Central role of liver in anticancer and radioprotective activities of Toll-like receptor 5 agonist.

Vertebrate Toll-like receptor 5 (TLR5) recognizes bacterial flagellin proteins and activates innate immune responses to motile bacteria. In addition, activation of TLR5 signaling can inhibit growth of TLR5-expressing tumors and protect normal tissues from radiation and ischemia-reperfusion injuries. To understand the mechanisms behind these phenomena at the organismal level, we assessed nuclear factor kappa B (NF-κB) activation (indicative of TLR5 signaling) in tissues and cells of mice treated with CBLB502, a pharmacologically optimized flagellin derivative. This identified the liver and gastrointestinal tract as primary CBLB502 target organs. In particular, liver hepatocytes were the main cell type directly and specifically responding to systemic administration of CBLB502 but not to that of the TLR4 agonist LPS. To assess CBLB502 impact on other pathways, we created multireporter mice with hepatocytes transduced in vivo with reporters for 46 inducible transcription factor families and found that along with NF-κB, CBLB502 strongly activated STAT3-, phenobarbital-responsive enhancer module (PREM), and activator protein 1 (AP-1-) -driven pathways. Livers of CBLB502-treated mice displayed induction of numerous immunomodulatory factors and massive recruitment of various types of immune cells. This led to inhibition of growth of liver metastases of multiple tumors regardless of their TLR5 status. The changed liver microenvironment was not, however, hepatotoxic, because CBLB502 induced resistance to Fas-mediated apoptosis in normal liver cells. Temporary occlusion of liver blood circulation prevented CBLB502 from protecting hematopoietic progenitors in lethally irradiated mice, indicating involvement of a factor secreted by responding liver cells. These results define the liver as the key mediator of TLR5-dependent effects in vivo and suggest clinical applications for TLR5 agonists as hepatoprotective and antimetastatic agents.

Powerful Complex Immunoadjuvant Based on Synergistic Effect of Combined TLR4 and NOD2 Activation Significantly Enhances Magnitude of Humoral and Cellular Adaptive Immune Responses.

Binding of pattern recognition receptors (PRRs) by pathogen-associated molecular patterns (PAMPs) activates innate immune responses and contributes to development of adaptive immunity. Simultaneous stimulation of different types of PRRs can have synergistic immunostimulatory effects resulting in enhanced production of molecules that mediate innate immunity such as inflammatory cytokines, antimicrobial peptides, etc. Here, we evaluated the impact of combined stimulation of PRRs from different families on adaptive immunity by generating alum-based vaccine formulations with ovalbumin as a model antigen and the Toll-like receptor 4 (TLR4) agonist MPLA and the Nucleotide-binding oligomerization domain-containing protein 2 (NOD2) agonist MDP adsorbed individually or together on the alum-ovalbumin particles. Multiple in vitro and in vivo readouts of immune system activation all showed that while individual PRR agonists increased the immunogenicity of vaccines compared to alum alone, the combination of both PRR agonists was significantly more effective. Combined stimulation of TLR4 and NOD2 results in a stronger and broader transcriptional response in THP-1 cells compared to individual PRR stimulation. Immunostimulatory composition containing both PRR agonists (MPLA and MDP) in the context of the alum-based ovalbumin vaccine also enhanced uptake of vaccine particles by bone marrow derived dendritic cells (BMDCs) and promoted maturation (up-regulation of expression of CD80, CD86, MHCII) and activation (production of cytokines) of BMDCs. Finally, immunization of mice with vaccine particles containing both PRR agonists resulted in enhanced cellular immunity as indicated by increased proliferation and activation (IFN-γ production) of splenic CD4+ and CD8+ T cells following in vitro restimulation with ovalbumin and enhanced humoral immunity as indicated by higher titers of ovalbumin-specific IgG antibodies. These results indicate that combined stimulation of TLR4 and NOD2 receptors dramatically enhances activation of both the humoral and cellular branches of adaptive immunity and suggests that inclusion of agonists of these receptors in standard alum-based adjuvants could be used to improve the effectiveness of vaccination.

Preclinical Validation of a Single-Treatment Infusion Modality That Can Eradicate Extremity Melanomas.

Isolated limb perfusion (ILP) with the chemotherapeutic agent melphalan is an effective treatment option for extremity in-transit melanoma but is toxic and technically challenging to deliver locoregionally. CBL0137 is an experimental clinical drug with broad anticancer activity in animal models, owing to its ability to bind DNA in a nongenotoxic manner and inactivate the FACT chromatin modulator essential for tumor cell viability. Here, we report that CBL0137 delivered by ILP in a murine melanoma model is as efficacious as melphalan, displaying antitumor activity at doses corresponding to only a fraction of the systemic MTD of CBL0137. The ability to bind DNA quickly combined with a favorable safety profile made it possible to substitute CBL0137 in the ILP protocol, using an intra-arterial infusion method, to safely achieve effective tumor suppression. Our findings of a preclinical proof of concept for CBL0137 and its administration via intra-arterial infusion as a superior treatment compared with melphalan ILP allows for locoregional treatment anywhere a catheter can be placed. Cancer Res; 76(22); 6620-30. ©2016 AACR.

Limited role of N-terminal phosphoserine residues in the activation of transcription by p53.

The p53 tumor suppressor is phosphorylated in response to various cellular stress signals, such as DNA damage, leading to its release from MDM2 and consequent stabilization and activation as a transcription factor. In human U2OS cells, treatment with adriamycin causes p53 to be phosphorylated on all six serine residues tested, leading to the dissociation of p53 from MDM2 and transcription of the p21 and mdm2 genes. In contrast, in these cells, IPTG-dependent induction of p14ARF, which sequesters MDM2 away from p53, does not lead to detectable phosphorylation of any of the five N-terminal serine residues tested (6, 9, 15, 20, 37). Only C-terminal serine 392 is phosphorylated. However, the increase of p21 and mdm2 mRNAs was indistinguishable following treatment with adriamycin or induction of p14ARF. By using cDNA arrays to examine global p53-dependent gene expression in response to adriamycin or p14ARF, we found that most genes were regulated similarly by the two treatments. However, a subset of p53-regulated genes whose products have proliferative roles or regulate VEGF activity, newly described here, are repressed by p14ARF much more than by adriamycin. We conclude that the phosphorylation of p53 on N-terminal serine residues is not required for increased transcription of the great majority of p53-responsive genes and that the induction of p53 by p14ARF, with little phosphorylation, leads to substantial repression of genes whose products have roles in proliferation.

Proteotoxic stress targeted therapy (PSTT): induction of protein misfolding enhances the antitumor effect of the proteasome inhibitor bortezomib.

Proteotoxic stress (PS) is generated in cells under a variety of conditions involving accumulation of misfolded proteins. To avoid the toxicity of unmitigated PS, cells activate the heat shock response (HSR). HSR involves upregulation of factors such as ubiquitin and the non-housekeeping chaperone Hsp70 which assist with metabolism of aberrant proteins. The PS-HSR axis is a potential anticancer treatment target since many tumor cells display constitutive PS and dependence on HSR due to their rapid rates of proliferation and translation. In fact, induction of PS via stimulation of protein misfolding (hyperthermia), inhibition of proteasomes (bortezomib) or inhibition of Hsp90 (geldanamycin) have all been considered or used for cancer treatment. We found that combination of bortezomib with an inducer of protein misfolding (hyperthermia or puromycin) resulted in enhanced PS. HSR was also induced, but could not mitigate the elevated PS and the cells died via largely p53-independent apoptosis. Thus, combination treatments were more cytotoxic in vitro than the component single treatments. Consistent with this, combination of non-toxic doses of puromycin with bortezomib significantly increased the antitumor activity of bortezomib in a mouse model of multiple myeloma. These results provide support for using combination treatments that disrupt the balance of PS and HSR to increase the therapeutic index of anticancer therapies.

The Wilms tumor suppressor-1 target gene podocalyxin is transcriptionally repressed by p53.

Wilms tumors are a heterogeneous class of tumors in which Wilms tumor suppressor-1 (WT1) and the p53 tumor suppressor may be variously inactivated by mutation, reduced in expression, or even overexpressed in the wild-type state. The downstream transcriptional targets of WT1 and p53 that are critical for mediating their roles in Wilms tumorigenesis are not well defined. The WiT49 cell line is characteristic of anaplastic Wilms tumors that are refractory to treatment and expresses wild-type WT1 and mutant p53. We have used the small molecule compound CP-31398 (Pfizer) to restore wild-type p53 function to the codon 248 mutant p53 present in WiT49 cells. In these cells, CP-31398 activated transcription of p53-regulated promoters and enhanced UV light-induced apoptosis without altering the overall p53 protein level. These phenotypes were accompanied by restored binding of the p53 protein to promoter sequences in vivo. Gene expression profiling of CP-31398-treated WiT49 cells revealed subsets of putative p53 target genes that were up- or down-regulated. A preferred target of p53-mediated repression in this system is the podocalyxin (PODXL) gene. PODXL is also transcriptionally regulated by WT1 and has roles in cell adhesion and anti-adhesion. Our results show that PODXL is a bona fide target of p53-mediated transcriptional repression while being positively regulated by WT1. We propose that inappropriate expression of PODXL due to changes in WT1 and/or p53 activity may contribute to Wilms tumorigenesis.