Topotecan Can Compensate for Protracted Radiation Treatment Time Effects in High Grade Glioma Xenografts*

Drug Repositioning Screen on a New Primary Cell Line Identifies Potent Therapeutics for Glioblastoma

Glioblastoma is a malignant brain cancer with limited treatment options and high mortality rate. While established glioblastoma cell line models provide valuable information, they ultimately lose most primary characteristics of tumors under long-term serum culture conditions. Therefore, established cell lines do not necessarily recapitulate genetic and morphological characteristics of real tumors. In this study, in line with the growing interest in using primary cell line models derived from patient tissue, we generated a primary glioblastoma cell line, KUGBM8 and characterized its genetic alterations, long term growth ability, tumor formation capacity and its response to Temozolomide, the front-line chemotherapy utilized clinically. In addition, we performed a drug repurposing screen on the KUGBM8 cell line to identify FDA-approved agents that can be incorporated into glioblastoma treatment regimen and identified Topotecan as a lead drug among 1,200 drugs. We showed Topotecan can induce cell death in KUGBM8 and other primary cell lines and cooperate with Temozolomide in low dosage combinations. Together, our study provides a new primary cell line model that can be suitable for both in vitro and in vivo studies and suggests that Topotecan can offer promise as a therapeutic approach for glioblastoma.

DNA damage of glioblastoma multiform cells induced by Beta radiation of iodine-131 in the presence or absence of topotecan: a picogreen and colonogenic assay

Objective

Glioblastoma multiforme (GBM), one of the most common and aggressive malignant brain tumors, is highly resistant to radiotherapy. Numerous approaches have been pursued to find new radiosensitizers. We used a picogreen and colonogenic assay to appraise the DNA damage and cell death in a spheroid culture of GBM cells caused by iodine-131 (I-131) beta radiation in the presence of topotecan (TPT).

Materials and Methods

U87MG cells were cultured as spheroids with approximate diameters of 300 μm. Cells were treated with beta radiation of I-131 (at a dose of 2 Gy) and/ or TPT (1 μg/ml for 2 hours). The numbers of cells that survived were compared with untreated cells using a colonogenic assay. In addition, we evaluated possible DNA damages by the picogreen method. The relation between DNA damage and cell death was assessed in the experimental study of groups.

Results

The findings showed that survival fraction (SF) in the I-131+TPT group (39%) was considerably less than the I-131 group (58.92%; p<0.05). The number of single strand breaks (SSB) and double strand breaks (DSB), in the DNA of U87MG cells treated with beta radiation of I-131 and TPT (I-131+TPT) significantly increased compared to cells treated with only I-131 or TPT (p<0.05). The amount of SSB repair was more than DSB repair (p<0.05). The relationship between cell death and DNA damage was close (r≥0.6) and significant (p<0.05) in the irradiated and treated groups. Also the maximum rate of DNA repair occurred 24 hours after the treatments. A significant difference was not observed on other days of the restoration.

Conclusion

The findings in the present study indicated that TPT can sensitize U87MG cells to radiation and increase DNA damages. Potentially, TPT can cause an increase in damage from DSB and SSB by its inhibitory effects on topoisomerase enzyme and the cell cycle. The increased complex damages following the use of a genotoxic agent and beta I-131 radiation, causes a significant increase the cell death because of the difficult repair process. By assessing the relationship between DNA damage and cell death, the picogreen method can be useful in predicting colonogenic assay. Consequently, it is suggested that co-treatment with I-131 beta radiation and TPT can improve GBM treatment.

Effect of p53 activity on the sensitivity of human glioblastoma cells to PARP-1 inhibitor in combination with topoisomerase I inhibitor or radiation

Poly (ADP-Ribose) polymerase-1 (PARP-1) is involved in the DNA repairing system by sensing and signaling the presence of DNA damage. Inhibition of PARP-1 is tested in combination with DNA damaging agents such as topoisomerase I inhibitors or ionizing radiations (RT) for the treatment of glioblastoma (GBM). Disruption of p53, widely prevalent in GBMs, plays a major role in DNA repairing system. The current study investigates whether p53 activity has an effect on the sensitivity of human GBM cells to PARP-1 inhibitors in combination with topoisomerase I inhibitor topotecan (TPT) and/or RT. Human GBM cell lines carrying a different functional status of p53 were treated with PARP-1 inhibitor NU1025, in combination with TPT and/or RT. Cytotoxic effects were examined by analyzing the antiproliferative activity, the cell cycle perturbations, and the DNA damage induced by combined treatments. PARP inhibition enhanced the antiproliferative activity, the cell cycle perturbations and the DNA damage induced by both TPT or RT in GBM cells. These effects were influenced by the p53 activity: cells carrying an active p53 were more sensitive to the combination of PARP inhibitor and RT, while cells carrying an inactive p53 displayed a higher sensitivity to the combination of PARP inhibitor and TPT. Our study suggests that p53 activity influences the differential sensitivity of GBM cells to combined treatments of TPT, RT, and PARP inhibitors. © 2014 International Society for Advancement of Cytometry.

Phenomenological modeling of tumor diameter growth based on a mixed effects model

Over the last few years, taking advantage of the linear kinetics of the tumor growth during the steady-state phase, tumor diameter-based rather than tumor volume-based models have been developed for the phenomenological modeling of tumor growth. In this study, we propose a new tumor diameter growth model characterizing early, late and steady-state treatment effects. Model parameters consist of growth rhythms, growth delays and time constants and are meaningful for biologists. Biological experiments provide in vivo longitudinal data. The latter are analyzed using a mixed effects model based on the new diameter growth function, to take into account inter-mouse variability and treatment factors. The relevance of the tumor growth mixed model is firstly assessed by analyzing the effects of three therapeutic strategies for cancer treatment (radiotherapy, concomitant radiochemotherapy and photodynamic therapy) administered on mice. Then, effects of the radiochemotherapy treatment duration are estimated within the mixed model. The results highlight the model suitability for analyzing therapeutic efficiency, comparing treatment responses and optimizing, when used in combination with optimal experiment design, anti-cancer treatment modalities.

Topotecan in combination with radiotherapy in unresectable glioblastoma: a phase 2 study

Improving glioblastoma multiforme (GBM) treatment with radio-chemotherapy remains a challenge. Topotecan is an attractive option as it exhibits growth inhibition of human glioma as well as brain penetration. The present study assessed the combination of radiotherapy (60 Gy/30 fractions/40 days) and topotecan (0.9 mg/m(2)/day on days 1-5 on weeks 1, 3 and 5) in 50 adults with histologically proven and untreated GBM. The incidence of non-hematological toxicities was low and grade 3-4 hematological toxicities were reported in 20 patients (mainly lymphopenia and neutropenia). Partial response and stabilization rates were 2% and 32%, respectively, with an overall time to progression of 12 weeks. One-year overall survival (OS) rate was 42%, with a median OS of 40 weeks. Topotecan in combination with radiotherapy was well tolerated. However, while response and stabilization concerned one-third of the patients, the study did not show increased benefits in terms of survival in patients with unresectable GBM.

Increased permeability of the blood-brain barrier to chemotherapy in metastatic brain tumors: establishing a treatment paradigm

There is no accepted standard of care for the chemotherapy treatment of metastatic brain tumors, which has been generally limited to lipophilic alkylators, which may not have efficacy against the tumor that metastasized to the brain. More than 50% of chemotherapy agents are natural product drugs, which are rarely used in the treatment of metastatic brain tumors because they are thought to not cross the blood-brain barrier (BBB). A major protein constituent in the BBB is P-glycoprotein (P-gp), which pumps natural product chemotherapy drugs and toxins out of the CNS. However, P-gp expression in the neovasculature of metastatic brain tumors is similar to the P-gp expression in the neovasculature of the primary, extracranial tumor. In contrast, gliomas have higher P-gp expression in their neovasculature, similar to the greater intrinsic expression of P-gp in normal brain vasculature. This decreased immunohistochemical expression of P-gp in the neovasculature of metastatic tumors, as well as our recent pharmacologic demonstration of increased tissue concentrations of paclitaxel in metastatic brain tumors compared with gliomas, support the idea that the choice of chemotherapy agents should be based on the histologic origin of the metastatic brain tumor and not on the lipophilicity of the drug. Our hypothesis is that metastatic brain tumors from tumors with intrinsically low P-gp expression (eg, lung, melanoma, and untreated breast) may be more permeable to natural product chemotherapy drugs than gliomas. This information could lead to a paradigm shift in the use of natural product drugs for metastatic brain tumors.

Ferumoxtran-10 enhancement in orthotopic xenograft models of human brain tumors: an indirect marker of tumor proliferation?

PURPOSE

Ferumoxtran-10 belongs to the Ultra Small Particles of Iron Oxide (USPIO) class of contrast agents and induces delayed tumor enhancement in brain tumors, reflecting the trapping of iron oxide particles by the macrophages and activated microglia. The aim of the study was to compare Ferumoxtran-10 contrast enhancement in four human high-grade glioma xenograft models (TCG2, TCG3, TCG4, and U87) with different growing profiles.

MATERIALS AND METHODS

Fragments of human malignant glioma were orthotopically xenografted into the brain of four groups of nude mice. All mice underwent a MRI examination 24 h after intravenous administration of Ferumoxtran-10 (axial T1 SE weighted MR images). The contrast enhancement observed in the different tumor types was measured and was correlated to in vivo tumor growth and to histological parameters, such as proliferative tumor cell fraction, apoptosis, vascular density, and Perls' staining score.

RESULTS

A good relationship was observed: (a) between tumor-to-background contrast and proliferative index, (b) between tumor-to-background contrast and tumor growth, and (c) between tumor-to-background contrast and Perls' staining score. The registered MR enhancement contrasts were not influenced by apoptotic index and by vascular density in these experimental xenografts.

CONCLUSIONS

Tumor contrast enhancement 24 h after intravenous Ferumoxtran-10 administration seems to be well correlated to tumor proliferative index and tumor growth and could be used as an indirect marker of tumor proliferation.