Module 3 — Stability Summary (OBX-319)

Document ID: M3-STAB
Version: 1.0
Change History: 1.0 — Initial issue.
Standard(s): ICH Q5A-Q5E, Q6B, Q1A(R2), Q11, M4Q

Stability Summary — OBX-319

Long-term storage at 2-8 C protected from light; a proposed shelf life supported by real-time, accelerated, and stress ICH Q5C/Q1A(R2) data, with defined in-use (room-temperature) and transport-excursion allowances.

OBX-319 is a humanized IgG1 anti-CD19 x anti-CD20 bispecific monoclonal antibody produced in Chinese hamster ovary (CHO) cell culture and purified through a Protein A capture step followed by orthogonal polishing chromatography. As a large, conformationally complex glycoprotein, its quality is a function of higher-order structure, correct heavy/light chain pairing across the two distinct binding arms, and the integrity of both antigen-binding functions; consequently, stability is established on the physicochemical and biological attributes that govern potency, purity, and safety rather than on any single degradant. The stability program therefore follows the biotechnological-product framework of ICH Q5C in conjunction with the general principles of Q1A(R2), the specification framework of Q6B, and the manufacturing/control expectations of Q11, and is designed to demonstrate that the drug substance (DS) and the drug product (DP) — a subcutaneous solution presented in a Type I glass prefilled syringe with a coated elastomeric stopper — remain within their release and shelf-life acceptance criteria across the labeled storage period and defined excursions. The program is supported at all relevant conditions by stability-indicating, appropriately qualified/validated analytical methods capable of resolving the size, charge, and functional degradation pathways characteristic of a bispecific IgG1.

Design

Stability is evaluated under long-term, accelerated, and (as applicable) stress conditions per ICH Q1A(R2)/Q5C on representative drug-substance and drug-product batches, using stability-indicating methods for the attributes in 3.2.S.4 / 3.2.P.5.

Storage conditions and study matrix. The primary stability protocol comprises at minimum three DS and three DP batches manufactured from qualified cell-culture and downstream processes at the intended commercial scale, placed on study under the conditions defined for a refrigerated biotechnological product:

• Long-term: 2-8 C (nominal 5 C ± 3 C), protected from light, representing the proposed storage condition; pulled at the ICH-recommended cadence over the full claimed period (e.g., 0, 3, 6, 9, 12, 18, 24 months and annually thereafter) to establish the shelf life by real-time data with trend analysis per ICH Q1E.
• Accelerated: 25 C ± 2 C / 60% RH ± 5% RH, used to characterize degradation kinetics, to support handling and short-term temperature excursions, and to provide supportive evidence of the stability-indicating power of the analytical panel.
• Stress/forced degradation: elevated temperature (e.g., 40 C ± 2 C), low/high pH, oxidative stress, agitation/interfacial (air-liquid) stress, and repeated freeze-thaw applied to the DS, to deliberately generate and identify the relevant degradation products (size and charge variants, oxidized and deamidated species, fragments, and aggregates) and to confirm that each is detected and quantified by the control methods.

Because degradation of a monoclonal antibody is molecule-specific and biologics are generally not amenable to reduction of testing, a full study design (rather than bracketing or matrixing) is applied; where bracketing/matrixing of presentations is proposed it is justified per Q1D.

Attributes and stability-indicating methods. Testing at each pull point covers the panel that governs OBX-319 quality and is capable of trending change over the storage period:

• General/physical: appearance (color, clarity, visible particulates), pH, protein concentration (A280), and osmolality; sub-visible particulate matter by light obscuration (HIAC) with orthogonal flow imaging (MFI) to monitor protein particle formation.
• Size heterogeneity / aggregation and fragmentation: size-exclusion chromatography (SEC) for monomer, high-molecular-weight (HMW/aggregate) and low-molecular-weight (LMW/fragment) species; non-reduced and reduced CE-SDS for purity, fragmentation, and — importantly for a bispecific — resolution of half-antibody, homodimer/mispaired, and incompletely assembled species.
• Charge heterogeneity: imaged capillary isoelectric focusing (iCIEF) or cation-exchange chromatography (CEX) to trend acidic and basic variants arising from asparagine deamidation, aspartate isomerization, and N-/C-terminal processing during storage.
• Chemical modification / higher-order structure: peptide mapping (as needed) to localize methionine/tryptophan oxidation and deamidation hotspots, with orthogonal HOS confirmation (e.g., DSC, far/near-UV CD, or FTIR) on characterization/stress samples to demonstrate conformational integrity of both Fab arms and the Fc.
• Potency: a matrix of bioassays reflecting the dual mechanism — independent binding to CD19 and to CD20, simultaneous (bispecific) binding demonstrating co-engagement, Fc-effector function relevant to B-cell depletion, and a cell-based functional potency assay — reported against reference standard and trended for loss of activity.
• Glycan and Fc-function-relevant attributes: monitoring of glycosylation-dependent CQAs where these are shown to be stability-sensitive.
• Excipient/formulation and container integrity: polysorbate (surfactant) content to detect degradation that could precede particle formation, and container-closure integrity (CCI) by a validated deterministic method in lieu of, or supporting, sterility, consistent with the sterile parenteral presentation.

Photostability, freeze-thaw, in-use, and transport. A confirmatory photostability study is conducted per ICH Q1B to define the light-protection labeling reflected in the storage statement. DS freeze-thaw cycling supports frozen storage/handling of the substance. For the subcutaneous DP, an in-use / room-temperature hold study defines the permitted time the prefilled syringe may be kept at ambient conditions prior to administration, and a transport-simulation/excursion study (including thermal cycling and mechanical stress representative of the distribution chain) supports the defined temperature-excursion allowance. Endotoxin, sterility, and CCI are addressed within the sterile-product control strategy at the appropriate stability stations.

Analytical continuity and ongoing stability. Methods are the qualified/validated stability-indicating procedures described in 3.2.S.4 and 3.2.P.5; reference standards are qualified and bridged across batches so that potency and purity trends are comparable throughout the program. A post-approval stability commitment places the first commercial-scale batches, and at least one batch per year thereafter, on long-term study under a defined ongoing-stability protocol, with the annual product review assessing conformance to the shelf-life criteria.

Conclusion

The data support the proposed storage condition and shelf life in the type i glass prefilled syringe with a coated elastomeric stopper, with defined in-use and excursion allowances.

Real-time 2-8 C data, supported by accelerated and stress results and by the demonstrated stability-indicating capability of the size, charge, and functional methods, show that OBX-319 DS and DP remain within their 3.2.S.4 / 3.2.P.5 acceptance criteria across the claimed period, with any change in aggregation, fragmentation, charge variants, sub-visible particulates, and potency remaining within limits and statistically consistent with the assigned shelf life per ICH Q1E. The refrigerated, light-protected storage statement, the in-use room-temperature hold, and the transport-excursion allowance are each justified by the corresponding study arms, and the post-approval ongoing-stability commitment provides continued verification. These conclusions are specific to the bispecific IgG1 modality and its container-closure system and are consistent with the biotechnological-product stability expectations of ICH Q5C/Q6B.

Governing guidelines: ICH Q5A-Q5E, Q6B, Q1A(R2), Q11, M4Q.