Src Inhibitors Pyrazolo[3,4-d]pyrimidines, Si306 and Pro-Si306, Inhibit Focal Adhesion Kinase and Suppress Human Glioblastoma Invasion In Vitro and In Vivo

Inhibition of GPR68 kills glioblastoma in zebrafish xenograft models

OBJECTIVE

Inhibition and knockdown of GPR68 negatively affects glioblastoma cell survival in vitro by inducing ferroptosis. Herein, we aimed to demonstrate that inhibition of GPR68 reduces the survival of glioblastoma cells in vivo using two orthotopic larval xenograft models in Danio rerio, using GBM cell lines U87-MG and U138-MG. In vivo survival of the cancer cells was assessed in the setting of GPR68 inhibition or knockdown.

RESULTS

In vitro, shRNA-mediated knockdown of GPR68 inhibition demonstrated potent cytotoxic effects against U87 and U138 glioblastoma cell lines. This effect was associated with increased intracellular lipid peroxidation, suggesting ferroptosis as the underlying mechanism of cell death. Translating these findings in vivo, we established a novel xenograft model in zebrafish by successfully grafting fluorescently labeled human glioblastoma cells, which were previously shown to overexpress GPR68. shRNA knockdown of GPR68 significantly reduced the viability of grafted GBM cells within this model. Additionally, treatment with ogremorphin (OGM), a highly specific small molecule inhibitor of GPR68, also reduced the viability of grafted GBM cells with limited toxicity to the developing zebrafish embryos. This study suggests that therapeutic targeting of GPR68 with small molecules like OGM represents a promising approach for the treatment of GBM.

Preclinical and clinical advances to overcome hypoxia in glioblastoma multiforme

Glioblastoma multiforme (GBM) is the most common adult primary brain tumor. The standard clinical treatment of GBM includes a maximal surgical resection followed by concomitant radiotherapy (RT) and chemotherapy sessions with Temozolomide (TMZ) in addition to adjuvant TMZ cycles. Despite the severity of this protocol, GBM is highly resistant and recurs in almost all cases while the protocol remains unchanged since 2005. Limited-diffusion or chronic hypoxia has been identified as one of the major key players driving this aggressive phenotype. The presence of hypoxia within the tumor bulk contributes to the activation of hypoxia signaling pathway mediated by the hypoxia-inducing factors (HIFs), which in turn activate biological mechanisms to ensure the adaptation and survival of GBM under limited oxygen and nutrient supply. Activated downstream pathways are involved in maintaining stem cell-like phenotype, inducing mesenchymal shift, invasion, and migration, altering the cellular and oxygen metabolism, and increasing angiogenesis, autophagy, and immunosuppression. Therefore, in this review will discuss the recent preclinical and clinical approaches that aim at targeting tumor hypoxia to enhance the response of GBM to conventional therapies along with their results and limitations upon clinical translation.

Glioblastoma research on zebrafish xenograft models: a systematic review

Glioblastoma (GBM) constitutes the most common primary brain tumor in adults. The challenges in GBM therapeutics have shed light on zebrafish used as a promising animal model for preclinical GBM xenograft studies without a standardized methodology. This systematic review aims to summarize the advances in zebrafish GBM xenografting, compare research protocols to pinpoint advantages and underlying limitations, and designate the predominant xenografting parameters. Based on the PRISMA checklist, we systematically searched PubMed, Scopus, and ZFIN using the keywords "glioblastoma," "xenotransplantation," and "zebrafish" for papers published from 2005 to 2022, available in English. 46 articles meeting the review criteria were examined for the zebrafish strain, cancer cell line, cell labeling technique, injected cell number, time and site of injection, and maintenance temperature. Our review designated that AB wild-type zebrafish, Casper transparent mutants, transgenic Tg(fli1:EGFP), or crossbreeding of these predominate among the zebrafish strains. Orthotopic transplantation is more commonly employed. A number of 50-100 cells injected at 48 h post-fertilization in high density and low infusion volume is considered as an effective xenografting approach. U87 cells are used for GBM angiogenesis studies, U251 for GBM proliferation studies, and patient-derived xenograft (PDX) to achieve clinical relevance. Gradual acclimatization to 32-33 °C can partly address the temperature differential between the zebrafish and the GBM cells. Zebrafish xenograft models constitute valuable tools for preclinical studies with clinical relevance regarding PDX. The GBM xenografting research requires modification based on the objective of each research team. Automation and further optimization of the protocol parameters could scale up the anticancer drug trials.

Early investigation of a novel SI306 theranostic prodrug for glioblastoma treatment

Glioblastoma multiforme (GBM) is one of the most aggressive malignancies with a high recurrence rate and poor prognosis. Theranostic, combining therapeutic and diagnostic approaches, arises as a successful strategy to improve patient outcomes through personalized medicine. Src is a non-receptor tyrosine kinase (nRTK) whose involvement in GBM has been extensively demonstrated. Our previous research highlighted the effectiveness of the pyrazolo[3,4-d]pyrimidine SI306 and its more soluble prodrug CMP1 as Src inhibitors both in in vitro and in vivo GBM models. In this scenario, we decided to develop a theranostic prodrug of SI306, ProSI-DOTA(68 Ga) 1, which was designed to target GBM cells after hydrolysis and follow-up on the disease's progression and improve the therapy's outcome. First, the corresponding nonradioactive prodrug 2 was tested to evaluate its ADME profile and biological activity. It showed good metabolic stability, no inhibition of CYP3A4, suboptimal aqueous solubility, and slight gastrointestinal and blood-brain barrier passive permeability. Compound 2 exhibited a drastic reduction of cell vitality after 72 h on two different GBM cell lines (GL261 and U87MG). Then, 2 was subjected to complexation with the radionuclide Gallium-68 to give ProSI-DOTA(68 Ga) 1. The cellular uptake of 1 was evaluated on GBM cells, highlighting a slight but significant time-dependent uptake. The data obtained from our preliminary studies reflect the physiochemical properties of 1. The use of an alternative route of administration, such as the intranasal route, could overcome the physiochemical limitations and enhance the pharmacokinetic properties of 1, paving the way for its future development.

Small Molecule Tyrosine Kinase Inhibitors (TKIs) for Glioblastoma Treatment

In the last decade, many small molecules, usually characterized by heterocyclic scaffolds, have been designed and synthesized as tyrosine kinase inhibitors (TKIs). Among them, several compounds have been tested at preclinical and clinical levels to treat glioblastoma multiforme (GBM). GBM is the most common and aggressive type of cancer originating in the brain and has an unfavorable prognosis, with a median survival of 15-16 months and a 5-year survival rate of 5%. Despite recent advances in treating GBM, it represents an incurable disease associated with treatment resistance and high recurrence rates. For these reasons, there is an urgent need for the development of new pharmacological agents to fight this malignancy. In this review, we reported the compounds published in the last five years, which showed promising activity in GBM preclinical models acting as TKIs. We grouped the compounds based on the targeted kinase: first, we reported receptor TKIs and then, cytoplasmic and peculiar kinase inhibitors. For each small molecule, we included the chemical structure, and we schematized the interaction with the target for some representative compounds with the aim of elucidating the mechanism of action. Finally, we cited the most relevant clinical trials.

A PTP1B-Cdk3 Signaling Axis Promotes Cell Cycle Progression of Human Glioblastoma Cells through an Rb-E2F Dependent Pathway

PTP1B plays a key role in developing different types of cancer. However, the molecular mechanism underlying this effect is unclear. To identify molecular targets of PTP1B that mediate its role in tumorigenesis, we undertook a SILAC-based phosphoproteomic approach, which allowed us to identify Cdk3 as a novel PTP1B substrate. Substrate trapping experiments and docking studies revealed stable interactions between the PTP1B catalytic domain and Cdk3. In addition, we observed that PTP1B dephosphorylates Cdk3 at tyrosine residue 15 in vitro and interacts with it in human glioblastoma cells. Next, we found that pharmacological inhibition of PTP1B or its depletion with siRNA leads to cell cycle arrest with diminished activity of Cdk3, hypophosphorylation of Rb, and the downregulation of E2F target genes Cdk1, Cyclin A, and Cyclin E1. Finally, we observed that the expression of a constitutively active Cdk3 mutant bypasses the requirement of PTP1B for cell cycle progression and expression of E2F target genes. These data delineate a novel signaling pathway from PTP1B to Cdk3 required for efficient cell cycle progression in an Rb-E2F dependent manner in human GB cells.

Autophagy Inhibition Enhances Anti-Glioblastoma Effects of Pyrazolo[3,4-d]pyrimidine Tyrosine Kinase Inhibitors

Drug resistance presents a major obstacle to the successful treatment of glioblastoma. Autophagy plays a key role in drug resistance, particularly in relation to targeted therapy, which has prompted the use of autophagy inhibitors to increase the effectiveness of targeted therapeutics. The ability of two Src tyrosine kinase inhibitors, Si306 and its prodrug pro-Si306, to induce autophagy was evaluated in the human glioblastoma cell line U87 and its multidrug-resistant counterpart U87-TxR. Autophagy markers were assessed by flow cytometry, microscopy, and Western blot, and induction of autophagy by these compounds was demonstrated after 3 h as well as 48 h. The effects of Si306 and pro-Si306 on cell proliferation and cell death were examined in the presence or absence of autophagy inhibition by bafilomycin A1. Combined treatments of Si306 and pro-Si306 with bafilomycin A1 were synergistic in nature, and the inhibition of autophagy sensitized glioblastoma cells to Src tyrosine kinase inhibitors. Si306 and pro-Si306 more strongly inhibited cell proliferation and triggered necrosis in combination with bafilomycin A1. Our findings suggest that modulation of Si306- and pro-Si306-induced autophagy can be used to enhance the anticancer effects of these Src tyrosine kinase inhibitors and overcome the drug-resistant phenotype in glioblastoma cells.

Anti-Survival Effect of SI306 and Its Derivatives on Human Glioblastoma Cells

Glioblastoma (GBM) is the most common adult brain tumor and, although many efforts have been made to find valid therapies, the onset of resistance is the main cause of recurrence. Therefore, it is crucial to identify and target the molecular mediators responsible for GBM malignancy. In this context, the use of Src inhibitors such as SI306 (C1) and its prodrug (C2) showed promising results, suggesting that SI306 could be the lead compound useful to derivate new anti-GBM drugs. Therefore, a new prodrug of SI306 (C3) was synthesized and tested on CAS-1 and U87 human GBM cells by comparing its effect to that of C1 and C2. All compounds were more effective on CAS-1 than U87 cells, while C2 was the most active on both cell lines. Moreover, the anti-survival effect was associated with a reduction in the expression of epidermal growth factor receptor (EGFR)WT and EGFR-vIII in U87 and CAS-1 cells, respectively. Collectively, our findings demonstrate that all tested compounds are able to counteract GBM survival, further supporting the role of SI306 as progenitor of promising new drugs to treat malignant GBM.

New Therapeutic Strategy for Overcoming Multidrug Resistance in Cancer Cells with Pyrazolo[3,4-d]pyrimidine Tyrosine Kinase Inhibitors

Simple Summary

P-glycoprotein (P-gp) is an ATP-binding cassette transporter whose overexpression in cancer cells is one of the main causes of multidrug resistance (MDR). Tyrosine kinase inhibitors (TKIs) have been reported to interact with ABC transporters and in some cases, increase the susceptibility of cancer cells to chemotherapy. We investigated the potential of novel TKI pyrazolo[3,4-d] pyrimidines and their prodrugs to inhibit P-gp in two MDR cancer cell lines with P-gp overexpression. The tested compounds were able to suppress P-gp by inhibiting its ATPase activity. Interestingly, prodrugs displayed a stronger potential to modulate P-gp and showed higher interaction energies in the docking simulations compared to their parent drugs. Furthermore, prodrugs showed significant potential to inhibit P-gp activity even in prolonged treatment and therefore to enhance the efficacy of doxorubicin and paclitaxel in MDR cancer cells. All of these characteristics imply that the new TKIs could be considered a valuable strategy for combating resistant cancers, especially in combination with other chemotherapeutics.

Abstract

Tyrosine kinase inhibitors (TKIs) often interact with the multidrug resistant (MDR) phenotype of cancer cells. In some cases, TKIs increase the susceptibility of MDR cancer cells to chemotherapy. As the overexpression of membrane transporter P-glycoprotein (P-gp) is the most common alteration in MDR cancer cells, we investigated the effects of TKI pyrazolo[3,4-d]pyrimidines on P-gp inhibition in two cellular models comprising sensitive and corresponding MDR cancer cells (human non-small cell lung carcinoma and colorectal adenocarcinoma). Tested TKIs showed collateral sensitivity by inducing stronger inhibition of MDR cancer cell line viability. Moreover, TKIs directly interacted with P-gp and inhibited its ATPase activity. Their potential P-gp binding site was proposed by molecular docking simulations. TKIs reversed resistance to doxorubicin and paclitaxel in a concentration-dependent manner. The expression studies excluded the indirect effect of TKIs on P-gp through regulation of its expression. A kinetics study showed that TKIs decreased P-gp activity and this effect was sustained for seven days in both MDR models. Therefore, pyrazolo[3,4-d]pyrimidines with potential for reversing P-gp-mediated MDR even in prolonged treatments can be considered a new therapeutic strategy for overcoming cancer MDR.

Pyrazolo[3,4-d]pyrimidine Tyrosine Kinase Inhibitors Induce Oxidative Stress in Patient-Derived Glioblastoma Cells

Background: Glioblastoma (GBM) highly expresses Src tyrosine kinase involved in survival, proliferation, angiogenesis and invasiveness of tumor cells. Src activation also reduces reactive oxygen species (ROS) generation, whereas Src inhibitors are able to increase cellular ROS levels. Methods: Pro-oxidative effects of two pyrazolo[3,4-d]pyrimidine derivatives—Src tyrosine kinase inhibitors, Si306 and its prodrug pro-Si306—were investigated in human GBM cells U87 and patient-derived GBM-6. ROS production and changes in mitochondrial membrane potential were assessed by flow cytometry. The expression levels of superoxide dismutase 1 (SOD1) and 2 (SOD2) were studied by Western blot. DNA damage, cell death induction and senescence were also examined in GBM-6 cells. Results: Si306 and pro-Si306 more prominently triggered ROS production and expression of antioxidant enzymes in primary GBM cells. These effects were followed by mitochondrial membrane potential disruption, double-strand DNA breaks and senescence that eventually led to necrosis. Conclusion: Src kinase inhibitors, Si306 and pro-Si306, showed significant pro-oxidative potential in patient-derived GBM cells. This feature contributes to the already demonstrated anti-glioblastoma properties of these compounds in vitro and in vivo and encourages clinical investigations.

B4GalT1 Regulates Apoptosis and Autophagy of Glioblastoma In Vitro and In Vivo

Our study was designed to investigate the role of B4GalT1 in glioblastoma, in vitro and in vivo, to detect whether B4GalT1 knockdown could regulate the development of glioblastoma, and further observe the relationship between B4GalT1 knockdown and the apoptosis and autophagy of glioblastoma. To begin, we looked at TCGA and GEPIA systems to predict the potential function of B4GalT1. Western blot and RT-PCR were used to analyze the expression, or mRNA level, of B4GalT1 at different tissue or cell lines. Next, the occurrence and development of glioblastoma, in vitro and in vivo, was observed by using B4GalT1 knocked down by lentivirus. Finally, the apoptosis and autophagy of glioblastoma was observed in vitro and in vivo. Results show that B4GalT1 was a highly variable gene, and GEPIA and TCGA systems show B4GalT1 expression in GBM tumor tissue was higher than in normal tissue. Pair-wise gene correlation analysis revealed a probable relationship between B4GalT1 and autophagy related proteins. The B4GalT1 expression and mRNA level were increased in tumor cells, or U87 cells. B4GalT1 knocked down by lentivirus could inhibit glioblastoma development, in vitro and in vivo, by reducing tumor weight and volume, increasing survival, and weakening tumor cells proliferation, migration, invasion. B4GalT1 knockdown could increase apoptosis and autophagy of glioblastoma in vitro and in vivo. Our study demonstrates that B4GalT1 may be able to regulate apoptosis and autophagy of glioblastoma. Bax, Bcl-2, cleaved caspase-3, Beclin-1, and LC3 s may be the downstream target factors of B4GalT1 in apoptosis and autophagy, which may provide a new strategy to reduce glioblastoma development by regulating apoptosis and autophagy.