Transient CDK4/6 inhibition protects hematopoietic stem cells from chemotherapy-induced exhaustion.

Conventional cytotoxic chemotherapy is highly effective in certain cancers but causes dose-limiting damage to normal proliferating cells, especially hematopoietic stem and progenitor cells (HSPCs). Serial exposure to cytotoxics causes a long-term hematopoietic compromise ("exhaustion"), which limits the use of chemotherapy and success of cancer therapy. We show that the coadministration of G1T28 (trilaciclib), which is a small-molecule inhibitor of cyclin-dependent kinases 4 and 6 (CDK4/6), contemporaneously with cytotoxic chemotherapy protects murine hematopoietic stem cells (HSCs) from chemotherapy-induced exhaustion in a serial 5-fluorouracil treatment model. Consistent with a cell-intrinsic effect, we show directly preserved HSC function resulting in a more rapid recovery of peripheral blood counts, enhanced serial transplantation capacity, and reduced myeloid skewing. When administered to healthy human volunteers, G1T28 demonstrated excellent in vivo pharmacology and transiently inhibited bone marrow (BM) HSPC proliferation. These findings suggest that the combination of CDK4/6 inhibitors with cytotoxic chemotherapy should provide a means to attenuate therapy-induced BM exhaustion in patients with cancer.

A phase 1/2 trial of HQK-1001, an oral fetal globin inducer, in sickle cell disease.

Therapeutics which reduce the pathology in sickle cell syndromes are needed, particularly noncytotoxic therapeutics. Fetal hemoglobin (HbF, α(2) γ(2) ) is established as a major regulator of disease severity; increased HbF levels correlate with milder clinical courses and improved survival. Accordingly, sodium dimethylbutyrate (HQK-1001), an orally-bioavailable, promoter-targeted fetal globin gene-inducing agent, was evaluated in a randomized, blinded, dose-ranging Phase I/II trial in 24 adult patients with HbSS or S/ß thalassemia, to determine safety and tolerability of three escalating dose levels. The study therapeutic was administered once daily for two 6-week cycles, with a two-week interim dose holiday. Twenty-one patients completed the study. Five patients received study drug at 10 or 20 mg/kg doses, seven patients received study drug at 30 mg/kg/dose, and 4 patients received placebo. HQK-1001 was well-tolerated with no unexpected drug-related adverse events; a dose-limiting toxicity was not identified. Plasma drug levels were sustained above targeted levels for 24 hr. Increases in HbF above baseline were observed particularly with 30 mg/kg/day doses; in five of seven treated patients, a mean absolute increase in HbF of 0.2 g/dl and a mean increase in total hemoglobin (Hgb) of 0.83 g/dl above baseline were observed, whereas no increases occurred in placebo-treated controls. These findings of favorable PK profiles, tolerability, early rises in HbF, and total Hgb indicate that trials of longer duration appear warranted to more definitively evaluate the therapeutic potential of HQK-1001 in sickle cell disease.

Evaluation of safety and pharmacokinetics of sodium 2,2 dimethylbutyrate, a novel short chain fatty acid derivative, in a phase 1, double-blind, placebo-controlled, single-dose, and repeat-dose studies in healthy volunteers.

Pharmacologic induction of fetal globin synthesis is an accepted therapeutic strategy for treatment of the beta hemoglobinopathies and thalassemias, as even small increases in hemoglobin F (HbF) levels reduce clinical severity in sickle cell disease (SCD) and reduce anemia in beta thalassemia. Prior generation short chain fatty acid therapeutics, arginine butyrate (AB), and phenylbutyrate, increased fetal and total hemoglobin levels in patients, but were limited by high doses or intravenous (IV) infusion. A fetal globin-inducing therapeutic with convenient oral dosing would be an advance for these classic molecular diseases. Healthy adult human subjects were treated with a novel short chain fatty acids (SCFA) derivative, sodium 2,2 dimethylbutyrate (SDMB), or placebo, with 1 of 4 single dose levels (2, 5, 10, and 20 mg/kg) or daily doses (5, 10, or 15 mg/kg) over 14 days, and monitored for adverse clinical and laboratory events, drug levels, reticulocytes, and HbF assays. SDMB was well-tolerated with no clinically significant adverse events related to study medication. The terminal half-life ranged from 9 to 15 hours. Increases in mean absolute reticulocytes were observed at all dose levels in the 14-day study. The favorable pharmacokinetics (PK) profiles and safety findings indicate that SDMB warrants further investigation for treatment of anemic subjects with beta hemoglobinopathies.