My experiments to understand how ZnCl2 inhibits rhinovirus replication have been thwarted by the finding that concentrations of the salt higher than 0.1 mM are toxic for cultured HeLa cells. The cells can tolerate 0.1 mM but not 0.2 mM ZnCl2. Last week I asked whether I could identify a concentration between 0.1 and 0.2 mM that does not harm the cells but inhibits viral plaque formation >99%. Here are the results.
Unfortunately even 0.125 mM ZnCl2 is toxic to the cells – which is surprising since the cells can tolerate 0.1 mM. The goal of these experiments is to identify Zn-resistant rhinovirus mutants, and this cannot be done with cell monolayers that are not healthy.
I have one more idea for how to get around the ZnCl2 toxicity. To improve the formation of rhinovirus plaques, 25 mM MgCl2 is added to the agar overlay. It is possible that this high amount of magnesium, together with 0.2 mM ZnCl2 or higher, is toxic to cells. Therefore I will determine whether Zn toxicity is reduced if MgCl2 is omitted from the agar overlay. The rhinovirus plaques will be smaller but that is a reasonable trade-off for healthier monolayers.
If omitting MgCl2 doesn’t work, then I will have to select Zn resistant rhinovirus mutants in cells propagated in liquid cell culture medium. I’ll explain that approach next week.