Response of brain tumors to chemotherapy, evaluated in a clinically relevant xenograft model

The Molecular Mechanisms of Plant-Derived Compounds Targeting Brain Cancer

Glioblastoma multiforme (GBM) is one of the most aggressive and malignant forms of brain tumors. Despite recent advances in operative and postoperative treatments, it is almost impossible to perform complete resection of these tumors owing to their invasive and diffuse nature. Several natural plant-derived products, however, have been demonstrated to have promising therapeutic effects, such that they may serve as resources for anticancer drug discovery. The therapeutic effects of one such plant product, n-butylidenephthalide (BP), are wide-ranging in nature, including impacts on cancer cell apoptosis, cell cycle arrest, and cancer cell senescence. The compound also exhibits a relatively high level of penetration through the blood-brain barrier (BBB). Taken together, its actions have been shown to have anti-proliferative, anti-chemoresistance, anti-invasion, anti-migration, and anti-dissemination effects against GBM. In addition, a local drug delivery system for the subcutaneous and intracranial implantation of BP wafers that significantly reduce tumor size in xenograft models, as well as orthotopic and spontaneous brain tumors in animal models, has been developed. Isochaihulactone (ICL), another kind of plant product, possesses a broad spectrum of pharmacological activities, including impacts on cancer cell apoptosis and cell cycle arrest, as well as anti-proliferative and anti-chemoresistance effects. Furthermore, these actions have been specifically shown to have cancer-fighting effects on GBM. In short, the results of various studies reviewed herein have provided substantial evidence indicating that BP and ICH are promising novel anticancer compounds with good potential for clinical applications.

Sepia ink oligopeptide induces apoptosis in prostate cancer cell lines via caspase-3 activation and elevation of Bax/Bcl-2 ratio

Sepia ink oligopeptide (SIO) is a tripeptide extracted from Sepia ink. To test the hypothesis that SIO inhibits prostate cancer by inducing apoptosis, the effects of SIO on the proliferation of three human prostate cancer cell lines were examined using a CCK-8 assay. SIO significantly inhibited the proliferation of DU-145, PC-3 and LNCaP cells in a time- and dose-dependent manner. Flow cytometry studies showed that exposing DU-145, PC-3 and LNCaP cells to 5, 10, or 15 mg/mL SIO for 24 h increased the percentage of the early-stage apoptotic cells from 11.84% to 38.26% (DU-145), 22.76% to 39.96% (PC-3) and 5.05% to 16.11% (LNCaP), respectively. In addition, typical morphologic changes were observed in the cells with acridine orange/ethidium bromide staining. SIO treatment induced strong S and G₂/M phase cell cycle arrest in a dose-dependent manner in DU-145 and LNCaP. In contrast, SIO treatment induced strong Sub G₁ and G₀/G₁ phase cell cycle arrest in a dose-dependent manner in PC-3. SIO exposure for 24 h decreased the expression of the anti-apoptotic protein Bcl-2 and increased the expression of the apoptogenic protein Bax. Moreover, the Bax/Bcl-2expression ratio was increased. Concurrently, the expression of caspase-3 was upregulated. These data support our hypothesis that SIO has anticarcinogenic properties.

Local interstitial delivery of z-butylidenephthalide by polymer wafers against malignant human gliomas

We have shown that the natural compound z-butylidenephthalide (Bdph), isolated from the chloroform extract of Angelica sinensis, has antitumor effects. Because of the limitation of the blood-brain barrier, the Bdph dosage required for treatment of glioma is relatively high. To solve this problem, we developed a local-release system with Bdph incorporated into a biodegradable polyanhydride material, p(CPP-SA; Bdph-Wafer), and investigated its antitumor effects. On the basis of in vitro release kinetics, we demonstrated that the Bdph-Wafer released 50% of the available Bdph by the sixth day, and the release reached a plateau phase (90% of Bdph) by the 30th day. To investigate the in situ antitumor effects of the Bdph-Wafer on glioblastoma multiforme (GBM), we used 2 xenograft animal models-F344 rats (for rat GBM) and nude mice (for human GBM)-which were injected with RG2 and DBTRG-05MG cells, respectively, for tumor formation and subsequently treated subcutaneously with Bdph-Wafers. We observed a significant inhibitory effect on tumor growth, with no significant adverse effects on the rodents. Moreover, we demonstrated that the antitumor effect of Bdph on RG2 cells was via the PKC pathway, which upregulated Nurr77 and promoted its translocation from the nucleus to the cytoplasm. Finally, to study the effect of the interstitial administration of Bdph in cranial brain tumor, Bdph-Wafers were surgically placed in FGF-SV40 transgenic mice. Our Bdph-Wafer significantly reduced tumor size in a dose-dependent manner. In summary, our study showed that p(CPP-SA) containing Bdph delivered a sufficient concentration of Bdph to the tumor site and effectively inhibited the tumor growth in the glioma.

Multiagent chemotherapy studied in a xenograft model of medulloblastoma/primitive neuroectodermal tumour: analysis of the VETOPEC regimen

Brain tumours remain the most important challenge in the treatment of childhood cancer. The intraocular (io) xenograft model was used to study components and variations of the VETOPEC multiagent chemotherapy regimen in the medulloblastoma/primitive neuroectodermal tumour (MB/PNET) xenograft cell line JRMB-6. VETOPEC, a combination of vincristine (VCR), etoposide (VP-16) and escalated dose cyclophosphamide (CPA), has been shown to be highly active in clinical trials. A total of 190 xenografted tumours were treated with one of nine regimens: saline; single agent CPA, VP-16 (single dose [sd], five dosages daily [dx5] or continuous infusion, [ci]) or VCR; combinations of CPA (dx5)+VP-16 (dx5 or ci) or CPA (dx5)+VP-16 (ci)+VCR (sd). Results were calculated using both response (volume reduction >50%) and 'time to progression' (TtP). Effectiveness of CPA was confirmed. Single-agent VCR or VP-16 produced no response. No difference was documented in TtP with VCR, VP-16 (sd) or VP-16 (dx5) versus control, but a significant prolongation occurred when VP-16 was given by ci (p=0.001). With the 3-agent combination of CPA+VP-16 (ci)+VCR a significantly prolonged TtP was documented versus both single agent CPA (p=0.003) and the combination of CPA+VP-16 (dx5) (p=0.004). The results suggest improved efficacy of VP-16 when given as ci in both single-agent and combination settings. The addition of VP-16 (ci)+VCR to an already effective dosage of CPA further prolongs TtP. These data support and progress VETOPEC phase II clinical studies and suggest potential further benefits of prolonged exposure to VP-16 by ci.

Polynuclear platinum anticancer drugs are more potent than cisplatin and induce cell cycle arrest in glioma

We have evaluated the efficacy of the multinuclear platinum chemotherapeutics BBR3464, BBR3571, and BBR3610 against glioma cells in culture and animal models and investigated their mechanism of action at the cellular level. In a clonogenic assay, BBR3610, the most potent compound, had an IC90 dose (achieving 90% colony formation inhibition) that was 250 times lower than that of cisplatin for both LNZ308 and LN443 glioma cells. In subcutaneous xenografts of U87MG glioma cells, BBR3610 approximately doubled the time it took for a tumor to reach a predetermined size and significantly extended survival when these cells were implanted intracranially. Analysis of apoptosis and cell cycle distribution showed that BBR compounds induced G2/M arrest in the absence of cell death, while cisplatin predominantly induced apoptosis. Interestingly, the BBR compounds and cisplatin both induced extracellular signal-regulated kinase 1/2 phosphorylation, and inhibition of this pathway at the level of MEK antagonized the induction of G2/M arrest or apoptosis, respectively. Analysis of Chk1 and Chk2 status did not show any differential effects of the drugs, and it is thus unlikely to underlie the difference in response. Similarly, the drugs did not differentially modulate survivin levels, and knockdown of survivin did not convert the response to BBR3610 to apoptosis. Together, these findings support continued development of BBR3610 for clinical use against glioma and provide a framework for future investigation of mechanism of action.

The Antitumor Effects of Angelica sinensis on Malignant Brain Tumors In vitro and In vivo

PURPOSE

In this study, we have examined the antitumor effects of chloroform extract of Angelica sinensis (AS-C), a traditional Chinese medicine, on glioblastoma multiforme (GBM) brain tumors in vitro and in vivo.

EXPERIMENTAL DESIGN

In vitro, GBM cells were treated with AS-C, and the cell proliferation, changes in distributions of cell cycle, and apoptosis were determined. In vivo, human DBTRG-05MG and rat RG2 GBM tumor cells were injected s.c. or i.c. and were treated with AS-C. Effects on tumor growth were determined by tumor volume, magnetic resonance imaging, survival, and histology analysis.

RESULTS

The AS-C displays potency in suppressing growth of malignant brain tumor cells without cytotoxicity to fibroblasts. Growth suppression of malignant brain tumor cells by AS-C results from cell cycle arrest and apoptosis. AS-C can up-regulate expression of cdk inhibitors, including p21, to decrease phosphorylation of Rb proteins resulting in cell arrest at the G0-G1 phase for DBTRG-05MG and RG2 cells. The apoptosis-associated proteins are dramatically increased and activated in DBTRG-05MG cells and RG2 cells by AS-C but RG2 cells without p53 protein expression. In vitro results showed AS-C triggered both p53-dependent and p53-independent pathways for apoptosis. In in vivo studies, AS-C not only can suppress growths of malignant brain tumors of rat and human origin but also shrink the volumes of in situ GBM, significantly prolonging survivals.

CONCLUSIONS

The in vitro and in vivo anticancer effects of AS-C indicate that it has sufficient potential to warrant further investigation and development as a new anti-brain tumor agent.

What have we learnt from previous phase II trials to help in the management of childhood brain tumours?

Contrary to major advances in cure rates observed for almost all childhood cancers, progress in reducing brain tumour survival rates remains very limited. Although new drug development in oncology is founded on principles outlined in the organised methodology of phase I, II, and III trials, based on rigorous study design using standardised criteria, this approach has been applied very slowly in the field of neuro-oncology. There are multiple explanations for the paucity of well-conducted prospective clinical trials, such as the rarity and the heterogeneity of these tumours, and the reluctance of some investigators to enroll their patients in constraining trials. Data from the past two decades shows that several methodological problems preclude the drawing of any definite conclusions for the majority of drugs assessed. Among them, the necessity of a central neuropathological and neuroradiological review has been highlighted in, at least, two multicentric studies. Changes in histological diagnosis and grade have been reported in a proportion as high as 20%, and changes in response rate in 14% of the cases. This review of phase II trials for brain tumours reveals a wide array of sometimes arbitrary response definitions, that is if response is defined at all, and most series have enrolled small numbers of patients. We report on the different problems encountered in childhood brain tumours in these phase II trials, and their impact on phase III trials.

Medulloblastoma/primitive neuroectodermal tumour studied as a Matrigel enhanced subcutaneous xenograft model

An important role for pre-clinical models of medulloblastoma/primitive neuroectodermal tumour (MB/PNET) is inhibited by the limitations of conventional heterotransplantation. Nine cohorts of MB/PNET were studied for subcutaneous engraftment in nude mice by both conventional and Matrigel supplemented methods. While no subcutaneous tumours resulted from 63 conventional attempts, an aggregate 41 xenografts from 72 injections (57%) were produced when Matrigel was added to the cell suspension. In subsequent passage, engraftment rate approached 100%. To study the response to chemotherapeutic agents in the model, a total of 221 tumours in 3 cohorts were treated using one of the following: cisplatin, carboplatin, vincristine, cyclophosphamide, diaziquone, or saline control. While all agents demonstrated statistically significant activity, cyclophosphamide proved to be particularly effective. The potential applications of this xenograft model in the biologic as well as therapeutic study of MB/PNET deserve continuing investigation.