I am currently using NCI-H226 (lung squamous cell carcinoma cell line) ectopically expressing HER2 mutation for subcutaneous injection into male BALB/C nude mice. The injection number is 5 million cells from 80% confluent plates with >90% viability. The cells were resuspended in plain RPMI medium, mixing 1:1 with Matrigel. Each injection volume is ~80ul. The xenograft reached about 70-80mm in diameter after 1 week. However, the xenograft remained the same size after almost a month, no growth in dimension, only the texture hardened. I continued using this xenograft model for drug testing though. Xenografts upon drug treatment did shrank significantly compared to vehicle control group, but those in the control group did not increase in size.
The cells can grow well in vitro, with doubling time of ~90h (which is slower than the ~60h for parental H226). I have used such a large cell number for injection because previous attempts using fewer cell number would form xenografts that ultimately shrank and disappeared.
I have also used other lung cancer cell lines, including NCI-H2023 and NCI-H1581, carrying other mutations of other genes, for subcutaneous injection of this strain of mice. The injection cell number could be much less, say 1 or 2.5 million, yet the resulting xenografts still grew nicely for my studies. Therefore I suspect there may not be an issue with this host, but rather with the cell line, NCI-H226.
Because I am ectopically expressing my target mutation in a lung squamous carcinoma cell line, I need to use a cell line without prominent endogenous driver mutation. NCI-H226 is the only lung squamous carcinoma cell line that I could find for my study purpose.
So my questions are:
1. Does anyone have any idea on why this tumor xenograft does not grow in size after such a long period of time if these NCI-H226 cells could grow well in vitro?
2. If I really do use these cells for xenograft formation and in vivo drug testing, are the drug efficacy results reliable given that the tumors in the control group do not increase in size?
3. Are there any ways to redesign this experiment, e.g. changing the injection medium, using another cell line or mice strain etc., so that I could still test the drug efficacy for my target mutation in lung squamous cell carcinoma?
Many thanks for your help.
It seems clear that what impedes growth are factors related with the host.
It could be that the host is not fully immune suppressed, or the site of the injection is not appropriate.
Remove the transplant and see if it is infiltrated by cytotoxic T cells.
Tomas Koltai Hi Tomas, thank you very much for your suggestion. I have used this strain of BALB/C nude mice for similar studies with other lung cancer cell lines carrying other mutations, and the subcutaneous xenografts could grow rapidly. The only problem is with using this cell line, NCI-H226. Therefore I suspect there may not be an issue with the host, but likely with this cell line? But it's definitely worth a try to check if there are T cells infiltrating the xenograft.
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