Abstract 1739: Intratumoral INTASYL™ self-delivering RNAi targeting PD-1 provides in vivo tumor control and mechanistic modulation of tumor microenvironment analogous to that of systemic anti-PD-1 antibody
Authors: Cuiffo Benjamin , Maxwell Melissa , Yan Dingxue , Cardia James , Fricker Simon P. 
Published: July 2021

Abstract
The clinical success of immune checkpoint blockade (ICB) antibodies like those inhibiting PD-1 have revolutionized cancer care, however, durable responses are still limited. Systemic ICB can also elicit immune-related adverse effects (irAEs) whereas local intratumoral (IT) delivery has the potential to mitigate these toxicities. The INTASYL™ platform is a self-delivering RNAi technology that (1) provides efficient delivery into target cells without specialized formulations, mechanical perturbation, or drug delivery systems; and (2) specifically and durably silences target gene expression and (3) has been shown to be safe and effective in clinical applications following local administration. Here we demonstrate that IT treatment with the PD-1 targeting INTASYL PH-762 inhibits tumor growth in a dose dependent fashion in two tumor models, Hepa1-6 and CT26. Modulation of key immune cell populations in the tumor microenvironment (TME) by systemic antibody PD-1 inhibition are recapitulated under IT treatment with the PD-1 targeting INTASYL PH-762. Hepa1-6 or CT26 tumor cells were implanted subcutaneously into female C57BL/6 or BALB/c mice, respectively. Vehicle, non-targeting control (NTC-647) or murine PD-1 targeting INTASYL (mPH-762) were each administered IT at doses ranging from 0.02 - 2 mg/dose; murine anti-PD-1 monoclonal antibody (anti-PD-1 mAb) was administered intraperitoneally (IP) at 200 μg/dose, each on Days 1, 3, 7, 10 and 14. Tumor volumes and body weight were recorded. Tumors (N = 6/group) were isolated from the Hepa1-6 model for ex vivo analyses. All treatments were well tolerated. Treatment with mPH-762 inhibited tumor growth in Hepa1-6 in a dose dependent manner compared to PBS or NTC, with doses of 0.5 mg or 2 mg inhibiting tumor growth similar to anti-PD-1 mAb. In the TME, treatment with mPH-762 modulated tumor immune populations toward antitumor phenotypes, including significantly increasing overall %CD45+ cells and CD8+ T cells, reducing putative Tregs, and increasing median M1/M2 tumor associated macrophage ratios compared to PBS or NTC-647 in a dose associated manner and similar to anti-PD-1 mAb. Dose-correlating on-target silencing of PD-1 protein expression was observed under treatment with mPH-762 but not anti-PD-1 mAb across key TME cell populations.
In conclusion, in vivo tumor control elicited by the PD-1 silencing INTASYL mPH-762 (IT) was akin to that provided by systemic anti-PD-1 mAb (IP). Similar modulation of TME immune cell populations associated with antitumor efficacy were observed under both systemic Ab and local INTASYL (IT) treatments. As INTASYL is efficacious and may mitigate irAEs caused by antibody ICB, INTASYL PH-762 warrants further investigation in patients. ​
Citation Format: Benjamin Cuiffo, Melissa Maxwell, Dingxue Yan, James Cardia, Simon P. Fricker. Intratumoral INTASYL™ self-delivering RNAi targeting PD-1 provides in vivo tumor control and mechanistic modulation of tumor microenvironment analogous to that of systemic anti-PD-1 antibody [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1739.