Fanconi anemia (FA) is a rare genetic disease that often presents as a bone marrow failure (BMF) syndrome but also can affect any other organ. Etiologically, loss of function mutations in more than 21 different gene members of the FA core complex (i.e. FANCA-FANCV) have been associated with FA. The FA core complex is involved in interstrand cross-link DNA damage repair during cell division. Impaired DNA repair causes genomic instability which consequently can cause apoptosis of the cell or malignant transformation. In addition to impaired DNA repair mechanisms, FA cells exhibit increased sensitivity to pro-inflammatory cytokines (e.g. IFN-gamma, TNF-alpha) and elevated levels of these cytokines have been associated with bone marrow failure in subjects with FA and other inherited bone marrow failure syndromes.
Patients with FA may present with congenital anomalies, such as microcephaly or short stature. However, the failure of the hematopoietic stem cell (HSC) compartment to produce sufficient numbers of peripheral blood cells, and progression to myelodysplastic syndrome (MDS) and acute myelogenous leukemia (AML) are the greatest risk factors for morbidity and mortality, particular in young patients with FA. In a few reported cases, spontaneous somatic reversion of inherited mutations has resulted in a selective growth advantage of corrected HSCs that subsequently restored hematopoiesis. However, therapeutic options are limited in FA. Although HSC transplantation outcomes have significantly improved over the past two decades, donor availability, graft failure, and FA-specific transplant toxicities are still significant hurdles towards a curative treatment of FA-associated BMF. Moreover, attempts at genetic correction of FA are not yet ready for patient care.
The thrombopoietin (TPO) mimetic eltrombopag (EPAG) has recently been shown to be effective in restoring tri-lineage hematopoiesis in patients with treatment refractory acquired severe aplastic anemia (SAA). Of particular interest for patients with FA is the observation that EPAG also improves the repair of double strand DNA breaks, a mechanism that is impaired in patients with FA. Additionally, our pre-clinical studies indicate that EPAG evades INF-gamma blockade of signal transduction from the TPO receptor (cMPL) resulting in improved survival and proliferation of HSCs. Based on these clinical and pre-clinical studies, we hypothesize that EPAG will improve peripheral blood cell counts in patients with FA and thus reduce morbidity and mortality.
This phase II clinical trial proposes to treat patients with FA for 6 months with EPAG to assess safety and efficacy at improving hematological manifestations of FA. Responders at 6 months will be able to continue EPAG on the extension part of this protocol for an additional 3 years. During this time frame we anticipate further improvement of peripheral blood cells counts that will eventually result in the discontinuation of EPAG after a tapering period. Translational studies will explore EPAG effects on DNA repair activity, apoptosis, global transcriptome and TPO signaling pathways in patient s hematopoietic stem and progenitor cells (HSPCs).