Selective small molecule inhibitors of p110α and δ isoforms of phosphoinosityl-3-kinase are cytotoxic to human acute myeloid leukemia progenitors.

The phosphoinosityl-3-kinase (PI3K) pathway is frequently constitutively active in blast cells from acute myeloid leukemia (AML) patients. RNA and protein from all four catalytic isoforms of PI3K (p110α, β, γ, and δ) were expressed in 38 AML samples, which also showed expression of phosphorylated Akt Ser473, indicating PI3K activation. Initial treatment of 12 AML samples with inhibitors targeting each of the four isoforms demonstrated that p110α and δ inhibition are more effective in killing AML blast colony-forming cells (CFC) than p110β or γ inhibition.

Liposomal encapsulation of a synergistic molar ratio of cytarabine and daunorubicin enhances selective toxicity for acute myeloid leukemia progenitors as compared to analogous normal hematopoietic cells.

Objective: To evaluate the possibility of improved selective killing of acute myeloid leukemia (AML) cells with CPX-351 (a liposomal formulation of cytarabine and daunorubicin). CPX-351 and the same molar ratio of free drugs were compared for cytotoxicity against colony-forming cells (CFCs) and subpopulations of cells enriched for primitive progenitors from AML patients and normal granulocyte colony-stimulating factor-mobilized peripheral blood (PB) and bone marrow (BM) donors.

Materials And Methods: AML blasts (n = 13) and normal PB and BM cells (n = 7) were incubated for 24 hours in various concentrations of CPX-351 or free drugs before plating in CFC assay or staining with anti-CD34 and anti-CD38 antibodies, Annexin-V, and propidium iodide followed by fluorescence-activated cell sorting analysis.

Variant diphtheria toxin-interleukin-3 fusion proteins with increased receptor affinity have enhanced cytotoxicity against acute myeloid leukemia progenitors.

A fusion protein linking a truncated form of diphtheria toxin (DT(388)) to human interleukin-3 (DT(388)IL3) kills malignant progenitors from some patients with acute myeloid leukemia (AML) while sparing normal progenitors. This study evaluated two variants of DT(388)IL3 with increased affinity for the IL-3 receptor (IL-3R) for their cytotoxicity to AML progenitors and determined the ability of quantitative reverse transcription-PCR assessment of expression of the IL-3R subunits to predict the effectiveness of wild-type DT(388)IL3 and its variants. Both the IL-3 deletion variant (Delta125-133) and the amino acid substitution variant (K116W) showed enhanced toxicity against AML colony-forming cells (AML-CFC; but not normal CFC) compared with wild-type DT(388)IL3 with the K116W variant achieving >90% AML-CFC kill with 17 of 23 patient samples.

The efficacy of diphtheria-growth factor fusion proteins is enhanced by co-administration of cytosine arabinoside in an immunodeficient mouse model of human acute myeloid leukemia.

Addition of cytosine arabinoside (Ara-C) to truncated diphtheria toxin (DT388) fused to granulocyte macrophage-colony stimulating factor (GMCSF) or interleukin-3 (IL3) was studied in a NOD/SCID mouse model of human AML. Ara-C alone did not reduce the % human AML cells in mouse bone marrow (BM). DT388IL3 or DT388GMCSF alone reduced but did not eradicate engraftment for two of four and two of three samples, respectively.

A diphtheria toxin-interleukin 3 fusion protein is cytotoxic to primitive acute myeloid leukemia progenitors but spares normal progenitors.

The relative cytotoxicity of a diphtheria toxin (DT) human interleukin 3(IL3) fusion protein (DT(388)IL3) was tested against primitive normal (n = 3)and acute myeloid leukemia (AML) progenitors (n = 7). After 24-h culture with 50 ng/ml DT(388)IL3, the mean percentages of kill of AML colony-forming cells (CFCs), long-term culture-initiating cells (LTC-ICs), and suspension culture-ICs (SC-ICs) were 82% (range, 47-100), 56% (range, 28-91), and 74% (range, 43-87), respectively, with most surviving progenitors being cytogenetically normal. Engraftment of DT(388)IL-3-treated AML cells in nonobese diabetic/severe combined immunodeficient (NOD/SCID) mice followed for 16 weeks was eradicated for two of these samples.