Lack of Efficacy of Bevacizumab Plus Irinotecan in Children with Recurrent Malignant Glioma and Diffuse Brainstem Glioma:A Pediatric Brain Tumor Consortium Study

PURPOSE:A phase Ⅱ study of bevacizumab(BVZ) plus irinotecan(CPT-11) was conducted in children with recurrent malignant glioma(MG) and intrinsic brainstem glioma(BSG).PATIENTS AND METHODS:Eligible patients received two doses of BVZ

New insights into estrogenic regulation of O^6-methylguanine DNA-methyltransferase (MGMT) in human breast cancer cells： Co-degradation of ER-α and MGMT proteins by fulvestrant or O^6-benzylguanine indicates fresh avenues for therapy

Endocrine therapy using estrogen receptor-u （ER-α） antagonists for attenuating horm2one-driven cell proliferation is a major treatment modality for breast cancers. To exploit any DNA repair deficiencies associated with endocrine therapy, we investigated the functional and physical interactions of ER-α with O^6-methylguanine DNA methyltransferase （MGMT）, a unique DNA repair protein that confers tumor resistance to various anticancer alkylating agents. The ER-α -positive breast cancer cell lines （MCF-7, T47D） and ER- negative cell lines （MDAMB- 468, MDAMB-231）, and established inhibitors of ER-α and MGMT, namely, ICI-182,780 （Faslodex） and O^6- benzylguanine, respectively, were used to study MGMT- ER interactions. The MGMT gene promoter was found to harbor one full and two half estrogen-responsive elements （EREs） and two antioxidant-responsive elements （AREs）. MGMT expression was upregulated by estrogen, downregulated by tamoxifen in Western blot and promoter-linked reporter assays. Similarly, both transient and stable transfections of Nrf-2 （nuclear factor-erythroid 2-related factor-2） increased the levels of MGMT protein and activity 3 to 4-fold reflecting novel regulatory nodes for this dragresistance determinant. Of the different ER-α antagonists tested, the pure anti-estrogen fulvestrant was most potent in inhibiting the MGMT activity in a dose, time and ER-α dependent manner, similar to O^6-benzylguanine. Interestingly, fulvestrant exposure led to a degradation of both ER-α and MGMT proteins and O^6-benzylguanine also induced a specific loss of ER-a and MGMT proteins in MCF-7 and T47D breast cancer cells with similar kinetics. Immunoprecipitation revealed a specific association of ER-a and MGMT proteins in breast cancer cells. Furthermore, silencing of MGMT gene expression triggered a decrease in the levels of both MGMT and ER-a proteins. The involvement of proteasome in the drug-induced degradation of both proteins was also demonstrated. Fulvestrant enhanced the cytotoxicity of MGMT-targeted alkylating agents, namely, temozolomide and BCNU by 3 to 4-fold in ER-α positive cells, but not in ER-negative cells. We conclude that MGMT and ER-α proteins exist as a complex and are co-targeted for ubiquitin-conjugation and subsequent proteasomal degradation. The findings offer a clear rationale for combining alkylating agents with endocrine therapy.

Immunotherapy for pediatric brain tumors

Immunotherapy, while effective against lymphoid cancers and some solid tumors, has shown less benefit against pediatric brain tumors. Tumor heterogeneity, a suppressive immune microenvironment, and the blood-brain barrier have the potential to diminish any immune-based approach and limit efficacy. More importantly, most pediatric brain tumors are immunologically quiescent, stemming from a low mutational burden. This review focuses on innate vs. adaptive immunotherapeutic approaches and describes how the immunologic context of pediatric brain tumors can help identify well-suited immunotherapies for our patients. In this framework, we will discuss past and current approaches using virotherapy, immunoconjugates, monoclonal antibodies, active immunization, and adoptive cel-lular therapy, and share our thoughts on how immunotherapy can cure children with brain tumors.