Abstract 2647: RVU120, a selective CDK8/CDK19 inhibitor, demonstrates efficacy against hormone-independent breast cancer cells in vitro and in vivo

Breast cancer (BC) is a complex and heterogenous disease, and various approaches have been used to classify BC into several subtypes to improve diagnostic and therapeutic outcomes. One of the features of BC is deregulated transcription, which allows for classification of the disease based on gene expression signature into four basic types: Luminal A, Luminal B, HER2-enriched, and triple negative (TNBC)/basal-like. Novel therapeutic approaches targeting oncogenic transcriptional programs may represent a promising strategy, in particular for TNBC, where the lack of common genetic alterations has so far limited the development of targeted therapies.

The CDK8 module functions as a master coordinator of transcription, bridging enhancers and core promoters. Meta-analysis of curated TCGA data reveals that >15% of all BC have increased expression of CDK8 and/or CDK19, and that elevated expression of both genes is associated with decreased overall survival. High CDK8 expression is inversely correlated with the expression of estrogen receptor (ER) and positively correlated with occurrence of TP53 mutations.

RVU120 is a specific, low nM, selective inhibitor of CDK8/CDK19, currently being tested in a first-in-human Phase Ib clinical trial in patients with metastatic or advanced solid tumors progressing from previous lines of therapy (ClinicalTrials.gov: NCT05052255).

In order to establish a rationale for treatment of BC with RVU120 we have interrogated a panel of cell lines representing various subtypes of BC. These studies revealed that TNBC and ER-/PR-/HER2+ cells were highly sensitive to RVU120 and also to two other non-related CDK8/19 inhibitors, indicating a class effect. In contrast, CDK8/19 inhibitors were not able to inhibit mitogenic effect of estrogen, confirming differential efficacy in hormone - independent BC.

Detailed transcriptional profiling of RVU120-responder cells revealed high enrichment of STAT3 target genes, SOX4 target genes and gene hallmarks of epithelial to mesenchymal transition (EMT), signatures associated with invasiveness and stemness. Non-responder cells were characterized by enrichment of transcriptional signatures of ER activity. Further proteomic profiling show that the top responder cells were the Mesenchymal Stem-Like (MSL) molecular subtype of TNBC and were positive for transactivated pSTAT3. Transcriptomic RNAseq profiling of MSL TNBC cell lines indicated that among genes inhibited by RVU120 there was high enrichment of STAT1 (interferon signature), STAT3 (IL6- signaling) and STAT5 (IL2 signaling) dependent genes. Single agent efficacy of RVU120 has been confirmed in subcutaneous TNBC xenograft models in vivo at well tolerated doses. Overall, these studies provide rationale for further development of RVU120 in TNBC patients.

Citation Format: Urszula Pakulska, Marta Obacz, Aniela Gołas, Milena Mazan, Magdalena Masiejczyk, Agata Stachowicz, Justyna Martyka, Michał Combik, Kinga Kęska, Katarzyna Wiklik, Kristina Goller, Elżbieta Adamczyk, Krzysztof Brzózka, Tomasz Rzymski. RVU120, a selective CDK8/CDK19 inhibitor, demonstrates efficacy against hormone-independent breast cancer cells in vitro and in vivo [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2647.

Abstract P5-17-13: Selective CDK8/CDK19 inhibitor RVU120 demonstrates efficacy against hormone-independent breast cancer cells in vitro and in vivo

Breast cancer (BC) is a complex and heterogenous disease, and various approaches have been used to classify BC into several subtypes to improve diagnostic and therapeutic outcomes. One of the features of BC is deregulated transcription, which allows for classification of the disease based on gene expression signature into four basic types: Luminal A, Luminal B, HER2-enriched, and triple negative (TNBC)/basal-like. Novel therapeutic approaches targeting oncogenic transcriptional programs may represent a promising strategy, in particular for TNBC, where the lack of common genetic alterations has so far limited the development of targeted therapies. The CDK8 module of the mediator complex represents an effective therapeutic target across multiple hematologic malignancies and solid tumors. CDK8 module of mediator functions as a master coordinator of transcription, bridging enhancers and core promoters. Meta-analysis of transcriptomic data revealed that higher CDK8 expression and its paralog CDK19 is associated with shorter relapse-free survival (RFS) in all molecular subtypes of BC. Our analysis of curated TCGA data revealed that >15% of all BC have alterations in either CDK8 or CDK19. Increased expression of CDK8 in BC can be partially attributed to copy number gains and amplifications. High CDK8 expression was inversely correlated with the expression of estrogen receptor (ER) and positively correlated with occurrence of TP53 mutations. In order to identify whether increased expression of CDK8/19 in BC could be associated with increased sensitivity to pharmacological inhibition of both kinases, we have interrogated a panel of BC cell lines representing various subtypes with RVU120 - a specific, selective inhibitor of CDK8/CDK19, currently being tested in a first-in-human Phase Ib clinical trial. The highest sensitivity to RVU120 in clonogenic assays has been observed for TNBC and ER-/PR-/HER2+ cells with high STAT3 phosphorylation levels. In contrast, neither RVU120 nor other CDK8 inhibitors were able to inhibit mitogenic effect of estrogen, confirming differential efficacy in hormone - independent BC. Detailed transcriptional profiling of responder cells revealed high enrichment of TNF/NFKB and STAT target genes (signatures associated with inflammatory phenotypes) and SOX4 target genes (signatures associated with invasiveness and stemness). Non-responder cells were characterized by enrichment of transcriptional signatures of ER activity. Efficacy of RVU120 in TNBC cells has been corroborated in a three-dimensional (3D) spheroid viability assay that could predict in vivo efficacy of RVU120 in tested xenograft models and recapitulated using other chemically non-related CDK8 inhibitors, indicating a class effect. Single agent efficacy of RVU120 has been confirmed in subcutaneous TNBC xenograft models in vivo at well tolerated doses. These studies provide rationale for further development of RVU120 in TNBC patients.

Citation Format: Tomasz Rzymski, Aniela Gołas, Milena Mazan, Urszula Pakulska, Magdalena Masiejczyk, Agata Stachowicz, Justyna Martyka, Michał Combik, Katarzyna Wiklik, Kristina Goller, Marta Obacz, Elżbieta Adamczyk, Krzysztof Brzózka. Selective CDK8/CDK19 inhibitor RVU120 demonstrates efficacy against hormone-independent breast cancer cells in vitro and in vivo [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P5-17-13.

Abstract 4532A: Development of selective small molecule STING agonists suitable for systemic administration

Background: Stimulator of Interferon Genes (STING) is a major player in the activation of robust innate immune response leading to initiation and enhancement of tumor-specific adaptive immunity. Several clinical and pre-clinical programs are developing cyclic dinucleotides - analogues of endogenous STING ligands. However their chemical nature and stability limit their use as systemic immuno-therapeutics. Herein, we present potent and selective non-nucleotide, non-macrocyclic, small molecule direct STING agonists, structurally unrelated to known chemotypes and suitable for systemic administration.

Methods: Binding to recombinant STING protein was examined using FTS, MST, FP and crystallography studies. Phenotypic screen was performed in THP-1 Dual reporter cells. Human macrophages (HMDM) and dendritic cells (HMDC) were differentiated from monocytes (obtained from PBMC) in the presence of M-CSF and GM-CSF/IL-4 for HMDM and HMDC, respectively. Mouse bone marrow-derived dendritic cells (BMDC) were obtained from C57BL/6 or STING KO mice and differentiated with mIL-4 and mGM-CSF. STING agonists were administered into BALB/c mice and cytokine release was measured in plasma. Additionally, mice were inoculated with CT26 murine colon carcinoma cells and the compound was administered, followed by the regular tumor growth monitoring. Finally, the compound was administered to C57BL/6 WT and STING KO mice in several escalating doses.

Results: Ryvu's agonists demonstrate a strong binding affinity to recombinant STING proteins across tested species. They trigger pro-inflammatory cytokine release from human PBMC and HMDC and induce dendritic cell maturation regardless of the STING haplotype. Systemic in vivo administration leads to dose-dependent upregulation of STING-dependent pro-inflammatory cytokines, suggesting immune activation which translates into efficacy in vivo in CT26 mouse colorectal cancer model and complete tumor remissions. Furthermore, cured animals develop lasting immunological response demonstrated by diminished tumor growth or lack of palpable tumors in re-challenged mice.

Conclusion: Ryvu's STING agonists selectively activate STING-dependent signaling in both mouse and human immune cells promoting anti-tumor immunity. Treatment with Ryvu's STING agonists leads to engagement of the immune system which results in complete tumor remission and development of immunological memory against cancer cells. The compounds show good selectivity and ADME properties enabling development for systemic administration as a single agent or in combinations with immunotherapies or targeted agents.

Citation Format: Stefan Chmielewski, Magdalena Zawadzka, Jolanta Mazurek, Maciej K. Rogacki, Karolina Gluza, Katarzyna Wójcik-Jaszczyńska, Aleksandra Poczkaj, Grzegorz Ćwiertnia, Grzegorz Topolnicki, Maciej Kujawa, Eliza Zimoląg, Urszula Głowniak-Kwitek, Magdalena Mroczkowska, Agnieszka Gibas, Marcin Leś, Sylwia Sudoł, Marek Wronowski, Kinga Michalik, Katarzyna Banaszak, Katarzyna Wiklik, Federico Malusa, Michał Combik, Karolina Wiatrowska, Łukasz Dudek, Jose Alvarez, Anna Rajda, Faustyna Gajdosz, Aniela Gołas, Katarzyna Wnuk-Lipińska, Kamil Kuś, Ewelina Gabor-Worwa, Charles Fabritius, Luigi Stasi, Peter Littlewood, Krzysztof Brzózka, Monika Dobrzańska. Development of selective small molecule STING agonists suitable for systemic administration [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 4532A.

Abstract 4983: Discovery and characterization of next-generation small molecule direct STING agonists

Accumulating evidence highlights an important role of type I interferon response in the immune surveillance mechanisms. IFNβ release by antigen-presenting cells promotes spontaneous anti-tumor CD8+ T cell priming being largely dependent on activation of Stimulator of Interferon Genes (STING). STING agonists promote regression of established tumors and generation of long-term immunologic memory in preclinical animal models. Herein we report the discovery of potent and selective, first-in-class non-nucleotide, non-macrocyclic, small molecule direct STING agonists with molecular weight below 500, structurally unrelated to known cyclic dinucleotide chemotypes with potential for systemic administration. Activation of STING pathway was monitored in THP-1 Dual reporter monocytic cell line as well as peripheral blood mononuclear cells (PBMC) or antigen presenting cells from human and mouse origin. Surface expression of the antigen-presenting cell maturation markers i.e. CD80, CD86, CD83 and HLA-DR was assessed by flow cytometry. Binding affinity was confirmed by three independent assays. RNA sequencing was performed on total RNA isolated from THP-1 cells and PBMC isolated from 2 healthy human donors. Direct binding to both mouse and human STING protein of Selvita agonists have been confirmed in biophysical binding assays (FTS, MST and FP) and by crystallography studies. The compounds have fine-tunable ADME properties with good solubility, permeability and human plasma stability. They selectively activates STING-dependent signaling in both THP-1 reporter assays and in primary cells of human and mouse origin. In addition, RNA sequencing data confirmed selectivity of the Selvita compounds. In vitro functional assays demonstrated their ability to induce cytokine responses (IFNβ, TNFα) in a panel of human peripheral blood mononuclear cell (PBMC), human monocyte derived macrophage (HMDM) and human dendritic cells samples with various STING haplotypes including refractory alleles. Additionally, the compounds efficiently induced cytokine release in mouse bone marrow-derived macrophages and dendritic cells. Pro-inflammatory cytokine profile was accompanied by up-regulation of the maturation markers, i.e. CD80, CD86, CD83 and HLA-DR, on the surface of human antigen presenting cells. These data demonstrate potent, novel, next-generation small molecule STING agonists activating STING-dependent signaling in both mouse and human immune cells to promote potential antitumor immunity. The compounds show good selectivity and in vitro ADME properties enabling further development for systemic administration as a single agent or in combinatory immunotherapies for cancer treatment.

Citation Format: Monika Dobrzańska, Stefan Chmielewski, Magdalena Zawadzka, Jolanta Mazurek, Karolina Gluza, Katarzyna Wójcik-Jaszczyńska, Maciej Kujawa, Grzegorz Topolnicki, Grzegorz Ćwiertnia, Aleksandra Poczkaj, Izabela Dolata, Magdalena Mroczkowska, Agnieszka Gibas, Marcin Leś, Sylwia Sudoł, Adam Radzimierski, Kinga Michalik, Magdalena Sieprawska-Lupa, Katarzyna Banaszak, Katarzyna Wiklik, Federico Malusa, Michał Combik, Karolina Wiatrowska, Agnieszka Adamus, Lukasz Dudek, Jose Alvarez, Charles Fabritius, Anna Rajda, Maciej Rogacki, Faustyna Gajdosz, Peter Littlewood, Luigi Stasi, Krzysztof Brzózka. Discovery and characterization of next-generation small molecule direct STING agonists [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4983.

SEL120-34A is a novel CDK8 inhibitor active in AML cells with high levels of serine phosphorylation of STAT1 and STAT5 transactivation domains

Inhibition of oncogenic transcriptional programs is a promising therapeutic strategy. A substituted tricyclic benzimidazole, SEL120-34A, is a novel inhibitor of Cyclin-dependent kinase 8 (CDK8), which regulates transcription by associating with the Mediator complex. X-ray crystallography has shown SEL120-34A to be a type I inhibitor forming halogen bonds with the protein's hinge region and hydrophobic complementarities within its front pocket. SEL120-34A inhibits phosphorylation of STAT1 S727 and STAT5 S726 in cancer cells in vitro. Consistently, regulation of STATs- and NUP98-HOXA9- dependent transcription has been observed as a dominant mechanism of action in vivo. Treatment with the compound resulted in a differential efficacy on AML cells with elevated STAT5 S726 levels and stem cell characteristics. In contrast, resistant cells were negative for activated STAT5 and revealed lineage commitment. In vivo efficacy in xenotransplanted AML models correlated with significant repression of STAT5 S726. Favorable pharmacokinetics, confirmed safety and in vivo efficacy provide a rationale for the further clinical development of SEL120-34A as a personalized therapeutic approach in AML.

Estimating the effectiveness of species identification by sequencing of two chloroplast DNA loci (matK and rbcL) in selected groups of Polish flora

This paper focuses on assessing the effectiveness of species identification using barcoding standard loci (matK and rbcL) for a selected group of Polish flora. 55 samples of 17 species from six taxonomic groups representing various parts of the system, including Monocots and Dicots as well as Pteridophytes, were selected. PCR amplification success was 100% (of all samples) for the rbcL primer and 64% for matK primers giving in sum 87 fragments for sequencing. The aligned sequences show that in the

Morphological versus genetic diversity of Viola reichenbachiana and V. riviniana (sect. Viola, Violaceae) from soils differing in heavy metal content

Morphological characters, AFLP markers and flow cytometry were used to investigate the morphological and genetic variability and differentiation of Viola reichenbachiana and V. riviniana in non-metallicolous (NM) and metallicolous (M) populations. The aims were to clarify the taxonomic status of plants occurring in ore-bearing areas, to determine any relationship in V. reichenbachiana and V. riviniana from sites not polluted with heavy metals, and to examine the genetic variability and differentiation of M and NM populations of both species. Multivariate analyses based on morphological characters showed significant differences between V. reichenbachiana and V. riviniana from non-polluted sites, high levels of intra- and inter-population variability, and the occurrence of inter-specific hybrids. Plants from M populations showed hybrid characters but also fell within the range of V. riviniana or V. reichenbachiana. There were no significant differences in relative genome size between plants from polluted areas and V. riviniana from NM populations. Bayesian analysis of population genetic structure based on AFLP markers distinguished two main groups: V. reichenbachiana and V. riviniana together with the M populations. That analysis also revealed the occurrence of populations of inter-specific hybrids from non-polluted areas. Further Bayesian analysis of V. riviniana including NM and M populations separated all the studied M populations from NM populations. We conclude that plants forming the M populations are well adapted to a metal-polluted environment, and could be considered as stabilised introgressive forms resulting from unidirectional (asymmetric) introgression toward V. riviniana.