Early application of mechanistic PKPD modelling to guide the preclinical development of a therapeutic mAb targeting complement receptor 2 (CR2/CD21) as a novel target for the treatment of autoimmune disease
Previously held under moratorium in Chemistry department (GSK) from 10th March 2021 until 13th June 2023.
The confidentiality statement on each page of this thesis DOES NOT apply.Mechanistic PKPD modelling has become the state of the art for the integration of preclinical data to improve early projection of the clinical efficacy of small molecule drug candidates. However, its application to the development of monoclonal antibody (mAb) based drug candidates has been relatively restricted to date. Typically, a key limiting factor is the necessity for a surrogate molecule to explore target pharmacology in well-established preclinical animal models. A need driven by the limited cross-species reactivity often seen with the fully human mAbs preferred for clinical development. Consequently, pharmacology is rarely established beyond target engagement during preclinical development, limiting the early projection of clinical efficacy.
The present work sought to explore the application of mechanistic PKPD modelling, early in the preclinical drug discovery environment, using a surrogate mAb as a tool with which to explore the pharmacology of the novel drug target complement receptor 2 (CD21). CD21 is thought to play a key role in the regulation of humoral immunity. As such, CD21 is receiving interest as a novel mechanism by which to treat autoimmune conditions characterised by the aberrant production of destructive autoantibodies, such as systemic lupus erythematosus.
Characterisation of three potential surrogate mAbs targeting murine CD21 identified nondose-linear pharmacokinetics related to on target binding, characteristic of target mediated drug disposition (TMDD). To describe this behaviour, a minimal physiologically based pharmacokinetic (mPBPK) model was developed, incorporating target abundance, kinetics and binding affinity. This model highlighted critical gaps in the understanding of CD21 kinetics, particularly regarding the origin and impact of the soluble form of the protein (sCD21). Further experiments identified that the plasma concentration of sCD21(/35) in mice remained unchanged (12.8 nM) following treatment with an anti-CD21 mAb, despite near complete loss of B cell expressed CD21. This challenged the theory that sCD21 results from ectodomain shedding of membrane receptor, implicating secretion as a predominant source of the soluble protein in mice.
To explore the pharmacology of CD21 neutralisation, T-dependent immunisation was selected as a well-established acute mechanistic model of humoral immunity. To align with target biology and the clinical strategy, the protocol was optimised to comprise of a single IV immunisation with the T-dependent antigen keyhole limpet haemocyanin (KLH) at 1.2 mg/kg to C57BL/6 mice. The in vivo model was qualified using the clinically validated S1P receptor modulator Fingolimod. A relationship was established between Fingolimod blood exposure and its pharmacodynamic effect on the T-dependent antibody (IgG) response (TDAR), using an integrated PKPD model. This resulted in an estimated EC50 of 4.59 nM (SE 3.09), showing remarkable similarity to reported EC50 estimates across species (versus peripheral lymphocyte reduction). The potential to translate this model system to project clinical efficacy was also demonstrated, providing an excellent prediction of the reported efficacy of Fingolimod on KLH induced TDAR (IgG) in the clinic.
Furthermore, CD21 pharmacology was explored in the mouse TDAR model using the widely published mAb 7G6 as a surrogate. A relationship was established between 7G6 plasma exposure and its pharmacodynamic effect on the KLH induced TDAR (IgM) using an integrated PKPD model, with an estimated EC50 of 0.13 nM (SE 0.02). Comparison with the measured receptor occupancy on peripheral B cells indicates this corresponds with approximately 60% target occupancy. Collectively, these data support the rationale that maintenance of mAb exposure to achieve >95% CD21 receptor occupancy at trough is an appropriate clinical benchmark. However, it also highlights that critical knowledge gaps remain with regard to CD21 and its pharmacology that would require further investigation.Mechanistic PKPD modelling has become the state of the art for the integration of preclinical data to improve early projection of the clinical efficacy of small molecule drug candidates. However, its application to the development of monoclonal antibody (mAb) based drug candidates has been relatively restricted to date. Typically, a key limiting factor is the necessity for a surrogate molecule to explore target pharmacology in well-established preclinical animal models. A need driven by the limited cross-species reactivity often seen with the fully human mAbs preferred for clinical development. Consequently, pharmacology is rarely established beyond target engagement during preclinical development, limiting the early projection of clinical efficacy.
The present work sought to explore the application of mechanistic PKPD modelling, early in the preclinical drug discovery environment, using a surrogate mAb as a tool with which to explore the pharmacology of the novel drug target complement receptor 2 (CD21). CD21 is thought to play a key role in the regulation of humoral immunity. As such, CD21 is receiving interest as a novel mechanism by which to treat autoimmune conditions characterised by the aberrant production of destructive autoantibodies, such as systemic lupus erythematosus.
Characterisation of three potential surrogate mAbs targeting murine CD21 identified nondose-linear pharmacokinetics related to on target binding, characteristic of target mediated drug disposition (TMDD). To describe this behaviour, a minimal physiologically based pharmacokinetic (mPBPK) model was developed, incorporating target abundance, kinetics and binding affinity. This model highlighted critical gaps in the understanding of CD21 kinetics, particularly regarding the origin and impact of the soluble form of the protein (sCD21). Further experiments identified that the plasma concentration of sCD21(/35) in mice remained unchanged (12.8 nM) following treatment with an anti-CD21 mAb, despite near complete loss of B cell expressed CD21. This challenged the theory that sCD21 results from ectodomain shedding of membrane receptor, implicating secretion as a predominant source of the soluble protein in mice.
To explore the pharmacology of CD21 neutralisation, T-dependent immunisation was selected as a well-established acute mechanistic model of humoral immunity. To align with target biology and the clinical strategy, the protocol was optimised to comprise of a single IV immunisation with the T-dependent antigen keyhole limpet haemocyanin (KLH) at 1.2 mg/kg to C57BL/6 mice. The in vivo model was qualified using the clinically validated S1P receptor modulator Fingolimod. A relationship was established between Fingolimod blood exposure and its pharmacodynamic effect on the T-dependent antibody (IgG) response (TDAR), using an integrated PKPD model. This resulted in an estimated EC50 of 4.59 nM (SE 3.09), showing remarkable similarity to reported EC50 estimates across species (versus peripheral lymphocyte reduction). The potential to translate this model system to project clinical efficacy was also demonstrated, providing an excellent prediction of the reported efficacy of Fingolimod on KLH induced TDAR (IgG) in the clinic.
Furthermore, CD21 pharmacology was explored in the mouse TDAR model using the widely published mAb 7G6 as a surrogate. A relationship was established between 7G6 plasma exposure and its pharmacodynamic effect on the KLH induced TDAR (IgM) using an integrated PKPD model, with an estimated EC50 of 0.13 nM (SE 0.02). Comparison with the measured receptor occupancy on peripheral B cells indicates this corresponds with approximately 60% target occupancy. Collectively, these data support the rationale that maintenance of mAb exposure to achieve >95% CD21 receptor occupancy at trough is an appropriate clinical benchmark. However, it also highlights that critical knowledge gaps remain with regard to CD21 and its pharmacology that would require further investigation
