TP-0184 Inhibits ALK2/ACVR1, Decreases Hepcidin Levels, and Demonstrates Activity in Preclinical Mouse Models of Functional Iron Deficiency

Background

Hepcidin is a liver peptide hormone that functions as a master regulator of bioavailable iron. Hepcidin levels become constitutively high in chronic inflammatory conditions where functional iron deficiency (FID) becomes a challenge. Approaches to target hepcidin expression or function have emerged as attractive strategies to reverse the complications of functional iron deficiency. Targeting the activation of the ALK2/ACVR1 receptor has been validated as a promising approach to target hepcidin. Activation of ALK2/ACVR1 in the liver induces the SMAD-driven transcription of hepcidin which, by promoting the degradation of the iron transporter ferroportin, leads to reduced serum iron levels and subsequent functional anemia. Current therapeutic approaches for anemia of chronic disease (ACD) rely on transfusions, intravenous iron and the use of erythropoietin-based therapies, none of which adequately address the underlying pathological deficit of functionally low iron levels. TP-0184 has been developed as a potent and selective inhibitor of ALK2/ACVR1, and it was hypothesized that targeting of ALK2/ACVR1 with TP-0184 would reverse the effects of FID in preclinical models of anemia. TP-0184 is a small-molecule inhibitor of ALK2 kinase activity, exhibiting an IC₅₀ of 5 nM in biochemical assays.

Aims

The current study seeks to establish proof-of-concept that TP-0184 targets ALK2/ACVR1 and reverses the effects of FID. Utilizing the unique experience in a single patient IND, the clinical effects of TP-0184 on serum hepcidin levels was evaluated.

Methods

Multiple preclinical models of anemia were used to evaluate the efficacy of TP-0184. These models included: a short-term chemical induced anemia by turpentine oil (TO), a model of anemia of cancer using the TC-1 syngenic lung cancer cell line, and an infectious disease model using heat-inactivated Brucella abortus (HKBA).

Results

TP-0184 has demonstrated consistent preclinical activity in three mouse efficacy models of FID. In the first model, TP-0184 reversed hepcidin induction more than 6.8-fold in mice induced with TO. The simplicity of the TO model has allowed the exploration of numerous dose levels and treatment schedules of TP-0184 and the ability to correlate these with pharmacokinetic plasma levels of the compound. In the second model, TP-0184 reversed elevated hepcidin levels and increased iron levels induced in TC-1 tumor bearing mice. Hepcidin was reduced nearly 3-fold with doses as low as 25 mg/kg. In the third model, TP-0184 abrogated reductions in hemoglobin and total red blood cell counts induced by intraperitoneal injection of HKBA. In addition to these preclinical models, a single cancer patient received oral administration of TP-0184 in an emergency setting. Although the primary objectives of the single patient study did not include anemia, pharmacokinetic and pharmacodynamic measurements related to anemia were measured in the patient. The patient was administered 2 cycles of TP-0184, where each cycle evaluated a different formulation. Before the first cycle, the patient had a baseline serum hepcidin level of 559 pg/mL. These levels dropped to below the detectable limit within 24 hours of the first dose with TP-0184. Hepcidin levels remained undetectable for the duration of TP-0184 treatment. After a break in treatment, the patient was administered a second cycle of TP-0184 in an alternative formulation. During this cycle, the patient's hepcidin levels decreased from 182 pg/mL to 69 pg/mL after 24 hours of the first dose (cycle 2). With daily dosing, the patient's serum hepcidin levels continued to decrease to undetectable levels by at least 9 days. Importantly, serum iron levels mirrored serum hepcidin levels well. Plasma pharmacokinetics were also obtained in this patient.

Conclusion

Targeting ALK2/ACVR1 is an attractive strategy to downregulate hepcidin levels and reverse the effects of FID. TP-0184, a potent ALK2/ACVR1 inhibitor, has demonstrated consistent activity in multiple preclinical models and now has preliminary proof-of-concept evidence that it can modulate hepcidin levels in man. The development of TP-0184 is currently progressing through preclinical development and a Phase I first-in-human study focusing on FID is currently being planned.