Lonafarnib (SCH66336) improves the activity of temozolomide and radiation for orthotopic malignant gliomas

Ras Inhibitor Lonafarnib Rescues Structural and Functional Impairments of Synapses of Aβ1-42 Mice via α7nAChR-Dependent BDNF Upregulation

Alzheimer's disease (AD) is characterized pathologically by the structural and functional impairments of synapses in the hippocampus, inducing the learning and memory deficiencies. Ras GTPase is closely related to the synaptic function and memory. This study was to investigate the effects of farnesyl transferase inhibitor lonafarnib on the synaptic structure and function in AD male mice and explore the potential mechanism. Our results showed 50 mg/kg lonafarnib (intraperitoneal) rescued the impaired spatial memory and improved the damaged synaptic transmission and plasticity of Aβ1-42 mice. In addition, lonafarnib ameliorated the morphology of synaptic dendrites and spines in Aβ1-42 mice. Furthermore, lonafarnib enhanced α7nAChR cell surface expression and phosphorylation of downstream Akt and CaMKII in Aβ1-42 mice, which were inhibited by α7nAChR antagonist methyl lycaconitine (MLA), and increased the phosphorylation of CREB in a CaMKII- but not ERK-dependent way. Lonafarnib enhanced hippocampal brain-derived neurotrophic factor (BDNF) concentration in Aβ1-42 mice, which was sensitive to MLA and KN93 (an inhibitor of CaMKII), but not related to ERK and Akt pathways. H-Ras, but not Rhes, was related to the lonafarnib induced improvement of α7nAChR cell surface expression and BDNF content. Interestingly, lonafarnib induced improvement of synaptic transmission, plasticity and spatial cognition in Aβ1-42 mice was abolished by BDNF deprivation with TrkB/Fc chimera protein. Our results indicate that lonafarnib can rescue the structural and functional impairments of synapses in the Aβ1-42 mice, which may be related to the improvement of BDNF content through the H-Ras-α7nAChR-dependent CaMKII-CREB pathway, leading to the improvement of spatial cognition.SIGNIFICANCE STATEMENT Alzheimer's disease (AD) is characterized pathologically by the structural and functional impairments of synapses in the hippocampus, inducing the learning and memory deficiencies. However, no effective drugs have not been developed for the treatment of AD synaptic. This study for the first time reported the beneficial effects of Ras inhibitor lonafarnib on the synaptic structure and function in AD mice, providing an alternative way for the treatment of "synaptic disease" in AD patients.

Therapeutic Options in Neuro-Oncology

One of the biggest challenges in neuro-oncology is understanding the complexity of central nervous system tumors, such as gliomas, in order to develop suitable therapeutics. Conventional therapies in malignant gliomas reconcile surgery and radiotherapy with the use of chemotherapeutic options such as temozolomide, chloroethyl nitrosoureas and the combination therapy of procarbazine, lomustine and vincristine. With the unraveling of deregulated cancer cell signaling pathways, targeted therapies have been developed. The most affected signaling pathways in glioma cells involve tyrosine kinase receptors and their downstream pathways, such as the phosphatidylinositol 3-kinases (PI3K/AKT/mTOR) and mitogen-activated protein kinase pathways (MAPK). MAPK pathway inhibitors include farnesyl transferase inhibitors, Ras kinase inhibitors and mitogen-activated protein extracellular regulated kinase (MEK) inhibitors, while PI3K/AKT/mTOR pathway inhibitors are divided into pan-inhibitors, PI3K/mTOR dual inhibitors and AKT inhibitors. The relevance of the immune system in carcinogenesis has led to the development of immunotherapy, through vaccination, blocking of immune checkpoints, oncolytic viruses, and adoptive immunotherapy using chimeric antigen receptor T cells. In this article we provide a comprehensive review of the signaling pathways underlying malignant transformation, the therapies currently used in the treatment of malignant gliomas and further explore therapies under development, including several ongoing clinical trials.

An Overview of the Recent Development of Anticancer Agents Targeting the HIF-1 Transcription Factor

Hypoxia, a characteristic feature of solid tumors, is associated with the malignant phenotype and therapy resistance of cancers. Hypoxia-inducible factor 1 (HIF-1), which is responsible for the metazoan adaptive response to hypoxia, has been recognized as a rational target for cancer therapy due to its critical functions in hypoxic regions. In order to efficiently inhibit its activity, extensive efforts have been made to elucidate the molecular mechanism underlying the activation of HIF-1. Here, we provide an overview of relevant research, particularly on a series of HIF-1 activators identified so far and the development of anticancer drugs targeting them.

A Systematic Review of Glioblastoma-Targeted Therapies in Phases II, III, IV Clinical Trials

Glioblastoma (GBM), the most frequent and aggressive glial tumor, is currently treated as first line by the Stupp protocol, which combines, after surgery, radiotherapy and chemotherapy. For recurrent GBM, in absence of standard treatment or available clinical trials, various protocols including cytotoxic drugs and/or bevacizumab are currently applied. Despite these heavy treatments, the mean overall survival of patients is under 18 months. Many clinical studies are underway. Based on clinicaltrials.org and conducted up to 1 April 2020, this review lists, not only main, but all targeted therapies in phases II-IV of 257 clinical trials on adults with newly diagnosed or recurrent GBMs for the last twenty years. It does not involve targeted immunotherapies and therapies targeting tumor cell metabolism, that are well documented in other reviews. Without surprise, the most frequently reported drugs are those targeting (i) EGFR (40 clinical trials), and more generally tyrosine kinase receptors (85 clinical trials) and (ii) VEGF/VEGFR (75 clinical trials of which 53 involving bevacizumab). But many other targets and drugs are of interest. They are all listed and thoroughly described, on an one-on-one basis, in four sections related to targeting (i) GBM stem cells and stem cell pathways, (ii) the growth autonomy and migration, (iii) the cell cycle and the escape to cell death, (iv) and angiogenesis.

Contemporary Mouse Models in Glioma Research

Despite advances in understanding of the molecular pathogenesis of glioma, outcomes remain dismal. Developing successful treatments for glioma requires faithful in vivo disease modeling and rigorous preclinical testing. Murine models, including xenograft, syngeneic, and genetically engineered models, are used to study glioma-genesis, identify methods of tumor progression, and test novel treatment strategies. Since the discovery of highly recurrent isocitrate dehydrogenase (IDH) mutations in lower-grade gliomas, there is increasing emphasis on effective modeling of IDH mutant brain tumors. Improvements in preclinical models that capture the phenotypic and molecular heterogeneity of gliomas are critical for the development of effective new therapies. Herein, we explore the current status, advancements, and challenges with contemporary murine glioma models.

Farnesyl Transferase Inhibitor Lonafarnib Enhances α7nAChR Expression Through Inhibiting DNA Methylation of CHRNA7 and Increases α7nAChR Membrane Trafficking

Inhibition of Ras farnesylation in acute has been found to upregulate the α7 nicotinic acetylcholine receptor (α7nAChR) activity. This study was carried out to investigate the effect of chronic administration for 7 days of farnesyl transferase inhibitor lonafarnib (50 mg/kg, intraperitoneally injected) to male mice on the expression and activity of α7nAChR in hippocampal CA1 pyramidal cells. Herein, we show that lonafarnib dose dependently enhances the amplitude of ACh-evoked inward currents (I_ACh), owning to the increased α7nAChR expression and membrane trafficking. Lonafarnib inhibited phosphorylation of c-Jun and JNK, which was related to DNA methylation. In addition, reduced DNA methyltransferase 1 (DNMT1) expression was observed in lonafarnib-treated mice, which was reversed by JNK activator. Lonafarnib-upregulated expression of α7nAChR was mimicked by DNMT inhibitor, and repressed by JNK activator. However, only inhibited DNA methylation did not affect I_ACh, and the JNK activator partially decreased the lonafarnib-upregulated I_ACh. On the other hand, lonafarnib also increased the membrane expression of α7nAChR, which was partially inhibited by JNK activator or CaMKII inhibitor, without changes in the α7nAChR phosphorylation. CaMKII inhibitor had no effect on the expression of α7nAChR. Lonafarnib-enhanced spatial memory of mice was also partially blocked by JNK activator or CaMKII inhibitor. These results suggest that Ras inhibition increases α7nAChR expression through depressed DNA methylation of CHRNA7 via Ras-c-Jun-JNK pathway, increases the membrane expression of α7nAChR resulting in part from the enhanced CaMKII pathway and total expression of this receptor, and consequently enhances the spatial memory.

Disentangling the therapeutic tactics in GBM: From bench to bedside and beyond

Glioblastoma multiforme (GBM) is one of the most common and malignant form of adult brain tumor with a high mortality rate and dismal prognosis. The present standard treatment comprising surgical resection followed by radiation and chemotherapy using temozolomide can broaden patient's survival to some extent. However, the advantages are not palliative due to the development of resistance to the drug and tumor recurrence following the multimodal treatment approaches due to both intra- and intertumoral heterogeneity of GBM. One of the major contributors to temozolomide resistance is O⁶ -methylguanine-DNA methyltransferase. Furthermore, deficiency of mismatch repair, base excision repair, and cytoprotective autophagy adds to temozolomide obstruction. Rising proof additionally showed that a small population of cells displaying certain stem cell markers, known as glioma stem cells, adds on to the resistance and tumor progression. Collectively, these findings necessitate the discovery of novel therapeutic avenues for treating glioblastoma. As of late, after understanding the pathophysiology and biology of GBM, some novel therapeutic discoveries, such as drug repurposing, targeted molecules, immunotherapies, antimitotic therapies, and microRNAs, have been developed as new potential treatments for glioblastoma. To help illustrate, "what are the mechanisms of resistance to temozolomide" and "what kind of alternative therapeutics can be suggested" with this fatal disease, a detailed history of these has been discussed in this review article, all with a hope to develop an effective treatment strategy for GBM.

Autophagy as a Potential Therapy for Malignant Glioma

Glioma is the most frequent and aggressive type of brain neoplasm, being anaplastic astrocytoma (AA) and glioblastoma multiforme (GBM), its most malignant forms. The survival rate in patients with these neoplasms is 15 months after diagnosis, despite a diversity of treatments, including surgery, radiation, chemotherapy, and immunotherapy. The resistance of GBM to various therapies is due to a highly mutated genome; these genetic changes induce a de-regulation of several signaling pathways and result in higher cell proliferation rates, angiogenesis, invasion, and a marked resistance to apoptosis; this latter trait is a hallmark of highly invasive tumor cells, such as glioma cells. Due to a defective apoptosis in gliomas, induced autophagic death can be an alternative to remove tumor cells. Paradoxically, however, autophagy in cancer can promote either a cell death or survival. Modulating the autophagic pathway as a death mechanism for cancer cells has prompted the use of both inhibitors and autophagy inducers. The autophagic process, either as a cancer suppressing or inducing mechanism in high-grade gliomas is discussed in this review, along with therapeutic approaches to inhibit or induce autophagy in pre-clinical and clinical studies, aiming to increase the efficiency of conventional treatments to remove glioma neoplastic cells.

Potential roads for reaching the summit: an overview on target therapies for high-grade gliomas

Background:

The tailored targeting of specific oncogenes represents a new frontier in the treatment of high-grade glioma in the pursuit of innovative and personalized approaches. The present study consists in a wide-ranging overview of the target therapies and related translational challenges in neuro-oncology.

Methods:

A review of the literature on PubMed/MEDLINE on recent advances concerning the target therapies for treatment of central nervous system malignancies was carried out. In the Medical Subject Headings, the terms “Target Therapy”, “Target drug” and “Tailored Therapy” were combined with the terms “High-grade gliomas”, “Malignant brain tumor” and “Glioblastoma”. Articles published in the last five years were further sorted, based on the best match and relevance. The ClinicalTrials.gov website was used as a source of the main trials, where the search terms were “Central Nervous System Tumor”, “Malignant Brain Tumor”, “Brain Cancer”, “Brain Neoplasms” and “High-grade gliomas”.

Results:

A total of 137 relevant articles and 79 trials were selected. Target therapies entailed inhibitors of tyrosine kinases, PI3K/AKT/mTOR pathway, farnesyl transferase enzymes, p53 and pRB proteins, isocitrate dehydrogenases, histone deacetylases, integrins and proteasome complexes. The clinical trials mostly involved combined approaches. They were phase I, II, I/II and III in 33%, 42%, 16%, and 9% of the cases, respectively.

Conclusion:

Tyrosine kinase and angiogenesis inhibitors, in combination with standard of care, have shown most evidence of the effectiveness in glioblastoma. Resistance remains an issue. A deeper understanding of the molecular pathways involved in gliomagenesis is the key aspect on which the translational research is focusing, in order to optimize the target therapies of newly diagnosed and recurrent brain gliomas. (www.actabiomedica.it)

Systematic target actionability reviews of preclinical proof-of-concept papers to match targeted drugs to paediatric cancers

Background

Children with cancer are in urgent need of new therapies, as approximately 25% of patients experience a relapse and 20% succumb to their disease. Moreover, the majority of survivors suffer from clinically relevant health problems. Repurposing of targeted agents developed for adult indications could provide novel therapeutic options for paediatric cancer patients. To prioritise targeted drugs for paediatric clinical development, we applied a systematic review methodology to develop a Target Actionability Review (TAR) strategy. These TARs assess the strength and completeness of published preclinical proof-of-concept (PoC) data by structured critical appraisal of and summarising the available scientific literature for a specific target (pathway) and the associated drugs in paediatric tumours.

Methods

A sensitive literature search in PubMed was performed and relevant papers were identified. For each paper, the individual experimental findings were extracted, marked for paediatric tumour type and categorised into nine separate PoC data modules. Each experimental finding was scored for experimental outcome and quality independently by two reviewers; discrepancies were assessed by a third reviewer and resolved by adjudication. Scores corresponding to one PoC module were merged for each tumour type and visualised in a heat map matrix in the publicly available R2 data portal [r2.amc.nl].

Results and conclusions

To test our TAR methodology, we conducted a pilot study on MDM2 and TP53. The heat map generated from analysis of 161 publications provides a rationale to support drug development in specific paediatric solid and brain tumour types. Furthermore, our review highlights tumour types where preclinical data are incomplete or lacking and for which additional preclinical testing is advisable.

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A new strategy to review literature on targeted compounds in paediatric cancer.

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Results help to guide and prioritise clinical development of novel targeted agents.

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Outcomes are visualised in a publicly available, interactive heat map.

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We applied this unique methodology to MDM2 and TP53 and MDM2 inhibitors.

Loss of GTPase activating protein neurofibromin stimulates paracrine cell communication via macropinocytosis

Neurofibromin, the protein product of the neurofibromatosis type 1 (NF1) tumor suppressor gene, is a negative regulator of Ras signaling. Patients with mutations in NF1 have a strong predisposition for cardiovascular disease, which contributes to their early mortality. Nf1 heterozygous (Nf1^+/-) bone marrow to wild type chimeras and mice with heterozygous recombination of Nf1 in myeloid cells recapitulate many of the vascular phenotypes observed in Nf1^+/- mutants. Although these results suggest that macrophages play a central role in NF1 vasculopathy, the underlying mechanisms are currently unknown. In the present study, we employed macrophages isolated from either Nf1^+/- or Lysm Cre⁺/Nf1^f/f mice to test the hypothesis that loss of Nf1 stimulates macropinocytosis in macrophages. Scanning electron microscopy and flow cytometry analysis of FITC-dextran internalization demonstrated that loss of Nf1 in macrophages stimulates macropinocytosis. We next utilized various cellular and molecular approaches, pharmacological inhibitors and genetically modified mice to identify the signaling mechanisms mediating macropinocytosis in Nf1-deficient macrophages. Our results indicate that loss of Nf1 stimulates PKCδ-mediated p47^phox phosphorylation via RAS activation, leading to increased NADPH oxidase 2 activity, reactive oxygen species generation, membrane ruffling and macropinocytosis. Interestingly, we also found that Nf1-deficient macrophages internalize exosomes derived from angiotensin II-treated endothelial cells via macropinocytosis in vitro and in the peritoneal cavity in vivo. As a result of exosome internalization, Nf1-deficient macrophages polarized toward an inflammatory M1 phenotype and secreted increased levels of proinflammatory cytokines compared to controls. In conclusion, the findings of the present study demonstrate that loss of Nf1 stimulates paracrine endothelial to myeloid cell communication via macropinocytosis, leading to proinflammatory changes in recipient macrophages.

Autophagic and Apoptotic Pathways as Targets for Chemotherapy in Glioblastoma

Glioblastoma multiforme is the most malignant and aggressive type of brain tumor, with a mean life expectancy of less than 15 months. This is due in part to the high resistance to apoptosis and moderate resistant to autophagic cell death in glioblastoma cells, and to the poor therapeutic response to conventional therapies. Autophagic cell death represents an alternative mechanism to overcome the resistance of glioblastoma to pro-apoptosis-related therapies. Nevertheless, apoptosis induction plays a major conceptual role in several experimental studies to develop novel therapies against brain tumors. In this review, we outline the different components of the apoptotic and autophagic pathways and explore the mechanisms of resistance to these cell death pathways in glioblastoma cells. Finally, we discuss drugs with clinical and preclinical use that interfere with the mechanisms of survival, proliferation, angiogenesis, migration, invasion, and cell death of malignant cells, favoring the induction of apoptosis and autophagy, or the inhibition of the latter leading to cell death, as well as their therapeutic potential in glioma, and examine new perspectives in this promising research field.

MicroRNA-378 enhances radiation response in ectopic and orthotopic implantation models of glioblastoma

Glioblastoma multiforme (GBM) is the most common and highly malignant primary brain tumor, which is virtually incurable due to its therapeutic resistance to radiation and chemotherapy. To develop novel therapeutic approaches for treatment of GBM, we examined the role of miR-378 on tumor growth, angiogenesis, and radiation response in ectopic and orthotopic U87 glioblastoma models. Cell and tumor growth rates, in vitro and in vivo radiation sensitivities, and tumor vascular density were evaluated in U87-GFP and U87-miR-378 tumor lines. Ectopic tumor response to radiation was evaluated under normal blood flow and clamp hypoxic conditions. Results show that in vitro, miR-378 expression moderately increased cell growth rate and plating efficiency, but did not alter radiation sensitivity. U87-miR-378 tumors exhibited a higher transplantation take rate than U87-GFP tumors. In vivo, under oxygenated condition, subcutaneous U87-miR-378 tumors receiving 25 Gy showed a tendency for longer tumor growth delay (TGD) than control U87-GFP tumors. In contrast, under hypoxic condition, U87-miR-378 xenografts exhibited substantially shorter TGD than U87-GFP tumors, indicating that under normal blood flow conditions, U87-miR-378 tumors were substantially more oxygenated than U87-GFP tumors. Intracranial multi-photon laser-scanning microscopy demonstrated increased vascular density of U87-miR-378 versus control U87-GFP tumors. Finally, miR-378 increased TGD following 12 Gy irradiation in U87 intracranial xenografts, and significantly prolonged survival of U87-miR-378 tumor-bearing mice (P = 0.04). In conclusion, higher miR-378 expression in U87-miR-378 cells promotes tumor growth, angiogenesis, radiation-induced TGD, and prolongs survival of orthotopic tumor-bearing hosts. Regulation of VEGFR2 by miR-378 significantly increased vascular density and oxygenation in U87 xenografts.

Deregulated expression and activity of Farnesyl Diphosphate Synthase (FDPS) in Glioblastoma

Glioblastoma (GBM), the most aggressive brain cancer, is highly dependent on the mevalonate (MVA) pathway for the synthesis of lipid moieties critical for cell proliferation but the function and regulation of key intermediate enzymes like farnesyl-diphosphate synthase (FDPS), up to now, remained unknown. A deregulated expression and activity of FDPS was the central research idea of the present study. FDPS mRNA, protein and enzyme activity were analyzed in a cohort of stage III-IV glioma patients (N = 49) and primary derived cells. FDPS silencing helped to clarify its function in the maintenance of malignant phenotype. Interestingly, compared to tumor-free peripheral (TFB) brain and normal human astrocytes (NHA), FDPS protein expression and enzyme activity were detected at high degree in tumor mass where a correlation with canonical oncogenic signaling pathways such as STAT3, ERK and AKT was also documented. Further, FDPS knockdown in U87 and GBM primary cells but not in NHA, enhanced apoptosis. With the effort to develop a more refined map of the connectivity between signal transduction pathways and metabolic networks in cancer FDPS as a new candidate metabolic oncogene in glioblastoma, might suggest to further target MVA pathway as valid therapeutic tool.

Predicting Drug Combination Index and Simulating the Network-Regulation Dynamics by Mathematical Modeling of Drug-Targeted EGFR-ERK Signaling Pathway

Synergistic drug combinations enable enhanced therapeutics. Their discovery typically involves the measurement and assessment of drug combination index (CI), which can be facilitated by the development and applications of in-silico CI predictive tools. In this work, we developed and tested the ability of a mathematical model of drug-targeted EGFR-ERK pathway in predicting CIs and in analyzing multiple synergistic drug combinations against observations. Our mathematical model was validated against the literature reported signaling, drug response dynamics, and EGFR-MEK drug combination effect. The predicted CIs and combination therapeutic effects of the EGFR-BRaf, BRaf-MEK, FTI-MEK, and FTI-BRaf inhibitor combinations showed consistent synergism. Our results suggest that existing pathway models may be potentially extended for developing drug-targeted pathway models to predict drug combination CI values, isobolograms, and drug-response surfaces as well as to analyze the dynamics of individual and combinations of drugs. With our model, the efficacy of potential drug combinations can be predicted. Our method complements the developed in-silico methods (e.g. the chemogenomic profile and the statistically-inferenced network models) by predicting drug combination effects from the perspectives of pathway dynamics using experimental or validated molecular kinetic constants, thereby facilitating the collective prediction of drug combination effects in diverse ranges of disease systems.

The challenges and the promise of molecular targeted therapy in malignant gliomas

Malignant gliomas are the most common malignant primary brain tumors and one of the most challenging forms of cancers to treat. Despite advances in conventional treatment, the outcome for patients remains almost universally fatal. This poor prognosis is due to therapeutic resistance and tumor recurrence after surgical removal. However, over the past decade, molecular targeted therapy has held the promise of transforming the care of malignant glioma patients. Significant progress in understanding the molecular pathology of gliomagenesis and maintenance of the malignant phenotypes will open opportunities to rationally develop new molecular targeted therapy options. Recently, therapeutic strategies have focused on targeting pro-growth signaling mediated by receptor tyrosine kinase/RAS/phosphatidylinositol 3-kinase pathway, proangiogenic pathways, and several other vital intracellular signaling networks, such as proteasome and histone deacetylase. However, several factors such as cross-talk between the altered pathways, intratumoral molecular heterogeneity, and therapeutic resistance of glioma stem cells (GSCs) have limited the activity of single agents. Efforts are ongoing to study in depth the complex molecular biology of glioma, develop novel regimens targeting GSCs, and identify biomarkers to stratify patients with the individualized molecular targeted therapy. Here, we review the molecular alterations relevant to the pathology of malignant glioma, review current advances in clinical targeted trials, and discuss the challenges, controversies, and future directions of molecular targeted therapy.

Glioblastoma multiforme: Pathogenesis and treatment

Each year, about 5-6 cases out of 100,000 people are diagnosed with primary malignant brain tumors, of which about 80% are malignant gliomas (MGs). Glioblastoma multiforme (GBM) accounts for more than half of MG cases. They are associated with high morbidity and mortality. Despite current multimodality treatment efforts including maximal surgical resection if feasible, followed by a combination of radiotherapy and/or chemotherapy, the median survival is short: only about 15months. A deeper understanding of the pathogenesis of these tumors has presented opportunities for newer therapies to evolve and an expectation of better control of this disease. Lately, efforts have been made to investigate tumor resistance, which results from complex alternate signaling pathways, the existence of glioma stem-cells, the influence of the blood-brain barrier as well as the expression of 0(6)-methylguanine-DNA methyltransferase. In this paper, we review up-to-date information on MGs treatment including current approaches, novel drug-delivering strategies, molecular targeted agents and immunomodulative treatments, and discuss future treatment perspectives.

Management of diffuse pontine gliomas in children: recent developments

The prognosis for children with diffuse intrinsic pontine gliomas (DIPGs) is dismal. Although DIPGs constitute only 10-15 % of all pediatric brain tumors, they are the main cause of death in this group with a median survival of less than 12 months. Standard therapy involves radiotherapy, which produces transient neurologic improvement. Despite several clinical trials having been conducted, including trials on targeted agents to assess their efficacy, there is no clear improvement in prognosis. However, knowledge of DIPG biology is increasing, mainly as a result of research using biopsy and autopsy samples. In this review, we discuss recent studies in which systemic therapy was administered prior to, concomitantly with, or after radiotherapy. The discussion also includes novel therapeutic options in DIPG. Continuing multimodal and multitargeted therapies might lead to an improvement in the dismal prognosis of the disease.

Phase 1/1b study of lonafarnib and temozolomide in patients with recurrent or temozolomide refractory glioblastoma

BACKGROUND

Lonafarnib is an oral selective farnesyltransferase inhibitor, a class of drugs which have shown activity in preclinical glioma models. Temozolomide (TMZ) is an alkylating agent that is the first-line chemotherapy for glioblastoma.

METHODS

The current study combined the cytotoxic agent TMZ with the cytostatic agent lonafarnib for patients with recurrent glioblastoma to establish a maximum tolerated dose (MTD) of the combination and its preliminary efficacy. Three dose cohorts of lonafarnib were studied in the phase 1 component of the trial (100 mg twice daily [bid], 150 mg bid, and 200 bid) with dose-dense schedule of TMZ (150 mg/m² daily) administered in an alternating weekly schedule. After establishing the MTD of lonafarnib, a subsequent expansion phase 1b was undertaken to evaluate efficacy, primarily measured by 6-month progression-free survival (PFS-6).

RESULTS

Fifteen patients were enrolled into the phase 1 component and 20 patients into the phase 1b component. The MTD of lonafarnib in combination with TMZ was 200 mg bid. Among the patients enrolled into the study, 34 were eligible for 6-month progression evaluation and 35 patients were evaluable for time-to-progression analysis. The PFS-6 rate was 38% (95% confidence interval [CI] = 22%, 56%) and the median PFS was 3.9 months (95% CI = 2.5, 8.4). The median disease-specific survival was 13.7 months (95% CI = 8.9, 22.1). Hematologic toxicities, particularly lymphopenia, were the most common grade 3 and 4 adverse events. There were no treatment-related deaths.

CONCLUSIONS

These results demonstrate that TMZ can be safely combined with a farnesyltransferase inhibitor and that this regimen is active, although the current study cannot determine the relative contributions of the 2 agents or the contribution of the novel administration schedule.

Recent advances in protein prenyltransferases: substrate identification, regulation, and disease interventions

Protein post-translational modifications increase the functional diversity of the proteome by covalently adding chemical moieties onto proteins thereby changing their activation state, cellular localization, interacting partners, and life cycle. Lipidation is one such modification that enables membrane association of naturally cytosolic proteins. Protein prenyltransferases irreversibly install isoprenoid units of varying length via a thioether linkage onto proteins that exert their cellular activity at membranes. Substrates of prenyltransferases are involved in countless signaling pathways and processes within the cell. Identification of new prenylation substrates, prenylation pathway regulators, and dynamic trafficking of prenylated proteins are all avenues of intense, ongoing research that are challenging, exciting, and have the potential to significantly advance the field in the near future.

Novel delivery strategies for glioblastoma

Brain tumors--particularly glioblastoma multiforme--pose an important public health problem in the United States. Despite surgical and medical advances, the prognosis for patients with malignant gliomas remains grim: current therapy is insufficient with nearly universal recurrence. A major reason for this failure is the difficulty of delivering therapeutic agents to the brain: better delivery approaches are needed to improve treatment. In this article, we summarize recent progress in drug delivery to the brain, with an emphasis on convection-enhanced delivery of nanocarriers. We examine the potential of new delivery methods to permit novel drug- and gene-based therapies that target brain cancer stem cells and discuss the use of nanomaterials for imaging of tumors and drug delivery.

Using the heat-shock response to discover anticancer compounds that target protein homeostasis

Unlike normal tissues, cancers experience profound alterations in protein homeostasis. Powerful innate adaptive mechanisms, especially the transcriptional response regulated by Heat Shock Factor 1 (HSF1), are activated in cancers to enable survival under these stressful conditions. Natural products that further tax these stress responses can overwhelm the ability to cope and could provide leads for the development of new, broadly effective anticancer drugs. To identify compounds that drive the HSF1-dependent stress response, we evaluated over 80,000 natural and synthetic compounds as well as partially purified natural product extracts using a reporter cell line optimized for high-throughput screening. Surprisingly, many of the strongly active compounds identified were natural products representing five diverse chemical classes (limonoids, curvularins, withanolides, celastraloids, and colletofragarones). All of these compounds share the same chemical motif, an α,β-unsaturated carbonyl functionality, with strong potential for thiol-reactivity. Despite the lack of a priori mechanistic requirements in our primary phenotypic screen, this motif was found to be necessary albeit not sufficient, for both heat-shock activation and inhibition of glioma tumor cell growth. Within the withanolide class, a promising therapeutic index for the compound withaferin A was demonstrated in vivo using a stringent orthotopic human glioma xenograft model in mice. Our findings reveal that diverse organisms elaborate structurally complex thiol-reactive metabolites that act on the stress responses of heterologous organisms including humans. From a chemical biology perspective, they define a robust approach for discovering candidate compounds that target the malignant phenotype by disrupting protein homeostasis.