Chemo Reversal assay in ABCB1-expressing cells for one set of SAR compounds
The three major subfamilies of human multidrug resistance (MDR) proteins (ABCB, ABCC, and ABCG) influence oral absorption and disposition of a wide variety of drugs and as a result, their expression levels have important consequences for susceptibility to drug-induced side effects, interactions, and treatment efficacy [Sparreboom et al, 2003; Mercier et al, 2003]. Dual treatment with ABC more ..
BioActive Compound: 1
University of New Mexico Assay Overview
High-throughput multiplex screening for ABC transporter inhibitors
Assay Provider: Richard Larson
Screening Center / PI: UNMCMD / Larry Sklar
Chemistry Center / PI: KU Specialized Chemistry Center / Jeff Aube
Assay Development: J Jacob Strouse, Irena Ivnitski-Steele
Assay Implementation: J Jacob Strouse, Hadya Njus, Diane Jimenez-Stinson, Anna Waller, Mark Carter
Assay Background and Significance:
The three major subfamilies of human multidrug resistance (MDR) proteins (ABCB, ABCC, and ABCG) influence oral absorption and disposition of a wide variety of drugs and as a result, their expression levels have important consequences for susceptibility to drug-induced side effects, interactions, and treatment efficacy [Sparreboom et al, 2003; Mercier et al, 2003]. Dual treatment with ABC transporter inhibitors in conjunction with chemotherapeutics is a common treatment strategy to circumvent MDR in cancers. However, manifestation of significant side effects, toxic dose effects, and changes in chemotherapy pharmacokinetics are of constant concern and provide ample justification for identifying new classes of modulators and exploring the biology around them. More than 48 members of the ABC transporter superfamily have been identified and three of these members, MDR1/Pgp (ABCB1), MRP1 (ABCC1), and BCRP (ABCG2), have unambiguously been shown to contribute to cancer multidrug resistance [Kubota et al, 2001].
The primary HTS associated with this project was a high-throughput flow cytometry-based duplex assay [Ramirez et al, 2003] reported in PubChem AIDs 1325 and 1326. The ABCB1 and ABCG2 transporters were evaluated in parallel using the fluorescent J-aggregate-forming lipophilic cation 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazolcarbocyanine iodide (JC-1) as substrate. ABCB1-expressing cells (CCRF-Adr) were color-coded with FarRed DDAO CellTrace SE (Invitrogen) to allow their distinction from ABCG2-expressing cells (Ig-MXP3) via a red fluorescence emission wavelength of 665 +/- 10 nm (635 nm excitation). A total of 194394 compounds was tested with 200 and 130 actives noted in ABCB1 and ABCG2, respectively. A subsequent cherry pick resulted in single point confirmatory testing of 273 compounds (AIDs 1451 and 1453) revealed 18 and 16 actives in ABCB1 and ABCG2 respectively.
In the chemosensitization assay reported here, these actives were validated by assessing the viability of drug resistant cells in the presence of a known chemotherapeutic agent (Daunorubicin (DNR) or Mitoxantrone (Mtx)for ABCB1 and ABCG2-expressing cells, respectively. Compound effectiveness is evaluated by the concentration at which test compound will restore the killing effect of the drug.
To quantify the effects of hit compounds in conferring
sensitivity in drug-resistant cells, the ABCB1 or ABCG2-reversal agent (test compound) concentrations that result in a 50% decrease of cell viability in 100,000 cells/mL maintained in a fixed concentration of selective agent is determined.
Cells (either Jurkat/DNR or Igrove for testing ABCB1 or ABCG2, respectively) are incubated with test compound (concentration range of 3 logs 1-100 microM) over a 3-day period in the presence of selective agent: either DNR for ABCB1 transporter testing, or Mtx for ABCG2 transporter testing. Cell viability is determined by trypan blue staining and enumeration under light microscopy. A chemreversal index (Chem Reversal50) is determined from the viability assessment.
Using a similar approach, an assessment is determined of the direct toxic effects of the transporter-reversal agents that resulted in cell death in resistant cells maintained in medium alone (Toxic Dose50; TD50). Results are compared with the survival of parental cells in the presence of drug (the positive control, resulting in 100% cell death) as well as the survival of drug-resistant cells in the presence of chemotherapeutic drug (the negative control yielding 100% cell viability). The differences between the Chem Reversal50 (CR50) and TD50 curves yields an approximation of an in vitro "therapeutic index" for each compound.
PUBCHEM_ACTIVITY_SCORE is based on Ratio of Chem Reversal50 to Toxic Dose50 for all compounds with Toxic Dose50 less than 15 microM. An Active test compound has a ratio greater than 10.
NIH Roadmap, UNMCMD, chemoreversal assay, drug-resistance transporters, ABCB1, ABCG2
Categorized Comment - additional comments and annotations
Data Table (Concise)