Multitargeted tyrosine kinase inhibitor stimulates expression of IL-6 and activates JAK2/STAT5 signaling in acute myelogenous leukemia cells

A novel anti-c-Kit antibody-drug conjugate to treat wild-type and activating-mutant c-Kit-positive tumors

c‐Kit overexpression and activating mutations, which are reported in various cancers, including gastrointestinal stromal tumor (GIST), small‐cell lung cancer (SCLC), acute myeloid leukemia, acral melanoma, and systemic mastocytosis (SM), confer resistance to tyrosine kinase inhibitors (TKIs). To overcome TKI resistance, an anti‐c‐Kit antibody–drug conjugate was developed in this study to treat wild‐type and mutant c‐Kit‐positive cancers. NN2101, a fully human IgG1, was conjugated to DM1, a microtubule inhibitor, through N‐succinimidyl‐4‐(N‐maleimidomethyl) cyclohexane‐1‐carboxylate (SMCC) (to give NN2101‐DM1). The antitumor activity of NN2101‐DM1 was evaluated in vitro and in vivo using various cancer cell lines. NN2101‐DM1 exhibited potent growth‐inhibitory activities against c‐Kit‐positive cancer cell lines. In a mouse xenograft model, NN2101‐DM1 exhibited potent growth‐inhibitory activities against imatinib‐resistant GIST and SM cells. In addition, NN2101‐DM1 exhibited a significantly higher anti‐cancer effect than carboplatin/etoposide against SCLC cells where c‐Kit does not mediate cancer pathogenesis. Furthermore, the combination of NN2101‐DM1 with imatinib in imatinib‐sensitive GIST cells induced complete remission compared with treatment with NN2101‐DM1 or imatinib alone in mouse xenograft models. These results suggest that NN2101‐DM1 is a potential therapeutic agent for wild‐type and mutant c‐Kit‐positive cancers.

Biological and therapeutic implications of a unique subtype of NPM1 mutated AML

In acute myeloid leukemia (AML), molecular heterogeneity across patients constitutes a major challenge for prognosis and therapy. AML with NPM1 mutation is a distinct genetic entity in the revised World Health Organization classification. However, differing patterns of co-mutation and response to therapy within this group necessitate further stratification. Here we report two distinct subtypes within NPM1 mutated AML patients, which we label as primitive and committed based on the respective presence or absence of a stem cell signature. Using gene expression (RNA-seq), epigenomic (ATAC-seq) and immunophenotyping (CyToF) analysis, we associate each subtype with specific molecular characteristics, disease differentiation state and patient survival. Using ex vivo drug sensitivity profiling, we show a differential drug response of the subtypes to specific kinase inhibitors, irrespective of the FLT3-ITD status. Differential drug responses of the primitive and committed subtype are validated in an independent AML cohort. Our results highlight heterogeneity among NPM1 mutated AML patient samples based on stemness and suggest that the addition of kinase inhibitors to the treatment of cases with the primitive signature, lacking FLT3-ITD, could have therapeutic benefit.

Regulation of IL-6-type cytokine responses by MAPKs

IL-6 (interleukin 6)-type cytokines are pleiotropic molecules, critical for cellular homoeostasis and with well-recognized roles in several human diseases. They all activate JAK (Janus kinase)/STAT (signal transducer and activator of transcription) signalling and, depending on the particular cytokine, cell type and cellular environment, they can also trigger the activation of MAPK (mitogen-activated protein kinase) and PI3K (phosphoinositide 3-kinase) cascades. Although it is clear that JAK/STAT and MAPK reciprocally regulate each other, how these signalling pathways are fully integrated remains to be fully understood. Not only do cells have to be able to integrate and conciliate what are often contradictory signalling cues, but they are also subject to complex regulatory mechanisms involving these pathways. More specifically, we have shown recently that ERK2 (extracellular-signal-regulated kinase 2) is required for the transcriptional regulation of gp130 (glycoprotein 130), a key receptor complex component for most IL-6-type cytokines. ERK2 not only binds to the gp130 promoter and is required for full expression of the protein, but it also regulates the stability of gp130 mRNA. This function of ERK2 is not shared by ERK1 and it probably represents an entirely novel function for this prominent kinase.

Interleukin-6: a potential biomarker of resistance to multitargeted receptor tyrosine kinase inhibitors in castration-resistant prostate cancer

OBJECTIVE

To determine if cellular interleukin-6 production predicts response to tyrosine kinase inhibitors (TKIs). As clinical experience using TKIs in patients with castration-resistant prostate cancer (CRPC) matures, Phase II trials show a heterogeneous response to sunitinib in CRPC patients. Change in serum prostate-specific antigen (PSA) level has proven unreliable for prediction of CRPC response to TKIs. Interleukin-6 (IL-6), a critical mediator of prostate cancer pathogenesis, has been shown to rise in patients with disease progression. As such, we investigated whether cellular IL-6 production can predict TKI response in both in vitro and in vivo models.

METHODS

IL-6 mRNA levels and protein expression were examined by reverse transcriptase-polymerase chain reaction and enzyme-linked immunosorbent assay, respectively. Apoptosis was examined using the terminal dUTP nick-end labeling assay. For in vivo studies, a CRPC xenograft model in C.B17/Icr-scid mice was used.

RESULTS

PC-3 and DU-145 CRPC cell lines exhibited a heterogeneous response to sunitinib and pazopanib. Dose-dependent reduction of IL-6 was observed in TKI-sensitive DU-145 cells. In contrast, the TKI-resistant PC-3 cells failed to suppress IL-6 secretion. Instead, in the presence of tumor necrosis factor-alpha, IL-6 rose significantly upon administration of TKIs. Findings of in vitro experiments were confirmed in an in vivo mouse model of CRPC.

CONCLUSION

Sensitivity of CRPC cells to TKIs is heterogeneous. These findings are consistent with results of recently published Phase II clinical trials using sunitinib in patients with CRPC. A substantial rise in IL-6 occurs both in vitro and in vivo in the presence of TKIs in resistant PC-3 cells but not in TKI-sensitive DU-145 cells. These findings suggest that IL-6 may represent a biomarker for TKI resistance in patients with CRPC.

Long-term exposure of gastrointestinal stromal tumor cells to sunitinib induces epigenetic silencing of the PTEN gene

Although sunitinib possesses significant clinical effects on imatinib-resistant gastrointestinal stromal tumors (GISTs), the individuals with GIST eventually become resistant to treatment with this tyrosine kinase inhibitor. The mechanism of resistance to sunitinib is still under investigation. To address this issue, we have established sunitinib-resistant GIST-T1 sublines (designated as GIST-T1R) by culturing cells with increasing concentrations of sunitinib. GIST-T1R cells were also resistant to imatinib-mediated growth inhibition. Examination of intracellular signaling found that Akt/ mammalian target of rapamycin (mTOR) signaling remained activated in GIST-T1R but not in parental GIST-T1 cells, after exposure of these cells to sunitinib, as measured by immunoblotting. Further study found that the phosphatase and tensin homolog deleted on chromosome ten (PTEN) gene was silenced by methylation of the promoter region of the gene. Notably, forced-expression of PTEN in GIST-T1R cells negatively regulated the Akt/mTOR pathways and sensitized these cells to sunitinib-mediated growth arrest and apoptosis. Taken together, epigenetic silence of PTEN might be one of the mechanisms which cause drug-resistance in individuals with GIST after exposure to tyrosine kinase inhibitors. Blockade of the PI3K/Akt signaling with the specific inhibitors could be useful in such a case.

Long-term exposure of leukemia cells to multi-targeted tyrosine kinase inhibitor induces activations of AKT, ERK and STAT5 signaling via epigenetic silencing of the PTEN gene

Imatinib induces complete molecular response in patients with chronic myeloid leukemia (CML) and chronic eosinophilic leukemia (CEL). However, development of resistance to imatinib has emerged as an important clinical problem for molecular-targeted therapy in CML and CEL. In this study, we have established the imatinib-resistant CEL EOL-1 sub-lines (designated as EOL-1R) by culturing cells with increasing concentrations of imatinib for 6 months. Interestingly, EOL-1R cells showed epigenetic silencing of the phosphatase and tensin homolog deleted on chromosome ten (PTEN) gene. Exposure of EOL-1R cells to imatinib failed to dephosphorylate AKT, ERK and STAT5, although PDGFRalpha was effectively inactivated. The forced expression of PTEN negatively regulated these signal pathways and sensitized EOL-1R cells to imatinib. Notably, hypermethylation of the promoter region of the PTEN gene in association with the downregulation of this gene's transcripts was identified in imatinib-resistant leukemia cells isolated from individuals with CEL, CML and Philadelphia-positive acute lymphoblastic leukemia. In addition, anti-epigenetic agents restored PTEN expression, resulting in the sensitization of EOL-1R cells to imatinib. Taken together, epigenetic silence of PTEN is one of the mechanisms that cause drug resistance in individuals with leukemia after exposure to imatinib. Anti-epigenetic agents may be useful for overcoming drug resistance in such a case.

Development of novel adenosine monophosphate-activated protein kinase activators

In light of the unique ability of thiazolidinediones to mediate peroxisome proliferator-activated receptor (PPAR)gamma-independent activation of adenosine monophosphate-activated protein kinase (AMPK) and suppression of interleukin (IL)-6 production, we conducted a screening of an in-house, thiazolidinedione-based focused compound library to identify novel agents with these dual pharmacological activities. Cell-based assays pertinent to the activation status of AMPK and mammalian homologue of target of rapamycin (i.e., phosphorylation of AMPK and p70 ribosomal protein S6 kinase, respectively) and IL-6/IL-6 receptor signaling (i.e., IL-6 production and signal transducer and activator of transcription 3 phosphorylation, respectively) in lipopolysaccharide (LPS)-stimulated THP-1 human macrophages were used to screen this compound library, which led to the identification of compound 53 (N-{4-[3-(1-methyl-cyclohexylmethyl)-2,4-dioxo-thiazolidin-5-ylidene-methyl]-phenyl}-4-nitro-3-trifluoro-methyl-benzenesulfonamide) as the lead agent. Evidence indicates that this drug-induced suppression of LPS-stimulated IL-6 production was attributable to AMPK activation. Furthermore, compound 53-mediated AMPK activation was demonstrated in C-26 colon adenocarcinoma cells, indicating that it is not a cell line-specific event.

Sunitinib impairs the proliferation and function of human peripheral T cell and prevents T-cell-mediated immune response in mice

Sunitinib (sunitinib malate; SU11248; SUTENT) is a novel multi-targeted receptor tyrosine kinase inhibitor currently approved for the treatment of metastatic renal cell carcinoma. To analyze the possible use of this compound in combination with immunotherapeutic approaches, we investigated the effects of sunitinib on the human peripheral T cells and the induction of primary immune responses in mice. Sunitinib inhibited the proliferation of primary human T cells from normal healthy volunteers as well as from renal cell carcinoma (RCC) and other cancer patients. The inhibition was recoverable after drug withdrawal because sunitinib did not induce T-cell apoptosis even at 0.8 muM. In addition, sunitinib led to accumulation in G(0)/G(1) phase of the cell cycle, inhibition of cytokine production, downregulation of activation markers expression and blockade of Zap-70 signaling in the T cells. Sunitinib significantly reduced the ear swelling induced by picryl chloride in mice. In light of these findings, the effects of sunitinib on the immune system should be emphasized for the therapy of metastatic renal cell carcinoma patients to avoid the impairment of T lymphocytes.