Unaltered IL-2 encapsulated in acoustically active lipid microspheres for systemic but targeted microdose delivery to tumor microenvironment.

Document Type


Publication Date


Publication Title

2021 ASCO Annual Meeting


oregon; portland; chiles


Research Funding:

Vesselon, Inc

Background:In order to take local advantage of exogenous interleukin-2 (IL-2) on effector T-cells within the tumor microenvironment while simultaneously avoiding systemic Treg immunosuppressive effects, microdoses of recombinant human IL-2 (rhIL-2) were encapsulated in gas-filled lipid microspheres (eIL-2), then activated with ultrasound. This novel therapeutic agent (eIL-2) was selectively delivered to the tumor via sonoporation and its anti-tumor effects were determined alone and in combination with PD-1 blockade.Methods:In an MC38 colon cancer model, jugular button catheters (Instech) were surgically implanted in a total of 56 animals (8 animals per arm) prior to tumor inoculation to facilitate repeatable IV injection of both anti-PD-1 (RMP1-14; BioXCell) and microspheres. Imagent perflexane lipid microspheres were incubated with rhIL-2 and the high concentration infranatant was separated, discarded, and replaced with sterile saline to resuspend microspheres to formulate eIL-2 on-site. Tumor-bearing mice were dosed on Days 1, 4, 8, and 12. Ultrasound (US) settings used were 2.2 MHz frequency, and 0.339 mechanical index (MI) during insonation. Once every 10 seconds a microbubble destruct pulse of 1.304 MI lasting 1,100 milliseconds was applied. Total insonation time was 5 minutes using a commercial ultrasound scanner (Mindray TE7) operating within diagnostically safe exposure limits. Study groups included Group 1: no treatment; Group 2: aPD-1, 3 mg/kg; Group 3: aPD-1, 3 mg/kg, Imagent + US; Group 4: Free rhIL-2, 10,000 IU (0.61μg)/animal; Group 5: eIL-2, approximately 0.2 μg encapsulated/animal; Group 6: Free rhIL-2, 10,000 IU (0.61μg)/animal, aPD-1, 3 mg/kg; Group 7: eIL-2, approximately 0.1 μg encapsulated/animal, aPD-1, 3 mg/kg.Results:The anti-PD-1 dose of 3 mg/kg demonstrated an expected tumor growth inhibition over control of -38.2% on Day 6, -35.6% on Day 8 and -30.3% on Day 12. Adding eIL-2 + ultrasound external stimuli approximately doubled the tumor inhibition effect of RMP1-14 to -68.1% on Day 6, -69.2% on Day 8 and -62.0% on Day 12. We also analyzed cytokine levels in the peripheral blood (Day 12) using a multiplex ELISA and observed elevated levels of pro-inflammatory cytokines including IFN-g, IL-12, and IL-1a, which likely serve to enhance anti-tumor immunity. IL-15 was also increased following treatment, which supports effector T cell survival.Conclusions:Using a novel form of recombinant human interleukin-2 encapsulated within a gas-filled lipid microsphere, we demonstrated that ultrasound-activated local delivery via sonoporation plus systemic PD-1 blockade led to improved tumor control and increased expression of pro-inflammatory cytokines. This novel approach enhances the efficacy of checkpoint blockade for the treatment of solid tumors. Further experiments are underway to interrogate mechanisms of action.

Clinical Institute



Earle A. Chiles Research Institute