Recombinant Human Chymotrypsin Pharma Grade API, model rHC-01, is produced by submerged fermentation of a non-pathogenic Escherichia coli K-12 strain carrying a codon-optimized synthetic gene encoding the human chymotrypsin B sequence. Fermentation is performed in a 200 L fed-batch stainless-steel bioreactor at 37 °C ± 0.5 °C, dissolved oxygen 30% ± 5%, and pH 6.8–7.2. The cell paste is harvested by continuous disc-stack centrifugation, resuspended in lysis buffer, and disrupted by high-pressure homogenization at 800–1000 bar. Inclusion bodies are washed, solubilized in 6 M guanidine hydrochloride with 10 mM dithiothreitol, and refolded by 20-fold dilution into a redox buffer containing 2 M urea, 0.2 M arginine, 3 mM reduced glutathione, and 0.6 mM oxidized glutathione at pH 8.5. The active enzyme is purified by hydrophobic interaction chromatography, cation-exchange chromatography, and size-exclusion chromatography. The cation-exchange step is operated at pH 5.5 with 50 mM sodium acetate, and the elution gradient from 0.0 M to 0.3 M sodium chloride is applied over 10 column volumes. The size-exclusion step removes high-molecular-weight aggregates and clipped species, with aggregate content controlled to ≤ 2.0% by SEC-HPLC. The purified bulk is concentrated by tangential-flow ultrafiltration with a 10 kDa cutoff membrane, dialyzed against 5 mM sodium acetate pH 5.0, and lyophilized. Model rHC-01 oral grade and injectable grade are differentiated by residual endotoxin, bioburden, and particulate-matter acceptance limits, not by active enzyme identity.

Specification Profile and Compendial Alignment

Release testing follows the USP Chymotrypsin monograph for enzyme activity and the relevant general chapters for impurity, water, and microbiological control. Table 1 lists the typical release profile. Each batch is also tested for identity by peptide mapping using trypsin digestion and RP-HPLC; the peptide map must match the reference standard at a similarity score of ≥ 0.85. The residual moisture specification is critical because water content above 3.0% increases solid-state autolysis and reduces tablet stability. The bacterial endotoxin limit for the injectable grade is ≤ 0.10 EU/mg, which is consistent with a maximum dose of 10 mg and the Ph. Eur. 2.6.14 threshold for parenteral products. The oral grade permits ≤ 100 CFU/g by Ph. Eur. 2.6.12, while the injectable grade is terminally sterile-filtered and filled under Grade A laminar airflow. Host-cell protein and DNA limits are set according to ICH Q11 residual DNA guidance, with residual DNA ≤ 10 pg/mg and host-cell protein ≤ 50 ppm.

Manufacture is conducted under ICH Q7 and 21 CFR 211 for APIs. Process validation comprises three consecutive batches with critical process parameters monitored in real time by distributed control system. Column resin lifetime is validated for 20 cycles; cleaning validation by total organic carbon and protein swab confirms residual carryover below 1 ppm. The lyophilized cake may vary from cracked to uniform; this is not a failure criterion because it does not affect reconstitution time.

For tablet and capsule manufacturing, rHC-01 is preblended with microcrystalline cellulose and sodium starch glycolate in a bin blender at 15 rpm for 10 minutes. Magnesium stearate is added as a lubricant at 0.5% w/w and mixed for 3 minutes to avoid excessive shear. Dry granulation by roller compaction is preferred for tablet formulations requiring particle size enlargement; the roller pressure is maintained at 6–8 kN/cm, and the compact is milled through a 1.0 mm screen. Aqueous wet granulation is not recommended because the enzyme is sensitive to heat and hydrolysis. If wet granulation is unavoidable, the drying step must maintain product temperature below 30 °C and the granulate moisture below 2.5%. Capsule filling is performed at relative humidity below 35% RH and temperature 20–25 °C. Dissolution testing by USP <711> uses 900 mL of 50 mM phosphate buffer pH 6.8 at 37 °C with paddle speed 50 rpm; the release criterion is not less than 80% of label activity at 30 minutes.

Granule presentations are prepared by blending the API with pregelatinized starch and sorbitol, filling into aluminum foil sachets under nitrogen. The sachet headspace oxygen is controlled below 2.0% v/v to limit oxidation of methionine residues. The blend is passed through a 500 μm sieve prior to filling to ensure content uniformity according to USP <905>.

When the Lyophilized API Is Redissolved for Injectable Manufacturing

Injectable formulations are prepared by reconstituting rHC-01 in Water for Injection at 2–10 mg/mL under Grade A laminar airflow in a 316L stainless steel jacketed vessel. The solution is adjusted to pH 5.5–6.5 with 0.1 M hydrochloric acid or 0.1 M sodium hydroxide, and stirred at 100–150 rpm with a bottom-mounted magnetic mixer. Tonicity is adjusted with sodium chloride 0.9% w/v. The solution is prefiltered through a 0.45 μm PVDF membrane and sterile-filtered through a 0.22 μm PES membrane. A minimum filtrate flux of 50 L/m²/h is maintained to limit shear-induced aggregation; the transmembrane pressure should not exceed 0.5 bar during the final sterile filtration.

Extended liquid-state hold is a critical process point. At pH 6.0 and 25 °C, activity loss after 24 h is less than 5%; at pH 8.0 and 37 °C, activity loss exceeds 15% because of autolysis. Holding tanks are jacketed at 2–8 °C, and the total duration from reconstitution to filling should not exceed 8 h. Terminal sterilization by moist heat is contraindicated: exposure at 121 °C for 15 min reduces specific activity by more than 90%. Aseptic filtration is mandatory. The filling line is equipped with online particle monitoring to comply with USP <790> and Ph. Eur. 2.9.19. Glass vials are Type I borosilicate per USP <660> and Ph. Eur. 3.2.1, with chlorobutyl stoppers.

Freeze-thaw stability of the reconstituted solution is limited to three cycles at -20 °C ± 2 °C; activity loss per cycle is ≤ 5% and subvisible particle counts remain below the Ph. Eur. 2.9.19 limit for small-volume parenterals. The lyophilized powder is stored at -20 °C ± 5 °C. After reconstitution, solutions should be used within 8 h at 2–8 °C and must not be refrozen more than once.

What Distinguishes Recombinant Human Chymotrypsin from Pancreatic Extracts?

Chymotrypsin from bovine pancreas is obtained as a mixture of chymotrypsin A and B along with variable amounts of trypsin, elastase, carboxypeptidase A, and undefined pancreatic lipids. Recombinant fermentation of the human chymotrypsin B sequence provides a single molecular species with a predictable disulfide bond pattern. Table 2 summarizes the main distinguishing attributes.

The recombinant product is particularly suited to controlled-release dosage forms in which residual trypsin would otherwise alter the release-controlling polymer or prematurely degrade co-formulated peptide APIs. The absence of animal-derived proteases simplifies regulatory submissions under EMA/410/01 Rev. 3 and FDA 21 CFR 211.160. For oral granules, the API is blended with pregelatinized starch and filled into sachets under nitrogen purge; the headspace oxygen is controlled below 2.0% v/v to protect methionine residues from oxidation.

rHC-01 should not be combined with reducing sugars in aqueous granulating fluids because Maillard-type conjugation of lysine residues reduces activity. The product retains catalytic activity in the pH 6.0–8.5 range with an esterase optimum at pH 7.8–8.0; it is inactivated below pH 2.0 and above pH 10.0. In comparison with recombinant trypsin, rHC-01 cleaves after aromatic residues rather than after lysine or arginine, which modifies the peptide mapping profile and reduces the risk of activating certain precursor proteins during processing. Compared with porcine pepsin, rHC-01 operates at neutral to slightly alkaline pH and is not acid-stable. The product is not compatible with oxidizing agents, strong acids, acetone above 40% v/v, or heavy-metal ions such as Fe³⁺ and Cu²⁺.

The oral grade is not interchangeable with the injectable grade; oral material may exceed the injectable endotoxin limit and cannot be terminally sterilized. Injectable grade rHC-01 is supplied in sterile double-bagged containers with a documented sterility assurance level of ≤ 10⁻⁶. Packaging of rHC-01 bulk powder is performed in amber glass or HDPE containers with screw caps under argon, with desiccant. Storage at -20 °C ± 5 °C protects activity for 24 months from the date of manufacture. Once opened, the container should be re-purged with nitrogen and resealed; repeated warming to room temperature accelerates moisture uptake and should be avoided. When used in parenteral processing, the lyophilized powder is equilibrated to 15–25 °C in the unopened container before reconstitution to prevent condensation on the cake surface.