Narazaciclib, a novel multi-kinase inhibitor with potent activity against CSF1R, FLT3 and CDK6, shows strong anti-AML activity in defined preclinical models.

CSF1R is a receptor tyrosine kinase responsible for the growth/survival/polarization of macrophages and overexpressed in some AML patients. We hypothesized that a novel multi-kinase inhibitor (TKi), narazaciclib (HX301/ON123300), with high potency against CSF1R (IC50 ~ 0.285 nM), would have anti-AML effects. We tested this by confirming HX301's high potency against CSF1R (IC50 ~ 0.285 nM), as well as other kinases, e.g. FLT3 (IC50 of ~ 19.77 nM) and CDK6 (0.53 nM). An in vitro proliferation assay showed that narazaciclib has a high growth inhibitory effect in cell cultures where CSF1R or mutant FLT3-ITD variants that may be proliferation drivers, including primary macrophages (IC50 of 72.5 nM) and a subset of AML lines (IC50 < 1.5 µM). In vivo pharmacology modeling of narazaciclib using five AML xenografts resulted in: inhibition of MV4-11 (FLT3-ITD) subcutaneous tumor growth and complete suppression of AM7577-PDX (FLT3-ITD/CSF1Rmed) systemic growth, likely due to the suppression of FLT3-ITD activity; complete suppression of AM8096-PDX (CSF1Rhi/wild-type FLT3) growth, likely due to the inhibition of CSF1R ("a putative driver"); and nonresponse of both AM5512-PDX and AM7407-PDX (wild-type FLT3/CSF1Rlo). Significant leukemia load reductions in bone marrow, where disease originated, were also achieved in both responders (AM7577/AM8096), implicating that HX301 might be a potentially more effective therapy than those only affecting peripheral leukemic cells. Altogether, narazaciclib can potentially be a candidate treatment for a subset of AML with CSF1Rhi and/or mutant FLT3-ITD variants, particularly second generation FLT3 inhibitor resistant variants.

NSCLC harboring EGFR exon-20 insertions after the regulatory C-helix of kinase domain responds poorly to known EGFR inhibitors.

Anecdote clinical observations hint that non-small cell lung cancer (NSCLC) with exon-20 insertions might respond poorly to epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs), contrasting to those with classic mutations. Lack of patient-derived experimental models has been a major hurdle for the discovery of new treatment for the diseases. We established two NSCLC-PDXs harboring two different exon-20 insertions, LU0387-adenocarcinoma (ADC) with a nine-base insertion at 2319 (H773-V774insNPH) and LU3075-squamous cell carcinoma (SCC) with a nine-base insertion at 2316 (P772-H773insDNP). Both insertions immediately follow the regulatory C-helix of the kinase domain. Contrary to the generally good responses to EGFR inhibitors observed in PDXs with classic mutations, both exon-20 insertions are largely resistant to cetuximab and TKIs in vivo, suggesting fundamental difference from the classic EGFR mutations, consistent with the poor response rate to TKI seen in anecdotal clinic reports. It is worth noting that although responses are generally poor, they differ between the two exon-20 mutants depending on the type of TKI. In vitro drug sensitivity assays using established primary cell lines from our two PDXs largely confirmed the in vivo data. Our data from patient-derived experimental models confirmed that exon-20 insertions in domain immediately following the C-helix confer poor response to all known EGFR inhibitors, and suggested that these models can be utilized to facilitate the discovery of new therapies targeting NSCLC harboring exon-20 insertions.

HnRNP A1/A2 and SF2/ASF regulate alternative splicing of interferon regulatory factor-3 and affect immunomodulatory functions in human non-small cell lung cancer cells.

Heterogeneous nuclear ribonucleoparticule A1/A2 (hnRNP A1/A2) and splicing factor 2/alternative splicing factor (SF2/ASF) are pivotal for precursor messenger RNA (pre-mRNA) splicing. Interferon regulatory factor-3 (IRF-3) plays critical roles in host defense against viral and microbial infection. Truncated IRF-3 proteins resulting from alternative splicing have been identified and characterized as functional antagonists to full-length IRF-3. In this study, we examined the molecular mechanism for splicing regulation of IRF-3 pre-mRNA and first reported the regulatory effect of hnRNP A1/A2 and SF2/ASF on IRF-3 splicing and activation. RNA interference-mediated depletion of hnRNP A1/A2 or SF2/ASF in human non-small cell lung cancer (NSCLC) cells increased exclusion of exons 2 and 3 of IRF-3 gene and reduced expression levels of IRF-3 protein and IRF-3 downstream effector molecules interferon-beta and CXCL10/IP-10. In addition, direct binding of hnRNP A1 and SF2/ASF to specific binding motifs in IRF-3 intron 1 was confirmed by RNA electrophoretic mobility shift assay. Subsequent minigene splicing assay showed that IRF-3 minigenes with mutated hnRNPA 1/A2 or SF2/ASF binding motifs increased exclusion of exons 2 and 3. Moreover, knockdown of hnRNP A1/A2 or SF2/ASF in NSCLC cells reinforced phytohemagglutinin-induced tumor necrosis factor-alpha release by peripheral blood mononuclear cells (PBMC) but suppressed that of interleukin-10 in NSCLC/PBMC co-cultures. Taken together, our results suggest that specific knockdown for hnRNP A1/A2 or SF2/ASF increase exclusion of exons 2 and 3 of IRF-3 pre-mRNA and influence immunomodulatory functions of human NSCLC cells.

Molecular characteristics of CTA056, a novel interleukin-2-inducible T-cell kinase inhibitor that selectively targets malignant T cells and modulates oncomirs.

Interleukin-2-inducible T-cell kinase (Itk) is a member of the Btk (Bruton's tyrosine kinase) family of tyrosine kinases. Itk plays an important role in normal T-cell functions and in the pathophysiology of both autoimmune diseases and T-cell malignancies. Here, we describe the initial characterization of a selective inhibitor, 7-benzyl-1-(3-(piperidin-1-yl)propyl)-2-(4-(pyridin-4-yl)phenyl)-1H-imidazo[4,5-g]quinoxalin-6(5H)-one (CTA056), that was developed through screening a 9600-compound combinatorial solution phase library, followed by molecular modeling, and extensive structure-activity relationship studies. CTA056 exhibits the highest inhibitory effects toward Itk, followed by Btk and endothelial and epithelial tyrosine kinase. Among the 41 cancer cell lines analyzed, CTA056 selectively targets acute lymphoblastic T-cell leukemia and cutaneous T-cell lymphoma. Normal T cells are minimally affected. Incubation of Jurkat and MOLT-4 cells with CTA056 resulted in the inhibition of the phosphorylation of Itk and its effectors including PLC-γ, Akt, and extracellular signal-regulated kinase, as well as the decreased secretion of targeted genes such as interleukin-2 and interferon-γ. Jurkat cells also underwent apoptosis in a dose-dependent manner when incubated with CTA056. The potent apoptosis-inducing potential of CTA056 is reflected by the significant modulation of microRNAs involved in survival pathways and oncogenesis. The in vitro cytotoxic effect on malignant T cells is further validated in a xenograft model. The selective expression and activation of Itk in malignant T cells, as well as the specificity of CTA056 for Itk, make this molecule a potential therapeutic agent for the treatment of T-cell leukemia and lymphoma.

Tip60 modulates PLAGL2-mediated transactivation by acetylation.

Pleiomorphic adenoma gene (PLAG) family proteins are oncogenes involved in various malignancies including lipoblastomas, hepatoblastomas, and acute myeloid leukemia. Overexpression of PLAGL2 induces cell transformation and proliferation, but little is known about how its activities are regulated. We previously showed that transcriptional activity of PLAGL2 is negatively regulated by sumoylation. Here we report that Tip60 modulates PLAGL2 functions through acetylation. Tip60 associates with PLAGL2 through its zinc finger domain and acetylates PLAGL2. Wild-type but not the histone acetyltransferase (HAT)-minus mutant form of Tip60 enhances PLAGL2-mediated transactivation. In addition, coexpression of Tip60 and PLAGL2 completely abolishes the sumoylation of PLAGL2. Both Tip60 and DN-Ubc9 increase transactivation activity of wild-type but not the sumoylation deficient form of PLAGL2 (K250, 269, 356R), indicating that Tip60 acetylates PLAGL2 and abolishes the sumoylation of PLAGL2 possibly through modification of the same lysine residues (K250, 269, 356) within PLAGL2. Tip60 effects vary between different PLAGL2 target gene promoters, suggesting that Tip60 is a novel promoter-specific coactivator of PLAGL2. This is the first demonstration that Tip60 can function as a sumoylation inhibitor in part through its intrinsic acetyltransferase activity to regulate specific gene expression.

PLAGL2 controls the stability of Pirh2, an E3 ubiquitin ligase for p53.

PLAGL2 (Pleomorphic Adenoma Gene Like 2) is an oncoprotein involved in various malignancies including lipoblastomas, hepatoblastomas, and acute myeloid leukemia. Although PLAGL2 is known to mainly act as a transcription factor, other functions which may contribute to its oncogenic potential are not clear. Pirh2 (P53 induced RING-H2 protein) is a p53 inducible E3 ligase involved in the ubiquitination of p53, while the mechanisms to regulate its activities are largely unknown. In this study, we show for the first time that Pirh2 forms dimers through its N- and C-terminus in cells and Pirh2 dimers interact with PLAGL2. The interaction between PLAGL2 and Pirh2 dimers prevents proteasomal degradation of Pirh2. This study thus uncovers a novel function of PLAGL2 as an oncoprotein through regulating the stability of Pirh2. Given the importance of Pirh2 in regulating p53 stability, its interaction with PLAGL2 may provide valuable therapeutic targets in treating Pirh2-overexpression malignancies.

AKT/PKB signaling mechanisms in cancer and chemoresistance.

During the past decade, Akt (also known as protein kinase B, PKB) has been extensively studied. It regulates a variety of cellular processes by mediating extracellular (mitogenic growth factor, insulin and stress) and intracellular (altered tyrosine receptor kinases, Ras and Src) signals. Activation of Akt by these signals is via its pleckstrin homology (PH) domain binding to products of phosphatidylinositol 3-kinase (PI3K). This process is negatively regulated by a dual phosphatase PTEN tumor suppressor. Today, more than 30 Akt substrates have been identified. These phosphorylation events mediate the effects of Akt on cell survival, growth, differentiation, angiogenesis, migration and metabolism. Further, PI3K/PTEN/Akt pathway is frequently altered in many human malignancies and overexpression of Akt induces malignant transformation and chemoresistance. Thus, the Akt pathway is a major target for anti-cancer drug development. This review focuses on Akt signaling mechanism in oncogenesis and chemoresistance, and ongoing translational efforts to therapeutically target Akt.

The association of the expression level of protein tyrosine phosphatase PRL-3 protein with liver metastasis and prognosis of patients with colorectal cancer.

PURPOSE: To investigate PRL-3 protein expression in normal colorectal epithelia and colorectal cancers with monoclonal antibody (MAb) against PRL-3. METHODS: MAb against PRL-3 was prepared with the hybridoma technique, and its specificity was confirmed with ELISA and Western blotting assays. The expression of PRL-3 protein in normal colorectal epithelia and colorectal cancers was examined by immunohistochemistry assay. Logistic regression and survival analysis were performed to determine the clinical significance of PRL-3 expression. RESULTS: MAb 3B6 against PRL-3 was obtained and showed high specificity. PRL-3 protein was expressed in two of 28 (7.1%) normal colorectal epithelia, 21 of 88 (23.9%) primary colorectal cancers, 22 of 41 (53.7%) metastatic lymph nodes and eight of 12 (66.7%) liver metastases, respectively. The PRL-3 expression rates of metastases were significantly higher than those of primary colorectal cancers and normal colorectal epithelia (P < 0.05). PRL-3 expression was significantly associated with the liver metastasis of colorectal cancer (P = 0.004) and tended to shorten survival time (P = 0.0145). CONCLUSIONS: This is the first study demonstrating that PRL-3 is a potential marker for liver metastasis of colorectal cancer and negatively influences the prognosis of colorectal cancer patients.

[Mycoplasma infection and cancer].

Mycoplasmas are widespread in nature as conditional pathogen, which may be the unique prokaryote that can cohabit with eukaryote and interact permanently with mammalian cells. Mycoplasma infection can be detected in many tumor tissues, continuous infection of mycoplasma can lead to transformation of mammalian cells, up-regulating expression of oncogenes, and some biologic changes of tumor cells, suggesting association of mycoplasma infection with tumorigenesis.

Identification of antigens by monoclonal antibody PD4 and its expression in Escherichia coli.

AIM: To clone and express the antigen of monoclonal antibody (MAb) PD4 for further investigation of its function. METHODS: MGC803 cDNA expression library was constructed and screened with PD4 as probes to clone the antigen. After failed in the library screening, immunoprecipitation and SDS-polyacrylamide gel electrophoresis were applied to purify the antigen for sequence analysis. The antigen coming from Mycoplasma hyorhinis (M. hyorhinis) was further confirmed with Western blot analysis by infecting M. hyorhinis -free HeLa cells and eliminating the M. hyorhinis from MGC803 cells. The full p37 gene was cloned by PCR and expressed successfully in Escherichia coli after site-directed mutations. Immunofluorescence assay was used to demonstrate if p37 protein could directly bind to gastric tumor cell AGS. RESULTS: The cDNA library constructed with MGC803 cells was screened by MAb PD4 as probes. Unfortunately, the positive clones identified with MAb PD4 were also reacted with unrelated antibodies. Then, immunoprecipitation was performed and the purified antigen was identified to be a membrane protein of Mycoplasma hyorhinis (M. hyorhinis) by sequencing of N-terminal amino acid residues. The membrane protein was intensively verified with Western blot by eliminating M. hyorhinis from MGC803 cells and by infecting M. hyorhinis-free HeLa cells. The full p37 gene was cloned and expressed successfully in Escherichia coli after site-directed mutations. Immunofluorescence demonstrated that p37 protein could directly bind to gastric tumor cell AGS. CONCLUSION: The antigen recognized by MAb PD4 is from M. hyorhinis, which suggests the actions involved in MAb PD4 is possibly mediated by p37 protein or M. hyorhinis. As p37 protein can bind directly to tumor cells, the pathogenic role of p37 involved in tumorigenesis justifies further investigation.