Human glioma cell sensitivity to the sequence-specific alkylating agent methyl-lexitropsin.

PURPOSE: Defining the cytotoxicity of individual adducts in DNA is necessary for mechanistic understanding of human brain tumor resistance to therapeutic alkylating agents and for design of DNA repair-related antiresistance strategies. Our purpose is to characterize the sensitivity of human glioma cells to methyl-lexitropsin (Me-lex), a sequence-specific alkylator that produces 3-methyladenine (3-meA) as the predominant (>90%) DNA lesion. EXPERIMENTAL DESIGN: We quantitated the Me-lex cytotoxicity of 10 human glioma cell lines that differ in O(6)-methylguanine (O(6)-meG)-DNA methyltransferase (MGMT) and mismatch repair activity. We used antisense suppression of alkyladenine DNA glycosylase (AAG) and Ape1 to assess the contribution of 3-meA and abasic sites to lethality and measured abasic sites. RESULTS: (a) The LD(10) for Me-lex varied widely among the cell lines. (b) MGMT-proficient lines were more resistant than MGMT-deficient lines, an unexpected finding because Me-lex produces very little O(6)-meG. (c) Suppression of AAG increased Me-lex killing and reduced abasic site content. (d) Suppression of Ape1 increased Me-lex killing and increased abasic site content. (e) Ablation of MGMT had no effect on Me-lex cytotoxicity. CONCLUSIONS: (a) Me-lex is cytotoxic in human glioma cells and AAG promotes resistance, indicating that 3-meA is a lethal lesion in these cells. (b) Abasic sites resulting from 3-meA repair are cytotoxic and Ape1 promotes resistance to these derivative lesions. (c) A factor(s) associated with MGMT expression, other than repair of O(6)-meG, contributes to Me-lex resistance. (d) Me-lex may have clinical utility in the adjuvant therapy of gliomas. (e) AAG and Ape1 inhibitors may be useful in targeting alkylating agent resistance.

Neuroradiological findings of trisomy 13 in a rare long-term survivor.

Patau syndrome remains a difficult diagnosis for parents and a challenging conversation for clinicians due to the overall poor prognosis. Previous population-based reports have documented the sobering life expectancies of these patients, with few surviving to 1 year of age. Despite the high mortality rate in infants born with trisomy 13, there are several reports of survival into late childhood and early adulthood. While clinical outcomes have been well documented, there has been a paucity of literature describing postnatal imaging findings in long-term survivors. We present a case report of a 2-year-old girl with trisomy 13 who underwent brain magnetic resonance imaging examination at our institution to evaluate for possible structural abnormalities contributing to central sleep apnea. We describe the clinical and postnatal neuroimaging findings of this rare patient with trisomy 13. Understanding the spectrum of neuroradiological findings in long-term survivors with trisomy 13, in combination with other organ system abnormalities, could add important clinical information and help better predict patient outcomes and expectations among parents.

O6-methylguanine-DNA methyltransferase, O6-benzylguanine, and resistance to clinical alkylators in pediatric primary brain tumor cell lines.

PURPOSE: Primary brain tumors are the leading cause of cancer death in children. Our purpose is (a) to assess the contribution of the DNA repair protein O6-methylguanine-DNA methyltransferase (MGMT) to the resistance of pediatric brain tumor cell lines to clinical alkylating agents and (b) to evaluate variables for maximal potentiation of cell killing by the MGMT inhibitor O6-benzylguanine, currently in clinical trials. Few such data for pediatric glioma lines, particularly those from low-grade tumors, are currently available. EXPERIMENTAL DESIGN: We used clonogenic assays of proliferative survival to quantitate cytoxicity of the chloroethylating agent 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) and the methylating agent temozolomide in 11 glioma and five medulloblastoma lines. Twelve lines are newly established and characterized here, nine of them from low-grade gliomas including pilocytic astrocytomas. RESULTS: (a) MGMT is a major determinant of BCNU resistance and the predominant determinant of temozolomide resistance in both our glioma and medulloblastoma lines. On average, O(6)-benzylguanine reduced LD10 for BCNU and temozolomide, 2.6- and 26-fold, respectively, in 15 MGMT-expressing lines. (b) O6-Benzylguanine reduced DT (the threshold dose for killing) for BCNU and temozolomide, 3.3- and 138-fold, respectively. DT was decreased from levels higher than, to levels below, clinically achievable plasma doses for both alkylators. (c) Maximal potentiation by O6-benzylguanine required complete and prolonged suppression of MGMT. CONCLUSIONS: Our results support the use of O6-benzylguanine to achieve full benefit of alkylating agents, particularly temozolomide, in the chemotherapy of pediatric brain tumors.