title: N3-substituted temozolomide analogs overcome methylguanine-DNA methyltransferase and mismatch repair precipitating apoptotic and autophagic cancer cell death.
abstract: Glioblastoma multiforme (GBM) treatment includes temozolomide (TMZ) chemotherapy. O6-Methylguanine lesions are repaired by methylguanine-DNA methyltransferase (MGMT). Response to TMZ requires low MGMT and functional mismatch repair (MMR); resistance, conferred by MGMT or MMR deficiency, represents a barrier to successful treatment. TMZ analogs were synthesized, substituting N3-methyl with propargyl (1) or sulfoxide (2). MTT assays were conducted in SNB19 and U373 isogenic glioma cell lines (V = vector control; M = MGMT-transfected). TMZ potency was reduced >5-fold in SNB19M and U373M cells; in contrast, MGMT-expressing cells were equisensitive as vector controls to analogs 1 and 2 . GI50 values <50 μM of analogs 1 or 2 were detected in V cells possessing acquired TMZ resistance: SNB19VR (hMSH6 loss) and U373VR (MGMT upregulation). Analogs 1 and 2 inhibited MMR-deficient colorectal carcinoma cell growth (irrespective of p53); G2/M cell cycle arrest preceded apoptosis. γH2AX foci inferred the generation of DNA double-strand breaks by analogs 1 and 2 . Acridine orange-stained vesicles, intracellular punctate GFP-LC3 protein and double-membraned autophagosomes indicate that TMZ, 1 and 2 induce autophagy in apoptotis-resistant GBM cells. Analogs 1 and 2 elicit in vitro antitumor activity irrespective of MGMT, MMR and p53. Such imidazotetrazines may treat MGMT+ GBM and possess broader spectrum activity causing apoptosis and autophagy in malignancies which evade apoptosis.
authors.affiliation: Faculty of Medicine, Kunming University of Science and Technology, Kunming, China.
authors.forename: Jihong
authors.initials: J
authors.lastname: Zhang
authors.forename: Marc
authors.initials: M
authors.lastname: Hummersone
authors.forename: Charles S
authors.initials: CS
authors.lastname: Matthews
authors.forename: Malcolm F G
authors.initials: MF
authors.lastname: Stevens
authors.forename: Tracey D
authors.initials: TD
authors.lastname: Bradshaw
mesh_terms: D018906:Antineoplastic Agents, Alkylating / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D001343:Autophagy / Q000187:drug effects*; D002453:Cell Cycle / Q000187:drug effects; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D053903:DNA Breaks, Double-Stranded; D053843:DNA Mismatch Repair / Q000187:drug effects*; D015254:DNA Modification Methylases / Q000032:analysis*; D045643:DNA Repair Enzymes / Q000032:analysis*; D003606:Dacarbazine / Q000031:analogs & derivatives* / Q000494:pharmacology; D005909:Glioblastoma / Q000188:drug therapy* / Q000473:pathology; D006657:Histones / Q000032:analysis; D006801:Humans; D000077204:Temozolomide; D016159:Tumor Suppressor Protein p53 / Q000032:analysis / Q000502:physiology; D025521:Tumor Suppressor Proteins / Q000032:analysis*
chemical_list: D018906:Antineoplastic Agents, Alkylating; C468783:H2AX protein, human; D006657:Histones; D016159:Tumor Suppressor Protein p53; D025521:Tumor Suppressor Proteins; D003606:Dacarbazine; D015254:DNA Modification Methylases; C515491:MGMT protein, human; D045643:DNA Repair Enzymes; D000077204:Temozolomide