Maxwell Tom

Pharmacologic inhibition of histone demethylation as a therapy for pediatric brainstem glioma

Pediatric brainstem gliomas often harbor oncogenic K27M mutation of histone H3.3. Here we show that GSKJ4 pharmacologic inhibition of K27 demethylase JMJD3 increases cellular H3K27 methylation in K27M tumor cells and demonstrate potent antitumor activity both in vitro against K27M cells and in vivo against K27M xenografts. Our results demonstrate that increasing H3K27 methylation by inhibiting K27 demethylase is a valid therapeutic strategy for treating K27M-expressing brainstem glioma.

Gene Expression Profile Identifies Tyrosine Kinase c-Met as a Targetable Mediator of Antiangiogenic Therapy Resistance

Purpose: To identify mediators of glioblastoma antiangiogenic therapy resistance and target these mediators in xenografts. Experimental Design: We conducted microarray analysis comparing bevacizumab-resistant glioblastomas (BRG) with pretreatment tumors from the same patients. We established novel xenograft models of antiangiogenic therapy resistance to target candidate resistance mediator(s). Results: BRG microarray analysis revealed upregulation versus pretreatment of receptor tyrosine kinase c-Met, which underwent further investigation because of its prior biologic plausibility as a bevacizumab resistance mediator. BRGs exhibited increased hypoxia versus pretreatment in a manner correlating with their c-Met upregulation, increased c-Met phosphorylation, and increased phosphorylation of c-Met–activated focal adhesion kinase and STAT3. We developed 2 novel xenograft models of antiangiogenic therapy resistance. In the first model, serial bevacizumab treatment of an initially responsive xenograft generated a xenograft with acquired bevacizumab resistance, which exhibited upregulated c-Met expression versus pretreatment. In the second model, a BRG-derived xenograft maintained refractoriness to the MRI tumor vasculature alterations and survival-promoting effects of bevacizumab. Growth of this BRG-derived xenograft was inhibited by a c-Met inhibitor. Transducing these xenograft cells with c-Met short hairpin RNA inhibited their invasion and survival in hypoxia, disrupted their mesenchymal morphology, and converted them from bevacizumab-resistant to bevacizumab-responsive. Engineering bevacizumab-responsive cells to express constitutively active c-Met caused these cells to form bevacizumab-resistant xenografts. Conclusion: These findings support the role of c-Met in survival in hypoxia and invasion, features associated with antiangiogenic therapy resistance, and growth and therapeutic resistance of xenografts resistant to antiangiogenic therapy. Therapeutically targeting c-Met could prevent or overcome antiangiogenic therapy resistance. Clin Cancer Res; 19(7); 1773–83. ©2012 AACR.

Microarray analysis verifies two distinct phenotypes of glioblastomas resistant to anti-angiogenic therapy.

Purpose: To identify mechanisms and mediators of resistance to antiangiogenic therapy in human glioblastoma. Experimental Design: We carried out microarray gene expression analysis and immunohistochemistry comparing 21 recurrent glioblastomas progressing during antiangiogenic treatment with VEGF neutralizing antibody bevacizumab to paired pretreatment tumors from the same patients. Results: Microarray analysis revealed that bevacizumab-resistant glioblastomas (BRG) had two clustering patterns defining subtypes that reflect radiographic growth patterns. Enhancing BRGs (EBRG) exhibited MRI enhancement, a long-established criterion for glioblastoma progression, and expressed mitogen-activated protein kinases, neural cell adhesion molecule-1 (NCAM-1), and aquaporin 4. Compared with their paired pretreatment tumors, EBRGs had unchanged vascularity and hypoxia, with increased proliferation. Nonenhancing BRGs (NBRG) exhibited minimal MRI enhancement but had FLAIR-bright expansion, a newer criterion for glioblastoma recurrence since the advent of antiangiogenic therapy, and expressed integrin α5, laminin, fibronectin1, and PDGFRβ. NBRGs had less vascularity, more hypoxia, and unchanged proliferation than their paired pretreatment tumors. Primary NBRG cells exhibited more stellate morphology with a 3-fold increased shape factor and were nearly 4-fold more invasive in Matrigel chambers than primary cells from EBRGs or bevacizumab-naive glioblastomas (P < 0.05). Conclusion: Using microarray analysis, we found two resistance patterns during antiangiogenic therapy with distinct molecular profiles and radiographic growth patterns. These studies provide valuable biologic insight into the resistance that has limited antiangiogenic therapy to date. Clin Cancer Res; 18(10); 2930–42. ©2012 AACR.

Targeting Wee1 for the treatment of pediatric high-grade gliomas

BACKGROUND We investigated the efficacy of the Wee1 inhibitor MK-1775 in combination with radiation for the treatment of pediatric high-grade gliomas (HGGs), including diffuse intrinsic pontine gliomas (DIPGs). METHODS Gene expression analysis was performed for 38 primary pediatric gliomas (3 grade I, 10 grade II, 11 grade III, 14 grade IV) and 8 normal brain samples using the Agilent 4 × 44 K array. Clonogenic survival assays were carried out in pediatric and adult HGG cell lines (n = 6) to assess radiosensitizing effects of MK-1775. DNA repair capacity was evaluated by measuring protein levels of γ-H2AX, a marker of double strand DNA breaks. In vivo activity of MK-1775 with radiation was assessed in 2 distinct orthotopic engraftment models of pediatric HGG, including 1 derived from a genetically engineered mouse carrying a BRAF(V600E) mutation, and 1 xenograft model in which tumor cells were derived from a patients DIPG. RESULTS Wee1 is overexpressed in pediatric HGGs, with increasing expression positively correlated with malignancy (P = .007 for grade III + IV vs I + II) and markedly high expression in DIPG. Combination treatment of MK-1775 and radiation reduced clonogenic survival and increased expression of γ-H2AX to a greater extent than achieved by radiation alone. Finally, combined MK-1775 and radiation conferred greater survival benefit to mice bearing engrafted, orthotopic HGG and DIPG tumors, compared with treatment with radiation alone (BRAF(V600E) model P = .0061 and DIPG brainstem model P = .0163). CONCLUSION Our results highlight MK-1775 as a promising new therapeutic agent for use in combination with radiation for the treatment of pediatric HGGs, including DIPG.

Factors predicting postoperative hyponatremia and efficacy of hyponatremia management strategies after more than 1000 pituitary operations

OBJECT Syndrome of inappropriate antidiuretic hormone secretion-induced hyponatremia is a common morbidity after pituitary surgery that can be profoundly symptomatic and cause costly readmissions. The authors calculated the frequency of postoperative hyponatremia after 1045 consecutive operations and determined the efficacy of interventions correcting hyponatremia. METHODS The authors performed a retrospective review of 1045 consecutive pituitary surgeries in the first 946 patients treated since forming a dedicated pituitary center 5 years ago. Patients underwent preoperative and daily inpatient sodium checks, with outpatient checks as needed. RESULTS Thirty-two patients presented with hyponatremia; 41% of these patients were symptomatic. Postoperative hyponatremia occurred after 165 operations (16%) a mean of 4 days after surgery (range 0-28 days); 19% of operations leading to postoperative hyponatremia were associated with postoperative symptoms (38% involved dizziness and 29% involved nausea/vomiting) and 15% involved readmission for a mean of 5 days (range 1-20 days). In a multivariate analysis including lesion size, age, sex, number of prior pituitary surgeries, surgical approach, pathology, lesion location, and preoperative hypopituitarism, only preoperative hypopituitarism predicted postoperative hyponatremia (p = 0.006). Of patients with preoperative hyponatremia, 59% underwent medical correction preoperatively and 56% had persistent postoperative hyponatremia. The mean correction rates were 0.4 mEq/L/hr (no treatment; n = 112), 0.5 mEq/L/hr (free water restriction; n = 24), 0.7 mEq/L/hr (salt tablets; n = 14), 0.3 mEq/L/hr (3% saline; n = 20), 0.7 mEq/L/hr (intravenous vasopressin receptor antagonist Vaprisol; n = 22), and 1.2 mEq/L/hr (oral vasopressin receptor antagonist tolvaptan; n = 9) (p = 0.002, ANOVA). While some patients received more than 1 treatment, correction rates were only recorded when a treatment was given alone. CONCLUSIONS After 1045 pituitary operations, postoperative hyponatremia was associated exclusively with preoperative hypopituitarism and was most efficiently managed with oral tolvaptan, with several interventions insignificantly different from no treatment. Promptly identifying hyponatremia in high-risk patients and management with agents like tolvaptan can improve safety and decrease readmission. For readmitted patients with severely symptomatic hyponatremia, the intravenous vasopressin receptor antagonist Vaprisol is another treatment option.

Incidence of headache as a presenting complaint in over 1000 patients with sellar lesions and factors predicting postoperative improvement.

INTRODUCTION Due to the high incidence of headaches and pituitary tumors, neurosurgeons often evaluate patients with benign-appearing sellar lesions and headaches without insight into whether the headache is attributable to the lesion. We sought to evaluate the incidence of headache as a presenting complaint in patients undergoing transsphenoidal surgery for various pathologies and to identify factors predicting postoperative improvement. METHODS We conducted a 5-year retrospective review of our first 1015 transsphenoidal surgeries since establishing a dedicated pituitary center. RESULTS Of 1015 patients, 329 (32%) presented with headache. Of these 329 patients, 241 (73)% had headache as their chief complaint. Headache was most common in patients with apoplexy (84%), followed by Rathkes cleft cysts (RCCs) (60%). Multivariate analyses revealed diagnosis (P = 0.001), younger age (P = 0.001), and female gender (P = 0.006) to be associated with headache. Of patients presenting with headaches, 11% reported improvement at 6-week follow-up and 53% improved at 6-month follow-up. Multivariate analyses revealed gross total resection (GTR; P = 0.04) and decreased duration of headache (P = 0.04) to be associated with improvement, while diagnosis, age, gender, lesion size, whether headache was a chief complaint, and location of headache were not associated with improvement (P > 0.05). CONCLUSION In analyzing over 1000 consecutive patients undergoing transsphenoidal surgery, younger patients, females, and patients with RCCs and apoplexy were more likely to present with headache. Patients who underwent GTR and had shorter duration of headache were more likely to experience headache improvement. This information can be used to counsel patients preoperatively.

Improved versus worsened endocrine function after transsphenoidal surgery for nonfunctional pituitary adenomas: rate, time course, and radiological analysis.

OBJECTIVE The impact of transsphenoidal surgery for nonfunctional pituitary adenomas (NFAs) on preoperative hypopituitarism relative to the incidence of new postoperative endocrine deficits remains unclear. The authors investigated rates of hypopituitarism resolution and development after transsphenoidal surgery. METHODS Over a 5-year period, 305 transsphenoidal surgeries for NFAs performed at The California Center for Pituitary Disorders were retrospectively reviewed. RESULTS Patients with preoperative endocrine deficits (n = 153, 50%) were significantly older (mean age 60 vs 54 years; p = 0.004), more frequently male (65% vs 44%; p = 0.0005), and had larger adenomas (2.4 cm vs 2.1 cm; p = 0.02) than patients without preoperative deficits (n = 152, 50%). Of patients with preoperative endocrine deficits, 53% exhibited symptoms. Preoperative deficit rates were 26% for the thyroid axis; 20% and 16% for the male and female reproductive axes, respectively; 13% for the adrenocorticotropic hormone (ACTH)/cortisol axis, and 19% for the growth hormone (GH)/insulin-like growth factor-1 (IGF-1) axis. Laboratory normalization rates 6 weeks and 6 months after surgery without hormone replacement were 26% and 36% for male and 13% and 13% for female reproductive axes, respectively; 30% and 49% for the thyroid axis; 3% and 3% for the cortisol axis; and 9% and 22% for the IGF-1 axis (p < 0.05). New postoperative endocrine deficits occurred in 42 patients (13.7%). Rates of new deficits by axes were: male reproductive 3% (n = 9), female reproductive 1% (n = 4), thyroid axis 3% (n = 10), cortisol axis 6% (n = 19), and GH/IGF-1 axis 4% (n = 12). Patients who failed to exhibit any endocrine normalization had lower preoperative gland volumes than those who did not (0.24 cm(3) vs 0.43 cm(3), respectively; p < 0.05). Multivariate analyses revealed that no variables predicted new postoperative deficits or normalization of the female reproductive, cortisol, and IGF-1 axes. However, increased preoperative gland volume and younger age predicted the chances of a patient with any preoperative deficit experiencing normalization of at least 1 axis. Younger age and less severe preoperative hormonal deficit predicted normalization of the thyroid and male reproductive axes (p < 0.05). CONCLUSIONS After NFA resection, endocrine normalization rates in this study varied with the hormonal axis and were greater than the incidence of new endocrine deficits. Low preoperative gland volume precluded recovery. Patient age and the severity of the deficiency influenced the recovery of the thyroid and male reproductive axes, the most commonly impaired axes and most likely to normalize postoperatively. This information can be of use in counseling patients with hypopituitarism who undergo NFA surgery.