Identification of Novel Pathways and Small Molecules Able to Down Regulate Oncogenes Expression By Compounds Screening Approaches in Acute Leukemia and Neuroblastoma Cells

Targeting anaplastic lymphoma kinase (ALK), a receptor tyrosine kinase initially identified as a potent oncogenic driver in anaplastic large-cell lymphoma (ALCL) in the form of nucleophosmin (NPM)-ALK fusion protein, using tyrosine kinase inhibitors has shown to be a promising therapeutic approach for ALK-expressing tumors. However, resistance to ALK inhibitors is a ubiquitous problem in ALK-expressing cell lines as well as treated patients. Amplified ALK or mutated ALK was identified in ~14% of neuroblastomas (NB), the most common and aggressive childhood malignancy, and phase I trial of ALK inhibitor such as crizotinib showed a lack of response in patients harboring certain ALK mutations. Previous reports have suggested that mechanism of resistance is mediated by mutations in the ALK kinase domain impairing binding of an inhibitor to an ALK protein. Thus, new treatment modalities are urgently needed to sensitize patients to crizotinib thereby improving the management of hematological or solid malignancies harboring ALK mutations. To identify compounds with the potential of inhibiting oncogenic activity of ALK in NB, we implemented a high throughput chemical screen in 4 NB-derived cell lines, using a curated library of ~450 compounds. In the compounds screening, JAK-STAT kinase inhibitor (cucurbitacin I) was the most discriminatory with regard to sensitivity for ALK-mutated cell lines. Since Gamma cytokine JAK/STAT system as a target in the treatment of T-cell or myeloid malignancies, we analyzed the cytotoxicity of cucurbitacin I antitumor effect using an MTT assay revealed cucurbitacin I to possess potent cytotoxic activity across a broad spectrum of hematopoietic malignancies, with T-acute lymphoblastic leukemia (ALL) and acute myeloid leukemia (AML) being especially responsive. For example, T-ALL cell lines, as well as AML lines, were potently inhibited by cucurbitacin I (IC₅₀values:T-ALL lines, ICH-TALL-UK, 103.2 nM; MOLT-14, 35.6 nM; KCMC-T, 134.2 nM; Jurkat, 77 nM; ICH-TALL-SM, 47.7 nM; MOLT-4, 22.2 nM. AML lines, HEL, 66.7 nM; Kasumi-3, 4.5 nM; KG-1, 53.6 nM; THP-1, 337.2 nM). In an expanded panel of 20 NB cell lines, those with or without MYCN-amplification or 11q loss of heterozygousity which have been identified as two major oncogenic events in NB pathogenesis, especially in the high-risk group were the most sensitive to low nanomolar concentrations of cucurbitacin I. In NB cell lines harboring F1174L or R1275Q-mutated ALK, crizotinib combined with cucurbitacin I enhanced tumor responses and showed synergistic cytotoxicity.Although crizotinib and cucurbitacin I alone or combination therapy (cucurbitacin I + crizotinib) did not result in decreased viability over control compared with vehicle, the combination therapy in all of 6 cell lines with ALK aberrations and 10 of 13 ALK wild-type cell lines with MYCN amplification or 11q LOH was more effective than vehicle, crizotinib alone, and cucurbitacin I alone. Analysis of downstream signalling through MAPK, AKT and STAT3 pathways showed that NIH3T3 cells stably expressed F1174L mutated ALK or TGW cells harboring R1275Q-mutated ALK, expressed lower levels of pERK, pAKT and pSTAT3 in combination therapy compared with cells treated with cucurbitacin I or crizotinib alone. These findings may provide a indication that the combination of low-dose ALK and STAT3 inhibitors may be benefitical for the treatment of NB, by enhancing efficacy while reducing toxicity. In conclusion, our studies suggested that NB, T-ALL or AML cell lines also exhibited potent cytotoxic responses to the cucurbitacin I and the combination of ALK and JAK-STAT inhibitors could be a valuable therapeutic option for ALK mutated malignancies such as high-risk NB with potential clinical application.