A review of natural products and small-molecule therapeutics acting on central nervous system malignancies: Approaches for drug development, targeting pathways, clinical trials, and challenges

In 2021, the World Health Organization released the fifth edition of the central nervous system (CNS) tumor classification. This classification uses histopathology and molecular pathogenesis to group tumors into more biologically and molecularly defined entities. The prognosis of brain cancer, particularly malignant tumors, has remained poor worldwide, approximately 308,102 new cases of brain and other CNS tumors were diagnosed in the year 2020, with an estimated 251,329 deaths. The cost and time-consuming nature of studies to find new anticancer agents makes it necessary to have well-designed studies. In the present study, the pathways that can be targeted for drug development are discussed in detail. Some of the important cellular origins, signaling, and pathways involved in the efficacy of bioactive molecules against CNS tumorigenesis or progression, as well as prognosis and common approaches for treatment of different types of brain tumors, are reviewed. Moreover, different study tools, including cell lines, in vitro, in vivo, and clinical trial challenges, are discussed. In addition, in this article, natural products as one of the most important sources for finding new chemotherapeutics were reviewed and over 700 reported molecules with efficacy against CNS cancer cells are gathered and classified according to their structure. Based on the clinical trials that have been registered, very few of these natural or semi-synthetic derivatives have been studied in humans. The review can help researchers understand the involved mechanisms and design new goal-oriented studies for drug development against CNS malignancies.

Repurposing synthetic and natural derivatives induces apoptosis in an orthotopic glioma-induced xenograft model by modulating WNT/β-catenin signaling

BACKGROUND

Glioblastomas arise from multistep tumorigenesis of the glial cells. Despite the current state-of-art treatment, tumor recurrence is inevitable. Among the innovations blooming up against glioblastoma, drug repurposing could provide profound premises for treatment enhancement. While considering this strategy, the efficacy of the repurposed drugs as monotherapies were not up to par; hence, the focus has now shifted to investigate the multidrug combinations.

AIM

To investigate the efficacy of a quadruple-combinatorial treatment comprising temozolomide along with chloroquine, naringenin, and phloroglucinol in an orthotopic glioma-induced xenograft model.

METHODS

Antiproliferative effect of the drugs was assessed by immunostaining. The expression profiles of WNT/β-catenin and apoptotic markers were evaluated by qRT-PCR, immunoblotting, and ELISA. Patterns of mitochondrial depolarization was determined by flow cytometry. TUNEL assay was performed to affirm apoptosis induction. In vivo drug detection study was carried out by ESI-Q-TOF MS analysis.

RESULTS

The quadruple-drug treatment had significantly hampered glioma proliferation and had induced apoptosis by modulating the WNT/β-catenin signaling. Interestingly, the induction of apoptosis was associated with mitochondrial depolarization. The quadruple-drug cocktail had breached the blood-brain barrier and was detected in the brain tissue and plasma samples.

CONCLUSION

The quadruple-drug combination served as a promising adjuvant therapy to combat glioblastoma lethality in vivo and can be probed for translation from bench to bedside.

Epothilones as Natural Compounds for Novel Anticancer Drugs Development

Epothilone is a natural 16-membered macrolide cytotoxic compound produced by the metabolism of the cellulose-degrading myxobacterium Sorangium cellulosum. This review summarizes results in the study of epothilones against cancer with preclinical results and clinical studies from 2010-2022. Epothilone have mechanisms of action similar to paclitaxel by inducing tubulin polymerization and apoptosis with low susceptibility to tumor resistance mechanisms. It is active against refractory tumors, being superior to paclitaxel in many respects. Since the discovery of epothilones, several derivatives have been synthesized, and most of them have failed in Phases II and III in clinical trials; however, ixabepilone and utidelone are currently used in clinical practice. There is robust evidence that triple-negative breast cancer (TNBC) treatment improves using ixabepilone plus capecitabine or utidelone in combination with capecitabine. In recent years innovative synthetic strategies resulted in the synthesis of new epothilone derivatives with improved activity against refractory tumors with better activities when compared to ixabepilone or taxol. These compounds together with specific delivery mechanisms could be developed in anti-cancer drugs.

Complementary and Alternative Medicine for Gliomas: Systematic Review and Critical Appraisal of Current Literature

BACKGROUND

Many patients with glioma and their caregivers seek complementary and alternative medicine (CAM) methods to comfort themselves, cope with cancer medication side effects, and feel they are taking control of their disease.

OBJECTIVE

To summarize existing evidence on safety and efficacy of CAM treatments for gliomas.

METHODS

We performed an exhaustive electronic literature search for in vitro, animal, and clinical studies (English language, all years available) on CAM modalities for gliomas.

RESULTS

A total of 378 studies (315 unique articles) were analyzed. Distribution was as follows: in vitro-274 (73%), animal-77 (20%), and clinical-26 (7%, 2491 patients). Most studies were conducted in China (n = 135, 43%), followed by the United States (n = 62, 20%) and Spain (n = 17, 5%-6%). Resveratrol was the most commonly investigated CAM therapy in the in vitro (n = 62) and in vivo (n = 17) setting. Safety/toxicity was examined in 21% of in vitro (cytotoxic at same dose in 48%), 39% of in vivo (no evidence of organ toxicity), and 50% of clinical studies (adverse events reported in 6). Cytotoxicity was the most frequent end point among in vitro (60%) and animal studies (56%), followed by synergistic action with chemotherapy and inhibition of invasiveness and migration. Finally, 7 of 26 studies found no clinical effect, whereas 5 reported possible impact on progression-free or overall survival, 3 demonstrated decrease or arrest of tumor progression, and 2 showed positive impact on symptoms and quality of life.

CONCLUSION

These findings will hopefully educate providers and patients and stimulate further research in the field of CAM therapy for gliomas.

The Improvement of Epothilone D Yield by the Disruption of epoK Gene in Sorangium cellulosum Using TALEN System

Epothilones are a kind of 16-member macrolides with strong anticancer activity, which was produced by Sorangium cellulosum. Epothlione D shows better drug resistance and safety than taxol in clinical trials. However, the low yield of epothilone D in Sorangium cellulosum and thereof toxicity limited the application of epothilone D. In this study, the epoK gene in gene cluster for epothilone was firstly inactivated by the employment of TALEN gene knockout system. The qRT-PCR analysis and sequencing were performed to confirm the gene deletion of epoK, resulting in the epothilone D yield improvement by 34.9±1.6% and the decrease of epothilone B yield by 34.2±2.5%, which was demonstrated by LC-MS analysis. This study would lay a foundation for the yield improvement of epothilones D, B and thereof derivatives in S. cellulosum by genetic engineering, thus promoting the applications of epothilones in the field of anticancer.

Rehabilitation enhances epothilone-induced locomotor recovery after spinal cord injury

Microtubule stabilization through epothilones is a promising preclinical therapy for functional recovery following spinal cord injury that stimulates axon regeneration, reduces growth-inhibitory molecule deposition and promotes functional improvements. Rehabilitation therapy is the only clinically validated approach to promote functional improvements following spinal cord injury. However, whether microtubule stabilization can augment the beneficial effects of rehabilitation therapy or act in concert with it to further promote repair remains unknown. Here, we investigated the pharmacokinetic, histological and functional efficacies of epothilone D, epothilone B and ixabepilone alone or in combination with rehabilitation following a moderate contusive spinal cord injury. Pharmacokinetic analysis revealed that ixabepilone only weakly crossed the blood-brain barrier and was subsequently excluded from further investigations. In contrast, epothilones B and D rapidly distributed to CNS compartments displaying similar profiles after either subcutaneous or intraperitoneal injections. Following injury and subcutaneous administration of epothilone B or D, rats were subjected to 7 weeks of sequential bipedal and quadrupedal training. For all outcome measures, epothilone B was efficacious compared with epothilone D. Specifically, epothilone B decreased fibrotic scaring which was associated with a retention of fibronectin localized to perivascular cells in sections distal to the lesion. This corresponded to a decreased number of cells present within the intralesional space, resulting in less axons within the lesion. Instead, epothilone B increased serotonergic fibre regeneration and vesicular glutamate transporter 1 expression caudal to the lesion, which was not affected by rehabilitation. Multiparametric behavioural analyses consisting of open-field locomotor scoring, horizontal ladder, catwalk gait analysis and hindlimb kinematics revealed that rehabilitation and epothilone B both improved several aspects of locomotion. Specifically, rehabilitation improved open-field locomotor and ladder scores, as well as improving the gait parameters of limb coupling, limb support, stride length and limb speed; epothilone B improved these same gait parameters but also hindlimb kinematic profiles. Functional improvements by epothilone B and rehabilitation acted complementarily on gait parameters leading to an enhanced recovery in the combination group. As a result, principal component analysis of gait showed the greatest improvement in the epothilone B plus rehabilitation group. Thus, these results support the combination of epothilone B with rehabilitation in a clinical setting.

Obstacles to Glioblastoma Treatment Two Decades after Temozolomide

Simple Summary

Glioblastomas are the most common and aggressive brain tumors in adults, with a median survival of 15 months. Treatment is surgical removal, followed by chemotherapy and/or radiotherapy. Current chemotherapeutics do not kill all the tumor cells and some cells survive, leading to the appearance of a new tumor resistant to the treatment. These treatment-resistant cells are called tumor stem cells. In addition, glioblastoma cells have a high capacity for migration, forming new tumors in areas distant from the original tumor. Studies are now focused on understanding the molecular mechanisms of chemoresistance and controlling drug entry into the brain to improve drug performance. Another promising therapeutic approach is the use of viruses that specifically destroy glioblastoma cells, preserving the neural tissue around the tumor. In this review, we summarize the main biological features of glioblastoma and the therapeutic targets that are currently under study for new clinical trials.

Abstract

Glioblastomas are considered the most common and aggressive primary brain tumor in adults, with an average of 15 months’ survival rate. The treatment is surgery resection, followed by chemotherapy with temozolomide, and/or radiotherapy. Glioblastoma must have wild-type IDH gene and some characteristics, such as TERT promoter mutation, EGFR gene amplification, microvascular proliferation, among others. Glioblastomas have great heterogeneity at cellular and molecular levels, presenting distinct phenotypes and diversified molecular signatures in each tumor mass, making it difficult to define a specific therapeutic target. It is believed that the main responsibility for the emerge of these distinct patterns lies in subcellular populations of tumor stem cells, capable of tumor initiation and asymmetric division. Studies are now focused on understanding molecular mechanisms of chemoresistance, the tumor microenvironment, due to hypoxic and necrotic areas, cytoskeleton and extracellular matrix remodeling, and in controlling blood brain barrier permeabilization to improve drug delivery. Another promising therapeutic approach is the use of oncolytic viruses that are able to destroy specifically glioblastoma cells, preserving the neural tissue around the tumor. In this review, we summarize the main biological characteristics of glioblastoma and the cutting-edge therapeutic targets that are currently under study for promising new clinical trials.

An in silico hierarchal approach for drug candidate mining and validation of natural product inhibitors against pyrimidine biosynthesis enzyme in the antibiotic-resistant Shigella flexneri

Shigella flexneri is the main causative agent of the communicable diarrheal disease, shigellosis. It is estimated that about 80-165 million cases and > 1 million deaths occur every year due to this disease. S. flexneri causes dysentery mostly in young children, elderly and immunocompromised patients, all over the globe. Recently, due to the emergence of S. flexneri antibiotic resistance strains, it is a dire need to predict novel therapeutic drug targets in the bacterium and screen natural products against it, which could eliminate the curse of antibiotic resistance. Therefore, in current study, available antibiotic-resistant genomes (n = 179) of S. flexneri were downloaded from PATRIC database and a pan-genome and resistome analysis was conducted. Around 5059 genes made up the accessory, 2469 genes made up the core, and 1558 genes made up the unique genome fraction, with 44, 34, and 13 antibiotic-resistant genes in each fraction, respectively. Core genome fraction (27% of the pan-genome), which was common to all strains, was used for subtractive genomics and resulted in 384 non-homologous, and 85 druggable targets. Dihydroorotase was chosen for further analysis and docked with natural product libraries (Ayurvedic and Streptomycin compounds), while the control was orotic acid or vitamin B13 (which is a natural binder of this protein). Dynamics simulation of 50 ns was carried out to validate findings for top-scored inhibitors. The current study proposed dihydroorotase as a significant drug target in S. flexneri and 4-tritriacontanone & patupilone compounds as potent drugs against shigellosis. Further experiments are required to ascertain validity of our findings.

Microtubule Targeting Agents in Disease: Classic Drugs, Novel Roles

Microtubule-targeting agents (MTAs) represent one of the most successful first-line therapies prescribed for cancer treatment. They interfere with microtubule (MT) dynamics by either stabilizing or destabilizing MTs, and in culture, they are believed to kill cells via apoptosis after eliciting mitotic arrest, among other mechanisms. This classical view of MTA therapies persisted for many years. However, the limited success of drugs specifically targeting mitotic proteins, and the slow growing rate of most human tumors forces a reevaluation of the mechanism of action of MTAs. Studies from the last decade suggest that the killing efficiency of MTAs arises from a combination of interphase and mitotic effects. Moreover, MTs have also been implicated in other therapeutically relevant activities, such as decreasing angiogenesis, blocking cell migration, reducing metastasis, and activating innate immunity to promote proinflammatory responses. Two key problems associated with MTA therapy are acquired drug resistance and systemic toxicity. Accordingly, novel and effective MTAs are being designed with an eye toward reducing toxicity without compromising efficacy or promoting resistance. Here, we will review the mechanism of action of MTAs, the signaling pathways they affect, their impact on cancer and other illnesses, and the promising new therapeutic applications of these classic drugs.

Inhibiting microcephaly genes as alternative to microtubule targeting agents to treat brain tumors

Medulloblastoma (MB) and gliomas are the most frequent high-grade brain tumors (HGBT) in children and adulthood, respectively. The general treatment for these tumors consists in surgery, followed by radiotherapy and chemotherapy. Despite the improvement in patient survival, these therapies are only partially effective, and many patients still die. In the last decades, microtubules have emerged as interesting molecular targets for HGBT, as various microtubule targeting agents (MTAs) have been developed and tested pre-clinically and clinically with encouraging results. Nevertheless, these treatments produce relevant side effects since they target microtubules in normal as well as in cancerous cells. A possible strategy to overcome this toxicity could be to target proteins that control microtubule dynamics but are required by HGBT cells much more than in normal cell types. The genes mutated in primary hereditary microcephaly (MCPH) are ubiquitously expressed in proliferating cells, but under normal conditions are selectively required during brain development, in neural progenitors. There is evidence that MB and glioma cells share molecular profiles with progenitors of cerebellar granules and of cortical radial glia cells, in which MCPH gene functions are fundamental. Moreover, several studies indicate that MCPH genes are required for HGBT expansion. Among the 25 known MCPH genes, we focus this review on KNL1, ASPM, CENPE, CITK and KIF14, which have been found to control microtubule stability during cell division. We summarize the current knowledge about the molecular basis of their interaction with microtubules. Moreover, we will discuss data that suggest these genes are promising candidates as HGBT-specific targets.

Gymnema sylvestre Extract Restores the Autophagic Pathway in Human Glioblastoma Cells U87Mg

Simple Summary

The treatment of GBM is extremely difficult and complicated by the heterogeneous nature of neoplastic cells. The problems inherent in treating any central nervous system tumour are due to the anatomical complexity and the limited repair mechanisms of the surrounding unaffected tissues. The choice of the most suitable treatment for GBM depends on several factors: the location of the disease, the extent, and the nature of the tumour. The limit of this choice is mainly due to the degree of complexity of the disease and to the mechanisms of drug resistance that the neoplasm develops during the treatment. Herbal medicines and their derived phytocompounds are increasingly recognised as useful complementary treatments for cancer. Numerous clinical studies have reported the beneficial effects of herbal medicines on survival, immune modulation, and quality of life of cancer patients when used in combination with conventional therapies. In this study, we investigated all the mechanisms that control tumour cell growth after induction with Gymnema sylvestre (GS) extract and the key proteins that regulate these mechanisms in glioblastoma cells. The study is of great translational interest because the natural substances used could be proposed as natural adjuvant drugs for the treatment of glioblastoma, and therefore could act by modulating new molecular targets for the control of brain tumour cell growth.

Abstract

Glioblastoma is a brain tumour, characterised by recurrent or innate resistance to conventional chemoradiotherapy. Novel natural molecules and phyto-extracts have been proposed as adjuvants to sensitise the response to Temozolomide (TMZ). In this study, we investigated the effect of GS extract on human glioblastoma cells U87Mg. According to the IC50-values, GS extract displayed a significant cytotoxicity. This was confirmed by cell growth inhibition and alteration in metabolic activity evaluated by cell count and MTT assay. GS induced reduction in Pro-caspase 9, 3, but not PARP cleavage nor DNA fragmentation. Thus, in GS-induced cytotoxicity, cell death is not associated with apoptosis. In this context, short-term treatment of U87Mg cells with GS extract (1 mg/mL) reduced the phosphorylation levels of mTOR and of its downstream target P70 S6 kinase, highlighting the role of GS extract into autophagy induction. The activation of autophagic flux by GS extract was confirmed by Western blot analysis, which revealed the reduction in p62 and the concomitant increase in LC3B II/I ratio. Immunofluorescence evidenced the accumulation of LC3B puncta in U87Mg cells pretreated with autophagy inhibitor Bafilomycin A1. Furthermore, as main key regulators of type II programmed cell death, p53, p21 and CDK4 were also investigated and were inhibited by GS treatment. In conclusion, GS extract could be considered as an autophagy inducer in glioblastoma cells U87Mg.

Cytoskeletal proteins as glioblastoma biomarkers and targets for therapy: A systematic review

Glioblastoma, the most common primary brain malignancy, is an exceptionally fatal cancer. Lack of suitable biomarkers and efficient treatment largely contribute to the therapy failure. Cytoskeletal proteins are crucial proteins in glioblastoma pathogenesis and can potentially serve as biomarkers and therapeutic targets. Among them, GFAP, has gained most attention as potential diagnostic biomarker, while vimentin and microtubules are considered as prospective therapeutic targets. Microtubules represent one of the best anti-cancer targets due to their critical role in cell proliferation. Despite testing in clinical trials, the efficiency of taxanes, epothilones, vinca-domain binding drugs, colchicine-domain binding drugs and γ-tubulin binding drugs remains to be confirmed. Moreover, tumor treating field that disrupts microtubules draw attention because of its high efficiency and is called "the fourth cancer treatment modality". Thereby, because of the involvement of cytoskeleton in key physiological and pathological processes, its therapeutic potential in glioblastoma is currently extensively investigated.

A brain-penetrant microtubule-targeting agent that disrupts hallmarks of glioma tumorigenesis

BACKGROUND

Glioma is sensitive to microtubule-targeting agents (MTAs), but most MTAs do not cross the blood brain barrier (BBB). To address this limitation, we developed the new chemical entity, ST-401, a brain-penetrant MTA.

METHODS

Synthesis of ST-401. Measures of MT assembly and dynamics. Cell proliferation and viability of patient-derived (PD) glioma in culture. Measure of tumor microtube (TM) parameters using immunofluorescence analysis and machine learning-based workflow. Pharmacokinetics (PK) and experimental toxicity in mice. In vivo antitumor activity in the RCAS/tv-a PDGFB-driven glioma (PDGFB-glioma) mouse model.

RESULTS

We discovered that ST-401 disrupts microtubule (MT) function through gentle and reverisible reduction in MT assembly that triggers mitotic delay and cell death in interphase. ST-401 inhibits the formation of TMs, MT-rich structures that connect glioma to a network that promotes resistance to DNA damage. PK analysis of ST-401 in mice shows brain penetration reaching antitumor concentrations, and in vivo testing of ST-401 in a xenograft flank tumor mouse model demonstrates significant antitumor activity and no over toxicity in mice. In the PDGFB-glioma mouse model, ST-401 enhances the therapeutic efficacies of temozolomide (TMZ) and radiation therapy (RT).

CONCLUSION

Our study identifies hallmarks of glioma tumorigenesis that are sensitive to MTAs and reports ST-401 as a promising chemical scaffold to develop brain-penetrant MTAs.

A tropomyosin-like Meretrix meretrix Linnaeus polypeptide inhibits the proliferation and metastasis of glioma cells via microtubule polymerization and FAK/Akt/MMPs signaling

Glioblastoma (GBM) represents the most common, aggressive and deadliest primary tumors with poor prognosis as available therapeutic approaches fail to control its aberrant proliferation and high invasiveness. Thus, the therapeutic agents targeting these two characteristics will be more effective. In present study, a novel polypeptide (MM15), which was originally purified from Meretrix meretrix Linnaeus and has been proven to possess potent antitumor activity by our laboratory, was recombinant expressed and identified as a tropomyosin homologous protein. The recombinant polypeptide (re-MM15) could induce the U87 cell cycle arrest in G2/M phase and cell apoptosis by inducing tubulin polymerization. Additionally, re-MM15 displayed the significant inhibition to the migration and invasion of U87 cells through downregulating FAK/Akt/MMPs signaling. Furthermore, the in vivo analysis suggested that re-MM15 significantly blocked tumor growth in U87 xenograft model. Collectively, our results indicated that re-MM15, with anti-GBM properties in vitro and in vivo, has promising potential as a new anticancer candidate for GBM.

Modified carbazoles destabilize microtubules and kill glioblastoma multiform cells

Small molecules that target microtubules (MTs) represent promising therapeutics to treat certain types of cancer, including glioblastoma multiform (GBM). We synthesized modified carbazoles and evaluated their antitumor activity in GBM cells in culture. Modified carbazoles with an ethyl moiety linked to the nitrogen of the carbazole and a carbonyl moiety linked to distinct biaromatic rings exhibited remarkably different killing activities in human GBM cell lines and patient-derived GBM cells, with IC₅₀ values from 67 to >10,000 nM. Measures of the activity of modified carbazoles with tubulin and microtubules coupled to molecular docking studies show that these compounds bind to the colchicine site of tubulin in a unique low interaction space that inhibits tubulin assembly. The modified carbazoles reported here represent novel chemical tools to better understand how small molecules disrupt MT functions and kill devastating cancers such as GBM.

Radiosynthesis and Evaluation of [11C]HD-800, a High Affinity Brain Penetrant PET Tracer for Imaging Microtubules

Microtubules (MTs) are highly abundant throughout the cytoskeleton, and their dysfunction is implicated in the pathogenesis of malignancies, various neurodegenerative disorders, and brain injuries. Validated radiotracers reported so far for MTs are [¹¹C]paclitaxel, [¹⁸F]fluoropaclitaxel, and [¹¹C]docetaxel; however, they are well-characterized substrates of efflux transporters and consequently have poor uptake into the brain due to minimal blood brain barrier (BBB) penetration. PET imaging of MT expression requires radiolabeled BBB penetrating MT ligands, and it may offer a direct and more sensitive approach for early diagnosis, monitoring disease progression, and treatment effects in brain diseases and assessing the clinical potential of targeted therapeutics and treatments. We have identified N-(4-methoxyphenyl)-N-5-dimethylfuro[2,3-d]pyrimidin-4-amine (HD-800) as a high affinity and selective colchicine site tubuline inhibitor amenable to radiolabel with C-11, a positron emitting isotope. HD-800 and desmethyl-HD-800 were synthesized in one step with 75% and 80% yields respectively from commercial synthons. The radiosynthesis of [¹¹C]HD-800 was achieved in 45 ± 5% yield at EOS. Ex vivo biodistribution binding data of [¹¹C]HD-800 indicate that the radioligand penetrated the BBB and it was retained in brain with 75% specific binding. Apart from the brain, specific binding was observed in muscle (55%), heart (50%), lungs (43%), blood (37%), and pancreas (30%). MicroPET imaging in mice showed excellent binding in brain that was blocked by preadministration of unlabeled HD-800 and a colchicine site binding MT ligand MPC-6827. The above results indicate that [¹¹C]HD-800 may be a suitable PET ligand for the in vivo quantification of MT inside and outside the brain.

Continuous low-dose infusion of patupilone increases the therapeutic index in mouse and rat tumour models

Patupilone is a microtubule-targeted cytotoxic agent with clinical efficacy, but causes diarrhoea in more than 80% of patients. The efficacy and tolerability of patupilone delivered continuously by subcutaneous (s.c.) mini-pumps [(mini-pump dose (MPD)] or by intravenous bolus administration [intravenous bolus dose (IVBD)] were compared preclinically to determine whether the therapeutic index could be improved. The antiproliferative potency in vitro of patupilone was determined by measuring total cell protein. Tumours were grown s.c. in rats (A15) or nude mice (KB31, KB8511) or intracranially in nude mice (NCI-H460-Luc). Efficacy was monitored by measuring tumour volumes, bioluminescence or survival. Toxicity was monitored by body weight and/or diarrhoea. Total drug levels in blood, plasma, tissues or dialysates were quantified ex-vivo by liquid chromatography-mass spectroscopy/mass spectroscopy. Patupilone was potent in vitro with GI50s of 0.24-0.28 nmol/l and GI90s of 0.46-1.64 nmol/l. In rats, a single IVBD of patupilone dose dependently inhibited the growth of A15 tumours, but also caused dose-dependent body weight loss and diarrhoea, whereas MPD achieved similar efficacy, but no toxicity. In mice, MPD showed efficacy similar to that of IVBD against KB31 and KB8511 tumours, but with reduced toxicity. In a mouse intracranial tumour model, IVBD was more efficacious than MPD, consistent with patupilone concentrations in the brain. MPD provided constant plasma levels, whereas IVBD had very high C0/Cmin ratios of 70-280 (rat) or 8000 (mouse) over the dosing cycle. Overall, the correlation of plasma and tumour levels with response indicated that a Cave of at least GI90 led to tumour stasis. Continuous low concentrations of patupilone by MPD increased the therapeutic index in s.c. rodent tumour models compared with IVBD by maintaining efficacy, but reducing toxicity.

Natural products: a hope for glioblastoma patients

Glioblastoma (GBM) is one of the most aggressive malignant tumors with an overall dismal survival averaging one year despite multimodality therapeutic interventions including surgery, radiotherapy and concomitant and adjuvant chemotherapy. Few drugs are FDA approved for GBM, and the addition of temozolomide (TMZ) to standard therapy increases the median survival by only 2.5 months. Targeted therapy appeared promising in in vitro monolayer cultures, but disappointed in preclinical and clinical trials, partly due to the poor penetration of drugs through the blood brain barrier (BBB). Cancer stem cells (CSCs) have intrinsic resistance to initial chemoradiation therapy (CRT) and acquire further resistance via deregulation of many signaling pathways. Due to the failure of classical chemotherapies and targeted drugs, research efforts focusing on the use of less toxic agents have increased. Interestingly, multiple natural compounds have shown antitumor and apoptotic effects in TMZ resistant and p53 mutant GBM cell lines and also displayed synergistic effects with TMZ. In this review, we have summarized the current literature on natural products or product analogs used to modulate the BBB permeability, induce cell death, eradicate CSCs and sensitize GBM to CRT.

GBM-associated mutations and altered protein expression are more common in young patients

Background

Geriatric glioblastoma (GBM) patients have a poorer prognosis than younger patients, but IDH1/2 mutations (more common in younger patients) confer a favorable prognosis. We compared key GBM molecular alterations between an elderly (age ≥ 70) and younger (18 < = age < = 45) cohort to explore potential therapeutic opportunities.

Results

Alterations more prevalent in the young GBM cohort compared to the older cohort (P < 0.05) were: overexpression of ALK, RRM1, TUBB3 and mutation of ATRX, BRAF, IDH1, and TP53. However, PTEN mutation was significantly more frequent in older patients. Among patients with wild-type IDH1/2 status, TOPO1 expression was higher in younger patients, whereas MGMT methylation was more frequent in older patients. Within the molecularly-defined IDH wild-type GBM cohort, younger patients had significantly more mutations in PDGFRA, PTPN11, SMARCA4, BRAF and TP53.

Methods

GBMs from 178 elderly patients and 197 young patients were analyzed using DNA sequencing, immunohistochemistry, in situ hybridization, and MGMT-methylation assay to ascertain mutational and amplification/expressional status.

Conclusions

Significant molecular differences occurred in GBMs from elderly and young patients. Except for the older cohort's more frequent PTEN mutation and MGMT methylation, younger patients had a higher frequency of potential therapeutic targets.

Fibroblast growth factor 13 regulates glioma cell invasion and is important for bevacizumab-induced glioma invasion

Glioblastoma has the poorest prognosis, and is characterized by excessive invasion and angiogenesis. To determine the invasive mechanisms, we previously used two glioma cell lines (J3T-1 and J3T-2) with different invasive phenotypes. The J3T-1 showed abundant angiogenesis and tumor cell invasion around neovasculature, while J3T-2 showed diffuse cell infiltration into surrounding healthy parenchyma. Microarray analyses were used to identify invasion-related genes in J3T-2 cells, and the expressed genes and their intracellular and intratumoral distribution patterns were evaluated in J3T-2 cell lines, human glioma cell lines, human glioblastoma stem cells and human glioblastoma specimens. To determine the role of the invasion-related genes, invasive activities were evaluated in vitro and in vivo. Fibroblast growth factor 13 (FGF13) was overexpressed in J3T-2 cells compared to J3T-1 cells, and in human glioma cell lines, human glioblastoma stem cells and human glioblastoma specimens, when compared to that of normal human astrocytes. Immunohistochemical staining and the RNA-seq (sequencing) data from the IVY Glioblastoma Atlas Project showed FGF13 expression in glioma cells in the invasive edges of tumor specimens. Also, the intracellular distribution was mainly in the cytoplasm of tumor cells and colocalized with tubulin. Overexpression of FGF13 stabilized tubulin dynamics in vitro and knockdown of FGF13 decreased glioma invasion both in vitro and in vivo and prolonged overall survival of several xenograft models. FGF13 was negatively regulated by hypoxic condition. Silencing of FGF13 also decreased in vivo bevacizumab-induced glioma invasion. In conclusion, FGF13 regulated glioma cell invasion and bevacizumab-induced glioma invasion, and could be a novel target for glioma treatment.

Review of Natural Product-Derived Compounds as Potent Antiglioblastoma Drugs

Common care for glioblastoma multiforme (GBM) is a surgical resection followed by radiotherapy and temozolomide- (TMZ-) based chemotherapy. Unfortunately, these therapies remain inadequate involving severe mortality and recurrence. Recently, new approaches discovering combinations of multiple inhibitors have been proposed along with the identification of key driver mutations that are specific to each patient. To date, this approach is still limited by the lack of effective therapy. Hopefully, novel compounds derived from natural products are suggested as potential solutions. Inhibitory effects of natural products on angiogenesis and metastasis and cancer suppressive effect of altering miRNA expression are provident discoveries. Angelica sinensis accelerates apoptosis by their key substances influencing factors of apoptosis pathways. Brazilin displays antitumor features by making influence on reactive oxygen species (ROS) intensity. Sargassum serratifolium, flavonoids, and so on have antimetastasis effect. Ficus carica controls miRNA that inhibits translation of certain secretory pathway proteins during the UPR. Serratia marcescens and patupilone (EPO 906) are physically assessed materials through clinical trials related to GBM progression. Consequently, our review puts emphasis on the potential of natural products in GBM treatment by regulating multiple malignant cancer-related pathway solving pending problem such as reducing toxicity and side effect.

The Application of REDOR NMR to Understand the Conformation of Epothilone B

The structural information of small therapeutic compounds complexed in biological matrices is important for drug developments. However, structural studies on ligands bound to such a large and dynamic system as microtubules are still challenging. This article reports an application of the solid-state NMR technique to investigating the bioactive conformation of epothilone B, a microtubule stabilizing agent, whose analog ixabepilone was approved by the U.S. Food and Drug Administration (FDA) as an anticancer drug. First, an analog of epothilone B was designed and successfully synthesized with deuterium and fluorine labels while keeping the high potency of the drug; Second, a lyophilization protocol was developed to enhance the low sensitivity of solid-state NMR; Third, molecular dynamics information of microtubule-bound epothilone B was revealed by high-resolution NMR spectra in comparison to the non-bound epothilone B; Last, information for the macrolide conformation of microtubule-bound epothilone B was obtained from rotational-echo double-resonance (REDOR) NMR data, suggesting the X-ray crystal structure of the ligand in the P450epoK complex as a possible candidate for the conformation. Our results are important as the first demonstration of using REDOR for studying epothilones.

Understanding cytoskeleton regulators in glioblastoma multiforme for therapy design

The cellular cytoskeleton forms the primary basis through which a cell governs the changes in size, shape, migration, proliferation, and forms the primary means through which the cells respond to their environment. Indeed, cell and tissue morphologies are used routinely not only to grade tumors but also in various high-content screening methods with an aim to identify new small molecules with therapeutic potential. This study examines the expression of various cytoskeleton regulators in glioblastoma multiforme (GBM). GBM is a very aggressive disease with a low life expectancy even after chemo- and radiotherapy. Cancer cells of GBM are notorious for their invasiveness, ability to develop resistance to chemo- and radiotherapy, and to form secondary site tumors. This study aims to gain insight into cytoskeleton regulators in GBM cells and to understand the effect of various oncology drugs, including temozolomide, on cytoskeleton regulators. We compare the expression of various cytoskeleton regulators in GBM-derived tumor and normal tissue, CD133-postive and -negative cells from GBM and neural cells, and GBM stem-like and differentiated cells. In addition, the correlation between the expression of cytoskeleton regulators with the clinical outcome was examined to identify genes associated with longer patient survival. This was followed by a small molecule screening with US Food and Drug Administration (FDA)-approved oncology drugs, and its effect on cellular cytoskeleton was compared to treatment with temozolomide. This study identifies various groups of cytoskeletal regulators that have an important effect on patient survival and tumor development. Importantly, this work highlights the advantage of using cytoskeleton regulators as biomarkers for assessing prognosis and treatment design for GBM.

Multicenter phase 2 study of patupilone for recurrent or progressive brain metastases from non-small cell lung cancer

BACKGROUND

Treatment options for patients with non-small cell lung cancer (NSCLC) with brain metastases are limited. Patupilone (EPO906), a blood-brain barrier-penetrating, microtubule-targeting, cytotoxic agent, has shown clinical activity in phase 1/2 studies in patients with NSCLC. This study evaluates the efficacy, pharmacokinetics, and safety of patupilone in NSCLC brain metastases.

METHODS

Adult patients with NSCLC and confirmed progressive brain metastases received patupilone intravenously at 10 mg/m(2) every 3 weeks. The primary endpoint of this multinomial 2-stage study combined early progression (EP; death or progression within 3 weeks) and progression-free survival at 9 weeks (PFS9w) to determine drug activity.

RESULTS

Fifty patients with a median age of 60 years (range, 33-74 years) were enrolled; the majority were men (58%), and most had received prior therapy for brain metastases (98%). The PFS9w rate was 36%, and the EP rate was 26%. Patupilone blood pharmacokinetic analyses showed mean areas under the concentration-time curve from time zero to 504 hours for cycles 1 and 3 of 1544 and 1978 ng h/mL, respectively, and a mean steady state distribution volume of 755 L/m(2) . Grade 3/4 adverse events (AEs), regardless of their relation with the study drug, included diarrhea (24%), pulmonary embolisms (8%), convulsions (4%), and peripheral neuropathy (4%). All patients discontinued the study drug: 31 (62%) for disease progression and 13 (26%) for AEs. Twenty-five of 32 deaths were due to brain metastases. The median time to progression and the overall survival were 3.2 and 8.8 months, respectively.

CONCLUSIONS

This is the first prospective study of chemotherapy for recurrent brain metastases from NSCLC. In this population, patupilone demonstrated activity in heavily treated patients.

Emerging microtubule targets in glioma therapy

Major advances in the genomics and epigenomics of diffuse gliomas and glioblastoma to date have not been translated into effective therapy, necessitating pursuit of alternative treatment approaches for these therapeutically challenging tumors. Current knowledge of microtubules in cancer and the development of new microtubule-based treatment strategies for high-grade gliomas are the topic in this review article. Discussed are cellular, molecular, and pharmacologic aspects of the microtubule cytoskeleton underlying mitosis and interactions with other cellular partners involved in cell cycle progression, directional cell migration, and tumor invasion. Special focus is placed on (1) the aberrant overexpression of βIII-tubulin, a survival factor associated with hypoxic tumor microenvironment and dynamic instability of microtubules; (2) the ectopic overexpression of γ-tubulin, which in addition to its conventional role as a microtubule-nucleating protein has recently emerged as a transcription factor interacting with oncogenes and kinases; (3) the microtubule-severing ATPase spastin and its emerging role in cell motility of glioblastoma cells; and (4) the modulating role of posttranslational modifications of tubulin in the context of interaction of microtubules with motor proteins. Specific antineoplastic strategies discussed include downregulation of targeted molecules aimed at achieving a sensitization effect on currently used mainstay therapies. The potential role of new classes of tubulin-binding agents and ATPase inhibitors is also examined. Understanding the cellular and molecular mechanisms underpinning the distinct behaviors of microtubules in glioma tumorigenesis and drug resistance is key to the discovery of novel molecular targets that will fundamentally change the prognostic outlook of patients with diffuse high-grade gliomas.

Incorporation of biomarkers in phase II studies of recurrent glioblastoma

The survival trends for glioblastoma (GBM) patients have remained largely static, reflecting a lack of improvement in the therapeutic options for patients. Less than 5 % of newly diagnosed GBM survives more than 5 years. Tumor relapse is nearly universal and the majority of patients do not respond to further systemic therapy. The results from phase II studies conducted with recurrent GBM patients have not translated to successful confirmatory studies and thus we have reached a significant roadblock in the development of new treatments for patients with recurrent GBM. The development of new, active, and potentially targeted drugs for the treatment of recurrent GBM represents a major unmet need. The incorporation of diagnostic/companion biomarker combinations into the phase II studies and appropriate stratification of the patients is lagging significantly behind other larger cancer groups such as breast, non-small cell lung cancer, and melanoma. We herein carried out a systematic review of the phase II clinical studies conducted in patients with recurrent GBM (2010-2013 inclusive) to assess the degree of biomarker incorporation within the clinical trial design.

Predictive biomarkers investigated in glioblastoma

Glioblastoma is the most aggressive primary brain tumor in adults. Consequently, new therapeutic strategies are needed. Tumor response to cytotoxic chemotherapy is heterogeneous across patients. Interestingly, predictive biomarkers of response to these classic chemotherapeutic agents have been identified in neuro-oncology (i.e., 1p/19q co-deletion, IDH mutation and O6-methylguanine DNA-methyltransferase promoter methylation). The most emblematic biomarker in glioblastoma is O6-methylguanine DNA-methyltransferase promoter methylation that predicts response to temozolomide. In parallel, innovative drugs are emerging. Some of these agents have shown some activity but in a limited number of glioblastoma patients. One of the major challenges is to identify molecular predictors of response to these smart drugs for an efficient personalized medicine. These novel agents have been tested in clinical trials enrolling glioblastoma patients. Although none of them has been validated prospectively in Phase III clinical trials, interesting molecular predictors of response to these drugs have been investigated and are presented in this review, which also reports more advanced biomarkers.

Phase II trial of patupilone in patients with brain metastases from breast cancer

BACKGROUND

For patients with progressive breast cancer brain metastasis (BCBM) after whole brain radiotherapy (WBRT), few options exist. Patupilone is an epothilone that crosses the blood-brain barrier. We hypothesized that patupilone would produce a 35% 3-month CNS progression-free survival in women with BCBM after WBRT.

METHODS

This multicenter phase II trial included 2 cohorts. Group A included women with progressive BCBM after WBRT. Group B was an exploratory cohort of patients with either leptomeningeal metastases or untreated brain metastases. The primary goal was to observe a 35% 3-month CNS progression-free survival in Group A. The sample size was 45 for Group A and 10 for Group B. Patients received patupilone 10 mg/m(2) once every 3 weeks until progression. Responses were scored according to the Macdonald criteria.

RESULTS

Fifty-five patients (45 in Group A, 10 in Group B) enrolled. In Group A, the 3-month CNS progression-free survival was 27%, the median overall survival was 12.7 months, and the overall response rate was 9%. In Group B, which enrolled 5 patients with leptomeningeal disease and 5 with no prior WBRT, no responses occurred and 8 patients had CNS progression before 3 months. Systemic responses occurred in 15% of patients, including a complete response in liver metastases. Diarrhea occurred in 87% of patients; 25% had grade 3 and 4 adverse events.

CONCLUSIONS

Patupilone in patients with BCBM did not meet the efficacy criteria and had significant gastrointestinal toxicity. Further study of brain-penetrant agents is warranted for patients with CNS metastases from breast cancer.

A conceptually new treatment approach for relapsed glioblastoma: coordinated undermining of survival paths with nine repurposed drugs (CUSP9) by the International Initiative for Accelerated Improvement of Glioblastoma Care

To improve prognosis in recurrent glioblastoma we developed a treatment protocol based on a combination of drugs not traditionally thought of as cytotoxic chemotherapy agents but that have a robust history of being well-tolerated and are already marketed and used for other non-cancer indications. Focus was on adding drugs which met these criteria: a) were pharmacologically well characterized, b) had low likelihood of adding to patient side effect burden, c) had evidence for interfering with a recognized, well-characterized growth promoting element of glioblastoma, and d) were coordinated, as an ensemble had reasonable likelihood of concerted activity against key biological features of glioblastoma growth. We found nine drugs meeting these criteria and propose adding them to continuous low dose temozolomide, a currently accepted treatment for relapsed glioblastoma, in patients with recurrent disease after primary treatment with the Stupp Protocol. The nine adjuvant drug regimen, Coordinated Undermining of Survival Paths, CUSP9, then are aprepitant, artesunate, auranofin, captopril, copper gluconate, disulfiram, ketoconazole, nelfinavir, sertraline, to be added to continuous low dose temozolomide. We discuss each drug in turn and the specific rationale for use- how each drug is expected to retard glioblastoma growth and undermine glioblastoma's compensatory mechanisms engaged during temozolomide treatment. The risks of pharmacological interactions and why we believe this drug mix will increase both quality of life and overall survival are reviewed.

Interphase microtubules: chief casualties in the war on cancer?

Microtubule-targeting agents (MTAs) profoundly affect interphase cells, such as by disrupting axonal transport, transcription, translation, mitochondrial permeability, immune cell function, directional migration and centrosome clustering. This finding is antithetical to the conventionally held notion that MTAs act on mitosis to trigger arrest-mediated apoptotic cell death. Furthermore, the paucity of mitotic cells in patient tumors and lack of correlation of MTA efficacy with tumor proliferation rate provide strong impetus to re-examine the mechanistic basis of action of MTAs, with an eye toward interphase activities. Whereas targeted antimitotics have unequivocally failed their promise across clinical studies, MTAs constitute a mainstay of chemotherapy. This paradox necessitates the conclusion that MTAs exert mitosis-independent effects, spurring a dramatic paradigm shift in our understanding of the mode of action of MTAs.

Can taxanes provide benefit in patients with CNS tumors and in pediatric patients with tumors? An update on the preclinical development of cabazitaxel

PURPOSE

While first-generation taxanes are valuable treatment options for many solid tumors, they are limited by an inability to cross the blood-brain barrier (BBB) and by limited efficacy in pediatric patients. Following promising preclinical data for the next-generation taxane cabazitaxel, including activity in tumor models fully sensitive, poorly sensitive or insensitive to docetaxel, and its ability to cross the BBB, further preclinical studies of cabazitaxel relevant to these two clinical indications were performed.

METHODS

Cabazitaxel brain distribution was assessed in mice, rats and dogs. Cabazitaxel antitumor activity was assessed in mice bearing intracranial human glioblastoma (SF295; U251) xenografts, and subcutaneous cell line-derived human pediatric sarcoma (rhabdomyosarcoma RH-30; Ewing's sarcoma TC-71 and SK-ES-1) or patient-derived pediatric sarcoma (osteosarcoma DM77 and DM113; Ewing's sarcoma DM101) xenografts. The activity of cabazitaxel-cisplatin combination was evaluated in BALB/C mice bearing the syngeneic murine colon adenocarcinoma, C51.

RESULTS

Cabazitaxel penetrated rapidly in the brain, with a similar brain-blood radioactivity exposure relationship across different animal species. In intracranial human glioblastoma models, cabazitaxel demonstrated superior activity to docetaxel both at early (before BBB disruption) and at advanced stages, consistent with enhanced brain penetration. Compared with similar dose levels of docetaxel, cabazitaxel induced significantly greater tumor growth inhibition across six pediatric tumor models and more tumor regressions in five of the six models. Therapeutic synergism was observed between cisplatin and cabazitaxel, regardless of administration sequence.

CONCLUSIONS

These preclinical data suggest that cabazitaxel could be an effective therapy in CNS and pediatric tumors, supporting ongoing clinical evaluation in these indications.

The microtubule stabilizer patupilone counteracts ionizing radiation-induced matrix metalloproteinase activity and tumor cell invasion

Background

Ionizing radiation (IR) in combination with microtubule stabilizing agents (MSA) is a promising combined treatment modality. Supra-additive treatment responses might result from direct tumor cell killing and cooperative indirect, tumor cell-mediated effects on the tumor microenvironment. Here we investigated deregulation of matrix metalloproteinase (MMP) activity, as an important component of the tumor microenvironment, by the combined treatment modality of IR with the clinically relevant MSA patupilone.

Methods

Expression, secretion and activity of MMPs and related tissue inhibitors of metalloproteinases (TIMPs) were determined in cell extracts and conditioned media derived from human fibrosarcoma HT1080 and human glioblastoma U251 tumor cells in response to treatment with IR and the MSA patupilone. Treatment-dependent changes of the invasive capacities of these tumor cell lines were analysed using a Transwell invasion assay. Control experiments were performed using TIMP-directed siRNA and TIMP-directed inhibitory antibodies.

Results

Enzymatic activity of secreted MMPs was determined after treatment with patupilone and irradiation in the human fibrosarcoma HT1080 and the human glioblastoma U251 tumor cell line. IR enhanced the activity of secreted MMPs up to 2-fold and cellular pretreatment with low dose patupilone (0.05-0.2 nM) counteracted specifically the IR-induced MMP activity. The cell invasive capacity of HT1080 and U251 cells was increased after irradiation with 2 Gy by 30% and 50%, respectively, and patupilone treatment completely abrogated IR-induced cell invasion. Patupilone did not alter the level of MMP expression, but interestingly, the protein level of secreted TIMP-1 and TIMP-2 was lower after combined treatment than after irradiation treatment alone. Furthermore, siRNA depletion of TIMP-1 or TIMP-2 prevented IR-mediated induction of MMP activity and cell invasion.

Conclusions

These results indicate that patupilone counteracts an IR-induced MMP activation process by the reduction of secreted TIMP-1 and TIMP-2 proteins, which are required for activation of MMPs. Since IR-induced MMP activity could contribute to tumor progression, treatment combination of IR with patupilone might be of great clinical benefit for tumor therapy.