Improved Drug Resistance Profile Research Articles

Structure-based design, synthesis, and biological characterization of indolylarylsulfone derivatives as novel human immunodeficiency virus type 1 inhibitors with potent antiviral activities and favorable drug-like profiles.

In the current antiretroviral landscape, continuous efforts are still needed to search for novel chemotypes of human immunodeficiency virus type 1(HIV-1) inhibitors with improved drug resistance profiles and favorable drug-like properties. Herein, we report the design, synthesis, biological characterization, and druggability evaluation of a class of non-nucleoside reverse transcriptase inhibitors. Guided by the available crystallographic information, a series of novel indolylarylsulfone derivatives were rationally discovered via the substituent decorating strategy to fully explore the chemical space of the entrance channel. Among them, compound 11h bearing the cyano-substituted benzyl moiety proved to be the most effective inhibitor against HIV-1 wild-type and mutant strains (EC50 = 0.0039-0.338 μM), being far more potent than or comparable to etravirine and doravirine. Besides, 11h did not exhibit cytotoxicity at the maximum test concentration. Meanwhile, the binding target of 11h was further confirmed to be reverse transcriptase (IC50 = 0.055 μM). Preliminary structure-activity relationship were discussed to guide further optimization work. Molecular docking and dynamics simulation studies were investigated in detail to rationalize the biological evaluation results. Further drug-likeness assessment indicated that 11h possessed excellent physicochemical properties. Moreover, no apparent hERG blockade liability and cytochrome P450 inhibition were observed for 11h. Notably, 11h was characterized by favorable in vitro metabolic stability with moderate clearance rates and long half-lives in human plasma and liver microsomes. Overall, 11h holds great promise as an ideal Anti-HIV-1 lead compound due to its potent antiviral efficacy, low toxicity, and favorable drug-like profiles.

Discovery of 2,4,6-trisubstituted pyrimidine derivatives as novel potent HIV-1 NNRTIs by exploiting the tolerant region II of the NNIBP

The rapid emergence of drug resistance severely reduces the clinical response of human immunodeficiency virus-1 (HIV-1) to non-nucleoside reverse transcriptase inhibitors (NNRTIs). Herein, a series of 2,4,6-trisubstituted pyrimidine derivatives was designed and synthesized, with the aim to identify novel anti-HIV-1 agents with improved drug resistance profiles. The antiviral activity results demonstrated that all compounds showed excellent potency to wild-type (WT) HIV-1 strain (EC50 = 3.61–15.5 nM). Moreover, 13c was proved to be the most potent inhibitor against the whole tested viral panel, with EC50 ranging from 4.68 to 229 nM. In addition, 13c yielded moderate HIV-1 RT inhibition with IC50 value of 0.231 μM, which demonstrated it was a classical NNRTI. Molecular docking was further conducted to illustrate its binding mode with HIV-1 RT. These encouraging results indicated that 13c can be used as a lead compound for further study.

Design and optimization of piperidine-substituted thiophene[3,2-d]pyrimidine-based HIV-1 NNRTIs with improved drug resistance and pharmacokinetic profiles

HIV-1 reverse transcriptase (RT) has received great attention as an attractive therapeutic target for acquired immune deficiency syndrome (AIDS), but the inevitable drug resistance and side effects have always been major challenges faced by non-nucleoside reverse transcriptase inhibitors (NNRTIs). This work aimed to identify novel chemotypes of anti-HIV-1 agents with improved drug-resistance profiles, reduced toxicity, and excellent druggability. A series of diarylpyrimidine (DAPY) derivatives were prepared via structural modifications of the leads K-5a2 and 25a. Among them, 15a with dimethylphosphine oxide moiety showed the most prominent antiviral potency against all of the tested viral panel, being 1.6-fold (WT, EC50 = 1.75 nmol/L), 3.0-fold (L100I, EC50 = 2.84 nmol/L), 2.4-fold (K103N, EC50 = 1.27 nmol/L), 3.3-fold (Y181C, EC50 = 5.38 nmol/L), 2.9-fold (Y188L, EC50 = 7.96 nmol/L), 2.5-fold (E138K, EC50 = 4.28 nmol/L), 4.8-fold (F227L/V106A, EC50 = 3.76 nmol/L) and 5.3-fold (RES056, EC50 = 15.8 nmol/L) more effective than that of the marketed drug ETR. Molecular docking results illustrated the detailed interactions formed by compound 15a and WT, F227L/V106A, and RES056 RT. Moreover, 15a·HCl carried outstanding pharmacokinetic (t1/2 = 1.32 h, F = 40.8%) and safety profiles (LD50 > 2000 mg/kg), which demonstrated that 15a HCl is a potential anti-HIV-1 drug candidate.

Structure-based design of diarylpyrimidines and triarylpyrimidines as potent HIV-1 NNRTIs with improved metabolic stability and drug resistance profiles.

Non-nucleoside reverse transcriptase inhibitors (NNRTIs) are an important component of anti-acquired immunodeficiency syndrome treatment regimen. In the present work, with the previously reported compound K-16c as lead, a series of novel 2,4,5-trisubstituted pyrimidine derivatives were designed based on the cocrystal structure of K-16c/RT, with the aim to improve the anti-human immunodeficiency virus type-1 (HIV-1)activities and metabolic stability properties. Compound 11b1 exhibited the most potent antiviral activity against wild-type (WT) and a panel of single mutant HIV-1 strains (EC50 = 2.4-12.4 nM), being superior to or comparable to those of the approved drug etravirine. Meanwhile, 11b1 exhibited moderate cytotoxicity (CC50 = 4.96 μM) and high selectivity index (SI = 1189) toward HIV-1WTstrain. As for HIV-1 RT inhibition test, 11b1 possessed excellent inhibitory potency (IC50 = 0.04 μM) and confirmed its target was RT. Moreover, the molecular dynamics simulation was performed to elucidate the improved drug resistance profiles. Moreover, 11b1 was demonstrated with favorable safety profiles and pharmacokinetic properties in vivo, indicating that 11b1 is a potential anti-HIV-1 drug candidate worthy of further development.

Discovery of N-substituted oseltamivir derivatives as novel neuraminidase inhibitors with improved drug resistance profiles and favorable drug-like properties

To yield potent neuraminidase inhibitors with improved drug resistance and favorable drug-like properties, two series of novel oseltamivir derivatives targeting the 150-cavity of neuraminidase were designed, synthesized, and biologically evaluated. Among the synthesized compounds, the most potent compound 43b bearing 3-floro-4-cyclopentenylphenzyl moiety exhibited weaker or slightly improved inhibitory activity against wild-type neuraminidases (NAs) of H1N1, H5N1, and H5N8 compared to oseltamivir carboxylate (OSC). Encouragingly, 43b displayed 62.70- and 5.03-fold more potent activity than OSC against mutant NAs of H5N1–H274Y and H1N1–H274Y, respectively. In cellular antiviral assays, 43b exerted equivalent or more potent activities against H1N1, H5N1, and H5N8 compared to OSC with no significant cytotoxicity up to 200 μM. Notably, 43b displayed potent antiviral efficacy in the embryonated egg model, in which achieved a protective effect against H5N1 and H5N8 similar to OSC. Molecular docking studies were implemented to reveal the binding mode of 43b in the binding pocket. Moreover, 43b possessed improved physicochemical properties and ADMET properties compared to OSC by in silico prediction. Taken together, 43b appeared to be a promising lead compound for further investigation.

Abstract P246: Discovery and characterization of selective, FGFR1 sparing, inhibitors of FGFR2/3 oncogenic mutations for the treatment of cancers

Abstract Background: Targeting FGFR genetic alterations using small molecule inhibitors is a validated therapeutic strategy for urothelial carcinoma and cholangiocarcinoma. However, the current FDA-approved pan-FGFR inhibitors, erdafitinib and pemigatinib, are subject to FGFR1-mediated dose-limiting toxicities (e.g., hyperphosphatemia). These treatments necessitate a high rate of dose reductions, interruptions, and discontinuations, thereby potentially limiting efficacy. In addition, drug-resistant mutations (e.g., gatekeeper) in FGFR2 and FGFR3 genes rapidly emerge in patients treated with these drugs. Our research goals are to reveal the full spectrum of oncogenic FGFR2 and FGFR3 mutations that drive tumor growth and to discover an inhibitor that selectively targets these mutations together with FGFR2 and FGFR3 gene fusion and drug-resistance mutations, while minimizing FGFR1 activity and associated toxicities. We hypothesize that this will deliver an FGFR precision medicine with enhanced anti-tumor activity, an improved drug resistance profile, and broader mutational coverage. Methods: Applying the Mutation-Allostery-Pharmacology (MAP) platform technology developed by Black Diamond Therapeutics, we defined a spectrum of 34 allosteric FGFR2/3 oncogenic mutations, including over 28 previously uncharacterized mutations that we now show to be oncogenic. The MAP platform allowed us to further classify those mutations into functional clusters or families of mutations that can be targeted using a single compound. While located throughout the extracellular and kinase domains, we demonstrated how these functional clusters activate FGFR2 or FGFR3. Among the mechanisms identified, a functional cluster of mutations is activated due to disulfide-bond mediated dimerization. Results: Herein, we report the discovery of a series of orally available, selective FGFR2/3 inhibitors that 1) shows antiproliferative potency across all 34 mutations; 2) spares FGFR1-wild-type; 3) is active against gatekeeper mutations and 4) shows favorable selectivity versus a subset of closely related kinases in the human kinome. In addition to being potent against FGFR2 and FGFR3 primary mutations, we demonstrated that our FGFR1 sparing inhibitors retain potency against the most prevalent FGFR2 resistant mutations. When dosed orally, one example was well tolerated and exhibited dose-dependent PK/PD and anti-tumor efficacy and regression in several FGFR2 and FGFR3 driven xenograft models in mice. In addition, when dosed at efficacious doses, no FGFR1-mediated hyperphosphatemia was observed in these animals instead of the animals that were treated with pan FGFR inhibitors. Conclusion: Our data support the development of rationally designed selective inhibitors targeting a spectrum of FGFR2/3 mutations while sparing dose limiting FGFR1 activity. Citation Format: Etienne Dardenne, Fernando Padilla, Sara Rasmussen, Shao Ning Yang, Ahmet Mentes, Luisa Shin Ogawa, Anthony Trombino, Darlene Romashko, Maria Chevtsova, Shalabh Thakur, Elisabeth Buck, Christopher Roberts, Matthew Lucas, Tai-An Lin. Discovery and characterization of selective, FGFR1 sparing, inhibitors of FGFR2/3 oncogenic mutations for the treatment of cancers [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2021 Oct 7-10. Philadelphia (PA): AACR; Mol Cancer Ther 2021;20(12 Suppl):Abstract nr P246.

35MO Discovery and characterization of selective, FGFR1-sparing, inhibitors of FGFR2/3 oncogenic mutations for the treatment of cancers

Targeting FGFR genetic alterations using small molecule inhibitors is a validated therapeutic strategy for urothelial carcinoma and cholangiocarcinoma. However, the current FDA-approved pan-FGFR inhibitors, erdafitinib and pemigatinib, are subject to FGFR1-mediated dose-limiting toxicities (e.g., hyperphosphatemia). These treatments necessitate a high rate of dose reductions, interruptions, and discontinuations, thereby potentially limiting efficacy. In addition, drug-resistant mutations (e.g., gatekeeper) in FGFR2 and FGFR3 genes rapidly emerge in patients treated with these drugs. Our research goals are to reveal the full spectrum of oncogenic FGFR2 and FGFR3 mutations that drive tumor growth and to discover an inhibitor that selectively targets these mutations together with FGFR2 and FGFR3 gene fusion and drug-resistance mutations, while minimizing FGFR1 activity and associated toxicities. We hypothesize that this will deliver an FGFR precision medicine with enhanced anti-tumor activity, an improved drug resistance profile, and broader mutational coverage. Applying the Mutation-Allostery-Pharmacology (MAP) platform technology developed by Black Diamond Therapeutics, we define a spectrum of 20 allosteric FGFR2/3 oncogenic mutations, including 10 previously uncharacterized mutations that we now show to be oncogenic. We demonstrated how this mutation family is activated due to disulfide-bond mediated dimerization; hence we term these mutations locked-dimer (Lo-Di) FGFR oncogenes. Herein, we report the discovery of a series of orally available, selective Lo-Di-FGFR2/3 inhibitors that 1) shows antiproliferative potency across all 20 mutations; 2) spares FGFR1-wild-type; 3) is active against gatekeeper mutations and 4) shows favorable selectivity versus a subset of closely related kinases in the human kinome. When dosed orally, one example was well tolerated and exhibited dose-dependent PK/PD and anti-tumor efficacy and regression in the UM-UC-14 xenograft model in mice. Our data support the development of rationally designed selective inhibitors targeting a spectrum of FGFR2/3 mutations while sparing dose limiting FGFR1 activity.

Naphthoquinone-derivative as a synthetic compound to overcome the antibiotic resistance of methicillin-resistant S. aureus

The treatment of Staphylococcus aureus (S. aureus) infections has become more difficult due to the emergence of multidrug resistance in the bacteria. Here, we report the synthesis of a lawsone (2-hydroxy-1,4-naphthoquinone)-based compound as an antimicrobial agent against methicillin-resistant S. aureus (MRSA). A series of lawsone-derivative compounds were synthesized by means of tuning the lipophilicity of lawsone and screened for minimum inhibitory concentrations against MRSA to identify a candidate compound that possesses a potent antibacterial activity. The identified lawsone-derivative compound exhibited significantly improved drug resistance profiles against MRSA compared to conventional antibiotics. The therapeutic efficacy of the compound was validated using murine models of wound infection as well as non-lethal systemic infection induced by MRSA. Our study further revealed the multifaceted modes of action of the compound, mediated by three distinctive mechanisms: (1) cell membrane damage, (2) chelation of intracellular iron ions, and (3) generation of intracellular reactive oxygen species.

Structure-Based Bioisosterism Yields HIV-1 NNRTIs with Improved Drug-Resistance Profiles and Favorable Pharmacokinetic Properties.

The development of efficacious NNRTIs for AIDS therapy commonly encountered the rapid generation of drug-resistant mutations, which becomes a major impediment to effective anti-HIV treatment. Using a structure-based bioisosterism strategy, a series of piperidine-substituted thiophene[2,3-d]pyrimidine derivatives were designed and synthesized. Compound 9a yielded the greatest potency, exhibiting significantly better anti-HIV-1 activity than ETR against all of the tested NNRTI-resistant HIV-1 strains. In addition, the phenotypic (cross)resistance of 9a and other NRTIs to the different selected HIV-1 strains was evaluated. As expected, no phenotypic cross-resistance against the NRTIs (AZT and PMPA) was observed with the mutant 9ares strain. Furthermore, 9a was identified with improved solubility, lower CYP liability, and hERG inhibition. Remarkably, 9a exhibited optimal pharmacokinetic properties in rats (F = 37.06%) and safety in mice (LD50 > 2000 mg/kg), which highlights 9a as a promising anti-HIV-1 drug candidate.

Discovery of piperidine-substituted thiazolo[5,4-d]pyrimidine derivatives as potent and orally bioavailable HIV-1 non-nucleoside reverse transcriptase inhibitors

HIV-1 reverse transcriptase offers a key target for antiviral therapy. However, the rapid emergence of drug-resistant mutations in reverse transcriptase as well as the poor pharmacokinetic properties of HIV-1 non-nucleoside reverse transcriptase inhibitors (NNRTIs) limits their clinical use. Starting from a previous piperidine-substituted thiophene[3,2-d]pyrimidine compound (K-5a2), here we explore the chemical space around the thiophene ring located in the solvent-exposed regions of the NNRTI binding pocket in detail. Bioisosterism-based structural modification leads to the discovery of a number of compounds as potent in vitro reverse transcriptase inhibitors, providing improved drug resistance profiles compared to the listed drug Etravirine. Furthermore, 14a and 19a are identified as lead compounds with good solubility, appropriate ligand efficiency, and lower cytochrome P450 liability. Compound 19a exhibits useful in vivo pharmacokinetic properties in rat and safety in mice, suggesting that it may have the potential to be an effective drug candidate for treating AIDS.

Drug-like property-driven optimization of 4-substituted 1,5-diarylanilines as potent HIV-1 non-nucleoside reverse transcriptase inhibitors against rilpivirine-resistant mutant virus

On the basis of our prior structure-activity relationship (SAR) results, our current lead optimization of 1,5-diarylanilines (DAANs) focused on the 4-substituent (R1) on the central phenyl ring as a modifiable position related simultaneously to improved drug resistance profiles and drug-like properties. Newly synthesized p-cyanovinyl-DAANs (8a–8g) with different R1 side chains plus prior active p-cyanoethyl-DAANs (4a–4c) were evaluated not only for anti-HIV potency against both wild-type HIV virus and rilpivirine-resistant (E138K, E138K+M184I) viral replication, but also for multiple drug-like properties, including aqueous solubility, lipophilicity, and metabolic stability in human liver microsomes and human plasma. This study revealed that both ester and amide R1 substituents led to low nanomolar anti-HIV potency against wild-type and rilpivirine-resistant viral strains (E138K-resistance fold changes<3). The N-substituted amide-R1 side chains were superior to ester-R1 likely due to improved aqueous solubility, lipophilicity, and higher metabolic stability in vitro. Thus, three amide-DAANs 8e, 4a, and 4b were identified with high potency against wild-type and rilpivirine-resistant viral strains and multiple desirable drug-like properties.

Structural Modifications of Diarylpyrimidine-quinolone Hybrids as Potent HIV-1 NNRTIs with an Improved Drug Resistance Profile.

Earlier we reported the identification of diarylpyrimidine-quinolone hybrids as a new class of HIV-1 NNRTIs. A few of these hybrids displayed moderate inhibitory activity against wt HIV-1 replication at submicromolar level, however, all of them lacked inhibitory activity against the double mutant virus (K103N/Y181C), which is the most prevalent NNRTI resistant-associated double mutant observed in the clinic. In the present study, we designed and synthesized a new series of diarylpyrimidine-quinolone hybrids featuring a halogen group at C-6' position of quinolone ring. The biological results indicated that most of these hybrids could inhibit wt HIV-1 replication at nanomolar level ranging from 0.088 to 0.0096 μM. The most promising hybrid 5c displayed a significant EC50 value of 0.0096 μM against HIV-1 IIIB and of 0.98 μM against K103N/Y181C. Further docking studies revealed that these hybrids could be well located in the hydrophobic NNIBP of HIV-1 RT despite the bulky and polar properties of a quinolone 3-carboxylic acid scaffold in the molecules. These promising results suggested a high potential to further develop these hybrids as next-generation NNRTIs with improved antiviral efficacy and resistance profile.

Design, Synthesis, and Evaluation of Thiophene[3,2-d]pyrimidine Derivatives as HIV-1 Non-nucleoside Reverse Transcriptase Inhibitors with Significantly Improved Drug Resistance Profiles.

We designed and synthesized a series of human immunodeficiency virus type 1 (HIV-1) non-nucleoside reverse transcriptase inhibitors (NNRTIs) with a piperidine-substituted thiophene[3,2-d]pyrimidine scaffold, employing a strategy of structure-based molecular hybridization and substituent decorating. Most of the synthesized compounds exhibited broad-spectrum activity with low (single-digit) nanomolar EC50 values toward a panel of wild-type (WT), single-mutant, and double-mutant HIV-1 strains. Compound 27 was the most potent; compared with ETV, its antiviral efficacy was 3-fold greater against WT, 5-7-fold greater against Y181C, Y188L, E138K, and F227L+V106A, and nearly equipotent against L100I and K103N, though somewhat weaker against K103N+Y181C. Importantly, 27 has lower cytotoxicity (CC50 > 227 μM) and a huge selectivity index (SI) value (ratio of CC50/EC50) of >159101. 27 also showed favorable, drug-like pharmacokinetic and safety properties in rats in vivo. Molecular docking studies and the structure-activity relationships provide important clues for further molecular elaboration.

Using Hierarchical Virtual Screening To Combat Drug Resistance of the HIV-1 Protease.

Human immunodeficiency virus (HIV) protease inhibitors (PIs) are important components of highly active anti-retroviral therapy (HAART) that block the catalytic site of HIV protease, thus preventing maturation of the HIV virion. However, with two decades of PI prescriptions in clinical practice, drug-resistant HIV mutants have now been found for all of the PI drugs. Therefore, the continuous development of new PI drugs is crucial both to combat the existing drug-resistant HIV strains and to provide treatments for future patients. Here we purpose an HIV PI drug design strategy to select candidate PIs with binding energy distributions dominated by interactions with conserved protease residues in both wild-type and various drug-resistant mutants. On the basis of this strategy, we have constructed a virtual screening pipeline including combinatorial library construction, combinatorial docking, MM/GBSA-based rescoring, and reranking on the basis of the binding energy distribution. We have tested our strategy on lopinavir by modifying its two functional groups. From an initial 751 689 candidate molecules, 18 candidate inhibitors were selected using the pipeline for experimental validation. IC50 measurements and drug resistance predictions successfully identified two ligands with both HIV protease inhibitor activity and an improved drug resistance profile on 2382 HIV mutants. This study provides a proof of concept for the integration of MM/GBSA energy analysis and drug resistance information at the stage of virtual screening and sheds light on future HIV drug design and the use of virtual screening to combat drug resistance.

Design, synthesis, and biological evaluation of novel trifluoromethyl indoles as potent HIV-1 NNRTIs with an improved drug resistance profile.

A novel series of trifluoromethyl indole derivatives have been designed, synthesized and evaluated for anti-HIV-1 activities in MT-2 cells. The hydrophobic constant, acute toxicity, carcinogenicity and mutagenicity were predicted. Trifluoromethyl indoles 10i and 10k showed extremely promising activities against WT HIV-1 with IC50 values at the low nanomolar level, similar to efavirenz, better than nevirapine, and also possessed higher potency towards the drug-resistant mutant strain Y181C than nevirapine. Preliminary SAR and docking studies of detailed binding mode provided some insights for discovery of more potent NNRTIs.

Design, Synthesis, and Biological Evaluation of 1-[(2-Benzyloxyl/alkoxyl)methyl]-5-halo-6-aryluracils as Potent HIV-1 Non-nucleoside Reverse Transcriptase Inhibitors with an Improved Drug Resistance Profile

Because the emergence of drug-resistant mutants has limited the efficacy of non-nucleoside reverse transcriptase inhibitors (NNRTIs), it is essential to develop new antivirals with better drug resistance and pharmacokinetic profiles. Here we designed and synthesized a series of 1-[(2-benzyloxyl/alkoxyl)methyl]-5-halo-6-aryluracils, the HEPT analogues, and evaluated their biological activity using nevirapine and 18 (TNK-651) as reference compounds. Most of these compounds, especially 6b, 7b, 9b, 11b, and 7c, exhibited highly potent anti-HIV-1 activity against both wild-type and NNRTI-resistant HIV-1 strains. Compound 7b, which had the highest selectivity index (SI = 38 215), is more potent than nevirapine and 18. These results suggest that the introduction of a halogen at the C-5 position may contribute to the effectiveness of these compounds against RTI-resistant variants. In addition, meta substituents on the C-6 aromatic moiety could significantly enhance activity against NNRTI-resistant HIV-1 strains. These compounds can be further developed as next-generation NNRTIs with an improved antiviral efficacy and drug-resistance profile.

Cytotoxic esterified diterpenoid alkaloid derivatives with increased selectivity against a drug-resistant cancer cell line.

C-6 Esterifications of delpheline (1) were carried out to provide 20 new diterpenoid alkaloid derivatives (4-22, 24). Three natural alkaloids (1-3) and all synthesized compounds (4-25) were evaluated for cytotoxic activity against lung (A549), prostate (DU145), nasopharyngeal (KB), and vincristine-resistant nasopharyngeal (KB-VIN) cancer cell lines and interestingly, showed an improved drug resistance profile compared to paclitaxel. Particularly, 6-(4-fluoro-3-methylbenzoyl)delpheline (22) displayed 2.6-fold greater potency against KB-VIN cells compared with the parental non-drug resistant KB cells. 6-Acylation of 1 appears to be critical for producing cytotoxic activity in this alkaloid class and a means to provide promising new leads for further development into antitumor agents.

Structural Basis for the Improved Drug Resistance Profile of New Generation Benzophenone Non-Nucleoside HIV-1 Reverse Transcriptase Inhibitors

Owing to the emergence of resistant virus, next generation non-nucleoside HIV reverse transcriptase inhibitors (NNRTIs) with improved drug resistance profiles have been developed to treat HIV infection. Crystal structures of HIV-1 RT complexed with benzophenones optimized for inhibition of HIV mutants that were resistant to the prototype benzophenone GF128590 indicate factors contributing to the resilience of later compounds in the series (GW4511, GW678248). Meta-substituents on the benzophenone A-ring had the designed effect of inducing better contacts with the conserved W229 while reducing aromatic stacking interactions with the highly mutable Y181 side chain, which unexpectedly adopted a "down" position. Up to four main-chain hydrogen bonds to the inhibitor also appear significant in contributing to resilience. Structures of mutant RTs (K103N, V106A/Y181C) with benzophenones showed only small rearrangements of the NNRTIs relative to wild-type. Hence, adaptation to a mutated NNRTI pocket by inhibitor rearrangement appears less significant for benzophenones than other next-generation NNRTIs.

Cytotoxic calanquinone A from Calanthe arisanensis and its first total synthesis

Calanquinone A ( 1) was isolated from an EtOAc-soluble extract of Calanthe arisanensis through bioassay-guided fractionation. Its structure was identified by spectroscopic methods. Compound 1 showed potent cytotoxicity (EC 50 < 0.5 μg/mL) against lung (A549), prostate (PC-3 and DU145), colon (HCT-8), breast (MCF7), nasopharyngeal (KB), and vincristine-resistant nasopharyngeal (KB-VIN) cancer cell lines, and interestingly, showed an improved drug resistance profile compared to paclitaxel. The total synthesis of 1 was also achieved and is reported herein.

Relationship of Potency and Resilience to Drug Resistant Mutations for GW420867X Revealed by Crystal Structures of Inhibitor Complexes for Wild-Type, Leu100Ile, Lys101Glu, and Tyr188Cys Mutant HIV-1 Reverse Transcriptases

The selection of drug resistant viruses is a major problem in efforts to combat HIV and AIDS, hence, new compounds are required. We report crystal structures of wild-type and mutant HIV-1 RT with bound non-nucleoside (NNRTI) GW420867X, aimed at investigating the basis for its high potency and improved drug resistance profile compared to the first-generation drug nevirapine. GW420867X occupies a smaller volume than many NNRTIs, yet accesses key regions of the binding pocket. GW420867X has few contacts with Tyr188, hence, explaining the small effect of mutating this residue on inhibitor-binding potency. In a mutated NNRTI pocket, GW420867X either remains in a similar position compared to wild-type (RT(Leu100Ile) and RT(Tyr188Cys)) or rearranges within the pocket (RT(Lys101Glu)). For RT(Leu100Ile), GW420867X does not shift position, in spite of forming different side-chain contacts. The small bulk of GW420867X allows adaptation to a mutated NNRTI binding site by repositioning or readjustment of side-chain contacts with only small reductions in binding affinity.