Discovery of Clinical Development Candidate GDC-0084, a Brain Penetrant Inhibitor of PI3K and mTOR

Rational combination platform trial design for children and young adults with diffuse midline glioma: A report from PNOC

Background Diffuse midline glioma (DMG) is a devastating pediatric brain tumor unresponsive to hundreds of clinical trials. Approximately 80% of DMGs harbor H3K27M oncohistones, which reprogram the epigenome to increase the metabolic profile of the tumor cells. Methods We have previously shown preclinical efficacy of targeting both oxidative phosphorylation and glycolysis through treatment with ONC201, which activates the mitochondrial protease ClpP, and paxalisib, which inhibits PI3K/mTOR, respectively. Results ONC201 and paxalisib combination treatment aimed at inducing metabolic distress led to the design of the first DMG-specific platform trial PNOC022 (NCT05009992). Conclusions Here, we expand on the PNOC022 rationale and discuss various considerations, including liquid biome, microbiome, and genomic biomarkers, quality-of-life endpoints, and novel imaging modalities, such that we offer direction on future clinical trials in DMG.

MT-125 Inhibits Non-Muscle Myosin IIA and IIB, Synergizes with Oncogenic Kinase Inhibitors, and Prolongs Survival in Glioblastoma

We have identified a NMIIA and IIB-specific small molecule inhibitor, MT-125, and have studied its effects in GBM. MT-125 has high brain penetrance and retention and an excellent safety profile; blocks GBM invasion and cytokinesis, consistent with the known roles of NMII; and prolongs survival as a single agent in murine GBM models. MT-125 increases signaling along both the PDGFR- and MAPK-driven pathways through a mechanism that involves the upregulation of reactive oxygen species, and it synergizes with FDA-approved PDGFR and mTOR inhibitors in vitro . Combining MT-125 with sunitinib, a PDGFR inhibitor, or paxalisib, a combined PI3 Kinase/mTOR inhibitor significantly improves survival in orthotopic GBM models over either drug alone, and in the case of sunitinib, markedly prolongs survival in ∼40% of mice. Our results provide a powerful rationale for developing NMII targeting strategies to treat cancer and demonstrate that MT-125 has strong clinical potential for the treatment of GBM.

Highlights

MT-125 is a highly specific small molecule inhibitor of non-muscle myosin IIA and IIB, is well-tolerated, and achieves therapeutic concentrations in the brain with systemic dosing.Treating preclinical models of glioblastoma with MT-125 produces durable improvements in survival.MT-125 stimulates PDGFR- and MAPK-driven signaling in glioblastoma and increases dependency on these pathways.Combining MT-125 with an FDA-approved PDGFR inhibitor in a mouse GBM model synergizes to improve median survival over either drug alone, and produces tumor free, prolonged survival in over 40% of mice.

Genetic Silencing of AKT Induces Melanoma Cell Death via mTOR Suppression

Aberrant activation of the PI3K-AKT pathway is common in many cancers, including melanoma, and AKT1, 2 and 3 (AKT1-3) are bona fide oncoprotein kinases with well-validated downstream effectors. However, efforts to pharmacologically inhibit AKT have proven to be largely ineffective. In this study, we observed paradoxical effects following either pharmacologic or genetic inhibition of AKT1-3 in melanoma cells. Although pharmacological inhibition was without effect, genetic silencing of all three AKT paralogs significantly induced melanoma cell death through effects on mTOR. This phenotype was rescued by exogenous AKT1 expression in a kinase-dependent manner. Pharmacological inhibition of PI3K and mTOR with a novel dual inhibitor effectively suppressed melanoma cell proliferation in vitro and inhibited tumor growth in vivo. Furthermore, this single-agent-targeted therapy was well-tolerated in vivo and was effective against MAPK inhibitor-resistant patient-derived melanoma xenografts. These results suggest that inhibition of PI3K and mTOR with this novel dual inhibitor may represent a promising therapeutic strategy in this disease in both the first-line and MAPK inhibitor-resistant setting.

Advancements in dual-target inhibitors of PI3K for tumor therapy: Clinical progress, development strategies, prospects

Phosphoinositide 3-kinases (PI3Ks) modify lipids by the phosphorylation of inositol phospholipids at the 3'-OH position, thereby participating in signal transduction and exerting effects on various physiological processes such as cell growth, metabolism, and organism development. PI3K activation also drives cancer cell growth, survival, and metabolism, with genetic dysregulation of this pathway observed in diverse human cancers. Therefore, this target is considered a promising potential therapeutic target for various types of cancer. Currently, several selective PI3K inhibitors and one dual-target PI3K inhibitor have been approved and launched on the market. However, the majority of these inhibitors have faced revocation or voluntary withdrawal of indications due to concerns regarding their adverse effects. This article provides a comprehensive review of the structure and biological functions, and clinical status of PI3K inhibitors, with a specific emphasis on the development strategies and structure-activity relationships of dual-target PI3K inhibitors. The findings offer valuable insights and future directions for the development of highly promising dual-target drugs targeting PI3K.

Preclinical characterization of the absorption and disposition of the brain penetrant PI3K/mTOR inhibitor paxalisib and prediction of its pharmacokinetics and efficacy in human

Glioblastoma multiforme (GBM) is the most common primary brain tumour in adults. Available treatments have not markedly improved patient survival in the last twenty years. However, genomic investigations have showed that the PI3K pathway is frequently altered in this glioma, making it a potential therapeutic target.Paxalisib is a brain penetrant PI3K/mTOR inhibitor (mouse Kp,uu 0.31) specifically developed for the treatment of GBM. We characterised the preclinical pharmacokinetics and efficacy of paxalisib and predicted its pharmacokinetics and efficacious dose in humans.Plasma protein binding of paxalisib was low, with the fraction unbound ranging from 0.25 to 0.43 across species. The hepatic clearance of paxalisib was predicted to be low in mice, rats, dogs and humans, and high in monkeys, from hepatocytes incubations. The plasma clearance was low in mice, moderate in rats and high in dogs and monkeys. Oral bioavailability ranged from 6% in monkeys to 76% in rats.The parameters estimated from the pharmacokinetic/pharmacodynamic modelling of the efficacy in the subcutaneous U87 xenograft model combined with the human pharmacokinetics profile predicted by PBPK modelling suggested that a dose of 56 mg may be efficacious in humans. Paxalisib is currently tested in Phase III clinical trials.

Targeting DNA Repair and Survival Signaling in Diffuse Intrinsic Pontine Gliomas to Prevent Tumor Recurrence

Therapeutic resistance remains a major obstacle to successful clinical management of diffuse intrinsic pontine glioma (DIPG), a high-grade pediatric tumor of the brain stem. In nearly all patients, available therapies fail to prevent progression. Innovative combinatorial therapies that penetrate the blood-brain barrier and lead to long-term control of tumor growth are desperately needed. We identified mechanisms of resistance to radiotherapy, the standard of care for DIPG. On the basis of these findings, we rationally designed a brain-penetrant small molecule, MTX-241F, that is a highly selective inhibitor of EGFR and PI3 kinase family members, including the DNA repair protein DNA-PK. Preliminary studies demonstrated that micromolar levels of this inhibitor can be achieved in murine brain tissue and that MTX-241F exhibits promising single-agent efficacy and radiosensitizing activity in patient-derived DIPG neurospheres. Its physiochemical properties include high exposure in the brain, indicating excellent brain penetrance. Because radiotherapy results in double-strand breaks that are repaired by homologous recombination (HR) and non-homologous DNA end joining (NHEJ), we have tested the combination of MTX-241F with an inhibitor of Ataxia Telangiectasia Mutated to achieve blockade of HR and NHEJ, respectively, with or without radiotherapy. When HR blockers were combined with MTX-241F and radiotherapy, synthetic lethality was observed, providing impetus to explore this combination in clinically relevant models of DIPG. Our data provide proof-of-concept evidence to support advanced development of MTX-241F for the treatment of DIPG. Future studies will be designed to inform rapid clinical translation to ultimately impact patients diagnosed with this devastating disease.

Dual blockade of EGFR and PI3K signaling pathways offers a therapeutic strategy for glioblastoma

BACKGROUND

Glioblastoma multiforme (GBM) is a devastating disease that lacks effective drugs for targeted therapy. Previously, we found that the third-generation epidermal growth factor receptor (EGFR) inhibitor AZD-9291 persistently blocked the activation of the ERK pathway but had no inhibitory effect on the phosphoinositide 3-kinase (PI3K)/Akt pathway. Given that the PI3K inhibitor GDC-0084 is being evaluated in phase I/II clinical trials of GBM treatment, we hypothesized that combined inhibition of the EGFR/ERK and PI3K/Akt pathways may have a synergistic effect in the treatment of GBM.

METHODS

The synergistic effects of cotreatment with AZD-9291 and GDC-0084 were validated using cell viability assays in GBM and primary GBM cell lines. Moreover, the underlying inhibitory mechanisms were assessed through colony formation, EdU proliferation, and cell cycle assays, as well as RNA-seq analyses and western blot. The therapeutic effects of the drug combination on tumor growth and survival were investigated in mice bearing tumors using subcutaneously or intracranially injected LN229 xenografts.

RESULTS

Combined treatment with AZD-9291 and GDC-0084 synergistically inhibited the proliferation and clonogenic survival, as well as induced cell cycle arrest of GBM cells and primary GBM cells, compared to monotherapy. Moreover, AZD-9291 plus GDC-0084 combination therapy significantly inhibited the growth of subcutaneous tumors and orthotopic brain tumor xenografts, thus prolonging the survival of tumor-bearing mice. More importantly, the combination of AZD-9291 and GDC-0084 simultaneously blocked the activation of the EGFR/MEK/ERK and PI3K/AKT/mTOR signaling pathways, thereby exerting significant antitumor activity.

CONCLUSION

Our findings demonstrate that the combined blockade of the EGFR/MEK/ERK and PI3K/AKT/mTOR pathways is more effective against GBM than inhibition of each pathway alone, both in vitro and in vivo. Our results suggest that AZD-9291 combined with GDC-0084 may be considered as a potential treatment strategy in future clinical trials. Video Abstract.

Inhibitors of phosphoinositide 3-kinase (PI3K) and phosphoinositide 3-kinase-related protein kinase family (PIKK)

Phosphoinositide 3-kinases (PI3K) and phosphoinositide 3-kinase-related protein kinases (PIKK) are two structurally related families of kinases that play vital roles in cell growth and DNA damage repair. Dysfunction of PIKK members and aberrant stimulation of the PI3K/AKT/mTOR signalling pathway are linked to a plethora of diseases including cancer. In recent decades, numerous inhibitors related to the PI3K/AKT/mTOR signalling have made great strides in cancer treatment, like copanlisib and sirolimus. Notably, most of the PIKK inhibitors (such as VX-970 and M3814) related to DNA damage response have also shown good efficacy in clinical trials. However, these drugs still require a suitable combination therapy to overcome drug resistance or improve antitumor activity. Based on the aforementioned facts, we summarised the efficacy of PIKK, PI3K, and AKT inhibitors in the therapy of human malignancies and the resistance mechanisms of targeted therapy, in order to provide deeper insights into cancer treatment.

From signalling pathways to targeted therapies: unravelling glioblastoma's secrets and harnessing two decades of progress

Glioblastoma, a rare, and highly lethal form of brain cancer, poses significant challenges in terms of therapeutic resistance, and poor survival rates for both adult and paediatric patients alike. Despite advancements in brain cancer research driven by a technological revolution, translating our understanding of glioblastoma pathogenesis into improved clinical outcomes remains a critical unmet need. This review emphasises the intricate role of receptor tyrosine kinase signalling pathways, epigenetic mechanisms, and metabolic functions in glioblastoma tumourigenesis and therapeutic resistance. We also discuss the extensive efforts over the past two decades that have explored targeted therapies against these pathways. Emerging therapeutic approaches, such as antibody-toxin conjugates or CAR T cell therapies, offer potential by specifically targeting proteins on the glioblastoma cell surface. Combination strategies incorporating protein-targeted therapy and immune-based therapies demonstrate great promise for future clinical research. Moreover, gaining insights into the role of cell-of-origin in glioblastoma treatment response holds the potential to advance precision medicine approaches. Addressing these challenges is crucial to improving outcomes for glioblastoma patients and moving towards more effective precision therapies.

Unveiling Novel Avenues in mTOR-Targeted Therapeutics: Advancements in Glioblastoma Treatment

The mTOR signaling pathway plays a pivotal and intricate role in the pathogenesis of glioblastoma, driving tumorigenesis and proliferation. Mutations or deletions in the PTEN gene constitutively activate the mTOR pathway by expressing growth factors EGF and PDGF, which activate their respective receptor pathways (e.g., EGFR and PDGFR). The convergence of signaling pathways, such as the PI3K-AKT pathway, intensifies the effect of mTOR activity. The inhibition of mTOR has the potential to disrupt diverse oncogenic processes and improve patient outcomes. However, the complexity of the mTOR signaling, off-target effects, cytotoxicity, suboptimal pharmacokinetics, and drug resistance of the mTOR inhibitors pose ongoing challenges in effectively targeting glioblastoma. Identifying innovative treatment strategies to address these challenges is vital for advancing the field of glioblastoma therapeutics. This review discusses the potential targets of mTOR signaling and the strategies of target-specific mTOR inhibitor development, optimized drug delivery system, and the implementation of personalized treatment approaches to mitigate the complications of mTOR inhibitors. The exploration of precise mTOR-targeted therapies ultimately offers elevated therapeutic outcomes and the development of more effective strategies to combat the deadliest form of adult brain cancer and transform the landscape of glioblastoma therapy.

ABCB1 and ABCG2 Regulation at the Blood-Brain Barrier: Potential New Targets to Improve Brain Drug Delivery

The drug efflux transporters ABCB1 and ABCG2 at the blood-brain barrier limit the delivery of drugs into the brain. Strategies to overcome ABCB1/ABCG2 have been largely unsuccessful, which poses a tremendous clinical problem to successfully treat central nervous system (CNS) diseases. Understanding basic transporter biology, including intracellular regulation mechanisms that control these transporters, is critical to solving this clinical problem.In this comprehensive review, we summarize current knowledge on signaling pathways that regulate ABCB1/ABCG2 at the blood-brain barrier. In Section I, we give a historical overview on blood-brain barrier research and introduce the role that ABCB1 and ABCG2 play in this context. In Section II, we summarize the most important strategies that have been tested to overcome the ABCB1/ABCG2 efflux system at the blood-brain barrier. In Section III, the main component of this review, we provide detailed information on the signaling pathways that have been identified to control ABCB1/ABCG2 at the blood-brain barrier and their potential clinical relevance. This is followed by Section IV, where we explain the clinical implications of ABCB1/ABCG2 regulation in the context of CNS disease. Lastly, in Section V, we conclude by highlighting examples of how transporter regulation could be targeted for therapeutic purposes in the clinic. SIGNIFICANCE STATEMENT: The ABCB1/ABCG2 drug efflux system at the blood-brain barrier poses a significant problem to successful drug delivery to the brain. The article reviews signaling pathways that regulate blood-brain barrier ABCB1/ABCG2 and could potentially be targeted for therapeutic purposes.

Preclinical and clinical evaluation of Buparlisib (BKM120) in recurrent/refractory Central Nervous System Lymphoma

Central Nervous System (CNS) Lymphomas are aggressive brain tumors with limited treatment options. Targeting the phosphoinositide 3-kinase (PI3K) pathway yields promising responses across B-cell malignancies, but its therapeutic potential in CNS lymphomas remains unexplored. We present pre-clinical and clinical data on the pan-PI3K inhibitor Buparlisib in CNS lymphomas. In a primary CNS lymphoma-patient-derived cell line, we define the EC50. Four patients with recurrent CNS lymphoma were enrolled in a prospective trial. We evaluated Buparlisib plasma and cerebrospinal fluid pharmacokinetics, clinical outcomes, and adverse events. Treatment was well tolerated. Common toxicities include hyperglycemia, thrombocytopenia, and lymphopenia. The presence of Buparlisib in plasma and CSF was confirmed 2h post-treatment with a median CSF concentration below the EC50 defined in the cell line All four patients were evaluated for response and the median time to progression was 39 days. Buparlisib monotherapy did not lead to meaningful responses and the trial was prematurely stopped.Clinical Trial Registration: NCT02301364.

Enhanced Sestrin expression through Tanshinone 2A treatment improves PI3K-dependent inhibition of glioma growth

Glioblastomas are a highly aggressive cancer type which respond poorly to current pharmaceutical treatments, thus novel therapeutic approaches need to be investigated. One such approach involves the use of the bioactive natural product Tanshinone IIA (T2A) derived from the Chinese herb Danshen, where mechanistic insight for this anti-cancer agent is needed to validate its use. Here, we employ a tractable model system, Dictyostelium discoideum, to provide this insight. T2A potently inhibits cellular proliferation of Dictyostelium, suggesting molecular targets in this model. We show that T2A rapidly reduces phosphoinositide 3 kinase (PI3K) and protein kinase B (PKB) activity, but surprisingly, the downstream complex mechanistic target of rapamycin complex 1 (mTORC1) is only inhibited following chronic treatment. Investigating regulators of mTORC1, including PKB, tuberous sclerosis complex (TSC), and AMP-activated protein kinase (AMPK), suggests these enzymes were not responsible for this effect, implicating an additional molecular mechanism of T2A. We identify this mechanism as the increased expression of sestrin, a negative regulator of mTORC1. We further show that combinatory treatment using a PI3K inhibitor and T2A gives rise to a synergistic inhibition of cell proliferation. We then translate our findings to human and mouse-derived glioblastoma cell lines, where both a PI3K inhibitor (Paxalisib) and T2A reduces glioblastoma proliferation in monolayer cultures and in spheroid expansion, with combinatory treatment significantly enhancing this effect. Thus, we propose a new approach for cancer treatment, including glioblastomas, through combinatory treatment with PI3K inhibitors and T2A.

Platinum-Based Nanoformulations for Glioblastoma Treatment: The Resurgence of Platinum Drugs?

Current therapies for treating Glioblastoma (GB), and brain tumours in general, are inefficient and represent numerous challenges. In addition to surgical resection, chemotherapy and radiotherapy are presently used as standards of care. However, treated patients still face a dismal prognosis with a median survival below 15-18 months. Temozolomide (TMZ) is the main chemotherapeutic agent administered; however, intrinsic or acquired resistance to TMZ contributes to the limited efficacy of this drug. To circumvent the current drawbacks in GB treatment, a large number of classical and non-classical platinum complexes have been prepared and tested for anticancer activity, especially platinum (IV)-based prodrugs. Platinum complexes, used as alkylating agents in the anticancer chemotherapy of some malignancies, are though often associated with severe systemic toxicity (i.e., neurotoxicity), especially after long-term treatments. The objective of the current developments is to produce novel nanoformulations with improved lipophilicity and passive diffusion, promoting intracellular accumulation, while reducing toxicity and optimizing the concomitant treatment of chemo-/radiotherapy. Moreover, the blood-brain barrier (BBB) prevents the access of the drugs to the brain and accumulation in tumour cells, so it represents a key challenge for GB management. The development of novel nanomedicines with the ability to (i) encapsulate Pt-based drugs and pro-drugs, (ii) cross the BBB, and (iii) specifically target cancer cells represents a promising approach to increase the therapeutic effect of the anticancer drugs and reduce undesired side effects. In this review, a critical discussion is presented concerning different families of nanoparticles able to encapsulate platinum anticancer drugs and their application for GB treatment, emphasizing their potential for increasing the effectiveness of platinum-based drugs.

Overcoming the blood brain barrier in glioblastoma: Status and future perspective

Glioblastoma is the most common primary brain malignancy in adults. Treatment of glioblastoma patients is based on neurosurgery, radiation therapy and chemotherapy. Despite this multimodal therapeutic regimen, the prognosis of glioblastoma patients is poor. Indeed, glioblastoma is very resistant to treatments due to multiple molecular and cellular mechanisms including the existence of the blood-brain barrier (BBB). The BBB consists of multiple layers surrounding brain vessels and limits drug penetration within the brain. Therefore, overcoming the BBB is a strategy to increase bioavailability and efficacy of therapeutic agents against glioblastoma cells. The development of two approaches is ongoing: i) enhancing the delivery of drugs to the brain and ii) improving the penetration of drugs into the brain. One way to enhance drug delivery to the brain is through high-dose intravenous chemotherapy, with or without bone marrow transplantation, or via intra-arterial chemotherapy, with or without disrupting the BBB through osmotic means. Conversely, improving drug penetration within the brain can be achieved through modifying either the drug itself or the BBB. Promising results in terms of safety and signals of efficacy were obtained with these approaches in early phase clinical trials. More advanced comparative clinical trials are needed to investigate the clinical benefit for glioblastoma patients.

Validated HPLC-UV method for quantification of paxalisib, a pan PI3K and mTOR inhibitor in mouse plasma: Application to a pharmacokinetic study in mice

Paxalisib is a pan-PI3K and mTOR inhibitor, currently entering into Phase II clinical trials as a potential drug to treat glioblastoma patients. We report the development and validation of a high-performance liquid chromatography (HPLC) method for the quantitation of paxalisib in mouse plasma as per the US Food and Drug Administration regulatory guidelines. From the mouse plasma, paxalisib and the internal standard (IS; filgotinib) were extracted using ethyl acetate as an extraction solvent. The chromatographic separation of paxalisib and the IS was accomplished on a Symmetry C₁₈ (250 × 4.6 mm, 5.0 μm) column maintained at 40°C using 10 mm ammonium formate and acetonitrile in gradient conditions at a 0.8 ml/min flow-rate. The injection volume was 20 μl. The elution was monitored using a photo-diode array detector set at λ_max 280 nm. Paxalisib and the IS eluted at 6.5 and 5.9 min, respectively with a total run time of 10 min. The calibration curve was linear over the range of 111-4,989 ng/ml. Inter- and intraday precision and accuracy, stability studies, dilution integrity and incurred sample reanalysis were investigated and the results met the acceptance criteria. The validated HPLC method was extended to assess the pharmacokinetic parameters of paxalisib in mice.

Metabolic Interventions in Tumor Immunity: Focus on Dual Pathway Inhibitors

The metabolism of tumors and immune cells in the tumor microenvironment (TME) can affect the fate of cancer and immune responses. Metabolic reprogramming can occur following the activation of metabolic-related signaling pathways, such as phosphoinositide 3-kinases (PI3Ks) and the mammalian target of rapamycin (mTOR). Moreover, various tumor-derived immunosuppressive metabolites following metabolic reprogramming also affect antitumor immune responses. Evidence shows that intervention in the metabolic pathways of tumors or immune cells can be an attractive and novel treatment option for cancer. For instance, administrating inhibitors of various signaling pathways, such as phosphoinositide 3-kinases (PI3Ks), can improve T cell-mediated antitumor immune responses. However, dual pathway inhibitors can significantly suppress tumor growth more than they inhibit each pathway separately. This review discusses the latest metabolic interventions by dual pathway inhibitors as well as the advantages and disadvantages of this therapeutic approach.

From cells to organoids: The evolution of blood-brain barrier technology for modelling drug delivery in brain cancer

Brain cancer remains the deadliest cancer. The blood-brain barrier (BBB) is impenetrable to most drugs and is a complex 3D network of multiple cell types including endothelial cells, astrocytes, and pericytes. In brain cancers, the BBB becomes disrupted during tumor progression and forms the blood-brain tumor barrier (BBTB). To advance therapeutic development, there is a critical need for physiologically relevant BBB in vitro models. 3D cell systems are emerging as valuable preclinical models to accelerate discoveries for diseases. Given the versatility and capability of 3D cell models, their potential for modelling the BBB and BBTB is reviewed. Technological advances of BBB models and challenges of in vitro modelling the BBTB, and application of these models as tools for assessing therapeutics and nano drug delivery, are discussed. Quantitative, in vitro BBB models that are predictive of effective brain cancer therapies will be invaluable for accelerating advancing new treatments to the clinic.

Addressing the Reciprocal Crosstalk between the AR and the PI3K/AKT/mTOR Signaling Pathways for Prostate Cancer Treatment

The reduction in androgen synthesis and the blockade of the androgen receptor (AR) function by chemical castration and AR signaling inhibitors represent the main treatment lines for the initial stages of prostate cancer. Unfortunately, resistance mechanisms ultimately develop due to alterations in the AR pathway, such as gene amplification or mutations, and also the emergence of alternative pathways that render the tumor less or, more rarely, completely independent of androgen activation. An essential oncogenic axis activated in prostate cancer is the phosphatidylinositol-3-kinase (PI3K)/AKT/mammalian target of rapamycin (mTOR) pathway, as evidenced by the frequent alterations of the negative regulator phosphatase and tensin homolog (PTEN) and by the activating mutations in PI3K subunits. Additionally, crosstalk and reciprocal feedback loops between androgen signaling and the PI3K/AKT/mTOR signaling cascade that activate pro-survival signals and play an essential role in disease recurrence and progression have been evidenced. Inhibitors addressing different players of the PI3K/AKT/mTOR pathway have been evaluated in the clinic. Only a limited benefit has been reported in prostate cancer up to now due to the associated side effects, so novel combination approaches and biomarkers predictive of patient response are urgently needed. Here, we reviewed recent data on the crosstalk between AR signaling and the PI3K/AKT/mTOR pathway, the selective inhibitors identified, and the most advanced clinical studies, with a focus on combination treatments. A deeper understanding of the complex molecular mechanisms involved in disease progression and treatment resistance is essential to further guide therapeutic approaches with improved outcomes.

Recent advances in PI3K/PKB/mTOR inhibitors as new anticancer agents

The biochemical role of the PI3K/PKB/mTOR signalling pathway in cell-cycle regulation is now well known. During the onset and development of different forms of cancer it becomes overactive reducing apoptosis and allowing cell proliferation. Therefore, this pathway has become an important target for the treatment of various forms of malignant tumors, including breast cancer and follicular lymphoma. Recently, several more or less selective inhibitors targeting these proteins have been identified. In general, drugs that act on multiple targets within the entire pathway are more efficient than single targeting inhibitors. Multiple inhibitors exhibit high potency and limited drug resistance, resulting in promising anticancer agents. In this context, the present survey focuses on small molecule drugs capable of modulating the PI3K/PKB/mTOR signalling pathway, thus representing drugs or drug candidates to be used in the pharmacological treatment of different forms of cancer.

Combination of Ribociclib with BET-Bromodomain and PI3K/mTOR Inhibitors for Medulloblastoma Treatment In Vitro and In Vivo

Despite improvement in the treatment of medulloblastoma over the last years, numerous patients with MYC- and MYCN-driven tumors still fail current therapies. Medulloblastomas have an intact retinoblastoma protein RB, suggesting that CDK4/6 inhibition might represent a therapeutic strategy for which drug combination remains understudied. We conducted high-throughput drug combination screens in a Group3 (G3) medulloblastoma line using the CDK4/6 inhibitor (CDK4/6i) ribociclib at IC20, referred to as an anchor, and 87 oncology drugs approved by FDA or in clinical trials. Bromodomain and extra terminal (BET) and PI3K/mTOR inhibitors potentiated ribociclib inhibition of proliferation in an established cell line and freshly dissociated tumor cells from intracranial xenografts of G3 and Sonic hedgehog (SHH) medulloblastomas in vitro. A reverse combination screen using the BET inhibitor JQ1 as anchor, revealed CDK4/6i as the most potentiating drugs. In vivo, ribociclib showed single-agent activity in medulloblastoma models whereas JQ1 failed to show efficacy due to high clearance and insufficient free brain concentration. Despite in vitro synergy, combination of ribociclib with the PI3K/mTOR inhibitor paxalisib did not significantly improve the survival of G3 and SHH medulloblastoma-bearing mice compared with ribociclib alone. Molecular analysis of ribociclib and paxalisib-treated tumors revealed that E2F targets and PI3K/AKT/MTORC1 signaling genes were depleted, as expected. Importantly, in one untreated G3MB model HD-MB03, the PI3K/AKT/MTORC1 gene set was enriched in vitro compared with in vivo suggesting that the pathway displayed increased activity in vitro. Our data illustrate the difficulty in translating in vitro findings in vivo. See related article in Mol Cancer Ther (2022) 21(8):1306-1317.

Combined inhibition of topoisomerase I and poly(ADP-ribose) polymerase: A synergistic therapeutic strategy for glioblastoma with phosphatase and tensin homolog deficiency

Background

Deletions or loss-of-function mutations in phosphatase and tensin homolog (PTEN) are common in glioblastoma (GBM) and have been associated with defective DNA damage repair. Here we investigated whether PTEN deficiency presents a vulnerability to a simultaneous induction of DNA damage and suppression of repair mechanisms by combining topoisomerase I (TOP1) and PARP inhibitors.

Methods

Patient-derived GBM cells and isogenic PTEN-null and PTEN-WT glioma cells were treated with LMP400 (Indotecan), a novel non-camptothecin TOP1 inhibitor alone and in combination with a PARP inhibitor, Olaparib or Niraparib. RNAseq analysis was performed to identify treatment-induced dysregulated pathways.

Results

We found that GBM cells lacking PTEN expression are highly sensitive to LMP400; however, rescue of the PTEN expression reduces sensitivity to the treatment. Combining LMP400 with Niraparib leads to synergistic cytotoxicity by inducing G2/M arrest, DNA damage, suppression of homologous recombination-related proteins, and activation of caspase 3/7 activity significantly more in PTEN-null cells compared to PTEN-WT cells. LMP400 and Niraparib are not affected by ABCB1 and ABCG2, the major ATP-Binding Cassette (ABC) drug efflux transporters expressed at the blood-brain barrier (BBB), thus suggesting BBB penetration which is a prerequisite for potential brain tumor treatment. Animal studies confirmed both an anti-glioma effect and sufficient BBB penetration to prolong survival of mice treated with the drug combination.

Conclusions

Our findings provide a proof of concept for the combined treatment with LMP400 and Niraparib in a subset of GBM patients with PTEN deficiency.

Recent Advances in Dual PI3K/mTOR Inhibitors for Tumour Treatment

The PI3K-Akt-mTOR pathway is a viable target for cancer treatment and can be used to treat various malignant tumours, including follicular lymphoma and breast cancer. Both enzymes, PI3K and mTOR, are critical in this pathway. Hence, in recent years, an array of inhibitors targeting these two targets have been studied, showing dual PI3K/mTOR inhibition compared with single targeting small molecule inhibitors. Inhibitors not only inhibit cell proliferation but also promote cell apoptosis. These inhibitors show high potency and little drug resistance even at low doses, suggesting that PI3K/mTOR inhibitors are promising cancer drugs. Herein, we summarised the recent research of PI3K/mTOR dual inhibitors—for example, structure-activity relationship, pharmacokinetics, and clinical practice, and briefly commented on them.

Clinical Trial Registration:https://clinicaltrials.gov.

Identification of NVP-CLR457 as an Orally Bioavailable Non-CNS-Penetrant pan-Class IA Phosphoinositol-3-Kinase Inhibitor

Balanced pan-class I phosphoinositide 3-kinase inhibition as an approach to cancer treatment offers the prospect of treating a broad range of tumor types and/or a way to achieve greater efficacy with a single inhibitor. Taking buparlisib as the starting point, the balanced pan-class I PI3K inhibitor 40 (NVP-CLR457) was identified with what was considered to be a best-in-class profile. Key to the optimization to achieve this profile was eliminating a microtubule stabilizing off-target activity, balancing the pan-class I PI3K inhibition profile, minimizing CNS penetration, and developing an amorphous solid dispersion formulation. A rationale for the poor tolerability profile of 40 in a clinical study is discussed.

Structural effects of morpholine replacement in ZSTK474 on Class I PI3K isoform inhibition: Development of novel MEK/PI3K bifunctional inhibitors

Established roles for PI3K and MAPK signaling pathways in tumorigenesis has prompted extensive research towards the discovery of small-molecule inhibitors as cancer therapeutics. However, significant compensatory regulation exists between these two signaling cascades, leading to redundancy among survival pathways. Consequently, initial clinical trials aimed at either PI3K or MEK inhibition alone have proven ineffective and highlight the need for development of targeted and innovative therapeutic combination strategies. We designed a series of PI3K inhibitor derivatives wherein a single morpholine group of the PI3K inhibitor ZSTK474 was substituted with a variety of 2-aminoethyl functional groups. Analogs with pendant hydroxyl or methoxy groups maintained low nanomolar inhibition towards PI3Kα, PI3Kγ, and PI3Kδ isoforms in contrast to those with pendant amino groups which were significantly less inhibitory. Synthesis of prototype PI3K/MEK bifunctional inhibitors (6r, 6s) was guided by the structure-activity data, where a MEK-targeting inhibitor was tethered directly via a short PEG linker to the triazine core of the PI3K inhibitor analogs. These compounds (6r, 6s) displayed nanomolar inhibition towards PI3Kα, δ, and MEK (IC₅₀ ∼105-350 nM), and low micromolar inhibition for PI3Kβ and PI3Kγ (IC₅₀ ∼1.5-3.9 μM) in enzymatic inhibition assays. Cell viability assays demonstrated superior anti-proliferative activity for 6s over 6r in three tumor-derived cell lines (A375, D54, SET-2), which correlated with inhibition of downstream AKT and ERK1/2 phosphorylation. Compounds 6r and 6s also demonstrated in vivo tolerability with therapeutic efficacy through reduction of kinase activation and amelioration of disease phenotypes in the JAK2V617F mutant myelofibrosis mouse cancer model. Taken together, these results support further structure optimization of 6r and 6s as promising leads for combination therapy in human cancer as a new class of PI3K/MEK bifunctional inhibitors.

Inhibiting CK2 among Promising Therapeutic Strategies for Gliomas and Several Other Neoplasms

In gliomas, casein kinase 2 (CK2) plays a dominant role in cell survival and tumour invasiveness and is upregulated in many brain tumours. Among CK2 inhibitors, benzimidazole and isothiourea derivatives hold a dominant position. While targeting glioma tumour cells, they show limited toxicity towards normal cells. Research in recent years has shown that these compounds can be suitable as components of combined therapies with hyperbaric oxygenation. Such a combination increases the susceptibility of glioma tumour cells to cell death via apoptosis. Moreover, researchers planning on using any other antiglioma investigational pharmaceutics may want to consider using these agents in combination with CK2 inhibitors. However, different compounds are not equally effective when in such combination. More research is needed to elucidate the mechanism of treatment and optimize the treatment regimen. In addition, the role of CK2 in gliomagenesis and maintenance seems to have been challenged recently, as some compounds structurally similar to CK2 inhibitors do not inhibit CK2 while still being effective at reducing glioma viability and invasion. Furthermore, some newly developed inhibitors specific for CK2 do not appear to have strong anticancer properties. Further experimental and clinical studies of these inhibitors and combined therapies are warranted.

Wnt and PI3K/Akt/mTOR Survival Pathways as Therapeutic Targets in Glioblastoma

Glioblastoma (GBM) is a devastating type of brain tumor, and current therapeutic treatments, including surgery, chemotherapy, and radiation, are palliative at best. The design of effective and targeted chemotherapeutic strategies for the treatment of GBM require a thorough analysis of specific signaling pathways to identify those serving as drivers of GBM progression and invasion. The Wnt/β-catenin and PI3K/Akt/mTOR (PAM) signaling pathways are key regulators of important biological functions that include cell proliferation, epithelial–mesenchymal transition (EMT), metabolism, and angiogenesis. Targeting specific regulatory components of the Wnt/β-catenin and PAM pathways has the potential to disrupt critical brain tumor cell functions to achieve critical advancements in alternative GBM treatment strategies to enhance the survival rate of GBM patients. In this review, we emphasize the importance of the Wnt/β-catenin and PAM pathways for GBM invasion into brain tissue and explore their potential as therapeutic targets.

Synthesis of Novel (S)-3-(1-Aminoethyl)-8-pyrimidinyl-2-phenylisoquinolin-1(2H)-ones by Suzuki-Miyaura Coupling and Their Cell Toxicity Activities

A series of (S)-3-(1-aminoethyl)-8-pyrimidinyl-2-phenylisoquinoline-1(2H)-ones 3a-3k was synthesized in 40-98% yield through Suzuki-Miyaura coupling using Pd(PPh₃)₂Cl₂, Sphos, and K₂CO₃ in THF/H₂O mixed solvent. All newly synthesized compounds were evaluated for cell viability (IC₅₀) against MDA-MB-231, HeLa, and HepG2 cells. The antitumor activities of 3a-3k were improved when various pyrimidine motifs were introduced at position C-8 of the isoquinolinone ring.

Ponatinib, Lestaurtinib and mTOR/PI3K inhibitors are promising repurposing candidates against Entamoeba histolytica

Dysentery caused by Entamoeba histolytica affects millions of people annually. Current treatment regimens are based on metronidazole to treat invasive parasites combined with paromomycin for luminal parasites. Issues with treatment include significant side effects, inability to easily treat breastfeeding and pregnant women, the use of two sequential agents, and concern that all therapy is based on nitroimidazole agents with no alternatives if clinical resistance emerges. Thus, the need for new drugs against amebiasis is urgent. To identify new therapeutic candidates, we screened the ReFRAME library (11,948 compounds assembled for Repurposing, Focused Rescue, and Accelerated Medchem) against E. histolytica trophozoites. We identified 159 hits in the primary screen at 10 μM and 46 compounds were confirmed in secondary assays. Overall, 26 were selected as priority molecules for further investigation including 6 FDA approved, 5 orphan designation, and 15 which are currently in clinical trials (3 phase III, 7 phase II and 5 phase I). We found that all 26 compounds are active against metronidazole resistant E. histolytica and 24 are able to block parasite recrudescence after drug removal. Additionally, 14 are able to inhibit encystation and 2 (lestaurtinib and LY-2874455) are active against mature cysts. Two classes of compounds are most interesting for further investigations: the Bcr-Abl TK inhibitors, with the ponatinib (EC₅₀ 0.39) as most potent and mTOR or PI3K inhibitors with 8 compounds in clinical development, of which 4 have nanomolar potency. Overall, these are promising candidates and represent a significant advance for drug development against E. histolytica.

Development of PI3K inhibitors: Advances in clinical trials and new strategies (Review)

Phosphatidylinositol 3-kinases (PI3Ks) are the family of vital lipid kinases widely distributed in mammalian cells. The overexpression of PI3Ks leads to hyperactivation of the PI3K/AKT/mTOR pathway, which is considered a pivotal pathway in the occurrence and development of tumors. Hence, PI3Ks are viewed as promising therapeutic targets for anti-cancer therapy. To date, some PI3K inhibitors have achieved desired therapeutic effect via inhibiting the activity of PI3Ks or reducing the level of PI3Ks in clinical trials, among which, Idelalisib, Alpelisib and Duvelisib have been approved by the FDA for treatment of ER⁺/HER2^- advanced metastatic breast cancer and refractory chronic lymphocytic leukemia (CLL) and small lymphocytic lymphomas (SLL). This review focuses on the latest advances of PI3K inhibitors with efficacious anticancer activity, which are classified into Pan-PI3K inhibitors, isoform-specific PI3K inhibitors and dual PI3K/mTOR inhibitors based on the isoform affinity. Their corresponding structure characteristics and structures-activity relationship (SAR), together with the progress in the clinical application are mainly discussed. Additionally, the new PI3K inhibitory strategy, such as PI3K degradation agent, for the design of potential PI3K candidates to overcome drug resistance is referred as well.

Chemical and Structural Strategies to Selectively Target mTOR Kinase

Dysregulation of the mechanistic target of rapamycin (mTOR) pathway is implicated in cancer and neurological disorder, which identifies mTOR inhibition as promising strategy for the treatment of a variety of human disorders. First-generation mTOR inhibitors include rapamycin and its analogues (rapalogs) which act as allosteric inhibitors of TORC1. Structurally unrelated, ATP-competitive inhibitors that directly target the mTOR catalytic site inhibit both TORC1 and TORC2. Here, we review investigations of chemical scaffolds explored for the development of highly selective ATP-competitive mTOR kinase inhibitors (TORKi). Extensive medicinal chemistry campaigns allowed to overcome challenges related to structural similarity between mTOR and the phosphoinositide 3-kinase (PI3K) family. A broad region of chemical space is covered by TORKi. Here, the investigation of chemical substitutions and physicochemical properties has shed light on the compounds' ability to cross the blood brain barrier (BBB). This work provides insights supporting the optimization of TORKi for the treatment of cancer and central nervous system disorders.

Discovery of cinnoline derivatives as potent PI3K inhibitors with antiproliferative activity

Cinnoline is a potential pharmacophore which has rarely been reported for uses as PI3K inhibitors. In this study, a series of cinnoline derivatives were developed as PI3K inhibitors and evaluated for enzymatic and cellular activities. Most compounds displayed nanomolar inhibitory activities against PI3Ks, among which 25 displayed high LLE and micromolar inhibitory potency against three human tumor cell lines (IC₅₀ = 0.264 μM, 2.04 μM, 1.14 μM).

Regulation of mRNA Translation by Hormone Receptors in Breast and Prostate Cancer

Simple Summary

The estrogen and androgen receptors (ER, AR) are key oncogenic drivers and therapeutic targets in breast and prostate cancer, respectively. These receptors bind to DNA and regulate gene expression but emerging evidence indicates that they also play important roles in controlling the process of mRNA translation, which dictates cellular protein production. Here, we review the mechanisms by which abnormal activities of ER and AR can dysregulate mRNA translation in breast and prostate cancer cells. Specifically, we explore how the intricate cellular signalling pathways that keep mRNA translation in check are perturbed by aberrant ER and AR signalling, which can lead to enhanced cancer cell growth. We also discuss the potential of targeting mRNA translation as a strategy to treat patients with breast and prostate cancer.

Abstract

Breast and prostate cancer are the second and third leading causes of death amongst all cancer types, respectively. Pathogenesis of these malignancies is characterised by dysregulation of sex hormone signalling pathways, mediated by the estrogen receptor-α (ER) in breast cancer and androgen receptor (AR) in prostate cancer. ER and AR are transcription factors whose aberrant function drives oncogenic transcriptional programs to promote cancer growth and progression. While ER/AR are known to stimulate cell growth and survival by modulating gene transcription, emerging findings indicate that their effects in neoplasia are also mediated by dysregulation of protein synthesis (i.e., mRNA translation). This suggests that ER/AR can coordinately perturb both transcriptional and translational programs, resulting in the establishment of proteomes that promote malignancy. In this review, we will discuss relatively understudied aspects of ER and AR activity in regulating protein synthesis as well as the potential of targeting mRNA translation in breast and prostate cancer.

Targeting RTK-PI3K-mTOR Axis in Gliomas: An Update

Gliomas are the most common and challenging malignancies of the central nervous system (CNS), due to their infiltrative nature, tendency to recurrence, and poor response to treatments. Indeed, despite the advances in neurosurgical techniques and in radiation therapy, the modest effects of therapy are still challenging. Moreover, tumor recurrence is associated with the onset of therapy resistance; it is therefore critical to identify effective and well-tolerated pharmacological approaches capable of inducing durable responses in the appropriate patient groups. Molecular alterations of the RTK/PI3K/Akt/mTOR signaling pathway are typical hallmarks of glioma, and several clinical trials targeting one or more players of this axis have been launched, showing disappointing results so far, due to the scarce BBB permeability of certain compounds or to the occurrence of resistance/tolerance mechanisms. However, as RTK/PI3K/mTOR is one of the pivotal pathways regulating cell growth and survival in cancer biology, targeting still remains a strong rationale for developing strategies against gliomas. Future rigorous clinical studies, aimed at addressing the tumor heterogeneity, the interaction with the microenvironment, as well as diverse posology adjustments, are needed-which might unravel the therapeutic efficacy and response prediction of an RTK/PI3K/mTOR-based approach.

Therapeutic strategies of different HPV status in Head and Neck Squamous Cell Carcinoma

Head and neck squamous cell carcinoma (HNSCC) is the 9^th most common malignant tumor in the world. Based on the etiology, HNSCC has two main subtypes: human papillomavirus (HPV) -related and HPV-unrelated. HPV-positive HNSCC is more sensitive to treatment with favorable survival. Due to the different biological behaviors, individual therapy is necessary and urgently required to deduce the therapeutic intensity of HPV-positive disease and look for a more effective and toxicity-acceptable regimen for HPV-negative disease. EGFR amplification and PI3K/AKT/mTOR pathway aberrant activation are quite common in HPV-positive HNSCC. Besides, HPV infection alters immune cell infiltrating in HNSCC and encompasses a diverse and heterogeneous landscape with more immune infiltration. On the other hand, the chance of HPV-negative cancers harboring mutation on the P53 gene is significantly higher than that of HPV-positive disease. This review focuses on the updated preclinical and clinical data of HPV-positive and HPV-negative HNSCC and discusses the therapeutic strategies of different HPV status in HNSCC.

Transcriptomic Analysis of Diffuse Intrinsic Pontine Glioma (DIPG) Identifies a Targetable ALDH-Positive Subset of Highly Tumorigenic Cancer Stem-like Cells

Understanding the cancer stem cell (CSC) landscape in diffuse intrinsic pontine glioma (DIPG) is desperately needed to address treatment resistance and identify novel therapeutic approaches. Patient-derived DIPG cells demonstrated heterogeneous expression of aldehyde dehydrogenase (ALDH) and CD133 by flow cytometry. Transcriptome-level characterization identified elevated mRNA levels of MYC, E2F, DNA damage repair (DDR) genes, glycolytic metabolism, and mTOR signaling in ALDH⁺ compared with ALDH^-, supporting a stem-like phenotype and indicating a druggable target. ALDH⁺ cells demonstrated increased proliferation, neurosphere formation, and initiated tumors that resulted in decreased survival when orthotopically implanted. Pharmacologic MAPK/PI3K/mTOR targeting downregulated MYC, E2F, and DDR mRNAs and reduced glycolytic metabolism. In vivo PI3K/mTOR targeting inhibited tumor growth in both flank and an ALDH⁺ orthotopic tumor model likely by reducing cancer stemness. In summary, we describe existence of ALDH⁺ DIPGs with proliferative properties due to increased metabolism, which may be regulated by the microenvironment and likely contributing to drug resistance and tumor recurrence. IMPLICATIONS: Characterization of ALDH⁺ DIPGs coupled with targeting MAPK/PI3K/mTOR signaling provides an impetus for molecularly targeted therapy aimed at addressing the CSC phenotype in DIPG.

Research progress of mTOR inhibitors

Mammalian target of rapamycin (mTOR) is a highly conserved Serine/Threonine (Ser/Thr) protein kinase, which belongs to phosphatidylinositol-3-kinase-related kinase (PIKK) protein family. mTOR exists as two types of protein complex: mTORC1 and mTORC2, which act as central controller regulating processes of cell metabolism, growth, proliferation, survival and autophagy. The mTOR inhibitors block mTOR signaling pathway, producing anti-inflammatory, anti-proliferative, autophagy and apoptosis induction effects, thus mTOR inhibitors are mainly used in cancer therapy. At present, mTOR inhibitors are divided into four categories: Antibiotic allosteric mTOR inhibitors (first generation), ATP-competitive mTOR inhibitors (second generation), mTOR/PI3K dual inhibitors (second generation) and other new mTOR inhibitors (third generation). In this article, these four categories of mTOR inhibitors and their structures, properties and some clinical researches will be introduced. Among them, we focus on the structure of mTOR inhibitors and try to analyze the structure-activity relationship. mTOR inhibitors are classified according to their chemical structure and their contents are introduced systematically. Moreover, some natural products that have direct or indirect mTOR inhibitory activities are introduced together. In this article, we analyzed the target, binding mode and structure-activity relationship of each generation of mTOR inhibitors and proposed two hypothetic scaffolds (the inverted-Y-shape scaffold and the C-shape scaffold) for the second generation of mTOR inhibitors. These findings may provide some help or reference for drug designing, drug modification or the future development of mTOR inhibitor.

Multiparametric MR-PET Imaging Predicts Pharmacokinetics and Clinical Response to GDC-0084 in Patients with Recurrent High-Grade Glioma

PURPOSE

GDC-0084 is an oral, brain-penetrant small-molecule inhibitor of PI3K and mTOR. Because these two targets alter tumor vascularity and metabolism, respectively, we hypothesized multiparametric MR-PET could be used to quantify the response, estimate pharmacokinetic (PK) parameters, and predict progression-free survival (PFS) in patients with recurrent malignant gliomas.

PATIENTS AND METHODS

Multiparametric advanced MR-PET imaging was performed to evaluate physiologic response in a first-in-man, multicenter, phase I, dose-escalation study of GDC-0084 (NCT01547546) in 47 patients with recurrent malignant glioma.

RESULTS

Measured maximum concentration (C _max) was associated with a decrease in enhancing tumor volume (P = 0.0287) and an increase in fractional anisotropy (FA; P = 0.0418). Posttreatment tumor volume, ¹⁸F-FDG uptake, K^trans, and relative cerebral blood volume (rCBV) were all correlated with C _max. A linear combination of change in ¹⁸F-FDG PET uptake, apparent diffusion coefficient (ADC), FA, K^trans, v_p, and rCBV was able to estimate both C _max (R² = 0.4113; P < 0.0001) and drug exposure (AUC; R² = 0.3481; P < 0.0001). Using this composite multiparametric MR-PET imaging response biomarker to predict PK, patients with an estimated C _max > 0.1 μmol/L and AUC > 1.25 μmol/L*hour demonstrated significantly longer PFS compared with patients with a lower estimated concentration and exposure (P = 0.0039 and P = 0.0296, respectively).

CONCLUSIONS

Results from this study suggest composite biomarkers created from multiparametric MR-PET imaging targeting metabolic and/or physiologic processes specific to the drug mechanism of action may be useful for subsequent evaluation of treatment efficacy for larger phase II-III studies.

Is There a Role for Dual PI3K/mTOR Inhibitors for Patients Affected with Lymphoma?

The activation of the PI3K/AKT/mTOR pathway is a main driver of cell growth, proliferation, survival, and chemoresistance of cancer cells, and, for this reason, represents an attractive target for developing targeted anti-cancer drugs. There are plenty of preclinical data sustaining the anti-tumor activity of dual PI3K/mTOR inhibitors as single agents and in combination in lymphomas. Clinical responses, including complete remissions (especially in follicular lymphoma patients), are also observed in the very few clinical studies performed in patients that are affected by relapsed/refractory lymphomas or chronic lymphocytic leukemia. In this review, we summarize the literature on dual PI3K/mTOR inhibitors focusing on the lymphoma setting, presenting both the three compounds still in clinical development and those with a clinical program stopped or put on hold.

Role of P-glycoprotein in the brain disposition of seletalisib: Evaluation of the potential for drug-drug interactions

Seletalisib is an orally bioavailable selective inhibitor of phosphoinositide 3-kinase delta (PI3Kδ) in clinical development for the treatment of immune-mediated inflammatory diseases. The present study investigated the role of P-gp in seletalisib disposition, especially brain distribution, and the associated risks of interactions. Seletalisib was found to be actively transported by rodent and human P-gp in vitro (transfected LLC-PK1 cells; K_m of ca. 20 µM), with minimal or no affinity for the other tested transporters. A distribution study in knockout rats (single oral dosing at 750 mg kg^-1) showed that P-gp restricts the brain disposition of seletalisib while having minimal effect on its intestinal absorption. Restricted brain penetration was also observed in cynomolgus monkeys (single oral dosing at 30 mg kg^-1) using brain microdialysis and cerebrospinal fluid sampling (K_p,uu of 0.09 and 0.24, respectively). These findings opened the question of potential pharmacokinetic interaction between seletalisib and P-gp inhibitors. In vitro, CsA inhibited the active transport of seletalisib with an IC₅₀ of 0.13 µM. In rats, co-administration of high doses of CsA (bolus iv followed by continuous infusion) increased the brain distribution of seletalisib (single oral dosing at 5 mg kg^-1). The observed data were found aligned with those predicted by in vitro-in vivo extrapolation. Based on the same extrapolation method combined with literature data, only very few P-gp inhibitors (i.e. CsA, quinine, quinidine) were predicted to increase the brain disposition of seletalisib in the clinical setting (maximal 3-fold changes).

First-in-Human Phase I Study to Evaluate the Brain-Penetrant PI3K/mTOR Inhibitor GDC-0084 in Patients with Progressive or Recurrent High-Grade Glioma

PURPOSE

GDC-0084 is an oral, brain-penetrant small-molecule inhibitor of PI3K and mTOR. A first-in-human, phase I study was conducted in patients with recurrent high-grade glioma.

PATIENTS AND METHODS

GDC-0084 was administered orally, once daily, to evaluate safety, pharmacokinetics (PK), and activity. Fluorodeoxyglucose-PET (FDG-PET) was performed to measure metabolic responses.

RESULTS

Forty-seven heavily pretreated patients enrolled in eight cohorts (2-65 mg). Dose-limiting toxicities included 1 case of grade 2 bradycardia and grade 3 myocardial ischemia (15 mg), grade 3 stomatitis (45 mg), and 2 cases of grade 3 mucosal inflammation (65 mg); the MTD was 45 mg/day. GDC-0084 demonstrated linear and dose-proportional PK, with a half-life (∼19 hours) supportive of once-daily dosing. At 45 mg/day, steady-state concentrations exceeded preclinical target concentrations producing antitumor activity in xenograft models. FDG-PET in 7 of 27 patients (26%) showed metabolic partial response. At doses ≥45 mg/day, a trend toward decreased median standardized uptake value in normal brain was observed, suggesting central nervous system penetration of drug. In two resection specimens, GDC-0084 was detected at similar levels in tumor and brain tissue, with a brain tissue/tumor-to-plasma ratio of >1 and >0.5 for total and free drug, respectively. Best overall response was stable disease in 19 patients (40%) and progressive disease in 26 patients (55%); 2 patients (4%) were nonevaluable.

CONCLUSIONS

GDC-0084 demonstrated classic PI3K/mTOR-inhibitor related toxicities. FDG-PET and concentration data from brain tumor tissue suggest that GDC-0084 crossed the blood-brain barrier.

Identification of plicamycin, TG02, panobinostat, lestaurtinib, and GDC-0084 as promising compounds for the treatment of central nervous system infections caused by the free-living amebae Naegleria, Acanthamoeba and Balamuthia

The free-living amebae Naegleria, Acanthamoeba, and Balamuthia cause rare but life-threatening infections. All three parasites can cause meningoencephalitis. Acanthamoeba can also cause chronic keratitis and both Balamuthia and Acanthamoeba can cause skin and systemic infections. There are minimal drug development pipelines for these pathogens despite a lack of available treatment regimens and high fatality rates. To identify anti-amebic drugs, we screened 159 compounds from a high-value repurposed library against trophozoites of the three amebae. Our efforts identified 38 compounds with activity against at least one ameba. Multiple drugs that bind the ATP-binding pocket of mTOR and PI3K are active, highlighting these compounds as important inhibitors of these parasites. Importantly, 24 active compounds have progressed at least to phase II clinical studies and overall 15 compounds were active against all three amebae. Based on central nervous system (CNS) penetration or exceptional potency against one amebic species, we identified sixteen priority compounds for the treatment of meningoencephalitis caused by these pathogens. The top five compounds are (i) plicamycin, active against all three free-living amebae and previously U.S. Food and Drug Administration (FDA) approved, (ii) TG02, active against all three amebae, (iii and iv) FDA-approved panobinostat and FDA orphan drug lestaurtinib, both highly potent against Naegleria, and (v) GDC-0084, a CNS penetrant mTOR inhibitor, active against at least two of the three amebae. These results set the stage for further investigation of these clinically advanced compounds for treatment of infections caused by the free-living amebae, including treatment of the highly fatal meningoencephalitis.

An LC/ESI-MS/MS method to quantify the PI3K inhibitor GDC-0084 in human plasma and cerebrospinal fluid: Validation and clinical application

A liquid chromatography electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS) method was developed and validated to measure GDC-0084 in human plasma and cerebrospinal fluid (CSF). Reverse-phase chromatography with gradient elution was performed using a C₁₈ column (50 × 2.0 mm, 3 μm). Solid-phase extraction of plasma and CSF was employed to give excellent recovery. MS detection was performed with positive ion screening in multiple reaction monitoring mode. The precursor to the product ions (Q1 → Q3) selected for GDC-0084 and GDC-0084-d₆ were 383.2 → 353.2 and 389.2 → 353.2, respectively. A separate calibration curve was established for human plasma and CSF. Both calibration curves, ranging from 0.2 to 200 ng/mL, were linear and had acceptable intra- and inter-day precision and accuracy. The lower limit of quantitation and limit of detection for GDC-0084 in human plasma were 0.2 ng/mL (signal/noise ≥47) and 0.005 ng/mL (signal/noise ≥3.5), respectively, and for GDC-0084 in human CSF were 0.2 ng/mL (signal/noise ≥19.7) and 0.04 ng/mL (signal/noise ≥7.2). This method was successfully applied to analyze serial plasma samples obtained from children with diffuse intrinsic pontine gliomas and other midline gliomas who participated in pharmacokinetic studies as part of a phase I clinical trial of GDC-0084.

Practical approaches to evaluating and optimizing brain exposure in early drug discovery

Developing drugs for CNS related diseases continues to be one of the most challenging endeavors in drug discovery. This is at least in part related to the existence of the Blood Brain Barrier (BBB), a complex multicellular organization that provides selective access to required nutrients and hormones, while removing waste and restricting exposure to potential harmful toxins, pathogens, and xenobiotics. Consequently, designing and selecting molecules that can overcame this protection system are unique and critical aspects of the CNS drug discovery. Here we review modern CNS pharmacokinetic concepts and methods suitable for early drug discovery, and medicinal chemistry strategies towards molecules with optimal CNS exposure.

The Dual PI3K/mTOR Pathway Inhibitor GDC-0084 Achieves Antitumor Activity in PIK3CA-Mutant Breast Cancer Brain Metastases

PURPOSE

Previous studies have shown that the PI3K/Akt/mTOR pathway is activated in up to 70% of breast cancer brain metastases, but there are no approved agents for affected patients. GDC-0084 is a brain penetrant, dual PI3K/mTOR inhibitor that has shown promising activity in a preclinical model of glioblastoma. The aim of this study was to analyze the efficacy of PI3K/mTOR blockade in breast cancer brain metastases models.Experimental Design: The efficacy of GDC-0084 was evaluated in PIK3CA-mutant and PIK3CA wild-type breast cancer cell lines and the isogenic pairs of PIK3CA wild-type and mutant (H1047R/+) MCF10A cells in vitro. In vitro studies included cell viability and apoptosis assays, cell-cycle analysis, and Western blots. In vivo, the effect of GDC-0084 was investigated in breast cancer brain metastasis xenograft mouse models and assessed by bioluminescent imaging and IHC.

RESULTS

In vitro, GDC-0084 considerably decreased cell viability, induced apoptosis, and inhibited phosphorylation of Akt and p70 S6 kinase in a dose-dependent manner in PIK3CA-mutant breast cancer brain metastatic cell lines. In contrast, GDC-0084 led only to growth inhibition in PIK3CA wild-type cell lines in vitro. In vivo, treatment with GDC-0084 markedly inhibited the growth of PIK3CA-mutant, with accompanying signaling changes, and not PIK3CA wild-type brain tumors.

CONCLUSIONS

The results of this study suggest that the brain-penetrant PI3K/mTOR targeting GDC-0084 is a promising treatment option for breast cancer brain metastases with dysregulated PI3K/mTOR signaling pathway conferred by activating PIK3CA mutations. A national clinical trial is planned to further investigate the role of this compound in patients with brain metastases.

The TICking clock of EGFR therapy resistance in glioblastoma: Target Independence or target Compensation

Targeted therapy against driver mutations responsible for cancer progression has been shown to be effective in many tumor types. For glioblastoma (GBM), the epidermal growth factor receptor (EGFR) gene is the most frequently mutated oncogenic driver and has therefore been considered an attractive target for therapy. However, so far responses to EGFR-pathway inhibitors have been disappointing. We performed an exhaustive analysis of the mechanisms that might account for therapy resistance against EGFR inhibition. We define two major mechanisms of resistance and propose modalities to overcome them. The first resistance mechanism concerns target independence. In this case, cells have lost expression of the EGFR protein and experience no negative impact of EGFR targeting. Loss of extrachromosomally encoded EGFR as present in double minute DNA is a frequent mechanism for this type of drug resistance. The second mechanism concerns target compensation. In this case, cells will counteract EGFR inhibition by activation of compensatory pathways that render them independent of EGFR signaling. Compensatory pathway candidates are platelet-derived growth factor β (PDGFβ), Insulin-like growth factor 1 (IGFR1) and cMET and their downstream targets, all not commonly mutated at the time of diagnosis alongside EGFR mutation. Given that both mechanisms make cells independent of EGFR expression, other means have to be found to eradicate drug resistant cells. To this end we suggest rational strategies which include the use of multi-target therapies that hit truncation mutations (mechanism 1) or multi-target therapies to co-inhibit compensatory proteins (mechanism 2).

Challenges of developing small-molecule kinase inhibitors for brain tumors and the need for emphasis on free drug levels

Despite biological rationale and significant clinical study, the pursuit of small-molecule kinase inhibitors for the treatment of brain cancers has had very limited success. This Advance-in-Brief discusses the need for drugs to achieve free brain penetration to engage their targets where CNS tumors reside. This need to achieve free, as opposed to total, drug concentrations in the brain may be a contributing factor to why so many small-molecule kinase inhibitors have not realized success in the neuro-oncology setting. For kinase targets of interest for brain cancer, either the vast majority of small-molecule inhibitors have data suggesting that free brain penetration would be limited or there are inadequate data to suggest that free brain penetration could be expected. Therefore, kinase targets of interest in the treatment of brain cancers may be inadequately assessed due to a lack of freely brain-penetrant inhibitors available for clinical study. Encouraging recent drug discovery efforts that focused on achieving free brain penetration for cancers in the CNS are highlighted. Still, further efforts are needed to enable thorough clinical evaluation of biological hypotheses.