Enhanced survival and cure of F98 glioma-bearing rats following intracerebral delivery of carboplatin in combination with photon irradiation

Convection-enhanced delivery for high-grade glioma

Glioblastoma (GBM) is the most common adult primary malignant brain tumor and is associated with a dire prognosis. Despite multi-modality therapies of surgery, radiation, and chemotherapy, its 5-year survival rate is 6.8%. The presence of the blood-brain barrier (BBB) is one factor that has made GBM difficult to treat. Convection-enhanced delivery (CED) is a modality that bypasses the BBB, which allows the intracranial delivery of therapies that would not otherwise cross the BBB and avoids systemic toxicities. This review will summarize prior and ongoing studies and highlights practical considerations related to clinical care to aid providers caring for a high-grade glioma patient being treated with CED. Although not the main scope of this paper, this review also touches upon relevant technical considerations of using CED, an area still under much development.

X-rays minibeam radiation therapy at a conventional irradiator: Pilot evaluation in F98-glioma bearing rats and dose calculations in a human phantom

Minibeam radiation therapy (MBRT) is a type of spatial fractionated radiotherapy that uses submillimetric beams. This work reports on a pilot study on normal tissue response and the increase of the lifespan of glioma-bearing rats when irradiated with a tabletop x-ray system. Our results show a significant widening of the therapeutic window for brain tumours treated with MBRT: an important proportion of long-term survivals (60%) coupled with a significant reduction of toxicity when compared with conventional (broad beam) irradiations. In addition, the clinical translation of the minibeam treatment at a conventional irradiator is evaluated through a possible human head treatment plan.

Phase I trial of intracerebral convection-enhanced delivery of carboplatin for treatment of recurrent high-grade gliomas

Background

Carboplatin is a potent cytoreductive agent for a variety of solid tumors. However, when delivered systemically, clinical efficacy for the treatment of high grade gliomas is poor due to limited penetration across the blood-brain barrier (BBB). Direct intracerebral (IC) convection-enhanced delivery (CED) of carboplatin has been used to bypass the BBB and successfully treat the F98 rat glioma. Based on these studies, we initiated a Phase I clinical trial.

Objective

This Phase I clinical trial was conducted to establish the maximum tolerated dose and define the toxicity profile of carboplatin delivered intracerebrally via convection enhanced delivery (CED) for patients with high grade glial neoplasms.

Methods

Cohorts of 3 patients with recurrent WHO grade III or IV gliomas were treated with escalating doses of CED carboplatin (1–4 μg in 54mL over 72 hours) delivered via catheters placed at the time of recurrent tumor resection. The primary outcome measure was determination of the maximum tolerated dose (MTD). Secondary outcome measures included overall survival (OS), progression-free survival (PFS), and radiographic correlation.

Results

A total of 10 patients have completed treatment with infusion doses of carboplatin of 1μg, 2μg, and 4μg. The total planned volume of infusion was 54mL for each patient. All patients had previously received surgery and chemoradiation. Histology at treatment include GBM (n = 9) and anaplastic oligodendroglioma (n = 1). Median KPS was 90 (range, 70 to 100) at time of treatment. Median PFS and OS were 2.1 and 9.6 months after completion of CED, respectively. A single adverse event possibly related to treatment was noted (generalized seizure).

Conclusions

IC CED of carboplatin as a potential therapy for recurrent malignant glioma is feasible and safe at doses up to 4μg in 54mL over 72 hours. Further studies are needed to determine the maximum tolerated dose and potential efficacy.

Radiation Dose-Enhancement Is a Potent Radiotherapeutic Effect of Rare-Earth Composite Nanoscintillators in Preclinical Models of Glioblastoma

To improve the prognosis of glioblastoma, innovative radiotherapy regimens are required to augment the effect of tolerable radiation doses while sparing surrounding tissues. In this context, nanoscintillators are emerging radiotherapeutics that down-convert X-rays into photons with energies ranging from UV to near-infrared. During radiotherapy, these scintillating properties amplify radiation-induced damage by UV-C emission or photodynamic effects. Additionally, nanoscintillators that contain high-Z elements are likely to induce another, currently unexplored effect: radiation dose-enhancement. This phenomenon stems from a higher photoelectric absorption of orthovoltage X-rays by high-Z elements compared to tissues, resulting in increased production of tissue-damaging photo- and Auger electrons. In this study, Geant4 simulations reveal that rare-earth composite LaF3:Ce nanoscintillators effectively generate photo- and Auger-electrons upon orthovoltage X-rays. 3D spatially resolved X-ray fluorescence microtomography shows that LaF3:Ce highly concentrates in microtumors and enhances radiotherapy in an X-ray energy-dependent manner. In an aggressive syngeneic model of orthotopic glioblastoma, intracerebral injection of LaF3:Ce is well tolerated and achieves complete tumor remission in 15% of the subjects receiving monochromatic synchrotron radiotherapy. This study provides unequivocal evidence for radiation dose-enhancement by nanoscintillators, eliciting a prominent radiotherapeutic effect. Altogether, nanoscintillators have invaluable properties for enhancing the focal damage of radiotherapy in glioblastoma and other radioresistant cancers.

Radiation therapy combined with intracerebral convection-enhanced delivery of cisplatin or carboplatin for treatment of the F98 rat glioma

BACKGROUND

The purpose of this review is to summarize our own experimental studies carried out over a 13-year period of time using the F98 rat glioma as model for high grade gliomas. We evaluated a binary chemo-radiotherapeutic modality that combines either cisplatin (CDDP) or carboplatin, administered intracerebrally (i.c.) by means of convection-enhanced delivery (CED) or osmotic pumps, in combination with either synchrotron or conventional X-irradiation.

METHODS

F98 glioma cells were implanted stereotactically into the brains of syngeneic Fischer rats. Approximately 14 days later, either CDDP or carboplatin was administered i.c. by CED, followed 24 h later by radiotherapy using either a synchrotron or, subsequently, megavoltage linear accelerators (LINAC).

RESULTS

CDDP was administered at a dose of 3 µg in 5 µL, followed 24 h later with an irradiation dose of 15 Gy or carboplatin at a dose of 20 µg in 10 µL, followed 24 h later with 3 fractions of 8 Gy each, at the source at the European Synchrotron Radiation Facility (ESRF). This resulted in a median survival time (MeST) > 180 days with 33% long term survivors (LTS) for CDDP and a MeST > 60 days with 8 to 22% LTS, for carboplatin. Subsequently it became apparent that comparable survival data could be obtained with megavoltage X-irradiation using a LINAC source. The best survival data were obtained with a dose of 72 µg of carboplatin administered by means of Alzet® osmotic pumps over 7 days. This resulted in a MeST of > 180 days, with 55% LTS. Histopathologic examination of all the brains of the surviving rats revealed no residual tumor cells or evidence of significant radiation related effects.

CONCLUSIONS

The results obtained using this combination therapy has, to the best of our knowledge, yielded the most promising survival data ever reported using the F98 glioma model.

Destruction of tumor mass by gadolinium-loaded nanoparticles irradiated with monochromatic X-rays: Implications for the Auger therapy

Synchrotron generated monochromatic X-rays can be precisely tuned to the K-shell energy of high Z materials resulting in the release of the Auger electrons. In this work, we have employed this mechanism to destruct tumor spheroids. We first loaded gadolinium onto the surface of mesoporous silica nanoparticles (MSNs) producing gadolinium-loaded MSN (Gd-MSN). When Gd-MSN was added to the tumor spheroids, we observed efficient uptake and uniform distribution of Gd-MSN. Gd-MSN also can be taken up into cancer cells and localize to a site just outside of the cell nucleus. Exposure of the Gd-MSN containing tumor spheroids to monochromatic X-ray beams resulted in almost complete destruction. Importantly, this effect was observed at an energy level of 50.25 keV, but not with 50.0 keV. These results suggest that it is possible to use precisely tuned monochromatic X-rays to destruct tumor mass loaded with high Z materials, while sparing other cells. Our experiments point to the importance of nanoparticles to facilitate loading of gadolinium to tumor spheroids and to localize at a site close to the nucleus. Because the nanoparticles can target to tumor, our study opens up the possibility of developing a new type of radiation therapy for cancer.

Acoustic feedback enables safe and reliable carboplatin delivery across the blood-brain barrier with a clinical focused ultrasound system and improves survival in a rat glioma model

The blood-brain barrier (BBB) restricts delivery of most chemotherapy agents to brain tumors. Here, we investigated a clinical focused ultrasound (FUS) device to disrupt the BBB in rats and enhance carboplatin delivery to the brain using the F98 glioma model.

Methods: In each rat, 2-3 volumetric sonications (5 ms bursts at 1.1 Hz for 75s) targeted 18-27 locations in one hemisphere. Sonication was combined with Definity microbubbles (10 µl/kg) and followed by intravenous carboplatin (50 mg/kg). Closed-loop feedback control was performed based on acoustic emissions analysis.

Results: Safety and reliability were established in healthy rats after three sessions with carboplatin; BBB disruption was induced in every target without significant damage evident in MRI or histology. In tumor-bearing rats, concentrations of MRI contrast agent (Gadavist) were 1.7 and 3.3 times higher in the tumor center and margin, respectively, than non-sonicated tumors (P<0.001). Tissue-to-plasma ratios of intact carboplatin concentrations were increased by 7.3 and 2.9 times in brain and tumor respectively, at one hour after FUS and 4.2 and 2.4 times at four hours. Tumor volume doubling time in rats receiving FUS and carboplatin increased by 96% and 126% compared to rats that received carboplatin alone and non-sonicated controls, respectively (P<0.05); corresponding increases in median survival were 48% and 66% (P<0.01).

Conclusion: Overall, this work demonstrates that actively-controlled BBB disruption with a clinical device can enhance carboplatin delivery without neurotoxicity at level that reduces tumor growth and improves survival in an aggressive and infiltrative rat glioma model.

Convection-Enhanced Delivery in Malignant Gliomas: A Review of Toxicity and Efficacy

Malignant gliomas are undifferentiated or anaplastic gliomas. They remain incurable with a multitude of modalities, including surgery, radiation, chemotherapy, and alternating electric field therapy. Convection-enhanced delivery (CED) is a local treatment that can bypass the blood-brain barrier and increase the tumor uptake of therapeutic agents, while decreasing exposure to healthy tissues. Considering the multiple choices of drugs with different antitumor mechanisms, the supra-additive effect of concomitant radiation and chemotherapy, CED appears as a promising modality for the treatment of brain tumors. In this review, the CED-related toxicities are summarized and classified into immediate, early, and late side effects based on the time of onset, and local and systemic toxicities based on the location of toxicity. The efficacies of CED of various therapeutic agents including targeted antitumor agents, chemotherapeutic agents, radioisotopes, and immunomodulators are covered. The phase III trial PRECISE compares CED of IL13-PE38QQR, an interleukin-13 conjugated to Pseudomonas aeruginosa exotoxin A, to Gliadel® Wafer, a polymer loaded with carmustine. However, in this case, CED had no significant median survival improvement (11.3 months vs. 10 months) in patients with recurrent glioblastomas. In phase II studies, CED of recombinant poliovirus (PVSRIPO) had an overall survival of 21% vs. 14% for the control group at 24 months, and 21% vs. 4% at 36 months. CED of Tf-diphtheria toxin had a response rate of 35% in recurrent malignant gliomas patients. On the other hand, the TGF-β2 inhibitor Trabedersen, HSV-1-tk ganciclovir, and radioisotope 131I-chTNT-1/B mAb had a limited response rate. With this treatment, patients who received CED of the chemotherapeutic agent paclitaxel and immunomodulator, oligodeoxynucleotides containing CpG motifs (CpG-ODN), experienced intolerable toxicity. Toward the end of this article, an ideal CED treatment procedure is proposed and the methods for quality assurance of the CED procedure are discussed.

Liposomal formulations of carboplatin injected by convection-enhanced delivery increases the median survival time of F98 glioma bearing rats

BACKGROUND

Effectiveness of chemotherapy for treating glioblastoma (GBM) brain tumors is hampered by the blood-brain barrier which limits the entry into the brain of most drugs from the blood. To bypass this barrier, convection-enhanced delivery (CED) was proposed to directly inject drugs in tumor. However, the benefit of CED may be hampered when drugs diffuse outside the tumor to then induce neurotoxicity. Encapsulation of drugs into liposome aims at increasing tumor cells specificity and reduces neurotoxicity. However, the most appropriate liposomal formulation to inject drugs into brain tumor by CED still remains to be determined. In this study, four liposomal carboplatin formulations were prepared and tested in vitro on F98 glioma cells and in Fischer rats carrying F98 tumor implanted in the brain. Impact of pegylation on liposomal surface and relevance of positive or negative charge were assessed.

RESULTS

The cationic non-pegylated (L1) and pegylated (L2) liposomes greatly improved the toxicity of carboplatin in vitro compared to free carboplatin, whereas only a modest improvement and even a reduction of efficiency were measured with the anionic non-pegylated (L3) and the pegylated (L4) liposomes. Conversely, only the L4 liposome significantly increased the median survival time of Fisher rats implanted with the F98 tumor, compared to free carboplatin. Neurotoxicity assays performed with the empty L4' liposome showed that the lipid components of L4 were not toxic. These results suggest that the positive charge on liposomes L1 and L2, which is known to promote binding to cell membrane, facilitates carboplatin accumulation in cancer cells explaining their higher efficacy in vitro. Conversely, negatively charged and pegylated liposome (L4) seems to diffuse over a larger distance in the tumor, and consequently significantly increased the median survival time of the animals.

CONCLUSIONS

Selection of the best liposomal formulation based on in vitro studies or animal model can result in contradictory conclusions. The negatively charged and pegylated liposome (L4) which was the less efficient formulation in vitro showed the best therapeutic effect in animal model of GBM. These results support that relevant animal model of GBM must be considered to determine the optimal physicochemical properties of liposomal formulations.

Hybrid Gd3+/cisplatin cross-linked polymer nanoparticles enhance platinum accumulation and formation of DNA adducts in glioblastoma cell lines

New hybrid nanoparticles permitted MRI monitoring of a cisplatin infusion while enhancing drug accumulation and DNA adduct formation in glioblastoma cells.

Local DNA Repair Inhibition for Sustained Radiosensitization of High-Grade Gliomas

High-grade gliomas, such as glioblastoma (GBM) and diffuse intrinsic pontine glioma (DIPG), are characterized by an aggressive phenotype with nearly universal local disease progression despite multimodal treatment, which typically includes chemotherapy, radiotherapy, and possibly surgery. Radiosensitizers that have improved the effects of radiotherapy for extracranial tumors have been ineffective for the treatment of GBM and DIPG, in part due to poor blood-brain barrier penetration and rapid intracranial clearance of small molecules. Here, we demonstrate that nanoparticles can provide sustained drug release and minimal toxicity. When administered locally, these nanoparticles conferred radiosensitization in vitro and improved survival in rats with intracranial gliomas when delivered concurrently with a 5-day course of fractionated radiotherapy. Compared with previous work using locally delivered radiosensitizers and cranial radiation, our approach, based on the rational selection of agents and a clinically relevant radiation dosing schedule, produces the strongest synergistic effects between chemo- and radiotherapy approaches to the treatment of high-grade gliomas. Mol Cancer Ther; 16(8); 1456-69. ©2017 AACR.

Design, synthesis, and evaluation of cisplatin-containing EGFR targeting bioconjugates as potential therapeutic agents for brain tumors

The aim of this study was to evaluate four different platinated bioconjugates containing a cisplatin (cis-diamminedichloroplatinum [cis-DDP]) fragment and epidermal growth factor receptor (EGFR)-targeting moieties as potential therapeutic agents for the treatment of brain tumors using a human EGFR-expressing transfectant of the F98 rat glioma (F98_EGFR) to assess their efficacy. The first two bioconjugates employed the monoclonal antibody cetuximab (C225 or Erbitux^®) as the targeting moiety, and the second two used genetically engineered EGF peptides. C225-G₅-Pt was produced by reacting cis-DDP with a fifth-generation polyamidoamine dendrimer (G₅) and then linking it to C225 by means of two heterobifunctional reagents. The second bioconjugate (C225-PG-Pt) employed the same methodology except that polyglutamic acid was used as the carrier. The third and fourth bioconjugates used two different EGF peptides, PEP382 and PEP455, with direct coordination to the Pt center of the cis-DDP fragment. In vivo studies with C225-G₅-Pt failed to demonstrate therapeutic activity following intracerebral (ic) convection-enhanced delivery (CED) to F98_EGFR glioma-bearing rats. The second bioconjugate, C225-PG-Pt, failed to show in vitro cytotoxicity. Furthermore, because of its high molecular weight, we decided that lower molecular weight peptides might provide better targeting and microdistribution within the tumor. Both PEP382-Pt and PEP455-Pt bioconjugates were cytotoxic in vitro and, based on this, a pilot study was initiated using PEP455-Pt. The end point for this study was tumor size at 6 weeks following tumor cell implantation and 4 weeks following ic CED of PEP455-Pt to F98 glioma-bearing rats. Neuropathologic examination revealed that five of seven rats were either tumor-free or only had microscopic tumors at 42 days following tumor implantation compared to a mean survival time of 20.5 and 26.3 days for untreated controls. In conclusion, we have succeeded in reformatting the toxicity profile of cis-DDP and demonstrated the therapeutic efficacy of the PEP455-Pt bioconjugate in F98 glioma-bearing rats.

Convection-enhancement delivery of liposomal formulation of oxaliplatin shows less toxicity than oxaliplatin yet maintains a similar median survival time in F98 glioma-bearing rat model

Results of clinical trials with oxaliplatin in treating glioblastoma are dismal. Previous works showed that intravenous (i.v.) delivery of oxaliplatin did not increase the survival of F98 glioma-bearing Fisher rats. Low accumulation of the drug in tumor cells is presumed to be responsible for the lack of antitumor effect. In the present study, convection-enhanced delivery (CED) was used to directly inject oxaliplatin in brain tumor implanted in rats. Since CED can led to severe toxicity, the liposomal formulation of oxaliplatin (Lipoxal™) was also assessed. The maximum tolerated dose (MTD) of oxaliplatin was 10 μg, while that of Lipoxal™ was increased by 3-times reaching 30 μg. Median survival time (MeST) of F98 glioma-bearing rats injected with 10 μg oxaliplatin by CED was 31 days, 7.5 days longer than untreated control (p = 0.0002); while CED of 30 μg Lipoxal™ reached the same result. Compared to previous study on i.v. delivery of these drugs, their injection by CED significantly increased their tumoral accumulations as well as MeSTs in the F98 glioma bearing rat model. The addition of radiotherapy (15 Gy) to CED of oxaliplatin or Lipoxal™ increased the MeST by 4.0 and 3.0 days, respectively. The timing of radiotherapy (4 h or 24 h after CED) produced similar results. However, the treatment was better tolerated when radiotherapy was performed 24 h after CED. In conclusion, a better tumoral accumulation was achieved when oxaliplatin and Lipoxal™ were injected by CED. The liposomal encapsulation of oxaliplatin reduced its toxic, while maintaining its antitumor potential.

The quest to exploit the Auger effect in cancer radiotherapy - a reflective review

To identify the emergence of the recognition of the potential of the Auger effect for clinical application, and after tracing the salient milestones towards that goal, to evaluate the status quo and future prospects. It was not until 40 years after the discovery of Auger electrons, that the availability of radioactive DNA precursors enabled the biological power, and the clinical potential, of the Auger effect to be appreciated. Important milestones on the path to clinical translation have been identified and reached, but hurdles remain. Nevertheless the potential is still evident, and there is reasonable optimism that the goal of clinical translation is achievable.

Convection-enhancement delivery of platinum-based drugs and Lipoplatin(TM) to optimize the concomitant effect with radiotherapy in F98 glioma rat model

The prognosis for patients with glioblastoma remains poor with current treatments. Although platinum-based drugs are sometimes offered at relapse, their efficacy in this setting is still disputed. In this study, we use convection-enhanced delivery (CED) to deliver the platinum-based drugs (cisplatin, carboplatin, and Lipoplatin(TM) - liposomal formulation of cisplatin) directly into the tumor of F98 glioma-bearing rats that were subsequently treated with γ radiation (15 Gy). CED increased by factors varying between 17 and 111, the concentration of these platinum-based drugs in the brain tumor compared to intra-venous (i.v.) administration, and by 9- to 34-fold, when compared to intra-arterial (i.a.) administration. Furthermore, CED resulted in a better systemic tolerance to platinum drugs compared to their i.a. injection. Among the drugs tested, carboplatin showed the highest maximum tolerated dose (MTD). Treatment with carboplatin resulted in the best median survival time (MeST) (38.5 days), which was further increased by the addition of radiotherapy (54.0 days). Although the DNA-bound platinum adduct were higher at 4 h after CED than 24 h for carboplatin group, combination with radiotherapy led to similar improvement of median survival time. However, less toxicity was observed in animals irradiated 24 h after CED-based chemotherapy. In conclusion, CED increased the accumulation of platinum drugs in tumor, reduced the toxicity, and resulted in a higher median survival time. The best treatment was obtained in animals treated with carboplatin and irradiated 24 h later.

Tumoricidal activity of low-energy 160-KV versus 6-MV X-rays against platinum-sensitized F98 glioma cells

The purposes of this study were (i) to investigate the differences in effects between 160-kV low-energy and 6-MV high-energy X-rays, both by computational analysis and in vitro studies; (ii) to determine the effects of each on platinum-sensitized F98 rat glioma and murine B16 melanoma cells; and (iii) to describe the in vitro cytotoxicity and in vivo toxicity of a Pt(II) terpyridine platinum (Typ-Pt) complex. Simulations were performed using the Monte Carlo code Geant4 to determine enhancement in absorption of low- versus high-energy X-rays by Pt and to determine dose enhancement factors (DEFs) for a Pt-sensitized tumor phantom. In vitro studies were carried out using Typ-Pt and again with carboplatin due to the unexpected in vivo toxicity of Typ-Pt. Cell survival was determined using clonogenic assays. In agreement with computations and simulations, in vitro data showed up to one log unit reduction in surviving fractions (SFs) of cells treated with 1-4 µg/ml of Typ-Pt and irradiated with 160-kV versus 6-MV X-rays. DEFs showed radiosensitization in the 50-200 keV range, which fell to approximate unity at higher energies, suggesting marginal interactions at MeV energies. Cells sensitized with 1-5 or 7 µg/ml of carboplatin and then irradiated also showed a significant decrease (P < 0.05) in SFs. However, it was unlikely this was due to increased interactions. Theoretical and in vitro studies presented here demonstrated that the tumoricidal activity of low-energy X-rays was greater than that of high-energy X-rays against Pt-sensitized tumor cells. Determining whether radiosensitization is a function of increased interactions will require additional studies.

Radiation therapy combined with intracerebral administration of carboplatin for the treatment of brain tumors

BACKGROUND

In this study we determined if treatment combining radiation therapy (RT) with intracerebral (i.c.) administration of carboplatin to F98 glioma bearing rats could improve survival over that previously reported by us with a 15 Gy dose (5 Gy × 3) of 6 MV photons.

METHODS

First, in order to reduce tumor interstitial pressure, a biodistribution study was carried out to determine if pretreatment with dexamethasone alone or in combination with mannitol and furosemide (DMF) would increase carboplatin uptake following convection enhanced delivery (CED). Next, therapy studies were carried out in rats that had received carboplatin either by CED over 30 min (20 μg) or by Alzet pumps over 7 d (84 μg), followed by RT using a LINAC to deliver either 20 Gy (5 Gy × 4) or 15 Gy (7.5 Gy × 2) dose at 6 or 24 hrs after drug administration. Finally, a study was carried out to determine if efficacy could be improved by decreasing the time interval between drug administration and RT.

RESULTS

Tumor carboplatin values for D and DMF-treated rats were 9.4 ± 4.4 and 12.4 ± 3.2 μg/g, respectively, which were not significantly different (P = 0.14). The best survival data were obtained by combining pump delivery with 5 Gy × 4 of X-irradiation with a mean survival time (MST) of 107.7 d and a 43% cure rate vs. 83.6 d with CED vs. 30-35 d for RT alone and 24.6 d for untreated controls. Treatment-related mortality was observed when RT was initiated 6 h after CED of carboplatin and RT was started 7 d after tumor implantation. Dividing carboplatin into two 10 μg doses and RT into two 7.5 Gy fractions, administered 24 hrs later, yielded survival data (MST 82.1 d with a 25% cure rate) equivalent to that previously reported with 5 Gy × 3 and 20 μg of carboplatin.

CONCLUSIONS

Although the best survival data were obtained by pump delivery, CED was highly effective in combination with 20 Gy, or as previously reported, 15 Gy, and the latter would be preferable since it would produce less late tissue effects.

Synergistic effect of cisplatin and synchrotron irradiation on F98 gliomas growing in nude mice

Among brain tumors, glioblastoma multiforme appears as one of the most aggressive forms of cancer with poor prognosis and no curative treatment available. Recently, a new kind of radio-chemotherapy has been developed using synchrotron irradiation for the photoactivation of molecules with high-Z elements such as cisplatin (PAT-Plat). This protocol showed a cure of 33% of rats bearing the F98 glioma but the efficiency of the treatment was only measured in terms of overall survival. Here, characterization of the effects of the PAT-Plat on tumor volume and tumor blood perfusion are proposed. Changes in these parameters may predict the overall survival. Firstly, changes in tumor growth of the F98 glioma implanted in the hindlimb of nude mice after the PAT-Plat treatment and its different modalities have been characterized. Secondly, the effects of the treatment on tumor blood perfusion have been observed by intravital two-photon microscopy. Cisplatin alone had no detectable effect on the tumor volume. A reduction of tumor growth was measured after a 15 Gy synchrotron irradiation, but the whole therapy (15 Gy irradiation + cisplatin) showed the largest decrease in tumor growth, indicating a synergistic effect of both synchrotron irradiation and cisplatin treatment. A high number of unperfused vessels (52%) were observed in the peritumoral area in comparison with untreated controls. In the PAT-Plat protocol the transient tumor growth reduction may be due to synergistic interactions of tumor-cell-killing effects and reduction of the tumor blood perfusion.

Surface-engineered nanomaterials as X-ray absorbing adjuvant agents for Auger-mediated chemo-radiation

We report a prototype approach to formulate gold nanoparticle-based X-ray absorbing agents through surface-engineering of a cisplatin pharmacophore with modified polyacrylate. The resulting agents exhibit both chemo-therapeutic potency to cancer cells and Auger-mediated secondary electron emission, showing great potential to improve the therapeutic efficacy of chemo-radiation.

Photoactivation of gold nanoparticles for glioma treatment

Radiosensitization efficacy of gold nanoparticles (AuNPs) with low energy radiations (88 keV) was evaluated in vitro and in vivo on rats bearing glioma. In vitro, a significant dose-enhancement factor was measured by clonogenic assays after irradiation with synchrotron radiation of F98 glioma cells in presence of AuNPs (1.9 and 15 nm in diameter). In vivo, 1.9 nm nanoparticles were found to be toxic following intracerebral delivery in rats bearing glioma, whether no toxicity was observed using 15 nm nanoparticles at the same concentration (50 mg/mL). The therapeutic efficacy of gold photoactivation was determined by irradiating the animals after intracerebral infusion of AuNPs. Survival of rats that had received the combination of treatments (AuNPs: 50 mg/mL, 15 Gy) was significantly increased in comparison with the survival of rats that had received irradiation alone. In conclusion, this experimental approach is promising and further studies are foreseen for improving its therapeutic efficacy.

FROM THE CLINICAL EDITOR

These investigators report that gold nanoparticles of the correct size can be used to enhance the effects of irradiation in the context of a glioma model. Since many of the glioma varieties are currently incurable, this or similar approaches may find their way to clinical trials in the near future.

Photon activation therapy of RG2 glioma carrying Fischer rats using stable thallium and monochromatic synchrotron radiation

75 RG2 glioma-carrying Fischer rats were treated by photon activation therapy (PAT) with monochromatic synchrotron radiation and stable thallium. Three groups were treated with thallium in combination with radiation at different energy; immediately below and above the thallium K-edge, and at 50 keV. Three control groups were given irradiation only, thallium only, or no treatment at all. For animals receiving thallium in combination with radiation to 15 Gy at 50 keV, the median survival time was 30 days, which was 67% longer than for the untreated controls (p = 0.0020) and 36% longer than for the group treated with radiation alone (not significant). Treatment with thallium and radiation at the higher energy levels were not effective at the given absorbed dose and thallium concentration. In the groups treated at 50 keV and above the K-edge, several animals exhibited extensive and sometimes contra-lateral edema, neuronal death and frank tissue necrosis. No such marked changes were seen in the other groups. The results were discussed with reference to Monte Carlo calculated electron energy spectra and dose enhancement factors.

Preparation, biodistribution and neurotoxicity of liposomal cisplatin following convection enhanced delivery in normal and F98 glioma bearing rats

The purpose of this study was to evaluate two novel liposomal formulations of cisplatin as potential therapeutic agents for treatment of the F98 rat glioma. The first was a commercially produced agent, Lipoplatin™, which currently is in a Phase III clinical trial for treatment of non-small cell lung cancer (NSCLC). The second, produced in our laboratory, was based on the ability of cisplatin to form coordination complexes with lipid cholesteryl hemisuccinate (CHEMS). The in vitro tumoricidal activity of the former previously has been described in detail by other investigators. The CHEMS liposomal formulation had a Pt loading efficiency of 25% and showed more potent in vitro cytotoxicity against F98 glioma cells than free cisplatin at 24 h. In vivo CHEMS liposomes showed high retention at 24 h after intracerebral (i.c.) convection enhanced delivery (CED) to F98 glioma bearing rats. Neurotoxicologic studies were carried out in non-tumor bearing Fischer rats following i.c. CED of Lipoplatin™ or CHEMS liposomes or their "hollow" counterparts. Unexpectedly, Lipoplatin™ was highly neurotoxic when given i.c. by CED and resulted in death immediately following or within a few days after administration. Similarly "hollow" Lipoplatin™ liposomes showed similar neurotoxicity indicating that this was due to the liposomes themselves rather than the cisplatin. This was particularly surprising since Lipoplatin™ has been well tolerated when administered intravenously. In contrast, CHEMS liposomes and their "hollow" counterparts were clinically well tolerated. However, a variety of dose dependent neuropathologic changes from none to severe were seen at either 10 or 14 d following their administration. These findings suggest that further refinements in the design and formulation of cisplatin containing liposomes will be required before they can be administered i.c. by CED for the treatment of brain tumors and that a formulation that may be safe when given systemically may be highly neurotoxic when administered directly into the brain.

Intracerebral delivery of carboplatin in combination with either 6 MV photons or monoenergetic synchrotron X-rays are equally efficacious for treatment of the F98 rat glioma

BACKGROUND

The purpose of the present study was to compare side-by-side the therapeutic efficacy of a 6-day infusion of carboplatin, followed by X-irradiation with either 6 MV photons or synchrotron X-rays, tuned above the K-edge of Pt, for treatment of F98 glioma bearing rats.

METHODS

Carboplatin was administered intracerebrally (i.c.) to F98 glioma bearing rats over 6 days using AlzetTM osmotic pumps starting 7 days after tumor implantation. Radiotherapy was delivered in a single 15 Gy fraction on day 14 using a conventional 6 MV linear accelerator (LINAC) or 78.8 keV synchrotron X-rays.

RESULTS

Untreated control animals had a median survival time (MeST) of 33 days. Animals that received either carboplatin alone or irradiation alone with either 78.8 keV or 6 MV had a MeSTs 38 and 33 days, respectively. Animals that received carboplatin in combination with X-irradiation had a MeST of > 180 days with a 55% cure rate, irrespective of whether they were irradiated with either 78.8 KeV synchrotron X-rays or 6MV photons.

CONCLUSIONS

These studies have conclusively demonstrated the equivalency of i.c. delivery of carboplatin in combination with X-irradiation with either 6 MV photons or synchrotron X-rays.

Precision radiotherapy for brain tumors: A 10-year bibliometric analysis

OBJECTIVE:

Precision radiotherapy plays an important role in the management of brain tumors. This study aimed to identify global research trends in precision radiotherapy for brain tumors using a bibliometric analysis of the Web of Science.

DATA RETRIEVAL:

We performed a bibliometric analysis of data retrievals for precision radiotherapy for brain tumors containing the key words cerebral tumor, brain tumor, intensity-modulated radiotherapy, stereotactic body radiation therapy, stereotactic ablative radiotherapy, imaging-guided radiotherapy, dose-guided radiotherapy, stereotactic brachytherapy, and stereotactic radiotherapy using the Web of Science.

SELECTION CRITERIA:

Inclusion criteria: (a) peer-reviewed articles on precision radiotherapy for brain tumors which were published and indexed in the Web of Science; (b) type of articles: original research articles and reviews; (c) year of publication: 2002-2011. Exclusion criteria: (a) articles that required manual searching or telephone access; (b) Corrected papers or book chapters.

MAIN OUTCOME MEASURES:

(1) Annual publication output; (2) distribution according to country; (3) distribution according to institution; (4) top cited publications; (5) distribution according to journals; and (6) comparison of study results on precision radiotherapy for brain tumors.

RESULTS:

The stereotactic radiotherapy, intensity-modulated radiotherapy, and imaging-guided radiotherapy are three major methods of precision radiotherapy for brain tumors. There were 260 research articles addressing precision radiotherapy for brain tumors found within the Web of Science. The USA published the most papers on precision radiotherapy for brain tumors, followed by Germany and France. European Synchrotron Radiation Facility, German Cancer Research Center and Heidelberg University were the most prolific research institutes for publications on precision radiotherapy for brain tumors. Among the top 13 research institutes publishing in this field, seven are in the USA, three are in Germany, two are in France, and there is one institute in India. Research interests including urology and nephrology, clinical neurology, as well as rehabilitation are involved in precision radiotherapy for brain tumors studies.

CONCLUSION:

Precision radiotherapy for brain tumors remains a highly active area of research and development.

An evaluation of the safety and feasibility of convection-enhanced delivery of carboplatin into the white matter as a potential treatment for high-grade glioma

Glioblastoma multiforme (GBM) is the most common and most aggressive form of intrinsic brain tumour. Despite standard treatment involving surgical resection, chemotherapy and radiotherapy this disease remains incurable with the majority of tumours recurring adjacent to the resection cavity. Consequently there is a clear need to improve local tumour control. Convection-enhanced delivery (CED) is a practical technique for administering chemotherapeutics directly into peritumoural brain. In this study, we have tested the hypothesis that carboplatin would be an appropriate chemotherapeutic agent to administer by CED into peritumoural brain to treat GBM. Within this study we have evaluated the relationships between carboplatin concentration, duration of exposure and tumour cell kill in vitro using GBM cell lines and the relationship between carboplatin concentration and clinical and histological evidence of toxicity in vivo. In addition, we have used laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) to evaluate the distribution properties of carboplatin following CED into rat brain and to determine the rate at which carboplatin is cleared from the brain. Finally, we have compared the distribution properties of carboplatin and the MRI contrast agent gadolinium-DTPA in pig brain. The results of these experiments confirm that carboplatin can be widely distributed by CED and that it remains in the brain for at least 24 h after infusion completion. Furthermore, carboplatin provokes a significant GBM cell kill at concentrations that are not toxic to normal brain. Finally, we provide evidence that gadolinium-DTPA coinfusion is a viable technique for visualising carboplatin distribution using T1-weighted MR imaging.

Synchrotron radiation in cancer treatments and diagnostics: an overview

During the last 30 years many groups have carried out experiments and trials to develop new imaging and radiotherapy techniques in oncology, based on the use of synchrotron X-rays. There are several synchrotron biomedical stations around the world, which offer an excellent platform to improve either the imaging diagnosis or radiotherapy treatment for different tumour types. In the coming months the first radiotherapy clinical trials will be seen at the Biomedical Beamline at the ESRF synchrotron in Grenoble (France). In this article we highlight the results of some of the techniques and strategies that have been developed at different biomedical synchrotron stations.

Biological consequences of nanoscale energy deposition near irradiated heavy atom nanoparticles

Gold nanoparticles (GNPs) are being proposed as contrast agents to enhance X-ray imaging and radiotherapy, seeking to take advantage of the increased X-ray absorption of gold compared to soft tissue. However, there is a great discrepancy between physically predicted increases in X-ray energy deposition and experimentally observed increases in cell killing. In this work, we present the first calculations which take into account the structure of energy deposition in the nanoscale vicinity of GNPs and relate this to biological outcomes, and show for the first time good agreement with experimentally observed cell killing by the combination of X-rays and GNPs. These results are not only relevant to radiotherapy, but also have implications for applications of heavy atom nanoparticles in biological settings or where human exposure is possible because the localised energy deposition high-lighted by these results may cause complex DNA damage, leading to mutation and carcinogenesis.

Comparison of intracerebral delivery of carboplatin and photon irradiation with an optimized regimen for boron neutron capture therapy of the F98 rat glioma

In this report we have summarized our studies to optimize the delivery of boronophenylalanine (BPA) and sodium borocaptate (BSH) for boron neutron capture therapy (BNCT) of F98 glioma bearing rats. These results have been compared to a chemoradiotherapeutic approach using the same tumor model. The best survival data from our BNCT studies were obtained using a combination of BPA and sodium borocaptate BSH administered via the internal carotid artery, in combination with blood-brain barrier disruption (BBB-D). This treatment resulted in a mean survival time (MST) of 140 d with a 25% cure rate. The other approach combined intracerebral administration of carboplatin by either convection enhanced delivery (CED) or Alzet pump infusion, followed by external beam photon irradiation. This resulted in MSTs of 83 d and 112 d, respectively, with a cure rate of 40% for the latter. However, a significant problem that must be solved for both BNCT and this new chemoradiotherapeutic approach is how to improve drug uptake and microdistribution within the tumor.

Treatment plans optimization for contrast-enhanced synchrotron stereotactic radiotherapy

PURPOSE

Synchrotron stereotactic radiotherapy (SSRT) is a treatment that involves the targeting of high-Z elements into tumors followed by stereotactic irradiation with monochromatic x-rays from a synchrotron source, tuned at an optimal energy. The irradiation geometry, as well as the secondary particles generated at a higher yield by the medium energy x-rays on the high-Z atoms (characteristic x-rays, photoelectrons, and Auger electrons), produces a localized dose enhancement in the tumor. Iodine-enhanced SSRT with systemic injections of iodinated contrast agents has been successfully developed in the past six years in the team, and is currently being transferred to clinical trials. The purpose of this work is to study the impact on the SSRT treatment of the contrast agent type, the beam quality, the irradiation geometry, and the beam weighting for defining an optimized SSRT treatment plan.

METHODS

Theoretical dosimetry was performed using the MCNPX particle transport code. The simulated geometry was an idealized phantom representing a human head. A virtual target was positioned in the central part of the phantom or off-centered by 4 cm. The authors investigated the dosimetric characteristics of SSRT for various contrast agents: Iodine, gadolinium, and gold; and for different beam qualities: Monochromatic x-ray beams from a synchrotron source (30-120 keV), polychromatic x-ray beams from an x-ray tube (80, 120, and 180 kVp), and a 6 MV x-ray beam from a linear accelerator. Three irradiation geometries were studied: One arc or three noncoplanar arcs dynamic arc therapy, and an irradiation with a finite number of beams. The resulting dose enhancements, beam profiles, and histograms dose volumes were compared for iodine-enhanced SSRT. An attempt to optimize the irradiation scheme by weighing the finite x-ray beams was performed. Finally, the optimization was studied on patient specific 3D CT data after contrast agent infusion.

RESULTS

It was demonstrated in this study that an 80 keV beam energy was a good compromise for treating human brain tumors with iodine-enhanced SSRT, resulting in a still high dose enhancement factor (about 2) and a superior bone sparing in comparison with lower energy x-rays. This beam could easily be produced at the European Synchrotron Radiation Facility medical beamline. Moreover, there was a significant diminution of dose delivered to the bone when using monochromatic x-rays rather than polychromatic x-rays from a conventional tube. The data showed that iodine SSRT exhibits a superior sparing of brain healthy tissue in comparison to high energy treatment. The beam weighting optimization significantly improved the treatment plans for off-centered tumors, when compared to nonweighted irradiations.

CONCLUSIONS

This study demonstrated the feasibility of realistic clinical plans for low energy monochromatic x-rays contrast-enhanced radiotherapy, suitable for the first clinical trials on brain metastasis with a homogeneous iodine uptake.

Convection enhanced delivery of carboplatin in combination with radiotherapy for the treatment of brain tumors

The purpose of this study was to further evaluate the therapeutic efficacy of convection enhanced delivery (CED) of carboplatin in combination with radiotherapy for treatment of the F98 rat glioma. Tumor cells were implanted stereotactically into the brains of syngeneic Fischer rats, and 13 or 17 d. later carboplatin (20 μg/10 μl) was administered by either CED over 30 min or by Alzet osmotic pumps (0.5 μg/μl/h for 168 h.) beginning at 7 d after tumor implantation. Rats were irradiated with a 15 Gy fractionated dose (5 Gy × 3) of 6 MV photons to the whole brain beginning on the day after drug administration. Other groups of rats received either carboplatin or X-irradiation alone. The tumor carboplatin concentration following CED of 20 μg in 10 μl was 10.4 μg/g, which was equal to that observed following i.v. administration of 100 mg/kg b.w. Rats bearing small tumors, treated with carboplatin and X-irradiation, had a mean survival time (MST) of 83.4 d following CED and 111.8 d following pump delivery with 40% of the latter surviving >180 d (i.e. cured) compared to 55.2 d for CED and 77.2 d. for pump delivery of carboplatin alone and 31.8 d and 24.2 d, respectively, for X-irradiated and untreated controls. There was no microscopic evidence of residual tumor in the brains of all long-term survivors. Not surprisingly, rats with large tumors had much shorter MSTs. Only modest increases in MSTs were observed in animals that received either oral administration or CED of temozolomide plus X-irradiation (23.2 d and 29.3 d) compared to X-irradiation alone. The present survival data, and those previously reported by us, are among the best ever obtained with the F98 glioma model. Initially, they could provide a platform for a Phase I clinical trial to evaluate the safety and potential therapeutic efficacy of CED of carboplatin in patients with recurrent glioblastomas, and ultimately a Phase II trial of carboplatin in combination with radiation therapy.

Various drug delivery approaches to the central nervous system

IMPORTANCE OF THE FIELD

The presence of the blood-brain barrier (BBB), an insurmountable obstacle, in particular, and other barriers in brain and periphery contribute to hindrance of the successful diagnosis and treatment of a myriad of central nervous system pathologies. This review discusses several strategies adopted to define a rational drug delivery approach to the CNS along with a short description of the strategies implemented by the authors' group to enhance the analgesic activity, a CNS property, of chimeric peptide of Met-enkephalin and FMRFa (YGGFMKKKFMRFa-YFa).

AREAS COVERED IN THIS REVIEW

Various approaches for drug delivery to the CNS with their beneficial and non-beneficial aspects, supported by an extensive literature survey published recently, up to August 2009.

WHAT THE READER WILL GAIN

The reader will have the privilege of gaining an understanding of previous as well as recent approaches to breaching the CNS barriers.

TAKE HOME MESSAGE

Among the various strategies discussed, the potential for efficacious CNS drug targeting in future lies either with the non-invasively administered multifunctional nanosystems or these nanosystems without characterstics such as long systemic circulating capability and avoiding reticuloendothelial system scavenging system of the body, endogenous transporters and efflux inhibitors administered by convection-enhanced delivery.

Convection-enhanced delivery for the treatment of brain tumors

The brain is highly accessible for nutrients and oxygen, however delivery of drugs to malignant brain tumors is a very challenging task. Convection-enhanced delivery (CED) has been designed to overcome some of the difficulties so that pharmacological agents that would not normally cross the BBB can be used for treatment. Drugs are delivered through one to several catheters placed stereotactically directly within the tumor mass or around the tumor or the resection cavity. Several classes of drugs are amenable to this technology including standard chemotherapeutics or novel experimental targeted drugs. The first Phase III trial for CED-delivered, molecularly targeted cytotoxin in the treatment of recurrent glioblastoma multiforme has been accomplished and demonstrated objective clinical efficacy. The lessons learned from more than a decade of attempts at exploiting CED for brain cancer treatment weigh critically for its future clinical applications. The main issues center around the type of catheters used, number of catheters and their exact placement; pharmacological formulation of drugs, prescreening patients undergoing treatment and monitoring the distribution of drugs in tumors and the tumor-infiltrated brain. It is expected that optimizing CED will make this technology a permanent addition to clinical management of brain malignancies.

Efficacy of intracerebral delivery of cisplatin in combination with photon irradiation for treatment of brain tumors

We have evaluated the efficacy of intracerebral (i.c.) convection-enhanced delivery (CED) of cisplatin in combination with photon irradiation for the treatment of F98 glioma-bearing rats. One thousand glioma cells were stereotactically implanted into the brains of Fischer rats and 13 days later cisplatin (6 microg/20 microl) was administered i.c. by CED at a flow rate of 0.5 microl/min. On the following day the animals were irradiated with a single 15 Gy dose of X-rays, administered by a linear accelerator (LINAC) or 78.8 keV synchrotron X-rays at the European Synchrotron Radiation Facility (ESRF). Untreated controls had a mean survival time (MST) + or - standard error of 24 + or - 1 days compared to >59 + or - 13 days for rats that received cisplatin alone with 13% of the latter surviving >200 days. Rats that received cisplatin in combination with either 6 MV (LINAC) or 78.8 keV (synchrotron) X-rays had almost identical MSTs of >75 + or - 18 and >74 + or - 19 days, respectively with 17 and 18% long-term survivors. Microscopic examination of the brains of long-term surviving rats revealed an absence of viable tumor cells and cystic areas at the presumptive site of the tumor. Our data demonstrate that i.c. CED of cisplatin in combination with external X-irradiation significantly enhanced the survival of F98 glioma-bearing rats. This was independent of the X-ray beam energy and probably was not due to the production of Auger electrons as we previously had postulated. Our data provide strong support for the approach of concomitantly administering platinum-based chemotherapy in combination with radiotherapy for the treatment of brain tumors. Since a conventional LINAC can be used as the radiation source, this should significantly broaden the clinical applicability of this approach compared to synchrotron radiotherapy, which could only be carried out at a very small number of specialized facilities.

Longitudinal assessment of regional directed delivery in a rodent malignant glioma model

OBJECT

Direct delivery of chemotherapeutic agents for the treatment of brain tumors is an area of focus in the development of therapeutic paradigms because this method of delivery circumvents the blood-brain barrier without causing adverse systemic side effects. Few studies have investigated longitudinal tumor response to this type of therapy. In this study, the authors examined the time course of tumor response to direct delivery of a chemotherapeutic agent in a rodent malignant glioma model.

METHODS

To visualize tumor response to chemotherapy, the authors used bioluminescence imaging in a rodent model. Rat 9L gliosarcoma cells expressing a luciferase gene were inoculated into adult male rat striata. Ten days following surgery the animals were randomly divided into 4 groups. Groups 1 and 2 received 20 and 40 microl carboplatin (1 mg/ml), respectively, via convection-enhanced delivery (CED); Group 3 received 60 mg/kg carboplatin intraperitoneally; and Group 4 received no treatment. Tumor growth was correlated with luminescence levels twice weekly.

RESULTS

Differential growth curves were observed for the 4 groups. Systemically treated rats showed decreasing photon flux emission at 15.0 + or - 4.7 days; rats treated with 20- or 40-microl CED showed decreased emissions at 4.0 + or - 2.0 and 3.2 + or - 1.3 days after treatment, respectively. Histopathologically, 6 of 12 CED-treated animals exhibited no residual tumor at the end point of the study.

CONCLUSIONS

Direct and systemic delivery of carboplatin was examined to determine how the method of drug delivery affects tumor growth. The present report is one of the first in vivo studies to examine the time course of tumor response to direct drug delivery. The results indicate that direct drug delivery may be a promising option for treating gliomas.

Local delivery of ferrociphenol lipid nanocapsules followed by external radiotherapy as a synergistic treatment against intracranial 9L glioma xenograft

PURPOSE

The goal of the present study was to evaluate the efficacy of a new organometallic drug, ferrociphenol (Fc-diOH), in combination with external radiotherapy in intracerebral 9L glioma model. We tested the hypothesis that the combination of external radiotherapy with Fc-diOH could potentiate the action of this drug.

METHODS

9L cells were treated with Fc-diOH-LNCs (from 0.01 to 1 micromol/L) and irradiated with external radiotherapy (from 2 to 40 Gy). In vivo assessment was evaluated by the inoculation of 9L cells in Fisher rats. Chemotherapy with Fc-diOH-LNCs (0.36 mg/rat) was administered by means of convection-enhanced delivery (CED), and the treatment was followed by three irradiations of 6 Gy doses (total dose = 18 Gy).

RESULTS

In vitro evaluations evidenced that a combined treatment with Fc-diOH-LNCs and irradiations showed synergistic antitumor activity on 9L cells. Combining cerebral irradiation with CED of Fc-diOH-LNCs led to a significantly longer survival and the existence of long-term survivors compared to Fc-diOH-LNCs-treated animals (p < 0.0001) and to the group treated with blank LNCs + radiotherapy (p = 0.0079).

CONCLUSION

The synergistic effect between ferrociphenol-loaded LNCs and radiotherapy was due to a closely oxidative relationship. Upon these considerations, Fc-diOH-LNCs appear to be an efficient radiosensitive anticancer drug delivery system.

In vitro and in vivo optimization of an anti-glioma modality based on synchrotron X-ray photoactivation of platinated drugs

For the past 5 years, a radio-chemotherapy approach based on the photoactivation of platinum atoms (PAT-Plat) consisting of treating tumors with platinated compounds and irradiating them above the platinum K edge (78.4 keV) has been developed at the European Synchrotron Radiation Facility (Grenoble, France). Compared to other preclinical modalities, PAT-Plat provides the highest survivals of rats bearing the rodent F98 glioma. However, further investigations are required to optimize its efficiency and to allow its clinical application. Here we examined in vitro and in vivo whether monochromatic X rays are more efficient than high-energy photons in producing the PAT-Plat effect by measuring DNA double-strand breaks (DSBs) and survival of glioma-bearing rats and whether an increase in the platinum concentration in the tumor results in increased rat survival. DSBs were assessed by pulsed-field gel electrophoresis with different DNA fragment migration programs and with gamma-H2AX immunofluorescence. In vivo, F98 glioma cells were injected intracerebrally, treated with a single intracranial injection of cisplatin or carboplatin 13 days after tumor implantation, and irradiated the day after with 78.8 keV X rays or 6 MV photons. Our results indicate that 78.8 keV X rays are more efficient than high-energy photons at producing the PAT-Plat effect. At low concentrations, cisplatin is more efficient than carboplatin; this is likely due to more efficient DNA binding and DSB repair inhibition. High concentrations of carboplatin inside tumors do not necessarily lead to protracted survival of rats. The therapeutic benefit of anti-glioma synchrotron strategies appears to be correlated with the percentage of unrepaired DSBs but not with the number of DSBs induced.

Rat brain tumor models in experimental neuro-oncology: the C6, 9L, T9, RG2, F98, BT4C, RT-2 and CNS-1 gliomas

In this review we will describe eight commonly used rat brain tumor models and their application for the development of novel therapeutic and diagnostic modalities. The C6, 9L and T9 gliomas were induced by repeated injections of methylnitrosourea (MNU) to adult rats. The C6 glioma has been used extensively for a variety of studies, but since it arose in an outbred Wistar rat, it is not syngeneic to any inbred strain, and its potential to evoke an alloimmune response is a serious limitation. The 9L gliosarcoma has been used widely and has provided important information relating to brain tumor biology and therapy. The T9 glioma, although not generally recognized, was and probably still is the same as the 9L. Both of these tumors arose in Fischer rats and can be immunogenic in syngeneic hosts, a fact that must be taken into consideration when used in therapy studies, especially if survival is the endpoint. The RG2 and F98 gliomas were both chemically induced by administering ethylnitrosourea (ENU) to pregnant rats, the progeny of which developed brain tumors that subsequently were propagated in vitro and cloned. They are either weakly or non-immunogenic and have an invasive pattern of growth and uniform lethality, which make them particularly attractive models to test new therapeutic modalities. The CNS-1 glioma was induced by administering MNU to a Lewis rat. It has an infiltrative pattern of growth and is weakly immunogenic, which should make it useful in experimental neuro-oncology. Finally, the BT4C glioma was induced by administering ENU to a BD IX rat, following which brain cells were propagated in vitro until a tumorigenic clone was isolated. This tumor has been used for a variety of studies to evaluate new therapeutic modalities. The Avian Sarcoma Virus (ASV) induced tumors, and a continuous cell line derived from one of them designated RT-2, have been useful for studies in which de novo tumor induction is an important requirement. These tumors also are immunogenic and this limits their usefulness for therapy studies. It is essential to recognize the limitations of each of the models that have been described, and depending upon the nature of the study to be conducted, it is important that the appropriate model be selected.

Neurological grading, survival, MR imaging, and histological evaluation in the rat brainstem glioma model

OBJECTIVE

Convection-enhanced delivery using carboplatin in brainstem glioma models was reported to prolong survival. Functional impairment is of additional importance to evaluate the value of local chemotherapy. We established a neurological scoring system for the rat brainstem glioma model.

MATERIAL AND METHODS

In 46 male Fisher rats stereotactically 10(5) F-98 cells were implanted at 1.4-mm lateral to midline and at the lambdoid suture using guided screws. Following 4 days local delivery was performed using Alzet pumps (1 microl/h over 7 days) with either vehicle (5% dextrose) or carboplatin via one or two cannulas, respectively. All rats were subsequently tested neurologically using a specified neurological score. In 38 animals survival time was recorded. Representative MR imaging were acquired in eight rats, respectively, at day 12 after implantation. HE staining was used to evaluate tumor extension.

RESULTS

Neurological scoring showed significantly higher impairment in the high dose carboplatin group during the treatment period. Survival was significantly prolonged compared to control animals in the high dose carboplatin-one cannula group as well as in both low dose carboplatin groups (18.6 +/- 3 versus 26.3 +/- 9, 22.8 +/- 2, 23.6 +/- 2 days; p < 0.05). Overall neurological grading correlated with survival time. MR imaging showed a focal contrast enhancing mass in the pontine brainstem, which was less exaggerated after local chemotherapy. Histological slices visualized decreased cellular density in treatment animals versus controls.

CONCLUSION

Local chemotherapy in the brainstem glioma model showed significant efficacy for histological changes and survival. Our neurological grading enables quantification of drug and tumor-related morbidity as an important factor for functional performance during therapy.