pd-0325901 and Precursor-T-Cell-Lymphoblastic-Leukemia-Lymphoma

Mutations that deregulate Notch1 and Ras/phosphoinositide 3 kinase (PI3K)/Akt signalling are prevalent in T-cell acute lymphoblastic leukaemia (T-ALL), and often coexist. Here we show that the PI3K inhibitor GDC-0941 is active against primary T-ALLs from wild-type and Kras(G12D) mice, and addition of the MEK inhibitor PD0325901 increases its efficacy. Mice invariably relapsed after treatment with drug-resistant clones, most of which unexpectedly had reduced levels of activated Notch1 protein, downregulated many Notch1 target genes, and exhibited cross-resistance to γ-secretase inhibitors. Multiple resistant primary T-ALLs that emerged in vivo did not contain somatic Notch1 mutations present in the parental leukaemia. Importantly, resistant clones upregulated PI3K signalling. Consistent with these data, inhibiting Notch1 activated the PI3K pathway, providing a likely mechanism for selection against oncogenic Notch1 signalling. These studies validate PI3K as a therapeutic target in T-ALL and raise the unexpected possibility that dual inhibition of PI3K and Notch1 signalling could promote drug resistance in T-ALL.

Topics: Animals; Benzamides; Clone Cells; Diphenylamine; Down-Regulation; Drug Resistance, Neoplasm; Drug Synergism; Genes, ras; Indazoles; Male; Mice; Mice, Inbred C57BL; Mitogen-Activated Protein Kinase Kinases; Phosphoinositide-3 Kinase Inhibitors; Precursor T-Cell Lymphoblastic Leukemia-Lymphoma; Protein Kinase Inhibitors; Protein Structure, Tertiary; Proto-Oncogene Proteins c-akt; Receptor, Notch1; Signal Transduction; Sulfonamides

Mice that accurately model the genetic diversity found in human cancer are valuable tools for interrogating disease mechanisms and investigating novel therapeutic strategies. We performed insertional mutagenesis with the MOL4070LTR retrovirus in Mx1-Cre, Kras(G12D) mice and generated a large cohort of T lineage acute lymphoblastic leukemias (T-ALLs). Molecular analysis infers that retroviral integration within Ikzf1 is an early event in leukemogenesis that precedes Kras(G12D) expression and later acquisition of somatic Notch1 mutations. Importantly, biochemical analysis uncovered unexpected heterogeneity, which suggests that Ras signaling networks are remodeled during multistep tumorigenesis. We tested tumor-derived cell lines to identify biomarkers of therapeutic response to targeted inhibitors. Whereas all T-ALLs tested were sensitive to a dual-specificity phosphoinosityl 3-kinase/mammalian target of rapamycin inhibitor, biochemical evidence of Notch1 activation correlated with sensitivity to gamma-secretase inhibition. In addition, Kras(G12D) T-ALLs were more responsive to a MAP/ERK kinase inhibitor in vitro and in vivo. Together, these studies identify a genetic pathway involving Ikzf1, Kras(G12D), and Notch1 in T lineage leukemogenesis, reveal unexpected diversity in Ras-regulated signaling networks, and define biomarkers of drug responses that may inform treatment strategies.

Topics: Amino Acid Substitution; Amyloid Precursor Protein Secretases; Animals; Antineoplastic Agents; Benzamides; Cell Line, Tumor; Cell Lineage; Clone Cells; Diphenylamine; Enzyme Inhibitors; Genetic Loci; Humans; Ikaros Transcription Factor; Integrases; Mice; Models, Immunological; Mutant Proteins; Mutation; Precursor T-Cell Lymphoblastic Leukemia-Lymphoma; Proto-Oncogene Proteins p21(ras); Receptor, Notch1; Retroviridae; Signal Transduction