Stimulant for stem cell expansion in vivo to speed recovery of neutropenia secondary to chemotherapy and stem cell transplant

PROJECT SUMMARY Hematopoietic stem cell (HSC) transplants (HSCTs) are considered a potentially curative option for patients with certain cancers of the blood and bone marrow, and over 20,000 HSCTs are performed in the US each year. However, HSCTs are associated with high risk due to the required removal of diseased bone marrow before transplantation. Until the transplanted cells engraft and proliferate enough to reconstitute the patient’s immune system, the patient is considered neutropenic, during which time they are highly susceptible to infection. In addition to the potentially life-threatening physical risk to the patient, neutropenia necessitates long hospitalization time that can in part drive the expensive cost of HSCTs ranging from $200,000-400,000 in the US depending on donor cell type. A current strategy in clinical trials is to transplant larger pools of donor HSCs to shorten the neutropenic phase. However, currently investigated HSC expansion approaches will all rely on long-term (~3-week) ex vivo culturing of donor cells that depend on imperfect man-made culture systems that may disrupt the proper function of the stem cells and can be prohibitively expensive. Ship of Theseus’ innovative solution is a drug that will be used for a short, 24-hour exposure time to donor cells prior to transplantation that improves expansion in vivo. Our drug is a patented mutant of Homeobox protein B4 (HOXB4m). HOXB4 is well-established to promote HSC expansion without altering differentiation. However, its progression to the clinic was stopped because the half-life of HOXB4 protein was too short to be practical for clinical use and genetically overexpressing HOXB4 resulted in myeloproliferative disorders. Our patented, cell- penetrating/nuclear-targeting mutant has improved degradation resistance, elongating its intracellular half-life enough to be practical for clinical use while potentially avoiding adverse effects induced by constitutive overexpression. In our Phase I project, we successfully demonstrated rapid and diverse short-term bone marrow cell expansion in vitro, short-term reduction of neutropenic phase in vivo, and long-term hematopoietic reconstitution in vivo upon HOXB4m treatment. The goal of this Phase II SBIR proposal is to perform IND-enabling safety, pharmacokinetic/pharmacodynamic (PK/PD) while also optimizing the clinical protocol. This will be accomplished through two aims. In Aim 1, we will extend in vivo efficacy confirmation to a 24-hour incubation with HOXB4 protein tagged with a novel proprietary cell penetrating/nuclear-targeting peptide optimized in vitro in a mouse model of HSCT. In Aim 2, we will manufacture HOXB4m under GMP and conduct definitive toxicology and PK/PD studies in mice. Successful completion of this Phase II program will provide the necessary data to support an IND submission and eventual Phase I clinical trials. With HOXB4m, we can circumvent the original hurdles of HOXB4 and improve expansion in vivo to benefit HSCT patients by shortening the neutropenic phase to reduce infection, hospitalization time, and cost.