Drug discovery using spirooxindole cores: Success and Challenges [corrected]

Catalytic asymmetric synthesis of spirooxindoles: recent developments

The past four years have witnessed significant developments in the field of the catalytic asymmetric synthesis of spirooxindoles, and this feature article outlines the recent progress in this area, including the contributions of our group. This article is divided into sections according to the size and type of the generated spiro-ring fused at the C3-position of the oxindole core.

PLK4: a link between centriole biogenesis and cancer

INTRODUCTION

Polo like kinase (PLK) is known to play a pivotal role in various cell cycle processes to perpetuate proper division and growth of the cells. Polo like kinase-4 (PLK4) is one such kinase that appears in low abundance and plays a well-characterized role in centriole duplication. PLK4 deregulation (i.e. both overexpression and depletion of PLK4), leads to altered mitotic fidelity and thereby triggers tumorigenesis. Hence, over the last few years PLK4 has emerged as a potential therapeutic target for the treatment of various advanced cancers. Areas covered: In this review, we discuss the basic structure, expression, localization and functions of PLK4 along with its regulation by various proteins. We also discuss the role of altered PLK4 activity in the onset of cancer and the current pre-clinical and clinical inhibitors to regulate PLK4. Expert opinion: PLK4 mediated centriole duplication has a crucial role in maintaining mitotic correctness in normal cells, while its deregulation has a greater impact on genesis of cancer. Henceforth, a deep knowledge of the PLK4 levels, its role and interactions with various proteins in cancer is required to design effective inhibitors for clinical use.

A functional screening of the kinome identifies the Polo-like kinase 4 as a potential therapeutic target for malignant rhabdoid tumors, and possibly, other embryonal tumors of the brain

PURPOSE

Malignant rhabdoid tumors (MRTs) are deadly embryonal tumors of the infancy. With poor survival and modest response to available therapies, more effective and less toxic treatments are needed. We hypothesized that a systematic screening of the kinome will reveal kinases that drive rhabdoid tumors and can be targeted by specific inhibitors.

METHODS

We individually mutated 160 kinases in a well-characterized rhabdoid tumor cell line (MON) using lentiviral clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9). The kinase that most significantly impaired cell growth was further validated. Its expression was evaluated by microarray gene expression (GE) within 111 pediatric tumors, and functional assays were performed. A small molecule inhibitor was tested in multiple rhabdoid tumor cell lines and its toxicity evaluated in zebrafish larvae.

RESULTS

The Polo-like kinase 4 (PLK4) was identified as the kinase that resulted in higher impairment of cell proliferation when mutated by CRISPR/Cas9. PLK4 CRISPR-mutated rhabdoid cells demonstrated significant decrease in proliferation, viability, and survival. GE showed upregulation of PLK4 in rhabdoid tumors and other embryonal tumors of the brain. The PLK4 inhibitor CFI-400945 showed cytotoxic effects on rhabdoid tumor cell lines while sparing non-neoplastic human fibroblasts and developing zebrafish larvae.

CONCLUSIONS

Our findings indicate that rhabdoid tumor cell proliferation is highly dependent on PLK4 and suggest that targeting PLK4 with small-molecule inhibitors may hold a novel strategy for the treatment of MRT and possibly other embryonal tumors of the brain. This is the first time that PLK4 has been described as a potential target for both brain and pediatric tumors.

Activity of the novel polo-like kinase 4 inhibitor CFI-400945 in pancreatic cancer patient-derived xenografts

BACKGROUND

Polo-like kinase 4 (PLK4) plays a key role in centriole replication. Hence PLK4 inhibition disrupts mitosis, and offers a novel approach to treating chromosomally unstable cancers, including pancreatic cancer. CFI-400945 is a first in class small molecule PLK4 inhibitor, currently undergoing early phase clinical trials.

RESULTS

Treatment with CFI-400945 significantly reduced tumor growth and increased survival in four out of the six models tested. Consistent with PLK4 inhibition, we observed reduced expression of the proliferation marker Ki-67 associated with an increase in nuclear diameter during treatment with CFI-400945. Additionally, treatment with CFI-400945 resulted in a significant reduction of tumor-initiating cells.

DISCUSSION

These results support the further investigation of PLK4 as a drug target in pancreatic cancer.

METHODS

Sensitivity to CFI-400945 was tested in a series of six patient-derived pancreatic cancer xenografts, selected to represent the range of growth characteristics, genetic features, and hypoxia found in pancreatic cancer patients.

Synthesis of spiropyrazoline oxindoles by a formal [4 + 1] annulation reaction between 3-bromooxindoles and in situ-derived 1,2-diaza-1,3-dienes

A formal [4 + 1] annulation reaction of 3-bromooxindoles and in situ-derived 1,2-diaza-1,3-dienes has been developed to provide an efficient route to various spiropyrazoline oxindoles with high yields.

Synthesis and biological evaluation of (E)-4-(3-arylvinyl-1H-indazol-6-yl)pyrimidin-2-amine derivatives as PLK4 inhibitors for the treatment of breast cancer

SAR explorations identified (E)-4-(3-arylvinyl-1H-indazol-6-yl)pyrimidin-2-amine derivative14ias a potential PLK4 inhibitor with significant anti-breast cancer activityin vitroandin vivo.

Structurally novel steroidal spirooxindole by241 potently inhibits tumor growth mainly through ROS-mediated mechanisms

Cancer cells always have increased ROS levels, thus making them more vulnerable to persistent endogenous oxidative stress. The biochemical difference between cancer and normal cells could be exploited to achieve selective cancer cell killing by exogenous ROS-producing agents. Herein we described a structurally novel steroidal spirooxindole by241 and its anticancer efficacy. By241 exhibited potent inhibition against human cancer cells and less toxic to normal cells. By241 concentration-dependently induced apoptosis of MGC-803 and EC9706 cells, accompanied with the mitochondrial dysfunction and increased ROS levels. NAC can completely restore the decreased cell viability of MGC-803 cells caused by by241, suggesting ROS-mediated mechanisms. The expression levels of proteins involved in the mitochondrion-related pathways were detected, showing increased expression of proapoptotic proteins and decreased expression of anti-apoptotic proteins, and activation of caspases-9/-3, but without activating caspase-8 expression. Pretreatment with Z-VAD-FMK partially rescued by241-induced apoptosis of MGC-803 cells. Additionally, by241 inhibited mTOR, activated p53 and its downstream proteins, cleaved MDM2 and PI3K/AKT as well as NF-κB signaling pathway. In vivo experiments showed that by241 did not have significant acute oral toxicity and exerted good anticancer efficacy against MGC-803 bearing mice models. Therefore, by241 may serve as a lead for further development for cancer therapy.

NiFe2O4 Nanoparticles: A Green and Reusable Heterogeneous Catalyst for the Synthesis of Spiro[indole-3,2′-Pyrrole]-2,5′(1H,1′H)-Diones

NiFe2O4 nanoparticles were used as an efficient catalyst for the preparation of spiro[indole-3,2′-pyrrole]-2,5′(1 H,1′ H)-diones by the multi-component condensation reaction of arylamines, acetylenedicarboxylates and isatins under reflux conditions in ethanol.

Catalytic asymmetric synthesis of biologically important 3-hydroxyoxindoles: an update

Oxindole scaffolds are prevalent in natural products and have been recognized as privileged substructures in new drug discovery. Several oxindole-containing compounds have advanced into clinical trials for the treatment of different diseases. Among these compounds, enantioenriched 3-hydroxyoxindole scaffolds also exist in natural products and have proven to possess promising biological activities. A large number of catalytic asymmetric strategies toward the construction of 3-hydroxyoxindoles based on transition metal catalysis and organocatalysis have been reported in the last decades. Additionally, 3-hydroxyoxindoles as versatile precursors have also been used in the total synthesis of natural products and for constructing structurally novel scaffolds. In this review, we aim to provide an overview about the catalytic asymmetric synthesis of biologically important 3-substituted 3-hydroxyoxindoles and 3-hydroxyoxindole-based further transformations.

Multicomponent assembly of novel antiproliferative steroidal dihydropyridinyl spirooxindoles

Multicomponent assembly of steroidal dihydropyridinyl spirooxindoles from pregnenolone, isatins, malononitrile, and ammonium acetate is described, which involves the formation of two C-C bonds, two C-N bonds, and an all-carbon quaternary stereogenic center in a single operation. MTT assays showed that some of these compounds had moderate to excellent cytotoxicity against the tested cancer cell lines and were more potent than 5-FU. Particularly, compound 5o represented excellent inhibitory effect toward EC-109 (IC50=0.3 μM), being about 33-fold more potent than 5-FU.

DABCO-catalyzed unusual [4 + 2] cycloaddition reaction: non-substituted allenoate acts as a four-carbon synthon and facile synthesis of spirooxindoles

The first example of a non-substituted allenoate to act as a four-carbon synthon in a DABCO-catalyzed domino reaction is reported.

Highly enantioselective synthesis of spirocyclopropyloxindoles via a Rh(ii)-catalyzed asymmetric cyclopropanation reaction

An asymmetric cyclopropanation reaction of N-Boc diazooxindoles is described with good to excellent enantioselectivities, especially with alkyl alkenes (>90% ee).

Efficient three-component one-pot synthesis of steroidal polysubstituted anilines

An efficient and practical base-promoted cascade reaction has been developed to access steroidal polysubstituted anilines from simple precursors. The protocol reported herein achieved the formation of a benzene ring as well as three continuous C-C bonds in a single operation. The reaction mechanism was proposed on the basis of the key intermediate obtained. Besides, this method could be potentially employed for the synthesis of biphenyl compounds. The adjacent amine and nitrile groups existed in the final products have the potential for late stage functionalization, which would provide efficient access to steroidal compound collections with structural diversity and complexity.

Efficient synthesis of novel antiproliferative steroidal spirooxindoles via the [3+2] cycloaddition reactions of azomethine ylides

A series of novel steroidal spirooxindoles 3a-h were synthesized from pregnenolone in a high regioselective manner using the 1,3-dipolar cycloaddition as the key step. This protocol resulted in the formation of two C-C bonds, one C-N bond and the creation of one pyrrolidine ring and three contiguous stereocenters in a single operation. Biological evaluation showed that these synthesized steroidal spirooxindoles exhibited moderate to good antiproliferative activity against the tested cell lines and some of them were more potent than 5-FU. Among them, compounds 3e and 3f displayed the best antiproliferative activity against MCF-7 cells with the IC50 values of 4.0 and 3.9μM, respectively. Flow cytometry analysis demonstrated that compound 3d caused the cellular apoptosis and cell cycle arrest at G2/M phase in a concentration-dependent manner. Docking results indicated that compound 3d fitted well into the MDM2 active site 1RV1 by interacting with Lys94 and Thr101 residues.

Discovery of Novel Isatin-Based p53 Inducers

A series of isatin Schiff base derivatives were identified during in silico screening of the small molecule library for novel activators of p53. The compounds selected based on molecular docking results were further validated by a high-content screening assay using U2OS human osteosarcoma cells with an integrated EGFP-expressing p53-dependent reporter. The hit compounds activated and stabilized p53, as shown by Western blotting, at higher rates than the well-known positive control Nutlin-3. Thus, the p53-activating compounds identified by this approach represent useful molecular probes for various cancer studies.

Spirooxindole-derived morpholine-fused-1,2,3-triazoles: Design, synthesis, cytotoxicity and apoptosis inducing studies

A series of new spirooxindole-derived morpholine-fused-1,2,3-triazole derivatives has been synthesized from isatin spiro-epoxides. The protocol involves regiospecific isatin-epoxide ring opening with azide nucleophile followed by sequential O-propargylation, and intramolecular 1,3-dipolar cycloaddition reaction. These compounds have been evaluated for their antiproliferative activity against selected human tumor cell lines of lung (A549), breast (MCF-7), cervical (HeLa), and prostate (DU-145). Among the tested compounds, 6i, 6n and 6p showed potent growth inhibition against A549 cell line with IC50 values in the range of 1.87-4.36 μM, which are comparable to reference standards doxorubicin and 5-flourouracil. The compounds 6i and 6p treated A549 cells displayed typical apoptotic morphological features such as cell shrinkage, nuclear condensation, fragmentation, and decreased migration potential. Flow-cytometry analysis revealed that the compounds arrested the cells in G2/M phase of cell cycle. Hoechst and acridine orange/ethidium bromide staining studies also showed that the cell proliferation was inhibited through induction of apoptosis. Moreover, the compounds treatment led to collapse of the mitochondrial membrane potential (DΨm) and increased levels of reactive oxygen species (ROS) were noted in A549 cells.

3-Alkyl-3-(alkylamino)indolin-2-ones via Base-Mediated C-Arylation of 2-Nitrobenzenesulfonamides

Resin-bound intermediates prepared from polymer-supported amino acid esters, 2-nitrobenezenesulfonyl chlorides, and alcohols were used to synthesize 3-alkyl-3-(alkylamino) indolin-2-ones. The key step of the reaction sequence was the formation of a quaternary carbon via the base-mediated C-arylation of 2-nitrobenzenesulfonamides. The cleavage of the acyclic precursors from the resin and subsequent reduction of the nitro group by Zn in acetic acid triggered the spontaneous cyclization of the arylated compounds to indolinones. The synthesis was carried out using simple commercially available building blocks under mild conditions and provided the 3,3-disubstituted indolinone derivatives with good overall yields however, the arylation reaction resulted in the epimerization of the quaternary carbon.

Characteristic of core materials in polymeric micelles effect on their micellar properties studied by experimental and dpd simulation methods

Polymeric micelles are one important class of nanoparticles for anticancer drug delivery, but the impact of hydrophobic segments on drug encapsulation and release is unclear, which deters the rationalization of drug encapsulation into polymeric micelles. This paper focused on studying the correlation between the characteristics of hydrophobic segments and encapsulation of structurally different drugs (DOX and β-carotene). Poly(ϵ-caprolactone) (PCL) or poly(l-lactide) (PLLA) were used as hydrophobic segments to synthesize micelle-forming amphiphilic block copolymers with the hydrophilic methoxy-poly(ethylene glycol) (mPEG). Both blank and drug loaded micelles were spherical in shape with sizes lower than 50 nm. PCL-based micelles exhibited higher drug loading capacity than their PLLA-based counterparts. Higher encapsulation efficiency of β-carotene was achieved compared with DOX. In addition, both doxorubicin and β-carotene were released much faster from PCL-based polymeric micelles. Dissipative particle dynamics (DPD) simulation revealed that the two drugs tended to aggregate in the core of the PCL-based micelles but disperse in the core of PLLA based micelles. In vitro cytotoxicity investigation of DOX loaded micelles demonstrated that a faster drug release warranted a more efficient cancer-killing effect. This research could serve as a guideline for the rational design of polymeric micelles for drug delivery.