Patrick Grogan

Publications (2)10.96 Total impact

• Article: Evaluation of MGMT promoter methylation status and correlation with temozolomide response in orthotopic glioblastoma xenograft model.

  Gaspar J Kitange, Brett L Carlson, Ann C Mladek, Paul A Decker, Mark A Schroeder, Wenting Wu, Patrick T Grogan, Caterina Giannini, Karla V Ballman, Jan C Buckner, C David James, Jann N Sarkaria
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  ABSTRACT: CpG methylation within the O6-methylguanine-DNA-methyltransferase (MGMT) promoter is associated with enhanced survival of glioblastoma multiforme (GBM) patients treated with temozolomide (TMZ). Although MGMT promoter is methylated in approximately 50% of GBM, several studies have reported a lack of correlation between MGMT methylation and protein expression levels and consequently inaccurate discrimination of TMZ sensitive and resistant patients. To understand the limitations of currently used assays, TMZ responsiveness of 13 GBM xenograft lines was correlated with MGMT protein expression and MGMT promoter methylation determined by (1) standard methylation-specific polymerase chain reaction (MS-PCR), (2) quantitative MS-PCR (qMS-PCR), and (3) bisulfite sequencing. For each xenograft line, mice with established intracranial xenografts were treated with vehicle control or TMZ (66 mg/kgx5 days), and TMZ response was defined as relative prolongation in median survival for TMZ-treated versus control-treated mice. The relative survival benefit with TMZ was inversely related to MGMT protein expression (r=-0.75; P=0.003) and directly correlated with qMS-PCR (r=0.72; P=0.006). There was a direct correlation between MGMT methylation signal by qMS-PCR and the number of methylated CpG sites within the region amplified by MS-PCR (r=0.78, P=0.002). However, bisulfite sequencing revealed heterogeneity in the extent of CpG methylation in those tumors with a robust qMS-PCR signal. Three of the 4 GBM lines with a qMS-PCR signal greater than 10% had at least 1 unmethylated CpG site, while only one line was fully methylated at all 12 CpG sites. These data highlight one potential limitation of the evaluation of MGMT methylation by MS-PCR assay and suggest that more detailed evaluation of methylation at individual CpG sites relative to TMZ response may be worth pursuing.
  Journal of Neuro-Oncology 12/2008; 92(1):23-31. · 3.21 Impact Factor
• Article: Use of an orthotopic xenograft model for assessing the effect of epidermal growth factor receptor amplification on glioblastoma radiation response.

  Jann N Sarkaria, Brett L Carlson, Mark A Schroeder, Patrick Grogan, Paul D Brown, Caterina Giannini, Karla V Ballman, Gaspar J Kitange, Abjahit Guha, Ajay Pandita, C David James
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  ABSTRACT: The influence of epidermal growth factor receptor (EGFR) amplification on glioblastoma patient prognosis following definitive radiotherapy has been extensively investigated in clinical studies, and yet the relationship between EGFR status and radiation response remains unclear. The intent of the current study was to address this relationship using several EGFR-amplified glioblastoma xenografts in an orthotopic athymic mouse model. We examined the effect of radiation on the survival of nude mice with intracranial xenografts derived from 13 distinct patient tumors, 7 of which have amplified EGFR. Mice with established intracranial tumors were randomized to sham treatment or 12-Gy radiation in six fractions delivered over 12 days. For six of the xenografts, radiation of mice with intracranial tumor significantly extended survival, and four of these xenografts had EGFR amplification. For seven other xenografts, radiation treatment did not significantly extend survival, and three of these, including GBM12, had EGFR amplification. Similar to EGFR, the tumor genetic status of p53 or PTEN did not show preferential association with radiation-sensitive or radiation-resistant xenografts whereas hyperphosphorylation of Akt on Ser(473) was associated with increased radioresistance. To specifically investigate whether inhibition of EGFR kinase activity influences radiation response, we examined combined radiation and EGFR inhibitor treatment in mice with intracranial GBM12. The combination of oral erlotinib administered concurrently with radiation resulted only in additive survival benefit relative to either agent alone. Our results indicate that EGFR amplification, as a biomarker, is not singularly predictive of glioblastoma response to radiation therapy, nor does the inhibition of EGFR enhance the intrinsic radiation responsiveness of glioblastoma tumors. However, efficacious EGFR inhibitor and radiation monotherapy regimens can be used in combination to achieve additive antitumor effect against a subset of glioblastoma.
  Clinical Cancer Research 05/2006; 12(7 Pt 1):2264-71. · 7.74 Impact Factor