A Clinical Study of Tomaralimab (OPN-305), a Toll-like Receptor 2 (TLR-2) Antibody, in Heavily Pre-Treated Transfusion Dependent Patients with Lower Risk Myelodysplastic Syndromes (MDS) That Have Received and Failed on Prior Hypomethylating Agent (HMA) Therapy

INTRODUCTION: Innate immune sensors such as TLR2 are consistently overexpressed in bone marrow CD34+ cells from low risk MDS patients (pts), and a gain of function mutation in TLR2 correlates with progression. Ex vivo inhibition of TLR2 in cultures of CD34+ cells using Tomaralimab (OPN-305), a fully humanised antagonistic IgG4 monoclonal antibody, led to an increase in differentiation of erythroid cultures. We previously reported a human trial with Tomaralimab in low risk/Int-1 MDS that failed HMA therapy (HMA-F) using 5 mg/kg Tomaralimab (n=11), with 4 pts treated at a higher dose of 10 mg/kg monthly. Here we report response data in an expanded 10 mg/kg HMA-F cohort. Tomaralimab was administered as a third line therapy to heavily pre-treated transfusion-dependent (TD) pts with >50% of pts having received ≥4 previous therapies. The data indicate that Tomaralimab is a potential therapy for low risk/Int-1 MDS.

METHODS: We designed a phase I/II multi-site clinical trial of Tomaralimab for pts with low or Int-1 risk MDS after failure with prior therapy with HMA. Pts were treated every 4 weeks for up to 9 cycles, with the potential of continued use thereafter. Azacitidine (AZA) could be added back into the therapy regimen after 16 weeks of Tomaralimab monotherapy if there was no response. The primary endpoint was the induction of transfusion independence for two consecutive cycles as defined in IWG criteria (major responders). A minor response was characterised by at least a 50% reduction in the need for transfusions compared to their transfusions prior to Tomaralimab therapy. We also evaluated the toxicity, pharmacokinetic profile, receptor occupancy, cytokine profile, as well as a novel set of TLR2 related genes.

RESULTS: At the time of this report, 51 pts have received Tomaralimab at 10 mg/kg in HMA-F pts. The median age was 72 years and 79% of the pts were male. Twenty two pts were fully evaluable, having completed the study at Week 36 and either achieving transfusion independence or, if not, receiving AZA add-back unless previously withdrawn due to toxicity or disease progression. Pre-study, the average transfusion was 10 units (median = 3.5 units) and the average on-study was 2 units (median = 1.5 units). Even though these pts were very heavily pre-treated with previous therapies, there were 6 pts who met the primary endpoint (27%) across multiple centres, 5 of which were on Tomaralimab monotherapy at the time of response. Furthermore, there were 5 minor responders (23%), giving an overall response rate (ORR) of 50%. Additionally, 10 pts (45%) remained stable throughout the therapy window. There were no dose limiting toxicities or development of anti-drug antibodies. Tomaralimab receptor occupancy (RO) was measured by flow cytometry in both the BM (CD34+CD38- cells) and PB (CD14+ CD45+). Measured RO levels in both indicated that there was full receptor occupancy in both compartments and that Tomaralimab penetrated the BM. Compared to non-responders, there was a non-significant increase in the expression of TLR1, IRAK4, IL-6, GATA-2, CD71, TRAF6 and S100A9 and a non-significant decrease in GATA-1, TLR2 and TLR6. These are non-significant because of low numbers in the non-responder group. Gene expression was increased in all cases relative to age matched non-MDS healthy controls. Of these genes, of particular interest is S100A9. This has been shown in the literature to be increased in the BM plasma of MDS pts. Furthermore, using the cell line THP-1XBlue we showed that S100A9 signals via TLR2 in vitro and this effect was ameliorated by incubation with Tomaralimab.

CONCLUSIONS: Early data suggest that Tomaralimab therapy presents a novel and safe treatment for heavily pre-treated low risk/Int-1 MDS HMA-F pts. Tomaralimab exhibited a 50% ORR in heavily pre-treated, transfusion dependent HMA-F patents. Treatment was well tolerated and penetrated the bone marrow. RO in the blood could also be used as a surrogate for RO in the bone marrow. Surprisingly, there was no correlation between efficacy and cytokine concentration in the plasma, although cytokine changes in the bone marrow were not determined. There were however non-significant alterations in TLR2 and related genes in purified bone marrow cells from pts. Studies using these cells are underway to further elucidate the mechanism of action. In brief, Tomaralimab therapy presents a potential therapeutic option for heavily pre-treated low risk pts that have failed HMA therapy.