phosphorylation of STAT1, IκBα and p65 proteins compared with controls. These results indicate that endostatin regulates macrophage polarization, promoting the M1 phenotype by targeting NF-κB and STAT signaling.

Development of a (68)Ga-peptide tracer for PET GnRH1-imaging

OBJECTIVE

Total synthesis, quality control and preclinical evaluation of [(68)Ga]-DOTA-triptorelin ([(68)Ga]-DOTA-TRP) is reported as a possible PET radiotracer for GnRH receptor imaging.

METHODS

DOTA-TRP was totally synthesized in two steps and after characterization went through radiolabelling optimization studies followed by tracer stability. The biodistribution of the tracer in normal male rats and 4T1 tumour-bearing mice was performed in 120 min after i.v. injection.

RESULTS

The peptide and the conjugates were synthesized with >95 % chemical purity. [(68)Ga]-DOTA-TRP complex was prepared in high radiochemical purity (>99 %, ITLC, HPLC) and specific activity of 1400-2100 MBq/nM at 95 °C using 40-60 μg of the peptide in 5-7 min followed by solid phase purification. The IC50 [nM] DOTA-TRP was comparable to the intact peptide, 0.11 ± 0.01 and 0.22 ± 0.05, respectively. The biodistribution of the tracer demonstrated kidney, stomach, and testes significant uptake, all in accordance with GnRH receptor ligands. Significant tumour uptake was observed in 4T1 tumour-bearing female mice 30-120 min post-injection with tumour:blood and tumour:muscle ratios of 28 and >50 in 60 min, respectively. Kidney is rapidly washed from the tracer. [(68)Ga]-DOTA-TRP can be proposed as a possible tracer for GnRH-R imaging studies.

Identification of a highly immunogenic mouse breast cancer sub cell line, 4T1-S

Cancer vaccines serve as a promising clinical immunotherapeutic strategy that help to trigger an effective and specific antitumor immune response compared to conventional therapies. However, poor immunogenicity of tumor cells remains a major obstacle for clinical application, and developing new methods to modify the immunogenicity of tumor cells may help to improve the clinical outcome of cancer vaccines. 4T1 mouse breast cancer cell line has been known as poorly immunogenic and highly metastatic cell line. Using this model, we identified a sub cell line of 4T1-designated as 4T1-Sapporo (4T1-S)-which shows immunogenic properties when used as a vaccine against the same line. In 4T1-S-vaccinated mice, subcutaneous injection of 4T1-S resulted in an antitumor inflammatory response represented by significant enlargement of draining lymph nodes, accompanied with increased frequencies of activated CD8 T cells and a subpopulation of myeloid cells. Additionally, 4T1-S vaccine was ineffective to induce tumor rejection in nude mice, which importantly indicate that 4T1-S vaccine rely on T cell response to induce tumor rejection. Further analysis to identify mechanisms that control tumor immunogenicity in this model may help to develop new methods for improving the efficacies of clinical cancer vaccines.

Repeated PD-1/PD-L1 monoclonal antibody administration induces fatal xenogeneic hypersensitivity reactions in a murine model of breast cancer

Monoclonal antibodies (mAbs) targeting coinhibitory molecules such as PD-1, PD-L1 and CTLA-4 are increasingly used as targets of therapeutic intervention against cancer. While these targets have led to a critical paradigm shift in treatments for cancer, these approaches are also plagued with limitations owing to cancer immune evasion mechanisms and adverse toxicities associated with continuous treatment. It has been difficult to reproduce and develop interventions to these limitations preclinically due to poor reagent efficacy and reagent xenogenecity not seen in human trials. In this study, we investigated adverse effects of repeated administration of PD-1 and PD-L1 mAbs in the murine 4T1 mammary carcinoma model. We observed rapid and fatal hypersensitivity reactions in tumor bearing mice within 30-60 min after 4-5 administrations of PD-L1 or PD-1 mAb but not CTLA-4 antibody treatment. These events occurred only in mice bearing the highly inflammatory 4T1 tumor and did not occur in mice bearing non-inflammatory tumors. We observed that mortality was associated with systemic accumulation of IgG1 antibodies, antibodies specific to the PD-1 mAb, and accumulation of Gr-1^high neutrophils in lungs which have been implicated in the IgG mediated pathway of anaphylaxis. Anti-PD-1 associated toxicities were alleviated when PD-1 blockade was combined with the therapeutic HSP90 inhibitor, ganetespib, which impaired immune responses toward the xenogeneic PD-1 mAb. This study highlights a previously uncharacterized fatal hypersensitivity exacerbated by the PD-1/PD-L1 axis in the broadly used 4T1 tumor model as well as an interesting relationship between this particular class of checkpoint blockade and tumor-dependent immunomodulation.

Vasculature Disruption Enhances Bacterial Targeting of Autochthonous Tumors

Attenuated Salmonella enterica serovar Typhimurium (S. Typhimurium) has been developed as a vector to deliver therapeutic agents to tumors. The potential of S. Typhimurium in cancer therapy is largely due to its reported propensity to accumulate at greater than 1,000-fold higher concentrations in tumors relative to healthy tissues. In this study, we compared bacterial colonization of tumors in a subcutaneous transplantation model with a more clinically relevant autochthonous tumor model. Following intravenous administration of attenuated S. Typhimurium strain SL3261, we observed approximately 10,000-fold less bacteria in autochthonous tumors that sporadically develop in transgenic BALB-neuT mice compared to tumors developed from subcutaneous transplantation of 4T1 murine breast cancer cells in BALB/c mice. Treatment of BALB-neuT mice with a vasculature-disrupting agent (VDA) prior to bacterial treatment caused necrosis of tumor tissue and significantly increased the bacterial targeting of autochthonous tumors by approximately 1,000-fold. These observations emphasize the importance of appropriate model selection in developing bacteria-based cancer therapies and demonstrate the potential of combining VDA pre-treatment with bacteria to facilitate targeting of clinically relevant tumors.

In vivo antitumor and antimetastatic effects of flavokawain B in 4T1 breast cancer cell-challenged mice

Flavokawain B (FKB) is a naturally occurring chalcone that can be isolated through the root extracts of the kava-kava plant (Piper methysticum). It can also be synthesized chemically to increase the yield. This compound is a promising candidate as a biological agent, as it is reported to be involved in a wide range of biological activities. Furthermore, FKB was reported to have antitumorigenic effects in several cancer cell lines in vitro. However, the in vivo antitumor effects of FKB have not been reported on yet. Breast cancer is one of the major causes of cancer-related deaths in the world today. Any potential treatment should not only impede the growth of the tumor, but also modulate the immune system efficiently and inhibit the formation of secondary tumors. As presented in our study, FKB induced apoptosis in 4T1 tumors in vivo, as evidenced by the terminal deoxynucleotidyl transferase dUTP nick end labeling and hematoxylin and eosin staining of the tumor. FKB also regulated the immune system by increasing both helper and cytolytic T-cell and natural killer cell populations. In addition, FKB also enhanced the levels of interleukin 2 and interferon gamma but suppressed interleukin 1B. Apart from that, FKB was also found to inhibit metastasis, as evaluated by clonogenic assay, bone marrow smearing assay, real-time polymerase chain reaction, Western blot, and proteome profiler analysis. All in all, FKB may serve as a promising anticancer agent, especially in treating breast cancer.

Silibinin inhibits accumulation of myeloid-derived suppressor cells and tumor growth of murine breast cancer

Myeloid-derived suppressor cells (MDSC)s increase in blood and accumulate in the tumor microenvironment of tumor-bearing animals, contributing to immune suppression in cancer. Silibinin, a natural flavonoid from the seeds of milk thistle, has been developed as an anti-inflammatory agent and supportive care agent to reduce the toxicity of cancer chemotherapy. The goals of this study were to evaluate the effect of silibinin on MDSCs in tumor-bearing mice and antitumor activity of silibinin in a mouse model of breast cancer. 4T1 luciferase-transfected mammary carcinoma cells were injected into in the mammary fat pad female BALB/c mice, and female CB17-Prkdc Scid/J mice. Silibinin treatment started on day 4 or day 14 after tumor inoculation continued every other day. Tumor growth was monitored by bioluminescent imaging (BLI) measuring total photon flux. Flow cytometry measured total leukocytes, CD11b⁺ Gr-1⁺ MDSC, and T cells in the blood and tumors of tumor-bearing mice. The effects of silibinin on 4T1 cell viability in vitro were measured by BLI. Treatment with silibinin increased overall survival in mice harboring tumors derived from the 4T1-luciferase breast cancer cell line, and reduced tumor volumes and numbers of CD11b⁺Gr-1⁺ MDSCs in the blood and tumor, and increased the content of T cells in the tumor microenvironment. Silibinin failed to inhibit tumor growth in immunocompromised severe combined immunodeficiency mice, supporting the hypothesis that anticancer effect of silibinin is immune-mediated. The antitumor activity of silibinin requires an intact host immune system and is associated with decreased accumulation of blood and tumor-associated MDSCs.

Modified arabinoxylan from rice bran, MGN-3/biobran, sensitizes metastatic breast cancer cells to paclitaxel in vitro

BACKGROUND

There is an increased interest in alternative treatments that reduce the toxicity of chemotherapy by lowering the drug concentration, whilst maintaining potency against cancer cells. Previous studies have demonstrated that arabinoxylan from rice bran, MGN-3/Biobran, sensitizes human breast cancer cells (BCC) to daunorubicin (DNR). In the present study, we further evaluated the ability of MGN-3 to sensitize cells to another chemotherapy agent, paclitaxel.

MATERIALS AND METHODS

Non-metastatic MCF-7 (human BCC) and metastatic 4T1 (murine BCC) cells were cultured with different concentrations of paclitaxel in the presence or absence of MGN-3. Cell survival, DNA damage, and cell proliferation were examined.

RESULTS

MGN-3 increased the susceptibility of both types of cancer cells to paclitaxel by over 100-fold. Mechanistically, MGN-3 works synergistically with paclitaxel by causing DNA damage, enhancing apoptosis, and inhibiting cell proliferation in 4T1 cells.

CONCLUSION

Our data demonstrate that MGN-3 is an effective chemosensitizer and may represent a novel adjuvant for the treatment of metastatic breast cancer.

A role for HMGB1, HSP60 and Myd88 in growth of murine mammary carcinoma in vitro

Previously we reported that Myd88 contributed to tumor progression. To begin to decipher what may be inducing Myd88 dependent signaling we focused on proteins that could function as damage associated molecular pattern molecules (DAMPs) since DAMPs have been reported to be secreted by tumors, and certain DAMPs mediate effects through toll-like receptors. A screen of mammary carcinoma for DAMP expression showed HMGB1 and HSP60 were significantly elevated relative to normal mammary epithelium, and targeting these DAMPs, or receptors for these DAMPs influenced growth of tumor cells. Moreover, analysis using a Myd88 inhibitory peptide suggested that HMGB1 mediated its effects in a Myd88 dependent manner, and inhibiting Myd88 function decreased HMGB1 and HSP60 gene expression. Collectively, these data suggest that HMGB1 and HSP60 contribute to growth of mammary carcinoma cells, HMGB1 accomplishes this, at least in part, through Myd88 dependent signaling, and these DAMPs are expressed in a Myd88 dependent manner.