Synthesis and Quantitative Structure–Activity Relationship of Imidazotetrazine Prodrugs with Activity Independent of O6-Methylguanine-DNA-methyltransferase, DNA Mismatch Repair, and p53

Abstract

The antitumor prodrug Temozolomide is compromised by its dependence for activity on DNA mismatch repair (MMR) and the repair of the chemosensitive DNA lesion, O6-methylguanine (O6-MeG), by O6-methylguanine-DNA-methyltransferase (EC 2.1.1.63, MGMT). Tumor response is also dependent on wild-type p53. Novel 3-(2-anilinoethyl)-substituted imidazotetrazines are reported that have activity independent of MGMT, MMR and p53. This is achieved through a switch of mechanism so that bioactivity derives from imidazotetrazine-generated arylaziridinium ions that principally modify guanine-N7 sites on DNA. Mono-and bi-functional analogs are reported and a quantitative structureactivity relationship (QSAR) study identified the p-tolyl-substituted bi-functional congener as optimized for potency, MGMT-independence and MMR-independence. NCI60 data show the tumor cell response is distinct from other imidazotetrazines and DNA-guanine-N7 active agents such as nitrogen mustards and cisplatin. The new imidazotetrazine compounds are promising agents for further development and their improved in vitro activity validates the principles on which they were designed.

Evaluation of Novel Imidazotetrazine Analogues Designed to Overcome Temozolomide Resistance and Glioblastoma Regrowth

“…In contrast, the diazonium ions from DP68 and DP86 undergo an efficient, intra-molecular trapping reaction to form aziridinium ions, and these intermediates react with DNA, predominantly at N 7-G sites (17). The new agents were designed to generate anticancer activity from N 7-G adducts but should adducts occur at O 6-G, these would be resistant to repair by MGMT (18). Consistent with either mechanism, sensitivity to both compounds was unaffected by MGMT expression in the TMZ-resistant T98G, GBM6, or GBM12TMZ models, and a similar MGMT-independence was observed in A2780 ovarian carcinoma cells (18).…”

“…The new agents were designed to generate anticancer activity from N 7-G adducts but should adducts occur at O 6-G, these would be resistant to repair by MGMT (18). Consistent with either mechanism, sensitivity to both compounds was unaffected by MGMT expression in the TMZ-resistant T98G, GBM6, or GBM12TMZ models, and a similar MGMT-independence was observed in A2780 ovarian carcinoma cells (18). The early arrest in S-phase with DP68 treatment is consistent with DNA adducts that cannot be bypassed by the replication machinery, stalling replication forks.…”

“…The design of the imidazotetrazine compounds investigated herein sought a switch of chemical mechanism with the aims of avoiding known mechanisms of TMZ resistance and generating therapeutic benefit from the major reaction site, N 7-G (70% for TMZ), rather than the minor (5%) O 6-G site (17). In this study, we focus on two of the most promising compounds developed: the mono-functional DP86 and the bi-functional DP68 imidazotetrazines (Figure S1) (17, 18). These compounds are precursors of aziridinium ions, which are reactive intermediates of proven clinical utility related to those generated by nitrogen mustard drugs (Figure S2C-D).…”

“…Notably, there was also, no similarity to the nitrosoureas, which are also diazonium ion precursors, 0.45 ≥ P ≥ 0.05 or cisplatin, another N 7-G reactive agent 0.42 ≥ P ≥ 0.27. (18). This manuscript describes the biological effects of these novel DNA alkylating agents in GBM models and their relative activities in the context of MGMT-overexpression and other mechanisms of TMZ resistance.…”

Combined silencing expression of MGMT with EGFR or galectin-1 enhances the sensitivity of glioblastoma to temozolomide

“…Median survival is 14 months and the percentage of patients living for 5 years or more is < 10% (1,3). TMZ is an alkylating agent from the imidazotetrazine family; it acts by methylation of purine bases of DNA (O6-guanine; N7-guanine and N3-adenine) (4). The cytotoxicity of TMZ is mainly mediated by the formation of O-6 methyl guanine responsible of mispairment with thymine during DNA replication; this causes toxic lesions of DNA and cell cycle arrest (5,6).…”