You may need to do some experiments to obtain the IC50. Because I reviewed several articles regarding the IC50 of temozolomide in human glioblastoma multiforme, but none of them explicitly provided the specific IC50 value. These studies focused on the efficacy of temozolomide in vitro and in animal models, but did not explicitly mention the IC50 data.

A systematic review published in BMC Cancer assessed the consistency of temozolomide sensitivity in malignant glioma cell lines between in vitro studies. This research analyzed the effectiveness of temozolomide monotherapy but did not report the IC50 values.

A literature review and clinical outcomes study on temozolomide in the treatment of glioblastoma multiforme, published by MDPI, discussed the application of temozolomide in GBM treatment, literature review, and clinical outcomes, but did not provide specific IC50 values.

A study on the development and in vitro evaluation of temozolomide-loaded PLGA nanoparticles for local administration in glioblastoma multiforme, published on ScienceDirect, detailed the analysis of temozolomide’s efficacy in this context. However, it also did not include the IC50 values.

For more specific IC50 data, you may need to consult more specialized pharmacological or clinical research literature.

Ref: 1. https://bmccancer.biomedcentral.com/articles/10.1186/s12885-021-08972-5；

2.https://www.mdpi.com/1718-7729/31/7/296； 3.https://www.sciencedirect.com/science/article/abs/pii/S1773224719318763.

The IC50 values of TMZ in GBM cells are highly variable, ranging from 50 uM up to >500 uM. GBM is highly heterogenous. The drug response of GBM to TMZ depends on their culture condition (adherent vs serum-free), cell states (glioma stem cells vs differentiated), origins (cell lines vs patient-derived), mutational burdens, especially MGMT promoter methylation and transcriptomic subtypes, etc.

Hence, while the questions look simple, it is challenging to give you a direct answer.

If you want to know a general concentration to embark on your experiment, 50 uM is probably a good start.