What's in your G-418?
When evaluating G-418 products, consider more than just potency. Look at purity and working range. Taken together, these three characteristics provide a true evaluation of the effectiveness of your G-418.
- 15-30% lower concentrations of Geneticin® agent can be used as compared to other G-418 products to achieve comparable selection results.
- Surviving clonal colonies may arise faster and cells may appear healthier when using Geneticin® instead of lower purity G-418 products.
- Gentamicins that commonly contaminate G-418 preparations from other suppliers will add to potency in bacterial assays yet have no effect on mammalian cell selectivity.
- Other bacterial contaminants in impure G-418 may be toxic to mammalian cells, consequently lowering the ED 50 value.
Therefore, comparing potency values between different suppliers is not a relevant specification for mammalian cell selection.
- Toxic impurities lower the ED50 value, which means a more narrow working range of antibiotic selection.
- A consistent ED50 from a supplier assures performance reproducibility from lot-to-lot in mammalian cell culture applications.
This means when purchasing a new lot of Geneticin®, you do not need to re-optimize for ideal antibiotic concentration (assuming that no other media alterations). The wide ranges of ED50 displayed in different lots from alternative G-418 suppliers may require you to re-optimize for each lot. Lot-to-lot consistency with Geneticin® is sufficiently high that you will not notice any difference in selection performance between lots.
Table 1. Comparison of Geneticin® specifications with alternative G-418 suppliers.
||The Geneticin® Advantage
||66-75%||65-82%||Significantly higher purity|
|Potency claimed (µg/mg)
||More stringent potency assay
|Potency upon retest (µg/mg)
||Consistently higher actual potency
|ED50 Assay (µg/ml)
||Reliable selection lot-to-lot
Table 1. Multiple lots of G-418 from two different suppliers were analyzed according to Invitrogen raw material QC protocols for Geneticin®. It was observed that results obtained with G-418 from Supplier A and Supplier B displayed wide variations on all measured parameters, including an inconsistency between the actual potency and the value reported on the supplied product literature. Discrepancies between re-tested potency values and that claimed by other suppliers may be due to differences in G-418 reference lots and assay procedures.
Figure 1. Geneticin® displays greater purity than G-418 from alternative suppliers.
Figure 1. Comparison of HPLC data of Geneticin® with selected lots of G-418 from Supplier A and Supplier B. Samples were prepared and analyzed according to the procedure published in Clinical Chem. (1978), Vol. 24, No.11, p1940.