SIL-204 siRNA encapsulated in extended release microparticles for the treatment of localized cancer that harbors a KRAS G12x or G13D mutation.

745 Background: In a Phase 2 trial, treatment of non-resectable locally advanced pancreatic cancer (LAPC) patients harboring the KRAS G12D or G12V mutations, with SiG12DLoder combined with chemotherapy resulted in superior median overall survival (OS) of 9.3 months over chemotherapy (not statistically significant) and Objective Response Rate of 55% (35% over the chemotherapy control), when administered once every 3 months (Clinical trial # NCT01676259, ESMO 2023, abstract FPN: 1626). SIL-204 which is a modified version of siRNA siG12D is composed of a 21-base sense and 23-base antisense strands, both chemically modified and linked to a lipid. SIL-204 is encapsulated in biodegradable PLGA microparticles (MP), for direct release and injection into KRAS mutated solid tumors using an endoscopic ultrasound procedure. The strategy of preventing the synthesis of KRAS mutated protein may have an advantage over other approaches targeting KRAS function using small molecules. Methods: Methods are presented in results section. Results: SIL-204 has an increase stability over siG12D.To enhance stability, base modifications and phosphorothiate bonds at cleavage sites were implemented. SIL-204 exhibited a half-life of more than 48 hours in human serum. SIL-204 has robust KRAS silencing . When tested in Hepa1-6 cells transfected with individual human KRAS mutations, SIL-204 effectively silenced the various G12x mutations found in pancreatic cancer (D,V,R,C) at sub-nanomolar concentration (IC50 range=0.19-0.59) as well as G13D (IC50 =0.37). Addition of a hydrophobic tail to a prototype of SIL-204, SIL-101, increased the silencing of KRAS. Using PANC-1 cells (KRAS G12D mutation), lipid conjugation of the siRNA doubled the siRNA’s silencing efficiency in these cells. In addition, release of SIL-204 from the MP was tested in rats and indicates a prolong and sustained release over our intended treatment regimen SIL-204-MP was administered to tumors from human pancreatic tumor cell lines Capan-1 (KRAS G12V mutation and labelled with luciferase) grown in NSG mice and Panc-1 (grown in Athymic Nude mice). Bioluminescence imaging of tumor growth showed that SIL-204-MP significantly reduced Capan-1 tumor growth compared to vehicle controls, p<0.0005. Furthermore, histopathological analyses of tumor center slices from Capan-1 and Panc-1 models showed induction of significant tumor necrosis with SIL-204 compared to vehicle controls. Conclusions: The preclinical results of SIL-204-MP are promising and as the potential to further enhance the anti-tumor effect demonstrated by siG12DLoder in pancreatic patients. SIL-204 is now in toxicology studies as preparation for clinical trials in non-resectable pancreatic cancer.