STAT3 inhibitor Stattic and its analogues inhibit STAT3 phosphorylation and modulate cytokine secretion in senescent tumour cells

Signal transducer and activator of transcription 3 (STAT3) signalling serves an important role in carcinogenesis and cellular senescence, and its inhibition in tumour cells represents an attractive therapeutic target. Premature cellular senescence, a process of permanent proliferative arrest of cells in response to various inducers, such as cytostatic drugs or ionizing radiation, is accompanied by morphological and secretory changes, and by altered susceptibility to chemotherapeutic agents, which can thereby complicate their eradication by cancer therapies. In the present study, the responsiveness of proliferating and docetaxel (DTX)‑induced senescent cancer cells to small molecule STAT3 inhibitor Stattic and its analogues was evaluated using tumour cell lines. These agents displayed cytotoxic effects in cell viability assays on both proliferating and senescent murine TRAMP‑C2 and TC‑1 cells; however, senescent cells were markedly more resistant. Western blot analysis revealed that Stattic and its analogues effectively inhibited constitutive STAT3 phosphorylation in both proliferating and senescent cells. Furthermore, whether the Stattic‑derived inhibitor K1836 could affect senescence induction or modulate the phenotype of senescent cells was evaluated. K1836 treatment demonstrated no effect on senescence induction by DTX. However, the K1836 compound significantly modulated secretion of certain cytokines (interleukin‑6, growth‑regulated oncogene α and monocyte chemoattractant protein‑1). In summary, the present study demonstrated differences between proliferating and senescent tumour cells in terms of their susceptibility to STAT3 inhibitors and demonstrated the ability of the new STAT3 inhibitor K1836 to affect the secretion of essential components of the senescence‑associated secretory phenotype. The present study may be useful for further development of STAT3 inhibitor‑based therapy of cancer or age‑related diseases.

Type I interferon signaling in malignant blasts contributes to treatment efficacy in AML patients

While type I interferon (IFN) is best known for its key role against viral infection, accumulating preclinical and clinical data indicate that robust type I IFN production in the tumor microenvironment promotes cancer immunosurveillance and contributes to the efficacy of various antineoplastic agents, notably immunogenic cell death inducers. Here, we report that malignant blasts from patients with acute myeloid leukemia (AML) release type I IFN via a Toll-like receptor 3 (TLR3)-dependent mechanism that is not driven by treatment. While in these patients the ability of type I IFN to stimulate anticancer immune responses was abolished by immunosuppressive mechanisms elicited by malignant blasts, type I IFN turned out to exert direct cytostatic, cytotoxic and chemosensitizing activity in primary AML blasts, leukemic stem cells from AML patients and AML xenograft models. Finally, a genetic signature of type I IFN signaling was found to have independent prognostic value on relapse-free survival and overall survival in a cohort of 132 AML patients. These findings delineate a clinically relevant, therapeutically actionable and prognostically informative mechanism through which type I IFN mediates beneficial effects in patients with AML.

Discovery of small molecule mechanistic target of rapamycin inhibitors as anti-aging and anti-cancer therapeutics

To date, the most studied drug in anti-aging research is the mTOR inhibitor - rapamycin. Despite its almost perfect anti-aging profile, rapamycin exerts one significant limitation - inappropriate physicochemical properties. Therefore, we have decided to utilize virtual high-throughput screening and fragment-based design in search of novel mTOR inhibiting scaffolds with suitable physicochemical parameters. Seven lead compounds were selected from the list of obtained hits that were commercially available (4, 5, and 7) or their synthesis was feasible (1, 2, 3, and 6) and evaluated in vitro and subsequently in vivo. Of all these substances, only compound 3 demonstrated a significant cytotoxic, senolytic, and senomorphic effect on normal and cancerous cells. Further, it has been confirmed that compound 3 is a direct mTORC1 inhibitor. Last but not least, compound 3 was found to exhibit anti-SASP activity concurrently being relatively safe within the test of in vivo tolerability. All these outstanding results highlight compound 3 as a scaffold worthy of further investigation.

Chronic inflammation decreases HSC fitness by activating the druggable Jak/Stat3 signaling pathway

Chronic inflammation represents a major threat to human health since long-term systemic inflammation is known to affect distinct tissues and organs. Recently, solid evidence demonstrated that chronic inflammation affects hematopoiesis; however, how chronic inflammation affects hematopoietic stem cells (HSCs) on the mechanistic level is poorly understood. Here, we employ a mouse model of chronic multifocal osteomyelitis (CMO) to assess the effects of a spontaneously developed inflammatory condition on HSCs. We demonstrate that hematopoietic and nonhematopoietic compartments in CMO BM contribute to HSC expansion and impair their function. Remarkably, our results suggest that the typical features of murine multifocal osteomyelitis and the HSC phenotype are mechanistically decoupled. We show that the CMO environment imprints a myeloid gene signature and imposes a pro-inflammatory profile on HSCs. We identify IL-6 and the Jak/Stat3 signaling pathway as critical mediators. However, while IL-6 and Stat3 blockage reduce HSC numbers in CMO mice, only inhibition of Stat3 activity significantly rescues their fitness. Our data emphasize the detrimental effects of chronic inflammation on stem cell function, opening new venues for treatment.

Design, synthesis, and in vitro evaluation of BP-1-102 analogs with modified hydrophobic fragments for STAT3 inhibition

Twelve novel analogs of STAT3 inhibitor BP-1-102 were designed and synthesised with the aim to modify hydrophobic fragments of the molecules that are important for interaction with the STAT3 SH2 domain. The cytotoxic activity of the reference and novel compounds was evaluated using several human and two mouse cancer cell lines. BP-1-102 and its two analogs emerged as effective cytotoxic agents and were further tested in additional six human and two murine cancer cell lines, in all of which they manifested the cytotoxic effect in a micromolar range. Reference compound S3I-201.1066 was found ineffective in all tested cell lines, in contrast to formerly published data. The ability of selected BP-1-102 analogs to induce apoptosis and inhibition of STAT3 receptor-mediated phosphorylation was confirmed. The structure–activity relationship confirmed a demand for two hydrophobic substituents, i.e. the pentafluorophenyl moiety and another spatially bulky moiety, for effective cytotoxic activity and STAT3 inhibition.

Abstract 6686: SO-C101 displays strong anti-tumor effect in TC-1 and TRAMP-C2 tumor mice and in combination with PD-1 blockade prevents tumor development in a NK and CD8+ T cells dependent manner

SO-C101 (RLI-15) is a superagonist fusion protein of interleukin (IL)-15 and the IL-15 receptor α (IL-15Rα) sushi+ domain designed to bypass the need of endogenous IL-15Rα, thereby leveraging the activity of IL-15 in vivo on target immune cells and reducing the toxicity of IL-15 as such. SO-C101 was previously shown to exhibit a potent anti-metastatic activity in Renca, B16F10 melanoma and delayed tumor growth in T cell-based mouse tumor models (CT26, MC38). Here we investigated the anti-tumor efficacy in predominantly natural killer (NK)-cell based mouse tumor models TC-1 and TRAMP-C2. We showed that SO-C101 monotherapy was effective in the treatment of established TC-1 tumors, which was dependent on the presence of both NK and CD8+ T cells, but not CD4+ T cells. In an early treatment setting SO-C101 significantly decreased the rate of tumor development also in dependence on NK and CD8+ T cells. SO-C101 effectively reduced tumor growth in TRAMP-C2 mice in early and advanced treatment settings. However, only in combination with anti-PD-1 antibody treatment the tumor development was prevented in majority of mice. This effect was durable, and the new tumor development was further significantly delayed after a tumor cell re-challenge, which suggests the involvement of memory T cells despite an important NK cell role in anti-tumor efficacy in these models. The efficacy of SO-C101 and anti-PD-1 treatment was not dependent on CD4+ T cells, but mainly on NK and CD8+ T cells. Interestingly, SO-C101 and anti-PD-1 treatment in double NK/CD8+ T cell-depleted mice decreased tumor growth which suggests an involvement of other immune cell populations in the anti-tumor efficacy. SO-C101 stimulated the proliferation and the cytotoxic activity of NK cells and memory CD8+ T cells without significant expansion of regulatory T cells. These data show the importance of various immune cell populations during SO-C101 monotherapy and the treatment in combination with anti-PD-1 antibodies, and set a base for further complex analysis of SO-C101 behavior. The therapeutic potential of SO-C101 is currently being tested in an ongoing Phase I clinical study in cancer patients.

Citation Format: Irena Adkins, Romana Mikyskova, Nada Hradilova, Guy de Martynoff, David Bechard, Ulrich Moebius, Milan Reinis, Radek Spisek. SO-C101 displays strong anti-tumor effect in TC-1 and TRAMP-C2 tumor mice and in combination with PD-1 blockade prevents tumor development in a NK and CD8+ T cells dependent manner [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 6686.

Abstract B35: Studies on photo-sensitivity of a glycol porphyrin derivative and its anti-tumor efficacy

Photodynamic therapy (PDT) has attracted great attention in cancer treatment. Porphyrin derivative with ethylene glycol chains linked to meta position of meso-tetraphenylporphyrin, mTPP(EG)4, is one of assumed compounds that can be used for treatment of cancer in photodynamic therapy (PDT). The aim of the study is to demonstrate the photodynamic efficacy in vitro and in vivo as well as to analyze its therapeutic mechanism. The cell viability, cell surface exposure of immunogenic molecules, maturation and phagocytic capacity of PDT-treated tumor cells were monitored by flow cytometry. The kinetics of key components of ER stress-mediated apoptotic pathway was analyzed by Western blotting. Our first results indicate a new and attractive possibility of immunogenic cell death induction. Initiation of immunogenic cell death by PDT was successfully demonstrated in vitro on human and mouse tumor cell lines. The effects of mTPP(EG)4 were compared with the effects of mTPP(EG)4 without subsequent photoactivation, hypericin-mediated PDT, and high hydrostatic pressure. In vivo assays evaluated immunogenicity of mTPP(EG)4 in mice and assessed the ability of PDT treated cells to induce effective immunity against transplanted syngeneic tumors (mouse TRAMP-C2, TC-1 and B16). The results obtained in this study will provide a basis for possible further preclinical experiments with mTPP(EG)4 or other derivatives, testing their potential in PDT and development of new antitumor therapies.

Citation Format: Sarka Vosahlikova, Irena Kusova Moserova, Jarmila Kralova, Milan Reinis, Romana Mikyskova, Jitka Palich Fucikova. Studies on photo-sensitivity of a glycol porphyrin derivative and its anti-tumor efficacy [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2018 Nov 27-30; Miami Beach, FL. Philadelphia (PA): AACR; Cancer Immunol Res 2020;8(4 Suppl):Abstract nr B35.

Abstract B96: Calreticulin exposure on malignant blasts correlates with improved NK cell-mediated cytotoxicity in AML patients

In some settings, cancer cells responding to treatment undergo an immunogenic form of cell death that is associated with the abundant emission of danger signals in the form of damage-associated molecular patterns (DAMPs). Accumulating preclinical and clinical evidence indicates that danger signals play a crucial role in the (re-)activation of antitumor immune responses in vivo, thus having a major impact on patient prognosis. We have previously demonstrated that the presence of calreticulin (CRT) on the surface of malignant blasts is a positive prognostic biomarker for patients with acute myeloid leukemia (AML). CRT exposure not only correlated with enhanced T cell-dependent antitumor immunity in this setting but also affected the number of circulating NK cells upon restoration of normal hematopoiesis. Here, we report that CRT exposure on malignant blasts is associated with enhanced NK cell cytotoxic and secretory functions, both in AML patients and in vivo in mice. The ability of CRT to stimulate NK cells relies on CD11c+CD14high cells that, upon exposure to CRT, display higher levels of IL-15Rα, maturation markers (CD86 and HLA-DR), and CCR7. CRT exposure on malignant blasts also correlates with the upregulation of genes coding for type I interferons (IFNs). This suggests that CD11c+CD14high cells have increased capacity to migrate to secondary lymphoid organs, where can efficiently deliver stimulatory signals (IL-15Rα/IL-15) to NK cells. These findings delineate a multipronged, clinically relevant mechanism whereby surface-exposed CRT favors NK cell activation in AML patients.

Citation Format: Iva Truxova, Lenka Kasikova, Cyril Salek, Michal Hensler, Daniel Lysak, Peter Holicek, Pavla Bilkova, Monika Holubova, Xiufen Chen, Romana Mikyskova, Milan Reinis, Marek Kovar, Barbora Tomalova, Justin Kline, Lorenzo Galluzzi, Radek Spisek, Jitka Fucikova. Calreticulin exposure on malignant blasts correlates with improved NK cell-mediated cytotoxicity in AML patients [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2019 Nov 17-20; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2020;8(3 Suppl):Abstract nr B96.

Calreticulin exposure on malignant blasts correlates with improved natural killer cell-mediated cytotoxicity in acute myeloid leukemia patients

In some settings, cancer cells responding to treatment undergo an immunogenic form of cell death that is associated with the abundant emission of danger signals in the form of damage-associated molecular patterns. Accumulating preclinical and clinical evidence indicates that danger signals play a crucial role in the (re-)activation of antitumor immune responses in vivo, thus having a major impact on patient prognosis. We have previously demonstrated that the presence of calreticulin on the surface of malignant blasts is a positive prognostic biomarker for patients with acute myeloid leukemia (AML). Calreticulin exposure not only correlated with enhanced T-cell-dependent antitumor immunity in this setting but also affected the number of circulating natural killer (NK) cells upon restoration of normal hematopoiesis. Here, we report that calreticulin exposure on malignant blasts is associated with enhanced NK cell cytotoxic and secretory functions, both in AML patients and in vivo in mice. The ability of calreticulin to stimulate NK-cells relies on CD11c⁺CD14^high cells that, upon exposure to CRT, express higher levels of IL-15Rα, maturation markers (CD86 and HLA-DR) and CCR7. CRT exposure on malignant blasts also correlates with the upregulation of genes coding for type I interferon. This suggests that CD11c⁺CD14^high cells have increased capacity to migrate to secondary lymphoid organs, where can efficiently deliver stimulatory signals (IL-15Rα/IL-15) to NK cells. These findings delineate a multipronged, clinically relevant mechanism whereby surface-exposed calreticulin favors NK-cell activation in AML patients.

Abstract 3775: Use of RLI-15 a clinical grade fusion protein with IL-15 superagonistic activity for the activation of anti-tumor immune response

RLI-15, a superagonist fusion protein of interleukin (IL)-15 and the IL-15 receptor α (IL-15Rα) sushi+ domain represents a promising candidate for the induction of anti-tumor immunity. RLI-15 was designed to bypass the need of endogenous IL-15Rα, thereby leveraging the activity of IL-15 in vivo on target immune cells. RLI-15 stimulates the proliferation and the cytotoxic activity of natural killer (NK) cells and memory CD8+ T cells with no significant expansion and activation of regulatory T cell compartment. RLI-15 was previously shown to exhibit a potent anti-metastatic activity in B16F10 melanoma and Renca renal cell carcinoma mouse models. RLI-15 also significantly delayed tumor growth and prolonged survival when combined with anti-PD1 therapy in CT26 and MC38 colon carcinoma models. Here, we report that the combination treatment with clinical-grade RLI-15 and an anti-PD1 antibody leads to a significant anti-tumor efficacy in a TRAMP-C2 prostate cancer mouse model with 70 % of mice remaining tumor free after the treatment. We evaluated the optimal schedule of such combination therapy to set the basis for the design of upcoming clinical trials. We further tested how the administration schedule affects the pharmacodynamics properties of clinical-grade RLI-15 and translates into the anti-tumor efficacy in metastatic Renca and CT26 mouse models. In cynomolgous monkeys, various schedules of administration of RLI-15 showed a dose-dependent expansion of peripheral blood lymphocytes, predominantly of NK cell and memory CD8+ T cell compartments. The toxicity in mice and cynomolgous monkeys was evaluated to determine the maximal tolerated dose of RLI-15. Furthermore, the activity of clinical-grade RLI-15 was tested in vitro on human PBMCs and the superiority over IL-2 and IL-15 stimulatory capacity has been confirmed. The complex analysis of RLI-15 behavior and of the induced anti-tumor immune response will be explored in the design of a planned Phase I clinical study in patients with both solid tumors and hematological malignancies.

Citation Format: Irena Adkins, Lenka Sadilkova, Nada Hradilova, Jakub Tomala, Barbora Tomalova, Marek Kovar, Romana Mikyskova, Milan Reinis, Guy de Martynoff, David Bechard, Ulrich Moebius, Radek Spisek. Use of RLI-15 a clinical grade fusion protein with IL-15 superagonistic activity for the activation of anti-tumor immune response [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3775.

Tumor growth accelerated by chemotherapy-induced senescent cells is suppressed by treatment with IL-12 producing cellular vaccines

Standard-of-care chemo- or radio-therapy can induce, besides tumor cell death, also tumor cell senescence. While senescence is considered to be a principal barrier against tumorigenesis, senescent cells can survive in the organism for protracted periods of time and they can promote tumor development. Based on this emerging concept, we hypothesized that elimination of such potentially cancer-promoting senescent cells could offer a therapeutic benefit. To assess this possibility, here we first show that tumor growth of proliferating mouse TC-1 HPV-16-associated cancer cells in syngeneic mice becomes accelerated by co-administration of TC-1 or TRAMP-C2 prostate cancer cells made senescent by pre-treatment with the anti-cancer drug docetaxel, or lethally irradiated. Phenotypic analyses of tumor-explanted cells indicated that the observed acceleration of tumor growth was attributable to a protumorigenic environment created by the co-injected senescent and proliferating cancer cells rather than to escape of the docetaxel-treated cells from senescence. Notably, accelerated tumor growth was effectively inhibited by cell immunotherapy using irradiated TC-1 cells engineered to produce interleukin IL-12. Collectively, our data document that immunotherapy, such as the IL-12 treatment, can provide an effective strategy for elimination of the detrimental effects caused by bystander senescent tumor cells in vivo.

Dendritic cells pulsed with tumor cells killed by high hydrostatic pressure inhibit prostate tumor growth in TRAMP mice

Dendritic cell (DC)-based vaccines pulsed with high hydrostatic pressure (HHP)-inactivated tumor cells have recently been shown to be a promising tool for prostate cancer chemoimmunotherapy. In this study, DC-based vaccines, both pulsed and unpulsed, were as effective as docetaxel (DTX) in reducing prostate tumors in the orthotopic transgenic adenocarcinoma of the mouse prostate (TRAMP) model. However, we did not observe any additive or synergic effects of chemoimmunotherapy on the tumor growth, while only the combination of DTX and pulsed dendritic cells resulted in significantly lower proliferation detected by Ki67 staining in histological samples. The DC-based vaccine pulsed with HHP-treated tumor cells was also combined with another type of cytostatic, cyclophosphamide, with similar results. In another clinically relevant setting, minimal residual tumor disease after surgery, administration of DC-based vaccines after the surgery of poorly immunogenic transplanted TRAMP-C2, as well as in immunogenic TC-1 tumors, reduced the growth of tumor recurrences. To identify the effector cell populations after DC vaccine application, mice were twice immunized with both pulsed and unpulsed DC vaccine, and the cytotoxicity of the spleen cells populations was tested. The effector cell subpopulations were defined as CD4⁺ and NK1.1⁺, which suggests rather unspecific therapeutic effects of the DC-based vaccines in our settings. Taken together, our data demonstrate that DC-based vaccines represent a rational tool for the treatment of human prostate cancer.