Pyrrolopyrimidine derivatives and purine analogs as novel activators of Multidrug Resistance-associated Protein 1 (MRP1, ABCC1)

Computer-aided pattern scoring (C@PS): a novel cheminformatic workflow to predict ligands with rare modes-of-action

The identification, establishment, and exploration of potential pharmacological drug targets are major steps of the drug development pipeline. Target validation requires diverse chemical tools that come with a spectrum of functionality, e.g., inhibitors, activators, and other modulators. Particularly tools with rare modes-of-action allow for a proper kinetic and functional characterization of the targets-of-interest (e.g., channels, enzymes, receptors, or transporters). Despite, functional innovation is a prime criterion for patentability and commercial exploitation, which may lead to therapeutic benefit. Unfortunately, data on new, and thus, undruggable or barely druggable targets are scarce and mostly available for mainstream modes-of-action only (e.g., inhibition). Here we present a novel cheminformatic workflow-computer-aided pattern scoring (C@PS)-which was specifically designed to project its prediction capabilities into an uncharted domain of applicability.

Physicochemistry shapes bioactivity landscape of pan-ABC transporter modulators: Anchor point for innovative Alzheimer's disease therapeutics

Alzheimer's disease (AD) is a devastating neurological disorder characterized by the pathological accumulation of macromolecular Aβ and tau leading to neuronal death. Drugs approved to treat AD may ameliorate disease symptoms, however, no curative treatment exists. Aβ peptides were discovered to be substrates of adenosine triphosphate-(ATP)-binding cassette (ABC) transporters. Activators of these membrane-bound efflux proteins that promote binding and/or translocation of Aβ could revolutionize AD medicine. The knowledge about ABC transporter activators is very scarce, however, the few molecules that were reported contain substructural features of multitarget (pan-)ABC transporter inhibitors. A cutting-edge strategy to obtain new drug candidates is to explore and potentially exploit the recently proposed multitarget binding site of pan-ABC transporter inhibitors as anchor point for the development of innovative activators to promote Aβ clearance from the brain. Molecular associations between functional bioactivities and physicochemical properties of small-molecules are key to understand these processes. This study provides an analysis of a recently reported unique multitarget dataset for the correlation between multitarget bioactivity and physicochemistry. Six novel pan-ABC transporter inhibitors were validated containing substructural features of ABC transporter activators, which underpins the relevance of the multitarget binding site for the targeted development of novel AD diagnostics and therapeutics.

Synthesis Strategies and Medicinal Value of Pyrrole and its Fused Heterocyclic Compounds

For several decades, interest in pyrrole and pyrrolopyrimidine derivatives increases owing to their biological importance, such as anti-tumor, anti-microbial, anti-inflammatory, anti-diabetic, anti-histaminic, anti-malarial, anti-Parkinson, antioxidant and anti-viral, specially recently against COVID-19. These tremendous biological features motivated scientists to discover more pyrrole and fused pyrrole derivatives, owing to the great importance of the pyrrole nucleus as a pharmacophore in many drugs, and motivated us to present this article, highlighting on the different synthetic pathways of pyrrole and its fused compounds specially pyrrolopyrimidine, as well as their medicinal value from 2017 till 2021.

A critical review on modulators of Multidrug Resistance Protein 1 in cancer cells

Multidrug resistance protein 1 (MRP1/ABCC1) is an ATP-dependent efflux transporter, and responsible for the transport of a broad spectrum of xenobiotics, toxins, and physiological substrates across the plasma membrane. As an efflux pump, it plays a significant role in the absorption and disposition of drugs including anticancer drugs, antivirals, antimalarials, and antibiotics and their metabolites across physiological barriers in cells. MRP1 is also known to aid in the regulation of several physiological processes such as redox homeostasis, steroid metabolism, and tissue defense. However, its overexpression has been reported to be a key clinical marker associated with multidrug resistance (MDR) of several types of cancers including lung cancer, childhood neuroblastoma, breast and prostate carcinomas, often resulting in a higher risk of treatment failure and shortened survival rates in cancer patients. Aside MDR, overexpression of MRP1 is also implicated in the development of neurodegenerative and cardiovascular diseases. Due to the cellular importance of MRP1, the identification and biochemical/molecular characterization of modulators of MRP1 activity and expression levels are of key interest to cancer research and beyond. This review primarily aims at highlighting the physiological and pharmacological importance of MRP1, known MRP1 modulators, current challenges encountered, and the potential benefits of conducting further research on the MRP1 transporter.

Binding mode analysis of ABCA7 for the prediction of novel Alzheimer's disease therapeutics

The adenosine-triphosphate-(ATP)-binding cassette (ABC) transporter ABCA7 is a genetic risk factor for Alzheimer's disease (AD). Defective ABCA7 promotes AD development and/or progression. Unfortunately, ABCA7 belongs to the group of 'under-studied' ABC transporters that cannot be addressed by small-molecules. However, such small-molecules would allow for the exploration of ABCA7 as pharmacological target for the development of new AD diagnostics and therapeutics. Pan-ABC transporter modulators inherit the potential to explore under-studied ABC transporters as novel pharmacological targets by potentially binding to the proposed 'multitarget binding site'. Using the recently reported cryogenic-electron microscopy (cryo-EM) structures of ABCA1 and ABCA4, a homology model of ABCA7 has been generated. A set of novel, diverse, and potent pan-ABC transporter inhibitors has been docked to this ABCA7 homology model for the discovery of the multitarget binding site. Subsequently, application of pharmacophore modelling identified the essential pharmacophore features of these compounds that may support the rational drug design of innovative diagnostics and therapeutics against AD.

Scaffold fragmentation and substructure hopping reveal potential, robustness, and limits of computer-aided pattern analysis (C@PA)

Computer-aided pattern analysis (C@PA) was recently presented as a powerful tool to predict multitarget ABC transporter inhibitors. The backbone of this computational methodology was the statistical analysis of frequently occurring molecular features amongst a fixed set of reported small-molecules that had been evaluated toward ABCB1, ABCC1, and ABCG2. As a result, negative and positive patterns were elucidated, and secondary positive substructures could be suggested that complemented the multitarget fingerprints. Elevating C@PA to a non-statistical and exploratory level, the concluded secondary positive patterns were extended with potential positive substructures to improve C@PA's prediction capabilities and to explore its robustness. A small-set compound library of known ABCC1 inhibitors with a known hit rate for triple ABCB1, ABCC1, and ABCG2 inhibition was taken to virtually screen for the extended positive patterns. In total, 846 potential broad-spectrum ABCB1, ABCC1, and ABCG2 inhibitors resulted, from which 10 have been purchased and biologically evaluated. Our approach revealed 4 novel multitarget ABCB1, ABCC1, and ABCG2 inhibitors with a biological hit rate of 40%, but with a slightly lower inhibitory power than derived from the original C@PA. This is the very first report about discovering novel broad-spectrum inhibitors against the most prominent ABC transporters by improving C@PA.

C@PA: Computer-Aided Pattern Analysis to Predict Multitarget ABC Transporter Inhibitors

Based on literature reports of the last two decades, a computer-aided pattern analysis (C@PA) was implemented for the discovery of novel multitarget ABCB1 (P-gp), ABCC1 (MRP1), and ABCG2 (BCRP) inhibitors. C@PA included basic scaffold identification, substructure search and statistical distribution, as well as novel scaffold extraction to screen a large virtual compound library. Over 45,000 putative and novel broad-spectrum ABC transporter inhibitors were identified, from which 23 were purchased for biological evaluation. Our investigations revealed five novel lead molecules as triple ABCB1, ABCC1, and ABCG2 inhibitors. C@PA is the very first successful computational approach for the discovery of promiscuous ABC transporter inhibitors.

Superior Pyrimidine Derivatives as Selective ABCG2 Inhibitors and Broad-Spectrum ABCB1, ABCC1, and ABCG2 Antagonists

In the search for highly effective modulators addressing ABCG2-mediated MDR, 23 pyrimidines were synthesized and biologically assessed. Seven derivatives with (a) nitrogen- and/or halogen-containing residue(s) had extraordinary potencies against ABCG2 (IC₅₀ < 150 nM). The compounds competitively inhibited ABCG2-mediated Hoechst 33342 transport but were not substrates of ABCG2. The most potent MDR reverser, compound 19, concentration-dependently increased SN-38-mediated cancer cell death at 11 nM (EC₅₀), time-dependently doubled SN-38 toxicity in a period of 7 days at 10 nM, and half-maximally accelerated cell death combined with SN-38 at 17 nM. No induction of ABCG2 was observed. Furthermore, 11 pyrimidines were revealed as triple ABCB1/ABCC1/ABCG2 inhibitors. Five possessed IC₅₀ values below 10 μM against each transporter, classifying them as some of the 50 most potent multitarget ABC transporter inhibitors. The most promising representative, compound 37, reversed ABCB1-, ABCC1-, and ABCG2-mediated MDR, making it one of the three most potent ABC transporter inhibitors and reversers of ABC transporters-mediated MDR.

Structural and Biological Investigations for a Series of N-5 Substituted Pyrrolo[3,2-d]pyrimidines as Potential Anti-Cancer Therapeutics

Pyrrolo[3,2-d]pyrimidines have been studied for many years as potential lead compounds for the development of antiproliferative agents. Much of the focus has been on modifications to the pyrimidine ring, with enzymatic recognition often modulated by C2 and C4 substituents. In contrast, this work focuses on the N5 of the pyrrole ring by means of a series of novel N5-substituted pyrrolo[3,2-d]pyrimidines. The compounds were screened against the NCI-60 Human Tumor Cell Line panel, and the results were analyzed using the COMPARE algorithm to elucidate potential mechanisms of action. COMPARE analysis returned strong correlation to known DNA alkylators and groove binders, corroborating the hypothesis that these pyrrolo[3,2-d]pyrimidines act as DNA or RNA alkylators. In addition, N5 substitution reduced the EC50 against CCRF-CEM leukemia cells by up to 7-fold, indicating that this position is of interest in the development of antiproliferative lead compounds based on the pyrrolo[3,2-d]pyrimidine scaffold.

Insight into structural features of phenyltetrazole derivatives as ABCG2 inhibitors for the treatment of multidrug resistance in cancer

ABCG2 is the principal ABC transporter involved in the multidrug resistance of breast cancer. Looking at the current demand in the development of ABCG2 inhibitors for the treatment of multidrug-resistant cancer, we have explored structural requirements of phenyltetrazole derivatives for ABCG2 inhibition by combining classical QSAR, Bayesian classification modelling and molecular docking studies. For classical QSAR, structural descriptors were calculated from the free software tool PaDEL-descriptor. Stepwise multiple linear regression (SMLR) was used for model generation. A statistically significant model was generated and validated with different parameters (For training set: r = 0.825; Q² = 0.570 and for test set: r = 0.894, r²_pred = 0.783). The predicted model was found to satisfy the Golbraikh and Trospha criteria for model acceptability. Bayesian classification modelling was also performed (ROC scores were 0.722 and 0.767 for the training and test sets, respectively). Finally, the binding interactions of phenyltetrazole type inhibitor with the ABCG2 receptor were mapped with the help of molecular docking study. The result of the docking analysis is aligned with the classical QSAR and Bayesian classification studies. The combined modelling study will guide the medicinal chemists to act faster in the drug discovery of ABCG2 inhibitors for the management of resistant breast cancer.

Identification of Thienopyrimidine Scaffold as an Inhibitor of the ABC Transport Protein ABCC1 (MRP1) and Related Transporters Using a Combined Virtual Screening Approach

A virtual screening protocol with combination of similarity search and pharmacophore modeling was applied to virtually screen a large compound library to gain new scaffolds regarding ABCC1 inhibition. Biological investigation of promising candidates revealed four compounds as ABCC1 inhibitors, three of them with scaffolds not associated with ABCC1 inhibition until now. The best hit molecule-a thienopyrimidine-was a moderately potent, competitive inhibitor of the ABCC1-mediated transport of calcein AM which also sensitized ABCC1-overexpressing cells toward daunorubicin. Further evaluation showed that it was a moderately potent, competitive inhibitor of the ABCB1-mediated transport of calcein AM, and noncompetitive inhibitor of the ABCG2-mediated pheophorbide A transport. In addition, the thienopyrimidine could also sensitize ABCB1- as well as ABCG2-overexpressing cells toward daunorubicin and SN-38, respectively, in concentration ranges that qualified it as one of the ten best triple ABCC1/ABCB1/ABCG2 inhibitors in the literature. Besides, three more new multitarget inhibitors were identified by this virtual screening approach.

Novel chalcone and flavone derivatives as selective and dual inhibitors of the transport proteins ABCB1 and ABCG2

During cancer chemotherapy, certain cancers may become cross-resistant to structurally diverse antineoplastic agents. This so-called multidrug resistance (MDR) is highly associated with the overexpression of ATP-binding cassette (ABC) transport proteins. These membrane-bound efflux pumps export a broad range of structurally diverse endo- and xenobiotics, including chemically unrelated anticancer agents. This translocation of drugs from the inside to the outside of cancer cells is mediated at the expense of ATP. In the last 40 years, three ABC transporters - ABCB1 (P-gp), ABCC1 (MRP1), and ABCG2 (BCRP) - have mainly been attributed to the occurrence of MDR in cancer cells. One of the strategies to overcome MDR is to inhibit the efflux transporter function by small-molecule inhibitors. In this work, we investigated new chalcone- and flavone-based compounds for selective as well as broad-spectrum inhibition of the stated transport proteins. These include substituted chalcones with variations at rings A and B, and flavones with acetamido linker at position 3. The synthesized molecules were evaluated for their inhibitory potential against ABCB1, ABCC1, and ABCG2 in calcein AM and pheophorbide A assays. In further investigations with the most promising candidates from each class, we proved that ABCB1- and ABCG2-mediated MDR could be reversed by the compounds. Moreover, their intrinsic toxicity was found to be negligible in most cases. Altogether, our findings contribute to the understanding of ABC transport proteins and reveal new compounds for ongoing evaluation in the field of ABC transporter-mediated MDR.

Alpha2beta1 Integrin (VLA-2) Protects Activated Human Effector T Cells From Methotrexate-Induced Apoptosis

β1 integrins are critical for T cell migration, survival and costimulation. The integrin α2β1, which is a receptor for collagen, also named VLA-2, is a major costimulatory pathway of effector T cells and has been implicated in arthritis pathogenesis. Herein, we have examined its ability to promote methotrexate (MTX) resistance by enhancing effector T cells survival. Our results show that attachment of anti-CD3-activated human polarized Th17 cells to collagen but not to fibronectin or laminin led to a significant reduction of MTX-induced apoptosis. The anti-CD3+collagen-rescued cells still produce significant amounts of IL-17 and IFNγ upon their reactivation indicating that their inflammatory nature is preserved. Mechanistically, we found that the prosurvival role of anti-CD3+collagen involves activation of the MTX transporter ABCC1 (ATP Binding Cassette subfamily C Member 1). Finally, the protective effect of collagen/α2β1 integrin on MTX-induced apoptosis also occurs in memory CD4⁺ T cells isolated from rheumatoid arthritis (RA) patients suggesting its clinical relevance. Together these results show that α2β1 integrin promotes MTX resistance of effector T cells, and suggest that it could contribute to the development of MTX resistance that is seen in RA.

9-Deazapurines as Broad-Spectrum Inhibitors of the ABC Transport Proteins P-Glycoprotein, Multidrug Resistance-Associated Protein 1, and Breast Cancer Resistance Protein

P-Glycoprotein (P-gp, ABCB1), multidrug resistance-associated protein 1 (MRP1, ABCC1), and breast cancer resistance protein (BCRP, ABCG2) are the three major ABC transport proteins conferring resistance to many structurally diverse anticancer agents, leading to the phenomenon called multidrug resistance (MDR). Much effort has been put into the development of clinically useful compounds to reverse MDR. Broad-spectrum inhibitors of ABC transport proteins can be of great use in cancers that simultaneously coexpress two or three transporters. In this work, we continued our effort to generate new, potent, nontoxic, and multiply effective inhibitors of the three major ABC transporters. The best compound was active in a very low micromolar concentration range against all three transporters and restored sensitivity toward daunorubicin (P-gp and MRP1) and SN-38 (BCRP) in A2780/ADR (P-gp), H69AR (MRP1), and MDCK II BCRP (BCRP) cells. Additionally, the compound is a noncompetitive inhibitor of daunorubicin (MRP1), calcein AM (P-gp), and pheophorbide A (BCRP) transport.

LncRNA plasmacytoma variant translocation 1 is an oncogene in bladder urothelial carcinoma

Bladder cancer (BC) is the most lethal malignant cancer of the genitourinary system, and bladder urothelial carcinoma (BUC) is the most common type of BC. The long non-coding RNA (lncRNA) plasmacytoma variant translocation 1 (PVT1) is overexpressed in several malignant tumors, including BC. Using a lncRNA array and quantitative real-time PCR, we detected greater expression of PVT1 in BUC tissues and cell lines resistant to doxorubicin (DOX) and cisplatin (DDP) than in DOX- and DDP-sensitive cells. PVT1 knockdown reduced proliferation and invasion by a DOX- and DDP-resistant T24/DR BUC cells, arrested cells in G1 phase, and increased apoptosis. PVT1 knockdown also sensitized T24/DR cells to DOX and DDP, and suppressed expression of multidrug resistance 1 (MDR1) and multidrug resistance associated protein 1 (MRP1). Wnt/β-catenin pathway activation in T24/DR cells reversed the effects of PVT1 knockdown on metastasis-associated behavior and chemoresistance. In sum, lncRNA PVT1 is overexpressed in multidrug resistant BUC tissues and cell lines, and PVT1 knockdown reduces BUC cell proliferation, invasiveness, and chemoresistance by modulating Wnt/β-catenin signaling. These results provide new insight into BUC chemoresistance mechanisms and suggest potential therapeutic targets for anti-BUC therapeutics.

Influence of microRNAs and Long Non-Coding RNAs in Cancer Chemoresistance

Innate and acquired chemoresistance exhibited by most tumours exposed to conventional chemotherapeutic agents account for the majority of relapse cases in cancer patients. Such chemoresistance phenotypes are of a multi-factorial nature from multiple key molecular players. The discovery of the RNA interference pathway in 1998 and the widespread gene regulatory influences exerted by microRNAs (miRNAs) and other non-coding RNAs have certainly expanded the level of intricacy present for the development of any single physiological phenotype, including cancer chemoresistance. This review article focuses on the latest research efforts in identifying and validating specific key molecular players from the two main families of non-coding RNAs, namely miRNAs and long non-coding RNAs (lncRNAs), having direct or indirect influences in the development of cancer drug resistance properties and how such knowledge can be utilised for novel theranostics in oncology.