Melatonin-vorinostat hybrid ligands show higher histone deacetylase and cancer cell growth inhibition than vorinostat.

Anticancer drug conjugates are an emerging approach for future cancer treatment. Here, we report a series of hybrid ligands merging the neurohormone melatonin with the approved histone deacetylase (HDAC) inhibitor vorinostat, using melatonin's amide side chain (3a-e), its indolic nitrogen (5a-d), and its ether oxygen (7a-d) as attachment points. Several hybrid ligands showed higher potency thanvorinostat in both HDAC inhibition and cellular assays on different cultured cancer cell lines. In the most potent HDAC1 and HDAC6 inhibitors, 3e, 5c, and 7c, the hydroxamic acid moiety of vorinostat is linked to melatonin through a hexamethylene spacer. Hybrid ligands 5c and 7c were also found to be potent growth inhibitors of MCF-7, PC-3M-Luc, and HL-60 cancer cell lines. As these compounds showed only weak agonist activity at melatonin MT1 receptors, the findings indicate that their anticancer actions are driven by HDAC inhibition.

Strychnine and its mono- and dimeric analogues: a pharmaco-chemical perspective.

Covering: up to November 2021Since its isolation in 1818, strychnine has attracted the attention of a plethora of chemists and pharmacologists who have established its structure, developed total syntheses, and examined its complex pharmacology. While numerous reviews on structure elucidation and total synthesis of strychnine are available, reports on structure-activity relationships (SARs) of this fascinating alkaloid are rare. In this review, we present and discuss structures, synthetic approaches, metabolic transformations, and the diverse pharmacological actions of strychnine and its mono- and dimeric analogues. Particular attention is given to its SARs at glycine receptors (GlyRs) in light of recently published high-resolution structures of strychnine-GlyR complexes. Other pharmacological actions of strychnine and its derivatives, such as their antagonistic properties at nicotinic acetylcholine receptors (nAChRs), allosteric modulation of muscarinic acetylcholine receptors as well as anti-cancer and anti-plasmodial effects are also critically reviewed, and possible future developments in the field are discussed.

Gefitinib-Tamoxifen Hybrid Ligands as Potent Agents against Triple-Negative Breast Cancer.

Anticancer drug conjugates may benefit from simultaneous action at two targets potentially overcoming the drawbacks of current cancer treatment, such as insufficient efficacy, high toxicity, and development of resistance. Compared to a combination of two single-target drugs, they may offer an advantage of pharmacokinetic simplicity and fewer drug-drug interactions. Here, we report a series of compounds connecting tamoxifen or endoxifen with the EGFR-inhibitor gefitinib via a covalent linkage. These hybrid ligands retain both ER antagonist activity and EGFR inhibition. The most potent analogues exhibited single-digit nanomolar activities at both targets. The amide-linked endoxifen-gefitinib drug conjugates 17b and 17c demonstrated the most favorable anti-cancer profile in cellular viability assays on MCF7, MDA-MB-231, MDA-MB-468, and BT-549 breast cancer cells. Most importantly, in TNBC cells 17b and 17c displayed nanomolar IC50-values (380 nM - 970 nM) and were superior in their anti-cancer activity compared to their control compounds and combinations thereof.

Anticancer Drug Conjugates Incorporating Estrogen Receptor Ligands.

Hormone-dependent cancers, such as certain types of breast cancer are characterized by over-expression of estrogen receptors (ERs). Anticancer drug conjugates combining ER ligands with other classes of anticancer agents may not only benefit from dual action at both anti-cancer targets but also from selective delivery of cytotoxic agents to ER-positive tumor cells resulting in less toxicity and adverse effects. Moreover, they could also take advantage of overcoming resistance typical for anti-hormonal monotherapy such as tamoxifen. In this review, we discuss the design, structures and pharmacological effects of numerous series of drug conjugates containing ER ligands such as selective ER modulators (tamoxifen, 4-hydroxytamoxifen, endoxifen), selective ER degraders (ICI-164384) and ER agonists (estradiol) linked to diverse anti-cancer agents including histone-deacetylase inhibitors, DNA-alkylating agents, antimitotic agents and epidermal growth factor receptor inhibitors.

A multi-stage virtual screening of FDA-approved drugs reveals potential inhibitors of SARS-CoV-2 main protease.

Coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is an ongoing global health emergency. Repurposing of approved pharmaceutical drugs for COVID-19 treatment represents an attractive approach to quickly identify promising drug candidates. SARS-CoV-2 main protease (Mpro) is responsible for the maturation of viral functional proteins making it a key antiviral target. Based on the recently revealed crystal structures of SARS-CoV-2 Mpro, we herein describe a multi-stage virtual screening protocol including pharmacophore screening, molecular docking and protein-ligand interaction fingerprints (PLIF) post-docking filtration for efficient enrichment of potent SARS-CoV-2 Mpro inhibitors. Potential hits, along with a cocrystallized control were further studied via molecular dynamics. A 150-ns production trajectory was followed by RMSD, free energy calculation, and H-bond analysis for each compound. The applied virtual screening protocol led to identification of five FDA-approved drugs with promising binding modes to key subsites of the substrate-binding pocket of SARS-CoV-2 Mpro. The identified compounds belong to different pharmaceutical classes, including several protease inhibitors, antineoplastic agents and a natural flavonoid. The drug candidates discovered in this study present a potential extension of the recently reported SARS-CoV-2 Mpro inhibitors that have been identified using other virtual screening protocols and may be repurposed for COVID-19 treatment.

Dual PARP and RAD51 Inhibitory Drug Conjugates Show Synergistic and Selective Effects on Breast Cancer Cells.

The genetic principle of synthetic lethality has most successfully been exploited in therapies engaging Poly-ADP-ribose-polymerase (PARP) inhibitors to treat patients with homologous recombination (HR)-defective tumors. In this work, we went a step further following the idea of a local molecular cooperation and designed hybrid compounds M1-M3. The drug conjugates M1-M3 combine Olaparib, the first PARP inhibitor approved for clinical use, with Cpd 1, an inhibitor of RAD51 that blocks its HR functions and yet permits RAD51 nucleoprotein filament formation on single-stranded DNA. While in M2 and M3, the parental drugs are linked by -CO-(CH2)n-CO-spacers (n = 2 and 4, respectively), they are directly merged omitting the piperazine ring of Olaparib in M1. Monitoring anti-survival effects of M1-M3 in six breast cancer cell lines of different molecular subtypes showed that in each cell line, at least one of the drug conjugates decreased viability by one to two orders of magnitude compared with parental drugs. While triple-negative breast cancer (TNBC) cells with frequent BRCA1 pathway dysfunction were sensitive to spacer-linked hybrid compounds M1 and M2 regardless of their HR capacities, non-TNBC cells were responsive to the merged drug conjugate M1 only, suggesting different spatial requirements for dual inhibition in these two groups of cell lines. These results demonstrate that, depending on chemical linkage, dual PARP1-RAD51 inhibitory drugs can either sensitize non-TNBC and re-sensitize TNBC cells, or discriminate between these groups of cells.

Discovery of Novel CCR5 Ligands as Anticolorectal Cancer Agents by Sequential Virtual Screening.

C-C chemokine receptor type 5 (CCR5) is a member of the G protein-coupled receptor. CCR5 and its interaction with chemokine ligands have been crucial for understanding and tackling human immunodeficiency virus (HIV)-1 entry into target cells. In recent years, the change in CCR5 expression has been related to the progression of different cancer types. Patients treated with the CCR5 ligand, maraviroc (MVC), showed a deceleration in tumor development especially for metastatic colorectal cancer. Based on the crystal structure of CCR5, we herein describe a multistage virtual screening protocol including pharmacophore screening, molecular docking, and protein-ligand interaction fingerprint (PLIF) postdocking filtration for discovery of novel CCR5 ligands. The applied virtual screening protocol led to the identification of four hits with binding modes showing access to the major and minor pockets of the MVC binding site. Compounds 2-4 showed a decrease in cellular proliferation upon testing on the metastatic colorectal cancer cell line, SW620, displaying 12, 16, and 4 times higher potency compared to MVC, respectively. Compound 3 induced apoptosis by arresting cells in the G0/G1 phase of the cell cycle similar to MVC. Further in vitro assays showed compound 3 drastically decreasing the CCR5 expression and cellular migration 48 h post treatment, indicating its ability to inhibit metastatic activity in SW620 cells. The discovered hits represent potential leads for the development of novel classes of anticolorectal cancer agents targeting CCR5.

Pharmacological, Mechanistic, and Pharmacokinetic Assessment of Novel Melatonin-Tamoxifen Drug Conjugates as Breast Cancer Drugs.

Tamoxifen is used to prevent and treat estrogen receptor-positive (ER+) breast cancer (BC); however, its chronic use can increase uterine cancer risk and induce tamoxifen resistance. Novel melatonin-tamoxifen drug conjugates may be promising to treat BC and may help offset the adverse effects of tamoxifen usage alone due to the presence of melatonin. We synthesized and screened five drug conjugates (C2, C4, C5, C9, and C15 linked) for their effects on BC cell (MCF-7, tamoxifen-resistant MCF-7, mouse mammary carcinoma, MDA-MB-231, and BT-549) viability, migration, and binding affinity to melatonin receptor 1 (MT1R) and estrogen receptor 1 (ESR1). C4 and C5 demonstrated the most favorable pharmacological characteristics with respect to binding profiles (affinity for ESR1 and MT1R) and their potency/efficacy to inhibit BC cell viability and migration in four phenotypically diverse invasive ductal BC cell lines. C4 and C5 were further assessed for their actions against tamoxifen-resistant MCF-7 cells and a patient-derived xenograft triple-negative BC cell line (TU-BcX-4IC) and for their mechanisms of action using selective mitogen-activated protein kinase kinase MEK1/2, MEK5, and phosphoinositide 3-kinase (PI3K) inhibitors. C4 and C5 inhibited tamoxifen-resistant MCF-7 cells with equal potency (IC50 = 4-8 µM) and efficacy (∼90% inhibition of viability and migration) but demonstrated increased potency (IC50 = 80-211 µM) and efficacy (∼140% inhibition) to inhibit migration versus cell viability (IC50 = 181-304 mM; efficacy ∼80% inhibition) in TU-BcX-4IC cells. Unique pharmacokinetic profiles were observed, with C4 having greater bioavailability than C5. Further assessment of C4 and C5 demonstrates that they create novel pharmacophores within each BC cell that is context specific and involves MEK1/2/pERK1/2, MEK5/pERK5, PI3K, and nuclear factor κB. These melatonin-tamoxifen drug conjugates show promise as novel anticancer drugs and further preclinical and clinical evaluation is warranted.

O-linked melatonin dimers as bivalent ligands targeting dimeric melatonin receptors.

A series of dimeric melatonin analogues 3a-e obtained by connecting two melatonin molecules through the methoxy oxygen atoms with spacers spanning 16-24 atoms and the agomelatine dimer 7 were synthesized and characterized in 2-[125-I]-iodomelatonin binding assays, bioluminescence resonance energy transfer (BRET) experiments, and in functional cAMP and ß-arrestin recruitment assays at MT1 and MT2 receptors. The binding affinity of 3a-e generally increased with increasing linker length. Bivalent ligands 3a-e increased BRET signals of MT1 dimers up to 3-fold compared to the monomeric control ligand indicating the simultaneous binding of the two pharmacophores to dimeric receptors. Bivalent ligands 3c and 7 exhibited important changes in functional properties on the Gi/cAMP pathway but not on the ß-arrestin pathway compared to their monomeric counterparts. Interestingly, 3c (20 atoms spacer) shows inverse agonistic properties at MT2 on the Gi/cAMP pathway. In conclusion, these findings indicate that O-linked melatonin dimers are promising tools to develop signaling pathway-based bivalent melatonin receptor ligands.

Drug conjugates-an emerging approach to treat breast cancer.

Breast cancer treatment using a single drug is associated with a high failure rate due, in part, to the heterogeneity of drug response within individuals, nonspecific target action, drug toxicity, and/or development of resistance. Use of dual-drug therapies, including drug conjugates, may help overcome some of these roadblocks by more selective targeting of the cancer cell and by acting at multiple drug targets rather than one. Drug-conjugate approaches include linking drugs to antibodies (antibody-drug conjugates), radionuclides (radioimmunoconjugates), nanoparticles (nanoparticle-drug conjugates), or to other drugs (drug-drug conjugates). Although all of these conjugates might be designed as effective treatments against breast cancer, the focus of this review will be on drug-drug conjugates because of the increase in versatility of these types of drugs with respect to mode of action at the level of the cancer cell either by creating a novel pharmacophore or by increasing the potency and/or efficacy of the drugs' effects at their respective molecular targets. The development, synthesis, and pharmacological characteristics of drug-drug conjugates will be discussed in the context of breast cancer with the hope of enhancing drug efficacy and reducing toxicities to improve patient quality of life.

Discovery of Nanomolar Dengue and West Nile Virus Protease Inhibitors Containing a 4-Benzyloxyphenylglycine Residue.

The dengue virus (DENV) and West Nile Virus (WNV) NS2B-NS3 proteases are attractive targets for the development of dual-acting therapeutics against these arboviral pathogens. We present the synthesis and extensive biological evaluation of inhibitors that contain benzyl ethers of 4-hydroxyphenylglycine as non-natural peptidic building blocks synthesized via a copper-complex intermediate. A three-step optimization strategy, beginning with fragment growth of the C-terminal 4-hydroxyphenylglycine to the benzyloxy ether, followed by C- and N-terminal optimization, and finally fragment merging generated compounds with in vitro affinities in the low nanomolar range. The most promising derivative reached Ki values of 12 nM at the DENV-2 and 39 nM at the WNV proteases. Several of the newly discovered protease inhibitors yielded a significant reduction of dengue and West Nile virus titers in cell-based assays of virus replication, with an EC50 value of 3.4 µM at DENV-2 and 15.5 µM at WNV for the most active analogue.

MT1 and MT2 melatonin receptors: ligands, models, oligomers, and therapeutic potential.

Numerous physiological functions of the pineal gland hormone melatonin are mediated via activation of two G-protein-coupled receptors, MT1 and MT2. The melatonergic drugs on the market, ramelteon and agomelatine, as well as the most advanced drug candidates under clinical evaluation, tasimelteon and TIK-301, are high-affinity nonselective MT1/MT2 agonists. A great number of MT2-selective ligands and, more recently, several MT1-selective agents have been reported to date. Herein, we review recent advances in the field focusing on high-affinity agonists and antagonists and those displaying selectivity toward MT1 and MT2 receptors. Moreover, the existing models of MT1 and MT2 receptors as well as the current status in the emerging field of melatonin receptor oligomerization are critically discussed. In addition to the already existing indications, such as insomnia, circadian sleep disorders, and depression, new potential therapeutic applications of melatonergic ligands including cardiovascular regulation, appetite control, tumor growth inhibition, and neurodegenerative diseases are presented.

PPAR Gamma Activators: Off-Target Against Glioma Cell Migration and Brain Invasion.

Today, there is increasing evidence that PPARgamma agonists, including thiazolidinediones (TDZs) and nonthiazolidinediones, block the motility and invasiveness of glioma cells and other highly migratory tumor entities. However, the mechanism(s) by which PPARgamma activators mediate their antimigratory and anti-invasive properties remains elusive. This letter gives a short review on the debate and adds to the current knowledge by applying a PPARgamma inactive derivative of the TDZ troglitazone (Rezulin) which potently counteracts experimental glioma progression in a PPARgamma independent manner.