Preclinical experiments, especially in vivo pharmacology, are by nature complex and often intricate. CrownBio recognize s that protocols, however well defined, do not always capture the insights of years of experience and ofter do not cover all contingencies. To help ensure that your experiments are successful, our experts have put together a set of frequently asked questions to help guide your initial project considerations.
At CrownBio advice is always FREE. We recommend that you take advantage of our in-house experts to design your experiments, answer your questions, and where needed, help troubleshoot your experiments. Ask anything.
Frequently Asked Questions
Questions & Answers
Company History
CrownBio-Beijing was granted with AAALAC accreditation in August 2007, and CrownBio-Taicang was accordingly granted with AAALAC accreditation in September, 2009. Both sites were granted with continuous Full Accreditation in February, 2011 after a routine 3-year-post-accrediation site visit. CrownBio received OLAW/NIH’s approval of our institution’s Animal Welfare Assurance in November, 2010.
CrownBio-Beijing was granted with AAALAC accreditation in August 2007, and CrownBio-Taicang was accordingly granted with AAALAC accreditation in September, 2009. Both sites were granted with continuous Full Accreditation in February, 2011 after a routine 3-year-post-accrediation site visit. CrownBio received OLAW/NIH’s approval of our institution’s Animal Welfare Assurance in November, 2010.
In Vivo Pharmacology
The T/C value (i.e., treated to control value) is a measure of the efficacy of a drug. In CrownBio's assay, the T/C value is determined by comparing tumor volume changes before and after treatment relative to controls. The lower the T/C value, the higher is the efficacy of the drug.
In Vitro Cell Biology
The IC50 values are automatically given by the Prism software. Our other customers have also questioned this, especially when the curve can not be fitted into a typical sigmodial curve, when the IC50 values seem making no sense. I can explain this:
The definition of IC50: half maximal inhibitory concentration. it is the half maximal (50%) inhibitory concentration (IC) of a substance. [From Wiki].Seems simple enough. But when you actually go to fit data to determine these values, there are several complexities and ambiguities. [the following are excerpted from the help file of Prism software]
The ideal situation
This figure shows an ideal situation:
The green symbols show measurements made with controls. The ones on the left (Blank) have no inhibitor, so define "100%". The ones on the right are in the presence of a maximal concentration of a standard inhibitor, so define "0%". The data of the experimental dose-response curve (red dots) extend all the way between the two control values. That is the ideal situation. There is no ambiguity about what IC50 means. [like the positive drugs we used in this CrownBio standardized study]
A situation where IC50 can be defined in two ways
This figure shows an unusual situation where the inhibition curve plateaus well above the control values (NS) defined by a high concentration of a standard drug. This leads to alternative definitions of IC50.
The graph below shows two definitions of the IC50.
The relative IC50 is by far the most common definition, and the adjective relative is usually omitted. It is the concentration required to bring the curve down to point half way between the top and bottom plateaus of the curve. The NS values are totally ignored with this definition of IC50. This definition is the one upon which classical pharmacological analysis of agonist and antagonist interactions is based.
The concentration that provokes a response halfway between the Blank and the NS value is sometimes called the absolute IC50, The horizontal dotted lines show how 100% and 0% are defined, which then defines 50%. This term is not entirely standard. Since this value does not quantify the potency of a drug, the authors of the International Union of Pharmacology Committee on Receptor Nomenclature think that the concept of absolute IC50 (and that term) is not useful (R. Neubig, personal communication). This is CrownBio's position. The concept (but not the term "absolute IC50") is used to quantify drugs that slow cell growth. The abbreviation GI50 is used for what we call here the absolute IC50.
Hope this explanation helps. Any comments or suggestions are appreciated. We think this kind of IC50 values is better, and when evaluating the compound, we should always take IC50 values, the maximal inhibition and the curve into consideration. However, if you need other forms of analysis, do not hesitate to contact us.