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Probe Reports from the NIH Molecular Libraries Program [Internet]. Bethesda (MD): National Center for Biotechnology Information (US); 2010-.

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ML336: Development of Quinazolinone-Based Inhibitors Against Venezuelan Equine Encephalitis Virus (VEEV)

, , , , , , , , , , , , , and .

Author Information and Affiliations

Received: ; Last Update: November 7, 2013.

Alphaviruses like Venezuelan Equine Encephalitis Virus (VEEV) are enveloped, positive-sense, single stranded RNA viruses that are geographically widely distributed. They are arthropod-borne viruses that are known to cause rash, arthritis, encephalitis, and death in humans. Of the more than 30 alphavirus pathogens known, about a third contributes to human disease, and currently there are no FDA approved treatments available for any of them. A renewed interest to find effective therapeutic leads for development has emerged due to the lack of effective countermeasures for these pathogens, the increased incidence of their prevalence with global climate changes, and the ease with which they can and have been weaponized as biological threats. VEEV vaccines to date show insufficient efficacy or adverse side effects that limit their use, and disclosed literature compounds possess weak anti-VEEV potency and/or involve host-mediated mechanisms of action, contributing to off-target effects. The high throughput-screen of the MLSMR revealed a subset of scaffolds that inhibited a VEEV-induced cytopathic effect in the low micromolar range. Medicinal chemistry optimization resulted in the development of ML336, a first-in-class probe that inhibited a VEEV-induced cytopathic effect in three strains of the virus (TC-83, V3526, and Trinidad donkey) in the low nanomolar range without showing cytotoxicity (> 50 μM, selectivity index > 1500). Furthermore, ML336 dramatically reduced viral titer (> 7.2 log) below a 1 μM compound concentration and features a favorable in vitro pharmacokinetic profile which includes moderate blood-brain barrier permeability. Importantly, ML336 appears to target the VEEV non-structural protein 2 (nsP2) which is necessary for transcription and replication of viral RNA. This finding alone distinguishes ML336 from all other compounds described to date, and in combination with its overall profile, makes it an ideal candidate for further in vivo development.

Assigned Assay Grant #: 1 R03 MH087448-01A1

Screening Center & PI: Southern Research Biocontainment Specialized Screening Center, E.Lucile White

Chemistry Center & PI: University of Kansas Specialized Chemistry Center, Dr. Jeffrey Aubé

Assay Submitter & Institution: Dr. Donghoon Chung, University of Louisville

PubChem Summary Bioassay Identifier (AID): Summary AID 588723

Probe Structure & Characteristics

Image ml336f1

Table 1ML336 Data Summary

CID ML#Target NameVEEV TC-83 CPE IC50 (nM)

SID 144087340
AID 651734
VEEV V3526 CPE IC50 (nM)

SID 144087340
AID 651884
VEEV Wild Type** CPE IC50 (nM)

SID 144087340
AID 651874
Cytotoxicity and Alphavirus SelectivityVEEV TC-83 Plaque Assay at 5 μM, Virus Titer Reduction (log)
SID 144087340, AID 651886
VEEV Wild Type** Plaque Assay at 5 μM, Virus Titer Reduction (log)
SID 144087340, AID 651883
Anti-target Name(s)CC50 or EC50 (μM)
SID 144087340
VEEV TC-83 Fold Selective*VEEV V3526 Fold Selective*VEEV Wild type Fold Selective*
CID 71301451
ML336
Venezuelan equine encephalitis virus (VEEV)322041Mammalian cell toxicity, Vero76 cellsCC50 > 50
AID 65173
> 1563> 2500> 1219> 7.20No viral replication observed at 5 μM to 0.50 μM (lower limit of assay)
Chikungunya virus (alphavirus)EC50 > 50
AID 651738
> 1563> 2500> 1219
Respiratory Syncytial Virus (non-alphavirus)EC50 > 25
AID 651932
> 781> 1250> 610
*

Selectivity = anti-target IC50 or CC50 (mammalian toxicity or CHIKV or RSV)/VEEV strain CPE IC50

**

Wild type = Trinidad Donkey strain of VEEV virus

ML336 evaluated at multiple concentrations. Results were >7.2 log at 5 μM and 1 μM, and 5.8 log at 0.5 μM.

1. Recommendations for Scientific Use of the Probe

What limitations in current state of the art is the probe addressing? There are no specific inhibitors or therapeutic countermeasures for any alphavirus infection. All compounds with some reported degree of VEEV activity are derived from other viral applications. Importantly, their mechanisms of action are dependent on inhibition of cellular metabolism, which is not selective for the virus and thus, can be potentially toxic to the host. Moreover most are weakly efficacious at best, hence rendering them unsatisfactory as starting points for development as potential alphavirus therapeutics. We have shown that probe ML336 potently inhibits a VEEV-induced cytopathic effect in three strains of the virus (TC-83, V3526, and wild type Trinidad donkey) in the low nanomolar range without showing cytotoxicity (> 50 μM). Furthermore, ML336 dramatically reduced viral titers below a 1 μM compound concentration and features a favorable in vitro pharmacokinetic profile which includes moderate blood-brain barrier permeability. Importantly, ML336 appears to target the non-structural protein 2 (nsP2) which is necessary for transcription and replication of viral RNA. This finding alone distinguishes ML336 from all other compounds described to date, and in combination with its overall profile, makes it an ideal candidate for further in vivo development.

What will the probe be used for? Probe ML336 and its analogs will be used primarily as anti-VEEV lead compounds with which further in vivo lead optimization work will be done, with the ultimate goal of delivering viable VEEV antiviral drug candidates. The compounds will be assessed for efficacy against serotypes of VEEV, other alphaviruses such as WEEV and EEEV, and they will be used as a platform to develop a PET imaging agent to track how effectively the probe penetrates and concentrates in infected brain tissue. The probe will also be used for advanced mechanism of action studies aimed at supporting our preliminary findings that the probe targets viral nsP2.

Who in the research community will use the probe? The lack of effective treatments for alphavirus infection, coupled with the historical weaponization of VEEV as a bioterrorism agent, makes the development of efficacious, safe and readily available antiviral leads for VEEV an interest to national security and protection of military personnel. The Department of Defense has sponsored repeated initiatives that specifically address the need for VEEV antivirals and agents effective against other alphaviruses (see solicitation: CBO-ALPHA-01 and http://globalbiodefense.com/2012/03/20/dod-seeks-new-drug-for-alphaviruses/). Effective VEEV leads will be used as tools to elucidate mechanisms of action and provide insight into the alphavirus life cycle. ML336 is a first in class VEEV inhibitor with a unique mechanism of action targeting viral nsP2 and it possesses an attractive physiochemical and pharmacokinetic profile. As such, probe ML336 will be of broad interest to the antiviral community as a standard point of reference for future leads and development.

What is the relevant biology to which the probe can be applied? There are more than 30 alphavirus pathogens known, about a third of these contribute to human disease, and currently there are no FDA approved treatments available for any of them. Alphavirus infections, spread mostly by mosquitoes, can enter the CNS where they grow within neurons, resulting in degradation and acute inflammation in brain tissues, or encephalitis, which can lead to death. Vaccines to date show insufficient efficacy or adverse side effects that limit their use, and disclosed literature compounds possess weak anti-VEEV potency and/or involve host-mediated mechanisms of action, contributing to off-target effects. Importantly, ML336 appears to specifically target the viral non-structural protein 2 (nsP2) which is necessary for transcription and replication of viral RNA which makes it a first-in-class probe. ML336 has a virus-specific mechanism of action, shows in vitro blood brain barrier (BBB) permeability, maintains cell viability by potently inhibiting VEEV infection and reduces viral titer at low concentrations of compound without inducing toxicity. ML336 and its analogs can be fluorinated without significantly altering the activity profile and as such, the probe is a suitable scaffold for incorporation of an 18F tracer for positron emission tomography (PET) for imaging of the real time bioavailability and localization of BBB penetrant anti-VEEV therapeutics.

2. Materials and Methods

2.1. Assays

The details of the primary HTS and additional assays can be found in the “Assay Description” section in the PubChem BioAssay view under the AIDs as listed (Table 2). Additionally the details for the primary HTS are provided in the Appendix at the end of this probe report.

Table 2. Summary of assays, listed by title and AID, used for the development of ML336.

Table 2

Summary of assays, listed by title and AID, used for the development of ML336.

2.2. Probe Chemical Characterization

A. Probe chemical name, structure and physiochemical data

The IUPAC name of the probe ML336 is (E)-2-((1,4-dimethylpiperazin-2-ylidene)amino)-5-nitro-N-phenylbenzamide. The batch prepared and submitted to the MLSMR is archived as SID 144087340, corresponding to CID 71301451.

Image ml336f2

B. Structure Verification and Purity: 1H NMR, 13C NMR, LCMS, and HRMS Data

Proton and carbon NMR data for ML336/ SID 144087340/ CID 71301451: Detailed analytical methods and instrumentation are described in Section 2.3, entitled “Probe Preparation” under general experimental and analytical details. The numerical experimental proton and carbon data are represented below for SID 152199106. The corresponding NMR data for SID 144087340 (a separate lot of ML336) was obtained and determined to match what is described for SID 152199106. The experimental proton and carbon spectra are included for reference (Appendix, Figures A6A and A6B, respectively).

Figure A6B. 13CNMR spectrum for ML336, SID 152199106, CID 71301451.

Figure A6B

13CNMR spectrum for ML336, SID 152199106, CID 71301451.

Proton NMR Data for ML336/ SID 144087340/ CID 7130145:1H NMR (500 MHz, CDCl3) δ 10.99 (s, 1H), 9.15 (d, J = 2.8 Hz, 1H), 8.15 (dd, J = 8.8, 2.8 Hz, 1H), 7.65 – 7.60 (m, 2H), 7.38 – 7.33 (m, 2H), 7.12 (tt, J = 7.3, 1.2 Hz, 1H), 6.80 (d, J = 8.8 Hz, 1H), 3.47 (t, J = 5.7 Hz, 2H), 3.28 (s, 3H), 3.13 (s, 2H), 2.69 (t, J = 5.7 Hz, 2H), 2.26 (s, 3H).

Carbon NMR Data for ML336/ SID 144087340/ CID 71301451:13C NMR (126 MHz, CDCl3) δ 162.63, 156.42, 153.97, 142.79, 138.19, 129.09, 127.64, 126.35, 126.16, 124.19, 123.75, 120.19, 55.12, 51.82, 49.66, 45.27, 36.88.

LCMS and HRMS Data for ML336, SID 144087340/ CID 71301451: Detailed analytical methods and instrumentation are described in section 2.3, entitled “Probe Preparation” under general experimental and analytical details. The numerical experimental LCMS and HRMS data are represented as follows:

For SID 152199106: LCMS retention time: 3.206 min. LCMS purity at 214 nm: 99.2%. HRMS m/z calculated for C19H22N5O3 [M++H] 368.1723, found 368.1718. The experimental HRMS and LCMS spectra are included for reference (Appendix, Figure A6C and A6D, respectively).

Figure A6C. High resolution MS for ML336, SID 152199106, CID 71301451.

Figure A6C

High resolution MS for ML336, SID 152199106, CID 71301451.

Figure A6D. LCMS purity data at 214 nM for ML336, SID 152199106, CID 71301451.

Figure A6D

LCMS purity data at 214 nM for ML336, SID 152199106, CID 71301451.

For SID 144087340: LCMS retention time: 3.213 min. LCMS purity at 214 nm: 96.5%. HRMS: m/z calculated for C19H22N5O3 [M++H] 368.1723, found 368.1729. The experimental HRMS and LCMS spectra are included for reference (Appendix, Figure A6E and A6F, respectively).

Figure A6E. High resolution MS for ML336, SID 144087340, CID 71301451.

Figure A6E

High resolution MS for ML336, SID 144087340, CID 71301451.

Figure A6F. LCMS purity data at 214 nM for ML336, SID 144087340, CID 71301451.

Figure A6F

LCMS purity data at 214 nM for ML336, SID 144087340, CID 71301451.

If available from a vendor, please provide details. This probe is not yet commercially available, as it was designed and prepared as an original analog for this project. A 20 mg sample of ML336 synthesized at the KUSCC has been deposited in the MLSMR; however, the compound is also available free of charge from the KUSCC.1

C. Solubility

Aqueous solubility2 was measured in phosphate buffered saline (PBS) at room temperature (23 °C). PBS by definition is 137 mM NaCl, 2.7 mM KCl, 10 mM sodium phosphate dibasic, 2 mM potassium phosphate monobasic and a pH of 7.4. Probe ML336 (SID 144087340, CID 71301451) was found to have a solubility measurement of 40.4 μg/mL, or 110.0 μM, under these conditions. Solubility in the TC-83 VEEV CPE assay medium, consisting of high glucose DMEM (Dulbecco's Modified Eagle's Medium) with 10% FBS and 1× Pen/Strep, was also assessed. Under these conditions, ML336 solubility was lower than that found in PBS, with a value of 13.1 μg/mL, or 35.7 μM; however, this concentration is well above (∼ 1100-fold) the ML336 IC50 observed in this CPE assay.

D. Stability

Chemical Stability: ML336 was evaluated for susceptibility to nucleophilic addition and formation of conjugates by treatment with dithiothreitol (DTT). Figure 1 represents the time course experiment with ML336 under various conditions. ML336 was dissolved at 10 μM in PBS at pH 7.4 (1% DMSO) and independently incubated at room temperature with no nucleophile present or 50 μM dithiothreitol (DTT). The test reactions were sampled every hour for eight hours and analyzed by LCMS. The analytical LCMS system utilized for the analysis was a Waters Acquity system with UV-detection and mass-detection (Waters LCT Premier). The analytical method conditions included a Waters Acquity HSS T3 C18 column (2.1 × 50mm, 1.8 μm) and elution with a linear gradient of 1% water to 100% CH3CN at 0.6 mL/min flow rate. Peaks on the 214 nm chromatographs were integrated using the Waters OpenLynx software. Absolute areas under the curve were compared at each time point to determine relative percent parent remaining. The masses of potential adducts and dimers of ML336 were searched for in the final samples to determine if any detectable adduct formed or dimerization had occurred. In the case of ML336, no adducts were detected at any time point using LCMS detection. All samples were prepared in duplicate. Ethacrynic acid, a known Michael acceptor, was used as a positive control.3

Figure 1. Chemical stability of ML336 over 8 h in the presence of a 5-fold concentration of dithiothreitol.

Figure 1

Chemical stability of ML336 over 8 h in the presence of a 5-fold concentration of dithiothreitol.

Table 3 summarizes the percent remaining of ML336 at the endpoints of each run in each experiment. The average amount of ML336 remaining after 8h when no nucleophile was added was 93.9%, and when 5X DTT was added, nearly 99% of parent ML336 remained after the same time period, indicating that ML336 was not generally susceptible to degradation or adduct formation in the presence of a thiol-based nucleophile.3

Table 3. Percent of ML336 remaining at the conclusion of the experiment (8h).

Table 3

Percent of ML336 remaining at the conclusion of the experiment (8h).

Aqueous Stability: Figure 2 represents the time course experiment with ML336 under various aqueous stability conditions. ML336 was dissolved at 10 μM in PBS at pH 7.4 (1% DMSO) or dissolved at 10 μM in 50% PBS/50% acetonitrile at pH 7.4 (1% DMSO). The samples were evaluated over 14 timepoints (0,1, 2, 3, 4, 5, 6, 7, 8, 16, 24, 32, 40, and 48 h) and analyzed by LCMS. The analytical LCMS system utilized for the analysis was a Waters Acquity system with UV-detection and mass-detection (Waters LCT Premier). The analytical method conditions included a Waters Acquity HSS T3 C18 column (2.1 × 50mm, 1.8 μm) and elution with a linear gradient of 1% water to 100% CH3CN at 0.6 mL/min flow rate. Peaks on the 214 nm chromatographs were integrated using the Waters OpenLynx software. Absolute areas under the curve were compared at each time point to determine relative percent parent remaining.3

Figure 2. Aqueous stability of ML336 over 48 h in PBS or PBS/acetonitrile.

Figure 2

Aqueous stability of ML336 over 48 h in PBS or PBS/acetonitrile.

In PBS, ML336 showed and average 82.93% remaining after 48h; however, no other mass peaks were observed. In order to account for precipitation/solubility effects, ML336 was also evaluated in 50/50 PBS:acetonitrile and was shown to have an average of 95.89% remaining after 48 h (Table 4).3

Table 4. Percent of ML336 remaining at the conclusion of the experiment (48h).

Table 4

Percent of ML336 remaining at the conclusion of the experiment (48h).

2.3. Probe Preparation

General experimental and analytical details:1H and 13C NMR spectra were recorded on a Bruker AM 400 spectrometer (operating at 400 and 101 MHz respectively) or a Bruker AVIII spectrometer (operating at 500 and 126 MHz respectively) in CDCl3 with 0.03% TMS as an internal standard or DMSO-d6. The chemical shifts (δ) reported are given in parts per million (ppm) and the coupling constants (J) are in Hertz (Hz). The spin multiplicities are reported as s = singlet, bs = broad singlet, d = doublet, t = triplet, q = quartet, dd = doublet of doublet and m = multiplet. The LCMS analysis was performed on an Agilent 1200 RRL chromatograph with photodiode array UV detection and an Agilent 6224 TOF mass spectrometer. The chromatographic method utilized the following parameters: a Waters Acquity BEH C-18 2.1 × 50mm, 1.7 um column; UV detection wavelength = 214 nm; flow rate = 0.4ml/min; gradient = 5 - 100% acetonitrile over 3 minutes with a hold of 0.8 minutes at 100% acetonitrile; the aqueous mobile phase contained 0.15% ammonium hydroxide (v/v). The mass spectrometer utilized the following parameters: an Agilent multimode source which simultaneously acquires ESI+/APCI+; a reference mass solution consisting of purine and hexakis(1H, 1H, 3H-tetrafluoropropoxy) phosphazine; and a make-up solvent of 90:10:0.1 MeOH:Water:Formic Acid which was introduced to the LC flow prior to the source to assist ionization. Melting points were determined on a Stanford Research Systems OptiMelt apparatus.

Probe ML336 was prepared by the route depicted in Figure 3. Anthranilic acid 1 was treated with 2-chloroacetyl chloride in the presence of triethylamine to afford 2-(chloromethyl)benzoxazinone 2. Dehydrative amidation was carried out by treating 2 with aniline and POCl3.4 The resulting 2-(chloromethyl)phenylquinazolinone 3 was aminated with mono-BOC-protected tert-butyl methyl(2-(methylamino)ethyl)carbamate to provide 4 which was subsequently deprotected with TFA to afford ML336 in 11% overall yield over four steps.5 This process has been used to prepare ML336 on a 260 mg scale.

Figure 3. Synthetic scheme for preparation of ML336.

Figure 3

Synthetic scheme for preparation of ML336.

Detailed protocols used for the assembly of ML336 are as follows:

Image ml336f6

2-(chloromethyl)-6-nitro-4H-benzo[d][1,3]oxazin-4-one. Following a previously reported procedure,4 2-amino-5-nitro-benzoic acid (6.718 g, 36.9 mmol, 1 eq) was placed under nitrogen and dissolved in CH2Cl2 (100 mL). After addition of triethylamine (5.9 mL, 42.3 mmol, 1.15 eq), the mixture was lowered to 0 °C in an ice bath and a solution of chloroacetyl chloride (3.2 mL, 40.2 mmol, 1.1 eq) in CH2Cl2 (50 mL) was slowly added. The reaction mixture was stirred at 0 °C for 1 hour, then at rt for 1 additional hour. The solvent was removed in vacuo and water was added to the remaining solid. The solid was filtered and rinsed with water (3 × 20 mL), followed by 5% Et2O/Hexanes (3 × 30 mL) to give 2-(chloromethyl)-6-nitro-4H-benzo[d][1,3]oxazin-4-one (8.87 g, 100%) along with residual triethylamine as a pale, yellow solid. The product was used in the following step without further purification. 1H NMR (400 MHz, acetone-d6) δ 8.96 – 8.91 (m, 2H), 8.48 (dd, J = 9.3, 2.8 Hz, 1H), 4.44 (s, 2H).

Image ml336f7

2-(chloromethyl)-6-nitro-3-phenylquinazolin-4(3H)-one. To a microwave vial was added 2-(chloromethyl)-6-nitro-4H-benzo[d][1,3]oxazin-4-one (1.47 g, 6.12 mmol, 1 eq) under Ar, and the solid was dissolved in acetonitrile (13 mL). Phosphorus oxychloride (1.15 mL, 12.34 mmol, 2 eq) was added, followed by the addition of solution of aniline (0.73 mL, 8.00 mmol, 1.3 eq) in acetonitrile (4 mL). The mixture was heated in a MW reactor at 150 °C for 15 min. The reaction mixture was transferred to a larger flask and slowly quenched with saturated aq. NaHCO3 (20 mL). The precipitate was filtered and rinsed with water (3 × 20 mL) to give 2-(chloromethyl)-6-nitro-3-phenylquinazolin-4(3H)-one (1.24 g, 64%) as a burnt-orange solid. 1H NMR (400 MHz, CDCl3) δ 9.13 (d, J = 2.6 Hz, 1H), 8.59 (dd, J = 8.9, 2.6 Hz, 1H), 7.91 (d, J = 9.0 Hz, 1H), 7.65 – 7.58 (m, 3H), 7.39 – 7.35 (m, 2H), 4.28 (s, 2H).

Image ml336f8

tert-butyl methyl(2-(methyl((6-nitro-4-oxo-3-phenyl-3,4-dihydroquinazolin-2-yl)methyl)amino)ethyl)carbamate. Following a previously reported procedure,5 2-(chloromethyl)-6-nitro-3-phenylquinazolin-4(3H)-one (1.40 g, 4.43 mmol, 1 eq) was dissolved in acetonitrile (18 mL). Potassium carbonate (1.226 g, 8.87 mmol, 2 eq), tert-butyl methyl(2-(methylamino)ethyl)carbamate (ChemBridge, 1.18 g, 6.25 mmol, 1.4 eq), and potassium iodide (0.280 g, 1.687 mmol, 0.4 eq) were added sequentially, and the mixture was heated in a MW reactor at 80 °C for 5 min. The crude reaction mixture was adsorbed onto Celite®, and the product was purified (2×) by flash chromatography (CombiFlash, 40 g silica, 0-10% MeOH/CH2Cl2, followed by CombiFlash, 80 g silica, 0-80% EtOAc/Hexanes) to give tert-butyl methyl(2-(methyl((6-nitro-4-oxo-3-phenyl-3,4-dihydroquinazolin-2-yl)methyl)amino)ethyl)carbamate (0.72 g, 35%) as a pale orange solid. 1H NMR (400 MHz, CDCl3) δ 9.13 (d, J = 2.6 Hz, 1H), 8.56 (dd, J = 9.0, 2.7 Hz, 1H), 7.89 (d, J = 9.0 Hz, 1H), 7.60 - 7.52 (m, 3H), 7.32 – 7.27 (m, 2H), 3.36 (s, 2H), 3.22 - 3.06 (m, 2H), 2.75 (br s, 3H), 2.48 (br s, 2H), 2.20 (s, 3H), 1.39 (br s, 9H).

Image ml336f9

PROBE ML336: (E)-2-((1,4-dimethylpiperazin-2-ylidene)amino)-5-nitro-N-phenylbenzamide. To a stirred solution of tert-butyl methyl(2-(methyl((6-nitro-4-oxo-3-phenyl-3,4-dihydroquinazolin-2-yl)methyl)amino)ethyl)carbamate (678 mg, 1.45 mmol) in CH2Cl2 (20 mL), TFA (9.5 mL, 124 mmol) was slowly added, and the resulting mixture was stirred at rt for 45 min. Water (40 mL) and CH2Cl2 (40 mL) were then added, and the mixture was adjusted to pH 10 using saturated aq. Na2CO3 (40 mL). The organic phase was separated and the aqueous layer was extracted with CH2Cl2 (2 × 40 mL). The combined organic phase was concentrated and purified by flash chromatography (CombiFlash, 40 g silica, 0-5% MeOH/ CH2Cl2) to give (E)-2-((1,4-dimethylpiperazin-2-ylidene)amino)-5-nitro-N-phenylbenzamide (265 mg, 49%) as a pale yellow solid. 1H NMR (500 MHz, CDCl3) δ 10.99 (s, 1H), 9.15 (d, J = 2.8 Hz, 1H), 8.15 (dd, J = 8.8, 2.8 Hz, 1H), 7.65 – 7.60 (m, 2H), 7.38 – 7.33 (m, 2H), 7.12 (tt, J = 7.3, 1.2 Hz, 1H), 6.80 (d, J = 8.8 Hz, 1H), 3.47 (t, J = 5.7 Hz, 2H), 3.28 (s, 3H), 3.13 (s, 2H), 2.69 (t, J = 5.7 Hz, 2H), 2.26 (s, 3H). 13C NMR (126 MHz, CDCl3) δ 162.63, 156.42, 153.97, 142.79, 138.19, 129.09, 127.64, 126.35, 126.16, 124.19, 123.75, 120.19, 55.12, 51.82, 49.66, 45.27, 36.88. LCMS retention time: 3.206 min, purity at 214 nm = 99.2%. HRMS m/z calculated for C19H22N5O3 [M++H] 368.1723, found 368.1718. Pale yellow needles, mp 168-173 °C (recrystallized from CH2Cl2).

3. Results

3.1. Dose Response Curves for Probe

Figure 3. Each data point represents the mean of % cell viability from triplicate runs.

Figure 3Each data point represents the mean of % cell viability from triplicate runs

Dose response curve and IC50 were generated using the Four Parameter Logistic Model or Sigmoidal Dose-Response model. A. Fourteen point CPE assay dose response curve for ML336 using TC-83 VEEV strain. B. CPE assay dose response curves for ML336 using wild type Trinidad donkey VEEV strain (triangles), V3526 VEEV strain (circles), and Chikungunya virus (squares)

3.2. Cellular Activity

All of the assays utilized in this project were cell-based (see Table 2, section 2.1). The probe and many analogs show potent inhibition of a VEEV-induced cytopathic effect and dramatic attenuation of viral turnover at sub- to low micromolar concentrations in cellular titer reduction assays. Cytotoxic effects were not observed for the series. As the mechanism of action appears to target the viral nsP2, ML336 and its analogs must penetrate host cells to engage cytoplasmic targets involved in viral replication.

3.3. Profiling Assays

Profiling against host targets. Probe ML336 was submitted to Eurofins PanLabs (formerly Ricerca Biosciences) to evaluate it in radioligand binding assays against a panel of 67 GPCRs, ion channels and transporters at a single concentration of 10 μM, each in duplicate. ML336 inhibited the human norepinephrine transporter with 91% inhibition at 10 μM, and an IC50 determination has been ordered and will be reported in due course. With the exception of this one target in the panel, inhibition was not observed above 36%. Norepinephrine inhibition (or reuptake inhibitors) is associated with treatment of depression, attention deficit hyperactivity disorder (ADHD), as well as other brain-related disorders. Given that ML336 is blood-brain barrier penetrant and has potential in the development as a PET imaging agent, the activity against the norepinephrine transporter (and notable lack of inhibition on dopamine and seratonin transporters) may indicate other therapeutic significance. For the full report, see Appendix.

NCI-60 panel. Probe ML336 was submitted to the NCI-60 panel for anti-cancer profiling. The NCI looks for one of two scenarios when evaluating a test compound at a single dose: (A) at least 8 cell lines with a growth percent of 40 or less (at least 60% inhibition), or (b) very specific and maybe strong inhibition of only a few cell lines. At a single dose of ML336 at 10 μM concentration, neither of these criteria was met to warrant confirmation in the standard, follow-up dose response assay. For the full report, see Appendix.

4. Discussion

4.1. Comparison to existing art and how the new probe is an improvement

Prior Art Overview: A number of compounds were identified from patent and literature sources with reported VEEV inhibitory activity (Figure 4, Table 5); however, closer inspection of the data and/or testing in the CPE assay and considering their dependency on host mediated mechanisms of action revealed these compounds were severely limited and not particularly relevant given the remarkable results seen with ML336.

Figure 4. Structures for which VEEV activity is reported.

Figure 4

Structures for which VEEV activity is reported.

Table 5. Data and liabilities of compounds with reported VEEV activity.

Table 5

Data and liabilities of compounds with reported VEEV activity.

The reported compounds are either weakly inhibitory against VEEV and/or do not act selectively on viral components. The interaction of these compounds via host mechanisms can lead to toxicity and was an undesirable characteristic for a new probe. Ribavirin (5) and carbodine (6) are nucleoside anti-metabolite prodrugs with notable clinical toxicities and are not specific in their mechanism of action to viral targets. For example, ribavirin has a broad in vitro inhibitory activity against RNA viruses. The activities include 1) depleting the cellular GTP pool (IMPDH inhibitor), 2) increasing mutations in the viral genome, and 3) inhibiting the GTP capping enzyme. Direct, antiviral activity for ribavirin6 against Sindbis virus (another alphavirus) has been disclosed, but inhibitory activity for VEEV has not yet been reported. Our internal assessment of ribavirin against VEEV in a CPE assay showed an IC50 of 126 μM. Carbodine (6) has been shown to have in vitro activity, but has associated toxicity and is only moderately efficacious in vivo.7 Urea VX-497 (7) is a potent, reversible uncompetitive IMP dehydrogenase (IMPDH) inhibitor with modest VEEV activity.8 IMPDH catalyzes an essential step in the de novo biosynthesis of guanine nucleotides, and as such, VX-497 is known to target cellular processes.

The quinazolinone structure (8) had a reported VEEV CPE IC50 of 16.7 μM, and importantly, it is the most closely related structurally to selected chemotypes for our investigation.9 The KU SCC synthesized the compound for assessment in our internal CPE assay; however, we found the IC50 for this compound to be > 25 μM. Completed SAR studies for our quinazolinone series leading to ML336 do not support that quinazolinone (8) should be active for VEEV.

Thienylpyrrole (9) is reported to inhibit WEEV viral replication with an IC50 = 9.3 μM.10 VEEV inhibition is referred to (< 100 μM) for the compound class but is not explicitly reported for any one compound. To dispel ambiguity, the KU SCC synthesized this lead compound and assessed it in our internal CPE assay, corroborating the finding with a VEEV IC50 > 25 μM.

Antioxidant 80 (10) is a broad spectrum antiviral agent11 due to its antioxidant activity, and it has notable CYP450 (2C9, 2C19) inhibition to the tune of about 3 μM.12 This compound was purchased and purified prior to submitting to the CPE assay, which resulted in a VEEV IC50 of > 50 μM. Didemnin (11) was reported in Pubchem13 as an active compound for a VEEV screen; however, it is a large cyclic peptide and does not represent prior art against which ML336, a small molecule, should be compared. Lastly, BIOder (12) is a recently disclosed compound14 (April 2012) that was reported during the course of our own project investigation and should not be considered prior art according to NIH; however, it is worth noting that BIOder inhibited VEEV via the host protein GSK-3β and was only partially efficacious in protecting mice from succumbing to VEEV infection. Moreover, BIOder has significant structural liabilities such as the presence of a diazodiimine and the electrophilic character of the dimeric core that are a cause for concern.

In summary, many of the compounds with disclosed anti-VEEV activity are weakly potent against VEEV, and when four selected compounds were assessed in an internal TC-83 CPE assay, we found them to have CPE IC50 values > 25 μM. Of the small molecule prior art compounds disclosed, quinazolinone compound 8 (CID 13182904) and thienylpyrrole 9 (CID 3240671) do not have described mechanisms of action and they have TC-83 CPE IC50 values > 25 μM. The depsipeptide didemnin 11 (CID 44287859) also has an unknown mechanism of action, but is not a small molecule against which ML336 can be compared. Moreover, didemnin is exceedingly cytotoxic which led to it being dropped from clinical evaluation.15 The remaining compounds (carbodine 6, VX-497 7, and recently disclosed BIOder 12) have mechanisms of action that involve host cellular targets. ML336 is a first-in-class probe that represents a significant improvement over the prior art landscape in terms of CPE nanomolar potency (∼ 16-fold more potent than BIOder), lack of notable cytotoxicity (> 50 μM in Vero 76 cells), ability to reduce VEEV viral titer by more than 7.2 log at 1 μM, and according to mechanistic data, ML336 appears to inhibit VEEV replication by means of viral nsP2 interference and not host-mediated targets.

5. References

1.
Contact the KU SCC for more information: http://www​.scc.ku.edu/contact.shtml
2.
Data provided by Layton Smith's lab, Arianna Mangravita-Novo, Sanford Burnham Institute
3.
Data provided by University of Kansas Analytical Chemistry Core, Specialized Chhemistry Center, Patrick Porubsky
4.
Compounds and compositions that cause non-apoptotic cell death and uses thereof. B. Stockwell US20080299076 A1.
5.
Acharyulu PVR, Dubey PK, Prasada Reddy PVV, Suresh T. Synthesis of Novel New 2-(2-(4-((3,4-Dihydro-4-oxo-3-aryl quinazolin-2-yl)methyl)piperazin-1-yl)acetoyloxy)-2-phenyl Acetic Acid Esters. Synthetic Communications. 2009;3:3217–3231.
6.
Malinoski F, Stollar V. Inhibition of sindbis virus replication by ribavirin: Influence of cultural conditions and of the host cell phenotype. Antiviral Research. 1981;1:287–299.
7.
Julander JG, Bowen RA, Rao JR, Day C, Shafer K, Smee DF, Morrey JD, Chu C. Treatment of Venezuelan equine encephalitis virus infection with (-)-carbodine. Antiviral Research. 2008;80:309–315. [PMC free article: PMC2612642] [PubMed: 18675850]
8.
Markland W, McQuaid TJ, Jain J, Kwong AD. Broad-spectrum antiviral activity of the IMP dehydrogenase inhibitor VX-497: a comparison with ribavirin and demonstration of antiviral additivity with alpha interferon. Antimicrobial Agents and Chemotherapy. 2000;44:859–866. [PMC free article: PMC89783] [PubMed: 10722482]
9.
Selvam P, et al. Novel 3-sulphonamido-quinazolin-4(3H)-one derivatives: microwave assisted synthesis and evaluation of antiviral activitiesagainst respiratory and biodefense viruses. Antivial Research and Chemotherapy. 2007;18:301–305. [PubMed: 18046963]
10.
Peng W, Peltier DC, Lasen MJ, Kirchcoff PD, Larsen SD, Neubig RR, Miller DJ. Identification of Thieno[3,2-b]Pyrrole Derivatives as Novel Small Molecule Inhibitors of Neurotropic Alphaviruses. J Infectious Diseases. 2009;199:950–957. [PMC free article: PMC2788236] [PubMed: 19239364]
11.
Panchal RG, Reid SP, Tran JP, Bergeron AA, Wells J, Kota KP, Aman J, Bavari S. Identification of an antioxidant small-molecule with broad-spectrum antiviral activity. Antiviral Research. 2012;93:23–29. [PubMed: 22027648]
12.
PubChem Bioassay data AID883 and AID899
13.
PubChem Bioassay data AID396870
14.
Kehn-Hall K, et al. Modulation of GSK-3beta activity in Venezuelan equine encephalitis virus infection. PLoS One. 2012;7:e34761. [PMC free article: PMC3319612] [PubMed: 22496857]
15.
Nuijen B, Bouma M, Manada C, Jimeno JM, Schellens JHM, Bult A, Beijnen JH. Anti-Cancer Drugs. 2000;11:793. [PubMed: 11142687]

Appendix

Quality control 1H-NMR and 13C-NMR spectra for ML336

Figure A6A. 1H NMR spectrum for ML336, SID 152199106, CID 71301451.

Figure A6A1H NMR spectrum for ML336, SID 152199106, CID 71301451

Quality control LCMS Purity and Mass ID data: HRMS and HPLC for ML336

Assay Description

HTS Primary and Confirmatory Assay Using TC-83
Protocol

Cell Culture: Vero 76 cells obtained from ATCC (CRL-1587) were cultured and maintained in MEM-E (Invitrogen, 10370-088) with 10% Hi-FBS (Invitrogen 16000), 1% Penicillin/Streptomycin/L-glutamine (Invitrogen 10378-024) and 1% HEPES (Invitrogen 15630-080). The cells are maintained at 37 °C, 5.0% CO2 to 100% confluence being passaged 1:4 every 3-4 days. For cell plating, cells were detached from flask bottom by using Trypsin-EDTA solution and then re-suspended in a growth media. Cells were passaged no more than ten times after being thawed.

VEEV culture: VEEV TC-83 was used for screening. The VEEV stock was prepared in Vero76 cells using an initial stock obtained from Dr. Chung.

Compound Dosing/Plating: The positive control was MPA at 10 μM final well concentration. The compounds were diluted in complete growth medium to 6× concentrated dosing solution which was dispensed into 384-well black clear-bottom tissue culture treated plates (5 μL volume).

Single Dose Compound Preparation: The MLSMR library was plated at 25 μM single dose concentration.

Dose Response Compound Preparation: The compounds were tested in a dose response format using a 1:2 serial dilution with the highest concentrations starting at 25 μM and extending to .05 μM over a 10-plate 1:2 serial dilution pattern. DMSO and compounds were diluted in assay media to 6× and 5μL was dispensed to assay plates. The final DMSO in the assay for all screening concentrations was 0.25%.

Virus Addition: VEEV stock was diluted in the culture media to 6.44 pfu/mL. (MOI 4e-5)

VEEV and Cell Plating: 3,000 cells/well alone or with VEEV virus at the previously indicated dilution(180,000 cells/ml) were plated in 25 uL using a Matrix WellMate. All additions were done using a Matrix WellMate housed in a class II Biosafety Cabinet within the BSL-2 laboratory. The plates were incubated in an actively humidified incubator with 5.0% CO2 at 37 °C for 72h and 95% humidity.

Endpoint Read: The assay plates were equilibrated to room temperature for 30 minutes and then an equal volume of CellTiter-Glo reagent (Promega Inc.) was added to each well. Plates were incubated for 10 min at room temperature and luminescence was measured using a Perkin Elmer Envision multi-label reader.

Time of Addition Assay: Vero 76 cells were seeded into a 6-well plate in a volume of 2 mL/well and incubated for overnight at 37 °C with 5% CO2 and high humidity. The next day, cell culture media from the 6-well plates was aspirated and the cells were infected with 5 MOI TC-83 VEEV. After the infection, cell culture media was replaced (1.5 mL per well of complete culture media, 0-hr post infection). At the time of addition, 1.5 mL of cell culture media containing a test compound was added to designated wells. Sixteen hours post infection, culture media was harvested and the progeny viruses were titrated. The virus titers of the progeny virus were measured with a “microplaque” method employing methyl cellulose as a semi-solid substance in a 96-well format. The harvested virus were diluted by 10-fold serial dilutions in DMEM supplemented with 5% FBS using the epMotion™ (Eppendorf Inc.) liquid handler.

Eurofins Panlabs Target Profiling Report

Summary

STUDY OBJECTIVE: To evaluate, in Radioligand Binding assays, the activity of compound CID60156253 (UK-13, PT# 1167309).

METHODS: Methods employed in this study have been adapted from the scientific literature to maximize reliability and reproducibility. Reference standards were run as an integral part of each assay to ensure the validity of the results obtained. Assays were performed under conditions described in the accompanying “Methods” section of this report. Where presented, IC50 values were determined by a non-linear, least squares regression analysis using MathIQ™ (ID Business Solutions Ltd., UK). Where inhibition constants (Ki) are presented, the Ki values were calculated using the equation of Cheng and Prusoff (Cheng, Y., Prusoff, W.H., Biochem. Pharmacol. 22:3099-3108, 1973) using the observed IC50 of the tested compound, the concentration of radioligand employed in the assay, and the historical values for the KD of the ligand (obtained experimentally at Eurofins Panlabs, Inc.). Where presented, the Hill coefficient (nH), defining the slope of the competitive binding curve, was calculated using MathIQ™. Hill coefficients significantly different than 1.0, may suggest that the binding displacement does not follow the laws of mass action with a single binding site. Where IC50, Ki, and/or nH data are presented without Standard Error of the Mean (SEM), data are insufficient to be quantitative, and the values presented (Ki, IC50, nH) should be interpreted with caution.

RESULTS: A summary of results meeting the significance criteria is presented in the following sections. Complete results are presented under the section labeled “Experimental Results”. Individual responses, if requested, are presented in the section labeled “Individual Responses”.

SUMMARY/CONCLUSION: Significant results are displayed in the following table(s) in rank order of potency for estimated IC50 and/or Ki values.

Summary of Significant Results

Biochemical assay results are presented as the percent inhibition of specific binding or activity throughout the report. All other results are expressed in terms of that assay's quantitation method.

  • For primary assays, only the lowest concentration with a significant response judged by the assays' criteria, is shown in this summary.
  • Where applicable, either the secondary assay results with the lowest dose/concentration meeting the significance criteria or, if inactive, the highest dose/concentration that did not meet the significance criteria is shown.
  • Unless otherwise requested, primary screening in duplicate with quantitative data (e.g., IC50 ± SEM, Ki ± SEM and nH) are shown where applicable for individual requested assays. In screening packages, primary screening in duplicate with semi-quantitative data (e.g., estimated IC50, Ki and nH) are shown where applicable (concentration range of 4 log units); available secondary functional assays are carried out (30 mM) and MEC or MIC determined only if active in primary assays >50% at 1 log unit below initial test concentration. Significant responses (≥ 50% inhibition or stimulation for Biochemical assays) were noted in the primary assays listed in Table 6:
Table 6. Results of Eurofins Profiling with ML336, Compound: CID60156253.

Table 6

Results of Eurofins Profiling with ML336, Compound: CID60156253.

Catalog #Assay NameSpeciesConcentration% Inhibition
204410Norepinephrine Transporter (NET)human10 μM91

Table 7Results of Eurofins Profiling with ML336, Compound: CID60156253 continued

Cat #Assay nameBatchSpeciesRep.Conc.% inhibition
241000Imidazoline I2, Central326329rat210 μM14
243520Interleukin IL-1326355hum210 μM2
250460Leukotriene, Cysteinyl CysLT1326336hum210 μM11
251600Melatonin MT1326356hum210 μM18
252610Muscarinic M1326408hum210 μM1
252710Muscarinic M2326409hum210 μM2
252810Muscarinic M3326348hum210 μM3
257010Neuropeptide Y Y1326330hum210 μM26
257110Neuropeptide Y Y2326331hum210 μM-6
258590Nicotinic Acetylcholine326298hum210 μM11
258700Nicotinic Acetylcholine α1, Bungarotoxin326300hum210 μM1
260130Opiate δ1 (OP1, DOP)326357hum210 μM-2
260210Opiate κ(OP2, KOP)326371hum210 μM10
260410Opiate μ(OP3, MOP)326372hum210 μM25
264500Phorbol Ester326373mouse210 μM0
265010Platelet Activating Factor (PAF)326383hum210 μM7
265600Potassium Channel [KATP]326384ham210 μM5
265900Potassium Channel hERG326385hum210 μM30
268420Prostanoid EP4326343hum210 μM5
268700Purinergic P2X326287rabbit210 μM14
268810Purinergic P2Y326288rat210 μM6
270000Rolipram326374rat210 μM35
271110Serotonin (5-Hydroxytryptamine) 5-HT1A326289hum210 μM2
271700Serotonin (5-Hydroxytryptamine) 5-HT2B326386hum210 μM10
271910Serotonin (5-Hydroxytryptamine) 5-HT3326387hum210 μM2
278110Sigma σ1326284hum210 μM7
279510Sodium Channel, Site 2326318rat210 μM9
255520Tachykinin NK1326382hum210 μM8
285900Thyroid Hormone326388rat210 μM2
220320Transporter, Dopamine (DAT)326376hum210 μM11
226400Transporter, GABA326281rat210 μM0
204410Transporter, Norepinephrine (NET)326375hum210 μM91
274030Transporter, Serotonin (5-Hydroxytryptamine)326377hum210 μM-6

Note: Items meeting criteria for significance (≥50% stimulation or inhibition) are highlighted.

*

Batch: Represents compounds tested concurrently in the same assay(s).

ham=Hamster; hum=Human;

NCI-60 Panel Profile
Table 8. Single dose profile of ML336 at 10 micromolar concentration.

Table 8Single dose profile of ML336 at 10 micromolar concentration

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