Sampling the Tumor Microenvironment
Pharmacological effects and pharmacokinetics of test compounds can be determined in the tumor microenvironment with high sensitivity and temporal resolution by in vivo microdialysis. The in vivo microdialysis technology allows detection of analytes in freely moving rodent models and is suitable for use in both syngeneic models and patient-derived xenograft (PDX) tumor models, allowing our models to be more translationally relevant. This data can inform target engagement and mechanism of action, and is critical for progressing the best version of your drug to the clinic.
Schematic of microdialysis in an in vivo tumor model
The in vivo microdialysis technique involves the noninvasive implantation of a semi-permeable membrane within the tissue of interest.
- This hollow fiber membrane is connected with inlet and outlet tubes; via the inlet tube, the probe is continuously perfused with a solution that resembles the sampled tissue of interest.
- Small molecules will diffuse across the pores of the membrane from the in vivo sampling site to the inside of the membrane across a diffusion gradient.
- The dialysate is collected via the microdialysis probe’s outlet tube at regular intervals. Analytes of interest are collected based on their physicochemical properties via customization of the membrane materials.
- The collected samples can be used to quantify levels of a wide range of analytes of interest (Figure 1). For example, effects of PD-1 treatment can be quantified by measuring levels of adenosine, inosine and cGMP in the tumor microenvironment.
The microdialysis probe can be positioned in the center or the periphery of the tumor, to study heterogeneity of release factors, and can also be positioned contralateral, allowing comparison of tumor and tumor-free flank. In addition, during the microdialysis experiment, blood samples can be collected.
Frequently Asked Questions (FAQs) on Tumor Microdialysis
What is in vivo microdialysis?
In vivo microdialysis is a minimally invasive sampling technique, designed to be used in conscious and freely moving animals. This allows continuous measurement of free analyte concentrations in the extracellular fluid, such as CSF, plasma, and fluids from the brain and other tissues. The samples are then analyzed using LC-MS and other methods to assess metabolites, therapeutic modality concentrations, and other fluid biomarkers. This technique was initially developed for CNS research but can be performed in any tissue type to assess the physiological or pharmacological functions of biochemicals or determine the distribution of new chemical entities within the body. Microdialysis sampling is an excellent way to model the pharmacokinetics of a given therapeutic compound. A novel and insightful application of this technology is the quantification of immunomodulators and oncometabolites in the tumor microenvironment.
How can in vivo microdialysis be used to sample the tumor microenvironment?
While in vivo microdialysis was originally developed as a method to sample the CNS, it has been used in oncology tumor models. This is a quantitative and sensitive method for the detection of multiple immunomodulators and oncometabolites from freely moving tumor-bearing mice. Tumor microdialysis in murine models can be used to elucidate the mechanisms by which oncology therapies, such as chemotherapy and immune checkpoint inhibitors, modulate the tumor microenvironment. This insight into target engagement and mechanism of action aids faster progression into the clinic.