Use of the Immunoproteasome Subunit LMP7 Inhibitor to Ameliorate Gvhd in an MHC-Matched miHA-Disparate Murine Model

Therapeutic targeting of the ubiquitin-proteasome pathway is currently used for the treatment of multiple myeloma. The immunoproteasome however, is a distinct class of proteasome found predominantly in monocytes and lymphocytes, and it is known to regulate antigen presentation on class I major histocompatibility complexes (MHC-I). ONX 0914 is a LMP7-selective peptide-epoxyketone proteasome inhibitor that is currently in pre-clinical development for the treatment of inflammatory diseases. In the current study, we evaluated the feasibility of using ONX 0914 in the B10.BR→CBA MHC-matched (H2^k), minor histocompatibility antigen (miHA)-disparate bone marrow transplantation (BMT) model to decrease the incidence of GVHD. This well established allogeneic BMT model is relevant to the MHC-matched sibling donor or completely matched unrelated donor clinical situation.

To evaluate the effects of ONX 0914 on GVHD, we tested different compound regimens in the model. CBA recipient mice were lethally irradiated (11 Gy, split dose, 4 h apart) and transplanted with 2×10⁶ anti-T cell depleted B10.BR bone marrow cells (ATBM) alone, or in combination with 1×10⁷ enriched B10.BR T cells (GVHD control and ONX 0914 treated groups). ONX 0914 was administrated in full (s.c., once/day at 8 mg/kg) or as a split dose (half dose, twice/day approximately 6 hr apart).

Treatment with the ONX 0914 compound significantly improved the survival of mice compared to control GVHD recipients when dosing was performed once/day for three consecutive days (0,1,2 post-BMT) [p = 0.02]. Alternating dosage (days 0,2,4) or daily drug treatment (days 0–4) provided comparable amelioration of GVHD in this model.

Our preclinical findings suggest that the immunoproteasome subunit LMP7 is potentially a novel therapeutic target in GVHD as demonstrated by the improved survival rate of recipient mice treated with ONX 0914 in the B10.BR→CBA BMT murine model.

Zilberberg:Onyx Pharmaceuticals: Research Funding. Dziopa:Onyx Pharmaceuticals: Research Funding. Korngold:Onyx Pharmaceuticals: Research Funding.