Abstract
PurposeDevelopment of therapeutics for retinal disease with improved durability is hampered by inadequate understanding of pharmacokinetic (PK) drivers following intravitreal injection. Previous work shows that hydrodynamic radius is correlated with vitreal half-life over the range of 3 to 7 nm, and that charge and hydrophobicity influence systemic clearance. Better understanding the molecular attributes affecting vitreal elimination half-life enables improved design of therapeutics and enhances clinical translatability.MethodsImpacts of charge and hydrophobicity on vitreal PK in the rabbit were systematically assessed using antibody and antibody fragment (Fab) variant series, including ranibizumab, altered through amino acid changes in hypervariable regions of the light chain. The impact of molecule size on vitreal PK was assessed in the rabbit, nonhuman primate, and human for a range of molecules (1–45 nm, net charge −1324 to +22.9 in rabbit), including published and internal data.ResultsNo correlation was observed between vitreal PK and charge or hydrophobicity. Equivalent rabbit vitreal PK was observed for ranibizumab and its variants with isoelectric points (pI) in the range of 6.8 to 10.2, and hydrophobicities of the variable domain unit (FvHI) between 1009 and 1296; additional variant series had vitreal PK similarly unaffected by pI (5.4–10.2) and FvHI (1004–1358). Strong correlations were observed between vitreal half-life and hydrodynamic radius for preclinical species (R2 = 0.8794–0.9366).ConclusionsDiffusive properties of soluble large molecules, as quantified by hydrodynamic radius, make a key contribution to vitreal elimination, whereas differences in charge or hydrophobicity make minor or negligible contributions.Translational RelevanceThese results support estimation of vitreal elimination rates based on molecular size in relevant preclinical species and humans.
Highlights
Age-related macular degeneration (AMD) and diabetic retinopathy (DR) are leading causes of vision loss in aging populations, expected to cause blindness or moderate to severe vision loss in more than 14 million people by 2020.1 Current therapies for retinal disease typically are administered via intravitreal injection (ITV), with maximum clinical benefit requiring frequent patient monitoring and monthly or bimonthly injections in many patients
In addition to the designed variants of ranibizumab discussed below, four more variant series (VS_2– VS_5; TA_6–TA_18) were identified among internal molecules, wherein minor sequence modifications were made during the normal course of drug development, resulting in alteration of charge and/ or hydrophobicity
The correlation between calculated hydrophobicity index of the variable domain unit (FvHI) and elution time of a subset of molecules (n 1⁄4 12) on a hydrophobic interaction column was strong (R2 1⁄4 0.8826; Supplementary Fig. S1), suggesting that sequence-based calculations are valid for ranking relative hydrophobicity
Summary
Age-related macular degeneration (AMD) and diabetic retinopathy (DR) are leading causes of vision loss in aging populations, expected to cause blindness or moderate to severe vision loss in more than 14 million people by 2020.1 Current therapies for retinal disease typically are administered via intravitreal injection (ITV), with maximum clinical benefit requiring frequent patient monitoring and monthly or bimonthly injections in many patients. Research has shown that patient compliance declines over time, with reduced treatment despite worsening visual outcomes.[2,3,4] Research is focused heavily on development of longeracting therapeutics to relieve patient burden, and to increase compliance and clinical benefit. For systemically administered large molecule therapies, distribution and elimination are driven by processes, including paracellular diffusion, convection, and pinocytosis.[5] Convective processes typically have a greater role than diffusion, given the large size and high polarity of protein therapeutics. Previous efforts have illustrated that charge, hydrophobicity, and FcRn recycling influence systemic clearance rates for protein therapeutics,[6,7] and that these properties may be manipulated to generate therapies with favorable systemic pharmacokinetic (PK) behavior.[8,9,10] For large molecules, such as monoclonal antibodies (Mabs) or antibody fragments (Fabs), the impact of size on systemic clearance rates typically is considered primarily with respect to the ‘‘renal filtration cut off’’ wherein no or very limited renal clearance occurs for molecules larger than albumin (68 kDa, ~80 3 80 3 30 A ).[11]
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