Identification of Novel Carbocyclic Pyrimidine Cyclic Dinucleotide STING Agonists for Antitumor Immunotherapy Using Systemic Intravenous Route.

Stimulator of Interferon Genes (STING) plays an important role in innate immunity by inducing type I interferon production upon infection with intracellular pathogens. STING activation can promote increased T-cell activation and inflammation in the tumor microenvironment, resulting in antitumor immunity. Natural and synthetic cyclic dinucleotides (CDNs) are known to activate STING, and several synthetic CDN molecules are being investigated in the clinic using an intratumoral administration route. Here, we describe the identification of STING agonist 15a, a cyclic dinucleotide structurally diversified from natural ligands with optimized properties for systemic intravenous (iv) administration. Our studies have shown that STING activation by 15a leads to an acute innate immune response as measured by cytokine secretion and adaptive immune response via activation of CD8+ cytotoxic T-cells, which ultimately provides robust antitumor efficacy.

Discovery of TAK-981, a First-in-Class Inhibitor of SUMO-Activating Enzyme for the Treatment of Cancer.

SUMOylation is a reversible post-translational modification that regulates protein function through covalent attachment of small ubiquitin-like modifier (SUMO) proteins. The process of SUMOylating proteins involves an enzymatic cascade, the first step of which entails the activation of a SUMO protein through an ATP-dependent process catalyzed by SUMO-activating enzyme (SAE). Here, we describe the identification of TAK-981, a mechanism-based inhibitor of SAE which forms a SUMO-TAK-981 adduct as the inhibitory species within the enzyme catalytic site. Optimization of selectivity against related enzymes as well as enhancement of mean residence time of the adduct were critical to the identification of compounds with potent cellular pathway inhibition and ultimately a prolonged pharmacodynamic effect and efficacy in preclinical tumor models, culminating in the identification of the clinical molecule TAK-981.

MLN8054 and Alisertib (MLN8237): Discovery of Selective Oral Aurora A Inhibitors.

The Aurora kinases are essential for cell mitosis, and the dysregulation of Aurora A and B have been linked to the etiology of human cancers. Investigational agents MLN8054 (8) and alisertib (MLN8237, 10) have been identified as high affinity, selective, orally bioavailable inhibitors of Aurora A that have advanced into human clinical trials. Alisertib (10) is currently being evaluated in multiple Phase II and III clinical trials in hematological malignancies and solid tumors.

Synthesis and evaluation of 4-(substituted styryl/alkenyl)-3,5-bis(4-hydroxyphenyl)-isoxazoles as ligands for the estrogen receptor.

A series of 3,5-bis (4-hydroxyphenyl) isoxazoles bearing a styryl/alkyl vinyl group at the 4-position were prepared and evaluated as ligands for the estrogen receptor-alpha (ERα). The target compounds were prepared using the Suzuki reaction to couple an iodo-isoxazole intermediate with a series of styryl/alkenyl boronic acids, followed by O-demethylation. The products were evaluated for their estrogen receptor-α ligand binding domain (ERα-LBD) binding affinity using a competitive binding assay. The 4-(4-hydroxystyryl) derivative 4h displays binding properties similar to those of the previously described pyrazole class of ER ligands, indicating that the ERα-LBD tolerates the presence of the added vinyl group at the 4-position of the isoxazole ring.

Characterization of Alisertib (MLN8237), an investigational small-molecule inhibitor of aurora A kinase using novel in vivo pharmacodynamic assays.

PURPOSE: Small-molecule inhibitors of Aurora A (AAK) and B (ABK) kinases, which play important roles in mitosis, are currently being pursued in oncology clinical trials. We developed three novel assays to quantitatively measure biomarkers of AAK inhibition in vivo. Here, we describe preclinical characterization of alisertib (MLN8237), a selective AAK inhibitor, incorporating these novel pharmacodynamic assays. EXPERIMENTAL DESIGN: We investigated the selectivity of alisertib for AAK and ABK and studied the antitumor and antiproliferative activity of alisertib in vitro and in vivo. Novel assays were used to assess chromosome alignment and mitotic spindle bipolarity in human tumor xenografts using immunofluorescent detection of DNA and alpha-tubulin, respectively. In addition, 18F-3'-fluoro-3'-deoxy-l-thymidine positron emission tomography (FLT-PET) was used to noninvasively measure effects of alisertib on in vivo tumor cell proliferation. RESULTS: Alisertib inhibited AAK over ABK with a selectivity of more than 200-fold in cells and produced a dose-dependent decrease in bipolar and aligned chromosomes in the HCT-116 xenograft model, a phenotype consistent with AAK inhibition. Alisertib inhibited proliferation of human tumor cell lines in vitro and produced tumor growth inhibition in solid tumor xenograft models and regressions in in vivo lymphoma models. In addition, a dose of alisertib that caused tumor stasis, as measured by volume, resulted in a decrease in FLT uptake, suggesting that noninvasive imaging could provide value over traditional measurements of response. CONCLUSIONS: Alisertib is a selective and potent inhibitor of AAK. The novel methods of measuring Aurora A pathway inhibition and application of tumor imaging described here may be valuable for clinical evaluation of small-molecule inhibitors.

An inhibitor of NEDD8-activating enzyme as a new approach to treat cancer.

The clinical development of an inhibitor of cellular proteasome function suggests that compounds targeting other components of the ubiquitin-proteasome system might prove useful for the treatment of human malignancies. NEDD8-activating enzyme (NAE) is an essential component of the NEDD8 conjugation pathway that controls the activity of the cullin-RING subtype of ubiquitin ligases, thereby regulating the turnover of a subset of proteins upstream of the proteasome. Substrates of cullin-RING ligases have important roles in cellular processes associated with cancer cell growth and survival pathways. Here we describe MLN4924, a potent and selective inhibitor of NAE. MLN4924 disrupts cullin-RING ligase-mediated protein turnover leading to apoptotic death in human tumour cells by a new mechanism of action, the deregulation of S-phase DNA synthesis. MLN4924 suppressed the growth of human tumour xenografts in mice at compound exposures that were well tolerated. Our data suggest that NAE inhibitors may hold promise for the treatment of cancer.