3.3. Anti-SSTR2 mAb and ADC Generation

The SSTR2 mAb was produced using hybridoma cells in a 2-L stirred-tank bioreactor (Chemglass, Vineland, NJ, USA), controlled at 37 °C, pH 7.0, DO 50%, and agitation 70 rpm [39,47]. The bioreactor was seeded with hybridoma cells at a VCD of 0.3 × 10⁶ cells/mL in Hybridoma-SFM basal medium supplemented with 4 g/L glucose, 6 mM L-glutamine, and 3.5 g/L Cell Boost #6 on Day 0. Fed-batch production was performed by feeding 4 g/L glucose, 6 mM L-glutamine, and 3.5 g/L Cell Boost #6 on Day 3. The anti-SSTR2 mAb was purified using an NGC liquid chromatography system (Bio-Rad, Hercules, CA, USA) equipped with Protein A and ion exchange columns [38,48]. The ADC was constructed by conjugating DM1 with purified anti-SSTR2 mAb via sulfo-SMCC linker following our previously developed platform [38,49]. ADC product was concentrated and purified using 10 kDa MWCO concentrator (Fisher) to remove most linker and free drugs first. Then, a PD SpinTrap^TM G25 column (GE Healthcare, Chicago, IL, USA) was applied to remove the chemicals used in conjugation. Finally, high-performance liquid chromatography (HPLC, Shimadzu, Columbia, MD, USA) equipped with an MABPac HIC-butyl column (Fisher) was used to remove unconjugated mAb and also analyze the drug–antibody ratio (DAR) of ADC. The purified ADC was neutralized to pH 7.0 with 1 M Tris solution, sterilized, and mixed with 0.1% sodium azide for long-term storage at −80 °C.