Pharmacokinetic Principles and Their Application to Central Nervous System Tumors

Phase I Study of Adavosertib with Radiotherapy and Temozolomide in Newly Diagnosed Glioblastoma and Intratumoral Drug Levels in Recurrent Glioblastoma

PURPOSE

Adavosertib is an oral small-molecule inhibitor of Wee1. The Adult Brain Tumor Consortium conducted a phase I study evaluating adavosertib in combination with radiation (RT) and temozolomide (TMZ) in patients with newly diagnosed glioblastoma (GBM), as well as a surgical window-of-opportunity study in recurrent GBM.

PATIENTS AND METHODS

The MTD of adavosertib was determined in adult patients with newly diagnosed GBM using a standard 3+3 design in two separate cohorts: with concurrent RT/TMZ or with adjuvant TMZ. A combination cohort with both concurrent and adjuvant adavosertib at MTD followed. We also performed intratumoral drug distribution studies in patients with recurrent GBM undergoing surgery.

RESULTS

As separate cohorts, the MTD for concurrent adavosertib with RT/TMZ was 200 mg daily Monday through Friday × 6 weeks during RT, and the MTD for adjuvant adavosertib with TMZ was 425 mg daily for 5 days of each 28-day cycle. However, six of 12 patients experienced dose-limiting toxicities (DLT) in the combination cohort. The mean ratios of the intratumoral to plasma concentration of adavosertib were 4.18 ± 3.36 for contrast-enhancing tissue and 0.74 ± 0.63 in nonenhancing tissue.

CONCLUSIONS

Adavosertib at 200 mg daily Monday through Friday × 6 weeks with RT/TMZ and at 425 mg daily on a 5-day/28-day cycle with TMZ had an unacceptable DLT rate. Additional dose levels in combination cohorts resulted in DLT, and we deemed concurrent adavosertib too toxic for further examination. Adavosertib 425 mg daily on a 5-day/28-day cycle with adjuvant TMZ is the recommended phase II dosage. Tissue pharmacokinetics in tissue homogenates and by microdialysis provided complementary information about drug penetration.

Pediatric oncology drug development and dosage optimization

Oncology drug discovery and development has always been an area facing many challenges. Phase 1 oncology studies are typically small, open-label, sequential studies enrolling a small sample of adult patients (i.e., 3-6 patients/cohort) in dose escalation. Pediatric evaluations typically lag behind the adult development program. The pediatric starting dose is traditionally referenced on the recommended phase 2 dose in adults with the incorporation of body size scaling. The size of the study is also small and dependent upon the prevalence of the disease in the pediatric population. Similar to adult development, the dose is escalated or de-escalated until reaching the maximum tolerated dose (MTD) that also provides desired biological activities or efficacy. The escalation steps and identification of MTD are often rule-based and do not incorporate all the available information, such as pharmacokinetic (PK), pharmacodynamic (PD), tolerability and efficacy data. Therefore, it is doubtful if the MTD approach is optimal to determine the dosage. Hence, it is important to evaluate whether there is an optimal dosage below the MTD, especially considering the emerging complexity of combination therapies and the long-term tolerability and safety of the treatments. Identification of an optimal dosage is also vital not only for adult patients but for pediatric populations as well. Dosage-finding is much more challenging for pediatric populations due to the limited patient population and differences among the pediatric age range in terms of maturation and ontogeny that could impact PK. Many sponsors defer the pediatric strategy as they are often perplexed by the challenges presented by pediatric oncology drug development (model of action relevancy to pediatric population, budget, timeline and regulatory requirements). This leads to a limited number of approved drugs for pediatric oncology patients. This review article provides the current regulatory landscape, incentives and how they impact pediatric drug discovery and development. We also consider different pediatric cancers and potential clinical trial challenges/opportunities when designing pediatric clinical trials. An outline of how quantitative methods such as pharmacometrics/modelling & simulation can support the dosage-finding and justification is also included. Finally, we provide some reflections that we consider helpful to accelerate pediatric drug discovery and development.

Strategies increasing the effectiveness of temozolomide at various levels of anti-GBL therapy

Glioblastoma (GBL) is the most common (60-70% of primary brain tumours) and the most malignant of the glial tumours. Although current therapies remain palliative, they have been proven to prolong overall survival. Within an optimal treatment regimen (incl. surgical resection, radiation therapy, and chemotherapy) temozolomide as the current anti-GBL first-line chemotherapeutic has increased the median overall survival to 14-15 months, and the percentage of patients alive at two years has been reported to rise from 10.4% to 26.5%. Though, the effectiveness of temozolomide chemotherapy is limited by the serious systemic, dose-related side effects. Therefore, the ponderation regarding novel treatment methods along with innovative formulations is crucial to emerging the therapeutic potential of the widely used drug simultaneously reducing the drawbacks of its use. Herein the complex temozolomide application restrictions present at different levels of therapy as well as, the currently proposed strategies aimed at reducing those limitations are demonstrated. Approaches increasing the efficacy of anti-GBL treatment are addressed. Our paper is focused on the most recent developments in the field of nano/biomaterials-based systems for temozolomide delivery and their functionalization towards more effective blood-brain-barrier crossing and/or tumour targeting. Appropriate designing accounting for the physical and chemical features of formulations along with distinct routes of administration is also discussed. In addition, considering the multiple resistance mechanisms, the molecular heterogeneity and the evolution of tumour the purposely selected delivery methods, the combined therapeutic approaches and specifically focused on GBL cells therapies are reviewed.

Targeting interleukin-13 receptor α2 (IL-13Rα2) for glioblastoma therapy with surface functionalized nanocarriers

Despite surgical and therapeutic advances, glioblastoma multiforme (GBM) is among the most fatal primary brain tumor that is aggressive in nature. Patients with GBM have a median lifespan of just 15 months when treated with the current standard of therapy, which includes surgical resection and concomitant chemo-radiotherapy. In recent years, nanotechnology has shown considerable promise in treating a variety of illnesses, and certain nanomaterials have been proven to pass the blood-brain barrier (BBB) and stay in glioblastoma tissues. Recent preclinical research suggests that the diagnosis and treatment of brain tumor is significantly explored through the intervention of nanomaterials that has showed enhanced effect. In order to elicit an antitumor response, it is necessary to retain the therapeutic candidates within glioblastoma tissues and this job is effectively carried out by nanocarrier particularly functionalized nanocarriers. In the arena of neoplastic diseases including GBM have achieved great attention in recent decades. Furthermore, interleukin-13 receptor α chain variant 2 (IL13Rα2) is a highly expressed and studied target in GBM that is lacked by the surrounding environment. The absence of IL13Rα2 in surrounding normal tissues has made it a suitable target in glioblastoma therapy. In this review article, we highlighted the role of IL13Rα2 as a potential target in GBM along with design and fabrication of efficient targeting strategies for IL13Rα2 through surface functionalized nanocarriers.

Drug Repurposing, a Fast-Track Approach to Develop Effective Treatments for Glioblastoma

Glioblastoma (GBM) remains one of the most difficult tumors to treat. The mean overall survival rate of 15 months and the 5-year survival rate of 5% have not significantly changed for almost 2 decades. Despite progress in understanding the pathophysiology of the disease, no new effective treatments to combine with radiation therapy after surgical tumor debulking have become available since the introduction of temozolomide in 1999. One of the main reasons for this is the scarcity of compounds that cross the blood-brain barrier (BBB) and reach the brain tumor tissue in therapeutically effective concentrations. In this review, we focus on the role of the BBB and its importance in developing brain tumor treatments. Moreover, we discuss drug repurposing, a drug discovery approach to identify potential effective candidates with optimal pharmacokinetic profiles for central nervous system (CNS) penetration and that allows rapid implementation in clinical trials. Additionally, we provide an overview of repurposed candidate drug currently being investigated in GBM at the preclinical and clinical levels. Finally, we highlight the importance of phase 0 trials to confirm tumor drug exposure and we discuss emerging drug delivery technologies as an alternative route to maximize therapeutic efficacy of repurposed candidate drug.

Fabrication and Modelling of a Reservoir-Based Drug Delivery System for Customizable Release

Localized therapy approaches have emerged as an alternative drug administration route to overcome the limitations of systemic therapies, such as the crossing of the blood–brain barrier in the case of brain tumor treatment. For this, implantable drug delivery systems (DDS) have been developed and extensively researched. However, to achieve an effective localized treatment, the release kinetics of DDS needs to be controlled in a defined manner, so that the concentration at the tumor site is within the therapeutic window. Thus, a DDS, with patient-specific release kinetics, is crucial for the improvement of therapy. Here, we present a computationally supported reservoir-based DDS (rDDS) development towards patient-specific release kinetics. The rDDS consists of a reservoir surrounded by a polydimethylsiloxane (PDMS) microchannel membrane. By tailoring the rDDS, in terms of membrane porosity, geometry, and drug concentration, the release profiles can be precisely adapted, with respect to the maximum concentration, release rate, and release time. The release is investigated using a model dye for varying parameters, leading to different distinct release profiles, with a maximum release of up to 60 days. Finally, a computational simulation, considering exemplary in vivo conditions (e.g., exchange of cerebrospinal fluid), is used to study the resulting drug release profiles, demonstrating the customizability of the system. The establishment of a computationally supported workflow, for development towards a patient-specific rDDS, in combination with the transfer to suitable drugs, could significantly improve the efficacy of localized therapy approaches.

Nanomedicine for brain cancer

CNS tumors remain among the deadliest forms of cancer, resisting conventional and new treatment approaches, with mortality rates staying practically unchanged over the past 30 years. One of the primary hurdles for treating these cancers is delivering drugs to the brain tumor site in therapeutic concentration, evading the blood-brain (tumor) barrier (BBB/BBTB). Supramolecular nanomedicines (NMs) are increasingly demonstrating noteworthy prospects for addressing these challenges utilizing their unique characteristics, such as improving the bioavailability of the payloadsviacontrolled pharmacokinetics and pharmacodynamics, BBB/BBTB crossing functions, superior distribution in the brain tumor site, and tumor-specific drug activation profiles. Here, we review NM-based brain tumor targeting approaches to demonstrate their applicability and translation potential from different perspectives. To this end, we provide a general overview of brain tumor and their treatments, the incidence of the BBB and BBTB, and their role on NM targeting, as well as the potential of NMs for promoting superior therapeutic effects. Additionally, we discuss critical issues of NMs and their clinical trials, aiming to bolster the potential clinical applications of NMs in treating these life-threatening diseases.

Drug Design: Where We Are and Future Prospects

Medicinal chemistry is facing new challenges in approaching precision medicine. Several powerful new tools or improvements of already used tools are now available to medicinal chemists to help in the process of drug discovery, from a hit molecule to a clinically used drug. Among the new tools, the possibility of considering folding intermediates or the catalytic process of a protein as a target for discovering new hits has emerged. In addition, machine learning is a new valuable approach helping medicinal chemists to discover new hits. Other abilities, ranging from the better understanding of the time evolution of biochemical processes to the comprehension of the biological meaning of the data originated from genetic analyses, are on their way to progress further in the drug discovery field toward improved patient care. In this sense, the new approaches to the delivery of drugs targeted to the central nervous system, together with the advancements in understanding the metabolic pathways for a growing number of drugs and relating them to the genetic characteristics of patients, constitute important progress in the field.

Molecular Mechanisms of Drug Resistance in Glioblastoma

Glioblastoma multiforme (GBM) is the most common and fatal primary brain tumor, is highly resistant to conventional radiation and chemotherapy, and is not amenable to effective surgical resection. The present review summarizes recent advances in our understanding of the molecular mechanisms of therapeutic resistance of GBM to already known drugs, the molecular characteristics of glioblastoma cells, and the barriers in the brain that underlie drug resistance. We also discuss the progress that has been made in the development of new targeted drugs for glioblastoma, as well as advances in drug delivery across the blood-brain barrier (BBB) and blood-brain tumor barrier (BBTB).