Practical and Statistical Considerations for the Long Term Follow-Up of Gene Therapy Trial Participants.

Study sponsors and market authorization holders are required by the US Food and Drug Administration (FDA) and European Medicines Agency (EMA) to enroll patients administered a gene therapy product, whether in a trial setting or post-licensure, in a long term follow-up safety study to continue the safety assessments of their product. These follow-up studies range between 5 and 15 years after dosing. This unprecedented duration of engagement with patients and caregivers raises logistical challenges that will require innovation and collaboration across sponsors and regulators. In this paper we delineate some of the key considerations for designing long term follow-up protocols in the gene therapy setting, with an eye toward platform and master protocol approaches, and offer guidance for innovative operational and statistical methods that can help assess the safety profile and durability of response for these novel therapeutics.

Giroctocogene fitelparvovec gene therapy for severe hemophilia A: 104-week analysis of the phase 1/2 Alta study.

ABSTRACT: Patients with hemophilia A require exogenous factor VIII (FVIII) or nonfactor hemostatic agents to prevent spontaneous bleeding events. Adeno-associated virus (AAV) vector-based gene therapy is under clinical investigation to enable endogenous FVIII production. Giroctocogene fitelparvovec is a recombinant AAV serotype 6 vector containing the coding sequence for the B-domain-deleted human F8 gene. In the ongoing phase 1/2, dose-ranging Alta study, 4 sequential cohorts of male participants with severe hemophilia A received a single IV dose of giroctocogene fitelparvovec. The primary end points are safety and changes in circulating FVIII activity. Interim results up to 214 weeks after treatment for all participants are presented. Eleven participants were dosed. Increases in alanine and aspartate aminotransferases were the most common treatment-related adverse events (AEs), which resolved with corticosteroid administration. Two treatment-related serious AEs (hypotension and pyrexia) were reported in 1 participant within 6 hours of infusion and resolved within 24 hours after infusion. At the highest dose level (3 × 1013 vg/kg; n = 5), the mean circulating FVIII activity level at week 52 was 42.6% (range, 7.8%-122.3%), and at week 104 it was 25.4% (range, 0.9%-71.6%) based on a chromogenic assay. No liver masses, thrombotic events, or confirmed inhibitors were detected in any participant. These interim 104-week data suggest that giroctocogene fitelparvovec is generally well tolerated with appropriate clinical management and has the potential to provide clinically meaningful FVIII activity levels, as indicated by the low rate of bleeding events in the highest dose cohort. This trial was registered at www.clinicaltrials.gov as #NCT03061201.

Priority Outcomes in Sickle Cell Disease Treatment: Co-Creation and Implementation of a Preference Exercise With Patients and Caregivers to Inform Drug Development.

Involving patients as co-leaders and co-creators in research is key to reflecting the patient's voice in decision-making. However, co-creation of patient-centered data to inform decisions is rare, especially in early drug development where patient input is critical to prioritizing patient-relevant outcomes and endpoints for use in clinical trials. Despite the industry's growing commitment to patient centricity, most patients are excluded from sharing their expertise in research; more inclusive methods of engaging patients as research partners are needed. We describe a collaboration between a pharmaceutical company and a patient organization in co-leading and co-creating a program to understand priorities of patients and caregivers for treatment features and outcomes in sickle cell disease to inform endpoint selection in clinical development. The results of this program will be used as a basis for continued interaction between patients and the sponsor and to inform ongoing clinical development and evidence-generation activities. This case study demonstrates an approach to meaningful collaborations between patient organizations and pharmaceutical companies aimed at including the patient's voice early in the medical product lifecycle.

Evolution of Antidrug Antibody Assays During the Development of Anti-Tissue Factor Pathway Inhibitor Monoclonal Antibody Marstacimab.

Tissue factor pathway inhibitor (TFPI) is an endogenous inhibitor of the extrinsic coagulation pathway. In patients with hemophilia A or B, inhibition of TFPI is an alternative therapeutic approach that augments the extrinsic coagulation pathway. Marstacimab is an investigational fully human monoclonal antibody that binds and neutralizes TFPI and is being evaluated as a prophylactic treatment to prevent or reduce the frequency of bleeding episodes in patients with severe hemophilia A or B, with or without inhibitors (antibodies against coagulation factors). However, the efficacy, safety, and pharmacokinetics of marstacimab may be affected by the induction of antidrug antibody (ADA) responses. Here, we describe the evolution and validation of three quasi-quantitative electrochemiluminescence-based methods to detect marstacimab ADAs, starting from their use in a first-in-human phase 1 study to their use in phase 2 and 3 clinical studies of patients with severe hemophilia. For all three methods, validation criteria evaluated the performance of the assays in screening and confirmatory cut points, precision, selectivity, drug tolerance, target interference, and stability. Additional criteria for validation were dilution linearity (Methods 1 and 2) and low positive control concentration, prozone effect, plate homogeneity, and robustness (Method 3). The three methods met validation criteria and are a potentially valuable tool in detecting the induction of marstacimab ADAs during treatment in patients with hemophilia.

Long-term safety and efficacy of the anti-tissue factor pathway inhibitor marstacimab in participants with severe haemophilia: Phase II study results.

Marstacimab, an investigational human monoclonal antibody targeting tissue factor pathway inhibitor, demonstrated safety and efficacy in preventing bleeding episodes in patients with haemophilia. This multicentre, open-label study investigated safety, tolerability, and efficacy of long-term weekly prophylactic marstacimab treatment in participants with severe haemophilia A and B, with or without inhibitors. Adult participants were enrolled from a previous phase Ib/II study or de novo and assigned to one of two subcutaneous (SC) marstacimab doses: once-weekly 300 mg or a 300-mg loading dose followed by once-weekly 150-mg doses, for up to 365 days. Study end-points included safety assessments and annualised bleeding rates (ABRs). Of 20 enrolled participants, 18 completed the study. Overall, 70% of participants had treatment-emergent adverse events, including injection site reactions, injection site haematoma, and haemarthrosis. No treatment-related serious adverse events or thrombotic events occurred. Across all dose cohorts, mean and median on-study ABRs ranged from 0 to 3.6 and 0 to 2.5 bleeding episodes/participant/year respectively, demonstrating comparable efficacy to that observed in the short-term parent study. No treatment-induced anti-drug antibodies were detected. Once-weekly SC marstacimab prophylaxis was well tolerated, with an acceptable safety profile, and maintained long-term efficacy up to 365 days. (Clinicaltrials.gov identifier, NCT03363321).

A phase 1b/2 clinical study of marstacimab, targeting human tissue factor pathway inhibitor, in haemophilia.

A phase 1b/2, three-month study of marstacimab, a human monoclonal antibody targeting tissue factor pathway inhibitor (TFPI), was conducted in participants with haemophilia A or B, with or without inhibitors. Participants assigned to four cohorts received escalating weekly doses based on inhibitor status (without inhibitors: 300 mg, a single 300-mg loading dose with subsequent 150-mg doses, or 450 mg; with inhibitors: 300 mg). Safety outcomes were treatment-emergent adverse events (TEAEs), injection site reactions, clinical and laboratory parameter changes. Efficacy was assessed by annualised bleeding rates (ABRs). Pharmacokinetics and pharmacodynamics (PD) were also evaluated. Among 26 treated participants [haemophilia A without inhibitor, n = 16 (61.5%); haemophilia A with inhibitor, n = 7 (26.9%); haemophilia B, n = 3 (11.5%)], 24 completed the study. Overall, 80.8% experienced TEAEs. ABR during treatment was significantly reduced versus an external on-demand control group (p < 0.0001) and versus pretreatment ABR (p < 0.0001), with significant reductions observed across all dose cohorts. Marstacimab exposure generally increased in a dose-related manner, with steady-state concentration reached by day 57. Changes in pharmacodynamic biomarkers occurred across all dose cohorts. Marstacimab was safe and well tolerated. Clinically meaningful reductions in ABR and treatment-related changes for all PD biomarkers indicated effective targeting of TFPI. (Clinicaltrials.gov identifier, NCT02974855).

Validation of patient-reported vaso-occlusive crisis day as an endpoint in sickle cell disease studies.

Individuals with sickle cell disease (SCD) experience vaso-occlusive crises (VOC). Historically, VOC episodes have been assessed through medical utilization, thereby excluding events managed at home. In order to validate a daily patient-reported outcome for patients with SCD to accurately report their VOC status and experience of a pain crisis, a SCD Diary was included in Evaluation of Longitudinal Pain Study in Sickle Cell Disease (ELIPSIS), a longitudinal, six-month, non-interventional study. The daily patient-completed diary included a description of SCD pain crisis, followed by questions on: pain crisis in the past 24 h (VOC Day question; respective response yes or no), worst pain, tiredness, and functioning. Thirty-five patients with SCD participated in ELIPSIS. Analyses were performed to validate the patient-reported VOC Day. Mean symptoms and functioning scores on the first or last VOC Day of a VOC Event were compared using t-tests with the mean of the three non-VOC Days before and after the event. Mean severity of symptoms and functioning scores on all VOC Days compared to all non-VOC Days were higher, with statistically significant mean differences between first/last VOC Days and respective three non-VOC Days (p's < .01). A subset of patients (n = 15) and caregivers (n = 9) were interviewed to evaluate their understanding of the SCD Diary questions. Nearly all confirmed that the pain crisis description accurately described the VOC experience, and participants expressed confidence differentiating SCD crisis pain from everyday pain. These results demonstrate patients can reliably report their experiences with VOC-related pain crises using the SCD Diary.

Phase 1b Study to Evaluate Safety, Tolerability, and Maximum Tolerated Dose of PF-05230907 for Intracerebral Hemorrhage.

BACKGROUND AND PURPOSE: This study aimed to determine the maximum tolerated dose and to evaluate the overall safety and tolerability of single doses of PF-05230907 in subjects with acute intracerebral hemorrhage. METHODS: Individuals presenting with intracerebral hemorrhage were enrolled in a phase 1, multicenter, open-label clinical trial. A Bayesian modified continual reassessment method design based on treatment-emergent thromboembolic or ischemic events was adopted. Sequential dosing, an external data monitoring committee, and prespecified stopping rules were incorporated as safeguards. RESULTS: Twenty-one subjects received PF-05230907. The mean (±SD) age in years and intracerebral hemorrhage volume in mL at baseline were 62 (±9) and 18 (±11), respectively. Two treatment-emergent thromboembolic or ischemic events occurred (deep vein thrombosis and cerebral ischemia), in the 30 µg/kg dose group. There were no other clear drug-related toxicities at dose levels ranging from 5 to 30 µg/kg. At the time of study termination, the maximum tolerated dose was estimated to be 24 µg/kg, with a mean fitted dose-toxicity estimate of 11.9% (95% CI, 1.2%-27.4%). CONCLUSIONS: Single doses of PF-05230907 appeared to be tolerated across a range of doses in the intracerebral hemorrhage population, with thrombotic events observed only at the highest dose level tested. Recruitment within the recommended therapeutic window of opportunity remains a challenge. Registration: URL: https://www.clinicaltrials.gov. Unique identifier: NCT02687191.

Evaluation of biomarkers for monitoring thrombogenic potential of FXaI16L.

: A zymogen-like activated factor X variant (FXa) is being developed for treating acute bleeding conditions. Activated factor V is an essential cofactor to FXa for activating prothrombin to thrombin. Thrombi/emboli formation was observed microscopically in FXa toxicity studies in animals. The objective of this research was to evaluate candidate biomarkers for FXa-induced thrombi/emboli formation to inform safety monitoring and dose-escalation decisions in FXa clinical trials. Effects of intravenous FXa administration on platelets, fibrinogen, activated partial thromboplastin time (aPTT), prothrombin time (PT), D-dimer, tissue factor pathway inhibitor, thrombin : antithrombin complex, antithrombin, and factor V, and protein C (PC) activities were evaluated in mice, rats, and monkeys. Mice had endogenous factor V activity 10× that of monkeys and were overly sensitive to FXa-induced thrombi/emboli formation. In monkeys, decreases in fibrinogen and prolongation in aPTT and PT emerged as potential biomarkers for impending FXa-induced thrombi/emboli formation, based on association of changes with microscopically observable thrombi/emboli (0-97 thrombi/emboli per monkey). PC decreases, measured by a clot-based assay, were also observed. A similar reduction in PC activity, when measured by clot-based assay, was observed in a phase 1 clinical trial. However, an in-vitro experiment with human plasma spiked with increasing concentrations of FXa indicated dose-dependent FXa-induced interference with clot-based assays and no depletion of PC or S by FXa in non-clot-based assays. Nonclinical biomarker studies identified fibrinogen, aPTT and PT as potential biomarkers for monitoring the clinical safety of FXa. Results of clot-based assays with FXa treatment should be interpreted with caution.

Safety, Tolerability, Pharmacokinetics, and Pharmacodynamics of Domagrozumab (PF-06252616), an Antimyostatin Monoclonal Antibody, in Healthy Subjects.

Safety, tolerability, anabolic effects, pharmacokinetics, and pharmacodynamics of single ascending and multiple doses of domagrozumab, an antimyostatin monoclonal antibody, were assessed following intravenous (IV) and subcutaneous (SC) administration in healthy subjects. A range of single ascending dose levels between 1 and 40 mg/kg IV and multiple doses (3 doses) of 10 mg/kg IV were tested (n = 8 per cohort). Additionally, a 3 mg/kg SC (n = 8) cohort also received domagrozumab. Magnetic resonance imaging and whole-body dual-energy x-ray absorptiometry imaging were conducted to investigate the anabolic effects of domagrozumab. Domagrozumab was well tolerated with no severe and 1 non-treatment-related serious adverse event. The most commonly reported adverse events were headache (21 subjects) and fatigue, upper respiratory tract infections, and muscle spasms (10 subjects each). Domagrozumab demonstrated typical IgG1 pharmacokinetics, with slow SC absorption and slow clearance, low volume of distribution, and a long half-life. Target engagement was observed with an increase in extent of myostatin modulation, plateauing at the 20 mg/kg IV dose. Downstream pharmacology following myostatin binding by domagrozumab was only observed in the 10 mg/kg single IV cohort (increase in whole-body lean mass of 5.38% using dual-energy x-ray absorptiometry) and the 10 mg/kg repeat-dose cohort (muscle volume increase of 4.49% using magnetic resonance imaging).

Bosutinib versus Placebo for Autosomal Dominant Polycystic Kidney Disease.

Overactivation of Src has been linked to the pathogenesis of autosomal dominant polycystic kidney disease (ADPKD). This phase 2, multisite study assessed the efficacy and safety of bosutinib, an oral dual Src/Bcr-Abl tyrosine kinase inhibitor, in patients with ADPKD. Patients with ADPKD, eGFR≥60 ml/min per 1.73 m2, and total kidney volume ≥750 ml were randomized 1:1:1 to bosutinib 200 mg/d, bosutinib 400 mg/d, or placebo for ≤24 months. The primary endpoint was annualized rate of kidney enlargement in patients treated for ≥2 weeks who had at least one postbaseline magnetic resonance imaging scan that was preceded by a 30-day washout (modified intent-to-treat population). Of 172 enrolled patients, 169 received at least one study dose. Per protocol amendment, doses for 24 patients who initially received bosutinib at 400 mg/d were later reduced to 200 mg/d. The annual rate of kidney enlargement was reduced by 66% for bosutinib 200 mg/d versus placebo (1.63% versus 4.74%, respectively; P=0.01) and by 82% for pooled bosutinib versus placebo (0.84% versus 4.74%, respectively; P<0.001). Over the treatment period, patients receiving placebo or bosutinib had similar annualized eGFR decline. Gastrointestinal and liver-related adverse events were the most frequent toxicities. In conclusion, compared with placebo, bosutinib at 200 mg/d reduced kidney growth in patients with ADPKD. The overall gastrointestinal and liver toxicity profile was consistent with the profile in prior studies of bosutinib; no new toxicities were identified. (ClinicalTrials.gov: NCT01233869).

Safety and efficacy of bosutinib (SKI-606) in chronic phase Philadelphia chromosome-positive chronic myeloid leukemia patients with resistance or intolerance to imatinib.

Bosutinib, a dual Src/Abl kinase inhibitor, has shown potent activity against chronic myeloid leukemia (CML). In this phase 1/2 study we evaluated bosutinib in patients with chronic phase imatinib-resistant or imatinib-intolerant CML. Part 1 was a dose-escalation study to determine the recommended starting dose for part 2; part 2 evaluated the efficacy and safety of bosutinib 500 mg once-daily dosing. The study enrolled 288 patients with imatinib-resistant (n = 200) or imatinib-intolerant (n = 88) CML and no other previous kinase inhibitor exposure. At 24 weeks, 31% of patients achieved major cytogenetic response (primary end point). After a median follow-up of 24.2 months, 86% of patients achieved complete hematologic remission, 53% had a major cytogenetic response (41% had a complete cytogenetic response), and 64% of those achieving complete cytogenetic response had a major molecular response. At 2 years, progression-free survival was 79%; overall survival at 2 years was 92%. Responses were seen across Bcr-Abl mutants, except T315I. Bosutinib exhibited an acceptable safety profile; the most common treatment-emergent adverse event was mild/moderate, typically self-limiting diarrhea. Grade 3/4 nonhematologic adverse events (> 2% of patients) included diarrhea (9%), rash (9%), and vomiting (3%). These data suggest bosutinib is effective and tolerable in patients with chronic phase imatinib-resistant or imatinib-intolerant CML. This trial was registered at http://www.clinicaltrials.gov as NCT00261846.

Upregulated ATM gene expression and activated DNA crosslink-induced damage response checkpoint in Fanconi anemia: implications for carcinogenesis.

Fanconi anemia (FA) predisposes to hematopoietic failure, birth defects, leukemia, and squamous cell carcinoma of the head and neck (HNSCC) and cervix. The FA/BRCA pathway includes 8 members of a core complex and 5 downstream gene products closely linked with BRCA1 or BRCA2. Precancerous lesions are believed to trigger the DNA damage response (DDR), and we focused on the DDR in FA and its putative role as a checkpoint barrier to cancer. In primary fibroblasts with mutations in the core complex FANCA protein, we discovered that basal expression and phosphorylation of ATM (ataxia telangiectasia mutated) and p53 induced by irradiation (IR) or mitomycin C (MMC) were upregulated. This heightened response appeared to be due to increased basal levels of ATM in cultured FANCA-mutant cells, highlighting the new observation that ATM can be regulated at the transcriptional level in addition to its well-established activation by autophosphorylation. Functional analysis of this response using gamma-H2AX foci as markers of DNA double-stranded breaks (DSBs) demonstrated abnormal persistence of only MMC- and not IR-induced foci. Thus, we describe a processing defect that leads to general DDR upregulation but specific persistence of DNA crosslinker-induced damage response foci. Underscoring the significance of these findings, we found resistance to DNA crosslinker-induced cell cycle arrest and apoptosis in a TP53-mutant, patient-derived HNSCC cell line, whereas a lymphoblastoid cell line derived from this same individual was not mutated at TP53 and retained DNA crosslinker sensitivity. Our results suggest that cancer in FA may arise from selection for cells that escape from a chronically activated DDR checkpoint.