Background:

Temozolomide (NSC 362856; CCRG 81045) is an oral DNA alkylating agent used to treat some brain cancers.
Temozolomide (TZM) is a methylating agent that crosses the blood-brain barrier and is indicated for malignant gliomas and metastatic melanomas. Temozolomide is effective against tumor cells that are characterized by low levels of O6-alkylguanine DNA alkyltransferase (OGAT) and a functional mismatch repair system (MR)[1]. Determination of the IC50 for Temozolomide (TZM) in different cell lines gave values ranging from 14.1 to 234.6 μM that fell into two clearly differentiated groups: cell lines with low IC50 values (<50 μM), which include A172 (14.1±1.1 μM) and LN229 cells (14.5±1.1 μM), and those with high IC50 values (>100 μM), which include SF268 (147.2±2.1 μM) and SK-N-SH cells (234.6±2.3 μM)[2].
Temozolomide (TZM), as a single agent, does not significantly increase mdian survival time (MST) with respect to control. Noteworthy, intracranial injection of NU1025, immediately before the administration of 100 or 200 mg/kg Temozolomide, significantly increases lifespans with respect to controls or to groups treated with Temozolomide only. When Temozolomide is fractionated, the increase in lifespan (ILS) obtained with this schedule is higher than that observed when NU1025 is combined with a single injection of Temozolomide (statistical comparison of survival curves: NU1025 intracranially+Temozolomide 100 mg/kg×2 vs NU1025+Temozolomide 200 mg/kg; P=0.023)[1].
Reference：
[1]. Tentori L, et al. Combined treatment with temozolomide and poly(ADP-ribose) polymerase inhibitor enhances survival of mice bearing hematologic malignancy at the central nervous system site. Blood. 2002 Mar 15;99(6):2241-4.
[2]. Perazzoli G, et al. Temozolomide Resistance in Glioblastoma Cell Lines: Implication of MGMT, MMR, P-Glycoprotein and CD133 Expression. PLoS One. 2015 Oct 8;10(10):e0140131.