Hi, I'm using Erlotinib treatment in Glioma cell lines, and since a few months it crystallize at high treatment doses (even lower doses, but less amount of crystals are seen), that's 10, 20 and 30 microM. I dissolved the powder in DMSO as indicated by the manufacturer. I don't know if the crystallisation is due to de solution's pH, medium, cell culture dishes (different kinds of plastic...)... someone can help me, please??? Thnxs.
Erlotinb is a lipophilic molecule with a secondary amine (logP 3.2 and pKa 4.6. according to chemicalize.org). The crystallization, or precipitation, you are describing is likely due to the very low solubility of erlotinib. The solubility is approximately 0.9 µM at neutral pH (estimated by Henderson-Hasselbalch relationship using a reported solubility of 0.4 mg/mL at pH 2 and the pKa of the compound).
While DMSO does provide an opportunity to introduce the compound to the assay it will not keep the drug in solution unless the DMSO concentration is very high. Depending on the robustness of your cells you could try to adjust pH or solubilize your compound using a surfactant or a cyclodextrin. It may however be a better idea to try to adjust concentrations used in the experiments as any solubilizing measure will affect the outcome. Due to the low pKa of the amine your medium needs to be quite acidic (i.e. pH 3 or 2) before a substantial increase in solubility could be expected. This would probably be very detrimental to the cells. Solubilizing efforts involving surfactants or inclusion complexing agents can potentially reduce the tendency for the drug to precipitate, but will also reduce the fraction of the drug that can interact with a potential target.
Best regards / Jonas Fagerberg