Noncovalent inhibition of C481S Bruton tyrosine kinase by GDC-0853: a new treatment strategy for ibrutinib-resistant CLL.

The clinical success of ibrutinib validates Bruton tyrosine kinase (BTK) inhibition as an effective strategy for treating hematologic malignancies, including chronic lymphocytic leukemia (CLL). Despite ibrutinib's ability to produce durable remissions in patients, acquired resistance can develop, mostly commonly by mutation of C481 of BTK in the ibrutinib binding site. Here, we characterize a novel BTK inhibitor, GDC-0853, to evaluate its preclinical efficacy in ibrutinib-naive and ibrutinib-resistant CLL. GDC-0853 is unique among reported BTK inhibitors in that it does not rely upon covalent reaction with C481 to stabilize its occupancy within BTK's adenosine triphosphate binding site. As with ibrutinib, GDC-0853 potently reduces B-cell receptor signaling, viability, NF-κB-dependent transcription, activation, and migration in treatment naïve CLL cells. We found that GDC-0853 also inhibits the most commonly reported ibrutinib-resistant BTK mutant (C481S) both in a biochemical enzyme activity assay and in a stably transfected 293T cell line and maintains cytotoxicity against patient CLL cells harboring C481S BTK mutations. Additionally, GDC-0853 does not inhibit endothelial growth factor receptor or ITK, 2 alternative targets of ibrutinib that are likely responsible for some adverse events and may reduce the efficacy of ibrutinib-antibody combinations, respectively. Our results using GDC-0853 indicate that noncovalent, selective BTK inhibition may be effective in CLL either as monotherapy or in combination with therapeutic antibodies, especially among the emerging population of patients with acquired resistance to ibrutinib therapy.

Selinexor is effective in acquired resistance to ibrutinib and synergizes with ibrutinib in chronic lymphocytic leukemia.

Despite the therapeutic efficacy of ibrutinib in chronic lymphocytic leukemia (CLL), complete responses are infrequent, and acquired resistance to Bruton agammaglobulinemia tyrosine kinase (BTK) inhibition is being observed in an increasing number of patients. Combination regimens that increase frequency of complete remissions, accelerate time to remission, and overcome single agent resistance are of considerable interest. We previously showed that the XPO1 inhibitor selinexor is proapoptotic in CLL cells and disrupts B-cell receptor signaling via BTK depletion. Herein we show the combination of selinexor and ibrutinib elicits a synergistic cytotoxic effect in primary CLL cells and increases overall survival compared with ibrutinib alone in a mouse model of CLL. Selinexor is effective in cells isolated from patients with prolonged lymphocytosis following ibrutinib therapy. Finally, selinexor is effective in ibrutinib-refractory mice and in a cell line harboring the BTK C481S mutation. This is the first report describing the combined activity of ibrutinib and selinexor in CLL, which represents a new treatment paradigm and warrants further evaluation in clinical trials of CLL patients including those with acquired ibrutinib resistance.

IPI-145 antagonizes intrinsic and extrinsic survival signals in chronic lymphocytic leukemia cells.

Chronic lymphocytic leukemia (CLL) displays constitutive phosphatidylinositol 3-kinase (PI3K) activation resulting from aberrant regulation of B-cell receptor (BCR) signaling. Previous studies have shown that an oral PI3K p110δ inhibitor idelalisib exhibits promising activity in CLL. Here, we demonstrate that a dual PI3K p110δ and p110γ inhibitor, IPI-145, antagonizes BCR crosslinking activated prosurvival signals in primary CLL cells. IPI-145 causes direct killing in primary CLL cells in a dose- and time-dependent fashion, but does not generate direct cytotoxicity to normal B cells. However, IPI-145 does reduce the viability of normal T and natural killer cells and decrease activated T-cell production of various inflammatory and antiapoptotic cytokines. Furthermore, IPI-145 overcomes the ibrutinib resistance resulting from treatment-induced BTK C481S mutation. Collectively, these studies provide rationale for ongoing clinical evaluation of IPI-145 as a targeted therapy for CLL and related B-cell lymphoproliferative disorders.

Assessing Information Gaps Associated with Initial Pediatric Study Plans for New Oncology Drug and Biological Products.

The Research Acceleration for Cure and Equity (RACE) for Children Act requires sponsors to submit a Pediatric Study Plan (PSP) with a proposed pediatric investigation of new molecularly targeted drugs and biologics that are intended for treatment of adult cancers, and whose target is relevant to pediatric cancer or provide a justification for a plan to request a deferral or waiver of the required investigation. A landscape analysis was performed to identify trends in information gaps associated with a sponsor's first initial PSP (iPSP) submission for oncologic new molecular entities received in 2021. Comments sent to sponsors by the US Food and Drug Administration (FDA) during the review process of each evaluated iPSP were categorized using nine flags relating to different portions of the PSP. For iPSPs that included a plan for a full waiver request, the most common information gap was inadequate justification based on molecular target relevance. All other sponsor proposed plans (deferral and/or partial waiver or investigation) were found to have information gaps related to clinical study features, clinical pharmacology, and/or missing clinical or nonclinical data. This landscape analysis of iPSPs shows the trends in comments that often occur during initial review and may help to provide sponsors with more direction for preparing an adequate iPSP to fulfill statutory requirements aimed at ensuring pediatric patients are considered in the development of new molecularly targeted drugs.

US FDA Postmarketing Requirements and Commitments: A Systematic Assessment of Clinical Pharmacology Studies and Their Impact on US FDA Prescribing Information.

Many of the conditions for the safe and effective use of new molecular entities (NMEs) are understood at the time of initial drug approval. However, some remaining knowledge gaps can be addressed after drug approval through postmarketing requirements (PMRs) or commitments (PMCs) established by the US Food and Drug Administration (FDA). Our objective was to conduct an assessment of clinical pharmacology-related PMRs and PMCs established at the time of approval and evaluate the impact of fulfilled PMRs and PMCs on prescription information (PI). This analysis included clinical pharmacology-related PMRs and PMCs established for NMEs approved between 2009 and 2020. Of the 1171 PMRs and PMCs, over one-third were clinical pharmacology-related. Of these, 46% were to evaluate drug interactions, 16% were to evaluate drug dosing in patients with hepatic impairment, and 10% were related to dose. The majority (57%) of PMRs and PMCs were fulfilled at the time of analysis, with a median time to fulfillment of approximately 2.3 years. The majority (94%) of the fulfilled PMRs and PMCs, either with or without a PI revision, resulted in new or modified instructions for use or supported existing instructions for use. This is the first time that clinical pharmacology-related PMRs and PMCs have been catalogued and analyzed to understand their impact on PI. An understanding of the knowledge gaps that exist at the time of drug approval could inform the most effective and efficient methods for evidence generation prior to and after new drug approval.

Informing a Comprehensive Risk Assessment of Infant Drug Exposure From Human Milk: Application of a Physiologically Based Pharmacokinetic Lactation Model for Sotalol.

Characterization of infant drug exposure through human milk is important and underexplored. Because infant plasma concentrations are not frequently collected in clinical lactation studies, modeling and simulation approaches can integrate physiology, available milk concentrations, and pediatric data to inform exposure in breastfeeding infants. A physiologically based pharmacokinetic model was built for sotalol, a renally eliminated drug, to simulate infant drug exposure from human milk. Intravenous and oral adult models were built, optimized, and scaled to an oral pediatric model for a breastfeeding-relevant age group (<2 years). Model simulations captured the data that were put aside for verification. The resulting pediatric model was applied to predict the impacts of sex, infant body size, breastfeeding frequency, age, and maternal dose (240 and 433 mg) on drug exposure during breastfeeding. Simulations suggest a minimal effect of sex or frequency on total sotalol exposure. Infants in the 90th percentile in height and weight have predicted exposures ≈20% higher than infants of the same age in the 10th percentile due to increased milk intake. The simulated infant exposures increase throughout the first 2 weeks of life and are maintained at the highest concentrations in weeks 2-4, with a consistent decrease observed as infants age. Simulations suggest that breastfeeding infants will have plasma concentrations in the lower range observed in infants administered sotalol. With further validation on additional drugs, physiologically based pharmacokinetic modeling approaches could use lactation data to a greater extent and provide comprehensive information to support decisions regarding medication use during breastfeeding.

Pharmacokinetic Evaluation in Pregnancy-Current Status and Future Considerations: Workshop Summary.

As pregnant individuals have traditionally been excluded from clinical trials, there is a gap in knowledge at the time of drug approval regarding safety, efficacy, and appropriate dosing for most prescription medications used during pregnancy. Physiologic changes in pregnancy can result in changes in pharmacokinetics that can impact safety or efficacy. This highlights the need to foster further research and collection of pharmacokinetic data in pregnancy to ensure appropriate drug dosing in pregnant individuals. Therefore, the US Food and Drug Administration and the University of Maryland Center of Excellence in Regulatory Science and Innovation hosted a workshop on May 16 and 17, 2022, titled "Pharmacokinetic Evaluation in Pregnancy." This is a summary of the workshop proceedings.

Efficiency of a randomized confirmatory basket trial design constrained to control the family wise error rate by indication.

Basket trials pool histologic indications sharing molecular pathophysiology, improving development efficiency. Currently, basket trials have been confirmatory only for exceptional therapies. Our previous randomized basket design may be generally suitable in the resource-intensive confirmatory phase, maintains high power even with modest effect sizes, and provides nearly k-fold increased efficiency for k indications, but controls false positives for the pooled result only. Since family wise error rate by indications may sometimes be required, we now simulate a variant of this basket design controlling family wise error rate at 0.025k, the total family wise error rate of k separate randomized trials. We simulated this modified design under numerous scenarios varying design parameters. Only designs controlling family wise error rate and minimizing estimation bias were allowable. Optimal performance results when k=3,4. We report efficiency (expected # true positives/expected sample size) relative to k parallel studies, at 90% power ("uncorrected") or at the power achieved in the basket trial ("corrected," because conventional designs could also increase efficiency by sacrificing power). Efficiency and power (percentage active indications identified) improve with a higher percentage of initial indications active. Up to 92% uncorrected and 38% corrected efficiency improvement is possible. Even under family wise error rate control, randomized confirmatory basket trials substantially improve development efficiency. Initial indication selection is critical.

Roadmap to 2030 for Drug Evaluation in Older Adults.

Changes that accompany older age can alter the pharmacokinetics (PK), pharmacodynamics (PD), and likelihood of adverse effects (AEs) of a drug. However, older adults, especially the oldest or those with multiple chronic health conditions, polypharmacy, or frailty, are often under-represented in clinical trials of new drugs. Deficits in the current conduct of clinical evaluation of drugs for older adults and potential steps to fill those knowledge gaps are presented in this communication. The most important step is to increase clinical trial enrollment of older adults who are representative of the target treatment population. Unnecessary eligibility criteria should be eliminated. Physical and financial barriers to participation should be removed. Incentives could be created for inclusion of older adults. Enrollment goals should be established based on intended treatment indications, prevalence of the condition, and feasibility. Relevant clinical pharmacology data need to be obtained early enough to guide dosing and reduce risk for participation of older adults. Relevant PK and PD data as well as patient-centered outcomes should be measured during trials. Trial data should be analyzed for differences in PK, PD, effectiveness, and safety arising from differences in age or from the presence of conditions common in older adults. Postmarket evaluations with real-world evidence and drug labeling updates throughout the product lifecycle reflecting new knowledge are also needed. A comprehensive plan is needed to ensure adequate evaluation of the safety and effectiveness of drugs in older adults.

Elucidating the Impact of Immunogenicity Assessment Postapproval: A Targeted Analysis of Immunogenicity Postmarketing Requirements and Commitments.

Insufficient availability of data to evaluate immunogenicity incidence or clinical impact during regulatory review could require further evaluation postapproval. Through a keyword search of all postmarketing requirements and commitments (PMRs/PMCs) associated with products with their original US Food and Drug Administration (FDA) approvals between 2009 and 2018, we identified products that had PMRs/PMCs established to address concerns or uncertainty related to immunogenicity. Of the 113 relevant products, 50% had an immunogenicity-related PMR/PMC; of these, 68% were related to developing immunogenicity assays and 48% requested an assessment of clinical impact. Fifty-five percent of the products with a fulfilled PMR/PMC had a change in the immunogenicity information in their labeling immediately following fulfillment. This work highlights that there are often unknowns associated with immunogenicity incidence and/or impact at the time of approval. Earlier regulatory discussions on immunogenicity assessments in premarket development could improve the understanding and communication of the risk/benefit profile and reduce the need for some immunogenicity PMRs/PMCs.

A Systematic Assessment of US Food and Drug Administration Dosing Recommendations For Drug Development Programs Amenable to Response-Guided Titration.

A key goal in drug development is optimized dosing for patients. Interactions between drug developers and regulatory scientists throughout development are important for the optimization of dosing and serve as a forum to discuss approaches for optimal dosing, such as precision or individualized dosing. To date, there has not been a systematic assessment of the advice provided by the US Food and Drug Administration (FDA) to drug developers from an individualized dosing perspective. Here, we reviewed FDA recommendations on dose selection for efficacy trials at end-of-phase meetings between the FDA and drug developers for 76 new molecular entities approved between 2013 and 2017 that are considered amenable for an individualized dosing method, response-guided titration. Forty FDA dosing recommendations were identified as specific to dose selection and design of the respective efficacy trials and subsequently: (i) characterized based on if they were supportive of individualized dosing and (ii) compared with dosing regimens used in efficacy trials and labeling at approval to evaluate if FDA recommendations were implemented. Of these 40 recommendations for efficacy trials, 35 (88%) were considered supportive of individualized dosing. Eighteen of these 40 recommendations (45%) were incorporated into efficacy trials and 11 (28%) were incorporated into labeling. This research suggests that early FDA-sponsor interactions can support the study of doses in efficacy trials that may lead to individualized dosing strategies in labeling.

Reasons for Premature Conclusion of Late Phase Clinical Trials: An Analysis of ClinicalTrials.gov Registered Phase III Trials.

BACKGROUND: Confirmatory phase III trials aim to provide decisive evidence about a medical product's safety and efficacy. Although these trials are planned and conducted based on accumulated knowledge, they are not without risk or uncertainty. A trial prematurely concluding contributes to great loss in both financial and human research resources. METHODS: We categorized and evaluated trials concluded prematurely after recruitment had begun, as registered in Clinical Trials.gov between January 2013 and August 2017. RESULTS: We found 9828 registered interventional phase III trials; of those, 320 were concluded prematurely. Many clinical trials were concluded prematurely for reasons related to reducing participant risk, such as interim stopping for safety, efficacy, or futility. Yet, 70% trials were halted for other reasons, such as insufficient recruitment (the most often cited reason) or unspecified business decisions. Of all prematurely concluded trials, 102 trials evaluated 72 different novel therapeutics; in 66.7% of these trials, the clinical development program was stopped entirely. Most of the prematurely concluded trials (78%) had not provided results to ClinicalTrials.gov at the time of this analysis. CONCLUSIONS: Evaluation of the factors that influence premature conclusion could inform solutions for improving research participation and help ensure trial completion. Registering and reporting results acknowledges the voluntary contribution and consent expectations of research participants.

Communicating Immunogenicity-Associated Risk in Current U.S. FDA Prescription Drug Labeling: A Systematic Evaluation.

BACKGROUND: Communicating the clinical impact of immunogenicity in labeling is important for safe and effective use of certain prescription products. Current U.S. Food and Drug Administration (FDA) guidance does not provide comprehensive recommendations on the communication of clinical impact of immunogenicity in labeling. To understand current labeling practice, we evaluated the immunogenicity data and clinical impact information in labeling of selected prescription products. METHODS: We created a database of 71 therapeutic biologics and drug products that had an immunogenicity assessment initially approved by FDA's Center for Drug Evaluation and Research between 2014 and 2018. We analyzed the content and format of immunogenicity information (e.g., anti-drug antibody incidence and/or immunogenicity impact on pharmacokinetics (PK), safety, and/or effectiveness) in the most recent approved labeling. RESULTS: Immunogenicity information was in the ADVERSE REACTIONS section in 98% of the reviewed labeling. Immunogenicity impact on PK was reported in 52% of the labeling, typically within the ADVERSE REACTIONS section, but supportive PK data were often not included in the CLINICAL PHARMACOLOGY section. Additionally, the immunogenicity impact on safety and/or effectiveness was communicated in 70% of the labeling, with 23% clearly communicating the effect as clinically meaningful, and 10% providing actionable recommendations. CONCLUSIONS: Most of the reviewed labeling includes immunogenicity information within the ADVERSE REACTIONS section. However, there is inconsistency in providing supportive PK data and high variability in reporting immunogenicity impact on safety and effectiveness in labeling. Development of a communication framework that allows for consistent inclusion of immunogenicity impact statements in labeling could improve how immunogenicity risk is conveyed in prescription drug labeling.

The regulation of tumor-suppressive microRNA, miR-126, in chronic lymphocytic leukemia.

The introduction of miR profiling of chronic lymphocytic leukemia (CLL) patients with different cytogenetic profiles and responses to therapy has allowed incorporation of important miR-mRNA interactions into the understanding of disease biology. In this study, we performed miR expression analysis using NanoString nCounter to discover differentially regulated miRs after therapy with the Bruton tyrosine kinase inhibitor ibrutinib. Of the differentially regulated miRs in the discovery set, miR-29c and miR-126 were confirmed using real-time PCR to be upregulated in CLL patient cells with ibrutinib therapy. In the validation set, an inverse correlation was observed between miR-126 levels and expression of its putative target p85ß, an isoform of the phosphoinositide 3-kinase p85 regulatory subunit. We found that mRNA for the host gene EGFL7, primary unprocessed miR-126, and mature miR-126 are all downregulated in CLL cells compared to normal B cells. Patients in later stages of disease have a greater decrease in miR-126 expression compared to treatment-naive patients, indicating that lower miR-126 levels may associate with disease progression. Overexpression of miR-126 in leukemia cell lines significantly downregulates p85ß expression and decreases activation of prosurvival mitogen-activated protein kinase (MAPK) signaling. These results implicate miR-126 in the pathology of CLL.

BTKC481S-Mediated Resistance to Ibrutinib in Chronic Lymphocytic Leukemia.

Purpose Therapeutic targeting of Bruton tyrosine kinase (BTK) with ibrutinib in chronic lymphocytic leukemia has led to a paradigm shift in therapy, and relapse has been uncommon with current follow-up. Acquired mutations in BTK and PLCG2 can cause relapse, but data regarding the prevalence and natural history of these mutations are limited. Patients and Methods Patients accrued to four sequential studies of ibrutinib were included in these analyses. Deep sequencing for BTK and PLCG2 was performed retrospectively on patients who experienced relapse and prospectively on a screening population. Results With a median follow-up time of 3.4 years, the estimated cumulative incidence of progression at 4 years is 19% (95% CI, 14% to 24%). Baseline karyotypic complexity, presence of del(17)(p13.1), and age less than 65 years were risk factors for progression. Among patients who experienced relapse, acquired mutations of BTK or PLCG2 were found in 85% (95% CI, 71% to 94%), and these mutations were detected an estimated median of 9.3 months (95% CI, 7.6 to 11.7 months) before relapse. Of a group of 112 patients examined prospectively, eight patients have experienced relapse, and all of these patients had acquired resistance mutations before relapse. A resistance mutation was detected in an additional eight patients who have not yet met criteria for clinical relapse. Conclusion Relapse of chronic lymphocytic leukemia after ibrutinib is an issue of increasing clinical significance. We show that mutations in BTK and PLCG2 appear early and have the potential to be used as a biomarker for future relapse, suggesting an opportunity for intervention.

Evaluation of time-dependent toxicity and combined effects for a series of mono-halogenated acetonitrile-containing binary mixtures.

Mixture and time-dependent toxicity (TDT) was assessed for a series of mono-halogenated acetonitrile-containing combinations. Inhibition of bioluminescence in Aliivibrio fischeri was measured after 15, 30 and 45-min of exposure. Concentration-response (x/y) curves were determined for each chemical alone at each timepoint, and used to develop predicted x/y curves for the dose-addition and independence models of combined effect. The x/y data for each binary mixture was then evaluated against the predicted mixture curves. Two metrics of mixture toxicity were calculated per combined effect model: (1) an EC50-based dose-addition (AQ) or independence (IQ) quotient and (2) the mixture/dose-addition (MX/DA) and mixture/independence (MX/I) metrics. For each single chemical and mixture tested, TDT was also calculated. After 45-min of exposure, 25 of 67 mixtures produced curves that were consistent with dose-addition using the MX/DA metric, with the other 42 being less toxic than predicted by MX/DA. Some mixtures had toxicity that was consistent with both dose-addition and independence. In general, those that were less toxic than predicted for dose-addition were also less toxic than predicted for independence. Of the 25 combinations that were consistent with dose-addition, 22 (88%) mixtures contained chemicals for which the individual TDT values were both >80%. In contrast, of the 42 non-dose-additive combinations, only 2 (4.8%) of the mixtures had both chemicals with individual TDT values >80%. The results support previous findings that TDT determinations can be useful for predicting chemical mixture toxicity.

Time-dependence in mixture toxicity prediction.

The value of time-dependent toxicity (TDT) data in predicting mixture toxicity was examined. Single chemical (A and B) and mixture (A+B) toxicity tests using Microtox(®) were conducted with inhibition of bioluminescence (Vibrio fischeri) being quantified after 15, 30 and 45-min of exposure. Single chemical and mixture tests for 25 sham (A1:A2) and 125 true (A:B) combinations had a minimum of seven duplicated concentrations with a duplicated control treatment for each test. Concentration/response (x/y) data were fitted to sigmoid curves using the five-parameter logistic minus one parameter (5PL-1P) function, from which slope, EC25, EC50, EC75, asymmetry, maximum effect, and r(2) values were obtained for each chemical and mixture at each exposure duration. Toxicity data were used to calculate percentage-based TDT values for each individual chemical and mixture of each combination. Predicted TDT values for each mixture were calculated by averaging the TDT values of the individual components and regressed against the observed TDT values obtained in testing, resulting in strong correlations for both sham (r(2)=0.989, n=25) and true mixtures (r(2)=0.944, n=125). Additionally, regression analyses confirmed that observed mixture TDT values calculated for the 50% effect level were somewhat better correlated with predicted mixture TDT values than at the 25 and 75% effect levels. Single chemical and mixture TDT values were classified into five levels in order to discern trends. The results suggested that the ability to predict mixture TDT by averaging the TDT of the single agents was modestly reduced when one agent of the combination had a positive TDT value and the other had a minimal or negative TDT value.