aProximate™ Kidney Transporter Assays - Newcells

Retinal platform

An in vitro, light responsive, retinal model for accurate predictions of in vivo outcomes you can have confidence in.


Kidney platform

The most advanced near-physiological high throughput kidney proximal tubule cells (PTC) model to investigate drug transport modalities in vitro.

Lung epithelia model

Lung model

A model to investigate airway physiology, viral infection, drug safety and environmental impacts on lung airway epithelia.

Sinusoid iPSC-derived Liver model

Liver model

We are developing a model of liver sinusoid derived from human induced pluripotent stem cells (iPSC).

aProximate™ Kidney Transporter Assays

aProximate™ kidney transporter assays: The most advanced near-physiological high throughput kidney proximal tubule cells (PTC) model to investigate drug transport modalities in vitro

Validated model: With most key kidney transporters expressed in the aProximate™ kidney transporter assays platform, the transport pathway of new drugs can be easily elucidated and validated to support regulatory applications. 

Drug kidney transporter assays

For new drugs, early understanding of drug handling in the kidney PTCs is a common strategy to mitigating the risk of failure during preclinical and clinical development. More so, as several drugs and metabolites are handled by the same transporters. For example, creatinine, an endogenous metabolite, and the immunomodulating drug pyrimethamine are both substrates for basolateral OCT2 and apical MATE transporters. OATs and MATE transport organic anions, organic compounds like creatinine but also organic cationic drugs, such as metformin, a common drug used to treat Type 2 diabetes.

The excretion of creatinine can be blocked by administering transporter inhibitors such as cimetidine and pyrimethamine. In addition, inhibition of OCT and MATE transporters by cimetidine and pyrimethamine in vivo also reduces metformin renal clearance. Cimetidine interferes with the uptake of metformin by proximal tubule cells and pyrimethamine with efflux of metformin. In vivo, this leads to a significant increase in systemic exposure and a decrease in metformin renal clearance because metformin and pyrimethamine compete for efflux mediated by MATEs.  

Example Protocol

Assay Format

  • Primary isolated kidney proximal tubule epithelial cells cultured on a 24-well Transwell® plates

Species Available

  • Human, rat, mouse, dog and NHP

Time points and replicates

  • 0, 30, 60, 90 minutes
  • Triplicates per concentration


  • Apical to Basal (Ja-b) and Basal to Apical (Jb-a) flux
  • Intracellular accumulation
  • Trans-epithelial electrical resistance (TEER)

Test article requirements

  • Radiolabelled test article or GC/LC analysis
  • Volumes added typically 0.2 ml (apical) and 1 ml (basolateral) per well
  • Six dose concentrations


  • Paracellular flux Is evaluated by measurement of radiolabelled mannitol flux
  • Control substrates for transporters of interest

These interactions are complex but can be predicted in vitro in human aProximate™ PTCs: metformin’s basolateral to apical flux (JBA) is significantly reduced by OCT and MATE inhibitors cimetidine and pyrimethamine. This demonstrates interactions between new drugs and renal transporters can be evaluated in vitro, to shed light on how new drugs are handled by kidney proximal tubule cells.

Predictions of drug/transporter interactions in aProximate™ showing a reduction in renal clearance of metformin upon inhibition of OCT and MATE transporters, comparable to that observed in vivo. 

Newcells aProximate™ platformDe-risk your drug discovery pipeline

Accelerate your research with a reliable and consistent supply of proximal tubule cells validated for drug safety & efficacy as well and drug transporter assays. The highly predictive platform provides detailed mechanistic insights into drug handling.  
Using in vitro aProximate™ platform accelerates and de-risk drug discovery and reduces the requirement for animal experiments for investigational studies of the kidney. 

aProximate™ The most advanced near-physiological high throughput kidney proximal tubule cell (PTC) model.

Recapitulates Proximal tubule physiology

  • Expression of all key renal transporters 
  • High throughput solution for industry 
  • Outperforms competitor in vitro models 
  • FDA approved kidney biomarkers 
  • Enables mitochondrial health monitoring 


In vitro models for accurate prediction of renal tubular xenobiotic transport in vivo. Vriend J. et al., Current Opinion in Toxicology, 2021, Vol 25,2021,Pages 15-22,ISSN 2468-2020,https://doi.org/10.1016/j.cotox.2020.12.001.

Freshly isolated primary human proximal tubule cells as an in vitro model for the detection of renal tubular toxicity. Bajaj et al., Toxicology. 2020 Sep;442:152535. doi: 10.1016/j.tox.2020.152535. Epub 2020 Jul 2.

In vitro platforms for de-risking nephrotoxicity during drug development, Brown and Primrose, Drug Target Review, Sept 2020.

Derivation of a System-Independent Ki for P-glycoprotein Mediated Digoxin Transport from System-Dependent IC50 Data. Chaudhry A, et al., Drug Metab Dispos. 2018 Mar;46(3):279-290. doi: 10.1124/dmd.117.075606. Epub 2018 Jan 9.

Characterisation of human tubular cell monolayers as a model of proximal tubular xenobiotic handling. Brown CD et al., Toxicol Appl Pharmacol. 2008 Dec 15;233(3):428-38. doi: 10.1016/j.taap.2008.09.018. Epub 2008 Oct 1. PMID: 18930752.

Abundance of Drug Transporters in the Human Kidney Cortex as Quantified by Quantitative Targeted Proteomics. Prasad B,. etal., Drug Metab Dispos. 2016 Dec;44(12):1920-1924. doi: 10.1124/dmd.116.072066. Epub 2016 Sep 12.

Predictive in vitro primary proximal tubule models for understanding nephrotoxicity in drug development programs. Brown C., March 2020, Webinar.

Reducing compound attrition by predicting renal tubular toxicity with in vitro PTEC models. Brown C., Sept 2020, Webinar.

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