Differential radiosensitizing potential of temozolomide in MGMT promoter methylated glioblastoma multiforme cell lines

Temozolomide – Just a Radiosensitizer?

Radiation concomitant with the DNA methylating drug temozolomide (TMZ) is the gold standard in the treatment of glioblastoma. In this adjuvant setting, TMZ is regarded to be a radiation sensitizer. However, similar to ionising radiation, TMZ induces DNA double-strand breaks and is itself a potent trigger of apoptosis, cellular senescence and autophagy, suggesting that radiation and TMZ act independently. Although cell culture experiments yielded heterogeneous results, some data indicate that the cytotoxic effect of radiation was only enhanced when TMZ was given before radiation treatment. Based on the molecular mechanism of action of TMZ, the importance of specific TMZ and radiation-induced DNA lesions, their repair as well as their interactions, possible scenarios for an additive or synergistic effect of TMZ and radiation are discussed, and suggestions for an optimal timing of radio-chemical treatments are proposed.

Genomic Instability and Cancer Risk Associated with Erroneous DNA Repair

Many cancers develop as a consequence of genomic instability, which induces genomic rearrangements and nucleotide mutations. Failure to correct DNA damage in DNA repair defective cells, such as in BRCA1 and BRCA2 mutated backgrounds, is directly associated with increased cancer risk. Genomic rearrangement is generally a consequence of erroneous repair of DNA double-strand breaks (DSBs), though paradoxically, many cancers develop in the absence of DNA repair defects. DNA repair systems are essential for cell survival, and in cancers deficient in one repair pathway, other pathways can become upregulated. In this review, we examine the current literature on genomic alterations in cancer cells and the association between these alterations and DNA repair pathway inactivation and upregulation.

Radiosurgery for Glioblastoma

Glioblastoma (GBM) is infiltrative neoplasm with limited treatment options and poor overall survival. Stereotactic radiosurgery (SRS) allows spatially precise and conformal delivery of high doses of radiation. Salvage SRS for locally recurrent GBM was shown to improve patient survival and have more favorable safety profile than repeated surgical resection. Boost SRS after fractionated radiation therapy is sometimes attempted; however, Radiation Therapy Oncology Group 93-05 randomized clinical trial did not demonstrate benefits of upfront SRS that was administered before fractionated radiation. Administration of bevacizumab with SRS is associated with improved survival and can allow SRS dose escalation.

Developing a clinically relevant radiosensitizer for temozolomide-resistant gliomas

The prognosis for patients with glioblastoma (GB) remains grim. Concurrent temozolomide (TMZ) radiation—the cornerstone of glioma control—extends the overall median survival of GB patients by only a few months over radiotherapy alone. While these survival gains could be partly attributed to radiosensitization, this benefit is greatly minimized in tumors expressing O⁶-methylguanine DNA methyltransferase (MGMT), which specifically reverses O⁶-methylguanine lesions. Theoretically, non-O⁶-methylguanine lesions (i.e., the N-methylpurine adducts), which represent up to 90% of TMZ-generated DNA adducts, could also contribute to radiosensitization. Unfortunately, at concentrations attainable in clinical practice, the alkylation capacity of TMZ cannot overwhelm the repair of N-methylpurine adducts to efficiently exploit these lesions. The current therapeutic application of TMZ therefore faces two main obstacles: (i) the stochastic presence of MGMT and (ii) a blunted radiosensitization potential at physiologic concentrations. To circumvent these limitations, we are developing a novel molecule called NEO212—a derivatization of TMZ generated by coupling TMZ to perillyl alcohol. Based on gas chromatography/mass spectrometry and high-performance liquid chromatography analyses, we determined that NEO212 had greater tumor cell uptake than TMZ. In mouse models, NEO212 was more efficient than TMZ at crossing the blood-brain barrier, preferentially accumulating in tumoral over normal brain tissue. Moreover, in vitro analyses with GB cell lines, including TMZ-resistant isogenic variants, revealed more potent cytotoxic and radiosensitizing activities for NEO212 at physiologic concentrations. Mechanistically, these advantages of NEO212 over TMZ could be attributed to its enhanced tumor uptake presumably leading to more extensive DNA alkylation at equivalent dosages which, ultimately, allows for N-methylpurine lesions to be better exploited for radiosensitization. This effect cannot be achieved with TMZ at clinically relevant concentrations and is independent of MGMT. Our findings establish NEO212 as a superior radiosensitizer and a potentially better alternative to TMZ for newly diagnosed GB patients, irrespective of their MGMT status.

Radioresistance in Glioblastoma and the Development of Radiosensitizers

Ionizing radiation is a common and effective therapeutic option for the treatment of glioblastoma (GBM). Unfortunately, some GBMs are relatively radioresistant and patients have worse outcomes after radiation treatment. The mechanisms underlying intrinsic radioresistance in GBM has been rigorously investigated over the past several years, but the complex interaction of the cellular molecules and signaling pathways involved in radioresistance remains incompletely defined. A clinically effective radiosensitizer that overcomes radioresistance has yet to be identified. In this review, we discuss the current status of radiation treatment in GBM, including advances in imaging techniques that have facilitated more accurate diagnosis, and the identified mechanisms of GBM radioresistance. In addition, we provide a summary of the candidate GBM radiosensitizers being investigated, including an update of subjects enrolled in clinical trials. Overall, this review highlights the importance of understanding the mechanisms of GBM radioresistance to facilitate the development of effective radiosensitizers.

Short delay in initiation of radiotherapy for patients with glioblastoma-effect of concurrent chemotherapy: a secondary analysis from the NRG Oncology/Radiation Therapy Oncology Group database

Background

We previously reported the unexpected finding of significantly improved survival for newly diagnosed glioblastoma in patients when radiation therapy (RT) was initiated later (>4 wk post-op) compared with earlier (≤2 wk post-op). In that analysis, data were analyzed from 2855 patients from 16 NRG Oncology/Radiotherapy Oncology Group (RTOG) trials conducted prior to the era of concurrent temozolomide (TMZ) with RT. We now report on 1395 newly diagnosed glioblastomas from 2 studies, treated with RT and concurrent TMZ followed by adjuvant TMZ. Our hypothesis was that concurrent TMZ has a synergistic/radiosensitizing mechanism, making RT timing less significant.

Methods

Data from patients treated with TMZ-based chemoradiation from NRG Oncology/RTOG 0525 and 0825 were analyzed. An analysis comparable to our prior study was performed to determine whether there was still an impact on survival by delaying RT. Overall survival (OS) was investigated using the Kaplan-Meier method and Cox proportional hazards model. Early progression (during time of diagnosis to 30 days after RT completion) was analyzed using the chi-square test.

Results

Given the small number of patients who started RT early following surgery, comparisons were made between >4 and ≤4 weeks delay of radiation from time of operation. There was no statistically significant difference in OS (hazard ratio = 0.93; P = 0.29; 95% CI: 0.80-1.07) after adjusting for known prognostic factors (recursive partitioning analysis and O6-methylguanine-DNA methyltransferase methylation status). Similarly, the rate of early progression did not differ significantly (P = 0.63).

Conclusions

We did not observe a significant prognostic influence of delaying radiation when given concurrently with TMZ for newly diagnosed glioblastoma. The effects of early (1-3 wk post-op) or late (>5 wk) initiation of radiation tested in our prior study could not be replicated.

Hypofractionated radiation therapy and temozolomide in patients with glioblastoma and poor prognostic factors. A prospective, single-institution experience

Background

Hypofractionated radiation therapy is a feasible and safe treatment option in elderly and frail patients with glioblastoma. The aim of this study was to evaluate the effectiveness of hypofractionated radiation therapy with concurrent temozolomide in terms of feasibility and disease control in primary glioblastoma patients with poor prognostic factors other than advanced age, such as post-surgical neurological complications, high tumor burden, unresectable or multifocal lesions, and potential low treatment compliance due to social factors or rapidly progressive disease.

Material and methods

GTV included the surgical cavity plus disease visible in T1WI-MRI, FLAIR-MRI and in the MET-uptake. The CTV was defined as the GTV plus 1.5–2 cm margin; the PTV was the CTV+0.3 cm margin. Forty, fourty-five, and fifty grays in 15 fractions were prescribed to 95% of PTV, CTV, and GTV, respectively. Treatment was delivered using IMRT or the VMAT technique. Simultaneously, 75 mg/m²/day of temozolomide were administered.

Results

Between January 2010 and November 2017, we treated a total of 17 patients. The median age at diagnosis was 68-years; median KPS was 50–70%. MGMT-methylation status was negative in 5 patients, and 8 patients were IDH-wildtype. Eight of 18 patients were younger than 65-years. Median tumor volume was 26.95cc; median PTV volume was 322cc. Four lesions were unresectable; 6 patients underwent complete surgical resection. Median residual volume was 1.14cc. Progression-free survival was 60% at 6 months, 33% at 1-year and 13% at 2-years (median OS = 7 months). No acute grade 3–5 toxicities were documented. Symptomatic grade 3 radiation necrosis was observed in one patient.

Conclusions

Patients with poor clinical factors other than advanced age can be selected for hypofractionated radiotherapy. The OS and PFS rates obtained in our series are similar to those in patients treated with standard fractionation, assuring good treatment adherence, low rates of toxicity and probable improved cost-effectiveness.

A Phase II Trial of Concurrent Temozolomide and Hypofractionated Stereotactic Radiotherapy for Complex Brain Metastases

PURPOSE

Complex brain metastases (BMs), such as large lesions, lesions within or close to eloquent locations, or multiple recurrent/progressive BMs, remain the most challenging forms of brain cancer because of decreased intracranial control rates and poor survival. In the present study, we report the results from a single institutional phase II trial of concurrent temozolomide (TMZ) with hypofractionated stereotactic radiotherapy (HFSRT) in patients with complex brain metastases, including assessment of its feasibility and toxicity.

PATIENTS AND METHODS

Fifty-four patients with histologically proven primary cancer and complex BMs were enrolled between 2010 and 2015. All the patients were treated with concurrent HFSRT and TMZ (administrated orally at a dosage of 75 mg/m² per day for at least 20 days). The primary endpoint was overall survival (OS).

RESULTS

The median follow-up time was 30.6 months. The local control rates at 1 and 2 years were 96% and 82%, respectively. The median OS was 17.4 months (95% confidence interval [CI], 12.6-22.2), and the OS rates at 1 and 2 years were 65% (95% CI, 52%-78%) and 33% (19%-47%). Only six patients (15.8%) died of intracranial disease. The median brain metastasis-specific survival was 46.9 months (95% CI, 35.5-58.4). Treatment-related grade 3-4 adverse events were rare and included one grade 3 hematological toxicity and two grade 3 liver dysfunctions.

CONCLUSION

Treatment using HFSRT concurrent with TMZ was well tolerated and could significantly extend OS compared with historical controls in complex BMs. Large randomized clinical trials are warranted. Trial registration ID: NCT02654106.

IMPLICATIONS FOR PRACTICE

The treatment using hypofractionated stereotactic radiotherapy concurrent with temozolomide appeared to be safe and could significantly extend overall survival compared with historical control in complex brain metastases. Large randomized clinical trials are warranted to verify our results.

CUX1 stimulates APE1 enzymatic activity and increases the resistance of glioblastoma cells to the mono-alkylating agent temozolomide

Background

Cut Like homeobox 1 (CUX1), which encodes an auxiliary factor in base excision repair, resides on 7q22.1, the most frequently and highly amplified chromosomal region in glioblastomas. The resistance of glioblastoma cells to the mono-alkylating agent temozolomide is determined to some extent by the activity of apurinic/apyrimidinic endonuclease 1 (APE1).

Methods

To monitor the effect of CUX1 and its CUT domains on APE1 activity, DNA repair assays were performed with purified proteins and cell extracts. CUX1 protein expression was analyzed by immunohistochemistry using a tumor microarray of 150 glioblastoma samples. The effect of CUX1 knockdown and overexpression on the resistance of glioblastoma cell lines to temozolomide was investigated.

Results

We show that CUT domains stimulate APE1 activity. In agreement with these findings, CUX1 knockdown causes an increase in the number of abasic sites in genomic DNA and a decrease in APE1 activity as measured in cell extracts. Conversely, ectopic CUX1 expression increases APE1 activity and lowers the number of abasic sites. Having established that CUX1 is expressed at high levels in most glioblastomas, we next show that the resistance of glioblastoma cells to temozolomide and to a combined treatment of temozolomide and ionizing radiation is reduced following CUX1 knockdown, but increased by overexpression of CUX1 or a short protein containing only 2 CUT domains, which is active in DNA repair but devoid of transcriptional activity.

Conclusion

These findings indicate that CUX1 expression level impacts on the response of glioblastoma cells to treatment and identifies the CUT domains as potential therapeutic targets.

Histopathologic quantification of viable tumor versus treatment effect in surgically resected recurrent glioblastoma

PURPOSE

The prognostic impact of the histopathologic features of recurrent glioblastoma surgical specimens is unknown. We sought to determine whether key histopathologic characteristics in glioblastoma tumors resected after chemoradiotherapy are associated with overall survival (OS).

METHODS

The following characteristics were quantified in recurrent glioblastoma specimens at our institution: extent of viable tumor (accounting for % of specimen comprised of tumor and tumor cellularity), mitoses per 10 high-power fields (0, 1-10, > 10), Ki-67 proliferative index (0-100%), hyalinization (0-6; none to extensive), rarefaction (0-6), hemosiderin (0-6), and % of specimen comprised of geographic necrosis (0-100%; converted to 0-6 scale). Variables associated with OS in univariate analysis, as well as age, eastern cooperative oncology group performance status (ECOG PS), extent of repeat resection, time from initial diagnosis to repeat surgery, and O⁶-methylguanine-DNA methyltransferase promoter methylation, were included in a multivariable Cox proportional hazards model.

RESULTS

37 specimens were assessed. In a multivariate model, high Ki-67 proliferative index was the only histopathologic characteristic associated with worse OS following repeat surgery for glioblastoma (hazard ratio (HR) 1.3, 95% CI 1.1-1.5, p = 0.003). Shorter time interval from initial diagnosis to repeat surgery (HR 1.11, 95% CI 1.02-1.21, p = 0.016) and ECOG PS ≥ 2 (HR 4.19, 95% CI 1.72-10.21, p = 0.002) were also independently associated with inferior OS.

CONCLUSION

In patients with glioblastoma undergoing repeat resection following chemoradiotherapy, high Ki-67 index in the recurrent specimen, short time to recurrence, and poor PS are independently associated with worse OS. Histopathologic quantification of viable tumor versus therapy-related changes has limited prognostic influence.

Sensitization of Cancer Cells to Radiation and Topoisomerase I Inhibitor Camptothecin Using Inhibitors of PARP and Other Signaling Molecules

Radiation and certain anticancer drugs damage DNA, resulting in apoptosis induction in cancer cells. Currently, the major limitations on the efficacy of such therapies are development of resistance and adverse side effects. Sensitization is an important strategy for increasing therapeutic efficacy while minimizing adverse effects. In this manuscript, we review possible sensitization strategies for radiation and anticancer drugs that cause DNA damage, focusing especially on modulation of damage repair pathways and the associated reactions.

Postoperative neoadjuvant temozolomide before radiotherapy versus standard radiotherapy in patients 60 years or younger with anaplastic astrocytoma or glioblastoma: a randomized trial

INTRODUCTION

A pilot study of temozolomide (TMZ) given before radiotherapy (RT) for anaplastic astrocytoma (AA) and glioblastoma (GBM) resulted in prolonged survival compared to historical controls receiving RT alone. We therefore investigated neoadjuvant TMZ (NeoTMZ) in a randomized trial. During enrollment, concomitant and adjuvant radio-chemotherapy with TMZ became standard treatment. The trial was amended to include concurrent TMZ.

PATIENTS AND METHODS

Patients, after surgery for GBM or AA, age ≤60 years and performance status (PS) 0-2, were randomized to either 2-3 cycles of TMZ, 200 mg/m² days 1-5 every 28 days, followed by RT 60 Gy in 30 fractions or RT only. Patients without progressive disease after two TMZ cycles, received the third cycle. From March 2005, TMZ 75 mg/m² was administered daily concomitant with RT. TMZ was recommended first-line treatment at progression. Primary endpoint was overall survival and secondary safety.

RESULTS

The study closed prematurely after enrolling 144 patients, 103 with GBM and 41 with AA. Median age was 53 years (range 24-60) and 89 (62%) were male. PS was 0-1 for 133 (92%) patients, 53 (37%) had complete surgical resection and 18 (12%) biopsy. Ninety-two (64%) received TMZ concomitant with RT. Seventy-two (50%) were randomized to neoadjuvant treatment. For the overall study population survival was 20.3 months for RT and 17.7 months for NeoTMZ (p = .76), this not reaching the primary objective. For the preplanned subgroup analysis, we found that NeoTMZ AA patients had a median survival of 95.1 months compared to 35.2 months for RT (p = .022). For patients with GBM, no difference in survival was observed (p = .10). MGMT and IDH status affected outcome.

CONCLUSIONS

No advantage of NeoTMZ was noted for the overall study population or subgroup of GBM, while NeoTMZ resulted in 5 years longer median survival for patients diagnosed as AA.

PEGylated squalenoyl-gemcitabine nanoparticles for the treatment of glioblastoma

New treatments for glioblastoma multiforme (GBM) are desperately needed, as GBM prognosis remains poor, mainly due to treatment resistance, poor distribution of therapeutics in the tumor tissue, and fast metabolism of chemotherapeutic drugs in the brain extracellular space. Convection-enhanced delivery (CED) of nanoparticles (NPs) has been shown to improve the delivery of chemotherapeutic drugs to the tumor bed, providing sustained release, and enhancing survival of animals with intracranial tumors. Here we administered gemcitabine, a nucleoside analog used as a first line treatment for a wide variety of extracranial solid tumors, within squalene-based NPs using CED, to overcome the above-mentioned challenges of GBM treatment. Small percentages of poly(ethylene) glycol (PEG) dramatically enhanced the distribution of squalene-gemcitabine nanoparticles (SQ-Gem NPs) in healthy animals and tumor-bearing animals after administration by CED. When tested in an orthotopic model of GBM, SQ-Gem-PEG NPs demonstrated significantly improved therapeutic efficacy compared to free gemcitabine, both as a chemotherapeutic drug and as a radiosensitizer. Furthermore, MR contrast agents were incorporated into the SQ-Gem-PEG NP formulation, providing a way to non-invasively track the NPs during infusion.

Craniospinal irradiation with concomitant and adjuvant temozolomide--a feasibility assessment of toxicity in patients with glioblastoma with a PNET component

There is no standard treatment for glioblastoma with elements of PNET (GBM-PNET). Conventional treatment for glioblastoma is surgery followed by focal radiotherapy with concurrent temozolomide. Given the increased propensity for neuroaxial metastases seen with GBM-PNETs, craniospinal irradiation (CSI) with temozolomide (TMZ) could be a feasible treatment option but little is known regarding its toxicity. The clinical records of all patients treated at two UK neuro-oncology centres with concurrent CSI and TMZ were examined for details of surgery, radiotherapy, chemotherapy and toxicities related to the CSI-TMZ component of their treatment. Eight patients were treated with CSI-TMZ, the majority (6/8) for GBM-PNET. All patients completed radiotherapy to the craniospinal axis 35-40 Gy in 20-24 daily fractions with a focal boost to the tumour of 14-23.4 Gy in 8-13 daily fractions. Concurrent TMZ was administered at 75 mg/m(2) for seven of the cohort, with the other patient receiving 50 mg/m(2). The most commonly observed non-haematological toxicities were nausea and vomiting, with all patients experiencing at least grade 2 symptoms of either or both. All patients had at least grade 3 lymphopaenia. Two patients experience grade 4 neutropaenia and grade 3 thrombocytopaenia. Three of the eight patients required omission of TMZ for part of their chemoradiotherapy and 3/8 required hospital admission at some point during chemoradiotherapy. The addition of TMZ to CSI did not interrupt radiotherapy. Principal toxicities were neutropaenia, lymphopaenia, thrombocytopaenia, nausea and vomiting. Treatment with CSI-TMZ merits further investigation and may be suitable for patients with tumours at high-risk of metastatic spread throughout the CNS who have TMZ-sensitive pathologies.

Initial Experience With Gallium-68 DOTA-Octreotate PET/CT and Peptide Receptor Radionuclide Therapy for Pediatric Patients With Refractory Metastatic Neuroblastoma

RATIONALE

Pediatric patients with refractory neuroblastoma have limited therapeutic options. Neuroblastoma may express somatostatin receptors (SSTRs) allowing imaging with 68Ga-DOTA-Octreotate (GaTATE) positron emission tomography/computed tomography (PET/CT) and peptide receptor radionuclide therapy (PRRT). We reviewed our experience with this theranostic combination.

MATERIALS AND METHODS

GaTATE studies (8 patients; 2 to 9 years old) were reviewed and compared with 123I-MIBG or posttreatment 131I-MIBG studies. Immunohistochemistry (IHC) for SSTR subtype 2 was performed in 5 patients. Four patients received PRRT.

RESULTS

GaTATE PET showed additional disease in 38% (3/8 patients), and upstaged 1 patient by detecting marrow involvement. IHC detected SSTR 2 in all patients assessed. Six patients were deemed suitable for PRRT on imaging. Four patients received 17 cycles of palliative PRRT (10 111In-DOTATATE; 5 177Lu-DOTATATE; 1 combined 111In and 177Lu-DOTATATE; 1 combined 177Lu and 90Y-DOTATATE) with no significant toxicity attributed to PRRT. All had objective responses. Two survivors are now 40 and 56 months from PRRT commencement.

CONCLUSIONS

GaTATE PET was positive in a high proportion of patients with refractory neuroblastoma, correlating with SSTR 2 on IHC, with additional disease identified compared with MIBG imaging. PRRT seems safe, feasible, with responses observed in patients with progression despite multimodality treatment. These data support ongoing clinical trials in such patients.

Methionine Uptake and Required Radiation Dose to Control Glioblastoma

PURPOSE

The purpose of this study was to retrospectively assess the feasibility of radiation therapy planning for glioblastoma multiforme (GBM) based on the use of methionine (MET) positron emission tomography (PET), and the correlation among MET uptake, radiation dose, and tumor control.

METHODS AND MATERIALS

Twenty-two patients with GBM who underwent MET-PET prior to radiation therapy were enrolled. MET uptake in 30 regions of interest (ROIs) from 22 GBMs, biologically effective doses (BEDs) for the ROIs and their ratios (MET uptake:BED) were compared in terms of whether the ROIs were controlled for >12 months.

RESULTS

MET uptake was significantly correlated with tumor control (odds ratio [OR], 10.0; P = .005); however, there was a higher level of correlation between MET uptake:BED ratio and tumor control (OR, 40.0; P < .0001). These data indicated that the required BEDs for controlling the ROIs could be predicted in terms of MET uptake; BED could be calculated as [34.0 × MET uptake] Gy from the optimal threshold of the MET uptake:BED ratio for tumor control.

CONCLUSIONS

Target delineation based on MET-PET was demonstrated to be feasible for radiation therapy treatment planning. MET-PET could not only provide precise visualization of infiltrating tumor cells but also predict the required radiation doses to control target regions.

Polish natural bee honeys are anti-proliferative and anti-metastatic agents in human glioblastoma multiforme U87MG cell line

Honey has been used as food and a traditional medicament since ancient times. However, recently many scientists have been concentrating on the anti-oxidant, anti-proliferative, anti-inflammatory and other properties of honey. In this study, we investigated for the first time an anticancer effect of different honeys from Poland on tumor cell line - glioblastoma multiforme U87MG. Anti-proliferative activity of honeys and its interferences with temozolomide were determined by a cytotoxicity test and DNA binding by [H³]-thymidine incorporation. A gelatin zymography was used to conduct an evaluation of metalloproteinases (MMP-2 and MMP-9) expression in U87MG treatment with honey samples. The honeys were previously tested qualitatively (diastase activity, total phenolic content, lead and cadmium content). The data demonstrated that the examined honeys have a potent anti-proliferative effect on U87MG cell line in a time- and dose-dependent manner, being effective at concentrations as low as 0.5% (multifloral light honey - viability 53% after 72 h of incubation). We observed that after 48 h, combining honey with temozolomide showed a significantly higher inhibitory effect than the samples of honey alone. We observed a strong inhibition of MMP-2 and MMP-9 for the tested honeys (from 20 to 56% and from 5 to 58% compared to control, respectively). Our results suggest that Polish honeys have an anti-proliferative and anti-metastatic effect on U87MG cell line. Therefore, natural bee honey can be considered as a promising adjuvant treatment for brain tumors.

Temozolomide for treatment of brain metastases: A review of 21 clinical trials

Brain metastases from solid tumours are associated with poor prognosis despite aggressive treatment. Temozolomide can be used for the treatment of glioblastoma multiforme as well as melanoma. It has also been shown to have activity in patients with brain metastases from various malignancies, since it can cross the blood-brain barrier. To better understand the efficacy of temozolomide in the treatment of brain metastases, we carried out a review of 21 published clinical trials to determine whether temozolomide would benefit patients with brain metastases from solid tumours. Information regarding complete response, partial response, stable disease, objective response and objective response rate were collected to assess clinical outcomes. A modest therapeutic effect was observed when temozolomide was used as a single agent, however, the combination of temozolomide with whole-brain radiotherapy and/or other anticancer drugs exhibited encouraging activity. Thus, future high quality studies are warranted to confirm our findings.

HIF-1α inhibition sensitizes pituitary adenoma cells to temozolomide by regulating MGMT expression

Suppression of hypoxia-inducible factor 1α (HIF-1α) has been shown to sensitize glioblastoma cells to temozolomide (TMZ) treatment via down-modulation of O6-methylguanine-DNA methyltransferase (MGMT) expression. To date, whether the efficacy of TMZ therapy is correlated with MGMT expression and whether HIF-1α suppression exerts similar effects in human pituitary adenoma cells have not been defined. In the present study, using an HIF-1α knockdown strategy and the HIF-1α inhibitor 2-methoxyestradiol (2ME), we demonstrated for the first time that HIF-1α suppression increases the efficacy of TMZ in human pituitary adenoma cells in vitro and in vivo. Our mechanistic study showed that HIF-1α suppression resulted in down-modulation of MGMT expression and decreased DNA damage repair ability as demonstrated by decreased RAD51 protein expression. These results suggest an HIF-1α-dependent regulation of MGMT expression in human pituitary adenoma cells, and HIF-1α knockdown or the HIF-1α inhibitor 2ME can confer TMZ sensitization in human pituitary adenomas. The clinical application of 2ME as an adjuvant therapy may be a potential approach to improve the efficacy of TMZ therapy for pituitary adenomas.

Temozolomide added to whole brain radiotherapy in patients with multiple brain metastases of non-small-cell lung cancer: a multicentric Austrian phase II study

BACKGROUND

This multicentric randomized phase II study investigated the feasibility and toxicity of temozolomide (TMZ) added to whole brain radiotherapy (WBRT) followed by adjuvant TMZ in patients with multiple brain metastases of non-small-cell lung cancer (NSCLC).

METHODS

Patients with multiple brain metastases from NSCLC aged ≥ 18 years, classified according to recursive partitioning analysis class I or II and with adequate organ functions were eligible. Treatment consisted of WBRT + TMZ 75 mg/m² for 2 weeks followed at day 28 by TMZ 100 mg/m²/day 2 weeks on/2 weeks off for up to 6 months (radiochemotherapy, RCT) or WBRT alone (radiotherapy, RT).

RESULTS

The study enrolled only 35 patients (22 patients in RCT and 13 in RT) and had to be closed prematurely due to poor accrual. The toxicity was mainly due to TMZ with WHO grade 3 and 4 thrombocytopenia in 3/22 versus 0/13, leucocytopenia in 1/22 versus 0/13 and lymphocytopenia in 7/22 versus 12/13 patients in RCT and RT respectively. Thirteen patients in RCT and six in RT progressed systemically and dropped out before first restaging of the response in brain. Median time to progression (TTP) was 2.4 months (95 % CI: 2-2.6 months) and 2.0 months (95 % CI: 0.5-3.5 months), median overall survival (OAS) was 3 months (95% CI: 1.7-3.1 months) and 6.3.months (95 % CI: 0.2-7.6 months) in RCT and RT, respectively.

CONCLUSIONS

Like other studies before on patients with brain metastases, insufficient number of recruited patients does not allow conclusions on efficacy and toxicity as the study closed prematurely.

Comparable cell survival between high dose rate flattening filter free and conventional dose rate irradiation

PURPOSE

Investigation of clonogenic cell survival and cell proliferation following single dose and fractionated delivery of high dose rate flattening filter free (FFF) irradiation compared to conventional dose rates.

MATERIAL AND METHODS

The human astrocytoma D384, glioma T98 and lung carcinoma SW1573 cell lines were irradiated using either a single dose (0-12 Gy) or a fractionated protocol of 5 daily fractions of 2 Gy (D384) or 3 Gy (SW1573). Cells were irradiated inside a phantom using fixed gantry beams of a linear accelerator. A sliding window technique created homogeneous dose distributions over the surface of the cell cultures. Irradiations using standard beams (6 MV, 600 MU/min.) and high dose rate FFF beams (10 MV, 2400 MU/min.) were compared. Cell survival was determined by clonogenic assay. In the fractionated irradiation set-up, the number of clonogenic cells was estimated by including tumor cell proliferation during the overall treatment time in the analysis.

RESULTS

All cell lines showed equal cell survival following irradiation using either the FFF beams or conventional flattened (FF) beams. This was observed after single dose exposure (0-12 Gy) as well as after fractionated irradiation (p = 0.08 for D384 and 0.20 for SW1373 cell lines).

CONCLUSION

FFF irradiation with a dose rate of 2400 MU/min and four times higher dose per pulse compared to irradiation with FF beams did not change cell survival for three human cancer cell lines up to a fraction dose of 12 Gy compared to irradiation using FF beams.

Evaluation of poly (ADP-ribose) polymerase inhibitor ABT-888 combined with radiotherapy and temozolomide in glioblastoma

BACKGROUND

The cytotoxicity of radiotherapy and chemotherapy can be enhanced by modulating DNA repair. PARP is a family of enzymes required for an efficient base-excision repair of DNA single-strand breaks and inhibition of PARP can prevent the repair of these lesions. The current study investigates the trimodal combination of ABT-888, a potent inhibitor of PARP1-2, ionizing radiation and temozolomide(TMZ)-based chemotherapy in glioblastoma (GBM) cells.

METHODS

Four human GBM cell lines were treated for 5 h with 5 μM ABT-888 before being exposed to X-rays concurrently with TMZ at doses of 5 or 10 μM for 2 h. ABT-888's PARP inhibition was measured using immunodetection of poly(ADP-ribose) (pADPr). Cell survival and the different cell death pathways were examined via clonogenic assay and morphological characterization of the cell and cell nucleus.

RESULTS

Combining ABT-888 with radiation yielded enhanced cell killing in all four cell lines, as demonstrated by a sensitizer enhancement ratio at 50% survival (SER50) ranging between 1.12 and 1.37. Radio- and chemo-sensitization was further enhanced when ABT-888 was combined with both X-rays and TMZ in the O6-methylguanine-DNA-methyltransferase (MGMT)-methylated cell lines with a SER50 up to 1.44. This effect was also measured in one of the MGMT-unmethylated cell lines with a SER50 value of 1.30. Apoptosis induction by ABT-888, TMZ and X-rays was also considered and the effect of ABT-888 on the number of apoptotic cells was noticeable at later time points. In addition, this work showed that ABT-888 mediated sensitization is replication dependent, thus demonstrating that this effect might be more pronounced in tumour cells in which endogenous replication lesions are present in a larger proportion than in normal cells.

CONCLUSIONS

This study suggests that ABT-888 has the clinical potential to enhance the current standard treatment for GBM, in combination with conventional chemo-radiotherapy. Interestingly, our results suggest that the use of PARP inhibitors might be clinically significant in those patients whose tumour is MGMT-unmethylated and currently derive less benefit from TMZ.

Toxicity and survival in primary glioblastoma patients treated with concomitant plus adjuvant temozolomide versus adjuvant temozolomide: results of a single-institution, retrospective, matched-pair analysis

BACKGROUND

To compare survival and hematological toxicity rates between two postoperative therapy regimens in patients with primary glioblastoma (GBM), namely temozolomide (TMZ) concomitant to radiation, followed by adjuvant TMZ, versus adjuvant TMZ after radiation only.

PATIENTS AND METHODS

A total of 191 patients with primary GBM were postoperatively treated with either radiation and concomitant TMZ, followed by adjuvant TMZ (Stupp protocol) (n = 154), or radiation followed by adjuvant TMZ (n = 37). The incidence of hematological adverse effects (AE) was recorded for all patients. From both treatment groups, 26 patients were matched according to age, Karnofsky performance scale (KPS) score, and O6-methylguanine-DNA-methyltransferase (MGMT) promoter methylation.

RESULTS

Hematological AEs were mild in both unmatched groups, but were significantly more frequent in the concomitant plus adjuvant TMZ group (p < 0.001). Matched-pair analysis confirmed significantly more frequent hematological AEs in the concomitant and adjuvant group compared to the sequential (adjuvant) TMZ group (p = 0,012). Patients treated with concomitant plus adjuvant TMZ showed significantly longer progression-free survival (PFS) (10.6 versus 6.6 months; p = 0.014), but no prolonged overall survival (OS) (16.9 vs. 15.6 months; p = 0.717) compared to patients who received the sequential treatment regimen.

CONCLUSION

In this retrospective study, the OS in patients with primary GBM treated with sequential TMZ following radiation appeared to be similar to that in patients treated with concomitant plus adjuvant TMZ. Given the significantly higher risk of hematological AE for concomitant treatment, the role of concomitant plus adjuvant TMZ use compared to sequential administration of TMZ, especially for patients with MGMT-unmethylated tumors, should be further evaluated.

Role of neurosurgery and radiation therapy in the management of brain tumors

In the United States, approximately 65,000 people are diagnosed with primary brain tumors each year, with an incidence of 19.3 cases per 100,000 person-years. These numbers represent a wide spectrum of disease, from benign to malignant, and prognosis varies widely based on disease. Treatment of primary brain tumors most often uses a combination of surgery and radiation. However, over the past several generations, technological advancements have significantly altered the treatment paradigm. This article reviews the current role of neurosurgery and radiation therapy in the management of primary brain tumors.

DW-MRI as a biomarker to compare therapeutic outcomes in radiotherapy regimens incorporating temozolomide or gemcitabine in glioblastoma

The effectiveness of the radiosensitizer gemcitabine (GEM) was evaluated in a mouse glioma along with the imaging biomarker diffusion-weighted magnetic resonance imaging (DW-MRI) for early detection of treatment effects. A genetically engineered murine GBM model [Ink4a-Arf^−/− Pten^loxP/loxP/Ntv-a RCAS/PDGF(+)/Cre(+)] was treated with gemcitabine (GEM), temozolomide (TMZ) +/− ionizing radiation (IR). Therapeutic efficacy was quantified by contrast-enhanced MRI and DW-MRI for growth rate and tumor cellularity, respectively. Mice treated with GEM, TMZ and radiation showed a significant reduction in growth rates as early as three days post-treatment initiation. Both combination treatments (GEM/IR and TMZ/IR) resulted in improved survival over single therapies. Tumor diffusion values increased prior to detectable changes in tumor volume growth rates following administration of therapies. Concomitant GEM/IR and TMZ/IR was active and well tolerated in this GBM model and similarly prolonged median survival of tumor bearing mice. DW-MRI provided early changes to radiosensitization treatment warranting evaluation of this imaging biomarker in clinical trials.

External beam radiotherapy of recurrent glioma: radiation tolerance of the human brain

Malignant gliomas relapse in close proximity to the resection site, which is the postoperatively irradiated volume. Studies on re-irradiation of glioma were examined regarding radiation-induced late adverse effects (i.e., brain tissue necrosis), to obtain information on the tolerance dose and treatment volume of normal human brain tissue. The studies were analyzed using the linear-quadratic model to express the re-irradiation tolerance in cumulative equivalent total doses when applied in 2 Gy fractions (EQD2_cumulative). Analysis shows that the EQD2_cumulative increases from conventional re-irradiation series to fractionated stereotactic radiotherapy (FSRT) to LINAC-based stereotactic radiosurgery (SRS). The mean time interval between primary radiotherapy and the re-irradiation course was shortened from 30 months for conventional re-irradiation to 17 and 10 months for FSRT and SRS, respectively. Following conventional re-irradiation, radiation-induced normal brain tissue necrosis occurred beyond an EQD2_cumulative around 100 Gy. With increasing conformality of therapy, the smaller the treatment volume is, the higher the radiation dose that can be tolerated. Despite the dose escalation, no increase in late normal tissue toxicity was reported. On basis of our analysis, the use of particle therapy in the treatment of recurrent gliomas, because of the optimized physical dose distribution in the tumour and surrounding healthy brain tissue, should be considered for future clinical trials.

Efficacy and toxicity of CyberKnife re-irradiation and "dose dense" temozolomide for recurrent gliomas

BACKGROUND

Stereotactic radiosurgery (SRS) can be a useful adjunct to the treatment of recurrent glioblastoma multiforme (GBM). Its combination with chemotherapy is attractive for the possible radiosensitization effect and cytotoxicity on tumor cells in distant areas. The aim of this study was to evaluate the efficacy and toxicity of CyberKnife SRS alone and combined with a "dose-dense" administration of temozolomide (TMZ) for recurrent GBM.

METHODS

Between July 2007 and July 2010, 23 patients underwent CyberKnife SRS. In 12 patients irradiation was combined with TMZ at 75 mg/m(2)/day for 21 days every 28 days. The median prescription dose in this group was 20 Gy (mean 20.7 ± 4 Gy) with a median number of fractions of 2. The median dose for the 11 patients who underwent SRS alone was 20 Gy (mean 19.9 ± 4.4 Gy; p = NS).

RESULTS

The median survival was 12 months for patients who underwent SRS/TMZ and 7 months for those who received SRS alone (p < 0.01). The 6-month progression-free survival (PFS) of the SRS/TMZ group was 66.7% vs. 18% for those who underwent SRS alone (p = 0.03). The median time to progression (TTP) was 7 months for patients who underwent SRS/TMZ and 4 months for those who underwent SRS alone (p = 0.01). Corticosteroid dependency was developed by most patients; radionecrosis was evident in one patient (4.3%) receiving TMZ. Grade 3 hematological toxicity was recorded in >40% of patients receiving chemotherapy.

CONCLUSIONS

The results suggest that Cyberknife re-treatments are relatively safe using selected dose/fraction schemes. The combination with TMZ improved patients' outcomes with OS and 6-month PFS that favorably compares with alternative treatments, but the incidence of major adverse effects was >40%. Further studies are warranted.

Can drugs enhance hypofractionated radiotherapy? A novel method of modeling radiosensitization using in vitro data

PURPOSE

Hypofractionated radiotherapy (hRT) is being explored for a number of malignancies. The potential benefit of giving concurrent chemotherapy with hRT is not known. We sought to predict the effects of combined modality treatments by using mathematical models derived from laboratory data.

METHODS AND MATERIALS

Data from 26 published clonogenic survival assays for cancer cell lines with and without the use of radiosensitizing chemotherapy were collected. The first three data points of the RT arm of each assay were used to derive parameters for the linear quadratic (LQ) model, the multitarget (MT) model, and the generalized linear quadratic (gLQ) model. For each assay and model, the difference between the predicted and observed surviving fractions at the highest tested RT dose was calculated. The gLQ model was fitted to all the data from each RT cell survival assay, and the biologically equivalent doses in 2-Gy fractions (EQD2s) of clinically relevant hRT regimens were calculated. The increase in cell kill conferred by the addition of chemotherapy was used to estimate the EQD2 of hRT along with a radiosensitizing agent. For comparison, this was repeated using conventionally fractionated RT regimens.

RESULTS

At a mean RT dose of 8.0 Gy, the average errors for the LQ, MT, and gLQ models were 1.63, 0.83, and 0.56 log units, respectively, favoring the gLQ model (p < 0.05). Radiosensitizing chemotherapy increased the EQD2 of hRT schedules by an average of 28% to 82%, depending on disease site. This increase was similar to the gains predicted for the addition of chemotherapy to conventionally fractionated RT.

CONCLUSIONS

Based on published in vitro assays, the gLQ equation is superior to the LQ and MT models in predicting cell kill at high doses of RT. Modeling exercises demonstrate that significant increases in biologically equivalent dose may be achieved with the addition of radiosensitizing agents to hRT. Clinical study of this approach is warranted.

Nanostructured Pt(NH(3))(4)Cl(2)/SiO(2) for nanomedicine: catalytic degradation of DNA in cancer cells

In vivo suppression of glioblastoma multiforme (GBM) in Wistar rats using silica-shelled biocatalytic Pt(NH(3))(4)Cl(2) nanoparticles is reported. These nanoparticles were synthesized by a sol-gel technique and characterized by SEM and HRTEM imaging. We confirmed morphological uniformity (30 nm) and surface acidity of the nanoparticles, respectively, by TEM imaging and FTIR spectral analysis. Interestingly, treatment of Wistar rats intraperitoneally inoculated with C(6) cells using the biocatalysts resulted in considerable tumor shrinkage. Efficiency of the biocatalyst to shrink a tumor is superior to that by the commercial cytotoxic agent cisplatin. The tumor suppression property of Pt(NH(3))(4)Cl(2) nanoparticles is attributed to catalytic damage of DNA in C(6) cells.

Valproic acid sensitizes human glioma cells for temozolomide and γ-radiation

Temozolomide (TMZ) is given in addition to radiotherapy in glioma patients, but its interaction with the commonly prescribed antiepileptic drug valproic acid (VPA) is largely unknown. Induction of DNA demethylation by VPA could potentially induce expression of the O(6)-methylguanine-DNA-methyltransferase (MGMT) protein, causing resistance to TMZ and thereby antagonizing its effect. Therefore, this study investigates the interaction between VPA, TMZ, and γ-radiation. Two glioma cell lines were used that differ in TMZ sensitivity caused by the absence (D384) or presence (T98) of the MGMT protein. VPA was administered before (24/48 h) or after (24 h) single doses of γ-radiation; or, after 24 h, VPA treatment was accompanied by a single dose of TMZ for another 24 h. For trimodal treatment the combination of VPA and TMZ was followed by single doses of γ-radiation. In both cell lines VPA caused enhancement of the radiation response after preincubation (DMF(0.2) 1.4 and 1.5) but not after postirradiation (DMF(0.2) 1.1 and 1.0). The combination of VPA and TMZ caused enhanced cytotoxicity (DMF(0.2) 1.7) in both the TMZ-sensitive cell line (D384) and the TMZ-resistant cell line (T98). The combination of VPA and TMZ caused a significant radiation enhancement (DMF(0.2) 1.9 and 1.6) that was slightly more effective than that of VPA alone. VPA does not antagonize the cytotoxic effects of TMZ. Preincubation with VPA enhances the effect of both γ-radiation and TMZ, in both a TMZ-sensitive and a TMZ-resistant human glioma cell line. VPA combined with TMZ may lead to further enhancement of the radiation response.

Glioblastoma: patterns of recurrence and efficacy of salvage treatments

BACKGROUND

It is controversial if distant recurrence of glioblastoma is more common after temozolomide (TMZ) concurrent with radiotherapy (RT). Optimal therapy for patients with recurrent disease after RT/TMZ is unclear. Our purpose was to evaluate recurrence patterns in glioblastoma and the effect of treatment at recurrence upon survival.

METHODS

We performed a retrospective review of 67 patients with newly diagnosed glioblastoma treated with RT/TMZ between 2003-2007. Statistical analyses included Kaplan-Meier method for survival, and multivariate Cox proportional hazards model for the effect of salvage treatment on survival.

RESULTS

58 patients (86.6%) recurred locally; 9 patients (13.4%) had a distant non-contiguous focus of new disease. Median survival(MS) was 17 months; median time-to-progression(TTP) 6.8 months. The local and distant groups had comparable prognostic factors. There was no difference in MS(p=0.35) or TTP(p=0.95) by location of recurrence. At relapse, 26 patients(38.8%) received continuous, dose-intense TMZ, 24(35.8%) other therapy(4.5% RT; 20.9% lomustine+/-procarbazine; 4.5% etoposide; 1.5% conventional TMZ; 4.5% TMZ then lomustine), and 17(25.4%) were untreated. Dose-intense TMZ was associated with prolonged MS compared to all other patients(21.5 months vs. 12.4 months, p=0.019, HR=3.86, 95%CI: 1.81-8.22) and similar to MS with other chemotherapy regimens(18.8 months, p=0.40, HR=1.30, 95% CI: 0.65-2.61).

CONCLUSION

The pattern of recurrence of glioblastoma treated with RT/TMZ was predominantly local. Second-line treatment with continuous dose-intense TMZ may prolong survival in patients with recurrent glioblastoma. Overall survival is similar to other conventional salvage regimens; however TMZ may be better tolerated. This study is limited by its retrospective nature and potential selection bias. Prospective controlled studies are needed.

Antiproliferative effects of Tubi-bee propolis in glioblastoma cell lines

Propolis is a resin formed by a complex chemical composition of substances that bees collect from plants. Since ancient times, propolis has been used in folk medicine, due to its biological properties, that include antimicrobial, anti-inflammatory, antitumoral and immunomodulatory activities. Glioblastoma is the most common human brain tumor. Despite the improvements in GBM standard treatment, patients’ prognosis is still very poor. The aim of this work was to evaluate in vitro the Tubi-bee propolis effects on human glioblastoma (U251 and U343) and fibroblast (MRC-5) cell lines. Proliferation, clonogenic capacity and apoptosis were analyzed after treatment with 1 mg/mL and 2 mg/mL propolis concentrations for different time periods. Additionally, glioblastoma cell lines were submitted to treatment with propolis combined with temozolomide (TMZ). Data showed an antiproliferative effect of tubi-bee propolis against glioblastoma and fibroblast cell lines. Combination of propolis with TMZ had a synergic anti-proliferative effect. Moreover, propolis caused decrease in colony formation in glioblastoma cell lines. Propolis treatment had no effects on apoptosis, demonstrating a cytostatic action. Further investigations are needed to elucidate the molecular mechanism of the antitumor effect of propolis, and the study of its individual components may reveal specific molecules with antiproliferative capacity.

Rad51 inhibition is an effective means of targeting DNA repair in glioma models and CD133+ tumor-derived cells

High grade gliomas (HGGs) are characterized by resistance to radiotherapy and chemotherapy. Targeting Rad51-dependent homologous recombination repair may be an effective target for chemo- and radiosensitization. In this study we assessed the role of Rad51-dependent repair on sensitivity to radiation and temozolomide (TMZ) as single agents or in combination. Repair protein levels in established glioma cell lines, early passage glioblastoma multiforme (GBM) cell lines, and normal human astrocytes (NHAs) were measured using western blot. Viability and clonogenic survival assays were used to measure the effects of Rad51 knockdown with radiation (XR) and TMZ. Immunocytochemistry was used to evaluate kinetics of Rad51 and γ-H2AX repair foci. Immunohistochemistry was used to assess Rad51 protein levels in glioma specimens. Repair proteins including Rad51 are upregulated in HGG cells compared with NHA. Established glioma cell lines show a dose-dependent increase in Rad51 foci formation after XR and TMZ. Rad51 levels are inversely correlated with radiosensitivity, and downregulation markedly increases the cytotoxicity of TMZ. Rad51 knockdown also promotes more residual γ-H2AX foci 24 h after combined treatment. Newly established GBM cell lines also have high Rad51 levels and are extremely sensitive to Rad51 knockdown. Clinical samples from recently resected gliomas of varying grades demonstrate that Rad51 levels do not correlate with tumor grade. Rad51-dependent repair makes a significant contribution to DNA repair in glioma cells and contributes to resistance to both XR and TMZ. Agents targeting Rad51-dependent repair would be effective adjuvants in standard combination regimens.

Temozolomide-induced inhibition of pituitary adenoma cells

Object

Aggressive pituitary adenomas frequently require multimodality treatment including pituitary-suppressive medications, microsurgery, and radiation therapy or radiosurgery. The effectiveness of temozolomide in terms of growth suppression and decreased hormonal production is evaluated.

Methods

Three pituitary adenoma cell lines—MMQ, GH3, and AtT20—were used. A dose escalation of temozolomide was performed for each cell line, and inhibition of cell proliferation was assessed using an MTT assay. Concentrations of temozolomide that produced statistically significant inhibition of cell proliferation for each cell type were identified. Extent of apoptosis for each selected temozolomide concentration was studied using TUNEL staining. The effect of temozolomide on prolactin secretion in MMQ and GH3 cells was also measured via ELISA.

Results

Significant inhibition of cell proliferation was noted for MMQ and GH3 cells at a concentration of 250 μM temozolomide. The AtT20 cells demonstrated statistically significant cell inhibition at a concentration of only 50 μM temozolomide (p < 0.05). Apoptosis significantly increased in all cell lines in as little as 24 hours of incubation at the respective temozolomide concentrations (p < 0.05). Prolactin secretion in the prolactin secreting MMQ and GH3 cell lines was inhibited by 250 μM temozolomide.

Conclusions

Temozolomide inhibits cell proliferation and induces apoptotic cell death in aggressive pituitary adenoma cells. A reduction in hormonal secretion in prolactinoma cells was also afforded by temozolomide. Temozolomide may prove useful in the multimodality management of aggressive pituitary adenomas.

Minimally cytotoxic doses of temozolomide produce radiosensitization in human glioblastoma cells regardless of MGMT expression

Concurrent treatment with the methylating agent temozolomide during radiotherapy has yielded the first significant improvement in the survival of adult glioblastomas (GBM) in the last three decades. However, improved survival is observed in a minority of patients, most frequently those whose tumors display CpG methylation of the O(6)-methylguanine (O(6)-meG)-DNA methyltransferase (MGMT) promoter, and adult GBMs remain invariably fatal. Some, although not all, preclinical studies have shown that temozolomide can increase radiosensitivity in GBM cells that lack MGMT, the sole activity in human cells that removes O(6)-meG from DNA. Here, we systematically examined the temozolomide dose dependence of radiation killing in established GBM cell lines that differ in ability to remove O(6)-meG or tolerate its lethality. Our results show that minimally cytotoxic doses of temozolomide can produce dose-dependent radiosensitization in MGMT-deficient cells, MGMT-proficient cells, and MGMT-deficient cells that lack mismatch repair, a process that renders cells tolerant of the lethality of O(6)-meG. In cells that either possess or lack MGMT activity, radiosensitization requires exposure to temozolomide before but not after radiation and is accompanied by formation of double-strand breaks within 45 minutes of radiation. Moreover, suppressing alkyladenine-DNA glycosylase, the only activity in human cells that excises 3-methyladenine from DNA, reduces the temozolomide dose dependence of radiosensitization, indicating that radiosensitization is mediated by 3-methyladenine as well as by O(6)-meG. These results provide novel information on which to base further mechanistic study of radiosensitization by temozolomide in human GBM cells and to develop strategies to improve the outcome of concurrent temozolomide radiotherapy.

Dose-dense temozolomide regimens: antitumor activity, toxicity, and immunomodulatory effects

Temozolomide is an oral alkylating agent with established antitumor activity in patients with primary brain tumors and melanoma. The originally approved temozolomide dosing regimen is 150 to 200 mg/m(2) per day (Days 1 to 5 every 28-day cycle [5 of 28 days]). However, extended dosing regimens (eg, 7 of 14 days, 21 of 28 days, 6 of 8 weeks, or continuously daily) allow for administration of a higher cumulative dose per cycle and have been shown to deplete O(6)-methylguanine-DNA methyltransferase, which may enhance cytotoxic activity. This article reviews efficacy and safety data from studies that investigated dose-dense temozolomide regimens in patients with recurrent glioma and advanced metastatic melanoma. The clinical benefits of these dose-dense regimens compared with the standard 5 of 28-day regimen have yet to be established. Although the toxicity profile of dose-dense temozolomide is generally similar to that of the standard 5 of 28-day regimen, it is associated with an increased incidence and severity of lymphocytopenia. The clinical management of temozolomide-associated lymphodepletion and the potential risks and benefits of extended dosing with temozolomide are discussed. Preclinical and clinical evidence suggests that temozolomide-associated lymphodepletion may enhance the host immune response to tumor-associated antigens and/or immunotherapy and may overcome tumor-mediated immunosuppression. Further studies exploring the clinical implications of lymphodepletion are warranted.

Absence of the MGMT protein as well as methylation of the MGMT promoter predict the sensitivity for temozolomide

Background:

The DNA repair protein O⁶-methylguanine-DNA methyltransferase (MGMT) can cause resistance to the alkylating drug temozolomide (TMZ). The purpose of this study was to determine the relationship between the MGMT status, determined by means of several techniques and methods, and the cytotoxic response to TMZ in 11 glioblastoma multiforme (GBM) cell lines and 5 human tumour cell lines of other origins.

Methods:

Cell survival was analysed by clonogenic assay. The MGMT protein levels were assessed by western blot analysis. The MGMT promoter methylation levels were determined using methylation-specific multiplex ligation-dependent probe amplification (MS-MLPA) and quantitative real-time methylation-specific PCR (qMSP). On the basis of the results of these techniques, six GBM cell lines were selected and subjected to bisulphite sequencing.

Results:

The MGMT protein was detected in all TMZ-resistant cell lines, whereas no MGMT protein could be detected in cell lines that were TMZ sensitive. The MS-MLPA results were able to predict TMZ sensitivity in 9 out of 16 cell lines (56%). The qMSP results matched well with TMZ sensitivity in 11 out of 12 (92%) glioma cell lines. In addition, methylation as detected by bisulphite sequencing seemed to be predictive of TMZ sensitivity in all six cell lines analysed (100%).

Conclusion:

The MGMT protein expression more than MGMT promoter methylation status predicts the response to TMZ in human tumour cell lines.

Exciting new advances in neuro-oncology: the avenue to a cure for malignant glioma

Malignant gliomas are the most common and deadly brain tumors. Nevertheless, survival for patients with glioblastoma, the most aggressive glioma, although individually variable, has improved from an average of 10 months to 14 months after diagnosis in the last 5 years due to improvements in the standard of care. Radiotherapy has been of key importance to the treatment of these lesions for decades, and the ability to focus the beam and tailor it to the irregular contours of brain tumors and minimize the dose to nearby critical structures with intensity-modulated or image-guided techniques has improved greatly. Temozolomide, an alkylating agent with simple oral administration and a favorable toxicity profile, is used in conjunction with and after radiotherapy. Newer surgical techniques, such as fluorescence-guided resection and neuroendoscopic approaches, have become important in the management of malignant gliomas. Furthermore, new discoveries are being made in basic and translational research, which are likely to improve this situation further in the next 10 years. These include agents that block 1 or more of the disordered tumor proliferation signaling pathways, and that overcome resistance to already existing treatments. Targeted therapies such as antiangiogenic therapy with antivascular endothelial growth factor antibodies (bevacizumab) are finding their way into clinical practice. Large-scale research efforts are ongoing to provide a comprehensive understanding of all the genetic alterations and gene expression changes underlying glioma formation. These have already refined the classification of glioblastoma into 4 distinct molecular entities that may lead to different treatment regimens. The role of cancer stem-like cells is another area of active investigation. There is definite hope that by 2020, new cocktails of drugs will be available to target the key molecular pathways involved in gliomas and reduce their mortality and morbidity, a positive development for patients, their families, and medical professionals alike.

Dose-dense temozolomide regimen for the treatment of brain metastases from melanoma, breast cancer, or lung cancer not amenable to surgery or radiosurgery: a multicenter phase II study

BACKGROUND

Brain metastases reduce survival because therapeutic options are limited. This phase II study evaluated the efficacy of single-agent therapy with alternating weekly, dose-dense temozolomide in pretreated patients with brain metastases prospectively stratified by primary tumor type.

METHODS

Eligible patients had bidimensionally measurable brain metastases from histologically/cytologically confirmed melanoma, breast cancer (BC), or non-small-cell lung cancer (NSCLC). Prior chemotherapy, radiotherapy, and whole-brain radiotherapy (WBRT) were allowed. Patients received temozolomide 150 mg/m(2)/day (days 1-7 and 15-21 every 28- or 35-day cycle).

RESULTS

In the intent-to-treat population (N = 157; 53 melanoma, 51 BC, and 53 NSCLC), one patient had complete response, nine (6%) had partial responses, and 31 (20%) had stable disease in the brain. Median progression-free survival was 56, 58, and 66 days for melanoma, BC, and NSCLC, respectively. Median overall survival was 100 days for melanoma, 172 days for NSCLC, and not evaluable in the BC group. Thrombocytopenia was the most common adverse event causing dose modification or treatment discontinuation. Grade 4 toxic effects were rare.

CONCLUSIONS

This alternating weekly, dose-dense temozolomide regimen was well tolerated and clinically active in heavily pretreated patients with brain metastases, particularly in patients with melanoma. Combining temozolomide with WBRT or other agents may improve clinical outcomes.

Differential Effects of the Proteasome Inhibitor NPI-0052 against Glioma Cells

Proteasome inhibitors are emerging as a new class of cancer therapeutics, and bortezomib has shown promise in the treatment of multiple myeloma and mantle cell lymphoma. However, bortezomib has failed to have an effect in preclinical models of glioma. NPI-0052 is a new generation of proteasome inhibitors with increased potency and strong inhibition of all three catalytic activities of the 26S proteasome. In this article, we test the antitumor efficacy of NPI-0052 against glioma, as a single agent and in combination with temozolomide and radiation using five different glioma lines. The intrinsic radiation sensitivities differed for all the lines and correlated with their PTEN expression status. In vitro, NPI-0052 showed a dose-dependent toxicity, and its combination with temozolomide resulted in radiosensitization of only the cell lines with a mutated p53. The effect of NPI-0052 as a single agent on glioma xenografts in vivo was only modest in controlling tumor growth, and it failed to radiosensitize the glioma xenografts to fractionated radiation. We conclude that NPI-0052 is not a suitable drug for the treatment of malignant gliomas despite its efficacy in other cancer types.

The neuropharmacokinetics of temozolomide in patients with resectable brain tumors: potential implications for the current approach to chemoradiation

PURPOSE

Intracerebral microdialysis (ICMD) is an accepted method for monitoring changes in neurochemistry from acute brain injury. The goal of this pilot study was to determine the feasibility of using ICMD to examine the neuropharmacokinetics of temozolomide in brain interstitium following oral administration.

EXPERIMENTAL DESIGN

Patients with primary or metastatic brain tumors had a microdialysis catheter placed in peritumoral brain tissue at the time of surgical debulking. Computerized tomography scan confirmed the catheter location. Patients received a single oral dose of temozolomide (150 mg/m2) on the first postoperative day, serial plasma and ICMD samples were collected over 24 hours, and temozolomide concentrations were determined by tandem mass spectrometry.

RESULTS

Nine patients were enrolled. Dialysate and plasma samples were successfully collected from seven of the nine patients. The mean temozolomide areas under the concentration-time curve (AUC) in plasma and brain interstitium were 17.1 and 2.7 microg/mL x hour, with an average brain interstitium/plasma AUC ratio of 17.8%. The mean peak temozolomide concentration in the brain was 0.6 +/- 0.3 microg/mL, and the mean time to reach peak level in brain was 2.0 +/- 0.8 hours.

CONCLUSIONS

The use of ICMD to measure the neuropharmacokinetics of systemically administered chemotherapy is safe and feasible. Concentrations of temozolomide in brain interstitium obtained by ICMD are consistent with published data obtained in a preclinical ICMD model, as well as from clinical studies of cerebrospinal fluid. However, the delayed time required to achieve maximum temozolomide concentrations in brain suggests that current chemoradiation regimens may be improved by administering temozolomide 2 to 3 hours before radiation.

Phase II study of fixed dose rate gemcitabine as radiosensitizer for newly diagnosed glioblastoma multiforme

PURPOSE

In order to evaluate the activity of gemcitabine as radiosensitizer for newly diagnosed glioblastoma multiforme (GBM), a prospective single-center phase II study was conducted.

METHODS

Eligible patients were required to have histologically proven GBM with evaluable and/or measurable disease after surgery. They were treated by standard cranial irradiation plus concomitant fixed dose rate gemcitabine given intravenously at 175 mg/m(2) weekly for 6 weeks. After chemo-radiotherapy, irrespective of tumor response, patients went on to receive oral temozolomide at 150-200 mg/m(2) for 5 days every 28 days.

RESULTS

Twenty-three patients were enrolled. Median age was 57 years (range 43-72) and median Karnofsky performance status was 90 (range 70-100). Seventeen patients had received subtotal resection of the tumor, while six patients had biopsied-only tumors. Four patients responded to treatment (17.5%) with additional 14 (61%) experiencing stable disease for an overall disease control rate of 78.5%. Median progression-free and overall survival were 6.8 and 10.1 months, respectively. The concomitant radiotherapy-gemcitabine combination was well tolerated and severe adverse events were rare, consisting of grade 3 neutropenia and hypertransaminasemia in two cases each. Twenty patients were assessable for methylguanine methyltransferase (MGMT) promoter methylation, 11 of which were found methylated. In the methylated and unmethylated cohorts, disease control was obtained in 10/11 patients (91%) and 7/9 patients (77.5%), respectively.

CONCLUSIONS

Concomitant radiotherapy-gemcitabine is active and well tolerated in newly diagnosed glioblastoma multiforme. Activity is observed both in tumors with methylated and unmethylated MGMT promoter.