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Latest Publication: Read our teams’ latest paper in Antibiotics, showing reduced nephrotoxicity of a novel formulation of polymyxin B compared to the clinical formulation using a validated primary human proximal tubule cell model.

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Proximal Tubule aProximate™

Model formats

  • 24-well Transwells (static and flow)
  • 96-well Transwells (static and flow)
  • Assay-ready plates for shipment (Human, 24-well & 96-well)

Cell types

  • aProximate™ - primary kidney proximal tubule cells


  • Human
  • Mouse
  • Rat
  • Dog
  • Non-human primate (NHP)

Kidney proximal tubule cell model for safety/efficacy and transporter studies

aProximate™ is one of the most advanced, near physiological, in vitro, kidney proximal tubule cell (PTC) models. aProximate™ PTCs are derived from fresh human kidney tissue and grown on Transwells® where they remain as a functional polarised cell layer that forms tight junctions. In contrast to other primary and immortalised kidney proximal tubule cells in culture, aProximate™ PTCs retain high expression of the key transporters involved in drug handling including Megalin and Cubilin, which is ideal for drug transporter studies. Studies with aProximate™ can give you a detailed mechanistic understanding of how new drugs are transported and eliminated through the kidney and how they interact with other drugs prescribed to the target patient population to help mitigate risk of renal toxicity.

Available analytical readouts

  • Flux and net transport measurements
  • Measurement of intracellular drug and metabolite concentrations
  • Identification of transporter-mediated drug-drug interactions
  • Early renal damage biomarkers
  • Cell viability
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A microscope image of a nephron model
Tight junctions between aProximate™ proximal tubule cells shown by ZO-1 staining

Multiple species

Freshly isolated PTCs

Validated model

aProximate™ Model Highlights

Accelerate your lead compound selection by understanding their mode of action in kidney tissue


Fully differentiated and polarised kidney proximal tubule cells


High level of expression of all key renal transporters


High predictivity of in vivo and clinical outcomes

Revival of aProximate™ Assay Ready Plates

Why use Newcells aProximate™ kidney proximal tubule cell model? Close Open

aProximate™ is an ideal model during early and late drug development for understanding drug handling in the kidney proximal tubule cells. In vitro drug testing and modelling in the proximal tubule is a common strategy for mitigating the risk of failure during preclinical and clinical development, especially as several drugs and metabolites are handled by the same transporters. Interactions between new drugs and renal transporters can easily and accurately be evaluated in vitro with aProximate™. The mechanistic insights provided can be used to support regulatory applications or as responses to regulatory agencies.

Primary kidney proximal tubule cells tend to dedifferentiate and lose key phenotypes overtime in culture, after a freeze-thaw cycle and after immortalization as shown by the loss of transporter and metabolic enzymes involved in drug transport and metabolism. They also display an altered balance between glycolytic and non-glycolytic pathways as well as altered redox activity compared to PTCs in vivo. aProximate™ PTCs distinguish themselves from other PTC cells as they are freshly isolated from kidney tissue, retaining accurate near-physiological phenotype and function.

aProximate proximal tubule cell (PTC) model. Schematic diagram of aProximate PTCs showing the expression of all key renal transporters (left) and the formation of tight junctions as shown by ZO-1 tight junction protein labelling (bottom right). Diagram of Transwell plates demonstrating the aProximate model: PTCs grown on filters remain fully differentiated as a polarised cell layer (top right).

Evaluation and prediction of nephrotoxicity remains a challenging priority during the early and late drug development process. For example, some classes of drugs such as anti-retrovirals, antibiotics, antisense oligonucleotides or siRNA therapies are known to accumulate in kidney proximal tubule cells affecting cell function, possibly inducing nephrotoxicity. Reliable predictive or investigative toxicology tools for early evaluation are needed to avoid drug-induced kidney injury during clinical studies, which are often undetected in animal models due to their low sensitivity. aProximate™ allows for the detection of FDA-qualified kidney-specific biomarkers in response to injury such as KIM-1, NGAL and Clusterin, which are more sensitive than blood and urine biomarkers such as creatinine. This confirms the suitability to assess kidney proximal tubule cell toxicity and evaluate renal drug safety during drug discovery using aProximate™ as an in vitro model.

aProximate™ is fully validated for many applications (For example, see our collaborative publication with Takeda pharmaceuticals: Bajaj et al., 2019

aProximate™ description Close Open
  1. Fully differentiated and functional kidney proximal tubule cells
  2. Form a polarised cell layer with tight junctions
  3. Expression of all key basolateral and apical transporters involved in drug handling, including Megalin and Cubilin
  4. Measurement of net flux
  5. Detection of clinical biomarkers to detect early nephrotoxicity
  6. Unique species comparison capability
  7. High throughput


aProximate™ expresses most relevant kidney transporters unlike other primary and immortalised PTCs such as RPTEC, KH2 and HEPTEC, which express very low or negligible levels. See table below.

Transporter gene Relative mRNA expression of kidney transporters
Human aProximate™ PTC RPTEC
MDR1 65.2 ± 7.1 26
BCRP 31.3 ± 5.5 TBC
MRP1 31.5 ± 33 6
MRP4 29.3 ± 4.8 24
OAT1 20.6 ± 4.6 ND
OAT3 27.8 ± 6.7 ND
OCT2 39.7 ± 4.3 1.8
OATP4C1 39.0 ± 2.7 34
SLC2A9 27.7 ± 4.8 ND
URAT1 34.6 ± 9.2 ND
MATE1 36.4 ± 4.2 0.6
MATE2K 15.1 ± 8.8 0.3
aProximate™ Assay-Ready plates Close Open

aProximate™ is now available for shipment to customers to perform kidney transporter and toxicity studies in-house. aProximate™ Assay-Ready plates (Human) are provided in either 24-well or 96-well Transwell® format. The cells are shipped in stasis media and require revival at 37oC prior to use. The model is provided with maintenance medium and user guide with a detailed protocol for recovery.

Download our poster presentation to find out more about how we validated the shipping process of primary human proximal tubule cell monolayers between laboratories.

aProximate Assay-Ready Plates (Human) User Guide

User Guide

Download our aProximate™ Assay-Ready plates user guide

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A microscope image of a nephron model
ZO-1 Immunocytochemistry staining of PTCs (red) and Hoescht nuclear staining.
A graph showing different levels of creatine uptake
Functional validation of aProximate™ assay-ready plates for transporter assays Functional validation studies for transcellular flux and uptake of creatinine revealed preferential basolateral-to-apical (JBA) creatinine transport, indicative of normal physiological function. A JBA uptake ratio >1.5 indicates that the cells are functional.


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