2-Guanidinoquinazolines as new inhibitors of the STAT3 pathway

Stimulation of natural killer cells with small molecule inhibitors of CD38 for the treatment of neuroblastoma

High-risk neuroblastoma (NB) accounts for 15% of all pediatric cancer deaths. Refractory disease for high-risk NB patients is attributed to chemotherapy resistance and immunotherapy failure. The poor prognosis for high-risk NB patients demonstrates an unmet medical need for the development of new, more efficacious therapeutics. CD38 is an immunomodulating protein that is expressed constitutively on natural killer (NK) cells and other immune cells in the tumor microenvironment (TME). Furthermore, CD38 over expression is implicated in propagating an immunosuppressive milieu within the TME. Through virtual and physical screening, we have identified drug-like small molecule inhibitors of CD38 with low micromolar IC50 values. We have begun to explore structure activity relationships for CD38 inhibition through derivatization of our most effective hit molecule to develop a new compound with lead-like physicochemical properties and improved potency. We have demonstrated that our derivatized inhibitor, compound 2, elicits immunomodulatory effects in NK cells by increasing cell viability by 190 ± 36% in multiple donors and by significantly increasing interferon gamma. Additionally, we have illustrated that NK cells exhibited enhanced cytotoxicity toward NB cells (14% reduction of NB cells over 90 minutes) when given a combination treatment of our inhibitor and the immunocytokine ch14.18-IL2. Herein we describe the synthesis and biological evaluation of small molecule CD38 inhibitors and demonstrate their potential utility as a novel approach to NB immunotherapy. These compounds represent the first examples of small molecules that stimulate immune function for the treatment of cancer.

Vinylene carbonate: beyond the ethyne surrogate in rhodium-catalyzed annulation with amidines toward 4-methylquinazolines

Vinylene carbonate: acetylation reagent rather than ethyne surrogate in rhodium-catalyzed annulation with amidines toward 4-methylquinazolines.

Quinazoline Ligands Induce Cancer Cell Death through Selective STAT3 Inhibition and G-Quadruplex Stabilization

The signal transducer and activator of transcription 3 (STAT3) protein is a master regulator of most key hallmarks and enablers of cancer, including cell proliferation and the response to DNA damage. G-Quadruplex (G4) structures are four-stranded noncanonical DNA structures enriched at telomeres and oncogenes’ promoters. In cancer cells, stabilization of G4 DNAs leads to replication stress and DNA damage accumulation and is therefore considered a promising target for oncotherapy. Here, we designed and synthesized novel quinazoline-based compounds that simultaneously and selectively affect these two well-recognized cancer targets, G4 DNA structures and the STAT3 protein. Using a combination of in vitro assays, NMR, and molecular dynamics simulations, we show that these small, uncharged compounds not only bind to the STAT3 protein but also stabilize G4 structures. In human cultured cells, the compounds inhibit phosphorylation-dependent activation of STAT3 without affecting the antiapoptotic factor STAT1 and cause increased formation of G4 structures, as revealed by the use of a G4 DNA-specific antibody. As a result, treated cells show slower DNA replication, DNA damage checkpoint activation, and an increased apoptotic rate. Importantly, cancer cells are more sensitive to these molecules compared to noncancerous cell lines. This is the first report of a promising class of compounds that not only targets the DNA damage cancer response machinery but also simultaneously inhibits the STAT3-induced cancer cell proliferation, demonstrating a novel approach in cancer therapy.

I2-Catalyzed oxidative synthesis of N,4-disubstituted quinazolines and quinazoline oxides

An easy and efficient approach to the synthesis of N,4-disubstituted quinazoline-2-amine and oxides is described. This transformation proceeds smoothly in the presence of molecular iodine. The metal-free protocol presented here is insensitive to air moisture and operationally simple. This versatile and synthetic methodology is broadly applicable to a variety of N,4-disubstituted quinazoline-2-amines and oxides, which are synthesized in good to excellent yields starting from readily available inexpensive precursors.

Unpacking the Pathogen Box-An Open Source Tool for Fighting Neglected Tropical Disease

The Pathogen Box is a 400-strong collection of drug-like compounds, selected for their potential against several of the world's most important neglected tropical diseases, including trypanosomiasis, leishmaniasis, cryptosporidiosis, toxoplasmosis, filariasis, schistosomiasis, dengue virus and trichuriasis, in addition to malaria and tuberculosis. This library represents an ensemble of numerous successful drug discovery programmes from around the globe, aimed at providing a powerful resource to stimulate open source drug discovery for diseases threatening the most vulnerable communities in the world. This review seeks to provide an in-depth analysis of the literature pertaining to the compounds in the Pathogen Box, including structure-activity relationship highlights, mechanisms of action, related compounds with reported activity against different diseases, and, where appropriate, discussion on the known and putative targets of compounds, thereby providing context and increasing the accessibility of the Pathogen Box to the drug discovery community.

New fluorescence-based high-throughput screening assay for small molecule inhibitors of tyrosyl-DNA phosphodiesterase 2 (TDP2)

Tyrosyl-DNA phosphodiesterase 2 (TDP2) repairs topoisomerase II (TOP2) mediated DNA damages and causes resistance to TOP2-targeted cancer therapy. Inhibiting TDP2 could sensitize cancer cells toward TOP2 inhibitors. However, potent TDP2 inhibitors with favorable physicochemical properties are not yet reported. Therefore, there is a need to search for novel molecular scaffolds capable of inhibiting TDP2. We report herein a new simple, robust, homogenous mix-and-read fluorescence biochemical assay based using humanized zebrafish TDP2 (14M_zTDP2), which provides biochemical and molecular structure basis for TDP2 inhibitor discovery. The assay was validated by screening a preselected library of 1600 compounds (Z' ≥ 0.72) in a 384-well format, and by running in parallel gel-based assays with fluorescent DNA substrates. This library was curated via virtual high throughput screening (vHTS) of 460,000 compounds from Chembridge Library, using the crystal structure of the novel surrogate protein 14M_zTDP2. From this primary screening, we selected the best 32 compounds (2% of the library) to further assess their TDP2 inhibition potential, leading to the IC₅₀ determination of 10 compounds. Based on the dose-response curve profile, pan-assay interference compounds (PAINS) structure identification, physicochemical properties and efficiency parameters, two hit compounds, 11a and 19a, were tested using a novel secondary fluorescence gel-based assay. Preliminary structure-activity relationship (SAR) studies identified guanidine derivative 12a as an improved hit with a 6.4-fold increase in potency over the original HTS hit 11a. This study highlights the importance of the development of combination approaches (biochemistry, crystallography and high throughput screening) for the discovery of TDP2 inhibitors.

High Content Imaging Assays for IL-6-Induced STAT3 Pathway Activation in Head and Neck Cancer Cell Lines

In the canonical STAT3 signaling pathway, IL-6 receptor engagement leads to the recruitment of latent STAT3 to the activated IL-6 complex and the associated Janus kinase (JAK) phosphorylates STAT3 at Y705. pSTAT3-Y705 dimers traffic into the nucleus and bind to specific DNA response elements in the promoters of target genes to regulate their transcription. However, IL-6 receptor activation induces the phosphorylation of both the Y705 and S727 residues of STAT3, and S727 phosphorylation is required to achieve maximal STAT3 transcriptional activity. STAT3 continuously shuttles between the nucleus and cytoplasm and maintains a prominent nuclear presence that is independent of Y705 phosphorylation. The constitutive nuclear entry of un-phosphorylated STAT3 (U-STAT3) drives expression of a second round of genes by a mechanism distinct from that used by pSTAT3-Y705 dimers. The abnormally elevated levels of U-STAT3 produced by the constitutive activation of pSTAT3-Y705 observed in many tumors drive the expression of an additional set of pSTAT3-independent genes that contribute to tumorigenesis. In this chapter, we describe the HCS assay methods to measure IL-6-induced STAT3 signaling pathway activation in head and neck tumor cell lines as revealed by the expression and subcellular distribution of pSTAT3-Y705, pSTAT3-S727, and U-STAT3. Only the larger dynamic range provided by the pSTAT3-Y705 antibody would be robust and reproducible enough for screening.

Mechanism of action of selective inhibitors of IL-6 induced STAT3 pathway in head and neck cancer cell lines

Studies indicate that elevated interleukin-6 (IL-6) levels engage IL6Rα-gp130 receptor complexes to activate signal transducer and activator of transcription 3 (STAT3) that is hyperactivated in many cancers including head and neck squamous cell carcinoma (HNSCC). Our previous HCS campaign identified several hits that selectively blocked IL-6-induced STAT3 activation. This study describes our investigation of the mechanism(s) of action of three of the four chemical series that progressed to lead activities: a triazolothiadiazine (864669), amino alcohol (856350), and an oxazole-piperazine (4248543). We demonstrated that all three blocked IL-6-induced upregulation of the cyclin D1 and Bcl-X_L STAT3 target genes. None of the compounds exhibited direct binding interactions with STAT3 in surface plasmon resonance (SPR) binding assays; neither did they inhibit the recruitment and binding of a phospho-tyrosine-gp130 peptide to STAT3 in a fluorescence polarization assay. Furthermore, they exhibited little or no inhibition in a panel of 83 cancer-associated in vitro kinase profiling assays, including lack of inhibition of IL-6-induced Janus kinase (JAK 1, 2, and 3) activation. Further, 864669 and 4248543 selectively inhibited IL-6-induced STAT3 activation but not that induced by oncostatin M (OSM). The compounds 864669 and 4248543 abrogated IL-6-induced phosphorylation of the gp130 signaling subunit (phospho-gp130Y₉₀₅) of the IL-6-receptor complex in HNSCC cell lines which generate docking sites for the SH2 domains of STAT3. Our data indicate that 864669 and 4248543 block IL-6-induced STAT activation by interfering with the recruitment, assembly, or activation of the hexamer-activated IL-6/IL-6Rα/gp130 signaling complex that occurs after IL-6 binding to IL-6Rα subunits.

HCS campaign to identify selective inhibitors of IL-6-induced STAT3 pathway activation in head and neck cancer cell lines

Signal transducer and activator of transcription factor 3 (STAT3) is hyperactivated in head and neck squamous cell carcinomas (HNSCC). Cumulative evidence indicates that IL-6 production by HNSCC cells and/or stromal cells in the tumor microenvironment activates STAT3 and contributes to tumor progression and drug resistance. A library of 94,491 compounds from the Molecular Library Screening Center Network (MLSCN) was screened for the ability to inhibit interleukin-6 (IL-6)-induced pSTAT3 activation. For contractual reasons, the primary high-content screening (HCS) campaign was conducted over several months in 3 distinct phases; 1,068 (1.1%) primary HCS actives remained after cytotoxic or fluorescent outliers were eliminated. One thousand one hundred eighty-seven compounds were cherry-picked for confirmation; actives identified in the primary HCS and compounds selected by a structural similarity search of the remaining MLSCN library using hits identified in phases I and II of the screen. Actives were confirmed in pSTAT3 IC50 assays, and an IFNγ-induced pSTAT1 activation assay was used to prioritize selective inhibitors of STAT3 activation that would not inhibit STAT1 tumor suppressor functions. Two hundred three concentration-dependent inhibitors of IL-6-induced pSTAT3 activation were identified and 89 of these also produced IC50s against IFN-γ-induced pSTAT1 activation. Forty-nine compounds met our hit criteria: they reproducibly inhibited IL-6-induced pSTAT3 activation by ≥70% at 20 μM; their pSTAT3 activation IC50s were ≤25 μM; they were ≥2-fold selective for pSTAT3 inhibition over pSTAT1 inhibition; a cross target query of PubChem indicated that they were not biologically promiscuous; and they were ≥90% pure. Twenty-six chemically tractable hits that passed filters for nuisance compounds and had acceptable drug-like and ADME-Tox properties by computational evaluation were purchased for characterization. The hit structures were distributed among 5 clusters and 8 singletons. Twenty-four compounds inhibited IL-6-induced pSTAT3 activation with IC50s ≤20 μM and 13 were ≥3-fold selective versus inhibition of pSTAT1 activation. Eighteen hits inhibited the growth of HNSCC cell lines with average IC50s ≤ 20 μM. Four chemical series were progressed into lead optimization: the guanidinoquinazolines, the triazolothiadiazines, the amino alcohols, and an oxazole-piperazine singleton.

Optimization of pyrazole-containing 1,2,4-triazolo-[3,4-b]thiadiazines, a new class of STAT3 pathway inhibitors

Structure-activity relationship studies of a 1,2,4-triazolo-[3,4-b]thiadiazine scaffold, identified in an HTS campaign for selective STAT3 pathway inhibitors, determined that a pyrazole group and specific aryl substitution on the thiadiazine were necessary for activity. Improvements in potency and metabolic stability were accomplished by the introduction of an α-methyl group on the thiadiazine. Optimized compounds exhibited anti-proliferative activity, reduction of phosphorylated STAT3 levels and effects on STAT3 target genes. These compounds represent a starting point for further drug discovery efforts targeting the STAT3 pathway.

Drugging Undruggable Molecular Cancer Targets

Cancer, more than any other human disease, now has a surfeit of potential molecular targets poised for therapeutic exploitation. Currently, a number of attractive and validated cancer targets remain outside of the reach of pharmacological regulation. Some have been described as undruggable, at least by traditional strategies. In this article, we outline the basis for the undruggable moniker, propose a reclassification of these targets as undrugged, and highlight three general classes of this imposing group as exemplars with some attendant strategies currently being explored to reclassify them. Expanding the spectrum of disease-relevant targets to pharmacological manipulation is central to reducing cancer morbidity and mortality.