The utility of exome sequencing in diagnosing pediatric neurodevelopmental disorders in a highly consanguineous population.

Exome sequencing (ES) has been utilized in diagnosing children with neurodevelopmental manifestations, this study aimed to investigate the utility of ES in children within a highly consanguineous population that presented with neurodevelopmental complaints. A retrospective chart review was performed for 405 children with neurodevelopmental complaints who have had ES and were evaluated in multiple centers in the United Arab Emirates over a four-year period. Within the cohort of 405 children, consanguinity was reported in 35% (144/405). The primary clinical presentations were developmental delay/cognitive impairment, distinctive facial features, hypotonia, seizures, and weakness. The diagnostic yield was 57% (231/405). Novel variants were identified in 54% (125/231) of positive cases. Within the positive cases, specific treatment was available in 6% (13/231) and copy number variants (CNV) were reported in 3% (8/231) of cases. In eight children, variants in genes that have not yet been linked to human disease that could potentially be the cause of the observed phenotype "candidate genes" were identified. ES was utilized effectively within this cohort with a high diagnostic yield and through the identification of novel gene variants, CNVs, candidate genes and secondary findings as well as the alteration of the treatment plan in cases where treatment was available.

Development of a multiscale mechanistic modeling framework integrating differential cellular kinetics of CAR T-cell subsets and immunophenotypes in cancer patients.

Chimeric antigen receptor (CAR) T-cell subsets and immunophenotypic composition of the pre-infusion product, as well as their longitudinal changes following infusion, are expected to affect CAR T-cell expansion, persistence, and clinical outcomes. Herein, we sequentially evolved our previously described cellular kinetic-pharmacodynamic (CK-PD) model to incorporate CAR T-cell product-associated attributes by utilizing published preclinical and clinical datasets from two affinity variants (FMC63 and CAT19 scFv) anti-CD19 CAR T-cells. In step 1, a unified cell-level PD model was used to simultaneously characterize the in vitro killing datasets of two CAR T-cells against CD19+ cell lines at varying effector:target ratios. In step 2, an augmented CK-PD model for anti-CD19 CAR T-cells was developed, by integrating CK dataset(s) from two bioanalytical measurements (quantitative polymerase chain reaction and flow cytometry) in patients with cancer. The model described the differential in vivo expansion properties of CAR T-cell subsets. The estimated expansion rate constant was ~1.12-fold higher for CAR+CD8+ cells in comparison to CAR+CD4+ T-cells. In step 3, the model was extended to characterize the disposition of four immunophenotypic populations of CAR T-cells, including stem-cell memory, central memory, effector memory, and effector cells. The model adequately characterized the longitudinal changes in immunophenotypes post anti-CD19 CAR T-cell infusion in pediatric patients with acute lymphocytic leukemia. Polyclonality in the pre-infusion product was identified as a categorical covariate influencing differentiation of immunophenotypes. In the future, this model could be leveraged a priori toward optimizing the composition of CAR T-cell infusion product, and further understand the CK-PD relationship in patients.

From Cold to Hot: Changing Perceptions and Future Opportunities for Quantitative Systems Pharmacology Modeling in Cancer Immunotherapy.

Immuno-oncology (IO) is a fast-expanding field due to recent success using IO therapies in treating cancer. As IO therapies do not directly kill tumor cells but rather act upon the patients' own immune cells either systemically or in the tumor microenvironment, new and innovative approaches are required to inform IO therapy research and development. Quantitative systems pharmacology (QSP) modeling describes the biological mechanisms of disease and the mode of action of drugs with mathematical equations, which has significant potential to address the big challenges in the IO field, from identifying patient populations that respond to different therapies to guiding the selection, dosing, and scheduling of combination therapy. To assess the perspectives of the community on the impact of QSP modeling in IO drug development and to understand current applications and challenges, the IO QSP working group-under the QSP Special Interest Group (SIG) of the International Society of Pharmacometrics (ISoP)-conducted a survey among QSP modelers, non-QSP modelers, and non-modeling IO program stakeholders. The survey results are presented here with discussions on how to address some of the findings. One of the findings is the differences in perception among these groups. To help bridge this perception gap, we present several case studies demonstrating the impact of QSP modeling in IO and suggest actions that can be taken in the future to increase the real and perceived impact of QSP modeling in IO drug research and development.

Development of minimal physiologically-based pharmacokinetic-pharmacodynamic models for characterizing cellular kinetics of CAR T cells following local deliveries in mice.

Chimeric antigen receptor (CAR) T cell therapies have revolutionized the treatment of hematologic malignancies and have potentials for solid tumor treatment. To overcome limited CAR T cell infiltration to solid tumors, local delivery of CAR T cells is a practical strategy that has shown promising therapeutic outcome and safety profile in the clinic. It is of great interest to understand the impact of dosing routes on CAR T cell distribution, subsequent proliferation and tumor killing in a quantitative manner to identify key factors that contribute to CAR T efficacy and safety. In this study, we established mouse minimal physiologically-based pharmacokinetic (mPBPK) models combined with pharmacodynamic (PD) components to delineate CAR T cell distribution, proliferation, tumor growth, and tumor cell killing in the cases of pleural and liver tumors. The pleural tumor model reasonably captured published CAR T cellular kinetic and tumor growth profiles in mice. The mPBPK-PD simulation of a liver tumor mouse model showed a substantial increase in initial tumor infiltration and earlier CAR T cell proliferation with local hepatic artery delivery compared to portal vein and intravenous (i.v.) injections whereas portal vein injection showed little difference from i.v. administration, suggesting the importance of having the injection site close to tumor for maximal effect of non-systemic administration. Blood flow rate in the liver tumor was found to be a sensitive parameter for cellular kinetics and efficacy, indicating a potential role of tumor vascularization in the efficacy of CAR T cell therapies.

Scleral Buckling Alone or in Combination with Pars Plana Vitrectomy for Rhegmatogenous Retinal Detachment Repair: A Meta-Analysis of 7,212 Eyes.

PURPOSE: The efficacy and safety of scleral buckling (SB) versus combination SB and pars plana vitrectomy (SB + PPV) for rhegmatogenous retinal detachment (RRD) repair remains unclear. METHODS: A systematic review and meta-analysis was conducted to identify comparative studies published from Jan 2000-Jun 2021 that reported on the efficacy and/or safety following SB and SB + PPV for RRD repair. Final best-corrected visual acuity (BCVA) represented the primary endpoint, while reattachment rates and ocular adverse events were secondary endpoints. A random-effects meta-analysis was performed, and 95% confidence intervals were calculated. RESULTS: Across 18 studies, 3912 SB and 3300 SB + PPV eyes were included. Final BCVA was nonsignificantly different between SB and SB + PPV (20/38 vs. 20/66 Snellen; WMD = -0.11 LogMAR; 95% CI: [-0.29, 0.07]; p = 0.23). Primary reattachment rate was similar between procedures (p = 0.74); however, SB alone achieved a significantly higher final reattachment rate (97.40% vs. 93.86%; RR = 1.03; 95% CI: [1.00, 1.06]; p = 0.04). Compared to SB + PPV, SB alone had a significantly lower risk of postoperative macular edema (RR = 0.69; 95% CI: [0.47, 1.00]; p = 0.05) and cataract formation (RR = 0.34; 95% CI: [0.12, 0.96]; p = 0.04). The incidence of macular hole, epiretinal membrane, residual subretinal fluid, proliferative vitreoretinopathy, elevated intraocular pressure, and extraocular muscle dysfunction were similar between SB and SB + PPV. CONCLUSIONS: There was no significant difference in final BCVA between SB + PPV and SB alone in RRD. SB alone offers a slightly higher final reattachment rate along with a reduced risk of macular edema and cataract. Primary reattachment rate and the incidence of other complications were similar between the two procedures.

Pars Plana Vitrectomy with and without Supplemental Scleral Buckle for the Repair of Rhegmatogenous Retinal Detachment: A Meta-analysis.

TOPIC: It is unclear whether there are differences in safety and efficacy between pars plana vitrectomy (PPV) alone and PPV with a supplemental scleral buckle (SB; PPV-SB) for the treatment of rhegmatogenous retinal detachment. CLINICAL RELEVANCE: This meta-analysis aimed to compare the safety and efficacy of these surgical procedures. METHODS: In this meta-analysis, Ovid MEDLINE, Embase, and Cochrane Library were systematically searched (January 2000-June 2021). The primary outcome was the final best corrected visual acuity (BCVA), whereas the secondary outcomes were reattachment rates and complications. The risk of bias was assessed using the Cochrane risk-of-bias tool for randomized controlled trials (RCTs) and the risk of bias in nonrandomized studies of interventions tool for nonrandomized studies. RESULTS: This study included 15 661 eyes from 38 studies (32 observational studies and 6 RCTs). The median follow-up duration was 6 months. The final BCVA was similar between PPV and PPV-SB (weighted mean difference [WMD], -0.03 logarithm of the minimum angle of resolution [-0.14 to 0.07]; P = 0.55). There was a significant difference in the single-operation success rate (SOSR) (88.2% versus 86.3%; relative risk [RR], 0.97 [0.95-1.00]; P = 0.03), favoring PPV-SB; however, there was no significant difference in the final reattachment rate (RR, 1.00 [0.99-1.01]; P = 0.56). Pars plana vitrectomy required a significantly higher number of operations to achieve final anatomical reattachment (WMD, 0.13 [0.02-0.24]; P = 0.02). In terms of complications, PPV was significantly less likely to be associated with macular edema (RR, 0.47 [0.25-0.88]; P = 0.02) and epiretinal membrane formation (RR, 0.70 [0.52-0.94]; P = 0.02), but these differences were no longer significant in studies published after 2010 or in RCTs. Significant proliferative vitreoretinopathy, lens status, and macular attachment status did not mediate differences in these effects. CONCLUSIONS: There were no significant differences in the final visual acuity outcomes between PPV and PPV-SB. Pars plana vitrectomy with supplemental SB was associated with a greater SOSR than standalone PPV, although the magnitude of the effect was small, with a high number needed to treat. The final reattachment rate was similar. In recent studies and in RCTs, the risk of complications was similar between the procedures.

Supply and demographic characteristics of Ontario's ophthalmologists from 2010 to 2019: a population-based analysis.

BACKGROUND: With an aging population in Ontario, ophthalmologists provide most of their care to older adults, which has prominent human resource implications. In this study, we sought to investigate the supply and demographic characteristics of Ontario's ophthalmologists. METHODS: In this retrospective, population-based analysis, we evaluated cohort demographics, including sex and career stage, of Ontario's ophthalmologists from 2010 to 2019, which we reported using descriptive statistics. Similarly, we detailed ophthalmologist supply within different areas of care using descriptive statistics. RESULTS: Over the study period, a median of 464 ophthalmologists were practising in Ontario each year. The proportion of female ophthalmologists increased from 18.7% in 2010 to 24.1% in 2019. The proportion of late-career ophthalmologists (aged > 55 yr) significantly increased by 6.4% over the study period and constituted 45.3% of the workforce in 2019. Comprehensive cataract surgery was the most common area of care. Although the number of ophthalmologists per 100 000 people remained stable over the study period (3.27 ophthalmologists/100 000 people in 2019), the number of ophthalmologists per 100 000 people aged 65 years and older fell by 18.4% from 2010 to 2019. The greatest supply reduction was among moderate-volume comprehensive cataract surgeons (-20.2% overall and -35.4% relative to the population aged ≥ 65 yr). INTERPRETATION: Between 2010 and 2019, the overall number of ophthalmologists in Ontario remained stable; however, we observed declines in the number of ophthalmologists per 100 000 people aged 65 years and older for most areas of care. Nearly half of the ophthalmology workforce is now older than 55 years and female representation is increasing.

Combination intravitreal anti-vascular endothelial growth factor inhibitors and macular laser photocoagulation relative to intravitreal injection monotherapy in macular oedema secondary to retinal vein occlusion: a meta-analysis of randomized controlled trials.

BACKGROUND/OBJECTIVES: This meta-analysis investigates the efficacy and safety of intravitreal anti-VEGF injections (IVI) compared to combination laser photocoagulation and IVI (LPC-IVI) in treating macular oedema secondary to retinal vein occlusion (RVO). SUBJECTS/METHODS: A literature search of MEDLINE, EMBASE and Cochrane CENTRAL was conducted from inception until March 2021. Randomized controlled trials that reported relevant efficacy and/or safety parameters following LPC-IVI relative to IVI were included. Meta-analysis was conducted with a random effects model. The primary outcome was best-corrected visual acuity (BCVA), while secondary outcomes were central macular thickness (CMT), central retinal thickness (CRT), central subfield thickness (CST), number of IVIs received, and incidence of adverse events. RESULTS: A total of 10 studies were included, for which 362 eyes were randomized to LPC-IVI and 365 to IVI. In comparing macular laser photocoagulation with IVI (MLP-IVI) in BRVO patients, no significant differences were seen in final BCVA (p = 0.78) or change in BCVA (p = 0.09) after treatment. Similarly, no significant differences were seen in final CMT (p = 0.54), change in CMT (p = 0.33), final CRT (p = 0.90), change in CRT (p = 0.97), or number of injections required (p = 0.78). The same results were seen in subgroup analyses for macular laser without peripheral laser in BRVO and CRVO patients. Consistent results were observed when considering peripheral LPC-IVI to IVI in BRVO and CRVO. CONCLUSIONS: No significant differences were seen between combination MLP-IVI or peripheral LPC-IVI relative to IVI monotherapy for final BCVA or OCT parameters in macular oedema secondary to RVO.

Pars plana vitrectomy versus scleral buckle: A comprehensive meta-analysis of 15,947 eyes.

Pars plana vitrectomy (PPV) and scleral buckling (SB) are two of the most common surgical treatments for rhegmatogenous retinal detachment (RRD). This meta-analysis compares the efficacy and safety of PPV and SB for RRD. A systematic literature review was performed using Ovid MEDLINE, EMBASE and Cochrane CENTRAL from 2000 to June, 2021. Comparative studies, randomized controlled trials and observational studies investigating PPV and SB for RRD repair were included. The primary endpoint was final best- corrected visual acuity (BCVA). Secondary endpoints were reattachment rates, total operation time, and incidence of adverse events. Subgroup analyses including phakic status, presence of PVR-C or greater at baseline, and macular attachment status were conducted. Across 41 studies (8 RCTs, 33 observational studies), 5,401 SB and 10,546 PPV eyes were included. SB achieved a statistically significant, but likely not clinically significant, better final BCVA than PPV (0.38 ± 0.53 vs. 0.33 ± 0.53 logMAR (20/48 vs. 20/43 Snellen); weighted mean difference [WMD]: 0.07; 95% confidence interval: [0.02-0.11]; P = 0.005). SB had a better final BCVA compared to PPV in observational studies (P = 0.007) but not in RCTs (P = 0.21). SB had a lower incidence of post-operative cataract formation (P < 0.00001) and iatrogenic breaks (P < 0.00001), but a higher incidence of choroidal/subretinal hemorrhage (P = 0.007), choroidal detachment (P = 0.004), and residual subretinal fluid (RSRF) (P < 0.00001). Primary (86.5% vs. 84.8%; P = 0.13) and final (96.7% vs. 97.7%; P = 0.12) reattachment rates were similar between PPV and SB. PPV had a significantly higher primary reattachment rate in RCTs (P = 0.02) but not in observational studies (P = 0.30). SB was associated with a better final BCVA than PPV; however, this result was primarily driven by observational studies and phakic patients who developed cataracts. Primary and final reattachment rates were similar between the comparators. SB was associated with a significantly lower incidence of iatrogenic breaks and cataracts, while PPV was associated with a reduced risk of choroidal detachment, subretinal hemorrhage, and RSRF.

Empty Sella in Neuro-Ophthalmology Patients Without Raised Intracranial Pressure.

BACKGROUND: Empty sella often supports a diagnosis of raised intracranial pressure (ICP) but is also seen in normal individuals. This study's objective was to determine the prevalence of empty and partially empty sella in neuro-ophthalmology patients undergoing MRI for indications other than papilledema or raised ICP. METHODS: Consecutive patients without papilledema or suspected raised ICP who underwent brain MRI between August 2017 and May 2021 were included in this study. Sagittal T1 images were evaluated by 2 independent, blinded neuroradiologists who graded the sella using the published criteria (Categories 1-5, with 1 being normal and 5 showing no visible pituitary tissue). Clinical parameters were also collected. RESULTS: A total of 613 patients (309 men; average age 56.69 ± 18.06 years) were included in this study with optic neuropathy as the most common MRI indication. A total of 176 patients had moderate concavity of the pituitary gland (Category 3), 81 had severe concavity (Category 4), and 26 had no visible pituitary tissue (Category 5). Sella appearance was mentioned in 92 patients' radiology reports (15%). There was a statistically significant difference in age between composite Categories 1 and 2 (mean 52.89 ± 18.91; P < 0.001) and composite Categories 4 and 5 (mean 63.41 ± 15.44), but not the other clinical parameters. CONCLUSION: Empty sella is common in neuro-ophthalmology patients without raised ICP; 17.4% of patients have severe concavity or no pituitary tissue visible. An isolated finding of empty or partially empty sella on imaging is therefore of questionable clinical value in this patient population.

Bench-to-bedside translation of chimeric antigen receptor (CAR) T cells using a multiscale systems pharmacokinetic-pharmacodynamic model: A case study with anti-BCMA CAR-T.

Despite tremendous success of chimeric antigen receptor (CAR) T cell therapy in clinical oncology, the dose-exposure-response relationship of CAR-T cells in patients is poorly understood. Moreover, the key drug-specific and system-specific determinants leading to favorable clinical outcomes are also unknown. Here we have developed a multiscale mechanistic pharmacokinetic (PK)-pharmacodynamic (PD) model for anti-B-cell maturation antigen (BCMA) CAR-T cell therapy (bb2121) to characterize (i) in vitro target cell killing in multiple BCMA expressing tumor cell lines at varying effector to target cell ratios, (ii) preclinical in vivo tumor growth inhibition and blood CAR-T cell expansion in xenograft mice, and (iii) clinical PK and PD biomarkers in patients with multiple myeloma. Our translational PK-PD relationship was able to effectively describe the commonly observed multiphasic CAR-T cell PK profile in the clinic, consisting of the rapid distribution, expansion, contraction, and persistent phases, and accounted for the categorical individual responses in multiple myeloma to effectively calculate progression-free survival rates. Preclinical and clinical data analysis revealed comparable parameter estimates pertaining to CAR-T cell functionality and suggested that patient baseline tumor burden could be more sensitive than dose levels toward overall extent of exposure after CAR-T cell infusion. Virtual patient simulations also suggested a very steep dose-exposure-response relationship with CAR-T cell therapy and indicated the presence of a "threshold" dose, beyond which a flat dose-response curve could be observed. Our simulations were concordant with multiple clinical observations discussed in this article. Moving forward, this framework could be leveraged a priori to explore multiple infusions and support the preclinical/clinical development of future CAR-T cell therapies.

Model-Based Cellular Kinetic Analysis of Chimeric Antigen Receptor-T Cells in Humans.

Chimeric antigen receptor (CAR)-T cell therapy has achieved considerable success in treating B-cell hematologic malignancies. However, the challenges of extending CAR-T therapy to other tumor types, particularly solid tumors, remain appreciable. There are substantial variabilities in CAR-T cellular kinetics across CAR-designs, CAR-T products, dosing regimens, patient responses, disease types, tumor burdens, and lymphodepletion conditions. As a "living drug," CAR-T cellular kinetics typically exhibit four distinct phases: distribution, expansion, contraction, and persistence. The cellular kinetics of CAR-T may correlate with patient responses, but which factors determine CAR-T cellular kinetics remain poorly defined. Herein, we developed a cellular kinetic model to retrospectively characterize CAR-T kinetics in 217 patients from 7 trials and compared CAR-T kinetics across response status, patient populations, and tumor types. Based on our analysis results, CAR-T cells exhibited a significantly higher cell proliferation rate and capacity but a lower contraction rate in patients who responded to treatment. CAR-T cells proliferate to a higher degree in hematologic malignancies than in solid tumors. Within the assessed dose ranges (107 -109 cells), CAR-T doses were weakly correlated with CAR-T cellular kinetics and patient response status. In conclusion, the developed CAR-T cellular kinetic model adequately characterized the multiphasic CAR-T cellular kinetics and supported systematic evaluations of the potential influencing factors, which can have significant implications for the development of more effective CAR-T therapies.

The Attitudes of Canadian Ophthalmology Residents and Pre-Clerkship Medical Students at an Ontario Medical School Towards Homeless Individuals: A Cross-Sectional Study.

Purpose: This cross-sectional study assessed the attitudes of Canadian ophthalmology residents (PGY1-5) and pre-clerkship medical students (year 1 and 2) at the University of Toronto towards individuals experiencing homelessness.Methods: Residents and students were invited to complete the Health Professionals' Attitudes Towards the Homeless Inventory (HPATHI) tool to assess attitudes, interests and confidence in working with the homeless population on a 5-point Likert scale. Comparisons were made between residents and pre-clerkship learners and between junior and senior residents using the Fisher exact test and Mann-Whitney U test.Results: Responses were received from 114 of 220 ophthalmology residents (52%) and 315 of 534 (59%) pre-clerkship medical students. Ophthalmology residents had significantly more negative overall attitudes (pre-clerk median = 4.4, resident median = 4.1, both still indicating positive attitudes) and interests (pre-clerk median = 4.0, resident median = 3.3, residents with more neutral interests) towards working with the homeless population compared to pre-clerkship medical students. Using both statistical methods, beliefs were significantly more negative in 7 of 9 'Attitude' items, 5 of 5 'Interest' items and 1 of 4 'Confidence' items. Ophthalmology residents were only more positive in 1 of 4 of the 'Confidence' items. Attitudes were similar across PGY1-5 training years, except PGY4 and PGY5 residents were more negative than PGY1-3 residents on 1 of 5 'Interest' items.Conclusions: Ophthalmology residents have an at least neutral perception of individuals experiencing homelessness, while medical students have a more positive opinion. Studies exploring optimal ways to advocate for this population are needed for Canada's eye-care trainees.

Visual impairment and the prevalence of ocular pathology in homeless children and adults globally: a systematic review.

BACKGROUND: Homelessness is a global issue in developing and developed countries. This article is the first systematic review to explore its impact on visual health globally. METHODS: A systematic literature search was conducted on OVID MEDLINE, EMBASE, and Cochrane CENTRAL. Peer-reviewed English-language studies with a focus on homeless children or adults that reported on ocular outcomes were included. Primary outcomes and secondary endpoints were reported via weighted averages. Primary outcomes between homeless children and homeless adults were compared using the Fisher exact test. RESULTS: There were 5774 individuals across 23 full-text articles included in the review. For studies reporting primary outcomes, 36.8% of homeless individuals self-reported dissatisfaction with their vision, 26.8% self-reported a previous ocular pathology, 26.3% had uncorrected refractive error, 25.6% were functionally visually impaired, 9.2% had at least one previous eye surgery or procedure, and 4.0% had nonrefractive visual impairment. Upon screening, 25.1% of homeless individuals had some type of ocular pathology, which included cornea and external eye diseases (13.4%), glaucoma (7.4%), cataracts (6.3%), retinal diseases (5.3%), ocular motility disorders (4.7%), trauma (2.3%), neuro-ophthalmological conditions (1.7%), and oculoplastic conditions (0.7%). Homeless adults had significantly more visual impairment (p < 0.001), uncorrected refractive error (p < 0.001), ocular pathology (p < 0.001), cataracts (p < 0.001), retinal pathology (p < 0.001), and neuro-ophthalmological conditions (p < 0.001) relative to children. CONCLUSIONS: Visual impairment in homeless individuals is higher than the general population. Uncorrected refractive error is a leading cause of visual impairment in this population. Additionally, homeless adults have significantly more visual impairment and ocular pathology than homeless children. Future studies should also explore if these differences are consistent in developing countries and investigate ways to increase eye care access for homeless individuals.

Evolution of the Systems Pharmacokinetics-Pharmacodynamics Model for Antibody-Drug Conjugates to Characterize Tumor Heterogeneity and In Vivo Bystander Effect.

The objective of this work was to develop a systems pharmacokinetics-pharmacodynamics (PK-PD) model that can characterize in vivo bystander effect of antibody-drug conjugate (ADC) in a heterogeneous tumor. To accomplish this goal, a coculture xenograft tumor with 50% GFP-MCF7 (HER2-low) and 50% N87 (HER2-high) cells was developed. The relative composition of a heterogeneous tumor for each cell type was experimentally determined by immunohistochemistry analysis. Trastuzumab-vc-MMAE (T-vc-MMAE) was used as a tool ADC. Plasma and tumor PK of T-vc-MMAE was analyzed in N87, GFP-MCF7, and coculture tumor-bearing mice. In addition, tumor growth inhibition (TGI) studies were conducted in all three xenografts at different T-vc-MMAE dose levels. To characterize the PK of ADC in coculture tumors, our previously published tumor distribution model was evolved to account for different cell populations. The evolved tumor PK model was able to a priori predict the PK of all ADC analytes in the coculture tumors reasonably well. The tumor PK model was subsequently integrated with a PD model that used intracellular tubulin occupancy to drive ADC efficacy in each cell type. The final systems PK-PD model was able to simultaneously characterize all the TGI data reasonably well, with a common set of parameters for MMAE-induced cytotoxicity. The model was later used to simulate the effect of different dosing regimens and tumor compositions on the bystander effect of ADC. The model simulations suggested that dose-fractionation regimen may further improve overall efficacy and bystander effect of ADCs by prolonging the tubulin occupancy in each cell type. SIGNIFICANCE STATEMENT: A PK-PD analysis is presented to understand bystander effect of Trastuzumab-vc-MMAE ADC in antigen (Ag)-low, Ag-high, and coculture (i.e., Ag-high + Ag-low) xenograft mice. This study also describes a novel single cell-level systems PK-PD model to characterize in vivo bystander effect of ADCs. The proposed model can serve as a platform to mathematically characterize multiple cell populations and their interactions in tumor tissues. Our analysis also suggests that fractionated dosing regimen may help improve the bystander effect of ADCs.

Antibody Coadministration as a Strategy to Overcome Binding-Site Barrier for ADCs: a Quantitative Investigation.

It has been proposed that the binding-site barrier (BSB) for antibody-drug conjugates (ADCs) can be overcome with the help of antibody coadministration. However, broad utility of this strategy remains in question. Consequently, here, we have conducted in vivo experiments and pharmacokinetics-pharmacodynamics (PK-PD) modeling and simulation (M&S) to further evaluate the antibody coadministration hypothesis in a quantitative manner. Two different Trastuzumab-based ADCs, T-DM1 (no bystander effect) and T-vc-MMAE (with a bystander effect), were evaluated in high-HER2 (N87) and low-HER2 (MDA-MB-453) expressing tumors, with or without the coadministration of 1, 3, or 8-fold higher Trastuzumab. The tumor growth inhibition (TGI) data was quantitatively characterized using a semi-mechanistic PK-PD model to determine the nature of drug interaction for each coadministration regimen, by estimating the interaction parameter ψ. It was found that the coadministration strategy improved ADC efficacy under certain conditions and had no impact on ADC efficacy in others. The benefit was more pronounced for N87 tumors with very high antigen expression levels where the effect on treatment was synergistic (a synergistic drug interaction, ψ = 2.86 [2.6-3.12]). The benefit was diminished in tumor with lower antigen expression (MDA-MB-453) and payload with bystander effect. Under these conditions, the coadministration regimens resulted in an additive or even less than additive benefit (ψ ≤ 1). As such, our results suggest that while antibody coadministration may be helpful for ADCs in certain circumstances, one should not broadly apply this strategy to all the scenarios without first identifying the costs and benefits of this approach.

Development of a quantitative relationship between CAR-affinity, antigen abundance, tumor cell depletion and CAR-T cell expansion using a multiscale systems PK-PD model.

The development of mechanism-based, multiscale pharmacokinetic-pharmacodynamic (PK-PD) models for chimeric antigen receptor (CAR)-T cells is needed to enable investigation of in vitro and in vivo correlation of CAR-T cell responses and to facilitate preclinical-to-clinical translation. Toward this goal, we first developed a cell-level in vitro PD model that quantitatively characterized CAR-T cell-induced target cell depletion, CAR-T cell expansion and cytokine release. The model accounted for key drug-specific (CAR-affinity, CAR-densities) and system-specific (antigen densities, E:T ratios) variables and was able to characterize comprehensive in vitro datasets from multiple affinity variants of anti-EGFR and anti-HER2 CAR-T cells. Next, a physiologically based PK (PBPK) model was developed to simultaneously characterize the biodistribution of untransduced T-cells, anti-EGFR CAR-T and anti-CD19 CAR-T cells in xenograft -mouse models. The proposed model accounted for the engagement of CAR-T cells with tumor cells at the site of action. Finally, an integrated PBPK-PD relationship was established to simultaneously characterize expansion of CAR-T cells and tumor growth inhibition (TGI) in xenograft mouse model, using datasets from anti-BCMA, anti-HER2, anti-CD19 and anti-EGFR CAR-T cells. Model simulations provided potential mechanistic insights toward the commonly observed multiphasic PK profile (i.e., rapid distribution, expansion, contraction and persistence) of CAR-T cells in the clinic. Model simulations suggested that CAR-T cells may have a steep dose-exposure relationship, and the apparent Cmax upon CAR-T cell expansion in blood may be more sensitive to patient tumor-burden than CAR-T dose levels. Global sensitivity analysis described the effect of other drug-specific parameters toward CAR-T cell expansion and TGI. The proposed modeling framework will be further examined with the clinical PK and PD data, and the learnings can be used to inform design and development of future CAR-T therapies.