Abstract 1136: Targeting DHX9 inhibition as a novel therapeutic modality in microsatellite instable colorectal cancer

DHX9 is a multifunctional DEAH-box ATP-independent RNA helicase which has been reported to play important roles in replication, transcription, translation, RNA splicing and RNA processing which contribute to DHX9’s role in maintenance of genomic stability. Functionally, DHX9’s role involves binding to as well as unwinding and/or resolving double-stranded and single-stranded DNA/RNA, DNA/RNA hybrids (R-loops), circular RNA and DNA/RNA G quadraplexes. Overexpression of DHX9 is evident in multiple cancer types, including colorectal cancer (CRC) and lung cancer. In addition, microsatellite instable (MSI) tumors exhibiting defective mismatch repair (dMMR) show a strong dependence on DHX9, making this helicase an attractive target for oncology drug discovery.

Here we describe data supporting targeting DHX9 in MSI CRC as a novel therapeutic, and the first identification of potent and selective in vitro and in vivo small molecule inhibitors of DHX9. We demonstrate that DHX9 inhibition in MSI CRC, delivered either through siRNA knockdown or compound treatment, leads to an increase in RNA/DNA secondary structures such as R-loops and circRNA (i.e. circBRIP1) inducing replication stress. Cell lines that are dMMR (i.e. MSI) are unable to resolve this replication stress, resulting in prevention of DNA replication in S phase and later onset of apoptosis. We were able to confirm this selective dependency in a panel of 20 CRC cell lines; anti-proliferative effects mediated by DHX9 inhibition were dependent on cell line dMMR status in a 10-day proliferation assay. Furthermore, compound 1, an orally bioavailable DHX9 inhibitor was used to investigate in vivo efficacy in MSI CRC (LS411N) and MSS CRC (SW480) xenograft models. Compound 1 was well tolerated across the 28-day treatment period with robust and durable tumor regression (TGI = 105 %) observed in the LS411N tumor xenograft model only. In addition, following cessation of treatment, minimal tumor regrowth was observed in a 28-day post treatment window. Tumor and plasma concentrations of compound 1 and changes in pharmacodynamic markers of DHX9 inhibition, such as circBRIP1 mRNA, were measured and resulting PK and PD data were highly correlated. Together, these preclinical data validate DHX9 as a tractable new target with potential utility as a novel treatment for patients with MSI CRC.

Citation Format: Jennifer Castro, Matthew H. Daniels, Chuang Lu, David Brennan, Deepali Gotur, Young-Tae Lee, Kevin Knockenhauer, April Case, Jie Wu, Shane M. Buker, Julie Liu, Brian A. Sparling, E. Allen Sickmier, Stephen J. Blakemore, P. Ann Boriack-Sjodin, Kenneth W. Duncan, Scott Ribich, Robert A. Copeland. Targeting DHX9 inhibition as a novel therapeutic modality in microsatellite instable colorectal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1136.

Conformational-Design-Driven Discovery of EZM0414: A Selective, Potent SETD2 Inhibitor for Clinical Studies

SETD2, a lysine N-methyltransferase, is a histone methyltransferase that plays an important role in various cellular processes and was identified as a target of interest in multiple myeloma that features a t(4,14) translocation. We recently reported the discovery of a novel small-molecule SETD2 inhibitor tool compound that is suitable for preclinical studies. Herein we describe the conformational-design-driven evolution of the advanced chemistry lead, which resulted in compounds appropriate for clinical evaluation. Further optimization of this chemical series led to the discovery of EZM0414, which is a potent, selective, and orally bioavailable inhibitor of SETD2 with good pharmacokinetic properties and robust pharmacodynamic activity in a mouse xenograft model.

Discovery of a First-in-Class Inhibitor of the Histone Methyltransferase SETD2 Suitable for Preclinical Studies

SET domain-containing protein 2 (SETD2), a histone methyltransferase, has been identified as a target of interest in certain hematological malignancies, including multiple myeloma. This account details the discovery of EPZ-719, a novel and potent SETD2 inhibitor with a high selectivity over other histone methyltransferases. A screening campaign of the Epizyme proprietary histone methyltransferase-biased library identified potential leads based on a 2-amidoindole core. Structure-based drug design (SBDD) and drug metabolism/pharmacokinetics (DMPK) optimization resulted in EPZ-719, an attractive tool compound for the interrogation of SETD2 biology that enables in vivo target validation studies.

Abstract 1768: Identification of a potent, orally-available SMARCA2/4 inhibitor with in vitro and in vivo activity in preclinical models of SMARCA4-mutant NSCLC

SWI/SNF-related, matrix-associated, actin-dependent regulator of chromatin subfamily A member 2 (SMARCA2) is an ATP-dependent DNA helicase and a catalytic component of the SWI/SNF complex. SWI/SNF-mediated nucleosome remodeling is a critical regulator of chromatin accessibility resulting in transcriptional regulation of gene sets that determine and maintain cell state. The role of SMARCA2 as the catalytic driver of SWI/SNF activity is mutually exclusive with that of its close paralog, SMARCA4. Loss of functional SMARCA4, as is reported in a subset of NSCLC and other cancer types generally confers a dependency on SMARCA2. Cancers lacking functional SMARCA4 have been shown to be sensitive to loss of SMARCA2 function either through genetic ablation or the use of a small molecule SMARCA2/4 inhibitor. We describe the identification and characterization of a small molecule SMARCA2/4 inhibitor Compound 1 and its selective activity in the SMARCA4-mutant setting both in in vitro and in vivo model systems. The compound demonstrates inhibition of SMARCA2 and SMARCA4 enzymatic activity in biochemical assays and broad selectivity against other helicases. Selective sensitivity in anti-proliferative assays of 15-fold was observed in NSCLC cell lines with SMARCA4 protein loss compared to those harboring WT SMARCA4 protein. Oral dosing demonstrates dose-dependent in vivo SMARCA2 inhibition and anti-tumor activity in SMARCA4-mutant NSCLC xenograft models. This compound is suitable for further exploration of the role of SMARCA2/4 and SWI/SNF in vitro and in vivo in cancer and other indications.

Citation Format: Allison E. Drew, Suzanne L. Jacques, Lindsey W. Eichinger, Chloe Pantano, Vinny Motwani, Cuyue Tang, Cuyue Tang, Neil Farrow, Dorothy Brach, Selene Howe, Alejandra Raimondi, Daniel T. Dransfield, Kenneth W. Duncan, Kim Stickland, Liyue Huang, John Lampe. Identification of a potent, orally-available SMARCA2/4 inhibitor with in vitro and in vivo activity in preclinical models of SMARCA4-mutant NSCLC [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 1768.

Abstract 2924: Aberrant SWI/SNF complexes lacking SMARCA2 or SMARCA4 differentially affect cell state and response to a novel SMARCA2/4 inhibitor

SWI/SNF-related, matrix-associated, actin-dependent regulator of chromatin subfamily A member 2 (SMARCA2) is an ATP-dependent DNA helicase and a catalytic component of the SWI/SNF complex. SWI/SNF-mediated nucleosome remodeling is a critical regulator of chromatin accessibility resulting in transcriptional regulation of gene sets that determine and maintain cell state. SMARCA2's role as the catalytic driver of SWI/SNF activity is mutually exclusive with that of its close paralog, SMARCA4. Here, we show that the synthetic lethal relationship between SMARCA2 and SMARCA4 can be genetically engineered bi-directionally in SMARCA2/SMARCA4 wild type (WT) cell lines. While knockout (KO) of either protein individually minimally affects cell growth, a genetically engineered cell line with loss of either SMARCA2 or SMARCA4 becomes sensitive to loss of its paralog. While SMARCA2 is infrequently lost through genetic mutation, SMARCA4 mutations occur in a wide variety of cancer types. We present CRISPR-Cas9 pooled screening data showing that cell lines with SMARCA4 mutations have a selective sensitivity to loss of SMARCA2 across multiple cancer indications, including NSCLC and ovarian carcinoma. SMARCA2 and SMARCA4, though partially redundant, also play unique roles within the cell as is evidenced by the unique set of transcriptional changes that occur in the SMARCA2/4 isogeneic cell lines, including the differential modulation of genes involved in TGFB signaling, regulation of angiogenesis, and in determinants of epithelial or mesenchymal cell state. ChIP-seq studies show changes in SWI/SNF occupancy as well as in the chromatin landscape that are specific to the loss of either SMARCA2 or SMARCA4. These isogenic cell lines also respond differently to treatment with a novel SMARCA2/4 inhibitor, Compound 1, in transcriptional as well as functional effects, providing evidence that dual inhibition with a small molecule may not be equivalent to the complete genetic ablation of these two proteins The NCI-H358 NCSLC cell line expresses WT SMARCA2 and SMARCA4 and is weakly sensitive to treatment with Compound 1. CRISPR-Cas9 mediated KO of SMARCA4 confers several-fold greater sensitivity to treatment with the novel inhibitor compared to the parental cell line. Surprisingly, KO of SMARCA2 does not confer sensitivity to inhibitor treatment. This selectivity sensitivity to treatment with Compound 1 that we observe in the SMARCA4-KO cell line is also observed across a panel of SMARCA4-mutant NSCLC. The relationship between the transcriptional and phenotypic changes that occur in these isogenic knockout lines as well as in SMARCA4-mutated NSCLC cell lines in response to SMARCA2/4 inhibitor treatment have revealed novel mechanisms driven by specific SWI/SNF complexes. These data have allowed us to better understand the potential therapeutic utility of a SMARCA2/4 inhibitor in both a SMARCA4-mut and SMARCA4-wt NSCLC patient population.

Citation Format: Lindsey W. Eichinger, Chloe Pantano, Vinny Motwani, Dorothy Brach, Selene Howe, Alejandra Raimondi, Daniel T. Dransfield, Kenneth W. Duncan, Kim Stickland, Cuyue Tang, Neil A. Farrow, John Lampe, Suzanne L. Jacques, Allison E. Drew. Aberrant SWI/SNF complexes lacking SMARCA2 or SMARCA4 differentially affect cell state and response to a novel SMARCA2/4 inhibitor [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 2924.

Identification of a peptide inhibitor for the histone methyltransferase WHSC1

WHSC1 is a histone methyltransferase that is responsible for mono- and dimethylation of lysine 36 on histone H3 and has been implicated as a driver in a variety of hematological and solid tumors. Currently, there is a complete lack of validated chemical matter for this important drug discovery target. Herein we report on the first fully validated WHSC1 inhibitor, PTD2, a norleucine-containing peptide derived from the histone H4 sequence. This peptide exhibits micromolar affinity towards WHSC1 in biochemical and biophysical assays. Furthermore, a crystal structure was solved with the peptide in complex with SAM and the SET domain of WHSC1L1. This inhibitor is an important first step in creating potent, selective WHSC1 tool compounds for the purposes of understanding the complex biology in relation to human disease.

Identification of a CARM1 Inhibitor with Potent In Vitro and In Vivo Activity in Preclinical Models of Multiple Myeloma

CARM1 is an arginine methyltransferase with diverse histone and non-histone substrates implicated in the regulation of cellular processes including transcriptional co-activation and RNA processing. CARM1 overexpression has been reported in multiple cancer types and has been shown to modulate oncogenic pathways in in vitro studies. Detailed understanding of the mechanism of action of CARM1 in oncogenesis has been limited by a lack of selective tool compounds, particularly for in vivo studies. We describe the identification and characterization of, to our knowledge, the first potent and selective inhibitor of CARM1 that exhibits anti-proliferative effects both in vitro and in vivo and, to our knowledge, the first demonstration of a role for CARM1 in multiple myeloma (MM). EZM2302 (GSK3359088) is an inhibitor of CARM1 enzymatic activity in biochemical assays (IC₅₀ = 6 nM) with broad selectivity against other histone methyltransferases. Treatment of MM cell lines with EZM2302 leads to inhibition of PABP1 and SMB methylation and cell stasis with IC₅₀ values in the nanomolar range. Oral dosing of EZM2302 demonstrates dose-dependent in vivo CARM1 inhibition and anti-tumor activity in an MM xenograft model. EZM2302 is a validated chemical probe suitable for further understanding the biological role CARM1 plays in cancer and other diseases.

Species differences in metabolism of EPZ015666, an oxetane-containing protein arginine methyltransferase-5 (PRMT5) inhibitor

1. Metabolite profiling and identification studies were conducted to understand the cross-species differences in the metabolic clearance of EPZ015666, a first-in-class protein arginine methyltransferase-5 (PRMT5) inhibitor, with anti-proliferative effects in preclinical models of Mantle Cell Lymphoma. EPZ015666 exhibited low clearance in human, mouse and rat liver microsomes, in part by introduction of a 3-substituted oxetane ring on the molecule. In contrast, a higher clearance was observed in dog liver microsomes (DLM) that translated to a higher in vivo clearance in dog compared with rodent. 2. Structure elucidation via high resolution, accurate mass LC-MS(n) revealed that the prominent metabolites of EPZ015666 were present in hepatocytes from all species, with the highest turnover rate in dogs. M1 and M2 resulted from oxidative oxetane ring scission, whereas M3 resulted from loss of the oxetane ring via an N-dealkylation reaction. 3. The formation of M1 and M2 in DLM was significantly abrogated in the presence of the specific CYP2D inhibitor, quinidine, and to a lesser extent by the CYP3A inhibitor, ketoconazole, corroborating data from human recombinant isozymes. 4. Our data indicate a marked species difference in the metabolism of the PRMT5 inhibitor EPZ015666, with oxetane ring scission the predominant metabolic pathway in dog mediated largely by CYP2D.

Structure and Property Guided Design in the Identification of PRMT5 Tool Compound EPZ015666

The recent publication of a potent and selective inhibitor of protein methyltransferase 5 (PRMT5) provides the scientific community with in vivo-active tool compound EPZ015666 (GSK3235025) to probe the underlying pharmacology of this key enzyme. Herein, we report the design and optimization strategies employed on an initial hit compound with poor in vitro clearance to yield in vivo tool compound EPZ015666 and an additional potent in vitro tool molecule EPZ015866 (GSK3203591).

Small molecule tyrosine kinase inhibitors for the treatment of intestinal inflammation

BACKGROUND

We developed a series of dendritic cell autoimmune modulators (DCAMs) based on small molecule Flt3 receptor tyrosine kinase inhibitors (TKIs) for the inhibition of intestinal inflammation and oral delivery.

METHODS

DCAMs were administered orally during and after induction of dextran sodium sulfate (DSS)-induced colitis. Dendritic cell recruitment and inflammatory responses were determined in the mucosal immune system during acute intestinal inflammatory responses and mucosal recovery. Bone marrow-derived macrophages were utilized to define the mechanisms by which DCAMs can modify responses to microbial signals.

RESULTS

Oral doses of DCAMs prevented severe weight loss and mucosal inflammation associated with DSS colitis in mice. The presence of DCAMs increased the number of CD11c(+) PDCA1(+) dendritic cells, induced interleukin (IL)-10 expression, and reduced inflammatory cytokine expression in the mucosal immune system. Surprisingly, DCAMs regulated innate immune responses in macrophages resulting in the inhibition of tumor necrosis factor alpha (TNF-α) production and the induction of IL-10 expression during Toll-like receptor-mediated signaling.

CONCLUSIONS

We identified two new imidazoacridinone derivatives that protect mice from severe colitis and promote mucosal recovery by enhancing protective cytokine production while inhibiting proinflammatory stimuli during microbial recognition. These compounds are promising candidates for further development into potent orally available drugs for the prevention of colitis and promotion of mucosal recovery.