Phase I and pharmacokinetic trial of PTC299 in pediatric patients with refractory or recurrent central nervous system tumors: a PBTC study

From bench to bedside: Advancing towards therapeutic treatment of vestibular schwannomas

Vestibular schwannomas are rare intracranial tumors originating from Schwann cells of the vestibular nerve. Despite their benign nature, these tumors can exert significant mass effects and debilitating symptoms, including gradual hearing loss, vertigo, facial nerve dysfunction, and headaches. Current clinical management options encompass wait-and-scan, surgery, radiation therapy, and off-label medication. However, each approach exhibits its own challenges and harbors limitations that underscore the urgent need for therapeutic treatments. Over the past 2 decades, extensive elucidation of the molecular underpinnings of vestibular schwannomas has unraveled genetic anomalies, dysregulated signaling pathways, downstream of receptor tyrosine kinases, disrupted extracellular matrix, inflammatory tumor microenvironment, and altered cerebrospinal fluid composition as integral factors in driving the development and progression of the disease. Armed with this knowledge, novel therapeutic interventions tailored to the unique molecular characteristics of those conditions are actively being pursued. This review underscores the urgency of addressing the dearth of Food and Drug Administration-approved drugs for vestibular schwannoma, highlighting the key molecular discoveries and their potential translation into therapeutics. It provides an in-depth exploration of the evolving landscape of therapeutic development, which is currently advancing from bench to bedside. These ongoing efforts hold the promise of significantly transforming the lives of vestibular schwannoma patients in the future.

The Present and Future of Optic Pathway Glioma Therapy

Optic pathway gliomas (OPGs) encompass two distinct categories: benign pediatric gliomas, which are characterized by favorable prognosis, and malignant adult gliomas, which are aggressive cancers associated with a poor outcome. Our review aims to explore the established standards of care for both types of tumors, highlight the emerging therapeutic strategies for OPG treatment, and propose potential alternative therapies that, while originally studied in a broader glioma context, may hold promise for OPGs pending further investigation. These potential therapies encompass immunotherapy approaches, molecular-targeted therapy, modulation of the tumor microenvironment, nanotechnologies, magnetic hyperthermia therapy, cyberKnife, cannabinoids, and the ketogenic diet. Restoring visual function is a significant challenge in cases where optic nerve damage has occurred due to the tumor or its therapeutic interventions. Numerous approaches, particularly those involving stem cells, are currently being investigated as potential facilitators of visual recovery in these patients.

The Neurodevelopmental and Molecular Landscape of Medulloblastoma Subgroups: Current Targets and the Potential for Combined Therapies

Medulloblastoma is the most common malignant pediatric brain tumor and is associated with significant morbidity and mortality in the pediatric population. Despite the use of multiple therapeutic approaches consisting of surgical resection, craniospinal irradiation, and multiagent chemotherapy, the prognosis of many patients with medulloblastoma remains dismal. Additionally, the high doses of radiation and the chemotherapeutic agents used are associated with significant short- and long-term complications and adverse effects, most notably neurocognitive delay. Hence, there is an urgent need for the development and clinical integration of targeted treatment regimens with greater efficacy and superior safety profiles. Since the adoption of the molecular-based classification of medulloblastoma into wingless (WNT) activated, sonic hedgehog (SHH) activated, group 3, and group 4, research efforts have been directed towards unraveling the genetic, epigenetic, transcriptomic, and proteomic profiles of each subtype. This review aims to delineate the progress that has been made in characterizing the neurodevelopmental and molecular features of each medulloblastoma subtype. It further delves into the implications that these characteristics have on the development of subgroup-specific targeted therapeutic agents. Furthermore, it highlights potential future avenues for combining multiple agents or strategies in order to obtain augmented effects and evade the development of treatment resistance in tumors.

Advances in Targeted Therapy for Neurofibromatosis Type 2 (NF2)-Associated Vestibular Schwannomas

PURPOSE OF REVIEW

Neurofibromatosis 2 (NF2) is an autosomal-dominant genetic disorder characterized by bilateral vestibular schwannomas (VS), meningiomas, ependymomas, spinal and peripheral schwannomas, optic gliomas, and juvenile cataracts. Ongoing studies provide new insight into the role of the NF2 gene and merlin in VS tumorigenesis.

RECENT FINDINGS

As NF2 tumor biology becomes increasingly understood, therapeutics targeting specific molecular pathways have been developed and evaluated in preclinical and clinical studies. NF2-associated VS are a source of significant morbidity with current treatments including surgery, radiation, and observation. Currently, there are no FDA-approved medical therapies for VS, and the development of selective therapeutics is a high priority. This manuscript reviews NF2 tumor biology and current therapeutics undergoing investigation for treatment of patients with VS.

Absorption, distribution, metabolism and excretion of 14C-Emvododstat following a single oral dose in rats and dogs

Emvododstat is a potent inhibitor of dihydroorotate dehydrogenase and is now in clinical development for the treatment of acute myeloid leukaemia and COVID-19.Following an oral dose administration in Long-Evans rats, ¹⁴C-emvododstat-derived radioactivity was widely distributed throughout the body, with the highest distribution in the endocrine, fatty, and secretory tissues and the lowest in central nervous system.Following a single oral dose of ¹⁴C-emvododstat in rats, 54.7% of the dose was recovered in faeces while less than 0.4% of dose was recovered in urine 7 days post-dose. Emvododstat was the dominant radioactive component in plasma and faeces.Following a single oral dose of ¹⁴C-emvododstat in dogs, 75.2% of the dose was recovered in faeces while 0.5% of dose was recovered in urine 8 days post-dose. Emvododstat was the dominant radioactive component in faeces, while emvododstat and its two metabolites (O-desmethyl emvododstat and emvododstat amide bond hydrolysis product) were the major circulating radioactivity in dog plasma.

The Tumor Microenvironment of Medulloblastoma: An Intricate Multicellular Network with Therapeutic Potential

Medulloblastoma (MB) is a heterogeneous disease in which survival is highly affected by the underlying subgroup-specific characteristics. Although the current treatment modalities have increased the overall survival rates of MB up to 70-80%, MB remains a major cause of cancer-related mortality among children. This indicates that novel therapeutic approaches against MB are needed. New promising treatment options comprise the targeting of cells and components of the tumor microenvironment (TME). The TME of MB consists of an intricate multicellular network of tumor cells, progenitor cells, astrocytes, neurons, supporting stromal cells, microglia, immune cells, extracellular matrix components, and vasculature systems. In this review, we will discuss all the different components of the MB TME and their role in MB initiation, progression, metastasis, and relapse. Additionally, we briefly introduce the effect that age plays on the TME of brain malignancies and discuss the MB subgroup-specific differences in TME components and how all of these variations could affect the progression of MB. Finally, we highlight the TME-directed treatments, in which we will focus on therapies that are being evaluated in clinical trials.

Emvododstat, a Potent Dihydroorotate Dehydrogenase Inhibitor, Is Effective in Preclinical Models of Acute Myeloid Leukemia

Blocking the pyrimidine nucleotide de novo synthesis pathway by inhibiting dihydroorotate dehydrogenase (DHODH) results in the cell cycle arrest and/or differentiation of rapidly proliferating cells including activated lymphocytes, cancer cells, or virally infected cells. Emvododstat (PTC299) is an orally bioavailable small molecule that inhibits DHODH. We evaluated the potential for emvododstat to inhibit the progression of acute myeloid leukemia (AML) using several in vitro and in vivo models of the disease. Broad potent activity was demonstrated against multiple AML cell lines, AML blasts cultured ex vivo from patient blood samples, and AML tumor models including patient-derived xenograft models. Emvododstat induced differentiation, cytotoxicity, or both in primary AML patient blasts cultured ex vivo with 8 of 10 samples showing sensitivity. AML cells with diverse driver mutations were sensitive, suggesting the potential of emvododstat for broad therapeutic application. AML cell lines that are not sensitive to emvododstat are likely to be more reliant on the salvage pathway than on de novo synthesis of pyrimidine nucleotides. Pharmacokinetic experiments in rhesus monkeys demonstrated that emvododstat levels rose rapidly after oral administration, peaking about 2 hours post-dosing. This was associated with an increase in the levels of dihydroorotate (DHO), the substrate for DHODH, within 2 hours of dosing indicating that DHODH inhibition is rapid. DHO levels declined as drug levels declined, consistent with the reversibility of DHODH inhibition by emvododstat. These preclinical findings provide a rationale for clinical evaluation of emvododstat in an ongoing Phase 1 study of patients with relapsed/refractory acute leukemias.

Recent advances and new discoveries in the pipeline of the treatment of primary spinal tumors and spinal metastases: a scoping review of registered clinical studies from 2000 to 2020

The field of spinal oncology has substantially evolved over the past decades. This review synthesizes and appraises what was learned and what will potentially be discovered from the recently completed and ongoing clinical studies related to the treatment of primary and secondary spinal neoplasms. This scoping review included all clinical studies on the treatment of spinal neoplasms registered in the ClinicalTrials.gov website from February 2000 to December 2020. The terms "spinal cord tumor," "spinal metastasis," and "metastatic spinal cord compression" were used. Of the 174 registered clinical studies on primary spinal tumors and spinal metastasis, most of the clinical studies registered in this American registry were interventional studies led by single institutions in North America (n = 101), Europe (n = 43), Asia (n = 24), or other continents (n = 6). The registered clinical studies mainly focused on treatment strategies for spinal neoplasms (90.2%) that included investigating stereotactic radiosurgery (n = 33), radiotherapy (n = 21), chemotherapy (n = 20), and surgical technique (n = 11). Of the 69 completed studies, the results from 44 studies were published in the literature. In conclusion, this review highlights the key features of the 174 clinical studies on spinal neoplasms that were registered from 2000 to 2020. Clinical trials were heavily skewed toward the metastatic population as opposed to the primary tumors which likely reflects the rarity of the latter condition and associated challenges in undertaking prospective clinical studies in this population. This review serves to emphasize the need for a focused approach to enhancing translational research in spinal neoplasms with a particular emphasis on primary tumors.

In Vitro Metabolism, Pharmacokinetics and Drug Interaction Potentials of Emvododstat, a DHODH Inhibitor

Emvododstat was identified as a potent inhibitor of dihydroorotate dehydrogenase and is now in clinical development for the treatment of acute myeloid leukaemia and COVID-19. The objective of this paper is to evaluate the metabolism, pharmacokinetics, and drug interaction potentials of emvododstat.Emvododstat showed high binding to plasma protein with minimal distribution into blood cells in mouse, rat, dog, monkey, and human whole blood.O-Demethylation followed by glucuronidation appeared to be the major metabolic pathway in rat, dog, monkey, and human hepatocytes. CYP2C8, 2C19, 2D6, and 3A4 were involved in O-desmethyl emvododstat metabolite formation. Both emvododstat and O-desmethyl emvododstat inhibited CYP2D6 activity and induced CYP expression to different extents in vitro.Emvododstat and O-desmethyl emvododstat inhibited BCRP transporter activity but did not inhibit bile salt transporters and other efflux or uptake transporters. Neither emvododstat nor O-desmethyl emvododstat was a substrate for common efflux or uptake transporters investigated.Emvododstat is bioavailable in mice, rats, dogs, and monkeys following a single oral dose. The absorption was generally slow with the mean plasma T_max ranging from 2 to 5 h; plasma exposure of O-desmethyl emvododstat was lower in rodents, but relatively higher in dogs and monkeys.

DHODH and cancer: promising prospects to be explored

Human dihydroorotate dehydrogenase (DHODH) is a flavin-dependent mitochondrial enzyme catalyzing the fourth step in the de novo pyrimidine synthesis pathway. It is originally a target for the treatment of the non-neoplastic diseases involving in rheumatoid arthritis and multiple sclerosis, and is re-emerging as a validated therapeutic target for cancer therapy. In this review, we mainly unravel the biological function of DHODH in tumor progression, including its crucial role in de novo pyrimidine synthesis and mitochondrial respiratory chain in cancer cells. Moreover, various DHODH inhibitors developing in the past decades are also been displayed, and the specific mechanism between DHODH and its additional effects are illustrated. Collectively, we detailly discuss the association between DHODH and tumors in recent years here, and believe it will provide significant evidences and potential strategies for utilizing DHODH as a potential target in preclinical and clinical cancer therapies.

Investigating dihydroorotate dehydrogenase inhibitor mediated mitochondrial dysfunction in hepatic in vitro models

Inhibition of dihydroorotate dehydrogenase (DHODH), the rate-limiting enzymatic step in de novo pyrimidine synthesis, has broad immunosuppressive effects in vivo and shows promise as a therapeutic target for the treatment of malignancies, viral infections and auto-immune diseases. Whilst there are numerous DHODH inhibitors under development, leflunomide and teriflunomide are the only FDA approved compounds on the market, each of which have been issued with black-box warnings for hepatotoxicity. Mitochondrial dysfunction is a putative mechanism by which teriflunomide and leflunomide elicit their hepatotoxic effects, however it is as yet unclear whether this is shared by other nascent DHODH inhibitors. The present study aimed to evaluate the propensity for DHODH inhibitors to mediate mitochondrial dysfunction in two hepatic in vitro models. Initial comparisons of cytotoxicity and ATP content in HepaRG® cells primed for oxidative metabolism, in tandem with mechanistic evaluations by extracellular flux analysis identified multifactorial toxicity and moderate indications of respiratory chain dysfunction or uncoupling. Further investigations using HepG2 cells, a hepatic line with limited capability for phase I xenobiotic metabolism, identified leflunomide and brequinar as positive mitochondrial toxicants. Taken together, biotransformation of some DHODH inhibitor species may play a role in mediating or masking hepatic mitochondrial liabilities.

Dihydroorotate dehydrogenase in oxidative phosphorylation and cancer

Dihydroorotate dehydrogenase (DHODH) is an enzyme of the de novo pyrimidine synthesis pathway that provides nucleotides for RNA/DNA synthesis essential for proliferation. In mammalian cells, DHODH is localized in mitochondria, linked to the respiratory chain via the coenzyme Q pool. Here we discuss the role of DHODH in the oxidative phosphorylation system and in the initiation and progression of cancer. We summarize recent findings on DHODH biology, the progress made in the development of new, specific inhibitors of DHODH intended for cancer therapy, and the mechanistic insights into the consequences of DHODH inhibition.

Targeting of Hematologic Malignancies with PTC299, A Novel Potent Inhibitor of Dihydroorotate Dehydrogenase with Favorable Pharmaceutical Properties

PTC299 was identified as an inhibitor of VEGFA mRNA translation in a phenotypic screen and evaluated in the clinic for treatment of solid tumors. To guide precision cancer treatment, we performed extensive biological characterization of the activity of PTC299 and demonstrated that inhibition of VEGF production and cell proliferation by PTC299 is linked to a decrease in uridine nucleotides by targeting dihydroorotate dehydrogenase (DHODH), a rate-limiting enzyme for de novo pyrimidine nucleotide synthesis. Unlike previously reported DHODH inhibitors that were identified using in vitro enzyme assays, PTC299 is a more potent inhibitor of DHODH in isolated mitochondria suggesting that mitochondrial membrane lipid engagement in the DHODH conformation in situ is required for its optimal activity. PTC299 has broad and potent activity against hematologic cancer cells in preclinical models, reflecting a reduced pyrimidine nucleotide salvage pathway in leukemia cells. Archived serum samples from patients treated with PTC299 demonstrated increased levels of dihydroorotate, the substrate of DHODH, indicating target engagement in patients. PTC299 has advantages over previously reported DHODH inhibitors, including greater potency, good oral bioavailability, and lack of off-target kinase inhibition and myelosuppression, and thus may be useful for the targeted treatment of hematologic malignancies.

Medulloblastoma in children and adolescents: a systematic review of contemporary phase I and II clinical trials and biology update

Survival rates for patients with medulloblastoma have improved in the last decades but for those who relapse outcome is dismal and new approaches are needed. Emerging drugs have been tested in the last two decades within the context of phase I/II trials. In parallel, advances in genetic profiling have permitted to identify key molecular alterations for which new strategies are being developed. We performed a systematic review focused on the design and outcome of early-phase trials evaluating new agents in patients with relapsed medulloblastoma. PubMed, clinicaltrials.gov, and references from selected studies were screened to identify phase I/II studies with reported results between 2000 and 2015 including patients with medulloblastoma aged <18 years. A total of 718 studies were reviewed and 78 satisfied eligibility criteria. Of those, 69% were phase I; 31% phase II. Half evaluated conventional chemotherapeutics and 35% targeted agents. Overall, 662 patients with medulloblastoma/primitive neuroectodermal tumors were included. The study designs and the response assessments were heterogeneous, limiting the comparisons among trials and the correct identification of active drugs. Median (range) objective response rate (ORR) for patients with medulloblastoma in phase I/II studies was 0% (0-100) and 6.5% (0-50), respectively. Temozolomide containing regimens had a median ORR of 16.5% (0-100). Smoothened inhibitors trials had a median ORR of 8% (3-8). Novel drugs have shown limited activity against relapsed medulloblastoma. Temozolomide might serve as backbone for new combinations. Novel and more homogenous trial designs might facilitate the development of new drugs.

Pediatric Patient With Renal Cell Carcinoma Treated by Successive Antiangiogenics Drugs: A Case Report and Review of the Literature

Antiangiogenic drugs are currently standard of care in adults with renal cell carcinoma (RCC), including translocation RCC. Although antitumor activity and toxicity profile are well known in adults, few data have been reported in children. Here we present the case of a patient diagnosed at 2 years old with a metastatic translocation RCC, consecutively treated with 5 tyrosine kinase inhibitors during 6 years. The antitumor activity and toxic effects are described, and a brief review of the literature is presented.

Discovery of Novel Small Molecule Inhibitors of VEGF Expression in Tumor Cells Using a Cell-Based High Throughput Screening Platform

Current anti-VEGF (Vascular Endothelial Growth Factor A) therapies to treat various cancers indiscriminately block VEGF function in the patient resulting in the global loss of VEGF signaling which has been linked to dose-limiting toxicities as well as treatment failures due to acquired resistance. Accumulating evidence suggests that this resistance is at least partially due to increased production of compensatory tumor angiogenic factors/cytokines. VEGF protein production is differentially controlled depending on whether cells are in the normal “homeostatic” state or in a stressed state, such as hypoxia, by post-transcriptional regulation imparted by elements in the 5’ and 3’ untranslated regions (UTR) of the VEGF mRNA. Using the Gene Expression Modulation by Small molecules (GEMS^™) phenotypic assay system, we performed a high throughput screen to identify low molecular weight compounds that target the VEGF mRNA UTR-mediated regulation of stress-induced VEGF production in tumor cells. We identified a number of compounds that potently and selectively reduce endogenous VEGF production under hypoxia in HeLa cells. Medicinal chemistry efforts improved the potency and pharmaceutical properties of one series of compounds resulting in the discovery of PTC-510 which inhibits hypoxia-induced VEGF expression in HeLa cells at low nanomolar concentration. In mouse xenograft studies, oral administration of PTC-510 results in marked reduction of intratumor VEGF production and single agent control of tumor growth without any evident toxicity. Here, we show that selective suppression of stress-induced VEGF production within tumor cells effectively controls tumor growth. Therefore, this approach may minimize the liabilities of current global anti-VEGF therapies.

Brief Report: A Phase 1b/Pharmacokinetic Trial of PTC299, a Novel PostTranscriptional VEGF Inhibitor, for AIDS-Related Kaposi's Sarcoma: AIDS Malignancy Consortium Trial 059

Vascular endothelial growth factor (VEGF) plays an important role in Kaposi's sarcoma (KS). We administered PTC299, a post-transcriptional inhibitor of pathogenic VEGF, to persons with HIV-related KS. Seventeen participants received 3 different doses of PTC299. Adverse events typically observed with VEGF inhibition were absent. Three participants had partial tumor responses and 11 had stable disease. There were no differences in exposure to PTC299 by antiretroviral regimen. Serum VEGF, but not KS-associated herpesvirus DNA, decreased on treatment. Given redundancies in the VEGF feedback loop, future trials should consider combining PTC299 with agents that inhibit different pathways implicated in KS and KS-associated herpesvirus proliferation.

Phase 1 Study of Safety, Tolerability, and Pharmacokinetics of PTC299, an Inhibitor of Stress-Regulated Protein Translation

PTC299 is a novel small molecule that specifically blocks the production of protein from selected mRNAs that under certain conditions use noncanonical ribosomal translational pathways. Hypoxia, oncogenic transformation, and viral infections limit normal translation and turn on these noncanonical translation pathways that are sensitive to PTC299. Vascular endothelial cell growth factor (VEGF) is an example of a transcript that is posttranscriptionally regulated. Single doses of PTC299 (0.03 to 3 mg/kg) were administered orally to healthy volunteers in a phase 1 single ascending‐dose study. In a subsequent multiple ascending‐dose study in healthy volunteers, multiple‐dose regimens (0.3 to 1.2 mg/kg twice a day or 1.6 mg/kg 3 times a day for 7 days) were evaluated. PTC299 was well tolerated in these studies. As expected in healthy volunteers, mean plasma VEGF levels did not change. Increases in C_max and AUC of PTC299 were dose‐proportional. The target trough plasma concentration associated with preclinical efficacy was achieved within 7 days at doses of 0.6 mg/kg twice daily and above. These data demonstrate that PTC299 is orally bioavailable and well tolerated and support clinical evaluation of PTC299 in cancer, certain viral infections, or other diseases in which deregulation of translational control is a causal factor.