Pyrimethamine sensitizes pituitary adenomas cells to temozolomide through cathepsin B‐dependent and caspase‐dependent apoptotic pathways

Invasive pituitary adenomas (PAs) are generally refractory to conventional therapy and salvage treatment with temozolomide (TMZ). In addition to antiprotozoan effects, pyrimethamine (PYR) has recently shown its strong antitumor activity as an antineoplastic agent or in combination with TMZ in metastatic melanoma cells. In this study, the effects of TMZ, PYR or TMZ/PYR combination on rat/mouse PA cell lines αT3‐1, GH3, MMQ and ATt‐20 as well as GH3 xenograft tumor model were evaluated. TMZ/PYR combination synergistically inhibited proliferation, invasion and induced apoptosis of these PA cell lines in vitro. Strikingly, combination treatment with TMZ and PYR produced synergistic antitumor activity and enhanced the survival rate of GH3 xenograft tumor models without increasing systemic side effects. In addition, TMZ/PYR induced cell cycle arrest, increased DNA damage, upregulated the expression of cathepsin B, BAX, cleaved PARP and phosphorylated histone H2AX as well as elevated caspase3/7, 8 and 9 activities. The decreased expression of Bcl‐2, MMP‐2 and MMP‐9 alone with cytochrome c release from mitochondria into the cytosol was also observed in the TMZ/PYR combination group. The increase in cell apoptosis due to combination with PYR was rescued by leucovorin. These data suggest that PYR may enhance the efficacy of TMZ via triggering both cathepsin B‐dependent and caspase‐dependent apoptotic pathways. Therefore, combination of PYR and TMZ may provide a novel regimen for invasive PAs refractory to standard therapy and TMZ.     

调强适形放疗联合替莫唑胺治疗恶性脑胶质瘤的临床观察

[目的]观察调强适形放疗(IMRT)联合替莫唑胺(TMZ)治疗恶性脑胶质瘤的临床疗效。[方法]28例术后病理诊断为高级别胶质瘤(WHOⅢ～Ⅳ)的患者,术后放射治疗为全脑左、右对穿野常规照射(WBRT)并后程调强加量照射。常规放射治疗剂量为40Gy/20f/4w,调强放射治疗剂量为20Gy/4f/2w;放疗同步口服替莫唑胺(TMZ)治疗6个周期,之后再接受至少2个周期的常规TMZ治疗。[结果]中位生存时间及无进展生存时间分别为11.5个月和7.2个月;1年总生存率为53.57%,2年总生存率为25.00%。常见的不良反应为恶心、呕吐,血液学毒性是白细胞和血小板下降,但仅限于Ⅰ～Ⅱ度。[结论]IMRT同步TMZ治疗恶性脑胶质瘤,安全有效,不良反应轻微。     

Nanotube x-ray for cancer therapy: a compact microbeam radiation therapy system for brain tumor treatment

Microbeam radiation therapy (MRT) is a promising preclinical modality for cancer treatment, with remarkable preferential tumoricidal effects, that is, tumor eradication without damaging normal tissue functions. Significant lifespan extension has been demonstrated in brain tumor-bearing small animals treated with MRT. So far, MRT experiments can only be performed in a few synchrotron facilities around the world. Limited access to MRT facilities prevents this enormously promising radiotherapy technology from reaching the broader biomedical research community and hinders its potential clinical translation. We recently demonstrated, for the first time, the feasibility of generating microbeam radiation in a laboratory environment using a carbon nanotube x-ray source array and performed initial small animal studies with various brain tumor models. This new nanotechnology-enabled microbeam delivery method, although still in its infancy, has shown promise for achieving comparable therapeutic effects to synchrotron MRT and has offered a potential pathway for clinical translation.     

Efficacy of protracted temozolomide dosing is limited in MGMT unmethylated GBM xenograft models

Background

Temozolomide (TMZ) is important chemotherapy for glioblastoma multiforme (GBM), but the optimal dosing schedule is unclear.

Methods

The efficacies of different clinically relevant dosing regimens were compared in a panel of 7 primary GBM xenografts in an intracranial therapy evaluation model.

Results

Protracted TMZ therapy (TMZ daily M–F, 3 wk every 4) provided superior survival to a placebo-treated group in 1 of 4 O⁶-DNA methylguanine-methyltransferase (MGMT) promoter hypermethylated lines (GBM12) and none of the 3 MGMT unmethylated lines, while standard therapy (TMZ daily M–F, 1 wk every 4) provided superior survival to the placebo-treated group in 2 of 3 MGMT unmethylated lines (GBM14 and GBM43) and none of the methylated lines. In comparing GBM12, GBM14, and GBM43 intracranial specimens, both GBM14 and GBM43 mice treated with protracted TMZ had a significant elevation in MGMT levels compared with placebo. Similarly, high MGMT was found in a second model of acquired TMZ resistance in GBM14 flank xenografts, and resistance was reversed in vitro by treatment with the MGMT inhibitor O⁶-benzylguanine, demonstrating a mechanistic link between MGMT overexpression and TMZ resistance in this line. Additionally, in an analysis of gene expression data, comparison of parental and TMZ-resistant GBM14 demonstrated enrichment of functional ontologies for cell cycle control within the S, G2, and M phases of the cell cycle and DNA damage checkpoints.

Conclusions

Across the 7 tumor models studied, there was no consistent difference between protracted and standard TMZ regimens. The efficacy of protracted TMZ regimens may be limited in a subset of MGMT unmethylated tumors by induction of MGMT expression.     

Standards of care for treatment of recurrent glioblastoma—are we there yet?

Newly diagnosed glioblastoma is now commonly treated with surgery, if feasible, or biopsy, followed by radiation plus concomitant and adjuvant temozolomide. The treatment of recurrent glioblastoma continues to be a moving target as new therapeutic principles enrich the standards of care for newly diagnosed disease. We reviewed PubMed and American Society of Clinical Oncology abstracts from January 2006 to January 2012 to identify clinical trials investigating the treatment of recurrent or progressive glioblastoma with nitrosoureas, temozolomide, bevacizumab, and/or combinations of these agents. At recurrence, a minority of patients are eligible for second surgery or reirradiation, based on appropriate patient selection. In temozolomide-pretreated patients, progression-free survival rates at 6 months of 20%–30% may be achieved either with nitrosoureas, temozolomide in various dosing regimens, or bevacizumab. Combination regimens among these agents or with other drugs have not produced evidence for superior activity but commonly produce more toxicity. More research is needed to better define patient profiles that predict benefit from the limited therapeutic options available after the current standard of care has failed.     

Temozolomide induces the expression of the glioma Big Potassium (gBK) ion channel,while inhibiting fascin-1 expression: possible targets for glioma therapy

Objective: Temozolomide (TMZ) improves Glioblastoma Multiforme (GBM) patient survival. The invasive behavior of the glioma cells is the cause of GBM relapse. The glioma BK ion channel (gBK) may provide glioma cells with a mechanism to invade surrounding tissue. gBK contains epitopes that cytolytic T lymphocytes (CTLs) can recognize and kill glioma cells. Fascin-1 is an actin crosslinking molecule that supports microvilli; these membrane protrusions provide a physical defense against CTLs. TMZ was investigated to determine its effect on gBK and fascin-1 expression.

Research design and methods: Human glioma cells cultured in TMZ were analyzed for their altered mRNA and gBK protein levels by using quantitative real time PCR, immunostaining and cellular functional assays.

Results: TMZ slowed glioma cell growth and inhibited their transmigratory properties due to loss of fascin-1. TMZ induced increased gBK and HLA expression and allowed these TMZ-treated cells to become better targets for gBK-specific CTLs.

Conclusions: Besides its traditional chemotherapeutic effect, TMZ can have four other targeted pathways: 1) slowed glioma cell growth; 2) inhibited glioma cell transmigration; 3) increased HLA-A2 and gBK tumor antigen production; 4) increased CTL-mediated cytolysis of the TMZ treated glioma cells due to the loss of their defensive membrane protrusions supported by fascin-1.     

Temozolomide for recurrent intracranial supratentorial platinum‐refractory ependymoma

BACKGROUND:

To the authors' knowledge, there currently is no standard therapy for platinum‐resistant ependymoma; hence, a need exists for new therapies. In the current study, a retrospective evaluation of temozolomide (TMZ) in adults with recurrent, supratentorial, platinum‐refractory, World Health Organization grade 2 ependymoma was performed, with an objective of determining 6‐month progression‐free survival (PFS).

METHODS:

A total of 25 patients, ages 28 to 63 years, with recurrent ependymoma were treated. All patients had previously been treated with surgery, radiotherapy, and platinum‐based chemotherapy (cisplatin in 15 patients and carboplatin in 10 patients). Nine patients underwent repeat surgery. Patients were treated at the time of second recurrence with TMZ (5 consecutive days), once every 4 weeks, which was defined as a single cycle. Neurologic evaluation was performed every 4 weeks and neuroradiographic assessment every 8 weeks.

RESULTS:

A total of 68 cycles of TMZ (median, 2 cycles; range, 1‐6 cycles) was administered. TMZ‐related toxicity included leukopenia (7 patients; 1 with grade 3 [grade was determine according to National Cancer Institute Common Toxicity Criteria [version 3.0]), constipation (6 patients; none with grade 3), fatigue (5 patients; none with grade 3), anemia (2; none with grade 3), thrombocytopenia (2; none with grade 3), and deep vein thrombosis (2; none with grade 3). One patient (4%) demonstrated a partial radiographic response, 9 (36%) had stable disease, and 15 (60%) developed progressive disease after 2 cycles of TMZ. Time to tumor progression ranged from 1 to 7 months (median, 2 months). Survival ranged from 2 to 8 months (median, 3 months). The 6‐month and 12‐month PFS were 2% and 0%, respectively.

CONCLUSIONS:

TMZ in this dose schedule demonstrated little efficacy in a cohort of adults with recurrent, intracranial, platinum‐refractory ependymoma. Cancer 2009. © 2009 American Cancer Society.     

O6-methylguanine-DNA methyltransferase depletion and DNA damage in patients with melanoma treated with temozolomide alone or with lomeguatrib

We evaluated the pharmacodynamic effects of the O⁶-methylguanine-DNA methyltransferase (MGMT) inactivator lomeguatrib (LM) on patients with melanoma in two clinical trials. Patients received temozolomide (TMZ) for 5 days either alone or with LM for 5, 10 or 14 days. Peripheral blood mononuclear cells (PBMCs) were isolated before treatment and during cycle 1. Where available, tumour biopsies were obtained after the last drug dose in cycle 1. Samples were assayed for MGMT activity, total MGMT protein, and O⁶-methylguanine (O⁶-meG) and N7-methylguanine levels in DNA. MGMT was completely inactivated in PBMC from patients receiving LM, but detectable in those on TMZ alone. Tumours biopsied on the last day of treatment showed complete inactivation of MGMT but there was recovery of activity in tumours sampled later. Significantly more O⁶-meG was present in the PBMC DNA of LM/TMZ patients than those on TMZ alone. LM/TMZ leads to greater MGMT inactivation, and higher levels of O⁶-meG than TMZ alone. Early recovery of MGMT activity in tumours suggested that more protracted dosing with LM is required. Extended dosing of LM completely inactivated PBMC MGMT, and resulted in persistent levels of O⁶-meG in PBMC DNA during treatment.