Identification of potential biomarkers for measuring inhibition of Src kinase activity in colon cancer cells following treatment with dasatinib

Regulation of SRC family kinases in human cancers

The nonreceptor protein tyrosine kinase Src plays a crucial role in the signal transduction pathways involved in cell division, motility, adhesion, and survival in both normal and cancer cells. Although the Src family kinases (SFKs) are activated in various types of cancers, the exact mechanisms through which they contribute to the progression of individual tumors remain to be defined. The activation of Src in human cancers may occur through a variety of mechanisms that include domain interaction and structural remodeling in response to various activators or upstream kinases and phosphatastes. Because of Src's prominent roles in invasion and tumor progression, epithelial-to-mesenchymal transition, angiogenesis, and the development of metastasis, Src is a promising target for cancer therapy. Several small molecule inhibitors of Src are currently being investigated in clinical trials. In this article, we will summarize the mechanisms regulating Src kinase activity in normal and cancer cells and discuss the status of Src inhibitor development against various types of cancers.

Curcumin enhances dasatinib-induced inhibition of growth and transformation of colon cancer cells

Colorectal cancer is the third most common form of malignancy, behind prostate and lung cancers. Despite recent advances in medicine, mortality from colorectal cancer remains high, highlighting the need for improved therapies. Numerous studies have demonstrated increased activation of EGFR and its family members (EGFRs), IGF-1R as well as c-Src in colorectal cancer. The current study was undertaken to examine the effectiveness of combination therapy of dasatinib (BMS-354825; Bristol-Myers Squibb), a highly specific inhibitor of Src family kinases (SFK) and a nontoxic dietary agent; curcumin (diferuloylmethane), in colorectal cancer in in vitro and in vivo experimental models. For the latter, we utilized C57BL/6 APC(Min+/-) mice. Initial in vitro studies revealed synergistic interactions between the two agents. Additionally, we have observed that combination treatment causes a much greater inhibition of the following metastatic processes than either agent alone: (i) colony formation, (ii) invasion through extracellular matrix and (iii) tubule formation by endothelial cells. Dasatinib affects the cell adhesion phenotype of colon cancer HCT-116 cells whereas the combination therapy enhances this effect to a greater extent. Preclinical investigation revealed that the combination therapy to be highly effective causing an over 95% regression of intestinal adenomas in Apc(Min+/-) mice, which could be attributed to decreased proliferation and increased apoptosis. In conclusion, our data suggest that combination treatment of dasatinib and curcumin could be a potential therapeutic strategy for colorectal cancer.

2D-DIGE analysis of phospho-enriched fractions from dasatinib-treated melanoma cell lines

Current therapeutic regimes for metastatic melanoma have failed to provide robust clinical responses. Dasatinib has shown anti-proliferative and anti-invasive effects in vitro; however, not all melanoma cells tested were sensitive to dasatinib. We used 2D-DIGE analysis of phospho-enriched fractions to identify phosphoproteins involved in regulating response to dasatinib in an isogenic pair of melanoma cell lines, one sensitive to dasatinib (WM-115) and the other resistant (WM-266-4). In WM-115 cells treated with dasatinib, 18 unique protein species with altered phosphorylation levels were detected. Dasatinib treatment of WM-266-4 cells resulted in phosphoprotein alterations to four unique protein species. Four phosphorylated forms of Annexin-A2 (ANXA2) were increased in WM-115 cells treated with dasatinib, whilst dasatinib treatment did not alter ANXA2 phosphoprotein levels in WM-266-4 cells. Immunoblotting confirmed that phosphorylation of ANXA2, on tyrosine residues, was increased in WM-115 cells treated with dasatinib. Subsequent knockdown of ANXA2 by siRNA significantly inhibited proliferation of WM-115 cells but did not significantly reduce proliferation of WM-266-4 cells. Therefore, ANXA2 plays a role in regulating proliferation in dasatinib-sensitive WM-115 cells and could potentially play a role in sensitivity to dasatinib in melanoma cells.

A bioinformatical and functional approach to identify novel strategies for chemoprevention of colorectal cancer

Comparing normal colorectal mucosa and adenomas focusing on deregulated pathways obtains insight into the biological processes of early colorectal carcinogenesis. Publicly available microarray expression data from 26 normal mucosa and 47 adenoma samples were analyzed. Biological pathways enriched in adenomas were identified with Gene Set Enrichment Analysis (GSEA). The analysis revealed 10, 11 and 16 gene sets distinguishing adenomas from normal mucosa according to Kyoto Encyclopedia of Genes and Genomes (KEGG), Gene Map Annotator and Pathway Profiler (GenMAPP) and Biocarta databases, respectively. Biological pathways known to be involved in colon carcinogenesis such as cell cycle (P=0.002) and Wnt signaling (P=0.007) were enriched in adenomas. In addition, we found enrichment of novel pathways such as retinoblastoma (Rb) pathway (P=0.002), Src pathway (P=0.004), folate biosynthesis (P=0.019) and Hedgehog signaling (P=0.037) in adenomas. Microarray results for Rb and Src pathway genes were validated by quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR) on mRNA isolated from an independent set of adenoma and normal colon samples. A high correlation between microarray data and qRT-PCR expression data was found. The relevance of targeting of identified pathways was shown using the Rb pathway inhibitors roscovitine and PD-0332991 and the Src pathway inhibitor dasatinib. All inhibitors used induced cell growth reduction in adenoma cells. This study shows a bioinformatical and functional approach leading to potentially new options for chemoprevention of colorectal cancer.

Dasatinib induces autophagic cell death in human ovarian cancer

BACKGROUND

Dasatinib, an inhibitor of Src/Abl family kinases, can inhibit tumor growth of several solid tumors. However, the effect and mechanism of action of dasatinib in human ovarian cancer cells remains unknown.

METHODS

Dasatinib-induced autophagy was determined by acridine orange staining, punctate localization of GFP-LC3, LC3 protein blotting, and electron microscopy. Significance of beclin 1, AKT, and Bcl-2 in dasatinib-induced autophagy and growth inhibition was assayed by small interfering RNA (siRNA) silencing and/or overexpression of the gene of interest.

RESULTS

Dasatinib inhibited cell growth by inducing little apoptosis, but substantial autophagy in SKOv3 and HEY ovarian cancer cells. In vivo studies showed dasatinib inhibited tumor growth and induced both autophagy and apoptosis in a HEY xenograft model. Knockdown of beclin 1 and Atg12 expression with their respective siRNAs diminished dasatinib-induced autophagy, whereas knockdown of p27Kip1 with specific siRNAs did not. Small hairpin RNA knockdown of beclin 1 expression reduced dasatinib-induced autophagy and growth inhibition. Dasatinib reduced the phosphorylation of AKT, mTOR, p70S6K, and S6 kinase expression. Constitutive expression of AKT1 and AKT2 inhibited dasatinib-induced autophagy in both HEY and SKOv3 cells. Dasatinib also reduced Bcl-2 expression and activity. Overexpression of Bcl-2 partially prevented dasatinib-induced autophagy.

CONCLUSIONS

Dasatinib induces autophagic cell death in ovarian cancer that partially depends on beclin 1, AKT, and Bcl-2. These results may have implications for clinical use of dasatinib.

Distinct interactions between c-Src and c-Met in mediating resistance to c-Src inhibition in head and neck cancer

PURPOSE

c-Src inhibition in cancer cells leads to an abrogation of invasion but a variable effect on apoptosis. The pathways downstream of c-Src promoting survival are not well characterized. Because cancer therapy that both decreases invasion and induces significant apoptosis would be ideal, we sought to characterize the mechanisms of resistance to c-Src inhibition.

EXPERIMENTAL DESIGN

c-Src was inhibited in a panel of oral cancer cell lines and subsequent survival and signaling measured. The interactions between c-Src and c-Met were evaluated using immunoprecitation and an in vitro kinase assay. Cytotoxicity was measured and the Chou-Talalay combination index calculated. An orthotopic model of oral cancer was used to assess the effects of c-Met and c-Src inhibitors.

RESULTS

Inhibition of c-Src resulted in c-Met inhibition in sensitive cells lines, but not in resistant cell lines. Isolated c-Met was a c-Src substrate in both sensitive and resistant cells, but there was no interaction of c-Src and c-Met in intact resistant cells. To examine the biological consequences of this mechanism, we demonstrated synergistic cytotoxicity, enhanced apoptosis, and decreased tumor size with the combination of c-Src and c-Met inhibitors.

CONCLUSIONS

Sustained c-Met activation can mediate resistance to c-Src inhibition. These data suggest that the differences between c-Met and c-Src signaling in sensitive and resistant cells are due to distinct factors promoting or inhibiting interactions, respectively, rather than to intrinsic structural changes in c-Src or c-Met. The synergistic cytotoxic effects of c-Src and c-Met inhibition may be important for the treatment of head and neck cancers.

Dasatinib: a potent SRC inhibitor in clinical development for the treatment of solid tumors

SRC is a tyrosine kinase that plays a role in oncogenic, invasive and bone-metastatic processes. It has therefore been prioritized as a candidate therapeutic target in patients with solid tumors. Several SRC inhibitors are now in development, of which dasatinib has been most explored. Preclinical studies in a wide variety of solid tumor cell lines, including prostate, breast and glioma, have shown that that dasatinib acts as a cytostatic agent, inhibiting the processes of cell proliferation, invasion and metastasis. Dasatinib also inhibits the activity of osteoclasts, which have a major role in the development of metastatic bone lesions. Dasatinib has additive or synergistic activity in combination with a number of other agents, including cytotoxic agents and targeted therapies, providing a rationale for combination treatment in a clinical setting. Emerging clinical data with dasatinib support experimental observations, with preliminary phase 1 and 2 data demonstrating activity, both as a single agent and as combination therapy, in a range of solid tumors. Future clinical trials will further assess the clinical value of SRC inhibition with dasatinib.

Focal adhesion kinase is required for intestinal regeneration and tumorigenesis downstream of Wnt/c-Myc signaling

The intestinal epithelium has a remarkable capacity to regenerate after injury and DNA damage. Here, we show that the integrin effector protein Focal Adhesion Kinase (FAK) is dispensable for normal intestinal homeostasis and DNA damage signaling, but is essential for intestinal regeneration following DNA damage. Given Wnt/c-Myc signaling is activated following intestinal regeneration, we investigated the functional importance of FAK following deletion of the Apc tumor suppressor protein within the intestinal epithelium. Following Apc loss, FAK expression increased in a c-Myc-dependent manner. Codeletion of Apc and Fak strongly reduced proliferation normally induced following Apc loss, and this was associated with reduced levels of phospho-Akt and suppression of intestinal tumorigenesis in Apc heterozygous mice. Thus, FAK is required downstream of Wnt Signaling, for Akt/mTOR activation, intestinal regeneration, and tumorigenesis. Importantly, this work suggests that FAK inhibitors may suppress tumorigenesis in patients at high risk of developing colorectal cancer.

Gene array and fluorescence in situ hybridization biomarkers of activity of saracatinib (AZD0530), a Src inhibitor, in a preclinical model of colorectal cancer

PURPOSE

To evaluate the efficacy of saracatinib (AZD0530), an oral Src inhibitor, in colorectal cancer (CRC) and to identify biomarkers that predict antitumor activity.

EXPERIMENTAL DESIGN

Twenty-three CRC cell lines were exposed to saracatinib, and baseline gene expression profiles of three sensitive and eight resistant cell lines in vitro and in vivo were used to predict saracatinib sensitivity in an independent group of 10 human CRC explant tumors using the gene array K-Top Scoring Pairs (K-TSP) method. In addition, fluorescence in situ hybridization (FISH) and immunoblotting determined both Src gene copy number and activation of Src, respectively.

RESULTS

Two of 10 explant tumors were determined to be sensitive to saracatinib. The K-TSP classifier (TOX>GLIS2, TSPAN7>BCAS4, and PARD6G>NXN) achieved 70% (7 of 10) accuracy on the test set. Evaluation of Src gene copy number by FISH showed a trend toward significance (P = 0.066) with respect to an increase in Src gene copy and resistance to saracatinib. Tumors sensitive to saracatinib showed an increase in the activation of Src and FAK when compared with resistant tumors.

CONCLUSIONS

Saracatinib significantly decreased tumor growth in a subset of CRC cell lines and explants. A K-TSP classifier (TOX>GLIS2, TSPAN7>BCAS4, and PARD6G>NXN) was predictive for sensitivity to saracatinib. In addition, increased activation of the Src pathway was associated with sensitivity to saracatinib. These results suggest that FISH, a K-TSP classifier, and activation of the Src pathway have potential in identifying CRC patients that would potentially benefit from treatment with saracatinib.

SRC: a century of science brought to the clinic

The SRC family kinases are the largest family of nonreceptor tyrosine kinases and one of the best-studied targets for cancer therapy. SRC, arguably the oldest oncogene, has been implicated in pathways regulating proliferation, angiogenesis, invasion and metastasis, and bone metabolism. More recently, researchers have proposed that the transforming ability of SRC is linked to its ability to activate key signaling molecules in these pathways, rather than through direct activity. It has been hypothesized that blocking SRC activation may inhibit these pathways, resulting in antitumor activity. However, successfully targeting SRC in a clinical setting remains a challenge, and SRC inhibitors have only recently begun to move through clinical development. Preclinical studies have identified specific molecular "subgroups" and histologies that may be more sensitive to SRC inhibition. In addition, other studies have demonstrated synergistic interactions between SRC inhibitors and other targeted therapies and cytotoxics. In this review, we summarize SRC biology and how it has been applied to the clinical development of SRC inhibitors. The status of SRC inhibitors, including dasatinib, saracatinib, and bosutinib, which are in phase 1, 2, and 3 trials, is highlighted.

Dasatinib synergizes with JSI-124 to inhibit growth and migration and induce apoptosis of malignant human glioma cells

Background:

Src family kinases (SFK) collectively regulate a variety of cellular functions in many cancer types, including proliferation, invasion, motility, survival, differentiation, and angiogenesis. Although Dasatinib (BMS-354825), an ATP-competitive, small molecule tyrosine kinase inhibitor, suppresses the activity of SFKs at nanomolar concentrations, IC50 values for antiproliferative effects in glioma cell lines were well above the clinically achievable range, suggesting the need to interfere with other components of receptor-induced downstream signaling in order to achieve an optimal therapeutic effect.

Materials and Methods:

The cytotoxic effects of combining Src and STAT3 inhibition on glioma cell lines were evaluated using assays to measure cell proliferation, apoptosis and migration. Western blotting and immunocytochemistry was used to monitor its effects on cell signaling and morphology.

Results:

Silencing Src and STAT3 expression each partially inhibited cell proliferation and migration. In addition, JSI-124 significantly enhanced the efficacy of dasatinib in vitro. Combination of dasatinib and JSI-124 achieved significant inhibition of migration in all cell lines, which correlated with the inhibition of Src and downstream mediators of adhesion (e.g. focal adhesion kinase). Cells exposed to dasatinib and JSI-124 exhibited morphological changes that were consistent with an upstream role for Src in regulating focal adhesion complexes.

Conclusions:

Targeting the Src and STAT pathways may contribute to the treatment of cancers that demonstrate increased levels of these signaling mediators, including malignant human glioma. Clinical studies in these tumor types are warranted.

Inhibition of Src impairs the growth of met-addicted gastric tumors

PURPOSE

We examined whether inhibition of Src tyrosine kinase, a downstream effector of the MET oncogene, can hinder the malignant properties of gastric tumors dependent on Met for growth and survival.

EXPERIMENTAL DESIGN

Sensitivity to Src inhibition was determined in vitro by measuring clonogenic survival (anchorage-independent growth) and in vivo by establishing xenograft models. Four "Met-addicted" gastric carcinoma cell lines (GTL16, MKN45, HS746T, and SNU5) and three Met-independent gastric carcinoma cell lines (KATO III, AGS, and NCI-N87) were treated with the Src inhibitor saracatinib (AZD0530). In GTL16 and KATO III, Src neutralization was also achieved by dasatinib and RNA interference. The biochemical and transcriptional consequences of Src inhibition were explored using anti-phosphoprotein antibodies and oligonucleotide microarrays.

RESULTS

Inhibition of Src in Met-addicted gastric carcinoma cell lines (a) decreased the phosphorylation/activation levels of signaling intermediates involved in cell proliferation and protection from apoptosis and down-modulated the expression of several cell cycle regulators; (b) reduced anchorage-independent growth; (c) enhanced impairment of cell viability produced by Met inhibition; and (d) delayed tumorigenesis in xenotransplantation models. Immunohistochemical analysis of tumor xenograft tissues following systemic treatment with saracatinib showed a reduction of tumor cell proliferation index, increased apoptosis, and diminished phospho-focal adhesion kinase and phospho-paxillin staining. Tumor stroma parameters such as angiogenesis or inflammatory infiltration were unaffected. In clonogenic survival assays, gastric carcinoma cells without addiction to Met were less sensitive than Met-addicted cells to Src inhibition.

CONCLUSIONS

Src is as a key downstream transducer of Met-driven tumor growth. Targeting Src might provide therapeutic benefit in Met-addicted tumors.

Dasatinib inhibits the development of metastases in a mouse model of pancreatic ductal adenocarcinoma

BACKGROUND & AIMS

Pancreatic ductal adenocarcinoma (PDAC) is a highly invasive and metastatic disease for which conventional treatments are of limited efficacy. A number of agents in development are potential anti-invasive and antimetastatic agents, including the Src kinase inhibitor dasatinib. The aim of this study was to assess the importance of Src in human PDAC and to use a genetically engineered mouse model of PDAC to determine the effects of dasatinib on PDAC progression.

METHODS

Src expression and activity was measured by immunohistochemistry in 114 human PDACs. Targeting expression of Trp53(R172H) and Kras(G12D) to the mouse pancreas results in the formation of invasive and metastatic PDAC. These mice were treated with dasatinib, and disease progression monitored. Cell lines were derived from mouse PDACs, and in vitro effects of dasatinib assessed.

RESULTS

Src expression and activity were up-regulated in human PDAC and this correlated with reduced survival. Dasatinib inhibited the migration and invasion of PDAC cell lines, although no effects on proliferation were seen at concentrations that inhibited Src kinase activity. In addition, dasatinib significantly inhibited the development of metastases in Pdx1-Cre, Z/EGFP, LSL-Kras(G12D/+), LSL-Trp53(R172H/+) mice. However, there was no survival advantage in the dasatinib-treated animals owing to continued growth of the primary tumor.

CONCLUSIONS

This study confirms the importance of Src in human PDAC and shows the usefulness of a genetically engineered mouse model of PDAC for assessing the activity of potential antimetastatic agents and suggests that dasatinib should be evaluated further as monotherapy after resection of localized invasive PDAC.

Phase 1 pharmacokinetic and drug-interaction study of dasatinib in patients with advanced solid tumors

BACKGROUND

The recently developed the Src and Abelson (Abl) kinase inhibitor dasatinib has antitumor effects in epithelial and mesenchymal tumors. Preclinical data have indicated that dasatinib is metabolized primarily through cytochrome P450 3A4 (CYP3A4) and may cause QT prolongation. In light of its improved tolerability, the authors were interested in the safety of a once-daily dasatinib regimen.

METHODS

The authors conducted a phase 1 trial of dasatinib in 29 patients with advanced solid tumors. Segment 1 of the trial was short term and sequential and was designed to determine whether the coadministration of the potent CYP3A4 inhibitor ketoconazole had an effect on the pharmacokinetics of dasatinib. Segment 2 was designed to evaluate the safety of dasatinib as dosing was increased. QT intervals were monitored closely in both segments. Efficacy was assessed in Segment 2 using both positron emission tomography and computed tomography.

RESULTS

Hematologic toxicities were markedly less than those observed in patients with leukemia, whereas nonhematologic toxicities were similar. The authors determined that the maximum recommended dose was 180 mg once daily based on the incidence of pleural effusion. Coadministration of ketoconazole led to a marked increase in dasatinib exposure, which was correlated with an increase in corrected QT (QTc) values of approximately 6 msec. No adverse cardiac events were observed.

CONCLUSIONS

The dose-limiting toxic effect for dasatinib was pleural effusion. The pharmacokinetic and cardiac studies indicated that coadministration of dasatinib with potent CYP3A4 inhibitors or agents that prolong the QTc interval should be avoided if possible. Close monitoring for toxicity and dose reduction should be considered if the coadministration of such agents cannot be avoided.

Dasatinib in solid tumors

IMPORTANCE OF THE FIELD

Dasatinib is an oral, potent adenosine triphosphate-competitive inhibitor of multiple tyrosine kinases including BCR-ABL, c-KIT, platelet-derived growth factor receptor, and Src family kinases (SFKs). It has gained much attention for its use in chronic myeloid leukemia and for the treatment of adults with Philadelphia chromosome-positive acute lymphoblastic leukemia. However, dasatinib is also being explored in solid tumors in ongoing Phase I and II clinical trials.

AREAS COVERED IN THIS REVIEW

The clinical efficacy of dasatinib in a wide variety of solid tumors and important Phase I/II studies utilizing dasatinib and the optimal dosage used in solid tumors. A literature search was conducted using PubMed/MEDLINE, www.clinicaltrials.gov , and the American Society of Clinical Oncology websites to find relevant Phase I/II clinical trials during 1987-2009.

WHAT THE READER WILL GAIN

The understanding that the biology and mechanism of Src activation in tumors are not well understood and finding the optimal use of SFK inhibitors in the clinical setting requires further investigation.

TAKE HOME MESSAGE

In reviewing the clinical safety data of dasatinib in its current use as a Src inhibitor in a wide variety of solid malignancies, dasatinib appears to be safe and is a promising agent for the treatment of metastatic solid tumors refractory to standard therapies.

Inhibition of focal adhesion kinase and src increases detachment and apoptosis in human neuroblastoma cell lines

Neuroblastoma is the most common extracranial solid tumor of childhood. Focal adhesion kinase (FAK) is an intracellular kinase that is overexpressed in a number of human tumors including neuroblastoma, and regulates both cellular adhesion and survival. We have studied the effects of FAK inhibition upon neuroblastoma using adenovirus-containing FAK-CD (AdFAK-CD). Utilizing an isogenic MYCN+/MYCN- neuroblastoma cell line, we found that the MYCN+ cells are more sensitive to FAK inhibition with AdFAK-CD than their MYCN negative counterparts. In addition, we have shown that phosphorylation of Src is increased in the untreated isogenic MYCN- neuroblastoma cells, and that the decreased sensitivity of the MYCN- neuroblastoma cells to FAK inhibition with AdFAK-CD is abrogated by the addition of the Src family kinase inhibitor, PP2. The results of the current study suggest that both FAK and Src play a role in protecting neuroblastoma cells from apoptosis, and that dual inhibition of these kinases may be important when designing therapeutic interventions for this tumor.

Dasatinib

Dasatinib, (former BMS 354825), is an orally available small-molecule multikinase inhibitor. It potently inhibits BCR-ABL and SRC-family kinases (SRC, LCK, YES, FYN), but also c-KIT, PDGFR-alpha and beta, and ephrin receptor kinase.Dasatinib is about 300 times more potent than imatinib in cells expressing unmutated BCR-ABL in vitro. The drug has demonstrated activity against clinically relevant mutations, including those associated with poor prognosis during ongoing imatinib therapy.Dasatinib is approved for the treatment of patients with BCR-ABL-positive chronic myeloid leukemia (CML), resistant or intolerant to imatinib in chronic, accelerated, and blast phase. It also is approved for the treatment of Philadelphia Chromosome positive (Ph+) acute lymphoblastic leukemia (ALL) resistant or intolerant to imatinib.A single daily dose of 100 mg in chronic phase CML results in high hematologic and molecular remission rates and prolongation of survival. In accelerated and blastic phase as well as in ALL, 70 mg twice daily is recommended. Complete hematologic and cytogenetic remissions (CR) frequently occur even in this patient group with poor prognosis. Remissions however are very short.Side effects of dasatinib are frequent but mostly moderate and manageable and include cytopenias and pleural effusions. The role of dasatinib in other diseases, including solid tumors, has to be identified.

Effects of Src kinase inhibition induced by dasatinib in non-small cell lung cancer cell lines treated with cisplatin

c-Src is a tyrosine kinase involved in tumor proliferation, migration, and angiogenesis and has been shown to modulate the cytotoxicity following cisplatin-induced DNA damages. c-Src is frequently activated in non-small cell lung cancer (NSCLC) tissues and cell lines, but no preclinical data regarding the effects of the novel potent Src inhibitor, dasatinib (BMS-354825), in the modulation of cisplatin resistance are currently available. The present study reports that treatment with dasatinib completely abrogated Src phosphorylation in the majority of the NSCLC cell lines tested (n = 7), with modest effects on cell proliferation and survival. In five cell lines, a higher cytotoxicity was observed delivering cisplatin in combination with dasatinib: the most evident effects were found in the squamous H520 cells due to the effective block of cisplatin-induced Src phosphorylation. Moreover, dasatinib treatment significantly blocked cisplatin-induced transcription of a panel of DNA repair and synthesis genes. In addition, a real-time PCR analysis done on tumor and matched normal lung specimens from 44 surgically resected NSCLC patients showed that Src transcripts are significantly upregulated in 23% of cases. In conclusion, Src-directed therapeutic strategies could interfere with cisplatin resistance, possibly allowing to reduce cisplatin doses, thus improving its efficacy. The data of this study support further clinical studies aimed to evaluate the efficacy of Src-inhibiting agents in combination with cisplatin in the treatment of NSCLC.

Activity of the multikinase inhibitor dasatinib against ovarian cancer cells

Background:

Here, we explore the therapeutic potential of dasatinib, a small-molecule inhibitor that targets multiple cytosolic and membrane-bound tyrosine kinases, including members of the Src kinase family, EphA2, and focal adhesion kinase for the treatment of ovarian cancer.

Methods:

We examined the effects of dasatinib on proliferation, invasion, apoptosis, cell-cycle arrest, and kinase activity using a panel of 34 established human ovarian cancer cell lines. Molecular markers for response prediction were studied using gene expression profiling. Multiple drug effect/combination index (CI) isobologram analysis was used to study the interactions with chemotherapeutic drugs.

Results:

Concentration-dependent anti-proliferative effects of dasatinib were seen in all ovarian cancer cell lines tested, but varied significantly between individual cell lines with up to a 3 log-fold difference in the IC₅₀ values (IC₅₀ range: 0.001–11.3 μmol l⁻¹). Dasatinib significantly inhibited invasion, and induced cell apoptosis, but less cell-cycle arrest. At a wide range of clinically achievable drug concentrations, additive and synergistic interactions were observed for dasatinib plus carboplatin (mean CI values, range: 0.73–1.11) or paclitaxel (mean CI values, range: 0.76–1.05). In this study, 24 out of 34 (71%) representative ovarian cancer cell lines were highly sensitive to dasatinib, compared with only 8 out of 39 (21%) representative breast cancer cell lines previously reported. Cell lines with high expression of Yes, Lyn, Eph2A, caveolin-1 and 2, moesin, annexin-1, and uPA were particularly sensitive to dasatinib.

Conclusions:

These data provide a clear biological rationale to test dasatinib as a single agent or in combination with chemotherapy in patients with ovarian cancer.

Quantitative real-time imaging of molecular dynamics during cancer cell invasion and metastasis in vivo

Despite our advanced understanding of primary cancer development and progression, metastasis and the systemic spread of the disease to secondary sites remains the leading cause of cancer-associated death. The metastatic process is therefore a major potential therapeutic target area for cancer researchers and elucidating the key steps that are susceptible to therapeutic intervention will be critical to improve our treatment strategies. Recent advances in intravital imaging are rapidly improving our insight into this process and are helping in the design of stage-specific drug regimes for the treatment of metastatic cancer. Here we discuss current developments in intravital imaging and our recent use of photobleaching and photoactivation in the analysis of dynamic biomarkers in living animals to assess the efficacy of therapeutic intervention on early stages of tumor cell metastasis.

Fyn and SRC are effectors of oncogenic epidermal growth factor receptor signaling in glioblastoma patients

Activating epidermal growth factor receptor (EGFR) mutations are common in many cancers including glioblastoma. However, clinical responses to EGFR inhibitors are infrequent and short-lived. We show that the Src family kinases (SFK) Fyn and Src are effectors of oncogenic EGFR signaling, enhancing invasion and tumor cell survival in vivo. Expression of a constitutively active EGFR mutant, EGFRvIII, resulted in activating phosphorylation and physical association with Src and Fyn, promoting tumor growth and motility. Gene silencing of Fyn and Src limited EGFR- and EGFRvIII-dependent tumor cell motility. The SFK inhibitor dasatinib inhibited invasion, promoted tumor regression, and induced apoptosis in vivo, significantly prolonging survival of an orthotopic glioblastoma model expressing endogenous EGFRvIII. Dasatinib enhanced the efficacy of an anti-EGFR monoclonal antibody (mAb 806) in vivo, further limiting tumor growth and extending survival. Examination of a large cohort of clinical samples showed frequent coactivation of EGFR and SFKs in glioblastoma patients. These results establish a mechanism linking EGFR signaling with Fyn and Src activation to promote tumor progression and invasion in vivo and provide rationale for combined anti-EGFR and anti-SFK targeted therapies.

Pharmacologic inhibitors of IkappaB kinase suppress growth and migration of mammary carcinosarcoma cells in vitro and prevent osteolytic bone metastasis in vivo

The NF-kappaB signaling pathway is known to play an important role in the regulation of osteoclastic bone resorption and cancer cell growth. Previous studies have shown that genetic inactivation of IkappaB kinase (IKK), a key component of NF-kappaB signaling, inhibits osteoclastogenesis, but the effects of pharmacologic IKK inhibitors on osteolytic bone metastasis are unknown. Here, we studied the effects of the IKK inhibitors celastrol, BMS-345541, parthenolide, and wedelolactone on the proliferation and migration of W256 cells in vitro and osteolytic bone destruction in vivo. All compounds tested inhibited the growth and induced apoptosis of W256 cells as evidenced by caspase-3 activation and nuclear morphology. Celastrol, BMS-345541, and parthenolide abolished IL1beta and tumor necrosis factor alpha-induced IkappaB phosphorylation and prevented nuclear translocation of NF-kappaB and DNA binding. Celastrol and parthenolide but not BMS-345541 prevented the activation of both IKKalpha and IKKbeta, and celastrol inhibited IKKalpha/beta activation by preventing the phosphorylation of TAK1, a key receptor-associated factor upstream of IKK. Celastrol and parthenolide markedly reduced the mRNA expression of matrix metalloproteinase 9 and urinary plasminogen activator, and inhibited W256 migration. Administration of celastrol or parthenolide at a dose of 1 mg/kg/day suppressed trabecular bone loss and reduced the number and size of osteolytic bone lesions following W256 injection in rats. Histomorphometric analysis showed that both compounds decreased osteoclast number and inhibited bone resorption. In conclusion, pharmacologic inhibitors of IKK are effective in preventing osteolytic bone metastasis in this model and might represent a promising class of agents to the prevention and treatment of metastatic bone disease associated with breast cancer.

The Src inhibitor AZD0530 blocks invasion and may act as a radiosensitizer in lung cancer cells

BACKGROUND

With the emergence of Src inhibitors in clinical trials, improved knowledge of the molecular responses of cancer cells to these agents is warranted. This will facilitate the development of tests to identify patients who may benefit from these agents, allow drug activity to be monitored and rationalize the combination of these agents with other treatment modalities.

METHODS

This study evaluated the molecular and functional effects of Src inhibitor AZD0530 in human lung cancer cells, by Western blotting and reverse transcription-polymerase chain reaction, and by assays for cell viability, migration, and invasion.

RESULTS

Src was activated in four of five cell lines tested and the level corresponded with the invasive potential and the histologic subtype. Clinically relevant, submicromolar concentrations of AZD0530 blocked Src and focal adhesion kinase, resulting in significant inhibition of cell migration and Matrigel invasion. Reactivation of STAT3 and up-regulation of JAK indicated a potential mechanism of resistance. AZD0530 gave a potent and sustained blockage of AKT and enhanced the sensitivity to irradiation.

CONCLUSIONS

The results indicated that AZD0530, aside from being a potent inhibitor of tumor cell invasion which could translate to inhibition of disease progression in the clinic, may also lower resistance of lung cancer cells to pro-apoptotic signals.

Absolute quantification of phosphorylation on the kinase activation loop of cellular focal adhesion kinase by stable isotope dilution liquid chromatography/mass spectrometry

A vital point of convergence for many signaling pathways at cellular focal adhesions is the interaction of two nonreceptor tyrosine kinases, focal adhesion kinase (FAK) and Src. The binding of Src to FAK leads to the phosphorylation of Y(576) and Y(577), located within the activation loop domain of FAK. However, it has not been possible previously to determine the absolute quantitative relationship between phosphorylated and nonphosphorylated forms of this activation loop domain in cells undergoing normal metabolism. We have developed a stable isotope dilution liquid chromatography-multiple reaction monitoring/mass spectrometry (LC-MRM/MS) technique that allows such determinations to be made. Isotopically labeled and phosphorylated FAK protein standards were synthesized and used to control for loss during immunoprecipitation of FAK. A control tryptic peptide, representing an unmodified region of FAK, was employed to monitor the mass balance of post-translational modifications (PTMs) on the activation loop domain. Absolute quantification was conducted using stable isotope labeled peptide standards with four endogenous amino acid overhangs at the trypsin digestion sites of both the amino and carboxy terminus. The LC-MRM/MS method was rigorously validated using in vitro kinase assays and employed to conduct absolute quantification of FAK phosphorylation in normal mouse embryonic fibroblasts (MEFs). This methodology will have particular utility for biomarker studies of kinase-inhibiting anticancer drugs and for quantitative proteomic investigations that examine kinase- and phosphatase-mediated cellular signal transduction pathways.

Efficacy and pharmacodynamic effects of bosutinib (SKI-606), a Src/Abl inhibitor, in freshly generated human pancreas cancer xenografts

Recently, Src tyrosine kinase has emerged as an attractive target for anticancer therapy, and Src is overexpressed in pancreatic cancer. The purpose of the study was to investigate the in vivo efficacy and pharmacodynamic effects of bosutinib (SKI-606), a Src/Abl inhibitor, using a panel of human pancreatic tumor xenografts. Surgically resected human pancreatic tumors were implanted into female nude mice and randomized to bosutinib versus control. Src and other pathways were analyzed by Western Blot, IHC, and Affymetrix U133 Plus 2.0 gene arrays. Of 15 patient tumors, 3 patient tumors were found to be sensitive to bosutinib, defined as tumor growth of <45% than that of control tumors. There were no definite differences between sensitive and resistant tumors in the baseline Src kinase pathway protein expression assessed by Western Blot. Caveolin-1 expression, as assessed by reverse transcription-PCR and immunohistochemistry, was frequently higher in sensitive cases. In sensitive tumors, bosutinib resulted in increased apoptosis. Phosphorylation of key signaling molecules downstream of Src, signal transducers and activators of transcription 3, and signal transducers and activators of transcription 3, were significantly inhibited by bosutinib. K-Top Scoring Pairs analysis of gene arrays gave a six-gene classifier that predicted resistance versus sensitivity in six validation cases. These results may aid the clinical development of bosutinib and other Src inhibitors in pancreas cancer.

SRC family kinase activity is up-regulated in hormone-refractory prostate cancer

PURPOSE

Although Src family kinase (SFK) inhibitors are now in clinical trials for the treatment of androgen-independent prostate cancer (AIPC), there are no studies relating SFK activation to patient survival. This study was designed to determine if SFK activation was up-regulated with the development of AIPC and if patients could be selected who were more likely to respond to therapy.

EXPERIMENTAL DESIGN

A unique cohort of matched prostate tumor samples, taken before hormone deprivation therapy and following hormone relapse, was used to determine by immunohistochemistry on an individual patient basis if SFK activity changed with progression to AIPC and whether this related to patient outcome measures. Using matched, hormone-sensitive and hormone-refractory cell lines, we determined if hormone status affected the way prostate cancer cells respond to suppression of SFK activity by the small-molecule inhibitor dasatinib.

RESULTS

In the current study, 28% of patients with AIPC exhibited an increase in SFK activity in prostate cancer tissue, these patients had significantly shorter overall survival (P<0.0001), and activated SFK expression correlated with the presence of distant metastases. Dasatinib inhibited phosphorylation of Src and Lyn and the downstream substrate FAK in hormone-sensitive and hormone-refractory cell lines. Although migration was reduced by dasatinib in both cell lines, proliferation of hormone-refractory cells only was inhibited.

CONCLUSION

Appropriate patient selection may allow better targeting of prostate cancer patients who are likely to respond to the treatment with SFK inhibitors at the same time improving the outcome of clinical trials.

Src inhibitor dasatinib inhibits growth of breast cancer cells by modulating EGFR signaling

EGF-receptor family members (EGFRs) as well as c-Src are over expressed in approximately 70% of breast cancer, and in most of the tumors c-Src is co-over expressed with at least one of the EGFRs, suggesting that they may interact functionally and play a role in the development and progression of the malignancy. We hypothesize that a small molecule inhibitor of c-Src dasatinib (BMS-354825; Bristol Myers Squibb), exerts its effects on breast cancer cells by modulating EGFR signaling. Indeed, we found that dasatinib causes inhibition of breast cancer cells overexpressing EGFR, HER-2 and HER-3 (MDA-MB-468, SKBR3, MDA-MB-453, and MDA-MB-231) in a dose and time-dependent manner. Dasatinib also stimulated apoptosis in MDA-MB-468 cells, which could be attributed to activation of both caspase-9 and -8 and arrest of the cell cycle at G0/G1 cycle. Furthermore, dasatinib markedly inhibited colony formation, cell invasion, migration and angiogenesis, accompanied by decreased phosphorylation of EGFR and c-Src and their downstream effector molecules Akt and Erks. Our data suggest that dasatinib mediates its action in part through EGFR signaling and could be a potential therapeutic agent for breast cancer.

Real-time study of E-cadherin and membrane dynamics in living animals: implications for disease modeling and drug development

The ability of tumor cells to invade and metastasize requires deregulation of interactions with adjacent cells and the extracellular matrix. A major challenge of cancer biology is to observe the dynamics of the proteins involved in this process in their functional and physiologic context. Here, for the first time, we have used photobleaching and photoactivation to compare the mobility of cell adhesion and plasma membrane probes in vitro and in tumors grown in mice (in vivo). We find differences between in vitro and in vivo recovery dynamics of two key molecules, the tumor suppressor E-cadherin and the membrane-targeting sequence of H-Ras. Our data show that E-cadherin dynamics are significantly faster in vivo compared with cultured cells, that the ratio of E-cadherin stabilized in cell-cell junctions is significantly higher in vivo, and that E-cadherin mobility correlates with cell migration. Moreover, quantitative imaging has allowed us to assess the effects of therapeutic intervention on E-cadherin dynamics using dasatinib, a clinically approved Src inhibitor, and show clear differences in the efficacy of drug treatment in vivo. Our results show for the first time the utility of photobleaching and photoactivation in the analysis of dynamic biomarkers in living animals. Furthermore, this work highlights critical differences in molecular dynamics in vitro and in vivo, which have important implications for the use of cultured disease models as surrogates for living tissue.

Inhibition of Src family kinases with dasatinib blocks migration and invasion of human melanoma cells

Src family kinases (SFK) are involved in regulating a multitude of biological processes, including cell adhesion, migration, proliferation, and survival, depending on the cellular context. Therefore, although SFKs are currently being investigated as potential targets for treatment strategies in various cancers, the biological responses to inhibition of SFK signaling in any given tumor type are not predictable. Dasatinib (BMS-354825) is a dual Src/Abl kinase inhibitor with potent antiproliferative activity against hematologic malignancies harboring activated BCR-ABL. In this study, we show that dasatinib blocks migration and invasion of human melanoma cells without affecting proliferation and survival. Moreover, dasatinib completely inhibits SFK kinase activity at low nanomolar concentrations in all eight human melanoma cell lines investigated. In addition, two known downstream targets of SFKs, focal adhesion kinase and Crk-associated substrate (p130(CAS)), are inhibited with similar concentrations and kinetics. Consistent with inhibition of these signaling pathways and invasion, dasatinib down-regulates expression of matrix metalloproteinase-9. We also provide evidence that dasatinib directly inhibits kinase activity of the EphA2 receptor tyrosine kinase, which is overexpressed and/or overactive in many solid tumors, including melanoma. Thus, SFKs and downstream signaling are implicated as having key roles in migration and invasion of melanoma cells.

Preclinical anticancer activity of the potent, oral Src inhibitor AZD0530

AZD0530, an orally available Src inhibitor, demonstrated potent antimigratory and anti-invasive effects in vitro, and inhibited metastasis in a murine model of bladder cancer. Antiproliferative activity of AZD0530 in vitro varied between cell lines (IC(50) 0.2 ->10μM). AZD0530 inhibited tumor growth in 4/10 xenograft models tested and dynamically inhibited in vivo phosphorylation of Src substrates paxillin and FAK in both growth-inhibition-resistant and -sensitive xenografts. The activity of AZD0530 in NBT-II bladder cancer cells in vitro was consistent with inhibition of cell migration and stabilization of cell-cell adhesion. These data suggest a dominant anti-invasive pharmacology for AZD0530 that may limit tumor progression in a range of cancers. AZD0530 is currently in Phase II clinical trials.

Quantification of focal adhesion kinase activation loop phosphorylation as a biomarker of Src activity

A recently developed stable isotope dilution liquid chromatography-multiple reaction/mass spectrometry method to quantify focal adhesion kinase (FAK) activation loop phosphorylation was used to study endogenous Src kinase activity. This revealed that bis-phosphorylated pTyr(576)/Tyr(577)-FAK was a biomarker of Src activity and inactivation in vitro and in cell culture. Mouse embryonic fibroblasts (MEFs) expressing endogenous Src family kinases contained 65% unmodified Tyr(576)/Tyr(577), 33% mono-phosphorylated-pTyr(576)-FAK, and 6% bis-phosphorylated-pTyr(576)/pTyr(577)-FAK. In contrast, MEFs expressing oncogenic Y(529)FSrc contained 38% unmodified Tyr(576)/Tyr(577)-FAK, 29% mono-phosphorylated-pTyr(576)-FAK, and 19% bis-phosphorylated-pTyr(576)/pTyr(577)-FAK. This new method has made it possible to accurately determine the absolute amounts of FAK phosphorylation that occur after Src inhibition in cell culture and in vitro with increasing concentrations of the Src inhibitor N-(5-chloro-1,3-benzodioxol-4-yl)-7-[2-(4-methylpiperazin-1-yl)ethoxy]-5-(tetrahydro-2H-pyran-4-yloxy)quinazolin-4-amine (AZD0530). Phosphorylation of FAK at Tyr(576)/Tyr(577) was inhibited by AZD0530 in a dose-dependent manner both in cell culture and in vitro. However, there was a substantial difference in the ability of AZD0530 to inhibit Src that was constitutively activated in a cellular context (IC(50) = 2.12 muM) compared with the isolated enzyme (IC(50) = 0.14 muM). When normal MEFs and Y(529)FSrc-expressing MEFs were treated with pervanadate (a global phosphatase inhibitor), pTyr(576)/pTyr(577)-FAK accounted for almost 60% of the total FAK present in the cells. This suggests that activation loop phosphorylation is regulated by tyrosine phosphatases. These results confirm that FAK phosphorylation is a useful biomarker of Src inhibition in vivo. The accuracy and specificity of stable isotope dilution liquid chromatography-mass spectrometry methodology offers significant advantages over current immunochemical approaches for monitoring Src activity.

A novel Src kinase inhibitor reduces tumour formation in a skin carcinogenesis model

The Src family tyrosine kinases are key modulators of cancer cell invasion and metastasis and a number of Src kinase inhibitors are currently in clinical development for the treatment of solid tumours. However, there is growing evidence that Src is also upregulated at very early stages of epithelial cancer development. We have investigated the role of Src in mouse skin, which is one of the most tractable models of epithelial homoeostasis and tumorigenesis. We found that Src protein expression and activity was regulated during the normal hair cycle and was increased specifically during the proliferative anagen phase and also in response to the tumour promoter 12-O-tetradecanoylphorbol-13-acetate (TPA). AZD0530, a selective Src inhibitor, prevented the TPA-induced proliferation of basal keratinocytes both in vivo and in vitro. Moreover, treatment with AZD0530 reduced papilloma formation following the well-established 7,12-dimethylbenz(a)anthracene/TPA skin carcinogenesis protocol but did not inhibit the subsequent proliferation of the papillomas. Furthermore, AZD0530 did not alter the malignant conversion of papillomas to squamous cell carcinoma suggesting a role for Src in early tumour development in the skin carcinogenesis model, rather than at later stages of tumour progression. Src expression and activity were also seen in human actinic keratoses that are hyperproliferative pre-malignant skin lesions, indicating that Src may also play a role in the early stages of human skin tumour development. Thus, Src inhibitors such as AZD0530 may therefore have chemopreventative properties in patients with hyperproliferative epidermal disorders.

Choice of fixative is crucial to successful immunohistochemical detection of phosphoproteins in paraffin-embedded tumor tissues

Protein phosphorylation is frequently used as an indicator of cellular signaling activity. Elevated phosphorylation of tyrosine kinase receptors plays an important role in cancer pathogenesis. However, phosphoproteins are usually poorly preserved in clinical tissue samples that are routinely fixed in 10% formalin. Nonetheless, in oncology clinical trials, use of phosphoproteins as biomarkers has been considered to be of great value in evaluating the effectiveness of a given drug candidate. Therefore, it is worthy of investigating whether alternative fixatives would improve the preservation of phosphoproteins in tissue. We compared the IHC staining of a number of phosphoproteins in xenograft and human surgical tumor tissues fixed in three different fixatives: 10% formalin, 4% paraformaldehyde (PFA), and Streck's tissue fixative (STF). We found that STF significantly enhanced the staining intensity of phosphoproteins compared with 10% formalin or 4% PFA. STF fixative also showed superiority of preservation of phosphoproteins in human surgical samples. Our results indicate that the choice of fixative could significantly affect the usability of clinical tissue samples for evaluating phosphoprotein by IHC.

Preclinical evaluation of dasatinib, a potent Src kinase inhibitor, in melanoma cell lines

BACKGROUND

Metastatic melanoma is a highly chemotherapy resistant tumour. The use of newer targeted therapies alone and in combination with chemotherapy may offer new hope of improving response to treatment. Dasatinib, a multi-target kinase inhibitor, is currently approved for the treatment of chronic myeloid leukaemia and has shown promising results in preclinical studies in a number of solid tumours.

METHODS

We examined the effects of dasatinib on proliferation, chemo-sensitivity, cell cycle arrest, apoptosis, migration and invasion in human melanoma cell lines. Expression and activation of Src kinase, FAK and EphA2 were also examined in the melanoma cells.

RESULTS

Dasatinib inhibited growth of three of the five melanoma cell lines. Comparison with sorafenib showed that in these three cell lines dasatinib inhibited growth at lower concentrations than sorafenib. Dasatinib in combination with the chemotherapy drug temozolomide showed greater efficacy than either drug alone. Dasatinib induced cell cycle arrest and apoptosis and significantly inhibited cell migration and invasion of melanoma cells. Dasatinib inhibition of proliferation was associated with reduced phosphorylation of Src kinase, while decreased phosphorylation of FAK was implicated in dasatinib-mediated inhibition of migration and invasion in melanoma cells.

CONCLUSION

Dasatinib has both anti-proliferative and anti-invasive effects in melanoma cells and combined with chemotherapy may have clinical benefit in the treatment of malignant melanoma.

Effects of dasatinib on EphA2 receptor tyrosine kinase activity and downstream signalling in pancreatic cancer

Eph receptors constitute the largest family of receptor tyrosine kinases in the human genome. EphA2 is one prominent member that is overexpressed and functionally altered in many invasive cancers, including pancreatic cancer. Dasatinib, which is a multi-targeted kinase inhibitor mainly developed for Bcr-Abl and Src family kinases, has recently been shown to have significant activity against EphA2. As selective small molecule EphA2 inhibitors are not currently available, we investigated the therapeutic potential to target EphA2 by dasatinib in pancreatic cancer cell lines. Using in vitro kinase assays, we found that EphA2 receptor tyrosine kinase was inhibited directly by dasatinib in a dose-dependent manner. Stimulation with ephrinA1 produced rapid increases of EphA2 phosphorylation that were inhibited by dasatinib, although the effects on activation of downstream signalling differed among the pancreatic cancer cell lines. Dasatinib also inhibited ligand-induced binding of EphA2 to the ubiquitin ligase Cbl, and the internalisation and degradation of EphA2, suggesting that these processes are dependent on kinase activity. Treatment with dasatinib decreased EphA2 phosphorylation in BxPC-3 xenografts, suggesting that dasatinib might have activity in pancreatic cancer due to EphA2 inhibition, besides its effects on Src.

Current and emerging therapies for metastatic colorectal cancer: applying research findings to clinical practice

PURPOSE

The results of clinical trials that led to modern first- and second-line chemotherapeutic regimens for metastatic colorectal cancer, including studies of recently introduced monoclonal antibody products that target vascular endothelial growth factor (VEGF) and epidermal growth factor receptor (EGFR), are described, as well as new therapeutic targets being studied and challenges in research to identify and evaluate new therapies.

SUMMARY

Modern chemotherapy regimens for first-line treatment of metastatic colorectal cancer contain fluorouracil, leucovorin, either oxaliplatin or irinotecan, and the VEGF inhibitor bevacizumab. The EGFR inhibitors cetuximab and panitumumab currently are reserved for second- or third-line therapy, but their role could change as the results of clinical research become available. The phosphatidylinositol 3-kinase (PI3K)/Akt/mammalian target of rapamycin pathway, src kinases, and insulin-like growth factor-1 receptor are among the targets of current research. Identifying the subset of patients with metastatic colorectal cancer who stand to benefit from a particular therapy presents a challenge in conducting clinical research.

CONCLUSION

Modern chemotherapeutic and monoclonal antibody regimens have improved survival in patients with meta-static colorectal cancer. The optimal combinations, timing, and sequence of agents remain to be determined.

Tyrosine kinase inhibition in diffuse large B-cell lymphoma: molecular basis for antitumor activity and drug resistance of dasatinib

Diffuse large B-cell lymphoma (DLBCL) is the most common type of non-Hodgkin lymphoma. Although some patients can be cured by current therapies, novel agents are needed to further improve outcomes. We hypothesized that Src tyrosine kinase inhibition by dasatinib may have antilymphoma effects. Here, we demonstrate that dasatinib inhibits cell growth through G(1)-S blockage in five of seven DLBCL cell lines at clinically achievable concentrations. Compared to resting B cells, DLBCL has increased tyrosine phosphorylation activities. As expected, dasatinib inhibits phosphorylation of several Src family kinase members. However, this inhibition occurs in all cell lines regardless of their proliferative response to the drug. In contrast, the activity of two downstream signaling molecules, Syk and phospholipase Cgamma2 (PLCgamma2), are well correlated with cell line sensitivity to dasatinib, suggesting that these molecules are crucial in mediating the proliferation of activated lymphoma cells. Furthermore, dasatinib inhibits B-cell receptor signaling in primary lymphoma cells. Together, our findings not only show dasatinib as a potentially useful therapy for DLBCL but also provide insights into the pathogenesis of the lymphoma. The results further suggest the possibility of using Syk and PLCgamma2 as biomarkers to predict dasatinib therapeutic response in prospective clinical trials.

The kinase inhibitor dasatinib induces apoptosis in chronic lymphocytic leukemia cells in vitro with preference for a subgroup of patients with unmutated IgVH genes

Src family kinases (SFKs) were described to be overexpressed in chronic lymphocytic leukemia (CLL). We wished to examine the effects of the Src and Abl kinase inhibitor dasatinib on the intracellular signaling and survival of CLL cells. Dasa-tinib showed a dose- and time-dependent reduction of global tyrosine phosphorylation and of activating phosphotyrosine levels of SFKs. Treatment with 100 nM dasatinib led to decreased levels of the activated, phosphorylated forms of Akt, Erk1/2, and p38, and induced PARP cleavage through caspase activity. In Mec1 and JVM-3 cell lines, dasatinib increased p53 protein levels and inhibited proliferation. In freshly isolated CLL cells, dasatinib reduced the expression of Mcl-1 and Bcl-x(L). Combination of 5 microM dasatinib and fludarabine increased the apoptosis induction of each by approximately 50%. In 15 primary CLL samples, cells with unmutated immunoglobulin variable heavy chain (IgV(H)) genes were more sensitive to dasatinib than those with mutated IgV(H) genes (P = .002). In summary, dasatinib shows potent inhibitory effects on the survival of CLL cells in vitro, most prominently in samples obtained from patients with unfavorable prognostic features.

Validation of PDGFRbeta and c-Src tyrosine kinases as tumor/vessel targets in patients with multiple myeloma: preclinical efficacy of the novel, orally available inhibitor dasatinib

Inhibition of multiple myeloma (MM) plasma cells in their permissive bone marrow microenvironment represents an attractive strategy for blocking the tumor/vessel growth associated with the disease progression. However, target specificity is an essential aim of this approach. Here, we identified platelet-derived growth factor (PDGF)-receptor beta (PDGFRbeta) and pp60c-Src as shared constitutively activated tyrosine-kinases (TKs) in plasma cells and endothelial cells (ECs) isolated from MM patients (MMECs). Our cellular and molecular dissection showed that the PDGF-BB/PDGFRbeta kinase axis promoted MM tumor growth and vessel sprouting by activating ERK1/2, AKT, and the transcription of MMEC-released proangiogenic factors, such as vascular endothelial growth factor (VEGF) and interleukin-8 (IL-8). Interestingly, pp60c-Src TK-activity was selectively induced by VEGF in MM tumor and ECs, and the use of small-interfering (si)RNAs validated pp60c-Src as a key signaling effector of VEGF loop required for MMEC survival, migration, and angiogenesis. We also assessed the antitumor/vessel activity of dasatinib, a novel orally bioactive PDGFRbeta/Src TK-inhibitor that significantly delayed MM tumor growth and angiogenesis in vivo, showing a synergistic cytotoxicity with conventional and novel antimyeloma drugs (ie, melphalan, prednisone, bor-tezomib, and thalidomide). Overall data highlight the biologic and therapeutic relevance of the combined targeting of PDGFRbeta/c-Src TKs in MM, providing a framework for future clinical trials.

Initial testing of dasatinib by the pediatric preclinical testing program

BACKGROUND

Dasatinib, a dual inhibitor of the src and abl tyrosine kinases, was recently approved by the Federal Drug Administration for the treatment of imatinib mesylate-resistant chronic myeloid leukemia.

PROCEDURES

Dasatinib was tested against the Pediatric Preclinical Testing Program (PPTP) in vitro panel at concentrations ranging from 0.1 nM to 1.0 microM and was tested in vivo at a dose of 50 mg/kg administered orally twice daily 5 days per week for 4 weeks for the solid tumor xenografts and once daily for the acute lymphoblastic leukemia (ALL) xenografts.

RESULTS

Dasatinib was selectively active against the cell lines of the PPTP in vitro panel, reaching an IC(50) in 6 of the 22 lines. The most sensitive were the AML line Kasumi-1, which has a gain-of-function c-Kit mutation (Asn822Lys), and the rhabdoid tumor line CHLA-266 (IC(50) approximately 10 nM for each). In the in vivo panel, dasatinib induced significant differences in EFS distribution in 8 of 32 (25%) solid tumor models and 3 of 7 ALL models. Using the time to event activity measure, dasatinib had intermediate activity against 1 of 27 (4%) evaluable solid tumor xenografts and 3 of 7 ALL xenografts. One xenograft in the ALL panel, a Philadelphia chromosome positive (Ph(+)) ALL xenograft, demonstrated a complete response.

CONCLUSIONS

Dasatinib was active at low nanomolar concentrations against a small subset of the PPTP's in vitro panel. Dasatinib had limited in vivo activity against the PPTP solid tumor xenografts, but was highly active against a Ph(+) ALL xenograft and also had anti-leukemia activity against two other xenografts.

Dual targeting of Src and ER prevents acquired antihormone resistance in breast cancer cells

Acquired resistance to endocrine therapies presents a major obstacle to the successful treatment of breast cancer patients. Previously, we have shown that acquisition of resistance to tamoxifen in breast cancer cells is accompanied by an elevation in Src kinase activity which promotes an aggressive, invasive phenotype in vitro. Here, we have explored the potential therapeutic effects of combining Src inhibition with anti-oestrogen treatment on the development of endocrine insensitivity in breast cancer cells. Treatment of MCF7 and T47D cells with tamoxifen alone resulted in an initial growth inhibitory phase followed by the eventual development of tamoxifen resistance together with an elevation of Src kinase activity, which was central to their increased invasive capacity. Chronic exposure of both cell types to the Src inhibitor, AZD0530, as a monotherapy resulted in outgrowth of AZD0530-resistant cells, in which Src kinase activity remained suppressed as did their in vitro invasive nature. Treatment of both MCF7 and T47D cells with AZD0530 in combination with tamoxifen resulted in a reduction of Src activity together with inhibition of focal adhesion kinase phosphorylation and a complete abrogation of their in vitro invasive behaviour. Furthermore, combination therapy significantly suppressed expression of cyclinD1 and c-myc and prevented cell proliferation and the subsequent emergence of a resistant phenotype, with total cell loss occurring by 12 weeks. These data demonstrate that pharmacological targeting of Src kinase, in conjunction with antihormone therapies, effectively prevents antihormone resistance in breast cancer cells in vitro and suggests a potential novel therapeutic benefit of Src kinase inhibitors clinically.

Src continues aging: current and future clinical directions

Aberrant activation of members of the Src family of nonreceptor protein tyrosine kinases is common in solid tumor malignancies and may contribute to the development and/or progression of these tumors. As a result, four Src inhibitors are now in more than 50 clinical trials for at least 14 different types of solid tumors. In this review, we briefly discuss the preclinical rationale for Src inhibitors, the development strategies most likely to be successful in the clinic, and the rationale for Src inhibitors in combination with other agents as part of a more comprehensive therapeutic strategy. As the use of Src family inhibitors in clinical trials on solid tumors is in its infancy, further studies on the roles of Src family kinases in tumor progression, chemoresistance, epidermal-to-mesenchymal transition, and other properties of tumor progression will be important in designing the most effective clinical trials using these inhibitors.

Identification and validation of phospho-SRC, a novel and potential pharmacodynamic biomarker for dasatinib (SPRYCEL), a multi-targeted kinase inhibitor

PURPOSE

Dasatinib (BMS-354825) is a potent, oral multi-targeted kinase inhibitor. It is an effective therapy for patients with imatinib-resistant or -intolerant Ph+ leukemias,. It has demonstrated promising preclinical anti-tumor activity, and is under clinical evaluation in solid tumors. To support the clinical development of dasatinib, we identified a pharmacodynamic biomarker to assess in vivo SRC kinase inhibition, with subsequent evaluation in cancer patients.

METHODS

The biomarker, phosphorylated SRC (phospho-SRC), was first identified in human prostate PC-3 tumor cells and peripheral blood mononuclear cells (PBMCs) in vitro. It was further assessed in nude mice bearing PC-3 xenografts. Phospho-SRC[pY418] in tumors and PBMC were measured by western blot analysis, and were quantified by ELISA assays. Dasatinib plasma concentrations were determined using LC/MS/MS.

RESULTS

In PC-3 cells, dasatinib showed dose-dependent anti-proliferative effect, which correlated with the inhibition of phospho-SRC[pY418] and of SRC kinase activity. With a single oral dose of 50 or 15 mg/kg, tumoral phospho-SRC[pY418] was maximally inhibited at 3 h, partially reversed between 7 and 17 h, and completely recovered after 24 h post dose. At 5 mg/kg, tumoral phospho-SRC[pY418] inhibition was less pronounced and recovered more rapidly to baseline level within 24h. Dasatinib (1 mg/kg) resulted in little inhibition. In PBMCs, a similar time course and extent of phospho-SRC[pY418] inhibition was observed. Inhibition of phospho-SRC[pY418] in vivo appeared to correlate with the preclinical in vivo efficacy and PK profiles of dasatinib in mice.

CONCLUSIONS

Phospho-SRC[pY418] may potentially be used as a biomarker to enable assessment of target inhibition in clinical studies exploring dasatinib antitumor activity.

Src kinase modulates the activation, transport and signalling dynamics of fibroblast growth factor receptors

The non-receptor tyrosine kinase Src is recruited to activated fibroblast growth factor receptor (FGFR) complexes through the adaptor protein factor receptor substrate 2 (FRS2). Here, we show that Src kinase activity has a crucial role in the regulation of FGFR1 signalling dynamics. Following receptor activation by ligand binding, activated Src is colocalized with activated FGFR1 at the plasma membrane. This localization requires both active Src and FGFR1 kinases, which are inter-dependent. Internalization of activated FGFR1 is associated with release from complexes containing activated Src. Src-mediated transport and subsequent activation of FGFR1 require both RhoB endosomes and an intact actin cytoskeleton. Chemical and genetic inhibition studies showed strikingly different requirements for Src family kinases in FGFR1-mediated signalling; activation of the phosphoinositide-3 kinase-Akt pathway is severely attenuated, whereas activation of the extracellular signal-regulated kinase pathway is delayed in its initial phase and fails to attenuate.

Increases in c-Yes expression level and activity promote motility but not proliferation of human colorectal carcinoma cells

Increases in the levels and/or activity of nonreceptor tyrosine kinases c-Src and c-Yes are often associated with colorectal carcinogenesis. The physiological consequences of increased c-Yes activity during the early and late stages of tumorigenesis, in addition to the degree of redundancy between c-Yes and c-Src in colorectal cancer cells, remain elusive. To study the consequences of increases in c-Yes levels and activity in later stages of colorectal carcinogenesis, we developed human colorectal cancer cell lines in which c-Yes levels and activity can be inducibly increased by a tightly controlled expression of wild-type c-Yes or by constitutively active mutants of c-Yes, c-YesY537F, and c-Yes Delta t6aa. c-Yes induction resulted in increased cell motility but did not promote proliferation either in vitro or in vivo. These results suggest that in later stages of colorectal carcinogenesis, elevations in c-Yes levels/activity may promote cancer spread and metastasis rather than tumor growth.

The new paradigm in the treatment of colorectal cancer: are we hitting the right target?

The treatment of advanced colorectal cancer has definitely advanced in the last 10 years as newer and more active cytotoxic chemotherapy agents have become available. Better understanding of different fundamental molecular changes in carcinogenesis has resulted in the emergence of important therapeutic targets in colon cancer treatment. The era of nihilism has been replaced by a time of optimism with the development of targeted therapy, with the promise of agents with improved activity and a better toxicity profile in the management of colon cancer. This review focuses on novel agents, particularly targeted therapy in both earlier and more advanced phases of clinical investigations.