A single molecular descriptor to predict solution behavior of therapeutic antibodies

Abstract

Despite the therapeutic success of monoclonal antibodies (mAbs), early identification of developable mAb drug candidates with optimal manufacturability, stability, and delivery attributes remains elusive. Poor solution behavior, which manifests as high solution viscosity or opalescence, profoundly affects the developability of mAb drugs. Using a diverse dataset of 59 mAbs, including 43 approved products, and an array of molecular descriptors spanning colloidal, conformational, charge-based, hydrodynamic, and hydrophobic properties, we show that poor solution behavior is prevalent (>30%) in mAbs and is singularly predicted (>90%) by the diffusion interaction parameter (k _D), a dilute-solution measure of colloidal self-interaction. No other descriptor, individually or in combination, was found to be as effective as k _D. We also show that well-behaved mAbs, a substantial subset of which bear high positive charge and pI, present no disadvantages with respect to pharmacokinetics in humans. Here, we provide a systematic framework with quantitative thresholds for selecting well-behaved therapeutic mAbs during drug discovery.

Fig. 1. Poor solution behavior is prevalent in mAbs.

Viscosity and opalescence of 59 mAbs at 150 mg/ml in 10 mM histidine·HCl (pH 6.0). Dashed lines indicate threshold values of 30 cP and 12 NTU for viscosity and opalescence, respectively. Antibodies with viscosity ≤30 cP and turbidity ≤12 NTU are designated green; those with viscosity >30 cP are designated tan; and those with turbidity >12 NTU are designated brown. In the inset at the bottom, mAbs were categorized overall as inviscid and clear (green), viscous (tan), or opalescent (brown). Products approved for subcutaneous injection are indicated by asterisks.

Fig. 2. Colloidal interactions in dilute solution underlie solution behavior.

(A) Antibodies arranged in descending order of k_D,His values reflecting most repulsive to most attractive. (B) Strip plot of rank-ordered mAbs as arranged in (A). (C) Opalescence versus viscosity of mAbs measured at 150 mg/ml in 10 mM histidine·HCl (pH 6.0). Data points are color-coded according to k_D,His ranges as indicated in the figure inset. Dashed lines bordering shaded areas represent threshold values for opalescence (12 NTU; brown) and viscosity (30 cP; tan). Well-behaved mAbs with high k_D,His values are clustered in the lower left corner (green). (D) k_D,His values for mAbs in each solution property category. A threshold of 20 ml/g is indicated with the dashed line. (E) k_D,His values organized by subclass: IgG1 (circles), IgG2 (squares), and IgG4 (triangles). (F) k_D,His-NaCl values for mAbs in each solution property category. A threshold of −15 ml/g is indicated with the dashed line. In (A), (B), and (D) to (F), individual mAbs are color-coded according to their solution behavior category: inviscid and clear (green), viscous (tan), or opalescent (brown). In (D) and (F), mean values within each category are indicated by the bold horizontal lines.

Fig. 3. Electrostatic repulsion dominates colloidal interactions in dilute solution.

(A) Twenty-three measured and calculated molecular descriptors arranged in order of decreasing favorable value from left to right. Individual mAbs are identified by the numbers in each box and color-coded according to their solution behavior category: inviscid and clear (green), viscous (tan), or opalescent (brown). The Spearman’s rank order correlation (ρ) for each descriptor with respect to k_D,His (row 1) is indicated in the rightmost column. (B) to (F) indicate selected molecular descriptors of mAbs [color-coded as in (A)]: (B) measured pI, (C) measured charge, (D) EHI, (E) Fv-CSP, and (F) Fab/Fc-CSP. (G) to (K) indicate the same descriptors organized by subclass as follows: IgG1 (circles), IgG2 (squares), and IgG4 (triangles). Selection thresholds for measured pI and charge (B and C) are indicated with black dashed lines. Solid horizontal lines in (B) to (K) represent mean values of a descriptor in a given category.