Ring A/B-Modified 17ß-Hydroxywithanolide Analogues as Antiproliferative Agents for Prostate Cancer and Potentiators of Immunotherapy for Renal Carcinoma and Melanoma.

Physachenolide C (1) is a 17ß-hydroxywithanolide natural product with a unique anticancer potential, as it exhibits potent and selective in vitro antiproliferative activity against prostate cancer (PC) cells and promotes TRAIL-induced apoptosis of renal carcinoma (RC) and poly I:C-induced apoptosis of melanoma cells. To explore the effect of ring A/B modifications of physachenolide C (1) on these biological activities, 23 of its natural and semisynthetic analogues were evaluated. Analogues 4-23 were prepared by chemical transformations of a readily accessible compound, physachenolide D (2). Compound 1 and its analogues 2-23 were evaluated for their antiproliferative activity against PC (LNCaP and 22Rv1), RC (ACHN), and melanoma (M14 and SK-MEL-28) cell lines and normal human foreskin fibroblast (HFF) cells. Most of the active analogues had selective and potent activity in reducing cell number for PC cell lines, some showing selectivity for androgen-independent and enzalutamide-resistant 22Rv1 cells compared to androgen-dependent LNCaP cells. Analogues with IC50s below 5.0 µM against ACHN cells, when tested in the presence of TRAIL, showed a significantly increased ability to reduce cell number, and those analogues active against the M14 and SK-MEL-28 cell lines exhibited enhanced activity when combined with poly I:C. These data provide additional structure-activity relationship information for 17ß-hydroxywithanolides and suggest that selective activities of some analogues may be exploited to develop natural products-based tumor-specific agents for cancer chemotherapy.

Small-Molecule Natural Product Physachenolide C Potentiates Immunotherapy Efficacy by Targeting BET Proteins.

Screening for sensitizers of cancer cells to TRAIL-mediated apoptosis identified a natural product of the 17ß-hydroxywithanolide (17-BHW) class, physachenolide C (PCC), as a promising hit. In this study, we show that PCC was also able to sensitize melanoma and renal carcinoma cells to apoptosis in response not only to TRAIL, but also to the synthetic polynucleotide poly I:C, a viral mimetic and immune activator, by reducing levels of antiapoptotic proteins cFLIP and Livin. Both death receptor and TLR3 signaling elicited subsequent increased assembly of a proapoptotic ripoptosome signaling complex. Administration of a combination of PCC and poly I:C in human M14 melanoma xenograft and a syngeneic B16 melanoma model provided significant therapeutic benefit as compared with individual agents. In addition, PCC enhanced melanoma cell death in response to activated human T cells in vitro and in vivo in a death ligand-dependent manner. Biochemical mechanism-of-action studies established bromo and extraterminal domain (BET) proteins as major cellular targets of PCC. Thus, by targeting of BET proteins to reduce antiapoptotic proteins and enhance caspase-8-dependent apoptosis of cancer cells, PCC represents a unique agent that can potentially be used in combination with various immunotherapeutic approaches to promote tumor regression and improve outcome. SIGNIFICANCE: These findings demonstrate that PCC selectively sensitizes cancer cells to immune-mediated cell death, potentially improving the efficacy of cancer immunotherapies. GRAPHICAL ABSTRACT: http://cancerres.aacrjournals.org/content/canres/81/12/3374/F1.large.jpg.

Cytotoxic and other withanolides from aeroponically grown Physalis philadelphica.

Eleven withanolides including six previously undescribed compounds, 16ß-hydroxyixocarpanolide, 24,25-dihydroexodeconolide C, 16,17-dehydro-24-epi-dioscorolide A, 17-epi-philadelphicalactone A, 16-deoxyphiladelphicalactone C, and 4-deoxyixocarpalactone A were isolated from aeroponically grown Physalis philadelphica. Structures of these withanolides were elucidated by the analysis of their spectroscopic (HRMS, 1D and 2D NMR, ECD) data and comparison with published data for related withanolides. Cytotoxic activity of all isolated compounds was evaluated against a panel of five human tumor cell lines (LNCaP, ACHN, UO-31, M14 and SK-MEL-28), and normal (HFF) cells. Of these, 17-epi-philadelphicalactone A, withaphysacarpin, philadelphicalactone C, and ixocarpalactone A exhibited cytotoxicity against ACHN, UO-31, M14 and SK-MEL-28, but showed no toxicity to HFF cells.

Withanolides from Aeroponically Grown Physalis peruviana and Their Selective Cytotoxicity to Prostate Cancer and Renal Carcinoma Cells.

Investigation of aeroponically grown Physalis peruviana resulted in the isolation of 11 new withanolides, including perulactones I-L (1-4), 17-deoxy-23ß-hydroxywithanolide E (5), 23ß-hydroxywithanolide E (6), 4-deoxyphyperunolide A (7), 7ß-hydroxywithanolide F (8), 7ß-hydroxy-17-epi-withanolide K (9), 24,25-dihydro-23ß,28-dihydroxywithanolide G (10), and 24,25-dihydrowithanolide E (11), together with 14 known withanolides (12-25). The structures of 1-11 were elucidated by the analysis of their spectroscopic data, and 12-25 were identified by comparison of their spectroscopic data with those reported. All withanolides were evaluated for their cytotoxic activity against a panel of tumor cell lines including LNCaP (androgen-sensitive human prostate adenocarcinoma), 22Rv1 (androgen-resistant human prostate adenocarcinoma), ACHN (human renal adenocarcinoma), M14 (human melanoma), SK-MEL-28 (human melanoma), and normal human foreskin fibroblast cells. Of these, the 17ß-hydroxywithanolides (17-BHWs) 6, 8, 9, 11-13, 15, and 19-22 showed selective cytotoxic activity against the two prostate cancer cell lines LNCaP and 22Rv1, whereas 13 and 20 exhibited selective toxicity for the ACHN renal carcinoma cell line. These cytotoxicity data provide additional structure-activity relationship information for the 17-BHWs.

17ß-Hydroxywithanolides as Sensitizers of Renal Carcinoma Cells to Tumor Necrosis Factor-α Related Apoptosis Inducing Ligand (TRAIL) Mediated Apoptosis: Structure-Activity Relationships.

Renal cell carcinoma (RCC) is a cancer with poor prognosis, and the 5-year survival rate of patients with metastatic RCC is 5-10%. Consequently, treatment of metastatic RCC represents an unmet clinical need. Screening of a 50 000-member library of natural and synthetic compounds for sensitizers of RCC cells to TRAIL-mediated apoptosis led to identification of the 17ß-hydroxywithanolide (17-BHW), withanolide E (1), as a promising lead. To explore structure-activity relationships, we obtained natural and semisynthetic withanolides 1, 2a, 2c, and 3-36 and compared their ability to sensitize TRAIL-mediated apoptosis in a panel of renal carcinoma cells. Our findings revealed that 17-BHWs with a α-oriented side chain are superior to known TRAIL-sensitizing withanolides belonging to withaferin A class with a ß-oriented side chain and demonstrated that the 17-BHW scaffold can be modified to enhance sensitization of RCCs to TRAIL-mediated apoptosis, thereby assisting development of natural-product-inspired drugs to treat metastatic RCC.

Metformin sensitizes lung cancer cells to treatment by the tyrosine kinase inhibitor erlotinib.

Lung cancer is one of the deadliest malignant tumors with limited treatment options. Although targeted therapy, using tyrosine-kinase inhibitors such as erlotinib (Erlo), has shown therapeutic benefit, only 15 % patients with mutated epidermal growth factor receptor (EGFR) in lung cancer cells are sensitive. Therefore, additional therapeutic strategy should be developed. In this study, we found that metformin (Met), which is widely used for the treatment of type 2 diabetes (T2D), sensitized lung cancer cells bearing wild-type EGFR to Erlo treatment by enriching cancer cells expressing higher levels of EGFR with persistent phosphorylation. As a consequence, combination of Met and Erlo more efficiently inhibited the growth of lung cancer cells both in vitro and in mice with xenografted tumors. Our results suggest a novel approach to treating lung cancer cases which are originally resistant to Erlo.

Using natural products to promote caspase-8-dependent cancer cell death.

The selective killing of cancer cells without toxicity to normal nontransformed cells is an idealized goal of cancer therapy. Thus, there has been much interest in tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), a protein that appears to selectively kill cancer cells. TRAIL has been reported to trigger apoptosis and under some circumstances, an alternate death signaling pathway termed necroptosis. The relative importance of necroptosis for cell death induction in vivo is under intensive investigation. Nonetheless, many cancer cells (particularly those freshly isolated from cancer patients) are highly resistant to TRAIL-mediated cell death. Therefore, there is an underlying interest in identifying agents that can be combined with TRAIL to improve its efficacy. There are numerous reports in which combination of TRAIL with standard antineoplastic drugs has resulted in enhanced cancer cell death in vitro. However, many of these chemotherapeutic drugs are nonspecific and associated with adverse effects, which raise serious concerns for cancer therapy in patients. By contrast, natural products have been shown to be safer and efficacious alternatives. Recently, a number of studies have suggested that certain natural products when combined with TRAIL can enhance cancer cell death. In this review, we highlight molecular pathways that might be targeted by various natural products to promote cell death, and focus on our recent work with withanolides as TRAIL sensitizers. Finally, we will suggest synergistic approaches for combining active withanolides with various forms of immunotherapy to promote cancer cell death and an effective antitumor immune response.

Human plasmacytoid dentritic cells elicit a Type I Interferon response by sensing DNA via the cGAS-STING signaling pathway.

Plasmacytoid dendritic cells (pDCs) are a major source of type I interferon (IFN) and are important for host defense by sensing microbial DNA via TLR9. pDCs also play a critical role in the pathogenesis of IFN-driven autoimmune diseases. Yet, this autoimmune reaction is caused by the recognition of self-DNA and has been linked to TLR9-independent pathways. Increasing evidence suggests that the cytosolic DNA receptor cyclic GMP-AMP (cGAMP) synthase (cGAS) is a critical component in the detection of pathogens and contributes to autoimmune diseases. It has been shown that binding of DNA to cGAS results in the synthesis of cGAMP and the subsequent activation of the stimulator of interferon genes (STING) adaptor to induce IFNs. Our results show that the cGAS-STING pathway is expressed and activated in human pDCs by cytosolic DNA leading to a robust type I IFN response. Direct activation of STING by cyclic dinucleotides including cGAMP also activated pDCs and knockdown of STING abolished this IFN response. These results suggest that pDCs sense cytosolic DNA and cyclic dinucleotides via the cGAS-STING pathway and that targeting this pathway could be of therapeutic interest.

IRF5 and IRF8 modulate the CAL-1 human plasmacytoid dendritic cell line response following TLR9 ligation.

Synthetic oligonucleotides (ODNs) containing CpG motifs stimulate human plasmacytoid dendritic cells (pDCs) to produce type-1 interferons (IFNs) and proinflammatory cytokines. Previous studies demonstrated that interferon regulatory factors (IRFs) play a central role in mediating CpG-induced pDC activation. This work explores the inverse effects of IRF5 and IRF8 (also known as IFN consensus sequence-binding protein) on CpG-dependent gene expression in the human CAL-1 pDC cell line. This cell line shares many of the phenotypic and functional properties of freshly isolated human pDCs. Results from RNA interference and microarray studies indicate that IRF5 upregulates TLR9-driven gene expression whereas IRF8 downregulates the same genes. Several findings support the conclusion that IRF8 inhibits TLR9-dependent gene expression by directly blocking the activity of IRF5. First, the inhibitory activity of IRF8 is only observed when IRF5 is present. Second, proximity ligation analysis shows that IRF8 and IRF5 colocalize within the cytoplasm of resting human pDCs and cotranslocate to the nucleus after CpG stimulation. Taken together, these findings suggest that IRF5 and IRF8, two transcription factors with opposing functions, control TLR9 signaling in human pDCs.

The Alarmin HMGN1 contributes to antitumor immunity and is a potent immunoadjuvant.

Alarmins are endogenous mediators that are elicited rapidly in response to danger signals, enhancing innate and adaptive immune responses by promoting the recruitment and maturation of antigen-presenting cells (APC). The nucleosome-binding protein HMGN1 is a potent alarmin that binds TLR4 and induces antigen-specific Th1 immune responses, but its contributions to antitumor immunity have not been explored. We found that ovalbumin (OVA)-expressing EG7 mouse thymoma cells grew much faster in Hmgn1-deficient mice than littermate-matched controls. Tumor-bearing Hmgn1(-/-) mice generated fewer OVA-specific CD8 cells in the spleen than EG7-bearing Hmgn1(+/+) mice, suggesting that HMGN1 supported T cell-mediated antitumor immunity. In addition, EG7 tumors expressing HMGN1 grew more slowly than control EG7 tumors, suggesting greater resistance to HMGN1-expressing tumors. This resistance relied on T cell-mediated immunity because it was abolished by in vivo depletion of CD4(+) and CD8(+) T cells. Moreover, mice vaccinated with a DNA vector expressing an HMGN1-gp100 fusion protein manifested gp100-specific, Th1-polarized immune responses, acquiring resistance to challenge with mouse B16F1 melanoma. Overall, our findings show that HMGN1 contributes to antitumor immunity and it may offer an effective adjuvant to heighten responses to cancer vaccines.

ß-Defensin 2 and 3 promote the uptake of self or CpG DNA, enhance IFN-α production by human plasmacytoid dendritic cells, and promote inflammation.

Alarmins are a group of structurally diverse host defense antimicrobial peptides that are important immune activators. In this article, we present a novel role for two potent alarmins, human ß-defensin 2 and 3 (HBD2 and 3), in promoting IFN-α production by human plasmacytoid dendritic cells. We demonstrate that HBD2 and 3 activate pDCs by enhancing the intracellular uptake of CpG and self DNA and promote DNA-induced IFN-α production in a TLR9-dependent manner. Both CpG and host DNA form aggregates that resemble DNA nets when combined with HBD2 and 3. Isothermal titration calorimetry studies to elucidate the nature of HBD3/CpG complexes demonstrate involvement of enthalpy-driven interactions, in addition to hydrophobic interactions, with the formation of complexes at a molar ratio of 2:1 defensin/CpG. The i.v. administration of HBD3/CpG complexes induced proinflammatory cytokines like IL-12, IFN-γ, IL-6, IFN-α, and IL-10 in serum, associated with an increased recruitment of APCs in the spleen. Subcutaneous injections of these complexes showed enhanced infiltration of inflammatory cells at the injection site, indicating a potential pathophysiological role for alarmin/DNA complexes in contributing to inflammation. Intraperitoneal immunization of HBD3/CpG complexes with OVA enhanced both cellular and humoral responses to OVA, compared with OVA/HBD3 or OVA/CPG alone, indicative of a much more potent adjuvant effect of the HBD3/CpG complexes. Thus, the ability of defensins to enhance cellular uptake of nucleic acids can lead to improved vaccine formulations by promoting their uptake by various cells, resulting in an enhanced immune response.

IRF-5 and NF-κB p50 co-regulate IFN-ß and IL-6 expression in TLR9-stimulated human plasmacytoid dendritic cells.

Synthetic oligonucleotides (ODN) expressing CpG motifs mimic the ability of bacterial DNA to trigger the innate immune system via TLR9. Plasmacytoid dendritic cells (pDCs) make a critical contribution to the ensuing immune response. This work examines the induction of antiviral (IFN-ß) and pro-inflammatory (IL-6) cytokines by CpG-stimulated human pDCs and the human CAL-1 pDC cell line. Results show that interferon regulatory factor-5 (IRF-5) and NF-κB p50 are key co-regulators of IFN-ß and IL-6 expression following TLR9-mediated activation of human pDCs. The nuclear accumulation of IRF-1 was also observed, but this was a late event that was dependant on type 1 IFN and unrelated to the initiation of gene expression. IRF-8 was identified as a novel negative regulator of gene activation in CpG-stimulated pDCs. As variants of IRF-5 and IRF-8 were recently found to correlate with susceptibility to certain autoimmune diseases, these findings are relevant to our understanding of the pharmacologic effects of "K" ODN and the role of TLR9 ligation under physiologic, pathologic, and therapeutic conditions.

Alarmin-induced cell migration.

Alarmins are endogenous, constitutively available, damage-associated molecular patterns that upon release can mobilize and activate various leukocytes for the induction of innate and adaptive immune responses. For our immune system to function appropriately, it relies on navigating various leukocytes to distinct places at the right time. The direction of cell migration is determined by chemotactic factors that include classical chemoattractants, chemokines, certain growth factors, and alarmins. This viewpoint provides an overview of alarmin-induced cell migration. Alarmins are capable of inducing the migration of diverse types of leukocytes and nonleukocytes either directly by triggering specific receptors or indirectly by inducing production of chemokines through the activation of various leukocytes via pattern recognition receptors. The receptors used by alarmins to directly induce cell migration can either be Gαi protein-coupled receptors or receptors such as the receptor for advanced glycation end products; however, the intracellular signaling events responsible for the direct chemotactic activities of alarmins are, to date, only partially elucidated. Given that alarmins act in concert with chemokines to regulate the recruitment and trafficking of leukocytes, these damage-associated molecular patterns are potentially involved in diverse biological processes as discussed in this viewpoint.

High-mobility group nucleosome-binding protein 1 acts as an alarmin and is critical for lipopolysaccharide-induced immune responses.

Alarmins are endogenous mediators capable of promoting the recruitment and activation of antigen-presenting cells (APCs), including dendritic cells (DCs), that can potentially alert host defense against danger signals. However, the relevance of alarmins to the induction of adaptive immune responses remains to be demonstrated. In this study, we report the identification of HMGN1 (high-mobility group nucleosome-binding protein 1) as a novel alarmin and demonstrate that it contributes to the induction of antigen-specific immune responses. HMGN1 induced DC maturation via TLR4 (Toll-like receptor 4), recruitment of APCs at sites of injection, and activation of NF-κB and multiple mitogen-activated protein kinases in DCs. HMGN1 promoted antigen-specific immune response upon co-administration with antigens, and Hmgn1(-/-) mice developed greatly reduced antigen-specific antibody and T cell responses when immunized with antigens in the presence of lipopolysaccharide (LPS). The impaired ability of Hmgn1(-/-) mice to mount antigen-specific immune responses was accompanied by both deficient DC recruitment at sites of immunization and reduced production of inflammatory cytokines. Bone marrow chimera experiments revealed that HMGN1 derived from nonleukocytes was critical for the induction of antigen-specific antibody and T cell responses. Thus, extracellular HMGN1 acts as a novel alarmin critical for LPS-induced development of innate and adaptive immune responses.

Granulysin activates antigen-presenting cells through TLR4 and acts as an immune alarmin.

Granulysin (GNLY), an antimicrobial protein present in the granules of human cytotoxic T lymphocytes and natural killer (NK) cells, is produced as an intact 15-kDa form that is cleaved to yield a 9-kDa form. Alarmins are endogenous mediators that can induce recruitment and activation of antigen-presenting cells (APCs) and consequently promote the generation of immune response. We hypothesized that GNLY might function as an alarmin. Here, we report that both 9- and 15-kDa forms of recombinant GNLY-induced in vitro chemotaxis and activation of both human and mouse dendritic cells (DCs), recruited inflammatory leucocytes, including APCs in mice, and promoted antigen-specific immune responses upon coadministration with an antigen. GNLY-induced APC recruitment and activation required the presence of Toll-like receptor 4. The observed activity of recombinant GNLY was not due to endotoxin contamination. The capability of the supernatant of GNLY-expressing HuT78 cells to activate DC was blocked by anti-GNLY antibodies. Finally we present evidence that supernatants of degranulated human NK92 or primary NK cells also activated DCs in a GNLY- and Toll-like receptor 4-dependent manner, indicating the physiologic relevance of our findings. Thus, GNLY is the first identified lymphocyte-derived alarmin capable of promoting APC recruitment, activation, and antigen-specific immune response.

[Gd@C(82)(OH)(22)](n) nanoparticles induce dendritic cell maturation and activate Th1 immune responses.

Dendritic cells play a pivotal role in host immune defense, such as elimination of foreign pathogen and inhibition of tumorigenesis. In this paper, we report that [Gd@C(82)(OH)(22)](n) could induce phenotypic maturation of dendritic cells by stimulating DC production of cytokines including IL-12p70, upregulating DC co-stimulatory (CD80, CD83, and CD86) and MHC (HLA-A,B,C and HLA-DR) molecules, and switching DCs from a CCL5-responsive to a CCL19-responsive phenotype. We found that [Gd@C(82)(OH)(22)](n) can induce dendritic cells to become functionally mature as illustrated by their capacity to activate allogeneic T cells. Mice immunized with ovalbumin in the presence of [Gd@C(82)(OH)(22)](n) exhibit enhanced ovalbumin-specific Th1-polarized immune response as evidenced by the predominantly increased production of IFNgamma, IL-1beta, and IL-2. The [Gd@C(82)(OH)(22)](n) nanoparticle is a potent activator of dendritic cells and Th1 immune responses. These new findings also provide a rational understanding of the potent anticancer activities of [Gd@C(82)(OH)(22)](n) nanoparticles reported previously.

The alarmin functions of high-mobility group proteins.

High-mobility group (HMG) proteins are non-histone nuclear proteins that bind nucleosomes and regulate chromosome architecture and gene transcription. Over the past decade, numerous studies have established that some HMG proteins can be released extracellularly and demonstrate distinct extracellular biological activities. Here, we will give a brief overview of HMG proteins and highlight their participation in innate/inflammatory and adaptive immune responses. They have the activities of alarmins, which are endogenous mediators that are rapidly released in response to danger signals initiated by infection and/or tissue damage and are capable of activating innate and adaptive immunity by promoting the recruitment and activation of antigen-presenting cells (APCs).

Alarmins link neutrophils and dendritic cells.

Neutrophils are the first major population of leukocyte to infiltrate infected or injured tissues and are crucial for initiating host innate defense and adaptive immunity. Although the contribution of neutrophils to innate immune defense is mediated predominantly by phagocytosis and killing of microorganisms, neutrophils also participate in the induction of adaptive immune responses. At sites of infection and/or injury, neutrophils release numerous mediators upon degranulation or death, among these are alarmins which have a characteristic dual capacity to mobilize and activate antigen-presenting cells. We describe here how alarmins released by neutrophil degranulation and/or death can link neutrophils to dendritic cells by promoting their recruitment and activation, resulting in the augmentation of innate and adaptive immune responses.

Lactoferrin acts as an alarmin to promote the recruitment and activation of APCs and antigen-specific immune responses.

Lactoferrin is an 80-kDa iron-binding protein present at high concentrations in milk and in the granules of neutrophils. It possesses multiple activities, including antibacterial, antiviral, antifungal, and even antitumor effects. Most of its antimicrobial effects are due to direct interaction with pathogens, but a few reports show that it has direct interactions with cells of the immune system. In this study, we show the ability of recombinant human lactoferrin (talactoferrin alfa (TLF)) to chemoattract monocytes. What is more, addition of TLF to human peripheral blood or monocyte-derived dendritic cell cultures resulted in cell maturation, as evidenced by up-regulated expression of CD80, CD83, and CD86, production of proinflammatory cytokines, and increased capacity to stimulate the proliferation of allogeneic lymphocytes. When injected into the mouse peritoneal cavity, lactoferrin also caused a marked recruitment of neutrophils and macrophages. Immunization of mice with OVA in the presence of TLF promoted Th1-polarized Ag-specific immune responses. These results suggest that lactoferrin contributes to the activation of both the innate and adaptive immune responses by promoting the recruitment of leukocytes and activation of dendritic cells.

Defensin participation in innate and adaptive immunity.

Defensins are endogenous, small, cysteine-rich antimicrobial peptides that are produced by leukocytes and epithelial cells. Substantial evidence accumulated in recent years indicates that mammalian defensins are multifunctional and, by interacting with host cell receptor(s), participate in both the innate and adaptive antimicrobial immunity of the host. A better understanding of the function of defensins in immunity has implications for the development of potential clinical therapeutics for the treatment of infection or cancer. Here we will briefly outline the classification, genes, expression, and structure of mammalian defensins and focus on their roles in innate and adaptive immune response of the host.