	Pancreatic cancer will be second only to lung cancer as the most common cause of death from cancer in US by 2030. Most patients are diagnosed with unresectable disease. In this setting, novel combinations of cytotoxics such as FOLFIRINOX and nab-paclitaxel plus gemcitabine have led to modest improvements in survival. At the time of disease progression, less than 50% of the patients will be fit to receive second-line therapy. Patients with advanced pancreatic cancer often develop debilitating cachexia. It is hypothesized that the disease induces a systemic inflammatory response following cytokine production mediated by cancer cells or stromal cells. Plasma levels of biomarkers associated with inflammation, such as C-reactive protein, have also been associated with poor outcomes in patients with advanced pancreatic cancer. The Jak/Stat pathway plays a key role in driving this inflammatory response. Janus kinases are the main signaling transducers for cytokine receptors. Activated Jak recruits and activates transcription factors (Stat) and different signaling pathways including Src, Ras, and the PI3K/Akt pathway. Jak inhibitors may inhibit cancer cell proliferation by disrupting these signaling pathways. Jak inhibitors may also impair the systemic inflammatory response underlying the development of cachexia. A randomized phase 2 trial recently failed to show a benefit in survival when ruxolitinib, a Jak2 inhibitor, was added to capecitabine in the second line. However, in a prespecified subset analysis, a modest improvement in survival was seen in patients with elevated C-reactive protein at baseline. Two randomized phase 3 trials are currently testing ruxolitinib in combination with capecitabine in patients with advanced pancreatic cancer. Patients must have elevated C-reactive protein at baseline to be eligible to participate in this study. In addition, a number of immune modulators are under development or have gained regulatory approval for different indications. This work will review ongoing clinical research with Jak inhibitors in advanced pancreatic cancer as well as some strategies for preclinical testing of vertical inhibition of the Jak pathway.

Pancreatic ductal adenocarcinoma (PDA) is the fourth most common cause of death from cancer in the United States. It is projected that by 2030 it will be second only to NSCLC as the leading cause of cancer related mortality in US.

 In 2015, 48,960 new cases will be diagnosed in the United States, and 40,560 patients will succumb to the disease.

 The overall 5-year survival rate is less than 5%.

 Therefore, novel treatments are urgently needed in this disease. Recent data from a randomized phase 2 trial showed that a subset of patients with PDA may benefit from targeting the Janus kinase pathway.

 Janus kinases (Jak) are the main signaling transducers for cytokine receptors. Cytokines regulate immune response and inflammation. They also play a role in oncogenesis.

 Four different non-receptor tyrosine Jaks (Jak1, Jak2, Jak3 and Tyk2) have been identified.

 Jak family members contain seven conserved JAK homology (JH) domains. JH1 and JH2 are composed of almost identical phosphate transferring domains, a kinase and pseudokinase domain. The JH2, or pseudokinase domain, is catalytically active and can phosphorylate the kinase domain (JH1).

 JH3-7 are characterized by N-terminal regions or sites of interaction with cytokine receptors. Tyk2 was the first member of the JAK family to be isolated.

 Inactivation of Tyk2 in mice decreased response to interferon-alpha/beta (IFNÉ‘/β), IL-12 and led to defective Stat3 activation.

 Homozygous Tyk2 mutations cause autosomal recessive hyper-IgE syndrome, a rare primary immunodeficiency disorder characterized by repeated staphylococcal skin infections, respiratory infections, and elevated levels of IgE.

 Jak1 is a signal transducer for IFNÉ‘/β, IFN-γ, IL-2, IL-4, IL-6, IL-7, IL-9, IL-15, and IL-21. Mice that have a Jak1 deficiency die perinatally.

 Jak2 is critical for signaling by IFNÉ‘/β, IL-3, IL-5, granulocyte-macrophage colony-stimulating factor (GM-CSF), erythropoietin (EPO), and growth hormone (GH). Its kinase activity, rather than its non-kinase status, is essential for mammalian development.

The critical role of Jak2 in hematopoiesis was initially elucidated in Jak2-deficient mice models more than 20 years ago.

In those models, Jak2-deficient embryos were characterized by an absence of red blood cells in the liver indicating impairment of liver hematopoiesis.

No JAK2 mutant embryos were detected beyond 10-12 days, demonstrating that, during that stage of their development, impairment of liver hematopoiesis was lethal. In addition, the response to other cytokines such as GM-CSF, IL-3, and IL-5 was also impaired in Jak2-deficient embryos.

 Lastly, Jak3 is primarily expressed in cells of the immune system.

Mutations in JAK3 have been identified in patients with autosomal recessive severe combined immunodeficiency (SCID).

Jaks are activated after binding to a dimerized cytokine or growth factor receptor (ie, IL-6, interferon, EPO, or GMCSF receptor). Activated Jak recruits and activates transcription factors (Stat) and different signaling pathways (Src, RAS and the PI3K-AKT pathway).

 Upon activation, Stat dimers translocate to the nucleus to initiate transcription of target genes involved in cell proliferation 

 Stat1 is the main transcriptional mediator of IFN. It can also be activated through IL-6. It regulates innate and adaptive immune responses. Stat1 deficiency in humans increases susceptibility to infections by mycobacteria and recurrent encephalitis secondary to herpes simplex virus type-1 (HSV-1).

 Stat3 can be activated by different cytokines (IL-6, IL-10, G-CSF) as well as receptor tyrosine kinases (ie, MET, EGFR) and non-receptor TK (Src). Stat3 is also required for G-CSF induced expansion of granulocytes. Ablation of Stat3 leads to embryonic lethality.

Activation of the JAK/STAT pathway occurs through aberrations in different components of the pathway including autocrine/ paracrine cytokine production, activating mutations of receptors or downstream transducers such as JAK and, finally, activating mutations in STAT 

. Levels of pStat3 are higher at the invasive margin of tumors, which suggests paracrine activation by stromal cells. Indeed, in different tumor types, cancer-associated fibroblasts are a source of IL-6, a cytokine receptor ligand.

 Constitutive activation of the JAK/STAT pathway has been reported in different proliferative disorders. Activating mutations within the JH2 pseudokinase domain (JAK2 V617F) disrupts the auto-inhibitory activity of JH2 and leads to constitutive activation of the kinase domain (JH1). JAK2 V617F mutations are present in more than 95% of patients with polycythemia vera as well as in more than 50% of patients with essential thrombocythemia or myelofibrosis.

In patients with myelofibrosis, ruxolitinib (Jak1/2 inhibitor) resulted in improved overall survival and gained FDA-approval in 2011 for that disorder.

Of note, a decrease in inflammatory cytokines (TNF-É‘, IL-6 and C-reactive protein) also occurred in response to ruxolitinib. Hematologic toxicity, including grade 3/4 anemia (45%), thrombocytopenia (13%) and neutropenia (7%), was commonly seen. Somatic mutations in JAK2 have been reported in 9% of patients with B-cell acute lymphoblastic leukemia (ALL).

 Activating JAK1 mutations are present in some patients with T-cell ALL as well as acute myeloid leukemia.

Activating mutations in MPL, which codes for the thrombopoietin receptor, are found in 9% of patients with myelofibrosis in the absence of JAK2 V617F mutations.

 Other cytokine receptors (CRLF2) can be overexpressed as a result of chromosomal rearrangements in high-risk children with B-cell ALL.

 Mutations in STAT3 are reported in 40% of patients with large granular leukemias as well as ABC diffuse large-B-cell lymphoma, nasopharyngeal and breast cancer.

Lastly, non-canonical pathway activation secondary to epigenetic modifications has also been reported. Jak2 can translocate to the nucleus and phosphorylate tyrosine 41 on the histone H3 tail. This prevents binding of heterochromatin protein 1É‘ (HP1É‘ is required for heterochromatin formation).

Disrupting heterochromatin formation promotes expression of transcription factors such as Myc.

Several lines of evidence suggest a role for inflammation in oncogenesis in pancreatic ductal adenocarcinoma (PDA). Chronic inflammation of the pancreas (pancreatitis) increases the risk of developing pancreatic cancer.

 The role of inflammation in PDA development has also been demonstrated in preclinical models. In a KRAS G12V mouse model, induction of chronic pancreatitis was necessary for PDA development during adulthood.

Moreover, IL-6-mediated Stat3 activation is required for progression from premalignant PanIN lesions to PDA in mice with KRAS G12D mutations. Inflammatory cytokines such as IL-6 contribute to the immunosuppressive role of the stroma through expansion of myeloid-derived suppressor cells (MDSCs).

In patients with resected PDA, JAK/STAT pathway activation was associated with a poor outcome.

 Lastly, plasma levels of biomarkers associated with inflammation, such as C-reactive protein (CRP), have also been associated with poor outcomes in patients with advanced PDA.

 It is hypothesized that PDA induces a systemic inflammatory response following cytokine production mediated by cancer cells or stromal cells. JAK/STAT-dependent cytokine signaling drives this inflammatory response.

Together with complications from PDA such as gastrointestinal obstruction, ascites or pancreatic insufficiency, this systemic inflammatory response is largely responsible for the cachexia characteristic of the disease.

The mechanism of JAK/STAT activation in PDA remains to be elucidated. Genomic analysis in a small series of 26 pancreatic cancer patients did not find oncogenic JAK V617F mutations.

 The Washington University group recently reported a JAK2 mutation (2964 G>C) in a pancreatic cancer patient.

 However, the mutation was predicted to be neutral. A search in the cBio- Portal for Cancer Genomics (www.cbioportal.org, data accessed on 2/25/2015) identified genetic aberrations in JAK2 in 2% of samples from patients with pancreatic cancer (n=90).

 A JAK2 S602I missense mutation and a JAK2 R443* nonsense mutation were found in one of the patients. Amplification in JAK2 (9p24) was reported in a different patient. Mutations in JAK1, most commonly truncating mutations, were present in 8% of samples. A missense mutation in JAK3 G712S was also identified in one patient.

		The Janus kinase pathway may be activated as a result of 1) Autocrine/Paracrine cytokine production 2) Activating mutations of cytokine receptors or JAK and 3) Activating mutations in STAT. Preclinical studies testing vertical inhibition of the pathway or combination of JAK inhibitors with different immunotherapies (IDO or checkpoint inhibitors) are needed to elucidate the role of JAK2 inhibition in the treatment of PDA.

TYK2 missense mutations (V318L and R607H) are present in 2% of samples. Overall, JAK mutations are reported in approximately 1-2% of patients with PDA. While JAK2 V617F mutations are predictive of response to Jak inhibitors in patients with myelofibrosis, there is no evidence yet that a JAK2 mutation will be predictive of response to Jak inhibitors in PDA.

Finally, it is also possible that genetic aberrations other than oncogenic mutations in JAK2 mediate STAT pathway activation in this disease. Indeed, high-throughput gene expression analysis has also found JAK2 enrichment in immune response pathways including JAK-STAT in PDA.

 Preclinical work in pancreatic cancer cell lines suggests that increased expression of gp130 and p-STAT3 may predict response to Jak2 inhibitors in this disease.

Ruxolitinib (INC424) is a Jak 1/2 inhibitor currently undergoing clinical testing in patients with advanced pancreatic cancer. The results of a second-line randomized phase 2 trial with capecitabine plus ruxolitinib or placebo in patients with metastatic pancreatic cancer (RECAP trial) were recently presented at ASCO.

 The study enrolled patients with a Karnofsky score of PS ≥60 who had disease progression with gemcitabine. The study was negative for its primary endpoint (overall survival in an intention-to-treat analysis). However, in a prespecified subset analysis, patients with serum CRP >13mg/L had an improvement in the 6-month survival rate (6mSR; 42% vs. 11%, HR=0.47, 

 = .01). Treatment was well tolerated. In general, the incidence of adverse events was similar in both groups. The incidence of pulmonary embolism (12% vs. 5%) as well as grade 3-4 anemia (15% vs. 2%) was increased in the ruxolitinib group. A larger number of patients in the ruxolitinib arm experienced weight gain (defined as a gain > 5% of baseline weight) not related to ascites or edema. This finding suggests Jak inhibitors might also be effective anticachexia drugs. It is hypothesized that selection of patients with increased CRP levels will enrich trials with patients likely to benefit from this Jak inhibitor. Two randomized phase 3 trials, JANUS1 (NCT02117479) and JANUS2 (NCT02119663) are currently evaluating capecitabine in combination with ruxolitinib or placebo in patients with advanced PDA and a level of CRP >10mg/L (

).45,46 Two phase 1b studies are testing different Jak 1/2 inhibitors (ruxolitinib or momelotinib [GS-0387]) in combination with nab-paclitaxel and gemcitabine in advanced PDA.

Jak inhibitors that preferentially target Jak1 are also undergoing clinical evaluation. INCB039110 (Jak1 inhibitor) is currently in being studied in a phase 1b clinical trial in combination with nab-paclitaxel plus gemcitabine in patients with advanced solid tumors.

 This trial will have a dose expansion cohort limited to patients with advanced PDA.

		Table 1. Ongoing Clinical Trials With Jak Inhibitors in Metastatic Pancreatic Cancer

		ABI indicates nab-paclitaxel; CAPOX, capecitabine plus oxaliplatin; RP2, randomized phase 2

Opportunities for Vertical Inhibition of an Inflammation Pathway in PDA

The portfolio of drugs targeting inflammation is increasing rapidly and, therefore, various opportunities to develop combinations of targeted anti-inflammatory drugs are now available 

. Early clinical trials with targeted therapy have recently shown that horizontal inhibition of different pathways is unlikely to be successful due to increased toxicity, which limits achieving optimal biological doses.

 In contrast to this, vertical inhibition of different signal transducers in a single pathway have proven successful.

 Vertical inhibition of the JAK/Stat pathway needs to be tested in preclinical models. This can include a combination of monoclonal antibodies against IL-6 or its receptor plus Jak inhibitors (

). In addition, monoclonal antibodies against colony stimulating factor 1 receptor (CSF1R) are undergoing clinical evaluation and offer additional opportunities to test vertical inhibition of the Jak pathway. Some cytotoxic agents (5-FU) inhibit MDSC and are currently being tested in combination with JAK inhibitors. Monoclonal antibodies against CXCR4 inhibit recruitment of immature myeloid cells to the tumor and could also be tested in preclinical models in combination with JAK inhibitors.

		Table 2. Potential Partners for Preclinical Testing of Vertical Inhibition in Combination With Jak Inhibitors

Lastly, novel strategies including testing drugs in patients at earlier stages of disease also need to be evaluated. In this regard, a recent phase 1b dose escalation study showed that testing immunotherapies in the neoadjuvant setting is feasible and safe.

 In this trial, patients were treated with FOLFIRINOX in combination with PF- 04136309 (a monoclonal antibody against CCR2, which depletes tumor-associated macrophages [TAM]). The high response rate (52%) was encouraging.

In conclusion, several lines of evidence support a role for inflammation in oncogenesis in PDA. This inflammatory response seems to be driven by JAK/STAT pathway. Jak inhibitors hold promise in a subset of PDA patients with elevated CRP. Additional preclinical work is needed to test whether vertical inhibition of the pathway will be an effective strategy.

: Departments of Internal Medicine (Division of Oncology) and Center for Investigational Therapeutics, Huntsman Cancer Institute, University of Utah, Salt Lake City.

Ignacio Garrido-Laguna, MD, PhD, Assistant Professor, GI Oncology/Phase 1 Program, Department of Internal Medicine, Oncology Division, University of Utah School of Medicine, Huntsman Cancer Institute, 2000 Circle of Hope, Suite 2100, Salt Lake City, UT 84112, Phone: 801-585-0255, Fax: 801-585-0124. E-mail: ignacio.garrido-laguna@hci.utah.edu.

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Articles

Experts review ongoing clinical research with JAK inhibitors in advanced pancreatic cancer as well as some strategies for preclinical testing of vertical inhibition of the JAK pathway.

JAK Inhibitors Used as Anti-inflammatory Therapeutics for Pancreatic Cancer

	The characterization of molecular abnormalities implicated in the tumorigenesis of sarcomas is being increasingly applied to the classification, prognostication and, in particular situations, management of these diseases. Nevertheless, despite a growing knowledge of the genetic alterations involved, the translation of these discoveries into therapeutic success has been limited and the treatment for the majority of patients still relies on conventional cytotoxic agents. In this review, we address the emerging therapeutic strategies aimed at specific molecular targets that could potentially change this panorama.

Sarcomas represent a diverse group of neoplasms of mesenchymal origin that correspond to approximately 1.5% of all malignancies in adults.

Genetic aberrations in sarcomas occur as either simple karyotypic abnormalities, such as chromosomal translocations, amplifications, and deletions, or complex/unbalanced karyotypic changes following accumulated nonspecific gains and losses. Chromosomal translocations resulting in gene fusions and subsequent transcriptional dysregulation account for the majority of the genetic hallmarks identified in sarcomas.

 In addition to the formation of chimeric transcription factors involving oncogenes, translocations may result in the activation of proteins with tyrosine kinase function or autocrine growth factors. Conversely, tumors without specific cytogenetic abnormalities are characterized by genome instability, which results in multiple and alternative genomic aberrations of unclear significance and a complex karyotype.

One of the major breakthroughs that emerged from a molecular-based approach is exemplified in gastrointestinal stromal tumors (GIST).

 Despite this initial enthusiasm, targeting molecular alterations has been less fruitful in other histologies, in which genetic alterations rarely act as driver mutations. In this review, we will focus on novel potential molecular targets in non-GIST sarcomas 

. PDGFR in Sarcomas Platelet-derived growth factor receptors (PDGFRs) are tyrosine-kinase receptors consisting of either α- or β-chains forming three possible receptors: PDGFR-αα, PDGFR-αβ, and PDGFR-ββ. The activation of PDGFR depends on the interaction with platelet-derived growth factor (PDGF) ligands in the extracellular domain, which include 5 different isoforms. After dimerization, each PDGFR partner phosphorylates tyrosine residues located on the cytosolic tails.

Across different subtypes of sarcomas, signaling through PDGF/PDGFR has been shown to promote progression through cell cycle and avoidance of apoptosis, and result in pro-angiogenic effects and modulation of the tumor stroma.

 Activation of PDGFR results in downstream signaling through multiple pathways involving phosphatidylinositol-3-kinase (PI3K), phospholipase-C gamma (PLCγ), Rous sarcoma oncogene (SRC) kinases and rat sarcoma oncogene (RAS)/mitogen-activated protein kinase (MAPK) proteins.

In normal cells, high expression of PDGFRβ is seen in fibroblasts, pericytes and smooth muscle, and PDGFRα in megakaryocytes, fibroblasts, myoblasts, pericytes, smooth muscle, and neurons.

In dermatofibrosarcoma protuberans (DFSP), inhibition of PDGFβ/PDGFRβ with tyrosine kinase inhibitors20-25 resulted in significant clinical activity, leading to approval of imatinib by the US Food and Drug Administration (FDA) for the treat ment of patients with advanced/metastatic disease. The molecular hallmark of DFSP is the recurrent translocation t(17;22) (q22;q13), that results in the fusion of the collagen type I alpha 1 (COL1A1) promoter to PDGF, leading to constitutive activation of this pathway.

In a pooled analysis including 24 patients treated with imatinib, objective response rate (ORR) was 46% and median time to tumor progression (mTTP) was 1.7 years.

In addition, the PDGF/PDGFR pathway has been associated with the pathogenesis of different sarcomas including rhabdomyosarcoma, Kaposi’s sarcoma, synovial sarcoma, chondrosarcoma, osteosarcoma, and Ewing family sarcoma. Elevated expression of PDGFβ and co-expression of PDGFβ and PDGFRα has been correlated with high histological grades and poor prognosis in sarcomas.

 Postulated mechanisms include the modulation of angiogenesis, regulation of stroma-derived fibroblasts and autocrine stimulation of cellular growth.

 Overexpression of mRNA for PDGFRα and PDGF has been documented in sarcoma, highlighting the relevance of this autocrine loop.

 In addition, preclinical data suggest that blocking PDGF/PDGFR results in a potentiation of response to chemotherapy.

Pazopanib, an oral, multi-targeted tyrosine kinase inhibitor also active against PDGFR, was shown to prolong progression-free survival (PFS) versus placebo in pretreated patients with advanced non-adipocytic soft tissue sarcomas (median PFS, 4.6 months vs 1.6 months; HR 0.31; 

 <.0001) in a phase lll trial, and is currently approved by the FDA.

There are ongoing studies focusing on more specific inhibition of PDGFRα. Olaratumab (IMC-3G3) is a recombinant IgG1-type monoclonal antibody that binds with high affinity to PDGFRα and prevents PDGF from binding to the receptor; olaratumab also blocks downstream signaling through Akt and mitogen-activated protein kinase (MAPK).

 A phase lb/ll study evaluating the efficacy of doxorubicin with or without olaratumab has recently completed accrual (NCT01185964), and results are pending; in addition, a drug interaction study to evaluate the effects of concurrent administration with doxorubicin is ongoing (NCT02326025).

Potential Targets for Inhibition: KDR, PTPRB, and PLCG1 in Angiosarcomas

Angiosarcomas (ASs) are malignancies of vascular origin associated with a significant risk of metastases and an poor prognosis.

 In addition to its vascular origin, plentiful evidence indicates the activation of pro-angiogenic pathways in the development of ASs, including overexpression of vascular endothelial growth factor (VEGF) and vascular endothelial growth factor receptors (VEGFRs).

 Bevacizumab, a recombinant monoclonal antibody targeting VEGF-A, was studied in a single arm, phase II trial in patients with tumors of vascular origin (AS, N=23; epithelioid hemangioendothelioma, N=7). Four objective responses occurred (2 patients with AS and 2 patients with epithelioid hemangioendothelioma), resulting in an ORR of 17% with 50% (N=15) achieving stable disease; median PFS was 12.4 weeks.

 In the recently presented ANGIOTAX-PLUS study, patients with AS were randomized to receive weekly paclitaxel with or without bevacizumab. There were no statistically significant differences in ORR (40% vs 50%), median PFS (6.8 months vs 6.9 months), or median OS (19.5 months vs 15.9 months) between treatment arms.

 Sorafenib, a multi-targeted tyrosine kinase inhibitor with anti-angiogenic properties, was investigated in a prospective study encompassing different histologies.

Among a subset of 37 evaluable ASs patients, ORR was 14% and median PFS was 3.8 months, with the majority of patients with AS having stable disease as best response.

 Similarly, sorafenib resulted in response rates of 0% and 14.6% and transient tumor control in phase ll trials reported by von Mehren et al and Ray-Coquard et al, respectively.

Recent studies applying whole genome, whole exome, and targeted sequencing techniques provided further insight into potential therapeutic targets in ASs. Using gene expression profiling, Antonescu et al showed upregulation of vascular-specific receptor tyrosine kinases, including kinase insert domain receptor (KDR) and tyrosine kinase with immunoglobulin-like and EGF-like domains 1 (TIE1) and FLT1. Of note, KDR gene mutations were associated with high expression of KDR protein and occurred in 10% of patients with ASs (all arising from the breast).

In an analysis of 26 primary and 29 secondary ASs, Styring et al demonstrated significant deregulation of 103 genes. Once again, secondary ASs showed a genetic signature distinct from primary ASs, with upregulation of MYC, KIT, and RET and downregulation of CDKN2C.

 reported at least 1 driver mutation in angiogenesis signaling genes in 15 of 39 ASs (38%), the most common being MYC. Of note, these driver mutations were not mutually exclusive.

 PTPRB truncating mutations were found in 26% (10 out of 39) of AS samples and exposure of PTPRB-silenced cell cultures to sunitinib or vatalanib resulted in suppression of angiogenesis. In addition, activating mutations of PLCG1, a signal transducer of tyrosine kinases involved in cell growth, signaling, and maintenance of membrane phospholipids, were documented in 9% of the cases.

In line with these observations, a retrospective series investigating the effects of sorafenib in cohorts limited to patients with RT-associated AS of the breast found MYC and FLT4 coamplification in 2 out of 3 patients with objective responses (in total, 9 patients were assessable for response; ORR = 33%).

In summary, although objective responses are limited to a subset of patients, tyrosine kinase inhibitors and agents targeting angiogenesis are active and able to induce disease stabilization in unselected AS patients, representing a reasonable alternative beyond conventional cytotoxic chemotherapy. Findings from molecularly-based studies provide conceptual models for further investigation of anti-angiogenic therapies in AS.

ALK in Inflammatory Myofibroblastic Tumors (IMTs)

Inflammatory myofibroblastic tumors (IMTs) are tumors composed of spindle cell proliferation mixed with a collagenous stroma in an inflammatory background of granulocytes, lymphocytes, and plasma cells.

 In almost 50% of the cases, IMT harbors chromosomal aberrations that result in rearrangements involving the anaplastic lymphoma kinase (ALK) locus on chromosome 2p23 or increased copy numbers without rearrangement. The product of this genetic variation is a receptor tyrosine kinase (RTK) that is constitutively activated, leading to cell growth and tumorigenesis.

Crizotinib is an oral tyrosine kinase inhibitor targeting ALK, MET, and ROS1 that was initially approved for the treatment of patients with non-small cell lung cancer. Recently, Butrynski et al reported a partial response in a patient with ALK-rearranged IMT treated with crizotinib, suggesting that this agent might also be effective in treating patients with ALK-rearranged IMT.41 Given these promising results and based on a strong rationale, a phase II trial is ongoing (NCT01524926).

MDM2 and CDK4 in Well-Differentiated/ Dedifferentiated Liposarcoma

Liposarcomas are soft tissue sarcomas of adipocytic origin that comprise different histologic subtypes, including welldifferentiated liposarcoma (WDLPS) and dedifferentiated liposarcoma (DDLPS).

WDLPS and DDLPS are marked by amplifications involving chromosome 12, which occur in more than 80% to 90% of the cases.

 These 12q gains result in co-amplification of cyclin-dependent kinase 4 (CDK4) and MDM2 oncogenes. Several agents targeting MDM2 and CDK4 are currently in development, although the success rate with inhibitors used as single agents has been limited.

CDK4 is a cyclin-dependent kinase that regulates the G1—S phase transition in the cell cycle and promotes tumorigenesis through inhibition of the retinoblastoma (Rb) protein family.

Following prolonged disease stabilization in patients with WDLPS/DDLPS in a phase I trial,

 our group reported the results of a phase II trial with the CDK4/6 inhibitor palbociclib (PD0332991), which demonstrated a PFS rate of 66% at 12 weeks. Among 29 evaluable patients with CDK4 amplification enrolled in the therapeutic cohort, the median PFS was 18 weeks.

 Palbociclib was recently approved by the FDA for the treatment of patients with breast cancer. LEE011, a distinct orally bioavailable CDK4/6 inhibitor, was also shown to be tolerable and able to induce long-lasting disease stabilizations in a phase I clinical trial including multiple solid tumors.

Stable disease sustained for more than 4 and 6 cycles occurred in 26% and 14% of the patients, respectively.

 Additional studies to better characterize the efficacy of LEE011 are ongoing (NCT01237236, NCT02187783, NCT02343172).

		Figure 1. Pathways for Targeted Therapy in Non-GIST Sarcomas

		(1) PDGF/PDGFR and downstream pathways MAPK, JAK/STAT and PIK3/Akt/mTOR; (2) Novel targets for inhibition of angiogenesis: KDR, FLT-1/4 tyrosine kinase receptors, PLCG1 signal transducer, and PTPRB phosphatase receptor; (3) ALK; (4) MDM2, and CDK4; (5) Microphthalmia family transcription factors MTF, TFE3, TFEB, and TFEC; (6) PIK3/Akt/mTOR pathway; (7) IDH family of enzymes.

The MDM2 gene encodes an E3 ubiquitin ligase that binds to tumor suppressor p53 and targets p53 for proteasomal degradation. Therefore, MDM2 amplification/overexpression leads to increased p53 inactivation and results in a pro-oncogenic effect. In a pilot study investigating the oral MDM2 inhibitor RO5045337 (also known as RG7112), both reactivation of the p53 pathway and decreased cell proliferation were demonstrated between pre- and posttreatment biopsies.

 Among 20 patients, there was 1 partial response and 14 patents achieved disease stabilization.

In another phase l dose escalation study that included a sarcoma extension cohort, RO5045337/RG7112 demonstrated manageable toxicities, biomarker activity, and objective responses in patients with liposarcomas.50 Nevertheless, the same drug in combination with doxorubicin (NCT01605526) resulted in high incidence of neutropenia and thrombocytopenia.

Additional agents targeting MDM2 are currently under clinical development. These include SAR405838, presently being investigated in early-phase clinical trials (NCT01636479, NCT01985191), and AMG-232, a MDM2 inhibitor derived from AM-8553 (NCT01723020, NCT02110355).

Microphthalmia Family Transcription Factors in Alveolar Soft Part Sarcomas and Clear Cell Sarcomas

The micropthalmia (MiT) family transcription factors includes MITF, TFE3, TFEB, and TFEC, which are involved in regulation of cell growth, differentiation, and survival. Dysregulation of MiT family members results in aberrant activation of multiple genes, including c-Met. This leads to oncogenesis in different cancer types and is thought to be particularly relevant in alveolar soft part sarcoma (ASPS) and clear cell sarcoma (CCS).

 The c-Met product is a receptor tyrosine kinase activated upon interation with hepatocyte growth fact (HGF) frequently expressed in mesenchymal cells and also linked to intracellular signaling through intracellular signaling MAPK and AKT pathways,

 providing a rationale for further study of MET and other TKI inhibitors in ASPS and CCS.

In ASPS, TFE is fused to the ASPL gene as a consequence of a typical unbalanced t(X;17)(p11;q25) translocation, resulting in the ASPL-TFE3 fusion protein. Although the function of ASPL needs to be further clarified, TFE3 acts as a transcription factor and the fusion transcripts lead to MET transcriptional upregulation through the c-Met gene.

Also an MiT-associated tumor, CCS expresses different cytogenetic abnormalities. Typically, EWSR1-ATF1 fusion results from the t(12;22)(q13;q12) translocation

; in a smaller subset of patients, t(2;22)(q34;q12) translocation produces a EWSR1-CREB1 fusion-gene.

 These abnormalities induce MITF and c-Met expression. In preclinical models, blockade of c-Met activity and HGF resulted in CCS cell growth arrest.

Disappointingly, a phase 2 study of the MET inhibitor tivatinib in MITF-associated tumors produced no objective responses in 27 ASPS patients. In the same trial, only one objective response occurred among 11 patients with CSS.

In both entities (ASPS and CSS), although responses were seen with multi-targeted tyrosine kinase inhibitors, the role of MET inhibitors remains to be further investigated and a clinical trial with cabozantinib is ongoing (NCT01755195).

The PI3K-Akt-mTOR Pathway in PEComas, Myxoid/ Round Cell Liposarcomas, and Angiosarcomas The phosphotidylinositol 3-kinase (PI3K)-Akt-mammalian target of rapamycin (mTOR) is a key pathway in the control of cell proliferation, survival, and angiogenesis. Several preclinical and translational studies have addressed the role of the PI3KAkt- mTOR pathway and investigated the mechanism of action of mTOR inhibitors; evidences of activation of this pathway have been well demonstrated in sarcomas.

Ridaforolimus showed some degree of activity in phase l/ll studies,

 but failed to demonstrate a survival benefit when used as a maintenance therapy in a randomized phase lll trial (

Different mTOR inhibitors, including temsirolimus, everolimus, and sirolimus, were also evaluated in small prospective trials.

Despite limited efficacy in unselected patients with sarcomas, a histology-driven approach could further clarify the role of mTOR inhibitors in the treatment of this group of malignancies. Perivascular epithelioid cell tumors (PEComas) are rare mesenchymal neoplasms that exhibit features of both smooth muscle and melanocytic origin

 and are often characterized by the presence of inactivating mutations in tuberous sclerosis complex (TSC) genes TSC1 and TSC2, which are upstream inhibitors of the mTOR complex 1 (mTORC1).

 Although data are limited due to the rarity of this disease, durable responses have been reported with sirolimus and everolimus. In a series of 5 patients with non-pulmonary PEComas treated with sirolimus or everolimus, 3 complete responses and 1 partial response occurred. Molecular studies identified TSC2 aberrations in 4 of these patients.

Barretina et al reported a relatively high prevalence of 

 mutations (18%) in patients with myxoid/round-cell liposarcomas.

 Similarly, Demicco et al showed that although activating 

mutations occurred in only 14% of the cases and more frequently in round cell than myxoid tumors (33% vs 3%; 

The characterization of molecular abnormalities implicated in the tumorigenesis of sarcomas is being increasingly applied to the classification, prognostication and, in particular situations, management of these diseases.

August 2015 | Contemporary Oncology®

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