Efficacy and safety of imatinib mesylate in advanced gastrointestinal stromal tumors

Protein Kinase C theta (PKCtheta) expression and constitutive activation in gastrointestinal stromal tumors (GISTs)

KIT expression is a key diagnostic feature of gastrointestinal stromal tumors (GISTs), and virtually all of the GISTs express oncogenic forms of the KIT or PDGFRA receptor tyrosine kinase proteins, which serve as therapeutic targets of imatinib mesylate (Gleevec; Novartis, Basel, Switzerland). However, KIT expression can be low in PDGFRA-mutant GISTs, increasing the likelihood of misdiagnosis as other types of sarcoma. We report that the signaling intermediate protein kinase C theta (PKCtheta) is a diagnostic marker in GISTs, including those that lack KIT expression and/or contain PDGFRA mutations. PKCtheta is strongly activated in most GISTs and hence may serve, along with KIT/PDGFRA, as a novel therapeutic target.

The novel marker, DOG1, is expressed ubiquitously in gastrointestinal stromal tumors irrespective of KIT or PDGFRA mutation status

We recently characterized gene expression patterns in gastrointestinal stromal tumors (GISTs) using cDNA microarrays, and found that the gene FLJ10261 (DOG1, discovered on GIST-1), encoding a hypothetical protein, was specifically expressed in GISTs. The immunoreactivity of a rabbit antiserum to synthetic DOG1 peptides was assessed on two soft tissue tumor microarrays. The tissue microarrays included 587 soft tissue tumors, with 149 GISTs, including 127 GIST cases for which the KIT and PDGFRA mutation status was known. Immunoreactivity for DOG1 was found in 136 of 139 (97.8%) of scorable GISTs. All seven GIST cases with a PDGFRA mutation were DOG1-positive, while most of these failed to react for KIT. The immunohistochemical findings were confirmed with in situ hybridization probes for DOG1, KIT, and PDGFRA. Other neoplasms in the differential diagnosis of GIST, including desmoid fibromatosis (0 of 17) and Schwannoma (0 of 3), were immunonegative for DOG1. Only 4 of 438 non-GIST cases were immunoreactive for DOG1. DOG1, a protein of unknown function, is expressed strongly on the cell surface of GISTs and is rarely expressed in other soft tissue tumors. Reactivity for DOG1 may aid in the diagnosis of GISTs, including PDGFRA mutants that fail to express KIT antigen, and lead to appropriate treatment with imatinib mesylate, an inhibitor of the KIT tyrosine kinase.

The novel marker, DOG1, is expressed ubiquitously in gastrointestinal stromal tumors irrespective of KIT or PDGFRA mutation status

We recently characterized gene expression patterns in gastrointestinal stromal tumors (GISTs) using cDNA microarrays, and found that the gene FLJ10261 (DOG1, discovered on GIST-1), encoding a hypothetical protein, was specifically expressed in GISTs. The immunoreactivity of a rabbit antiserum to synthetic DOG1 peptides was assessed on two soft tissue tumor microarrays. The tissue microarrays included 587 soft tissue tumors, with 149 GISTs, including 127 GIST cases for which the KIT and PDGFRA mutation status was known. Immunoreactivity for DOG1 was found in 136 of 139 (97.8%) of scorable GISTs. All seven GIST cases with a PDGFRA mutation were DOG1-positive, while most of these failed to react for KIT. The immunohistochemical findings were confirmed with in situ hybridization probes for DOG1, KIT, and PDGFRA. Other neoplasms in the differential diagnosis of GIST, including desmoid fibromatosis (0 of 17) and Schwannoma (0 of 3), were immunonegative for DOG1. Only 4 of 438 non-GIST cases were immunoreactive for DOG1. DOG1, a protein of unknown function, is expressed strongly on the cell surface of GISTs and is rarely expressed in other soft tissue tumors. Reactivity for DOG1 may aid in the diagnosis of GISTs, including PDGFRA mutants that fail to express KIT antigen, and lead to appropriate treatment with imatinib mesylate, an inhibitor of the KIT tyrosine kinase.

Indications for imatinib mesylate therapy and clinical management

Imatinib mesylate (Gleevec), Glivec, formerly STI571; Novartis Pharma AG; Basel, Switzerland) is a rationally-designed, molecularly-specific oral anticancer agent that selectively inhibits several protein tyrosine kinases central to the pathogenesis of human cancer. It has demonstrated remarkable clinical efficacy in patients with chronic myeloid leukemia and malignant gastrointestinal stromal tumors. Treatment with imatinib is generally well tolerated, and the risk for severe adverse effects is low. Adverse effects most commonly include mild-to-moderate edema, nausea and vomiting, diarrhea, muscle cramps, and cutaneous reactions. Hepatic transaminase level elevations and myelosuppression occur less frequently and resolve with interruption of imatinib therapy. In general, the incidence and severity of adverse effects tend to correlate with imatinib dose and, in chronic myeloid leukemia patients, the phase of disease; but, patient age and other factors are also associated with some types of reactions. With prompt and appropriate intervention, adverse effects in imatinib-treated patients have proven to be manageable across the spectrum of severity, and they seldom require permanent cessation of therapy. Dose reduction is not usually necessary, and reduction to subtherapeutic levels is not recommended.

Imaging of Gastrointestinal Stromal Tumors

Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal neoplasms of the gastrointestinal tract and are defined by their expression of KIT (CD117). This article includes 109 pathologically proven GISTs, with emphasis on their various computed tomography (CT) features. Although the images of GISTs on the CT scan are often distinct from those of epithelial tumors, radiologists should be familiar with these features for the accurate diagnosis of GISTs.

c-kit gene mutations in intracranial germinomas

Gain-of-function mutations of the c-kit gene and the expression of phosphorylated KIT are found in most gastrointestinal stromal tumors and mastocytosis. Further, almost all gonadal seminomas/dysgerminomas exhibit KIT membranous staining, and several reports have clarified that some (10-25%) have a c-kit gene mutation. But, whether intracranial germinomas also have a c-kit gene mutation remains unsolved. To elucidate the presence, frequency, and location of c-kit gene mutations in intracranial germinomas, we analyzed five mutational hot spots (exons 9, 10, 11, 13, and 17) in the c-kit genomic DNA of 16 germinomas using polymerase chain reaction and direct sequencing. We found c-kit gene mutations at exon 11 (W557C) or 17 (D816V, D820V, and N822Y) in four germinomas (25.0%), although no statistically significant difference in any clinicopathological factor was found between patients with or without mutations. These results are similar to those seen in gonadal seminoma/dysgerminoma patients, and confirm that intracranial germinomas are exact counterparts of gonadal seminomas/dysgerminomas, as would be expected on histological and immunohistochemical grounds. Moreover, molecular targeting drugs such as imatinib mesylate (STI571), which is a selective inhibitor of KIT, might be promising agents for the treatment of intracranial germinomas with c-kit gene mutations.

C-KIT expression in primary cutaneous T-cell lymphomas

BACKGROUND

Mutations of the stem cell factor receptor C-KIT play a major pathogenetic role in the development of different malignant diseases like human mastocytosis, myeloproliferative disorders, gastrointestinal stromal tumors, acute myelogenous leukemia, and sinonasal lymphomas. Furthermore, the expression of C-KIT has been described in Hodgkin's disease and nodal CD30+ anaplastic large cell lymphomas (ALCLs). As it is possible to inhibit C-KIT by innovative kinase inhibitors like STI571, it may be an attractive target for new therapeutical approaches. Therefore, we screened more than 50 different types of cutaneous T-cell lymphomas (TCLs) for the presence of C-KIT. Immunohistochemical stainings were performed on paraffin-embedded tissue sections using a polyclonal rabbit anti-human C-KIT antibody. Naphtol-ASD-chloroacetate esterase (NASDCE)-control stainings were performed on every positive sample to distinguish C-KIT-positive lymphoma cells from C-KIT-positive mast cells.

RESULTS

We found weak expression of C-KIT in seven of 18 patients with primary cutaneous CD30+ ALCL, two of eight patients with primary cutaneous pleomorphic TCL, six of 18 patients suffering from mycosis fungoides, and three of five patients with Sezary's syndrome. Generally, only a very small population of the lymphoma cells expressed C-KIT. This finding indicates a difference to the systemic variant of CD30+ ALCL. The potential use of C-KIT targeting new therapeutical approaches is therefore discussed critically, because C-KIT expression is very rare in all investigated types of primary cutaneous lymphoma.

Role of chemotherapy in patients with soft tissue sarcomas

The management of soft tissue sarcomas has been highlighted in the last few years by the responsiveness of gastrointestinal stromal tumors to imatinib (Gleevec, Novartis). In this article, the use of chemotherapeutic agents in the management of this and some of the 50 or more subtypes of sarcomas are discussed, and a brief review of the use of chemotherapy in the adjuvant or neoadjuvant setting for people with large extremity sarcomas is provided. Doxorubicin and ifosfamide (Mitoxana, Bristol-Myers Squibb) remain the best individual drugs for sarcomas overall, although dacarbazine and gemcitabine (Gemzar, Eli Lilly) with or without a taxane has activity in at least a subset of sarcomas. The data regarding adjuvant chemotherapy for extremity soft tissue sarcomas is still quite mixed, with little if any overall survival advantage found to support its incorporation into disease management. The finding of tyrosine kinase inhibitors such as imatinib with demonstrated activity in gastrointestinal stromal tumors and dermatofibrosarcoma protuberans, as well as the finding of new agents such as ecteinascidin-743 (Yondelis, PharmaMar) with at least some activity against soft tissue sarcomas, reinforces the idea that we should target individual subtypes of sarcoma, just as treatment varies by subtype for the hematological malignancies.

Gastrointestinal stromal tumors (GISTs) with KIT and PDGFRA mutations have distinct gene expression profiles

Most GISTs require oncogenic activation of the KIT or PDGFRA receptor tyrosine kinase proteins, and the genomic mechanisms of oncogene activation are heterogeneous. Notably, the kinase mutation type correlates with both tumor biology and imatinib response. For example, GISTs with KIT exon 11 mutations are typically gastric and have excellent imatinib response, whereas those with KIT exon 9 mutations generally arise in the small bowel and are less responsive to imatinib. To identify genes that might contribute to these biological differences, we carried out gene expression profiling of 26 GISTs with known KIT and PDGFRA mutational status. Expression differences were then evaluated further by RNA in situ hybridization, immunohistochemistry, and immunoblotting. Unsupervised hierarchical clustering grouped tumors with similar mutations together, but the distinction between the different groups was not absolute. Differentially expressed genes included ezrin, p70S6K, and PKCs, which are known to have key roles in KIT or PDGFRA signaling, and which might therefore contribute to the distinctive clinicopathological features in GISTs with different mutation types. These gene products could serve as highly selective therapeutic targets in GISTs containing the KIT or PDGFRA mutational types with which they are associated.

KIT-negative gastrointestinal stromal tumors: proof of concept and therapeutic implications

The diagnosis of gastrointestinal stromal tumor (GIST) is currently based on morphologic features and immunohistochemical demonstration of KIT (CD117). However, some tumors (in our estimation approximately 4%) have clinicopathologic features of GIST but do not express KIT. To determine if these lesions are truly GISTs, we evaluated 25 tumors with clinical and histologic features typical of GIST, but with negative KIT immunohistochemistry, for KIT and PDGFRA mutations using DNA extracted from paraffin-embedded tissue. Most tumors originated in the stomach (N = 14) or omentum/mesentery (N = 5). The neoplasms were composed of epithelioid cells (13 cases), admixed epithelioid and spindle cells (8 cases), or spindle cells (4 cases). Absence of KIT expression was confirmed by immunoblotting in 5 cases. Tumor karyotypes performed in 4 cases were noncomplex with monosomy 14 or 14q deletion, typical of GIST. Mutational analysis revealed PDGFRA and KIT mutations in 18 and 4 tumors, respectively, whereas 3 tumors did not have apparent KIT or PDGFRA mutations. The PDGFRA mutations primarily involved exon 18 (N = 15) and included 11 tumors with missense mutation in codon 842 (PDGFRA D842V or D842Y). In conclusion, a small subset of GISTs with otherwise typical clinicopathologic and cytogenetic features do not express detectable KIT protein. When compared with KIT-positive GISTs, these KIT-negative GISTs are more likely to have epithelioid cell morphology, contain PDGFRA oncogenic mutations, and arise in the omentum/peritoneal surface. Notably, some KIT-negative GISTs contain imatinib-sensitive KIT or PDGFRA mutations; therefore, patients with KIT-negative GISTs should not, a priori, be denied imatinib therapy.

New tools to monitor stress using non-invasive PET imaging

Noninvasive imaging using positron emission tomography (PET) is playing an increasing role in monitoring biochemical changes in vivo in various diseases. For example, many of the neurochemical systems activated by stress can be monitored using this technique. Examples of neurotransmitter interactions with CRH, serotonin, dopamine, and muscarinic cholinergic receptors demonstrate this approach.

The FIP1L1-PDGFRalpha kinase in hypereosinophilic syndrome and chronic eosinophilic leukemia

PURPOSE OF REVIEW

The idiopathic hypereosinophilic syndrome is a rare hematologic disorder characterized by sustained unexplained eosinophilia with associated end-organ damage and by a striking male predominance. The first insights into the molecular etiology of this heterogeneous disease were obtained from a "bedside-to-bench" approach. Successful empiric treatment of patients with the hypereosinophilic syndrome with the selective tyrosine kinase inhibitor imatinib mesylate (Gleevec, Novartis) ultimately led to the discovery of the FIP1L1-PDGFRalpha fusion kinase in about half of the hypereosinophilic syndrome cases.

RECENT FINDINGS

The FIP1L1-PDGFRA fusion gene is generated by a cryptic interstitial chromosomal deletion, del(4)(q12q12), which indicates that these cases are clonal hematopoietic malignancies and should be reclassified as chronic eosinophilic leukemias based on current World Health Organization recommendations. In addition, the FIP1L1-PDGFRA fusion gene was also identified in cases with systemic mast cell disease. In vitro and in vivo studies confirmed that FIP1L1-PDGFRalpha is a therapeutic target of imatinib, forming a rational basis for the treatment of FIP1L1-PDGFRA positive chronic eosinophilic leukemia and mastocytosis with imatinib. Similar to BCR-ABL-positive leukemias, resistance to imatinib due to point mutations in the PDGFRalpha kinase domain may develop. We have explored strategies to circumvent resistance to imatinib using alternative tyrosine kinase inhibitors such as PKC412.

SUMMARY

The discovery of the FIP1L1-PDGFRA fusion gene in the hypereosinophilic syndrome is an example of the power of clinical translational research and identifies interstitial chromosomal deletion as a novel mechanism to generate oncogenic tyrosine kinase fusion genes.

Gastrointestinal stromal tumor: Computed tomographic features

AIM

Gastrointestinal stromal tumor (GIST) is a rare type of cancer. Computed tomography (CT) is an imaging modality of choice for diagnosing GIST. The aim of this retrospective study was to review the CT imaging features of 17 GIST patients.

METHODS

From 1995 to 2003, there were 47 patients with pathologically proven GISTs at our hospital. Of these, 17 patients underwent preoperative CT. We collected and analyzed these CT images. The CT imaging features included tumor diameter, number and location, tumor margin, location of metastasis, hounsfield units of tumor and effect of contrasts. In addition, we also recorded the surgical findings, including complications, tumor size and location for comparative analysis.

RESULTS

The results showed that 12 (70%) tumors were located in the stomach and five (30%) were located in the jejunum mesentery. GISTs were extraluminal in 12 (70%) patients. The tumor margins of 13 (76%) tumors were well defined and irregular in four (24%). The effect of contrast enhancement on GIST CT imaging was homogenous enhancement in 13 (76%) and heterogeneous enhancement in four (24%). The hounsfield units (HU) were 30.41 +/-5.01 for precontrast images and postcontrast hounsfield units were 51.80 +/- 9.24.

CONCLUSION

The stomach was the commonest site of GIST occurrence among our patients. The CT features of GIST were well-defined tumor margins, homogenous enhancement on postcontrast CT images.

Sensitivity of oncogenic KIT mutants to the kinase inhibitors MLN518 and PD180970

Oncogenic mutations of the receptor tyrosine kinase KIT occur in gastrointestinal stromal tumors (GISTs), some cases of acute myelogenous leukemia (AML), and systemic mastocytosis (SM). GISTs commonly contain mutations of the KIT juxtamembrane region while SM and AML harbor active site KIT mutations. Imatinib, which potently inhibits juxtamembrane mutants, is effective for the treatment of GISTs but has no activity against active site mutants. We analyzed the inhibitory potential of 2 small molecule inhibitors, MLN518 and PD180970, against different classes of KIT mutants. Both compounds inhibit the growth of cell lines expressing juxtamembrane mutant KIT. MLN518 additionally targets active site mutant cell lines, inhibiting cell proliferation, KIT, and signal transducer and activator of transcription-3 (Stat3) phosphorylation and inducing apoptosis at concentrations that may be clinically achievable. As phase 1 clinical trials of MLN518 in AML have shown little toxicity, our data suggest MLN518 is a promising candidate for the treatment of SM or AML with KIT mutations.

Primary gastrointestinal stromal tumors in the omentum and mesentery: CT findings and pathologic correlations

OBJECTIVE

This study was undertaken to describe the CT features of primary gastrointestinal stromal tumors in the omentum and mesentery and to identify any pathologic correlation.

CONCLUSION

On contrast-enhanced CT, primary gastrointestinal stromal tumors in the omentum and mesentery are usually well-defined, huge masses that contain large areas of low-attenuation necrosis and hemorrhage and that lack central gas.

Surgery and imatinib in the management of GIST: emerging approaches to adjuvant and neoadjuvant therapy

Gastrointestinal stromal tumor (GIST) is a neoplasm of the gastrointestinal tract, mesentery, or omentum that expresses the protein-tyrosine kinase KIT (CD117) and is the most common mesenchymal tumor arising at these sites. Surgical resection is the first-line intervention for operable GISTs, particularly localized primary tumors, and it was historically the only effective treatment. However, more than half of all GIST patients present with locally advanced, recurrent, or metastatic disease. The 5-year survival rate ranges from 50% to 65% after complete resection of a localized primary GIST and decreases to approximately 35% for patients with advanced disease who undergo complete surgical resection. A total of 40% to 90% of all GIST surgical patients subsequently have postoperative recurrence or metastasis. Imatinib is a potent, specific inhibitor of KIT that has demonstrated significant activity and tolerability in the treatment of malignant unresectable or metastatic GIST, inducing tumor shrinkage of 50% or more or stabilizing disease in most patients. A key strategy for prolonging the survival of patients with GIST is to improve the outcome of surgery. It is possible that the adjuvant and neoadjuvant use of imatinib (e.g., rendering initially inoperable tumors resectable) in the overall management approach to advanced GIST may contribute to surgeons' success in attaining this objective.

Gastrointestinal Stromal Tumors of the Duodenum: CT and Barium Study Findings

OBJECTIVE

The purpose of this study was to describe the CT and radiographic features of gastrointestinal stromal tumors of the duodenum.

CONCLUSION

Gastrointestinal stromal tumors of the duodenum appear on barium studies as extrinsically compressing or submucosal masses with or without ulceration. These tumors usually appear on contrast-enhanced CT as well-defined masses with an exoenteric growth pattern and relatively good heterogeneous enhancement.

Novel mode of action of c-kit tyrosine kinase inhibitors leading to NK cell-dependent antitumor effects

Mutant isoforms of the KIT or PDGF receptors expressed by gastrointestinal stromal tumors (GISTs) are considered the therapeutic targets for STI571 (imatinib mesylate; Gleevec), a specific inhibitor of these tyrosine kinase receptors. Case reports of clinical efficacy of Gleevec in GISTs lacking the typical receptor mutations prompted a search for an alternate mode of action. Here we show that Gleevec can act on host DCs to promote NK cell activation. DC-mediated NK cell activation was triggered in vitro and in vivo by treatment of DCs with Gleevec as well as by a loss-of-function mutation of KIT. Therefore, tumors that are refractory to the antiproliferative effects of Gleevec in vitro responded to Gleevec in vivo in an NK cell-dependent manner. Longitudinal studies of Gleevec-treated GIST patients revealed a therapy-induced increase in IFN-gamma production by NK cells, correlating with an enhanced antitumor response. These data point to a novel mode of antitumor action for Gleevec.

Kinase inhibitors translate lab discoveries into exciting new cures for cancers

Genetic mutations can lead to abnormal activation of certain kinases that in turn lead to excessive cell division seen in cancers. Inhibitors of over activated kinases can theoretically inhibit cancer causing pathways and result in tumor shrinkage. These discoveries have sparked a revolution in drug discovery with many small molecule kinases inhibitors now being used in cancer clinical trials. The amazing success of Imatinib, a blocker of the bcr-abl kinase in chronic myeloid leukemia has shown that the drugs based on these strategies can improve cure rates in cancer. In this article, the authors review the concepts of kinase inhibition in cancer and principles behind the success of imitanib. The authors also review other promising kinase inhibitors being used in clinical trials that are expected to aid the fight against cancer.

Activation of the platelet-derived growth factor-receptor enhances survival of murine bone endothelial cells

The activation of the microvascular endothelial cell platelet-derived growth factor (PDGF) receptor (PDGF-R) by PDGF has been implicated in neoplastic angiogenesis. Here, we established cultures of murine bone microvascular endothelial cells and examined their response to stimulation with PDGF BB ligand and to blockade of PDGF-R signaling with the tyrosine kinase inhibitor STI571 (Gleevec). The addition of STI571 to cultures of bone endothelial cells blocked PDGF BB-induced phosphorylation in a dose-dependent manner and completely abrogated the activation of downstream targets Akt and ERK1/2. Coadministration of STI571 and Taxol also induced the activation of procaspase-3 and significant apoptosis. These data suggest that phosphorylation of PDGF-R stimulates survival pathways in bone endothelial cells and that by selectively inhibiting PDGF-R signaling with STI571, the cells are rendered sensitive to Taxol treatment. The therapeutic combination of STI571 and Taxol may be a powerful tool for targeting tumor-associated endothelial cells in the skeletal compartment.

High efficacy of imatinib for recurrent gastrointestinal stromal tumor in the jejunum: a case report

Gastrointestinal stromal tumor is a mesenchymal tumor of the digestive tract. Although there used to be no effective therapy for the tumor, there have been many recent reports on the efficacy of imatinib. We report on a 53-year-old female patient with a primary tumor of the jejunum who underwent 3 operations. As the tumor could not be removed at the 3rd operation, she was given imatinib orally. Results showed significant reduction ratios of the tumor area (83.0%) and volume (92.2%) at 18 months after starting imatinib administration. Also, the mean reduction ratios of the tumor area and volume per month (%/M) after starting imatinib treatment showed remarkable results, especially during the initial 3 weeks: 53.9%/M and 49.5%/M, respectively. Whether imatinib is the first choice of treatment for GIST or not, and what is the appropriate dose and period should be resolved.

Imaging of gastrointestinal stromal tumour (GIST)

Gastrointestinal stromal tumour (GIST) represents the most common kind of mesenchymal tumour that arises from the alimentary tract. GIST is currently defined as a gastrointestinal tract mesenchymal tumour containing spindle cells (or less commonly epithelioid cells or rarely both) and showing CD117 (c-kit protein) positivity. Targeted molecular therapy of non-resectable GIST using imatinib, a specific tyrosine kinase receptor inhibitor, represents a real milestone in the management of solid malignancy. Imaging studies, both anatomical and functional, are playing an increasingly important role in management of patients with GIST. This review illustrates the radiological appearance of GISTs and the site-specific roles of each imaging tool. Clinical features and radiological differential diagnosis of GIST are also discussed.

Pediatric gastrointestinal stromal tumors and leiomyosarcoma

BACKGROUND

With the introduction of molecularly targeted therapy for gastrointestinal stromal tumors (GISTs), it became important to distinguish GISTs from leiomyosarcomas (LMSs). The authors sought to characterize the clinicopathologic features of these tumors in pediatric patients.

METHODS

The authors reviewed the medical records of 11 patients for whom GIST or LMS was diagnosed between March 1962 and July 2002 at St. Jude Children's Research Hospital and reclassified the tumors according to current histologic and immunophenotypic criteria. The authors also reviewed the literature pertaining to pediatric GISTs and LMSs.

RESULTS

Seven patients had GISTs, and four had LMS. The median age of the patients at diagnosis was 11.5 years. At diagnosis, metastases were present in one patient with GISTs and in another with LMS. Unlike the focal distribution of CD117 (KIT) in LMS, diffuse and strong immunostaining was observed in GISTs. Only GISTs expressed CD34. Six patients underwent complete resection (four with GISTs and two with LMS), four patients underwent incomplete resection (three with GISTs and one with LMS), and one patient (with LMS) underwent a biopsy only. Radiotherapy or chemotherapy was used to treat one patient with GISTs and three patients with LMS. One patient with a high-risk GIST (largest dimension of 32 cm and high mitotic count) was treated with adjuvant imatinib mesylate outside the preferred setting of a clinical trial, due to concerns regarding the high risk of tumor recurrence. Four patients with GISTs and two with LMS survived median disease-free a median of 10.4 years and 4.3 years after diagnosis, respectively. Tumors in all but one survivor were completely resected.

CONCLUSIONS

KIT staining helped to distinguish GISTs from LMSs. Surgery was the treatment of choice for both entities, and tumor resectability was a key prognostic factor.

Stable expression of small interfering RNA sensitizes TEL-PDGFbetaR to inhibition with imatinib or rapamycin

Small molecule inhibitors, such as imatinib, are effective therapies for tyrosine kinase fusions BCR-ABL-TEL-PDGFbetaR-mediated human leukemias, but resistance may develop. The unique fusion junctions of these molecules are attractive candidates for molecularly targeted therapeutic intervention using RNA interference (RNAi), which is mediated by small interfering RNA (siRNA). We developed a retroviral system for stable expression of siRNA directed to the unique fusion junction sequence of TEL-PDGFbetaR in transformed hematopoietic cells. Stable expression of the siRNA resulted in approximately 90% inhibition of TEL-PDGFbetaR expression and its downstream effectors, including PI3K and mammalian target of rapamycin (mTOR). Expression of TEL-PDGFbetaR-specific siRNA (TPsiRNA) significantly attenuated the proliferation of TEL-PDGFbetaR-transformed Ba/F3 cells or disease latency and penetrance in mice induced by intravenous injection of these Ba/F3 cells. Although a 90% reduction in TEL-PDGFbetaR expression was insufficient to induce cell death, stable siRNA expression sensitized transformed cells to the PDGFbetaR inhibitor imatinib or to the mTOR inhibitor rapamycin. TPsiRNA also inhibited an imatinib-resistant TEL-PDGFbetaR mutant, and the inhibition was enhanced by siRNA in combination with PKC412, another PDGFbetaR inhibitor. Although siRNA delivery in vivo is a challenging problem, stable expression of siRNA, which targets oncogenic fusion genes, may potentiate the effects of conventional therapy for hematologic malignancies.

Stable expression of small interfering RNA sensitizes TEL-PDGFbetaR to inhibition with imatinib or rapamycin

Small molecule inhibitors, such as imatinib, are effective therapies for tyrosine kinase fusions BCR-ABL-TEL-PDGFbetaR-mediated human leukemias, but resistance may develop. The unique fusion junctions of these molecules are attractive candidates for molecularly targeted therapeutic intervention using RNA interference (RNAi), which is mediated by small interfering RNA (siRNA). We developed a retroviral system for stable expression of siRNA directed to the unique fusion junction sequence of TEL-PDGFbetaR in transformed hematopoietic cells. Stable expression of the siRNA resulted in approximately 90% inhibition of TEL-PDGFbetaR expression and its downstream effectors, including PI3K and mammalian target of rapamycin (mTOR). Expression of TEL-PDGFbetaR-specific siRNA (TPsiRNA) significantly attenuated the proliferation of TEL-PDGFbetaR-transformed Ba/F3 cells or disease latency and penetrance in mice induced by intravenous injection of these Ba/F3 cells. Although a 90% reduction in TEL-PDGFbetaR expression was insufficient to induce cell death, stable siRNA expression sensitized transformed cells to the PDGFbetaR inhibitor imatinib or to the mTOR inhibitor rapamycin. TPsiRNA also inhibited an imatinib-resistant TEL-PDGFbetaR mutant, and the inhibition was enhanced by siRNA in combination with PKC412, another PDGFbetaR inhibitor. Although siRNA delivery in vivo is a challenging problem, stable expression of siRNA, which targets oncogenic fusion genes, may potentiate the effects of conventional therapy for hematologic malignancies.

Inhibition of wild-type and mutant Bcr-Abl by AP23464, a potent ATP-based oncogenic protein kinase inhibitor: implications for CML

The deregulated, oncogenic tyrosine kinase Bcr-Abl causes chronic myeloid leukemia (CML). Imatinib mesylate (Gleevec, STI571), a Bcr-Abl kinase inhibitor, selectively inhibits proliferation and promotes apoptosis of CML cells. Despite the success of imatinib mesylate in the treatment of CML, resistance is observed, particularly in advanced disease. The most common imatinib mesylate resistance mechanism involves Bcr-Abl kinase domain mutations that impart varying degrees of drug insensitivity. AP23464, a potent adenosine 5'-triphosphate (ATP)-based inhibitor of Src and Abl kinases, displays antiproliferative activity against a human CML cell line and Bcr-Abl-transduced Ba/F3 cells (IC(50) = 14 nM; imatinib mesylate IC(50) = 350 nM). AP23464 ablates Bcr-Abl tyrosine phosphorylation, blocks cell cycle progression, and promotes apoptosis of Bcr-Abl-expressing cells. Biochemical assays with purified glutathione S transferase (GST)-Abl kinase domain confirmed that AP23464 directly inhibits Abl activity. Importantly, the low nanomolar cellular and biochemical inhibitory properties of AP23464 extend to frequently observed imatinib mesylate-resistant Bcr-Abl mutants, including nucleotide binding P-loop mutants Q252H, Y253F, E255K, C-terminal loop mutant M351T, and activation loop mutant H396P. AP23464 was ineffective against mutant T315I, an imatinib mesylate contact residue. The potency of AP23464 against imatinib mesylate-refractory Bcr-Abl and its distinct binding mode relative to imatinib mesylate warrant further investigation of AP23464 for the treatment of CML.

Late resistance to imatinib therapy in a metastatic gastrointestinal stromal tumour is associated with a second KIT mutation

Currently, there are no data on the secondary resistance of gastrointestinal stromal tumours to imatinib. Here, we report a case of metastatic gastrointestinal stromal tumour that relapsed during imatinib therapy. Mutation analysis showed that the imatinib-resistant liver tumour contained two c-kit mutations.

MLL-rearranged leukemias: insights from gene expression profiling

Gene expression analysis of human leukemias has provided insight into disease classification and mechanisms of oncogenesis. Its success is particularly evident for acute leukemias with rearrangement of the mixed lineage leukemia (MLL) gene on chromosome 11q23. Unlike most other recurrent translocations, MLL rearrangements are found in leukemias classified as acute myelogenous leukemia (AML) or acute lymphoblastic leukemia (ALL). In addition, MLL-rearranged leukemias often express both myeloid- and lymphoid-associated genes. These unusual characteristics have generated much interest in the cell of origin and the mechanism of transformation by MLL rearrangements. Here we review insights gained from characterization of MLL-rearranged human leukemias by genome-wide expression profiling and compare these to data from model systems.

Are there any prognostic factors for small intestinal stromal tumors?

BACKGROUND

Stromal tumors of the digestive tract, or gastrointestinal stromal tumors (GIST), originate from an intestinal mesenchymal precursor cell. Criteria that predict the outcome of small intestinal stromal tumors (SIST) after surgical resection are not clearly established. The aim of the study was to define prognostic criteria for SIST.

METHODS

All c-kit positive SIST treated in our center over a 10-year period were reviewed.

RESULTS

Eighteen patients with SIST treated by surgical resection were included. Overall actuarial 5-year survival was 74% (median follow-up of 69 months). We developed a panel of five criteria (tumor size, mitotic rate, proliferation index, presence of necrosis, and invasion of mucosa or adjacent structures) that permitted distinction between low and high malignant potential SIST. Presence of any four of these five criteria defined a high malignant potential SIST, and was associated with disease recurrence and poor prognosis after surgical resection (P <0.01). Patients with low malignant potential SIST had a 5-year survival of 92%, compared with 0% for high malignant potential SIST (P <0.01).

CONCLUSIONS

This study demonstrates that a panel of morphologic factors can reliably distinguish between low and high malignant potential SIST. Although patients with low malignant potential SIST have an excellent prognosis after surgical resection, the role of adjuvant treatment for high malignant potential SIST remains to be defined.

Phase I Trial Design for Solid Tumor Studies of Targeted, Non-Cytotoxic Agents: Theory and Practice

BACKGROUND

New targeted, non-cytotoxic anticancer agents, such as small-molecule kinase inhibitors, pose challenges to the current phase I paradigm of dose selection based on toxicity. Moreover, increasing the drug dose to toxicity may be unnecessary for drug effect, making the use of maximum tolerated dose as a surrogate of effective dose inappropriate in the phase I setting. Because little is known about the optimal methods of recommended phase II dose selection of targeted, non-cytotoxic therapies, we reviewed the strategies that were used in completed phase I studies of these drugs.

METHODS

We retrieved 60 publications of phase I studies involving 31 single agents representative of the most common targets of interest in the oncology literature. For each publication, we abstracted data regarding patient population, starting dose, methods of dose escalation and determination of recommended phase II dose, and inclusion of correlative studies in study conduct.

RESULTS

Of the 60 completed phase I studies, 36 used toxicity and eight used pharmacokinetic data as endpoints for selection of the recommended phase II dose. Nontraditional endpoints, such as measures of molecular drug effects in tumor or surrogate tissue or functional imaging studies, were not routinely incorporated into the study design and rarely formed the primary basis for dose selection.

CONCLUSIONS

To date, phase I studies of targeted anticancer agents have generally used traditional endpoints for selection of the recommended phase II dose. More research is needed to define suitable molecular measures of drug effect and the means to incorporate them in the early drug development process.

Development of Rationally Designed, Target-Based Agents for the Treatment of Advanced Colorectal Cancer

Although there have been several recent additions to the conventional armamentarium used to treat patients with advanced colorectal cancer, principally as a result of the development of selective and nonselective pharmacologic agents and antibodies, the general outcome of patients with advanced disease is still poor. However, a greater understanding of cancer biology, as well as major advances in biotechnology, is beginning to identify and characterize molecular aberrations that are common in patients with colorectal cancer. These advances have resulted in the development of a wide range of rationally designed, target-based anticancer therapeutic agents, which, by virtue of their selectivity, would be expected to produce less nonspecific toxicity and therefore higher therapeutic indices compared with nonspecific cytotoxic agents. This review will discuss several novel targets and therapeutic agents, particularly those designed to interrupt aberrant signal transduction and apoptotic processes. It will also emphasize the complexity of these systems and the need to incorporate novel clinical development paradigms based on a thorough scientific understanding of these targets.

A new mutation in the KIT ATP pocket causes acquired resistance to imatinib in a gastrointestinal stromal tumor patient

BACKGROUND & AIMS

Imatinib, a tyrosine kinase inhibitor of BCR-ABL, KIT, and platelet-derived growth factor receptor, is used in patients with chronic myelogenous leukemia (CML) and gastrointestinal stromal tumors (GIST). Primary and acquired resistance to the drug can occur in both diseases. Molecular mechanisms have been reported in CML and GIST for primary resistance, whereas extensive studies on the mechanisms responsible for secondary resistance have been almost exclusively reported for CML.

METHODS

In a patient with advanced GIST undergoing imatinib therapy, an isolated progressing peritoneal mass was excised, along with 2 still-responding lesions. Complementary DNA and genomic DNA were analyzed by sequencing for c-Kit gene mutations. KIT receptor expression and phosphorylation status were assessed by immunoprecipitation and Western blot. Transient-transfection experiments were performed with mutagenized KIT constructs, and their activation status was assessed.

RESULTS

In addition to an exon 11 mutation, shared among all of the analyzed lesions, a novel point mutation in c-Kit exon 14 resulting in T670I substitution was found only in the progressing lesion, which harbored a phosphorylated receptor, as opposed to the finding of an inactive receptor in responding lesions. Functional analyses showed that KIT/T670I is insensitive to imatinib and that T670I mutation, introduced in a receptor responding to imatinib, subverted its sensitivity to the drug.

CONCLUSIONS

This new mutation was confined to the progressing lesion; the resulting amino acidic substitution, T670I, affecting the ATP/imatinib pocket of KIT, makes it insensitive to the drug. Interestingly, this substitution is a homologue to the T315I mutation already reported in CML, where it is responsible for acquired resistance to imatinib.

Selective inhibitors of type I receptor kinase block cellular transforming growth factor-β signaling

Transforming growth factor (TGFbeta) is a 25-kDa dimeric polypeptide that plays a key role in a variety of physiological processes and disease states. Blocking TGFbeta signaling represents a potentially powerful and conceptually novel approach to the treatment of disorders in which the signaling pathway is constitutively activated, such as cancer, chronic inflammation with fibrosis and select immune disorders. In this paper, we describe the biological properties of a novel series of quinazoline-derived inhibitors of the type I transforming growth factor receptor kinase (TbetaKIs) that bind to the ATP-binding site and keep the kinase in its inactive conformation. These compounds effectively inhibited TGFbeta-induced Smad2 phosphorylation in cultured cells in vitro with an IC(50) between 20 and 300 nM. Moreover, TbetaKIs were able to broadly block TGFbeta-induced reporter gene activation. Finally, TbetaKIs inhibited TGFbeta-mediated growth inhibition of normal murine mammary epithelial cells (NMuMG) and mink lung epithelial cells (Mv1Lu), and TGFbeta-induced epithelial-mesenchymal transdifferentiation (EMT) of NMuMG cells. Thus, these chemical TbetaKIs have the potential to be further developed as anti-cancer and -fibrosis agents. In addition, they represent valuable new tools for dissecting the biochemical mechanisms of TGFbeta signal transduction and understanding the role of TGFbeta signaling pathways in different physiological and disease processes.

Apoptosis: target for novel drugs

Targeting apoptotic cell death pathways provides wide-ranging opportunities for the discovery and development of novel drugs. Some targeted therapies that selectively induce apoptosis in cancer cells are already marketed, and numerous pro-apoptotic drugs for treating cancer are currently being developed. The anti-apoptotic drugs that are most advanced in development are targeting acute disease indications such as stroke, myocardial infarction and sepsis, in which the role of apoptosis has been best defined and inhibitors of the apoptotic pathway have shown activity in various animal models. In the future, novel drugs might also result from an understanding of apoptotic pathways in chronic disorders.

A great majority of GISTs with PDGFRA mutations represent gastric tumors of low or no malignant potential

Gastrointestinal stromal tumors (GISTs) are KIT expressing spindle cell, epithelioid and rarely pleomorphic mesenchymal tumors. The majority of GISTs show gain-of-function KIT mutations. However, GISTs without KIT mutations and GISTs with weak or lack of immunohistochemical KIT expression have also been reported. Recently, gain-of-function mutations in exon 18 (activation loop) and exon 12 (juxtamembrane domain) of the PDGFRA were identified in such tumors. The purpose of this study was to test the hypothesis that PDGFRA mutation may define a specific clinicopathologic subgroup of GISTs. A total of 447 KIT exon 11 (juxtamembrane domain) mutation-negative GISTs were studied. DNA samples were obtained from formaldehyde-fixed paraffin-embedded tissues. Genomic sequences of PDGFRA exons 18 and 12 were evaluated for the mutations by PCR amplification and direct sequencing. PDGFRA exon 18 mutations were identified in 122 of 346 (35.3%) gastric GISTs and two of 75 (2.7%) intestinal GISTs. A great majority of these mutations represented simple T to A missense mutation at the codon 842 leading to substitution of the valine for aspartic acid (D842 V). However, in-frame deletions and deletions with point mutations clustering between codons 841-847 were found in approximately 23% of all exon 18 mutations. Mutations in PDGFRA exon 12 were found only in 10 of 170 (5.8%) gastric and one of 54 (1.9%) intestinal GISTs negative for KIT exon 11 and PDGFRA exon 18 mutations. There were seven substitutions of aspartic acid for valine at codon 561 (V561D) and four in-frame deletions with point mutations clustering between codons 566 and 571. The majority of GISTs with PDGFRA mutations had pure or predominant epithelioid morphology. Low mitotic activity, < or =5 mitoses/50HPF was detected in 81% of analyzed GISTs including larger, >5 cm tumors. Based on long-term follow-up (average 135 months), a majority (83.5%) of GISTs with PDGFRA mutations followed a benign course.

Neoadjuvant imatinib for unresectable gastrointestinal stromal tumor

We have evaluated the feasibility of the use of neoadjuvant imatinib mesylate in the management of unresectable localized gastrointestinal stromal tumors. In a pilot experience, two patients with unresectable gastrointestinal tumors were treated with neoadjuvant imatinib. Their treatment course and surgical outcomes are described. In both cases, the patient attained sufficient tumor regression to enable complete resection of tumor. We conclude that in the management of unresectable gastrointestinal stromal tumors, neoadjuvant administration of imatinib may facilitate sufficient tumor regression to facilitate subsequent tumor resection with curative intent.

Platelet-derived growth factor receptor inhibition to treat idiopathic hypereosinophilic syndrome

Hypereosinophilic syndrome (HES) is a heterogeneous group of rare disorders characterized by peripheral blood and tissue eosinophilia leading to end-organ damage. Hypereosinophilic syndrome can be fatal, particularly in patients with endomyocardial fibrosis, and treatment has traditionally been palliative or preventive. The disease shares features with myeloproliferative disorders, such as chronic myeloid leukemia, including responsiveness to hydroxyurea and interferon. The tyrosine kinase inhibitor imatinib, a highly effective treatment for chronic myeloid leukemia, has shown efficacy in normalizing eosinophil counts and resolving signs and symptoms in some HES patients. Fusion of the Fip1-like 1 gene (FIP1L1) and the platelet-derived growth factor receptor alpha gene (PDGFRA) was discovered in the majority of patients with imatinib-sensitive HES, and all patients with the fusion responded to imatinib. The product of this fusion gene, FIP1L1-PDGFRalpha, is a constitutively active protein-tyrosine kinase capable of transforming hematopoietic cells. The efficacy of relatively low imatinib concentrations in HES, mediated by inhibition of FIP1L1-PDGFRalpha kinase activity, causally implicates FIP1L1-PDGFRA in the pathogenesis in certain HES patients.

Role of KIT and platelet-derived growth factor receptors as oncoproteins

KIT and platelet-derived growth factor receptors (PDGFRs) play critical oncogenic roles in a broad spectrum of hematologic and solid tumors. These receptor tyrosine kinases, as well as ABL and BCR-ABL, are inhibited by imatinib. Tumors caused by chromosomal translocations that lead to overexpression of PDGFR ligand, resulting in continuous activation of wild-type PDGFRs, are likely to respond to imatinib, as are malignancies caused by gene amplification and overexpression of wild-type PDGFR or KIT receptors. Malignancies linked to chromosomal translocations that express PDGFR or KIT fusion protein-tyrosine kinases are also likely to respond to imatinib. Malignant cell responses to imatinib depend on whether any of these tyrosine kinase activities play essential roles in the oncogenesis of a given tumor, as well as the precise molecular mechanism underlying oncogenesis. For example, imatinib efficacy for malignancies arising from constitutively activating point mutations in tyrosine kinases depends on the exact location of the mutation in the kinase molecule.

Mechanisms of oncogenic KIT signal transduction in primary gastrointestinal stromal tumors (GISTs)

Most gastrointestinal stromal tumors (GISTs) express constitutively activated forms of the KIT receptor tyrosine kinase protein, resulting from oncogenic mutations in the extracellular, juxtamembrane, or kinase domains. KIT oncoproteins are detected early in GIST tumorigenesis, and most GIST patients respond well to treatment with the KIT kinase inhibitor imatinib mesylate (STI571, Gleevec). However, GISTs can develop resistance to imatinib, and additional therapeutic strategies are needed. Little is known about oncogenic KIT signal transduction in GISTs, and whether the type of KIT mutation accounts for selective activation of downstream signaling intermediates. We therefore evaluated KIT downstream signaling profiles in 15 primary GISTs with mutations in KIT exons 9, 11, 13, and 17, and in two human GIST cell lines. All GISTs showed constitutive phosphorylation at KIT tyrosine residues Y703 and Y721. Additionally, most GISTs showed activation of MAPK p42/44, AKT, S6K, STAT1, and STAT3. STAT5 and JNK were not demonstrably activated in any GIST. Using GIST in vitro models, we showed that activation of MAPK p42/44, AKT, and S6K was KIT dependent, whereas STAT1 and STAT3 phosphorylation was only partially dependent on KIT activation. Correlation of activated signaling pathways with the type of KIT mutation revealed low levels of AKT phosphorylation in exon 9 mutant GISTs in contrast to a subset of GISTs with exon 11 mutations. However, additional factors are likely to modify the engagement of signaling pathways in GISTs as suggested by the fact that four GISTs with identical KIT exon 9 mutations had differential activation of MAPK p42/44 and STAT proteins. In summary, in this first report on KIT signal transduction in primary GISTs and GIST cell lines, we identified pathways that are constitutively activated in a KIT-dependent manner and therefore warrant further study as molecular targets in GISTs.

Disease associated mutations at valine 804 in the RET receptor tyrosine kinase confer resistance to selective kinase inhibitors

We have recently demonstrated that the pyrazolopyrimidines PP1 and PP2 and the 4-anilinoquinazoline ZD6474 display a strong inhibitory activity (IC(50)< or =100 nM) towards constitutively active oncogenic RET kinases. Here, we show that most oncogenic MEN2-associated RET kinase mutants are highly susceptible to PP1, PP2 and ZD6474 inhibition. In contrast, MEN2-associated swap of bulky hydrophobic leucine or methionine residues for valine 804 in the RET kinase domain causes resistance to the three compounds. Substitution of valine 804 with the small amino- acid glycine renders the RET kinase even more susceptible to inhibition (ZD6474 IC(50): 20 nM) than the wild-type kinase. Our data identify valine 804 of RET as a structural determinant mediating resistance to pyrazolopyrimidines and 4-anilinoquinazolines.

EGFR Mutations in Lung Cancer: Correlation with Clinical Response to Gefitinib Therapy

Receptor tyrosine kinase genes were sequenced in non-small cell lung cancer (NSCLC) and matched normal tissue. Somatic mutations of the epidermal growth factor receptor gene EGFR were found in 15of 58 unselected tumors from Japan and 1 of 61 from the United States. Treatment with the EGFR kinase inhibitor gefitinib (Iressa) causes tumor regression in some patients with NSCLC, more frequently in Japan. EGFR mutations were found in additional lung cancer samples from U.S. patients who responded to gefitinib therapy and in a lung adenocarcinoma cell line that was hypersensitive to growth inhibition by gefitinib, but not in gefitinib-insensitive tumors or cell lines. These results suggest that EGFR mutations may predict sensitivity to gefitinib.