Synthesis and biological activity of obatoclax derivatives as novel and potent SHP-1 agonists

Synthesis and Biological Evaluation of 3-Amino-4,4-Dimethyl Lithocholic Acid Derivatives as Novel, Selective, and Cellularly Active Allosteric SHP1 Activators

Src homology 2 domain-containing protein tyrosine phosphatase 1 (SHP1), a non-receptor member of the protein tyrosine phosphatase (PTP) family, negatively regulates several signaling pathways that are responsible for pathological cell processes in cancers. In this study, we report a series of 3-amino-4,4-dimethyl lithocholic acid derivatives as SHP1 activators. The most potent compounds, 5az-ba, showed low micromolar activating effects (EC50: 1.54–2.10 μM) for SHP1, with 7.63–8.79-fold maximum activation and significant selectivity over the closest homologue Src homology 2 domain-containing protein tyrosine phosphatase 2 (SHP2) (>32-fold). 5az-ba showed potent anti-tumor effects with IC50 values of 1.65–5.51 μM against leukemia and lung cancer cells. A new allosteric mechanism of SHP1 activation, whereby small molecules bind to a central allosteric pocket and stabilize the active conformation of SHP1, was proposed. The activation mechanism was consistent with the structure–activity relationship (SAR) data. This study demonstrates that 3-amino-4,4-dimethyl lithocholic acid derivatives can be selective SHP1 activators with potent cellular efficacy.

Prodigiosin: a promising biomolecule with many potential biomedical applications

Pigments are among the most fascinating molecules found in nature and used by human civilizations since the prehistoric ages. Although most of the bio-dyes reported in the literature were discovered around the eighties, the necessity to explore novel compounds for new biological applications has made them resurface as potential alternatives. Prodigiosin (PG) is an alkaloid red bio-dye produced by diverse microorganisms and composed of a linear tripyrrole chemical structure. PG emerges as a really interesting tool since it shows a wide spectrum of biological activities, such as antibacterial, antifungal, algicidal, anti-Chagas, anti-amoebic, antimalarial, anticancer, antiparasitic, antiviral, and/or immunosuppressive. However, PG vehiculation into different delivery systems has been proposed since possesses low bioavailability because of its high hydrophobic character (XLogP3-AA = 4.5). In the present review, the general aspects of the PG correlated with synthesis, production process, and biological activities are reported. Besides, some of the most relevant PG delivery systems described in the literature, as well as novel unexplored applications to potentiate its biological activity in biomedical applications, are proposed.

BH3-mimetics: recent developments in cancer therapy

The hopeful outcomes from 30 years of research in BH3-mimetics have indeed served a number of solid paradigms for targeting intermediates from the apoptosis pathway in a variety of diseased states. Not only have such rational approaches in drug design yielded several key therapeutics, such outputs have also offered insights into the integrated mechanistic aspects of basic and clinical research at the genetics level for the future. In no other area of medical research have the effects of such work been felt, than in cancer research, through targeting the BAX-Bcl-2 protein-protein interactions. With these promising outputs in mind, several mimetics, and their potential therapeutic applications, have also been developed for several other pathological conditions, such as cardiovascular disease and tissue fibrosis, thus highlighting the universal importance of the intrinsic arm of the apoptosis pathway and its input to general tissue homeostasis. Considering such recent developments, and in a field that has generated so much scientific interest, we take stock of how the broadening area of BH3-mimetics has developed and diversified, with a focus on their uses in single and combined cancer treatment regimens and recently explored therapeutic delivery methods that may aid the development of future therapeutics of this nature.

Current overview on the clinical update of Bcl-2 anti-apoptotic inhibitors for cancer therapy

Apoptosis is one of the major mechanisms exhibited in response to cell death and induction of apoptosis in tumour cells signifies a potential target for cancer therapy. Bcl-2 family proteins play a key role in regulation of the apoptotic pathway. Bcl-2 overexpression is commonly associated with various cancers including breast cancer, prostate cancer, B-cell lymphomas and colorectal adenocarcinomas etc. Thus, Bcl-2 is a novel anti-cancer target attracting medicinal chemists across the globe. Research investigations underlying Bcl-2 target have resulted in the generation of small molecule inhibitors, named as 'BH3-mimetics' (Bcl-2 homology 3 mimetics). These drugs display binding to pro-survival Bcl-2 proteins resulting in actuation of apoptosis of cancer cells. The first BH3 mimetics discovered as an outcome of structure-based drug design and Nuclear Magnetic Resonance (NMR)-based screening was ABT-263, an N-acylsulfonamide analogue. Thrombocytopenia a major dose-limiting toxicity, associated with ABT-263 had provoked the invention of a highly selective Bcl-2 inhibitor venetoclax. Several Bcl-2 inhibitors as small molecules are under clinical development and the results indicated that these molecules alone or in combination could be of potential application in cancer therapy. This review summarizes an up to date knowledge of the available small molecule inhibitors, their discovery, synthesis, current clinical and pre-clinical status.

Novel imidazopyridine suppresses STAT3 activation by targeting SHP-1

The unregulated activation of STAT3 has been demonstrated to occur in many cancers and enhances tumour growth, migration, and invasion. Stimulation by cytokines, growth factors, and hormones triggers this activation by phosphorylating STAT3 at tyrosine 705. Novel imidazopyridine compounds were synthesized to evaluate the inhibition of STAT3 at Y705. Among the tested compounds, 16 reduced the level of phospho-STAT3, inhibited the downstream signalling cascade and subsequently attenuated the survival of hepatocellular carcinoma (HCC) cells. Further assays showed that the reduction effects of compound 16 on tyrosine 705 of STAT3 were attributed to up-regulation of protein tyrosine phosphatase SHP-1.

Ionophores: Potential Use as Anticancer Drugs and Chemosensitizers

Ion homeostasis is extremely important for the survival of both normal as well as neoplastic cells. The altered ion homeostasis found in cancer cells prompted the investigation of several ionophores as potential anticancer agents. Few ionophores, such as Salinomycin, Nigericin and Obatoclax, have demonstrated potent anticancer activities against cancer stem-like cells that are considered highly resistant to chemotherapy and responsible for tumor relapse. The preclinical success of these compounds in in vitro and in vivo models have not been translated into clinical trials. At present, phase I/II clinical trials demonstrated limited benefit of Obatoclax alone or in combination with other anticancer drugs. However, future development in targeted drug delivery may be useful to improve the efficacy of these compounds. Alternatively, these compounds may be used as leading molecules for the development of less toxic derivatives.

The tyrosine kinase inhibitor nintedanib activates SHP-1 and induces apoptosis in triple-negative breast cancer cells

Triple-negative breast cancer (TNBC) remains difficult to treat and urgently needs new therapeutic options. Nintedanib, a multikinase inhibitor, has exhibited efficacy in early clinical trials for HER2-negative breast cancer. In this study, we examined a new molecular mechanism of nintedanib in TNBC. The results demonstrated that nintedanib enhanced TNBC cell apoptosis, which was accompanied by a reduction of p-STAT3 and its downstream proteins. STAT3 overexpression suppressed nintedanib-mediated apoptosis and further increased the activity of purified SHP-1 protein. Moreover, treatment with either a specific inhibitor of SHP-1 or SHP-1-targeted siRNA reduced the apoptotic effects of nintedanib, which validates the role of SHP-1 in nintedanib-mediated apoptosis. Furthermore, nintedanib-induced apoptosis was attenuated in TNBC cells expressing SHP-1 mutants with constantly open conformations, suggesting that the autoinhibitory mechanism of SHP-1 attenuated the effects of nintedanib. Importantly, nintedanib significantly inhibited tumor growth via the SHP-1/p-STAT3 pathway. Clinically, SHP-1 levels were downregulated, whereas p-STAT3 was upregulated in tumor tissues, and SHP-1 transcripts were associated with improved disease-free survival in TNBC patients. Our findings revealed that nintedanib induces TNBC apoptosis by acting as a SHP-1 agonist, suggesting that targeting STAT3 by enhancing SHP-1 expression could be a viable therapeutic strategy against TNBC.

Sequential combination of docetaxel with a SHP-1 agonist enhanced suppression of p-STAT3 signaling and apoptosis in triple negative breast cancer cells

Triple negative breast cancer (TNBC) is an aggressive cancer for which prognosis remains poor. Combination therapy is a promising strategy for enhancing treatment efficacy. Blockade of STAT3 signaling may enhance the response of cancer cells to conventional chemotherapeutic agents. Here we used a SHP-1 agonist SC-43 to dephosphorylate STAT3 thereby suppressing oncogenic STAT3 signaling and tested it in combination with docetaxel in TNBC cells. We first analyzed messenger RNA (mRNA) expression of SHP-1 gene (PTPN6) in a public TNBC dataset (TCGA) and found that higher SHP-1 mRNA expression is associated with better overall survival in TNBC patients. Sequential combination of docetaxel and SC-43 in vitro showed enhanced anti-proliferation and apoptosis associated with decreased p-STAT3 and decreased STAT3-downstream effector cyclin D1 in the TNBC cell lines MDA-MB-231, MDA-MB-468, and HCC-1937. Ectopic expression of STAT3 reduced the increased cytotoxicity induced by the combination therapy. In addition, this sequential combination showed enhanced SHP-1 activity compared to SC-43 alone. Furthermore, the combination treatment-induced apoptosis was attenuated by small interfering RNA (siRNA) against SHP-1 or by ectopic expression of SHP-1 mutants that caused SC-43 to lose its SHP-1 agonist capability. Moreover, combination of docetaxel and SC-43 showed enhanced tumor growth inhibition compared to single-agent therapy in mice bearing MDA-MB-231 tumor xenografts. Our results suggest that the novel SHP-1 agonist SC-43 enhanced docetaxel-induced cytotoxicity by SHP-1 dependent STAT3 inhibition in human triple negative breast cancer cells. TNBC patients with high SHP-1 expressions show better survival. Docetaxel combined with SC-43 enhances cell apoptosis and reduces p-STAT3. SHP-1 inhibition reduces the enhanced effect of docetaxel-SC-43 combination. Docetaxel-SC-43 combination suppresses xenograft tumor growth and reduces p-STAT3.

KEY MESSAGES

TNBC patients with high SHP-1 expressions show better survival. Docetaxel combined with SC-43 enhances cell apoptosis and reduces p-STAT3. SHP-1 inhibition reduces the enhanced effect of docetaxel-SC-43 combination. Docetaxel-SC-43 combination suppresses xenograft tumor growth and reduces p-STAT3.

Sorafenib analogue SC-60 induces apoptosis through the SHP-1/STAT3 pathway and enhances docetaxel cytotoxicity in triple-negative breast cancer cells

Recurrent triple-negative breast cancer (TNBC) needs new therapeutic targets. Src homology region 2 domain-containing phosphatase-1 (SHP-1) can act as a tumor suppressor by dephosphorylating oncogenic kinases. One major target of SHP-1 is STAT3, which is highly activated in TNBC. In this study, we tested a sorafenib analogue SC-60, which lacks angiokinase inhibition activity, but acts as a SHP-1 agonist, in TNBC cells. SC-60 inhibited proliferation and induced apoptosis by dephosphorylating STAT3 in both a dose- and time-dependent manner in TNBC cells (MDA-MB-231, MDA-MB-468, and HCC1937). By contrast, ectopic expression of STAT3 rescued the anticancer effect induced by SC-60. SC-60 also increased the SHP-1 activity, but this effect was inhibited when the N-SH2 domain (DN1) was deleted or with SHP-1 point mutation (D61A), implying that SHP-1 is the major target of SC-60 in TNBC. The use of SC-60 in combination with docetaxel synergized the anticancer effect induced by SC-60 through the SHP-1/STAT3 pathway in TNBC cells. Importantly, SC-60 also displayed a significant antitumor effect in an MDA-MB-468 xenograft model by modulating the SHP-1/STAT3 axis, indicating the anticancer potential of SC-60 in TNBC treatment. Targeting SHP-1/p-STAT3 and the potential combination of SHP-1 agonist with chemotherapeutic docetaxel is a feasible therapeutic strategy for TNBC.

Obatoclax, saliphenylhalamide and gemcitabine inhibit Zika virus infection in vitro and differentially affect cellular signaling, transcription and metabolism

An epidemic of Zika virus (ZIKV) infection associated with congenital abnormalities such as microcephaly, is ongoing in the Americas and the Pacific. Currently there are no approved therapies to treat this emerging viral disease. Here, we tested three cell-directed broad-spectrum antiviral compounds against ZIKV replication using human retinal pigment epithelial (RPE) cells and a low-passage ZIKV strain isolated from fetal brain. We found that obatoclax, SaliPhe, and gemcitabine inhibited ZIKV infections at noncytotoxic concentrations. Moreover, all three compounds prevented production of viral RNA and proteins as well as activation of cellular caspase 8, 3 and 7. However, these compounds differentially affected ZIKV-mediated transcription, translation and posttranslational modifications of cellular factors as well as metabolic pathways indicating that these agents possess different mechanisms of action. Interestingly, combination of obatoclax and SaliPhe at nanomolar concentrations had a synergistic effect against ZIKV infection. Thus, our results provided the foundation for development of broad-spectrum cell-directed antivirals or their combinations for treatment of ZIKV and other emerging viral diseases.

New thiazacridine agents: Synthesis, physical and chemical characterization, and in vitro anticancer evaluation

A series of new thiazacridine agents were synthesized and evaluated as antitumor agents, in terms of not only their cytotoxicity but also their selectivity. The cytotoxicity assay confirmed that all compounds showed cytotoxic activity and selectivity. The new compound, 3-acridin-9-ylmethyl-5-(5-bromo-1 H-indol-3-ylmethylene)-thiazolidine-2,4-dione (LPSF/AA29 – 7a), proved to be the most promising compound as it presents lower half-maximal inhibitory concentration (IC50) values (ranging from 0.25 to 68.03 µM) depending on cell lineage. In HepG2 cells, the lowest IC50 value was exhibited by 3-acridin-9-ylmethyl-5-(4-piperidin-1-yl-benzylidene)-thiazolidine-2,4-dione (LPSF/AA36 – 7b; 46.95 µM). None of the synthesized compounds showed cytotoxic activity against normal cells (IC50 > 100 µM). The mechanism of death induction and cell cycle effects was also evaluated. Flow cytometric analysis revealed that the compounds LPSF/AA29 – 7a and LPSF/AA36 – 7b significantly increased the percentage of apoptotic cells and induced G2/M arrest in the cell cycle progression. Therefore, these new thiazacridine derivatives constitute promising antitumor agents whose cytotoxicity and selectivity properties indicate they have potential to contribute to or serve as a basis for the development of new cancer drugs in the future.

Anion binding, electrochemistry and solvatochromism of β-brominated oxoporphyrinogens

Effects of macrocycle bromination on the structural, electrochemical and anion binding properties of 5,10,15,20-tetrakis(3,5-di-t-butyl-4-oxo-cyclohexa-2,5-dienylidene)porphyrinogen, OxP, are reported. Bromination of 5,10,15,20-tetrakis(3,5-di-t-butyl-4-hydroxyphenyl)-porphinatocopper(II), [T(DtBHP)P]Cu(II) yielded β-Br8OxP, which was N-alkylated to β-Br8OxPBz2 and β-Br8OxPBz4 (where Bz = 4-bromobenzyl). β-Br8OxPBz2 crystallizes in orthorhombic space group Pccn [a = 23.5535(17) Å, b = 19.3587(14) Å c = 20.9760(15) Å, V = 9564.3(12) Å3]. It has a calix[4]pyrrole-like structure with a saddle conformation and two molecules of methanol occupy a central binding site made up of the non-alkylated pyrrole N–H groups. Computational and electrochemical studies revealed widening HOMO–LUMO band gaps for the brominated compounds over the non-brominated analogues consistent with the observed hypsochromic shifts in electronic absorption spectra. Solvatochromic and chromogenic effects on anion binding were both observed for β-Br8OxP and β-Br8OxPBz2 with binding affinities of anions being greater than those observed for the corresponding OxP and OxPBz2. Colorimetric sensor studies suggest that the OxP compounds reported here are possible candidates for use in the design of optoelectronic noses for detection of anions and anionic analyte species of biological interest.

RFX1-dependent activation of SHP-1 induces autophagy by a novel obatoclax derivative in hepatocellular carcinoma cells

Obatoclax is a small molecule which targets the Bcl-2 family, and is to treat leukemia, lymphoma and lung carcinoma. Previously, an obatoclax analogue, SC-2001, was found to disrupt the protein-protein interactions of the Bcl-2 family and also repress Bcl-XL and Mcl-1 expression via STAT3 inactivation. Here, we report a novel mechanism of autophagy induction by SC-2001 in liver cancer cells. The findings indicate that SC-2001 induced the autophagy marker LC3-II in four hepatocellular carcinoma (HCC) cells. Autophagosomes induced by SC-2001-treated cells were confirmed by electron microscopy. SC-2001 activated SHP-1, dephosphorylated STAT3 and Mcl-1, and subsequently released free beclin 1. Overexpression of STAT3 and Mcl-1 in PLC5 cells attenuated the induction of SC-2001 on autophagy. Abolishment of SHP-1 by a specific inhibitor aboragated the autophagic effects induced by SC-2001. In addition, it was further revealed that RFX-1, a transcription factor of SHP-1, is a critical regulator in SC-2001-mediated autophagy. Downregulation of RFX-1 by si-RNA protected cells from SC-2001-induced autophagy. Importantly, Huh7 tumor-bearing nude mice treated with SC-2001 showed downregulation of Mcl-1 and p-STAT3 protein expression and upregulation of SHP-1, LC3II, and RFX-1 protein expression. In summary, our data suggest that SC-2001 induces autophagic cell death in a RFX1/SHP-1/STAT3/Mcl-1 signaling cascade.

Copper-obatoclax derivative complexes mediate DNA cleavage and exhibit anti-cancer effects in hepatocellular carcinoma

Obatoclax is an indole-pyrrole compound that induces cancer cell apoptosis through targeting the anti-apoptotic Bcl-2 protein family. Previously, we developed a series of obatoclax derivatives and studied their STAT3 inhibition-dependent activity against cancer cell lines. The obatoclax analog, prodigiosin, has been reported to mediate DNA cleavage in cancer cells by coordinating with copper complexes. To gain an understanding of copper-obatoclax complex activity, we applied obatoclax derivatives to examine their copper-mediated nuclease activity as a means to establish a basis for structure activity relationship. Replacement of the indole ring of obatoclax with furanyl, thiophenyl or Boc-indolyl rings reduced the DNA cleavage ability. The same effect was achieved through the replacement of the obatoclax pyrrolyl ring with thiazolidinedione and thioacetal. Among the compounds tested, we demonstrated that the complex of obatoclax or compound 7 with copper exhibited potent DNA strand scission which correlated with HCC cell growth inhibition.

Obatoclax analog SC-2001 inhibits STAT3 phosphorylation through enhancing SHP-1 expression and induces apoptosis in human breast cancer cells

Interfering oncogenic STAT3 signaling is a promising anti-cancer strategy. We examined the efficacy and drug mechanism of an obatoclax analog SC-2001, a novel STAT3 inhibitor, in human breast cancer cells. Human breast cancer cell lines were used for in vitro studies. Apoptosis was examined by both flow cytometry and western blot. Signaling pathways were assessed by western blot. In vivo efficacy of SC-2001 was tested in xenograft nude mice. SC-2001 inhibited cell growth and induced apoptosis in association with downregulation of p-STAT3 (Tyr 705) in breast cancer cells. STAT3-regulated proteins, including Mcl-1, survivin, and cyclin D1, were repressed by SC-2001. Over-expression of STAT3 in MDA-MB-468 cells protected cells from SC-2001-induced apoptosis. Moreover, SC-2001 enhanced the expression of protein tyrosine phosphatase SHP-1, a negative regulator of STAT3. Furthermore, the enhanced SHP-1 expression, in conjunction with increased SHP-1 phosphatase activity, was mediated by upregulated transcription by RFX-1. Chromatin immunoprecipitation assay revealed that SC-2001 increased the binding capacity of RFX-1 to the SHP-1 promoter. Knockdown of either RFX-1 or SHP-1 reduced SC-2001-induced apoptosis, whereas ectopic expression of RFX-1 increased SHP-1 expression and enhanced the apoptotic effect of SC-2001. Importantly, SC-2001 suppressed tumor growth in association with enhanced RFX-1 and SHP-1 expression and p-STAT3 downregulation in MDA-MB-468 xenograft tumors. SC-2001 induced apoptosis in breast cancer cells, an effect that was mediated by RFX-1 upregulated SHP-1 expression and SHP-1-dependent STAT3 inactivation. Our study indicates targeting STAT3 signaling pathway may be a useful approach for the development of targeted agents for anti-breast cancer.

Arylpyrrole oligomers as tunable anion receptors

A novel class of oligomeric arylpyrrole receptors has been designed, prepared and analysed for their affinity towards anionic guests.