Adjuvant therapeutic potential of tonabersat in the standard treatment of glioblastoma: A preclinical F98 glioblastoma rat model study

Tonabersat enhances temozolomide-mediated cytotoxicity in glioblastoma by disrupting intercellular connectivity through connexin 43 inhibition

Glioblastoma cells rely on connexin 43 (Cx43)-based gap junctions (GJs) for intercellular communication, enabling them to integrate into a widely branched malignant network. Although there are promising prospects for new targeted therapies, the lack of clinically feasible GJ inhibitors has impeded their adoption in clinical practice. In the present study, we investigated tonabersat (TO), a blood-brain-barrier-penetrating drug with GJ-inhibitory properties, in regard to its potential to disassemble intercellular connectivity in glioblastoma networks. Fluorescence-guided measurements of calcein cell-to-cell transfer were used to study functional intercellular connectivity. Specific DNA fragmentation rates of propidium iodide-stained nuclei were measured as a surrogate readout for cell death using flow cytometry. CRISPR/Cas9-mediated gene editing of Cx43 served as a validation tool of cellular effects related to Cx43 GJ inhibition. 3' mRNA sequencing was performed for molecular downstream analysis. We found that TO reduced intercellular GJ-mediated cytosolic traffic and yielded a significant reduction of tumor microtube (TM) length. TO-mediated inhibition of cellular tumor networks was accompanied by a synergistic effect for temozolomide-induced cell death. CRISPR/Cas9 Cx43-knockout revealed similar results, indicating that TO-mediated inhibitory effects rely on the inhibition of Cx43-based GJs. Gene set enrichment analyses found that GJ-mediated synergistic cytotoxic effects were linked to a significant upregulation of cell death signaling pathways. In conclusion, TO disrupts TM-based network connectivity via GJ inhibition and renders glioblastoma cells more susceptible to cytotoxic therapy. Given its previous use in clinical trials for migraine therapy, TO might harbor the potential of bridging the idea of a GJ-targeted therapeutic approach from bench to bedside.

Development and validation of a stability-indicating HPLC method for assay of tonabersat in pharmaceutical formulations

A stability-indicating reversed-phase high-performance liquid chromatography (RP-HPLC) method was developed to assay tonabersat and assess its stability in pharmaceutical formulations. Chromatographic separation was achieved using a Kinetex® C18 column (2.6 µm, 150 x 3 mm, 100 Å) at 50 °C, with a 20 µL injection volume. A linear gradient of acetonitrile in water (5 - 33.5 %) was applied for 1 min, followed by a gradual increase to 100 % over 26 min at a flow rate of 0.5 mL/min. Tonabersat and its degradation products were detected at 275 nm and 210 nm, respectively. The optimized method was used to evaluate the stability of tonabersat in lipid-based pharmaceutical formulations at 5 ± 3 °C, 25 ± 2°C/60 ± 5 % RH, and 40 ± 2 °C/75 ± 5 % RH over 3 months. The method was validated as per ICH guidelines and demonstrated linearity in the range of 5 - 200 µg/mL (R2 = 0.99994) with good accuracy (98.25 - 101.58 % recovery) and precision (% RSD < 2.5 %). The limits of detection and quantitation were 0.8 µg/mL and 5 µg/mL, respectively. Forced degradation studies showed significant degradation on exposure to alkaline (90.33 ± 0.80 %), acidic (70.60 ± 1.57 %), and oxidative stress (33.95 ± 0.69 %) at 70 °C, but no degradation was observed on exposure to thermal or photolytic stress. No chemical degradation was observed in either formulation on storage. Thus, the method was sensitive, specific, and suitable for stability testing of tonabersat in pharmaceutical formulations.

Integrating and optimizing tonabersat in standard glioblastoma therapy: A preclinical study

Glioblastoma (GB), a highly aggressive primary brain tumor, presents a poor prognosis despite the current standard therapy, including radiotherapy and temozolomide (TMZ) chemotherapy. Tumor microtubes involving connexin 43 (Cx43) contribute to glioma progression and therapy resistance, suggesting Cx43 inhibition as a potential treatment strategy. This research aims to explore the adjuvant potential of tonabersat, a Cx43 gap junction modulator and blood-brain barrier-penetrating compound, in combination with the standard of care for GB. In addition, different administration schedules and timings to optimize tonabersat's therapeutic window are investigated. The F98 Fischer rat model will be utilized to investigate tonabersat's impact in a clinically relevant setting, by incorporating fractionated radiotherapy (three fractions of 9 Gy) and TMZ chemotherapy (29 mg/kg). This study will evaluate tonabersat's impact on tumor growth, survival, and treatment response through advanced imaging (CE T1-w MRI) and histological analysis. Results show extended survival in rats receiving tonabersat with standard care, highlighting its adjuvant potential. Daily tonabersat administration, both preceding and following radiotherapy, emerges as a promising approach for maximizing survival outcomes. The study suggests tonabersat's potential to reduce tumor invasiveness, providing a new avenue for GB treatment. In conclusion, this preclinical investigation highlights tonabersat's potential as an effective adjuvant treatment for GB, and its established safety profile from clinical trials in migraine treatment presents a promising foundation for further exploration.

An improved F98 glioblastoma rat model to evaluate novel treatment strategies incorporating the standard of care

Glioblastoma (GB) is the most common and malignant primary brain tumor in adults with a median survival of 12-15 months. The F98 Fischer rat model is one of the most frequently used animal models for GB studies. However, suboptimal inoculation leads to extra-axial and extracranial tumor formations, affecting its translational value. We aim to improve the F98 rat model by incorporating MRI-guided (hypo)fractionated radiotherapy (3 x 9 Gy) and concomitant temozolomide chemotherapy, mimicking the current standard of care. To minimize undesired tumor growth, we reduced the number of inoculated cells (starting from 20 000 to 500 F98 cells), slowed the withdrawal of the syringe post-inoculation, and irradiated the inoculation track separately. Our results reveal that reducing the number of F98 GB cells correlates with a diminished risk of extra-axial and extracranial tumor growth. However, this introduces higher variability in days until GB confirmation and uniformity in GB growth. To strike a balance, the model inoculated with 5000 F98 cells displayed the best results and was chosen as the most favorable. In conclusion, our improved model offers enhanced translational potential, paving the way for more accurate and reliable assessments of novel adjuvant therapeutic approaches for GB.

Progress in cancer neuroscience

Cancer of the central nervous system (CNS) can crosstalk systemically and locally in the tumor microenvironment and has become a topic of attention for tumor initiation and advancement. Recently studied neuronal and cancer interaction fundamentally altered the knowledge about glioma and metastases, indicating how cancers invade complex neuronal networks. This review systematically discussed the interactions between neurons and cancers and elucidates new therapeutic avenues. We have overviewed the current understanding of direct or indirect communications of neuronal cells with cancer and the mechanisms associated with cancer invasion. Besides, tumor-associated neuronal dysfunction and the influence of cancer therapies on the CNS are highlighted. Furthermore, interactions between peripheral nervous system and various cancers have also been discussed separately. Intriguingly and importantly, it cannot be ignored that exosomes could mediate the "wireless communications" between nervous system and cancer. Finally, promising future strategies targeting neuronal-brain tumor interactions were reviewed. A great deal of work remains to be done to elucidate the neuroscience of cancer, and future more research should be directed toward clarifying the precise mechanisms of cancer neuroscience, which hold enormous promise to improve outcomes for a wide range of malignancies.

Neurons as stromal drivers of nervous system cancer formation and progression

Similar to their pivotal roles in nervous system development, neurons have emerged as critical regulators of cancer initiation, maintenance, and progression. Focusing on nervous system tumors, we describe the normal relationships between neurons and other cell types relevant to normal nerve function, and discuss how disruptions of these interactions promote tumor evolution, focusing on electrical (gap junctions) and chemical (synaptic) coupling, as well as the establishment of new paracrine relationships. We also review how neuron-tumor communication contributes to some of the complications of cancer, including neuropathy, chemobrain, seizures, and pain. Finally, we consider the implications of cancer neuroscience in establishing risk for tumor penetrance and in the design of future anti-tumoral treatments.

The Role of Hyperexcitability in Gliomagenesis

Glioblastoma is the most common malignant primary brain tumor. Recent studies have demonstrated that excitatory or activity-dependent signaling-both synaptic and non-synaptic-contribute to the progression of glioblastoma. Glutamatergic receptors may be stimulated via neuron-tumor synapses or release of glutamate by the tumor itself. Ion currents generated by these receptors directly alter the structure of membrane adhesion molecules and cytoskeletal proteins to promote migratory behavior. Additionally, the hyperexcitable milieu surrounding glioma increases the rate at which tumor cells proliferate and drive recurrent disease. Inhibition of excitatory signaling has shown to effectively reduce its pro-migratory and -proliferative effects.

The pro- and anti-tumoral properties of gap junctions in cancer and their role in therapeutic strategies

Gap junctions (GJs), essential structures for cell-cell communication, are made of two hemichannels (commonly called connexons), one on each adjacent cell. Found in almost all cells, GJs play a pivotal role in many physiological and cellular processes, and have even been linked to the progression of diseases, such as cancer. Modulation of GJs is under investigation as a therapeutic strategy to kill tumor cells. Furthermore, GJs have also been studied for their key role in activating anti-cancer immunity and propagating radiation- and oxidative stress-induced cell death to neighboring cells, a process known as the bystander effect. While, gap junction (GJ)-based therapeutic strategies are being developed, one major challenge has been the paradoxical role of GJs in both tumor progression and suppression, based on GJ composition, cancer factors, and tumoral context. Therefore, understanding the mechanisms of action, regulation, and the dual characteristics of GJs in cancer is critical for developing effective therapeutics. In this review, we provide an overview of the current understanding of GJs structure, function, and paradoxical pro- and anti-tumoral role in cancer. We also discuss the treatment strategies to target these GJs properties for anti-cancer responses, via modulation of GJ function.

Synaptic input to brain tumors: clinical implications

The recent discovery of synaptic connections between neurons and brain tumor cells fundamentally challenges our understanding of gliomas and brain metastases and shows how these tumors can integrate into complex neuronal circuits. Here, we provide an overview of glutamatergic neuron-to-brain tumor synaptic communication (NBTSC) and explore novel therapeutic avenues. First, we summarize current concepts of direct synaptic interactions between presynaptic neurons and postsynaptic glioma cells, and indirect perisynaptic input to metastatic breast cancer cells. We explain how these novel structures drive brain tumor growth and invasion. Second, a vicious cycle of enhanced neuronal activity, including tumor-related epilepsy, and glioma progression is described. Finally, we discuss which future avenues to target NBTSC appear most promising. All in all, further characterization of NBTSC and the exploration of NBTSC-inhibiting therapies have the potential to reveal critical vulnerabilities of yet incurable brain tumors.

Danegaptide Prevents TGFβ1-Induced Damage in Human Proximal Tubule Epithelial Cells of the Kidney

Chronic kidney disease (CKD) is a global health problem associated with a number of comorbidities. Recent evidence implicates increased hemichannel-mediated release of adenosine triphosphate (ATP) in the progression of tubulointerstitial fibrosis, the main underlying pathology of CKD. Here, we evaluate the effect of danegaptide on blocking hemichannel-mediated changes in the expression and function of proteins associated with disease progression in tubular epithelial kidney cells. Primary human proximal tubule epithelial cells (hPTECs) were treated with the beta1 isoform of the pro-fibrotic cytokine transforming growth factor (TGFβ1) ± danegaptide. qRT-PCR and immunoblotting confirmed mRNA and protein expression, whilst a cytokine antibody array assessed the expression/secretion of proinflammatory and profibrotic cytokines. Carboxyfluorescein dye uptake and ATP biosensing measured hemichannel activity and ATP release, whilst transepithelial electrical resistance was used to assess paracellular permeability. Danegaptide negated carboxyfluorescein dye uptake and ATP release and protected against protein changes associated with tubular injury. Blocking Cx43-mediated ATP release was paralleled by partial restoration of the expression of cell cycle inhibitors, adherens and tight junction proteins and decreased paracellular permeability. Furthermore, danegaptide inhibited TGFβ1-induced changes in the expression and secretion of key adipokines, cytokines, chemokines, growth factors and interleukins. The data suggest that as a gap junction modulator and hemichannel blocker, danegaptide has potential in the future treatment of CKD.

Connexin therapeutics: blocking connexin hemichannel pores is distinct from blocking pannexin channels or gap junctions

Compounds that block the function of connexin and pannexin protein channels have been suggested to be valuable therapeutics for a range of diseases. Some of these compounds are now in clinical trials, but for many of them, the literature is inconclusive about the molecular effect on the tissue, despite evidence of functional recovery. Blocking the different channel types has distinct physiological and pathological implications and this review describes current knowledge of connexin and pannexin protein channels, their function as channels and possible mechanisms of the channel block effect for the latest therapeutic compounds. We summarize the evidence implicating pannexins and connexins in disease, considering their homeostatic versus pathological roles, their contribution to excesive ATP release linked to disease onset and progression.

Perampanel Add-on to Standard Radiochemotherapy in vivo Promotes Neuroprotection in a Rodent F98 Glioma Model

An abnormal glutamate signaling of glioblastoma may contribute to both tumor progression and the generation of glioma-associated epileptic seizures. We hypothesized that the AMPA receptor antagonist perampanel (PER) could attenuate tumor growth and epileptic events. F98 glioma cells, grown orthotopically in Fischer rats, were employed as a model of glioma to investigate the therapeutic efficiency of PER (15 mg/kg) as adjuvant to standard radiochemotherapy (RCT). The epileptiform phenotype was investigated by video-EEG analysis and field potential recordings. Effects on glioma progression were estimated by tumor size quantification, survival analysis and immunohistological staining. Our data revealed that orthotopically-growing F98 glioma promote an epileptiform phenotype in rats. RCT reduced the tumor size and prolonged the survival of the animals. The adjuvant administration of PER had no effect on tumor progression. The tumor-associated epileptic events were abolished by PER application or RCT respectively, to initial baseline levels. Remarkably, PER preserved the glutamatergic network activity on healthy peritumoral tissue in RCT-treated animals. F98 tumors are not only a robust model to investigate glioma progression, but also a viable model to simulate a glioma-associated epileptiform phenotype. Furthermore, our data indicate that PER acts as a potent anticonvulsant and may protect the tumor-surrounding tissue as adjuvant to RCT, but failed to attenuate tumor growth or promote animal survival.

Neuronal signatures in cancer

Despite advances in the treatment of solid tumors, the prognosis of patients with many cancers remains poor, particularly of those with primary and metastatic brain tumors. In the last years, "Cancer Neuroscience" emerged as novel field of research at the crossroads of oncology and classical neuroscience. In primary brain tumors, including glioblastoma (GB), communicating networks that render tumor cells resistant against cytotoxic therapies were identified. To build these networks, GB cells extend neurite-like protrusions called tumor microtubes (TMs). Synapses on TMs allow tumor cells to retrieve neuronal input that fosters growth. Single cell sequencing further revealed that primary brain tumors recapitulate many steps of neurodevelopment. Interestingly, neuronal characteristics, including the ability to extend neurite-like protrusions, neuronal gene expression signatures and interactions with neurons, have now been found not only in brain and neuroendocrine tumors but also in some cancers of epithelial origin. In this review, we will provide an overview about neurite-like protrusions as well as neurodevelopmental origins, hierarchies and gene expression signatures in cancer. We will also discuss how "Cancer Neuroscience" might provide a framework for the development of novel therapies.

Role of Connexins 30, 36, and 43 in Brain Tumors, Neurodegenerative Diseases, and Neuroprotection

Gap junction (GJ) channels and their connexins (Cxs) are complex proteins that have essential functions in cell communication processes in the central nervous system (CNS). Neurons, astrocytes, oligodendrocytes, and microglial cells express an extraordinary repertory of Cxs that are important for cell to cell communication and diffusion of metabolites, ions, neurotransmitters, and gliotransmitters. GJs and Cxs not only contribute to the normal function of the CNS but also the pathological progress of several diseases, such as cancer and neurodegenerative diseases. Besides, they have important roles in mediating neuroprotection by internal or external molecules. However, regulation of Cx expression by epigenetic mechanisms has not been fully elucidated. In this review, we provide an overview of the known mechanisms that regulate the expression of the most abundant Cxs in the central nervous system, Cx30, Cx36, and Cx43, and their role in brain cancer, CNS disorders, and neuroprotection. Initially, we focus on describing the Cx gene structure and how this is regulated by epigenetic mechanisms. Then, the posttranslational modifications that mediate the activity and stability of Cxs are reviewed. Finally, the role of GJs and Cxs in glioblastoma, Alzheimer's, Parkinson's, and Huntington's diseases, and neuroprotection are analyzed with the aim of shedding light in the possibility of using Cx regulators as potential therapeutic molecules.

Update on targeted cancer therapies, single or in combination, and their fine tuning for precision medicine

BACKGROUND

Until recently, patients who have the same type and stage of cancer all receive the same treatment. It has been established, however, that individuals with the same disease respond differently to the same therapy. Further, each tumor undergoes genetic changes that cause cancer to grow and metastasize. The changes that occur in one person's cancer may not occur in others with the same cancer type. These differences also lead to different responses to treatment. Precision medicine, also known as personalized medicine, is a strategy that allows the selection of a treatment based on the patient's genetic makeup. In the case of cancer, the treatment is tailored to take into account the genetic changes that may occur in an individual's tumor. Precision medicine, therefore, could be defined in terms of the targets involved in targeted therapy.

METHODS

A literature search in electronic data bases using keywords "cancer targeted therapy, personalized medicine and cancer combination therapies" was conducted to include papers from 2010 to June 2019.

RESULTS

Recent developments in strategies of targeted cancer therapy were reported. Specifically, on the two types of targeted therapy; first, immune-based therapy such as the use of immune checkpoint inhibitors (ICIs), immune cytokines, tumor-targeted superantigens (TTS) and ligand targeted therapeutics (LTTs). The second strategy deals with enzyme/small molecules-based therapies, such as the use of a proteolysis targeting chimera (PROTAC), antibody-drug conjugates (ADC) and antibody-directed enzyme prodrug therapy (ADEPT). The precise targeting of the drug to the gene or protein under attack was also investigated, in other words, how precision medicine can be used to tailor treatments.

CONCLUSION

The conventional therapeutic paradigm for cancer and other diseases has focused on a single type of intervention for all patients. However, a large literature in oncology supports the therapeutic benefits of a precision medicine approach to therapy as well as combination therapies.