Quantitative systems pharmacology: a promising approach for translational pharmacology

Biopharmaceutical companies have increasingly been exploring Quantitative Systems Pharmacology (QSP) as a potential avenue to address current challenges in drug development. In this paper, we discuss the application of QSP modeling approaches to address challenges in the translational of preclinical findings to the clinic, a high risk area of drug development. Three cases have been highlighted with QSP models utilized to inform different questions in translational pharmacology. In the first, a mechanism based asthma model is used to evaluate efficacy and inform biomarker strategy for a novel bispecific antibody. In the second case study, a mitogen-activated protein kinase (MAPK) pathway signaling model is used to make translational predictions on clinical response and evaluate novel combination therapies. In the third case study, a physiologically based pharmacokinetic (PBPK) model it used to guide administration of oseltamivir in pediatric patients.

Quantitative Systems Pharmacology: A Case for Disease Models

Quantitative systems pharmacology (QSP) has emerged as an innovative approach in model‐informed drug discovery and development, supporting program decisions from exploratory research through late‐stage clinical trials. In this commentary, we discuss the unique value of disease‐scale “platform” QSP models that are amenable to reuse and repurposing to support diverse clinical decisions in ways distinct from other pharmacometrics strategies.

Prospective Design of Anti-Transferrin Receptor Bispecific Antibodies for Optimal Delivery into the Human Brain

Anti‐transferrin receptor (TfR)‐based bispecific antibodies have shown promise for boosting antibody uptake in the brain. Nevertheless, there are limited data on the molecular properties, including affinity required for successful development of TfR‐based therapeutics. A complex nonmonotonic relationship exists between affinity of the anti‐TfR arm and brain uptake at therapeutically relevant doses. However, the quantitative nature of this relationship and its translatability to humans is heretofore unexplored. Therefore, we developed a mechanistic pharmacokinetic‐pharmacodynamic (PK‐PD) model for bispecific anti‐TfR/BACE1 antibodies that accounts for antibody‐TfR interactions at the blood‐brain barrier (BBB) as well as the pharmacodynamic (PD) effect of anti‐BACE1 arm. The calibrated model correctly predicted the optimal anti‐TfR affinity required to maximize brain exposure of therapeutic antibodies in the cynomolgus monkey and was scaled to predict the optimal affinity of anti‐TfR bispecifics in humans. Thus, this model provides a framework for testing critical translational predictions for anti‐TfR bispecific antibodies, including choice of candidate molecule for clinical development.

A Six-Stage Workflow for Robust Application of Systems Pharmacology

Quantitative and systems pharmacology (QSP) is increasingly being applied in pharmaceutical research and development. One factor critical to the ultimate success of QSP is the establishment of commonly accepted language, technical criteria, and workflows. We propose an integrated workflow that bridges conceptual objectives with underlying technical detail to support the execution, communication, and evaluation of QSP projects.

Challenges and Opportunities for Quantitative Clinical Pharmacology in Cancer Immunotherapy: Something Old, Something New, Something Borrowed, and Something Blue

Cancer immunotherapy (CIT) initiates or enhances the host immune response against cancer. Following decades of development, patients with previously few therapeutic options may now benefit from CIT. Although the quantitative clinical pharmacology (qCP) of previous classes of anticancer drugs has matured during this time, application to CIT may not be straightforward since CIT acts via the immune system. Here we discuss where qCP approaches might best borrow or start anew for CIT.

A Mechanistic Systems Pharmacology Model for Prediction of LDL Cholesterol Lowering by PCSK9 Antagonism in Human Dyslipidemic Populations

PCSK9 is a promising target for the treatment of hyperlipidemia and cardiovascular disease. A Quantitative Systems Pharmacology model of the mechanisms of action of statin and anti-PCSK9 therapies was developed to predict low density lipoprotein (LDL) changes in response to anti-PCSK9 mAb for different treatment protocols and patient subpopulations. Mechanistic interactions and cross-regulation of LDL, LDL receptor, and PCSK9 were modeled, and numerous virtual subjects were developed and validated against clinical data. Simulations predict a slightly greater maximum percent reduction in LDL cholesterol (LDLc) when anti-PCSK9 is administered on statin background therapy compared to as a monotherapy. The difference results primarily from higher PCSK9 levels in patients on statin background. However, higher PCSK9 levels are also predicted to increase clearance of anti-PCSK9, resulting in a faster rebound of LDLc. Simulations of subjects with impaired LDL receptor (LDLR) function predict compromised anti-PCSK9 responses in patients such as homozygous familial hypercholesterolemics, whose functional LDLR is below 10% of normal.

The Type 1 Diabetes PhysioLab Platform: a validated physiologically based mathematical model of pathogenesis in the non-obese diabetic mouse

Type 1 diabetes is an autoimmune disease whose clinical onset signifies a lifelong requirement for insulin therapy and increased risk of medical complications. To increase the efficiency and confidence with which drug candidates advance to human type 1 diabetes clinical trials, we have generated and validated a mathematical model of type 1 diabetes pathophysiology in a well-characterized animal model of spontaneous type 1 diabetes, the non-obese diabetic (NOD) mouse. The model is based on an extensive survey of the public literature and input from an independent scientific advisory board. It reproduces key disease features including activation and expansion of autoreactive lymphocytes in the pancreatic lymph nodes (PLNs), islet infiltration and beta cell loss leading to hyperglycaemia. The model uses ordinary differential and algebraic equations to represent the pancreas and PLN as well as dynamic interactions of multiple cell types (e.g. dendritic cells, macrophages, CD4+ T lymphocytes, CD8+ T lymphocytes, regulatory T cells, beta cells). The simulated features of untreated pathogenesis and disease outcomes for multiple interventions compare favourably with published experimental data. Thus, a mathematical model reproducing type 1 diabetes pathophysiology in the NOD mouse, validated based on accurate reproduction of results from multiple published interventions, is available for in silico hypothesis testing. Predictive biosimulation research evaluating therapeutic strategies and underlying biological mechanisms is intended to deprioritize hypotheses that impact disease outcome weakly and focus experimental research on hypotheses likely to provide insight into the disease and its treatment.

Systems biology for battling rheumatoid arthritis: Application of the Entelos PhysioLab platform

A large-scale mathematical model, the Entelos Rheumatoid Arthritis (RA) PhysioLab platform, has been developed to describe the inflammatory and erosive processes in afflicted joints of people suffering from RA. The platform represents the life cycle of inflammatory cells, endothelium, synovial fibroblasts, and chondrocytes, as well as their products and interactions. The interplay between these processes culminates in clinically relevant measures for inflammation and erosion. The simulation model is deterministic, which allows tracing back the mechanism of action for a particular simulation result. Different patient phenotypes are represented by different virtual patients. The RA PhysioLab platform has been used to systematically and quantitatively study the predicted therapeutic effect of modulating several molecular targets, which resulted in a ranking of putative drug targets and a workflow to confirm the simulations experimentally. In addition, critical pathways were identified that drive the predicted disease outcome. Within these pathways, targets were identified from public literature that were not previously associated with arthritis. The model provides insights into the biology of RA and can be used as a platform for hypothesis-driven research. Case studies of therapies directed against IL-12 and IL-15 illustrate the approach, with emphasis on the analysis of system dynamics.

Solid stress facilitates spheroid formation: potential involvement of hyaluronan

When neoplastic cells grow in confined spaces in vivo, they exert a finite force on the surrounding tissue resulting in the generation of solid stress. By growing multicellular spheroids in agarose gels of defined mechanical properties, we have recently shown that solid stress inhibits the growth of spheroids and that this growth-inhibiting stress ranges from 45 to 120 mmHg. Here we show that solid stress facilitates the formation of spheroids in the highly metastatic Dunning R3327 rat prostate carcinoma AT3.1 cells, which predominantly do not grow as spheroids in free suspension. The maximum size and the growth rate of the resulting spheroids decreased with increasing stress. Relieving solid stress by enzymatic digestion of gels resulted in gradual loss of spheroidal morphology in 8 days. In contrast, the low metastatic variant AT2.1 cells, which grow as spheroids in free suspension as well as in the gels, maintained their spheroidal morphology even after stress removal. Histological examination revealed that most cells in AT2.1 spheroids are in close apposition whereas a regular matrix separates the cells in the AT3.1 gel spheroids. Staining with the hyaluronan binding protein revealed that the matrix between AT3.1 cells in agarose contained hyaluronan, while AT3.1 cells had negligible or no hyaluronan when grown in free suspension. Hyaluronan was found to be present in both free suspensions and agarose gel spheroids of AT2.1. We suggest that cell-cell adhesion may be adequate for spheroid formation, whereas solid stress may be required to form spheroids when cell-matrix adhesion is predominant. These findings have significant implications for tumour growth, invasion and metastasis.

Role of tumor-host interactions in interstitial diffusion of macromolecules: cranial vs. subcutaneous tumors

The large size of many novel therapeutics impairs their transport through the tumor extracellular matrix and thus limits their therapeutic effectiveness. We propose that extracellular matrix composition, structure, and distribution determine the transport properties in tumors. Furthermore, because the characteristics of the extracellular matrix largely depend on the tumor-host interactions, we postulate that diffusion of macromolecules will vary with tumor type as well as anatomical location. Diffusion coefficients of macromolecules and liposomes in tumors growing in cranial windows (CWs) and dorsal chambers (DCs) were measured by fluorescence recovery after photobleaching. For the same tumor types, diffusion of large molecules was significantly faster in CW than in DC tumors. The greater diffusional hindrance in DC tumors was correlated with higher levels of collagen type I and its organization into fibrils. For molecules with diameters comparable to the interfibrillar space the diffusion was 5- to 10-fold slower in DC than in CW tumors. The slower diffusion in DC tumors was associated with a higher density of host stromal cells that synthesize and organize collagen type I. Our results point to the necessity of developing site-specific drug carriers to improve the delivery of molecular medicine to solid tumors.

Differential dynamics of CD4(+) and CD8(+) T-lymphocyte proliferation and activation in acute simian immunodeficiency virus infection

Although lymphocyte turnover in chronic human immunodeficiency virus and simian immunodeficiency virus (SIV) infection has been extensively studied, there is little information on turnover in acute infection. We carried out a prospective kinetic analysis of lymphocyte proliferation in 13 rhesus macaques inoculated with pathogenic SIV. A short-lived dramatic increase in circulating Ki-67(+) lymphocytes observed at 1 to 4 weeks was temporally related to the onset of SIV replication. A 5- to 10-fold increase in Ki-67(+) CD8(+) T lymphocytes and a 2- to 3-fold increase in Ki-67(+) CD3(-) CD8(+) natural killer cells accounted for >85% of proliferating lymphocytes at peak proliferation. In contrast, there was little change in the percentage of Ki-67(+) CD4(+) T lymphocytes during acute infection, although transient increases in Ki-67(-) and Ki-67(+) CD4(+) T lymphocytes expressing CD69, Fas, and HLA-DR were observed. A two- to fourfold decline in CD4(+) T lymphocytes expressing CD25 and CD69 was seen later in SIV infection. The majority of Ki-67(+) CD8(+) T lymphocytes were phenotypically CD45RA(-) CD49d(hi) Fas(hi) CD25(-) CD69(-) CD28(-) HLA-DR(-) and persisted at levels twofold above baseline 6 months after SIV infection. Increased CD8(+) T-lymphocyte proliferation was associated with cell expansion, paralleled the onset of SIV-specific cytotoxic T-lymphocyte activity, and had an oligoclonal component. Thus, divergent patterns of proliferation and activation are exhibited by CD4(+) and CD8(+) T lymphocytes in early SIV infection and may determine how these cells are differentially affected in AIDS.

Local imbalance of proangiogenic and antiangiogenic factors: a potential mechanism of focal necrosis and dormancy in tumors

Solid tumors produce both stimulators and inhibitors of angiogenesis. The suppression of metastases by some primary tumors has been attributed to the longer circulatory half-lives of the inhibitors. We propose that intrinsic differences in the physicochemical properties of these regulators may also explain focal suppression of angiogenesis within the primary tumor. We present a mathematical framework that describes production, diffusion, and degradation of these factors in tumor and host tissue and their effect on angiogenesis at local and distal sites. Results show focal suppression of angiogenesis, provide an explanation for tumor dormancy and focal necrosis, and predict a suppressive influence of primary tumors on angiogenesis at metastatic sites. They suggest generally that diffusible factors produced by tumors can stimulate responses in adjacent host tissue, preparing it for further tumor invasion. This study presents a new paradigm for the development of tumor necrosis and offers new insight into angiogenesis regulation and therapy. The framework established for modeling the competing effects of diffusible stimulators and inhibitors can be applied more generally to growth factors/inhibitors and other opposing factors produced in the tumor environment.