P36 Silencing of IGF-IR and IGF-I induce antitumoral immune response in breast cancer model

Role of insulin-like growth factor (IGF-I) and its type I receptor (IGF-IR) in tumorigenesis has been well documented as well as various approaches to counteract their action in cells and animals either for basic research or for therapeutic purpose. Few of these strategies like RNA or oligonucleotide antisense-based down- regulation of IGF-I or IGF-IR have shown in addition to in vivo tumor growth inhibition, an interesting triggering of antitumoral immune response. In our work, IGF-I and IGF-IR blockade through RNA interference and their potential immunological stimulation induced by IGFs inhibition are addressed in syngenic models using 2’Omethyl modified short interfering RNA. After screening various sequences of siRNAs using luciferase-based reporter constructs, real-time PCR and western blot analysis, we find some sequences, which are able to downregulate efficiently IGF-I and IGF-IR mRNA and proteins in murine hepatocarcinoma and breast cancer cells. Moreover, silencing of IGF-IR diminished the phosphorylation of downstream signaling pathway proteins AKT and ERK1/2, inhibited cell proliferation and induced a G0/G1 cell cycle block. When transfected with anti IGF-I or anti IGF-IR siRNA, C4HD cells, which belongs to a murine progestin-dependent mammary tumor model, significantly decreased their tumorigenicity in BALB/c mice. Histological analyses of such tumors revealed a low mitotic grade and the presence of lymphocyte infiltration, suggesting the involvement of an antitumoral immunological response. In another set of preliminary experiments, IGF-IR down-regulated C4HD cells were used as a cellular vaccine to induce a protective immune response. A moderate immune response was therefore observed against parental tumor challenge. Nevertheless, no significant tumor growth inhibition was clearly obtained with this vaccine protocol, despite an increase in delayed-type hypersensitivity and the presence of stimulated splenocytes and activated dendritic cells in lymph nodes. Our findings suggest that RNA interference technology may offer a new clinical approach for treatment of tumors expressing IGF-IR – or IGF-I – provided the use of modified short interfering RNA with a better understanding of IGF axis and immunological network relationship.