Class 1 PI3K clinical candidates and recent inhibitor design strategies: a medicinal chemistry perspective

Phosphatidylinositol 3-kinases (PI3Ks) are a family of lipid kinases that phosphorylate the 3-OH of the inositol ring of phosphoinositides, and deregulation of this pathway has implications in many diseases. The search for novel PI3K inhibitors has been at the forefront of academic and industrial medicinal chemistry with over 600 medicinal chemistry-based publications and patents appearing to date, leading to 38 clinical candidates and the launch of two drugs, idelalisib in 2014 and copanlisib in 2017. This Perspective will discuss medicinal chemistry design approaches to novel isoform-selective inhibitors through consideration of brief case histories of compounds that have progressed into clinical development or that have revealed new structural motifs in this highly competitive area of research

Concurrent reactive oxygen species generation and aneuploidy induction contribute to thymoquinone anticancer activity

Thymoquinone (TQ) is the main biologically active constituent of Nigella sativa. Many studies have confirmed its anticancer actions. Herein, we investigated the different anticancer activities of, and considered resistance mechanisms to, TQ. MTT and clonogenic data showed TQ’s ability to suppress breast MDA-MB-468 and T-47D proliferation at lower concentrations compared to other cancer and non-transformed cell lines tested (GI50 values ≤ 1.5 µM). Flow-cytometric analyses revealed that TQ consistently induced MDA-MB-468 and T-47D cell-cycle perturbation, specifically inducing pre-G1 populations. In comparison, less sensitive breast MCF-7 and colon HCT-116 cells exhibited only transient increases in pre-G1 events. Annexin V/PI staining confirmed apoptosis induction in MDA-MB-468 and HCT-116 cells, which was continuous in the former and transient in the latter. Experiments revealed the role of reactive oxygen species (ROS) generation and aneuploidy induction in MDA-MB-468 cells within the first 24 h of treatment. The ROS-scavenger NAD(P)H dehydrogenase (quinone 1) (NQO1; DT-diaphorase) and glutathione (GSH) were implicated in resistance to TQ. Indeed, western blot analyses showed that NQO1 is expressed in all cell lines in this study, except those most sensitive to TQ-MDA-MB-468 and T-47D. Moreover, TQ treatment increased NQO1 expression in HCT-116 in a concentration-dependent fashion. Measurement of GSH activity in MDA-MB-468 and HCT-116 cells found that GSH is similarly active in both cell lines. Furthermore, GSH depletion rendered these cells more sensitive to TQ’s antiproliferative actions. Therefore, to bypass putative inactivation of the TQ semiquinone metabolite, the benzylamine analogue was designed and synthesised following modification of TQ’s carbon-3 atom. However, the structural modification negatively impacted potency against MDA-MB-468 cells. In conclusion, we disclose the following: (i) The anticancer activity of TQ may be a consequence of ROS generation and aneuploidy; (ii) Early GSH depletion could substantially enhance TQ’s anticancer activity; (iii) Benzylamine substitution at TQ’s carbon-3 failed to enhance anticancer activity

Codrug Approach for the Potential Treatment of EML4-ALK Positive Lung Cancer

We report on the synergistic effect of PI3K inhibition with ALK inhibition for the possible treatment of EML4-ALK positive lung cancer. We have brought together ceritinib (ALK inhibitor) and pictilisib (PI3K inhibitor) into a single bivalent molecule (a codrug) with the aim of designing a molecule for slow release drug delivery that targets EML4-ALK positive lung cancer. We have joined the two drugs through a new, pH-sensitive linker where the resulting codrugs are hydrolytically stable at lower pH (pH 6.4) but rapidly cleaved at higher pH (pH 7.4). Compound (19), which was designed for optimal lung retention, demonstrated clean liberation of the drug payloads in vitro and represents a novel approach to targeted lung delivery

Design and elaboration of a tractable tricyclic scaffold to synthesize druglike inhibitors of dipeptidyl peptidase-4 (DPP-4), antagonists of the C–C Chemokine Receptor Type 5 (CCR5), and highly potent and selective phosphoinositol-3 Kinase δ (PI3Kδ) inhibitors

A novel molecular scaffold has been synthesized, and its incorporation into new analogues of biologically active molecules across multiple target classes will be discussed. In these studies, we have shown use of the tricyclic scaffold to synthesize potent inhibitors of the serine peptidase DPP-4, antagonists of the CCR5 receptor, and highly potent and selective PI3K δ isoform inhibitors. We also describe the predicted physicochemical properties of the resulting inhibitors and conclude that the tractable molecular scaffold could have potential application in future drug discovery programs

Lipophilic activated ester prodrug approach for drug delivery to the intestinal lymphatic system

The intestinal lymphatic system plays an important role in the pathophysiology of multiple diseases including lymphomas, cancer metastasis, autoimmune diseases, and human immunodeficiency virus (HIV) infection. It is thus an important compartment for delivery of drugs in order to treat diseases associated with the lymphatic system. Lipophilic prodrug approaches have been used in the past to take advantage of the intestinal lymphatic transport processes to deliver drugs to the intestinal lymphatics. Most of the approaches previously adopted were based on very bulky prodrug moieties such as those mimicking triglycerides (TG). We now report a study in which a lipophilic prodrug approach was used to efficiently deliver bexarotene (BEX) and retinoic acid (RA) to the intestinal lymphatic system using activated ester prodrugs. A range of carboxylic ester prodrugs of BEX were designed and synthesised and all of the esters showed improved association with chylomicrons, which indicated an improved potential for delivery to the intestinal lymphatic system. The conversion rate of the prodrugs to BEX was the main determinant in delivery of BEX to the intestinal lymphatics, and activated ester prodrugs were prepared to enhance the conversion rate. As a result, an 4-(hydroxymethyl)-1,3-dioxol-2-one ester prodrug of BEX was able to increase the exposure of the mesenteric lymph nodes (MLNs) to BEX 17-fold compared to when BEX itself was administered. The activated ester prodrug approach was also applied to another drug, RA, where the exposure of the MLNs was increased 2.4-fold through the application of a similar cyclic activated prodrug. Synergism between BEX and RA was also demonstrated in vitro by cell growth inhibition assays using lymphoma cell lines. In conclusion, the activated ester prodrug approach results in efficient delivery of drugs to the intestinal lymphatic system, which could benefit patients affected by a large number of pathological conditions