Tyrosine Kinase Oncoproteins Research Articles

Crizotinib in Sarcomatous Malignancies Harboring ALK Fusion With a Definitive Partner(s): Response and Efficacy

Sarcoma or sarcomatoid malignancies are a set of mesenchymal-origin malignancies with vast heterogeneity in clinical and molecular characteristics. Anaplastic lymphoma kinase (ALK) is a tyrosine kinase oncoprotein expressed by several tumors, including sarcomas. Crizotinib is an effective ALK inhibitor. In this review paper, we summarized findings from the literature regarding the use of crizotinib for the treatment of sarcoma and sarcomatoid malignancies harboring ALK fusions with definitive partners (with the given gene(s) name) from the years 2010 to 2021.One hundred and four articles were retrieved and after exclusion, 28 studies containing 33 patients were finally selected. All 33 patients were treated with crizotinib. Among the 33 cases, 19 were adult patients, 11 were pediatric patients, and 3 cases did not have data on age and/or gender. Most cases had a primary abdominal lesion (16/30), followed by thoracic (10/30), trunk (3/30), retroperitoneal (1/30), and one case of right medial thigh (case 7). Stage IV disease was reported in 76.7% (23/30) of patients. The objective response rate and disease control rate was 86.7% (26/30) and 96.7% (29/30), respectively, which were assessed on average of 8 weeks after crizotinib initiation. Rapid improvement of symptoms was observed within one to two weeks in some cases including patients with extensive diseases or poor performance. There was no difference in crizotinib response between pediatrics and adult cases. Crizotinib is effective; however, surgery remains the mainstay of therapy, with newer evidence showing concurrent crizotinib with surgery conferring long-term overall survival. However, we should still be cognizant of the heterogeneous landscape of crizotinib efficacy and its associated fatal adverse events.

Comparison of Hepatotoxicity Associated With New BCR-ABL Tyrosine Kinase Inhibitors vs Imatinib Among Patients With Chronic Myeloid Leukemia

Although BCR-ABL fusion oncoprotein tyrosine kinase inhibitors (BCR-ABL TKIs) can substantially improve the survival rate of chronic myeloid leukemia (CML), they are clinically accompanied by severe hepatotoxicity. To compare the relative risk (RR) of hepatotoxicity of new-generation BCR-ABL TKIs with that of imatinib, and to provide an overall assessment of the clinical benefit. PubMed, Embase, Cochrane library databases, and ClinicalTrials.gov were searched for clinical trials published between January 2000 and April 2020. Study selection was conducted independently by 2 investigators according to the inclusion and exclusion criteria published previously in the protocol: only randomized phase 2 or phase 3 clinical trials that compared bosutinib, dasatinib, nilotinib, or ponatinib with imatinib were included. Among the 2666 records identified, 9 studies finally fulfilled the established criteria. Two investigators extracted study characteristics and data independently using a standardized data extraction form. Data were extracted according to Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) reporting guidelines. When substantial heterogeneity was observed, pooled estimates were calculated based on the random-effect model; otherwise, the fixed-effect model was used. Data extracted included study characteristics, baseline patient information, interventions and data on all-grade and high-grade (grades 3 and 4) elevation of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels, overall survival, and major molecular response (MMR). The RRs and 95% CIs were calculated using the inverse variance method. Nine trials involving 3475 patients were analyzed; the median (range) age was 49 (18-91) years; 2059 (59.2%) were male patients. Increased risks were observed for each new-generation TKI except for dasatinib. Patients receiving new-generation TKIs were more likely to experience all grades of ALT elevation (pooled RR, 2.89; 95% CI, 1.78-4.69; P < .001) and grades 3 and 4 ALT elevation (pooled RR, 4.36; 95% CI, 2.00-9.50; P < .001) compared with those receiving imatinib. Patients receiving new-generation TKIs were also more likely to experience all grades of AST elevation (pooled RR, 2.20; 95% CI, 1.63-2.98; P < .001) and grades 3 and 4 AST elevation (pooled RR, 2.65; 95% CI, 1.59-4.42; P < .001) compared with those receiving imatinib. New-generation TKIs were associated with a significantly higher rate of MMR at 1 year compared with imatinib (pooled RR, 1.59; 95% CI, 1.44-1.75; P < .001). No statistical difference in overall survival at 1 year was found between new-generation TKIs and imatinib (pooled RR, 1.00; 95% CI, 1.00-1.01; P = .33). When compared to imatinib, bosutinib, nilotinib, and ponatinib had higher relative risks of hepatotoxicity. Treatment with new-generation TKIs was associated with a higher MMR rate at 1 year but not with 1-year overall survival.

Inhibitors Targeting STAT5 Signaling in Myeloid Leukemias: New Tetrahydroquinoline Derivatives with Improved Antileukemic Potential.

Signal transducers and activators of transcription 5A and 5B (STAT5A and STAT5B) are two closely related STAT family members that are crucial downstream effectors of tyrosine kinase oncoproteins such as FLT3-ITD in acute myeloid leukemia (AML) and BCR-ABL in chronic myeloid leukemia (CML). We recently developed and reported the synthesis of a first molecule called 17 f that selectively inhibits STAT5 signaling in myeloid leukemia cells and overcomes their resistance to chemotherapeutic agents. To improve the antileukemic effect of 17 f, we synthesized ten analogs of this molecule and analyzed their impact on cell growth, survival, chemoresistance and STAT5 signaling. Two compounds, 7 a and 7 a', were identified as having similar or higher antileukemic effects in various AML and CML cell lines. Both molecules were found to be more effective than 17 f at inhibiting STAT5 activity/expression and suppressing the chemoresistance of CML.

Sulfoxythiocarbamate S-4 inhibits HSP90 in human cutaneous squamous cell carcinoma cells

Cancer cells rely heavily on molecular chaperones, such as heat shock protein 90 (HSP90), and their co-chaperones. The development of HSP90 inhibitors is an attractive therapeutic approach that has the potential to affect multiple hallmarks of cancer. Such approach is particularly needed for tumors that carry large mutational burdens, including cutaneous squamous cell carcinomas (cSCC). We previously identified sulfoxythiocarbamate S-4 as an HSP90 inhibitor. In this study, we investigated the mechanism(s) by which S-4 compromises the viability of human cSCC cells. S-4 inhibits HSP90 and causes depletion of its clients HER2, a tyrosine kinase oncoprotein, and Bcl-2, an anti-apoptotic protein. The decrease in Bcl-2 is accompanied by cytochrome c release from mitochondria into the cytoplasm, suggesting apoptosis. In the surviving cells, depletion of the HSP90 clients cyclin D and CDK4 by S-4 prevents phosphorylation of the retinoblastoma protein Rb and the release of transcription factor E2F, inhibiting G1-S cell cycle progression and cell division. These findings illustrate the comprehensive effectiveness of S-4 and encourage future development of compounds of this type for cancer prevention and treatment.

Imatinib therapy in acute myeloid leukemia with DEK-NUP214 and FIP1L1-PDGFRA rearrangement: A case report.

The fusion product of FIP1-like-1 (FIP1L1) and platelet-derived growth factor receptor α (PDGFRA) gene rearrangement is a tyrosine kinase oncoprotein sensitive to imatinib. This gene rearrangement characterizes a novel clinico-biological class of myeloid and lymphoid neoplasms with eosinophilia and PDGFRA abnormalities. The DEK proto-oncogene (DEK) and nucleoporin 214 (NUP214) rearrangement is rare in patients with acute myeloid leukemia (AML); therefore, the coexistence of DEK-NUP214 and FIP1L1-PDGFRA rearrangements in patients with AML is extremely rare. The present study presents a rare relapse case of a patient with AML with DEK-NUP214 and FIP1L1-PDGFRA rearrangements, without marked eosinophilia in the peripheral blood or bone marrow. Low-dose imatinib monotherapy without intensive chemotherapy was used to achieve complete hematological remission.

Expression rate of ALK tyrosine kinase and TAG-72 oncoprotein in primary skin melanoma

Objective.Determine the frequency of occurrence of tyrosine kinase expression of the mutated ALK and TAG-72 gene among patients with primary melanoma of the skin, to identify their association with a number of histological parameters, and to assess the diagnostic value of the determination of ALK and TAG-72.Materials and methods.Paraffin blocks with surgical material from 40 patients with primary skin melanoma. For routine histological examination, the material was fixed with 10 % neutral formalin for 24 h, poured into paraffin, sections were prepared with a thickness of 4–5 μm, stained with hematoxylin and eosin. IHC study with monoclonal antibodies D57.3 to ALK was performed on an immunostender – Ventana, with antibodies B72.3 to TAG-72 – on Thermo Fischer. As a detection system used: Envision – for TAG-72 and Ventana – for ALK.Results.ALK mutation was detected in 7 (12 %), TAG-72 – 4 (10 %) cases. Evaluation of the correlation force between the presence of ALK and TAG-72 showed a direct average coupling strength (correlation coefficient was 0.31). A direct correlation of the mean force between the presence of TAG-72 oncoprotein, ALK mutation and ulceration in the patient was found – the correlation coefficient was 0.53 and 0.68, respectively. There was a statistically significant association between the presence of ALK and lymphoid infiltration, which in most cases (57 %) was pronounced (p &lt;0.05).Conclusion.Comparing the positive sign of the expression of ALK – 17.5 % and TAG-72 – 10 %, and the positive of their simultaneous detection – 7.5 %, it can be concluded that further studies to determine their diagnostic value are promising. The presence of severe lymphoid infiltration in ALK-positive patients claims a diagnostic value in primary skin melanoma.

Effect of Age on NK Cell Compartment in Chronic Myeloid Leukemia Patients Treated With Tyrosine Kinase Inhibitors.

Natural killer (NK) cells are a very important component of the innate immune response involved in the lysis of virus infected and tumor cells. Aging has a profound impact in the frequency, phenotype and function of NK cells. Chronic Myeloid Leukemia (CML) is caused by the BCR-ABL gene formation encoding aberrant oncoprotein tyrosine kinase. Treatment with tyrosine kinase inhibitors (TKIs) induces durable deep molecular response. The response to treatment and life expectancy is lower in older patients with chronic phase of CML than in younger patients. In this work we analyse NK cells from TKI-treated CML patients and healthy controls stratified according to age. We have analyzed the expression of NK receptors, activation markers, NK cell differentiation in CD56bright and CD56dim NK cell subsets and the expression of CD107a and IFN-γ in NK cells stimulated with K562. Whereas significant differences on the phenotype and function of NK cells were found between middle-aged (35–65 years old) and elderly (older than 65) healthy individuals, NK cells from TKI-treated CML patients do not show significant differences related with age in most parameters studied, indicating that age is not a limitation of the NK cell recovery after treatment with TKI. Our results also revealed differences in the expression of NK receptors, activation markers and functional assays in NK cells from TKI-treated CML patients compared with age-matched healthy controls. These results highlight the relevance of NK cells in TKI-treated patients and the need of an extensive analysis of the effect of aging on NK cell phenotype and function in these patients in order to define new NK-cell based strategies directed to control CML progression and achieve long-term disease remission after TKI cessation.

A novel BCR-ABL1 fusion gene with genetic heterogeneity indicates a good prognosis in a chronic myeloid leukemia case

BackgroundChronic myelogenous leukemia (CML) is a pluripotent hematopoietic stem cell disorder caused by the fusion of the BCR and ABL1 genes. Quantitative RT-PCR (qRT-PCR) is a routinely performed screening technique to identify BCR-ABL1 fusion genes, but a limitation of this method is its inability to recognize novel fusions that have not been previously characterized. Next-generation sequencing (NGS) is an effective and sensitive detection method for the determination of novel BCR-ABL1 fusion genes as well as previously characterized ones. The oncoprotein tyrosine kinase BCR-ABL1 is a constitutively active kinase involved in the activation of a number of signaling pathways, and it has been the therapeutic target for tyrosine kinase inhibitors (TKIs) such as imatinib. Reports have presented opposing viewpoints about the effect of the disrupted Src homology 3 (SH3) domain on TKI efficacy.FindingsWe here report that using NGS we identified a novel BCR-ABL1 fusion gene with breakpoints in the BCR intron 14 and the ABL1 intron 2, leading to partial deletion of its SH3 domain. In the present case, the patient received targeted therapy with the TKI imatinib at 400 mg/day and no adverse reaction was reported. The patient eventually entered remission with decreased proliferation of karyocytes and granulocytes. We also identified mutations in genes, including TP53, FLT3, ASXL1, SETBP1, CEBPA and CBL, that seemed to have an influence on the outcome of TKI therapy targeting the BCR-ABL1 protein.ConclusionsTogether with previously reported results, it is clear that the genetic heterogeneity of CML patients significantly affects the presentation of the disease and its progression and therefore should inform the design of the therapeutic strategy.

MiR-155 effectively induces apoptosis in K562 Philadelphia positive cell line through upregulation of p27kip1.

Introduction: Chronic myelogenous leukemia (CML) is a myeloproliferative disorder caused by the Philadelphia chromosome translocation, at (9; 22), which results in BCR-ABL fusion tyrosine kinase oncoprotein. This fusion induces down-regulation of miR-155. Upregulation of miR-155 can influence cell fate via the effect on p27kip1 and apoptosis. The aim of this study was to induce apoptosis in K562 CML cell line by overexpression of miR-155. Methods: The K562 cell line was transfected with pLenti-III-pre mir155-GFP constructs through electroporation. Then, overexpression of miR-155 as well as the expression level of p27kip1 and c-Myc was analyzed by quantitative PCR (qPCR). The level of p27 (Kip1) protein expression was measured by Western blot and the Annexin V method was carried out to investigate apoptosis. Results: Flow cytometric analysis results of K562 cells transfected with pLenti-III-pre mir155-GFP construct showed a significant increase in cell apoptosis. Gene expression and protein level of p27kip1 were upregulated. However, there was no change in c-Myc expression profile. Conclusion: miR-155 could be a promising approach to aid in the treatment of CML. However, further studies are required in this respect.

HGF-independent regulation of MET and GAB1 by nonreceptor tyrosine kinase FER potentiates metastasis in ovarian cancer.

Ovarian cancer cells disseminate readily within the peritoneal cavity, which promotes metastasis, and are often resistant to chemotherapy. Ovarian cancer patients tend to present with advanced disease, which also limits treatment options; consequently, new therapies are required. The oncoprotein tyrosine kinase MET, which is the receptor for hepatocyte growth factor (HGF), has been implicated in ovarian tumorigenesis and has been the subject of extensive drug development efforts. Here, we report a novel ligand- and autophosphorylation-independent activation of MET through the nonreceptor tyrosine kinase feline sarcoma-related (FER). We demonstrated that the levels of FER were elevated in ovarian cancer cell lines relative to those in immortalized normal surface epithelial cells and that suppression of FER attenuated the motility and invasive properties of these cancer cells. Furthermore, loss of FER impaired the metastasis of ovarian cancer cells in vivo. Mechanistically, we demonstrated that FER phosphorylated a signaling site in MET: Tyr1349. This enhanced activation of RAC1/PAK1 and promoted a kinase-independent scaffolding function that led to recruitment and phosphorylation of GAB1 and the specific activation of the SHP2-ERK signaling pathway. Overall, this analysis provides new insights into signaling events that underlie metastasis in ovarian cancer cells, consistent with a prometastatic role of FER and highlighting its potential as a novel therapeutic target for metastatic ovarian cancer.

Effects of imatinib and nilotinib on the whole transcriptome of cultured murine osteoblasts.

Numerous clinical observations have confirmed that breakpoint cluster region-abelson fusion oncoprotein tyrosine kinase inhibitors used in leukemia treatment alter bone physiology in a complex manner. The aim of the present study was to analyze the whole transcriptome of cultured murine osteoblasts and determine the changes following treatment with imatinib and nilotinib using Sequencing by Oligonucleotide Ligation and Detection next generation RNA sequencing. This study also aimed to identify candidate signaling pathways and network regulators by multivariate Ingenuity Pathway Analysis. Based on the right-tailed Fisher's exact test, significantly altered pathways including upstream regulators were defined for each drug. The correlation between these pathways and bone metabolism was also examined. The preliminary results suggest the two drugs have different mechanisms of action on osteoblasts, and imatinib was shown to have a greater effect on gene expression. Data also indicated the potential role of a number of genes and signaling cascades that may contribute to identifying novel targets for the treatment of metabolic bone diseases.

Complete and long‐lasting cytologic and molecular remission of FIP1L1‐PDGFRA‐positive acute eosinophil myeloid leukaemia, treated with low‐dose imatinib monotherapy

Myeloproliferative neoplasms associated with FIP1L1-PDGFR rearrangements represent a rare subset of myeloid and lymphoid malignancies, characterised by the presence of eosinophilia and abnormalities of PDGFRA, PDGFRB or FGFR1 genes. The fusion product of such genes is a tyrosine kinase oncoprotein sensitive to imatinib, which to date results to be the standard of care for FIP1L1-PDGFRA-positive chronic myeloproliferative disorders with eosinophilia. However, the coexistence of FIP1L1-PDGFRA rearrangement associated with acute myeloid leukaemia is extremely rare. Here, we report a rare case of FIP1L1-PDGFRA-positive acute myeloid leukaemia, with marked peripheral blood and bone marrow eosinophilia, treated with low dose of imatinib monotherapy, achieving a rapid and long-lasting complete cytologic and molecular remission, without need for intensive chemotherapy.

Engineering a BCR-ABL–activated caspase for the selective elimination of leukemic cells

Increased understanding of the precise molecular mechanisms involved in cell survival and cell death signaling pathways offers the promise of harnessing these molecules to eliminate cancer cells without damaging normal cells. Tyrosine kinase oncoproteins promote the genesis of leukemias through both increased cell proliferation and inhibition of apoptotic cell death. Although tyrosine kinase inhibitors, such as the BCR-ABL inhibitor imatinib, have demonstrated remarkable efficacy in the clinic, drug-resistant leukemias emerge in some patients because of either the acquisition of point mutations or amplification of the tyrosine kinase, resulting in a poor long-term prognosis. Here, we exploit the molecular mechanisms of caspase activation and tyrosine kinase/adaptor protein signaling to forge a unique approach for selectively killing leukemic cells through the forcible induction of apoptosis. We have engineered caspase variants that can directly be activated in response to BCR-ABL. Because we harness, rather than inhibit, the activity of leukemogenic kinases to kill transformed cells, this approach selectively eliminates leukemic cells regardless of drug-resistant mutations.

Well MET: Exosomes promote metastasis through transfer of MET from melanoma to bone marrow progenitors

Well <scp>MET</scp>: Exosomes promote metastasis through transfer of <scp>MET</scp> from melanoma to bone marrow progenitors

Identification of PTPN23 as a novel regulator of cell invasion in mammary epithelial cells from a loss-of-function screen of the ‘PTP-ome'

We used an RNAi-mediated loss-of-function screen to study systematically the role of the protein tyrosine phosphatase (PTP) superfamily of enzymes in mammary epithelial cell motility in the absence or presence of the oncoprotein tyrosine kinase ERBB2. We report that although shRNAs directed against most of the PTP family were without effect, suppression of three PTPs-PRPN23, PTPRG, and PTPRR-enhanced cell motility. Furthermore, we found that suppression of PTPN23, but not PTPRG or PTPRR, induced cell invasion. Suppression of PTPN23 increased E-cadherin internalization, impaired early endosome trafficking of E-cadherin, induced the expression of mesenchymal proteins, and caused cell scattering. The activity of SRC and β-catenin was elevated when PTPN23 was suppressed. Moreover, we identified SRC, E-cadherin, and β-catenin as direct substrates of PTPN23. Inhibition of SRC with the small molecular inhibitor SU6656 blocked the effects of PTPN23 depletion. These findings suggest that loss of PTPN23 may increase the activity of SRC and the phosphorylation status of the E-cadherin/β-catenin signaling complex to promote tumor growth and invasive behavior in breast cancer. In addition, our studies highlight functional specificity among PTPs and reveal new roles for PTPs in mammary epithelial cell biology.

Abstract 1780: Potentiating chronic myeloid leukaemia treatment using oligomeric disruption and RNAi

Abstract Exploiting multiple pathways to treat Chronic Myelogenous Leukemia (CML) may improve therapeutic efficacy. CML is caused by expression of the tyrosine kinase oncoprotein, Bcr-Abl, in hematopoietic stem cells resulting in an overproliferative granulocyte cell lineage. Increased circulation of granulocytes or granulocyte progenitors floods the circulatory system resulting in organ failure, infection, hemorrhage and eventually death. Imatinib (Gleevec®) therapy is initially effective in about two-thirds of patients; however resistance to this drug may develop over the course of the disease. Recent reports in the literature have combined imatinib therapy with RNA interference (RNAi) technology in vitro resulting in a more effective induction of apoptosis. An engineered peptide which binds the coiled-coil domain of Bcr-Abl prevents oligomerization and transactivation of the oncogene in K562 cells. This disruption of Bcr-Abl reduces proliferation and blocks downstream oncogenic signaling. To enhance therapeutic efficacy we have integrated short hairpin-mediated RNAi against known disease progression or anti-apoptotic proteins. RNAi targets include autophagy promoting factor ATG7, the aberrant oncoprotein MUC-1, and a leukemic stem cell factor Alox5. Experimental constructs were tested in Bcr-Abl containing K562 cells, a CML blast phase model. Colony forming assays, microscopy and flow cytometry were used to asses proliferation, transformative ability, and apoptosis. When combined with a plasmid encoding the peptide which disrupts Bcr-Abl function, an additive or synergistic enhancement of apoptosis is possible. Targeting CML-causing cells simultaneously through disparate cellular pathways promotes a more complete apoptosis in CML than with currently available TKI therapies. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1780. doi:10.1158/1538-7445.AM2011-1780

From Hen House to Bedside: Tracing Hanafusa's Legacy from Avian Leukemia Viruses to SRC to ABL and Beyond

The discovery of the Src oncogene was the first step on a long journey toward improved cancer chemotherapy. In this review, we explore Src and BCR-ABL, signal transduction, and recent advances in oncogene addiction and celebrate Hidesaboro Hanafusa and the many researchers who ushered in the age of target-directed therapy against tyrosine kinase oncoproteins.

Primary small cell carcinoma of the ureter: a case report involving immunohistochemical and molecular genetic analyses of KIT and PDGFRA genes

Sir,KIT and PDGFRA, both mapped to 4q12, encode receptor tyrosine kinase oncoproteins called KIT (CD117) and PDGFRA, respectively.1,2 Both molecules are transmembranous oncoproteins involved in the...

Abl Is Able to Inhibit Cell Engulfment

Programmed cell death is essential to development—it's how the tiny mitten of a growing hand becomes a glove of individuated fingers, for instance. To dispose of all those cellular corpses, nearby cells (or roving specialists such as the immune system's macrophages) engulf their dead neighbors and digest the remains. Engulfment, therefore, is a valuable process, and it is known to be promoted by two parallel signaling pathways. But preventing engulfment is also important (one can almost hear a little cell's faint cry, “I'm not dead yet!”); however, little is known about how the process is inhibited. In a new study, Michael Hurwitz and colleagues describe a pathway that does just that. To wrap itself around another cell, the engulfing cell must recruit new a membrane and completely reorganize its cytoskeleton, and these processes are regulated by the two pro-engulfment pathways, known as the CED-1 pathway (thought to be responsible primarily for membrane recruitment) and the CED-10 Rac pathway (thought to be responsible primarily for cytoskeletal rearrangement). Cytoskeletal remodeling is also controlled by a host of other regulators outside these pathways, though, including a multi-talented protein called Abl kinase. It interacts with dozens of partners (creating effects that are mostly not understood in vivo), and its dysregulation is linked to at least two forms of cancer. To explore the effects of Abl kinase in engulfment, the authors turned to the roundworm Caenorhabditis elegans, which produces an Abl kinase homolog called ABL-1. They found that disabling ABL-1 through mutation in animals defective for engulfment led to even more cells being engulfed, which is exactly what would be expected from the loss of an engulfment inhibitor. To quantify defects in the engulfment process, the authors simply counted corpses in the worm larvae, and they recognized that, rather than having a direct effect on engulfment itself, ABL-1 mutation might reduce corpse number by other means, such as suppressing cell death. But through direct observation of the developing larvae, they ruled out this and other alternatives, leading them to conclude that ABL-1 directly inhibited engulfment. The protein appears to exert its effect on the engulfing cell, because it inhibited engulfment when it was expressed everywhere except the engulfed cell. For many years, two molecular pathways were known to regulate the engulfment of apoptotic cells. Now, a third pathway has been identified in C. elegans that is inhibited by the Abl tyrosine kinase oncoprotein. Mutation of abl-1 was able to partially overcome the effect of complete inhibition of the membrane recruitment pathway but not the cytoskeletal rearrangement pathway. However, the cytoskeletal rearrangement pathway is also required for certain cell migrations, and mutation of abl-1 did partially overcome the effect of complete inhibition of the that pathway on cell migrations. These data suggested that ABL-1 acts independently of both pathways, but the effect of its loss is simply too weak to overcome the engulfment defect of complete inhibition of the cytoskeletal regulation pathway. Thus, ABL-1 appeared to inhibit a third engulfment regulatory pathway. The authors then explored the function of a known interactor with ABL-1, called ABI-1. In contrast to mutant ABL-1, mutations in ABI-1 reduced engulfment, just as mutations in the two previously known pro-engulfment pathways did. And it did so whether or not ABL-1 was mutated, suggesting that its effect is downstream of ABL-1. The picture that emerges, then, is that ABL-1 acts directly on ABI-1 to inhibit it, and thus inhibits engulfment. Along with deepening the understanding of programmed cell death control, these results may have some direct therapeutic relevance. Engulfment of infected cells by macrophages is a key means for the body to maintain health, and engulfment of cancerous cells might also prevent cancer development. Abl kinase inhibitors might promote macrophage activity in these conditions. Impaired engulfment is a hallmark of systemic lupus erythematosus, suggesting that inhibiting Abl kinase might be of use here as well. Testing these ideas shouldn't take long—not only do such inhibitors exist, but at least two are already approved and marketed for other conditions.

Abstract A36: Combinatorial attack on radiation-induced neoplastic transformation by phenylbutyrate: Involvement of Hsp90 molecular chaperone and histone deacetylase

Abstract A36 Phenyl fatty acids like phenylacetate (PA) and phenylbutyrate (PB) have shown anti-cancer efficacy in clinical trials and in both in vitro and in vivo models. The mechanism of action of these agents is not fully understood however. In vitro studies have demonstrated that PB treatment induces apoptosis and growth rate effects in a time- and dose- dependent manner in the p21ras-expressing hematopoietic cells, Ras-DC and the human chronic myeloid leukemia blast crisis cells, (CML-BC) K562 cells. Both leukemia cell types are characterized by deregulated activity of the oncoprotein tyrosine kinase known as Bcr-Abl frequently observed in radiation-associated leukemias. Molecular studies are underway to characterize the effect of PB on Bcr-Abl expression in these leukemia cells since Bcr-Abl is a well known client protein for Hsp90. Furthermore, gene expression profile analysis of PB treatment of leukemia cells and human osteoblast cells (HOS) demonstrated that PB down-regulated Hsp90 suggesting that PB may affect molecular chaperoning. The anti-leukemic activity of PB was investigated using the cobalt radiation-induced neoplastic transformation model, HOS cells. HOS cells were exposed to a total of 2 Gy (60Co, 50 cGy/exposure) and transformed foci were formed within 35 days. Cellular incubation with PB either pre- or post-radiation significantly suppressed the radiation-induced transformation. Molecular studies also showed that PB induced acetylation of histones H3 and H4 and apoptosis in this cell model. A radiation leukemia rodent model is currently being employed to evaluate PB’s anti-leukemia efficacy. Although preliminary, these data suggest that PB involvement in both Hsp90 molecular chaperoning and inhibition of histone deacetylase is mechanistically related to its anti-leukemia efficacy. Citation Information: Cancer Prev Res 2008;1(7 Suppl):A36.