NCNPR Screen Information

The National Center for Natural Products Research offers three in vitro biological screens (AP, LEM and OI) to test a variety of samples.  Screens are set up in a tiered process depending upon the sample type submitted (crude extract, column fraction or pure compound).  The time to completely analyze a sample also depends upon the sample type, as well as the screen itself (incubation periods, etc.).  There are many other factors to consider when determining if your sample is active or worth pursuing.  If you ever have any question about the status of a sample or any screening-related issue, please contact:

When reporting NCNPR screening data (journal articles, posters, presentations), please make sure that you properly acknowledge the funding source.

AP (Anti-malarial Screen)

The anti-malarial screen (AP) tests samples for their ability to inhibit the chloroquine-sensitive (D6) and/or chloroquine-resistant (W2) Plasmodium falciparum protozoan.  Crude extracts are initially tested against the D6 P. falciparum strain in a Primary Screen at 15867ng/mL in duplicate, and percent inhibitions (% inh.) are calculated relative to negative and positive controls.  Extracts showing ≥50% inhibition proceed to the Secondary Assay.

In the Secondary AP Assay, samples dissolved to 20mg/mL (crude extracts and some column fractions – CFs) are tested at 47600, 15867, and 5289ng/mL and IC₅₀s (test concentration in ng/mL that affords 50% inhibition of the protozoan relative to negative and positive controls) vs. both the D6 and W2 strains are reported.  Samples dissolved to 2mg/mL (pure compounds - XTL and some column fractions – CFs) are tested at 4760, 1587, and 529ng/mL and IC₅₀s vs. both the D6 and W2 strains are reported.  In addition to the P. falciparum strains, samples are tested in the VERO mammalian cell line as an indicator of general cytotoxicity.  The selectivity indices (SI) – ratio of VERO IC₅₀ to D6 or W2 IC₅₀ - are calculated.  All IC₅₀s are calculated using the XLFit fit curve fitting software.

The antimalarial drug controls chloroquine and artemisinin are used as positive controls.

LEM (Anti-leishmanial Screen)

The anti-leishmanial screen (LEM) tests samples for their ability to inhibit Leishmania donovani, a fly-borne protozoan that causes visceral leishmaniasis.  Crude extracts are initially tested in a Primary Screen at 80µg/mL in duplicate and percent inhibitions (% inh.) are calculated relative to negative and positive controls.  Extracts showing ≥50% inhibition proceed to the Secondary Assay.  In the Secondary LEM Assay, all samples (2 and 20mg/mL) are tested at 40, 8.0 and 1.6µg/mL and IC₅₀s as well as IC₉₀s (test concentration that affords 90% inhibition of the protozoan relative to controls) are reported.  Samples that have an IC₅₀ of <1.6µg/mL in the Secondary LEM assay proceed to the Tertiary Assay where the sample is tested at 40, 8, 1.6, 0.32, 0.064, 0.0128µg/mL and IC₅₀s and IC₉₀s are reported.  All IC₅₀s and IC₉₀s are calculated using the XLFit fit curve fitting software.

The drug controls pentamidine and amphotericin B are used as positive controls.

OI (Antifungal and antibacterial Screen)

The antimicrobial screen (OI) tests samples for their ability to inhibit a panel of 5 bacteria and 5 fungi that are pathogenic to humans:

Crude extracts are initially tested in a Primary Screen at 50µg/mL in duplicate and percent inhibitions (% inh.) are calculated relative to negative and positive controls.  Extracts showing ≥50% inhibition proceed to the Secondary Assay. 

In the Secondary OI Assay, samples dissolved to 20mg/mL (crude extracts and some column fractions – CFs) are tested at 200, 40, 8µg/mL and IC₅₀s vs. all 10 microbial strains are reported.  Samples dissolved to 2mg/mL (pure compounds - XTL and some column fractions – CFs) are tested at 20, 4, 0.8µg/mL and IC₅₀s vs. all 10 microbial strains are reported.  Pure compounds (XTL) that have an IC₅₀ of ≤7µg/mL in the Secondary OI assay proceed to the Tertiary Assay.

In the Tertiary OI Assay, pure compounds are tested vs. all 10 microbes at 20, 10, 5.0, … 0.02µg/mL and IC₅₀s are calculated.  In addition to the IC₅₀, the MIC (minimum inhibitory concentration) and either the MFC or MBC (minimum fungicidal or bactericidal concentration, respectively) are reported.  The MIC is the lowest test concentration (in µg/mL) that inhibits the organism 100%.  The MFC or MBC is the lowest test concentration (in µg/mL) that kills the organism.  While a pure compound may have an MIC, the cells may still be alive, just not growing.  The MFC and MBC is a way to monitor the “cidality” or killing ability of the test sample.  All IC₅₀s are calculated using the XLFit fit curve fitting software.

The antifungal drug control is amphotericin B and the antibacterial drug control is ciprofloxacin.