Questions & Answers
Do you have a question for IPS Therapeutique? IPST answers questions at length. Our clients rely on clear, complete answers to make decisions as they move forward with testing.
As questions appear to be of general interest, the questions and their answers will be posted below; return often for new questions and answers which may shed some light on your next challenge.
Q. Can IPST assure thermal neutral zone technology for animal studies?
A. Yes. The average temperature of the IPST animal housing room is 27 C. The thermal neutral zone is the range of temperatures in the immediate environment at which a healthy adult animal can maintain a normal body temperature without needing to use energy beyond its normal basal metabolic rate.
Q. What high-throughput assays can I use to screen for cardiac toxicity?
A. There are a number of variable-throughput assays which can be used for the screening of cardiac liability at the moment of lead-selection.
The highest-throughput systems involve hERG binding assays; they are extremely economical, rapid, and generate a significant proportion of false negatives/positives. For this reason, binding assays are used as an early screen when hundreds of test articles are to be ranked based on their hERG liability.
A lower-throughput alternative involves automated or manual patch-clamp hERG assays. Both assays rely on electrophysiological measurements: currents generated by cells are measured and compared in the absence and presence of a potential inhibitor. The assays are functional, as opposed to the binding assay, which is structural in nature. This functional probing of the effects of a test article onto the current amplitude yields considerably more reliable data, and most sponsors elect to test dozens of test articles at a time using either manual or automated patch-clamp.
But hERG assays focus on conduction only, and reveal no information on positive or negative inotropy – in this case, drug-induced changes in contractility of the cardiac tissues. Sponsors interested in contractility issues are numerous; they usually select a organ-bath-based ventricular tissue contraction assay to quantify the risk that their compounds change the contractility of the heart. Of course, the throughput is generally low, but exquisitely reliable, and cardiac contraction-relaxation experiment can be performed at a low price, which makes the method compatible with screening programs for a fair size of samples.
Q. Up to what concentrations do I need to test when running safety pharmacology assays?
A. The highest dose/concentration for which a demonstration of absence of cardiac toxicity (i.e. safety) is necessary depends on the geographical location of the regulatory filing. For instance, European regulators generally require the demonstration of a greater safety margin than do American regulators. In Europe, a highest concentration greater or equal to 100-fold the anticipated clinical plasma concentration. In the USA, this demonstration of safety can be limited to a dose/concentration equivalent to 30 times the anticipated plasma exposure levels.
As a general rule, it is beneficial to 1) cover 3-log orders in the selection of the doses/concentrations to be tested; 2) exceed the required safety margin expected for a given geographical location; and 3) aim to test as high as solubility permits when the regulatory objectives of 100-fold or 30-fold cannot be reached due to limits in solubility.
Q. What is a hERG positive signal, i.e. what level of inhibition is considered to represent a liability sufficient to raise and eyebrow during development?
A. The FDA has announced in September of 2011 that 50% inhibition is considered a positive hERG signal in preclinical safety profiling. Although an inhibition of 20% may be statistically significant, it is less likely to translate into a physiological threat (i.e. prolongation of the QT interval). As a result, current regulatory considerations are set at 50% hERG current inhibition.
Current thinking has it that the risk-to-benefit ratio determines the levels of risk which are acceptable.
Q. What is GLP?
A. The GLP acronym stands for Good Laboratory Practice and specifically refers to a quality system of management controls for research laboratories and organization working in preclinical studies. The GLP embodies a set of principles that provides a framework within which laboratory studies are planned, performed, recorded, reported and archived. It assures regulatory authorities that the data submitted are a true reflection of the results obtained during the study and can be relied upon when making risk/safety assessments.