326 The anti-TIGIT antibody M6223 induces significant anti-tumor efficacy and immune response via multiple mechanisms of action

BackgroundM6223 is a fully human antagonistic anti-T cell immunoreceptor with immunoglobulin and ITIM domains (TIGIT) antibody in IgG1 format with Fc-mediated effector function.MethodsThe ability of M6223 to block the interaction of TIGIT with its ligands, CD155 and CD112, and the interaction of TIGIT with CD226 was determined by a flow cytometry-based binding assay. The anti-tumor efficacy, immune profile, and effector function of M6223 were investigated in syngeneic tumor models in huTIGIT knock-in mice. M6223 was either formatted with an effector competent mouse IgG2c constant region (M6223-muIgG2c) or formatted with effector null mouse IgG1-D256A constant region (M6223-muIgG1) as two versions of chimeric antibodies for the in vivo studies.ResultsM6223 dose-dependently blocked the binding of TIGIT to its ligands, including CD155 and CD112, thereby inhibiting a TIGIT-mediated immunosuppressive pathway. In addition, M6223 interrupted the interaction of TIGIT with the costimulatory receptor CD226. By blocking the interactions, the chimeric protein M6223-muIgG2c showed anti-tumor efficacy in multiple tumor models, including an MC38 tumor model (figure 1), and generated tumor antigen-specific long-term protective immunity in immunocompetent huTIGIT knock-in mice. M6223 monotherapy dose-dependently elevated the ratio of CD8+ cytotoxic T cells to regulatory T cells and the ratio of CD226 to TIGIT expression in immune cells in the tumor microenvironment. We also found that M6223 selectively depleted suppressive and exhausted TIGIT+ immune cell subsets and the anti-tumor activity of effector null M6223-muIgG1 was significantly lost (p<0.0001), suggesting that Fc-mediated effector function contributes to M6223 anti-tumor activity. Antibody depletion studies demonstrated that CD8+ T cells and natural killer cells contributed to the anti-tumor activity of M6223 in a complementary manner.Abstract 326 Figure 1M6223-muIgG2c displayed dose-dependent anti-tumor efficacy. M6223-muIgG2c displayed dose-dependent anti-tumor efficacy in an MC38 tumor model in hTIGIT knock-in mice.ConclusionsGiven that TIGIT blockade can inhibit an immunosuppressive pathway as well as remove the suppression on a costimulatory pathway, M6223 has the potential to induce an anti-tumor immune response by three complementary mechanisms: direct blockade of the TIGIT pathway, stimulation of CD226 dimerization/activation, and depletion of TIGIT+ immune subsets by Fc-mediated effector function. Our data demonstrate that these complementary mechanisms orchestrate the anti-tumor activity of M6223. A Phase I, first-in-human clinical trial (NCT04457778) is underway to determine the safety, tolerability, maximum tolerated dose and recommended dose for expansion of M6223 as a single agent (Part 1A) and in combination with bintrafusp alfa (Part 1B) in patients with metastatic or locally advanced solid unresectable tumors.Ethics ApprovalAll animal experiments were performed in accordance with EMD Serono Research & Development Institute, Inc., Billerica, MA, USA, an affiliate of Merck KGaA (protocol 17-008, 20-005) and Wuxi AppTec Animal Care and Use Committee (IACUC) guidelines

A selective chemical probe for exploring the role of CDK8 and CDK19 in human disease.

There is unmet need for chemical tools to explore the role of the Mediator complex in human pathologies ranging from cancer to cardiovascular disease. Here we determine that CCT251545, a small-molecule inhibitor of the WNT pathway discovered through cell-based screening, is a potent and selective chemical probe for the human Mediator complex-associated protein kinases CDK8 and CDK19 with >100-fold selectivity over 291 other kinases. X-ray crystallography demonstrates a type 1 binding mode involving insertion of the CDK8 C terminus into the ligand binding site. In contrast to type II inhibitors of CDK8 and CDK19, CCT251545 displays potent cell-based activity. We show that CCT251545 and close analogs alter WNT pathway-regulated gene expression and other on-target effects of modulating CDK8 and CDK19, including expression of genes regulated by STAT1. Consistent with this, we find that phosphorylation of STAT1(SER727) is a biomarker of CDK8 kinase activity in vitro and in vivo. Finally, we demonstrate in vivo activity of CCT251545 in WNT-dependent tumors

Cholinergic receptor pathways involved in apoptosis, cell proliferation and neuronal differentiation

Acetylcholine (ACh) has been shown to modulate neuronal differentiation during early development. Both muscarinic and nicotinic acetylcholine receptors (AChRs) regulate a wide variety of physiological responses, including apoptosis, cellular proliferation and neuronal differentiation. However, the intracellular mechanisms underlying these effects of AChR signaling are not fully understood. It is known that activation of AChRs increase cellular proliferation and neurogenesis and that regulation of intracellular calcium through AChRs may underlie the many functions of ACh. Intriguingly, activation of diverse signaling molecules such as Ras-mitogen-activated protein kinase, phosphatidylinositol 3-kinase-Akt, protein kinase C and c-Src is modulated by AChRs. Here we discuss the roles of ACh in neuronal differentiation, cell proliferation and apoptosis. We also discuss the pathways involved in these processes, as well as the effects of novel endogenous AChRs agonists and strategies to enhance neuronal-differentiation of stem and neural progenitor cells. Further understanding of the intracellular mechanisms underlying AChR signaling may provide insights for novel therapeutic strategies, as abnormal AChR activity is present in many diseases

On the structure of the amino-terminal domain ED 1 of the B2 receptor

Receptors for kinins are classified into B 1 (Menke et al., 1994) and B2 (McEachern et al., 1991) sub- types. Both receptors belong to the seven transmembrane domain (TMD) receptor family which activate trimeric G-proteins. The cDNAs coding for the rat (McEachern et al., 1991), the human (Hess et al., 1992; Eggerickx et al., 1992) and the mouse (Yokoyama et al., 1994) B2 receptors contain several in-frame methionine codons which could be used as an initiation site for translation; however, none of them conforms to the 'canonical' consensus sequence often preceding the initiation codon (Kozak, 1989). On the basis of sequence similarity studies the third in-frame AUG of the human B2 receptor mRNA, starting at nucleotide 223 of clone CCD-16- 2, was assumed to be the preferred start codon (Hess et al., 1992). The underlying gene of the human B2 receptor consists of three exons interrupted by two introns (Ma et al., 1994): exon-1 is non-coding, the first two in-frame AUG codons are located on exon-2, and the third in-frame AUG is located on exon-3 together with the seven transmembrane spanning sequence segments. There is no evidence for alternative splicing of the human B2 receptor pre-mRNA (Kammerer et al., 1995). To clarify which in-frame AUG serves as the translation initiation codon, we have isolated the B2 receptor protein and determined its amino-terminal sequence (Abd Alia et al., in preparation). The sequence data indicate that the B2 receptor mRNA from human foreskin fibroblasts is translated from the first in-frame initiator AUG codon. We report here that the extra segment of 27 amino acid residues which precedes the predicted amino-terminus of the receptor protein does not significantly alter the binding characteristics of the receptor

Pharmacologic Inhibitor of DNA-PK, M3814, Potentiates Radiotherapy and Regresses Human Tumors in Mouse Models.

Physical and chemical DNA-damaging agents are used widely in the treatment of cancer. Double-strand break (DSB) lesions in DNA are the most deleterious form of damage and, if left unrepaired, can effectively kill cancer cells. DNA-dependent protein kinase (DNA-PK) is a critical component of nonhomologous end joining (NHEJ), one of the two major pathways for DSB repair. Although DNA-PK has been considered an attractive target for cancer therapy, the development of pharmacologic DNA-PK inhibitors for clinical use has been lagging. Here, we report the discovery and characterization of a potent, selective, and orally bioavailable DNA-PK inhibitor, M3814 (peposertib), and provide in vivo proof of principle for DNA-PK inhibition as a novel approach to combination radiotherapy. M3814 potently inhibits DNA-PK catalytic activity and sensitizes multiple cancer cell lines to ionizing radiation (IR) and DSB-inducing agents. Inhibition of DNA-PK autophosphorylation in cancer cells or xenograft tumors led to an increased number of persistent DSBs. Oral administration of M3814 to two xenograft models of human cancer, using a clinically established 6-week fractionated radiation schedule, strongly potentiated the antitumor activity of IR and led to complete tumor regression at nontoxic doses. Our results strongly support DNA-PK inhibition as a novel approach for the combination radiotherapy of cancer. M3814 is currently under investigation in combination with radiotherapy in clinical trials

Impact of p53 Status on Radiosensitization of Tumor Cells by MET Inhibition-Associated Checkpoint Abrogation

Signaling via the MET receptor tyrosine kinase has been implicated in crosstalk with cellular responses to DNA damage. Our group previously demonstrated that MET inhibition in tumor cells with deregulated MET activity results in radiosensitization via downregulation of the ATR-CHK1-CDC25 pathway, a major signaling cascade responsible for intra-S and G2/M cell cycle arrest following DNA damage. Here we aimed at studying the potential therapeutic application of ionizing radiation in combination with a MET inhibitor, EMD-1214063, in p53-deficient cancer cells that harbor impaired G1/S checkpoint regulation upon DNA damage. We hypothesized that upon MET inhibition, p53-deficient cells would bypass both G1/S and G2/M checkpoints, promoting premature mitotic entry with substantial DNA lesions and cell death in a greater extent than p53-proficient cells. Our data suggest that p53-deficient cells are more susceptible to EMD-1214063 and combined treatment with irradiation than wildtype p53 lines as inferred from elevated γH2AX expression and increased cytotoxicity. Furthermore, cell cycle distribution profiling indicates constantly lower G1 and higher G2/M population as well as higher expression of a mitotic marker p-histone H3 following the dual treatment in p53 knockdown isogenic variant, compared to the parental counterpart. IMPLICATIONS The concept of MET inhibition-mediated radiosensitization enhanced by p53 deficiency is of high clinical relevance, since p53 is frequently mutated in numerous types of human cancer. The current data point for a therapeutic advantage for an approach combining MET targeting along with DNA damaging agents for MET positive/p53 negative tumors

Deciphering MET-dependent modulation of global cellular responses to DNA damage by quantitative phosphoproteomics.

Increasing evidence suggests that interference with growth factor receptor tyrosine kinases (RTKs) signaling can affect DNA damage response (DDR) networks, with a consequent impact on cellular responses to DNA-damaging agents widely used in cancer treatment. In that respect, the MET RTK is deregulated in abundance and/or activity in a variety of human tumors. Using two proteomic techniques, we explored how disrupting MET signaling modulates global cellular phosphorylation response to ionizing radiation (IR). Following an immunoaffinity-based phosphoproteomic discovery survey we selected candidate phosphorylation sites for extensive characterization by targeted proteomics focusing on phosphorylation sites in both signaling networks. Several substrates of the DDR were confirmed to be modulated by sequential MET inhibition and IR, or MET inhibition alone. Upon combined treatment, for two substrates, NUMA1 S395 and CHEK1 S345, the gain and loss of phosphorylation, respectively, were recapitulated using in vivo tumor models by immunohistochemistry, with possible utility in future translational research. Overall, we have corroborated phosphorylation sites at the intersection between MET and the DDR signaling networks, and suggest that these represent a class of proteins at the interface between oncogene-driven proliferation and genomic stability