Model-Informed Approaches and Innovative Clinical Trial Design for Adeno-Associated Viral Vector-Based Gene Therapy Product Development: A White Paper.

The promise of viral vector-based gene therapy (GT) as a transformative paradigm for treating severely debilitating and life-threatening diseases is slowly coming to fruition with the recent approval of several drug products. However, they have a unique mechanism of action often necessitating a tortuous clinical development plan. Expertise in such complex therapeutic modality is still fairly limited in this emerging class of adeno-associated virus (AAV) vector-based gene therapies. Because of the irreversible mode of action and incomplete understanding of genotype-phenotype relationship and disease progression in rare diseases careful considerations should be given to GT product's benefit-risk profile. In particular, special attention needs to be paid to safe dose selection, reliable dose exposure response (including clinically relevant endpoints), or creative approaches in study design targeting small patient populations during clinical development. We believe that quantitative tools encompassed within model-informed drug development (MIDD) framework fits quite well in the development of such novel therapies, as they enable us to benefit from the totality of data approach in order to support dose selection as well as optimize clinical trial designs, end point selection, and patient enrichment. In this thought leadership paper, we provide our collective experiences, identify challenges, and suggest areas of improvement in applications of modeling and innovative trial design in development of AAV-based GT products and reflect on the challenges and opportunities for incorporating MIDD tools and more in rational development of these products.

Population pharmacokinetics, pharmacodynamics and pharmacogenetics modelling of oxypurinol in Hmong adults with gout and/or hyperuricemia.

AIMS: The aim of this study was to quantify identifiable sources of variability, including key pharmacogenetic variants in oxypurinol pharmacokinetics and their pharmacodynamic effect on serum urate (SU). METHODS: Hmong participants (n = 34) received 100 mg allopurinol twice daily for 7 days followed by 150 mg allopurinol twice daily for 7 days. A sequential population pharmacokinetic pharmacodynamics (PKPD) analysis with non-linear mixed effects modelling was performed. Allopurinol maintenance dose to achieve target SU was simulated based on the final PKPD model. RESULTS: A one-compartment model with first-order absorption and elimination best described the oxypurinol concentration-time data. Inhibition of SU by oxypurinol was described with a direct inhibitory Emax model using steady-state oxypurinol concentrations. Fat-free body mass, estimated creatinine clearance and SLC22A12 rs505802 genotype (0.32 per T allele, 95% CI 0.13, 0.55) were found to predict differences in oxypurinol clearance. Oxypurinol concentration required to inhibit 50% of xanthine dehydrogenase activity was affected by PDZK1 rs12129861 genotype (-0.27 per A allele, 95% CI -0.38, -0.13). Most individuals with both PDZK1 rs12129861 AA and SLC22A12 rs505802 CC genotypes achieve target SU (with at least 75% success rate) with allopurinol below the maximum dose, regardless of renal function and body mass. In contrast, individuals with both PDZK1 rs12129861 GG and SLC22A12 rs505802 TT genotypes would require more than the maximum dose, thus requiring selection of alternative medications. CONCLUSIONS: The proposed allopurinol dosing guide uses individuals' fat-free mass, renal function and SLC22A12 rs505802 and PDZK1 rs12129861 genotypes to achieve target SU.

The frequency of rs2231142 in ABCG2 among Native Hawaiian and Pacific Islander subgroups: implications for personalized rosuvastatin dosing.

Statins are among the most commonly prescribed medications worldwide. Rosuvastatin is a moderate- to high-intensity statin depending on the prescribed dose. Statin-associated muscle symptoms are the main side effects, contributing to low adherence to statins. The missense variant rs2231142 in ABCG2 affects the functionality of the ABCG2 transporter, altering the pharmacokinetics and pharmacodynamics of rosuvastatin. This special report aims to accentuate the importance of considering the ABCG2 genotype upon prescribing rosuvastatin in high cardiovascular disease risk subgroups, specifically Native Hawaiian and Pacific Islander populations. Based on the reported frequencies of rs2231142 in ABCG2, it may be justifiable to initiate low-dose rosuvastatin in Samoans relative to Marshallese or Native Hawaiians. Interpopulation differences in pharmacogenetic allele frequencies underscore the need to disaggregate broad population categories to achieve health equity in treatment outcomes.

Rosuvastatin is a medication that is used to decrease levels of bad cholesterol in the blood. One of the side effects of rosuvastatin is muscle aches, which can cause patients to stop taking their medication. ABCG2 is a gene responsible for encoding ABCG2, an important transporter that plays a role in how the body interacts with many medications, including rosuvastatin. Genetic variations in ABCG2 result in a functional or nonfunctional transporter. This special report aims to focus on the importance of considering genetic variations in ABCG2 among different population subgroups, in particular Native Hawaiians, Samoans and Marshallese. The ABCG2 genotype could inform clinicians about the most effective rosuvastatin dose to prescribe. This approach highlights the importance of individualized patient characteristics above and beyond race and ethnicity.

The frequency of rs2231142 in ABCG2 among Asian subgroups: implications for personalized rosuvastatin dosing.

Statins are widely used medications for the primary and secondary prevention of cardiovascular diseases. Statin-induced musculoskeletal symptoms are the primary adverse drug events contributing to poor adherence to lipid-lowering therapy. Rosuvastatin is characterized by interindividual differences in systemic exposure among different patient population subgroups. The missense variant Q141K within ABCG2, highly prevalent in some Asian subgroups, results in decreased transporter efflux function and increased exposure to rosuvastatin. We aim to highlight the implications of ABCG2 genotype in prescribing rosuvastatin and the ramifications of interpopulation differences in Q141K frequencies in the starting dose of rosuvastatin in major Asian subgroups, using the most recent genetic-based guidelines. The high frequency of Q141K in Filipinos could warrant a lower starting rosuvastatin dose versus non-Filipinos. The Q141K genotype frequencies in Asian subgroups suggest significant interpopulation differences, reinforcing the need to move beyond race-based to genotype-based rosuvastatin dosing.

Rosuvastatin, a commonly prescribed cholesterol-lowering drug, has differences in response between different population subgroups. Rosuvastatin may also cause muscle pains, contributing to low adherence to the medication. Asians have a significantly high frequency of genetic variation (Q141K) within ABCG2, a critical rosuvastatin-efflux pump, leading to less functional transporter and higher drug levels. This special report highlights the role of ABCG2 genotyping in prescribing rosuvastatin. Also, it describes the consequences of between-population differences in the Q141K frequency in deciding the starting dose in individuals of Asian background, using the most recent genetic-based guidelines. Among different Asian subgroups, Filipinos have the highest Q141K polymorphism frequency and are more likely to require a lower starting dose of rosuvastatin than other Asians. Knowledge of the Q141K frequency in different Asian subgroups could drive individualized rosuvastatin dosing and reduce racial disparities in drug safety and efficacy.

Cardiometabolic genomics and pharmacogenomics investigations in Filipino Americans: Steps towards precision health and reducing health disparities.

Background: Filipino Americans (FAs) are the third-largest Asian American subgroup in the United States (US). Some studies showed that FAs experience more cardiometabolic diseases (CMDs) than other Asian subgroups and non-Hispanic Whites. The increased prevalence of CMD observed in FAs could be due to genetics and social/dietary lifestyles. While FAs are ascribed as an Asian group, they have higher burdens of CMD, and adverse social determinants of health compared to other Asian subgroups. Therefore, studies to elucidate how FAs might develop CMD and respond to medications used to manage CMD are warranted. The ultimate goals of this study are to identify potential mechanisms for reducing CMD burden in FAs and to optimize therapeutic drug selection. Collectively, these investigations could reduce the cardiovascular health disparities among FAs. Rationale and design: This is a cross-sectional epidemiological design to enroll 300 self-identified Filipino age 18 yrs. or older without a history of cancer and/or organ transplant from Virginia, Washington DC, and Maryland. Once consented, a health questionnaire and disease checklist are administered to participants, and anthropometric data and other vital signs are collected. When accessible, we collect blood samples to measure basic blood biochemistry, lipids, kidney, and liver functions. We also extract DNA from the blood or saliva for genetic and pharmacogenetic analyses. CMD prevalence in FAs will be compared to the US population. Finally, we will conduct multivariate analyses to ascertain the role of genetic and non-genetic factors in developing CMD in FAs. Virginia Commonwealth University IRB approved all study materials (Protocol HM20018500). Summary: This is the first community-based study to involve FAs in genomics research. The study is actively recruiting participants. Participant enrollment is ongoing. At the time of this publication, the study has enrolled 97 participants. This ongoing study is expected to inform future research to reduce cardiovascular health disparities among FAs.

Challenges in pharmacotherapy for older adults: a framework for pharmacogenomics implementation.

Older adults are at high risk for inappropriate prescribing, developing polypharmacy, adverse drug events and poor treatment outcomes due to multimorbidity and geriatric syndromes. Pharmacogenomics could allow healthcare professionals to provide optimal patient care while minimizing the risk of adverse drug events and simplifying complex medication regimens. The implementation of pharmacogenomics in geriatrics medicine requires a broad multilayered bottom-up approach. These include curriculum redesign, rethinking experiential education and patient and provider education. There are barriers associated with adopting pharmacogenomics into clinical practice. These barriers may include economic factors, workflow and informatics support. However, addressing these barriers primarily requires creating a culture of innovative practices in patient care, ongoing interprofessional continuing education and an interdisciplinary approach for patient care.

HLA-B*58: 01 carrier status of Hmong in Minnesota: first in Hmong genotyping for prevalence of this biomarker of risk for severe cutaneous adverse reactions caused by allopurinol.

Allopurinol, a common medication to treat gout, is associated with severe cutaneous adverse reactions, and the occurrence is highly predicted by an individual's HLA-B*58:01 carrier status. Guidelines endorse preemptive testing in select Asian populations before initiating allopurinol. The Hmong, an Asian subpopulation originally from China who now live dispersed around the world, have a 2.5-fold higher risk of gout when compared to non-Hmong in Minnesota. Given the concern for severe cutaneous adverse reactions when prescribing allopurinol, we quantified the carrier status of HLA-B*58:01 in Hmong from two independent cohorts in Minnesota. Using a community-based participatory research approach, HLA-B*58:01 carrier status was determined in 49 US-born Hmong without a history of gout or allopurinol use. Further, 47 Hmong patients undergoing clinical evaluation to receive gout pharmacotherapy were also tested. The frequency of HLA-B*58:01 positive carrier status in these two cohorts were compared to published data from a Han Chinese (n = 2910) and a Korean cohort (n = 485) using a Fisher's exact test with a Bonferroni-corrected P-value <0.025 for significance. With one uninterpretable result, we identified two out of 95 people (2.1%) who carried HLA-B*58:01. This 2.1% incidence in these Hmong adults is notably lower than Han Chinese (19.6%, P < 0.0001) and Korean (12.2%, P = 0.0016) populations. Though commonly understood to be of Chinese descent, the lower prevalence within the Hmong underscores the risk of generalizing genotypic findings from Chinese to Asian subpopulations. We suggest no change to the current guidelines recommending which populations should be tested for HLA-B*58:01 before allopurinol use until further validation.