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.

Probing the roles of SUMOylation in cancer cell biology by using a selective SAE inhibitor.

Small ubiquitin-like modifier (SUMO) family proteins regulate target-protein functions by post-translational modification. However, a potent and selective inhibitor targeting the SUMO pathway has been lacking. Here we describe ML-792, a mechanism-based SUMO-activating enzyme (SAE) inhibitor with nanomolar potency in cellular assays. ML-792 selectively blocks SAE enzyme activity and total SUMOylation, thus decreasing cancer cell proliferation. Moreover, we found that induction of the MYC oncogene increased the ML-792-mediated viability effect in cancer cells, thus indicating a potential application of SAE inhibitors in treating MYC-amplified tumors. Using ML-792, we further explored the critical roles of SUMOylation in mitotic progression and chromosome segregation. Furthermore, expression of an SAE catalytic-subunit (UBA2) S95N M97T mutant rescued SUMOylation loss and the mitotic defect induced by ML-792, thus confirming the selectivity of ML-792. As a potent and selective SAE inhibitor, ML-792 provides rapid loss of endogenously SUMOylated proteins, thereby facilitating novel insights into SUMO biology.

Structure-activity relationship studies of thalidomide analogs with a taxol-like mode of action.

Anti-microtubule agents such as paclitaxel and docetaxel have played an important role in the treatment of cancer for many years. Recently, a small molecule that has a taxol-like mode of action (5HPP-33) was reported. Herein, the detailed structure-activity relationship (SAR) studies of 5HPP-33 analogs that are substituted at the isoindole and phenyl rings are described. Bulky substitutions (such as di-isopropyl groups) on the phenyl ring result in the isoindole and phenyl rings being perpendicular to each other. It was found that this conformation is critical for anti-microtubule activity. These studies have provided valuable information, which will be helpful in the design of more potent analogs.

Structure-activity-relationship studies of conformationally restricted analogs of combretastatin A-4 derived from SU5416.

A series of combretastatin A-4 analogs derived from the ATP competitive, VEGF receptor tyrosine kinase inhibitor, SU5416 were synthesized. The cytotoxic effects of the analogs were evaluated against PC-3 and MDA-MB-231 cancer cell lines, as well as their abilities to inhibit tubulin polymerization. Results are compared to those of compound 1, our lead compound previously reported.

A thalidomide analogue with in vitro antiproliferative, antimitotic, and microtubule-stabilizing activities.

We discovered a thalidomide analogue [5-hydroxy-(2,6-diisopropylphenyl)-1H-isoindole-1,3-dione (5HPP-33)] with antiproliferative activity against nine cancer cell lines in vitro. Flow cytometric analyses showed that the compound caused G2-M arrest, which occurred mainly at the mitotic phase. In addition, immunofluorescence microscopy and in vitro tubulin polymerization studies showed that 5HPP-33 has antimicrotubule activity with a paclitaxel-like mode of action. It is effective against four different paclitaxel-resistant cell lines. Thus, 5HPP-33 represents a potential antitumor agent.

Conformationally restricted analogs of Combretastatin A-4 derived from SU5416.

A series of compounds originally derived from the vascular endothelial growth factor receptor tyrosine kinase inhibitor, SU5416, was synthesized and evaluated. The most potent compound in this series, compound 7, structurally resembles the potent anti-microtubule agent Combretastatin A-4, inhibited tubulin polymerization, and showed potent growth inhibitory activities on both prostate and breast cancer lines with IC(50) values in low to subnanomolar range.

Structure-activity relationships studies of the anti-angiogenic activities of linomide.

The synthesis and anti-angiogenic activities of linomide and its analogues are reported. Three of the analogues are 3.3-69 times more potent than linomide at inhibiting blood vessel formation in the CAM angiogenesis assay. These compounds possessed considerable anti-proliferative activity against isolated HUVEC cells with no activity against epithelial-derived prostate tumor cells.