Effect of KRAS and P-STAT3 inhibition by SBT-100 on gemcitabine and pancreatic cancer growth in vivo.

e15727 Background: Over 90% of pancreatic cancers have KRAS mutations and hyper-expression of P-STAT3 oncoproteins, which if specifically targeted may help treatment of pancreatic cancers. Singh Biotechnology’s proprietary technology engineered SBT-100, a single domain antibody that is bispecific for KRAS & STAT3, which can cross the cell membranes and bind to these intracellular oncoproteins. Combining this targeted therapy with an established chemotherapy, such as gemcitabine, may improve patient’s response to treatment. Methods: Human pancreatic cancer cells (PANC-1 and BX-PC3) were used. Biacore assay demonstrates SBT-100 binding to KRAS, KRAS (G12D), and STAT3. Immunoprecipitation (IP) and western blot analysis confirmed binding to STAT3 by SBT-100. Pancreatic cancer cells were treated at varying doses of SBT-100 ranging from 0µg/ml to 200µg/ml ± gemcitabine, and after 72 hours growth inhibition was determined by a MTT assay. PANC-1 tumors were grown in athymic nude mice, divided into four groups and staged to a range of 100-150mm3 before treatment. Groups were: vehicle only, SBT-100, gemcitabine, and SBT-100 & gemcitabine. Animals received treatments for 14 days, then monitored for 7 days. Results: Biacore study shows SBT-100 binds KRAS with an affinity of 10-9M, KRAS (G12D) with 10-8M, and STAT3 with 10-8M. IP and western blot analysis demonstrates that SBT-100 binds P-STAT3. MTT assay demonstrates SBT-100 inhibits the growth of PANC-1 and BX-PC3 (p < 0.001). In PANC1 cells a combination of SBT-100 & gemcitabine demonstrates synergism in inhibiting growth of PANC-1, even at 1/8th the gemcitabine IC50 concentration. PANC-1 xenograft study demonstrates that combination therapy of SBT-100 & gemcitabine is superior to either SBT-100 or gemcitabine alone. Compared to the vehicle group, SBT-100 & gemcitabine is far superior (p < 0.001) and gives statistically significant suppression of pancreatic cancer growth in vivo. Conclusions: Targeted therapy for KRAS and P-STAT3 expressing tumors with SBT-100 & gemcitabine is synergistic for the treatment of pancreatic cancer. This study suggests that synergism maybe achieved with lower doses of gemcitabine, thereby reducing toxicity in patients.