OC 56.3 - Platelets transfected with a KRASG12D-silencing siRNA reduce pancreatic tumor mass in vivo in mice

Background: Pancreatic ductal adenocarcinoma (PDAC) is one of the deadliest solid cancers with a dismal 7% 5-year survival rate. There is evidence that aberrant KRAS is critical for PDAC growth and progression. The extraordinarily complex PDAC tumor microenvironment is a major hurdle to therapeutic delivery to PDAC.
Small-interfering RNAs (siRNAs) harbor tremendous therapeutic potential but no therapeutic siRNAs targeting KRAS have been explored so far for PDAC.

Aims: To assess whether platelets can efficiently deliver therapeutic siRNAs to PDAC in vitro and in vivo and display antitumor activity.

Methods: Human platelets transfected with KRASG12D siRNA were co-incubated in vitro with a PDAC cell line (Panc-1) for 48 hours which was then analyzed by q-PCR for mutant KRAS expression.
Moreover, human KRASG12D-siRNA-transfected platelets were repeatedly transfused (6 times, every 48 hours, from day 7 to day 20) in immunotolerant NSG mice, starting 7 days after the subcutaneous injection of 1x10^6 Human Panc-1 cells. Control mice were transfused with non-targeting scrambled-siRNA (NC)-transfected platelets. Tumor burden, circulating human platelets and animal weights were measured at different time intervals.

Results: KRASG12D expression in Panc-1 cells was strikingly reduced after co-incubation with KRASG12D-siRNA-transfected platelets (-92.86±0.11% vs control).
KRASG12D-siRNA-transfected platelets-transfused mice showed a statistically significant decrease of tumor volume and weight (figure). No significant differences in the two experimental groups were found regarding body weight and circulating human transfected platelets at day 11 (3.18±0.83% vs 3.99±0.51%).

Conclusion(s): Our data show that platelets transfected with a siRNA targeting KRASG12D and co-incubated with PDAC cells in vitro are able to strongly silence the tumor cell KRAS oncogene. The repeated transfusion of human siRNA-transfected platelets in mice in which PDAC was subcutaneously injected significantly reduced tumor progression. Platelets transfected with therapeutic siRNA seem to be an efficient vehicle for targeted delivery of therapeutic siRNA to PDAC.