High Potency Vasoactive Intestinal Peptide Receptor Antagonists Induce Durable Antileukemia/Tumor T Cell Memory in Mice with Once Daily Dosing

Introduction: Allogeneic bone marrow transplantation (allo-BMT) is curative for patients with myeloid leukemia (AML) through the activity of cytotoxic effector donor T cells, but high morbidity and mortality of allo-BMT limits the use of this therapy. A long-standing goal is the development of strategies that induce an autologous immune response to leukemic blasts by the patient's T cells. Vasoactive intestinal peptide (VIP) is a neuropeptide with pleiotropic functions, including modulation of immune and inflammatory responses. Previous studies demonstrated that VIP hybrid (VIPhyb), a peptide antagonist of VIP-signaling, induced T cell-dependent anti-leukemic activity in murine allotransplant models and promoted activation of mouse and human T cells (Li et al., 2016, Cancer Res). We developed a series of novel peptide VIP antagonists (VIP-ANT) based upon predicted binding affinity in silico to human VIP receptors VPAC1 and VPAC2. We tested the anti-cancer potential of these new VIP-ANT peptides in murine models of myeloid leukemia and mastocytoma, investigating the optimal dose and schedule of administration, and explored mechanisms underlying anti-tumor memory induced by VIP-ANT peptides.

Methods: B6 (CD45.1, or albino) mice were injected intravenously with 1 x 10⁶ C1498 cells (AML), and DBA/2j mice were injected subcutaneously with 5 x 10⁴ P815 cells (myeloid mastocytoma). Leukemia-bearing mice were treated with subcutaneous injections of VIP-ANT or control scrambled peptides. Treatment started six days after injection of cells when C1498 leukemia cells were detectable in the blood, and luciferase+ P815 cells as tumors were palpable. A range of VIP-ANT doses was administered s.c. at 10, 30, or 100 μg. Treatment schedules tested included twice daily for 14 doses, once daily, once every other day, once every three days, and once weekly for 7 doses. Some mice received a single dose at day +6 following leukemia cell injection. Lymphocyte kinetics and leukemia cell burden were analyzed weekly through submandibular peripheral blood collections. Mice without evidence of AML/mastocytoma >60 days post-inoculation received a second injection of a two-fold higher dose of C1498 (2 × 10⁶ cells) or P815 (1 × 10⁵ cells).

Results: We tested over 13 new VIP-ANT peptides. Daily or every other day (qod) administration of the novel VIP-ANT peptides to leukemia/tumor-bearing mice led to clearance of C1498 cells from blood or complete regression of P815 in 40 % of mice, leading to significantly improved survival over 60 days. Daily administration of 10 μg of novel VIP-ANT peptides for 7 days to leukemic mice prolonged survival(p<0.0001 VIP-ANT vs scramble, Fig 1A), with the fraction of mice that remained leukemia-free proportional to the predicted binding affinity of the VIP-ANT to human VPAC1 and VPAC2. With increased dose intensity and dose-density of ANT308, the most potent peptide, 40%-80% of mice survived to 70 days (median survival days (MSD) of 60 days) after ANT308 treatment compared with the survival of <20% in mice receiving scrambled peptide (MSD 36 days). Increasing the dose and schedule of ANT308 administration to 100 μg twice-daily led to 65% survival (MSD not reached) versus 40% with daily dosing, 30% with every-other-day dosing, and 0% survival with scrambled-sequence control peptide (MSD 33 days) (p<0.001, Fig 1B). Notably, the affinity of different VIP-ANT peptides to VPAC1 and VPAC2 VIP receptors significantly correlated with the survival of C1498-leukemic mice following prior treatment with the corresponding peptide. Prior treatment of leukemic mice with VIP-ANT induced protective immunological memory, rendering mice resistant to re-challenge with C1498 acute myeloid leukemia (80% survival) and P815 mastocytoma (60% survival) cells, compared with 0% survival (MSD 21 days) among immunologically naïve mice.

Conclusion: Blocking VIP-signaling with high-affinity VIP-R peptide antagonists represents a novel pharmacological approach to enhance adaptive T cell responses to leukemia/myeloid sarcoma-associated antigens in murine leukemia/tumor models. We are continuing PK and toxicology studies with the lead VIP-ANT peptides to support the development of phase 1 clinical trials for patients with relapsed AML.

Waller:Orca Bio: Research Funding; Verastem Oncology: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding.