Fully Human Monoclonal Antibodies to Hepatocyte Growth Factor with Therapeutic Potential against Hepatocyte Growth Factor/c-Met–Dependent Human Tumors

"Active" cancer immunotherapy by anti-Met antibody gene transfer

Gene therapy provides a still poorly explored opportunity to treat cancer by "active" immunotherapy as it enables the transfer of genes encoding antibodies directed against specific oncogenic proteins. By a bidirectional lentiviral vector, we transferred the cDNA encoding the heavy and light chains of a monoclonal anti-Met antibody (DN-30) to epithelial cancer cells. In vitro, the transduced cells synthesized and secreted correctly assembled antibodies with the expected high affinity, inducing down-regulation of the Met receptor and strong inhibition of the invasive growth response. The inhibitory activity resulted (a) from the interference of the antibody with the Met receptor intracellular processing ("cell autonomous activity," in cis) and (b) from the antibody-induced cleavage of Met expressed at the cell surface ("bystander effect," in trans). The monoclonal antibody gene transferred into live animals by systemic administration or by local intratumor delivery resulted in substantial inhibition of tumor growth. These data provide proof of concept both for targeting the Met receptor and for a gene transfer-based immunotherapy strategy.

Single-agent and combination therapeutic strategies to inhibit hepatocyte growth factor/MET signaling in cancer

Receptor tyrosine kinases are often aberrantly activated in human malignancies and contribute to cancer development and progression. Specific receptor tyrosine kinase inhibitors have been shown to be clinically effective therapies in subsets of cancer patients with either hematologic or solid tumors. Activation of the hepatocyte growth factor (HGF)/MET signaling pathway has been found to play a critical role in oncogenesis, cancer metastasis, and drug resistance. These observations have led to the development of agents that can effectively inhibit HGF/MET signaling through direct inhibition of the receptor (anti-MET antibodies), through inactivation of its ligand HGF (AMG102, L2G7), by interfering with HGF binding to MET (NK4), or by inhibiting MET kinase activity (PHA-665752 and SU11274). Moreover, the combination of anti-MET therapeutic agents with either signal transduction inhibitors (ERBB family or mTOR inhibitors) or with cytotoxic chemotherapy has been evaluated in preclinical models. These studies provide insight into the rational development of combination therapeutic strategies that can be evaluated in clinical trials. This review will discuss different strategies of MET inhibition with a specific focus on combination therapeutic approaches.

Hepatocyte growth factor and sonic Hedgehog expression in cerebellar neural progenitor cells costimulate medulloblastoma initiation and growth

Medulloblastomas are malignant brain tumors that arise by transformation of neural progenitor cells in the cerebellum in children. Treatment-related neurotoxicity has created a critical need to identify signaling molecules that can be targeted therapeutically to maximize tumor growth suppression and minimize collateral neurologic injury. In genetically engineered mice, activation of Sonic Hedgehog (Shh) signaling in neural stem cells in the developing cerebellum induces medulloblastomas. Hepatocyte growth factor (HGF) and its cell surface receptor c-Met are highly expressed in human medulloblastomas, and elevated levels of c-Met and HGF mRNA predict an unfavorable prognosis for patients. HGF is neuroprotective for cerebellar granule cells and promotes growth of human medulloblastoma cells in culture and in murine xenografts. We modeled the ability of HGF to induce medulloblastomas in mice using a version of the RCAS/tv-a system that allows gene transfer to cerebellar neural progenitors during their postnatal expansion phase when these cells are highly susceptible to transformation. Here, we report a high frequency of medulloblastoma formation in mice after postnatal expression of HGF in cooperation with Shh. Some tumors showed neurocytic differentiation similar to that in human nodular medulloblastomas with activated Shh signaling. Systemic administration of a monoclonal antibody against HGF prolonged survival of mice bearing Shh + HGF-induced medulloblastomas by stimulating apoptosis. These findings indicate a role for HGF in medulloblastoma initiation and growth and show efficacy of HGF-targeted therapy in a mouse model of endogenously arising tumors.

Noncompetitive inhibition of hepatocyte growth factor-dependent Met signaling by a phage-derived peptide

Dysregulation of hepatocyte growth factor (HGF)-induced signaling via its receptor tyrosine kinase Met results in tumor progression and metastasis. To initiate signaling, pro-HGF must be proteolytically activated to reveal a secondary Met binding site within the serine protease-like beta-chain of HGF. Although HGF/Met is a large complex, we sought to discover relatively small antagonists that might interfere with this critical Met binding region. Pools of disulfide-constrained random peptide libraries displayed on phage were selected for binding to HGF, ultimately resulting in a disulfide-constrained 15-mer peptide (VNWVCFRDVGCDWVL) termed HB10, which bound to the recombinant human HGF beta-chain (HGF beta) and competitively inhibited binding to Met with an IC(50) of 450 nM. In MDA-MB435 cells, HB10 reduced HGF-dependent Met phosphorylation by 70%, and phosphorylation of downstream kinases AKT and ERK1/ERK2 by 74% and 69%, respectively. Addition of HB10 also inhibited HGF-dependent migration of these cells with an IC(50) of approximately 20 microM. The 2D (1)H-NMR structure of HB10 revealed a beta-hairpin loop stabilized by the disulfide bond and cross-strand pairing of Trp3 and Trp13. HGF beta mutants deficient in Met binding also have reduced HB10 binding, suggesting an overlapping binding site. Notably HB10 did not inhibit full length HGF binding to Met. Thus steric hindrance of the interaction between HGF beta domain binding to Met is sufficient for inhibiting full-length HGF-dependent Met signaling and cell migration that is consistent with a noncompetitive inhibitory mechanism of Met signal transduction.

Design, synthesis, and biological evaluation of potent c-Met inhibitors

c-Met is a receptor tyrosine kinase that plays a key role in several cellular processes but has also been found to be overexpressed and mutated in different human cancers. Consequently, targeting this enzyme has become an area of intense research in drug discovery. Our studies began with the design and synthesis of novel pyrimidone 7, which was found to be a potent c-Met inhibitor. Subsequent SAR studies identified 22 as a more potent analog, whereas an X-ray crystal structure of 7 bound to c-Met revealed an unexpected binding conformation. This latter finding led to the development of a new series that featured compounds that were more potent both in vitro and in vivo than 22 and also exhibited different binding conformations to c-Met. Novel c-Met inhibitors have been designed, developed, and found to be potent in vitro and in vivo.

Identification of a novel recepteur d'origine nantais/c-met small-molecule kinase inhibitor with antitumor activity in vivo

Recepteur d'origine nantais (RON) is a receptor tyrosine kinase closely related to c-Met. Both receptors are involved in cell proliferation, migration, and invasion, and there is evidence that both are deregulated in cancer. Receptor overexpression has been most frequently described, but other mechanisms can lead to the oncogenic activation of RON and c-Met. They include activating mutations or gene amplification for c-Met and constitutively active splicing variants for RON. We identified a novel inhibitor of RON and c-Met, compound I, and characterized its in vitro and in vivo activities. Compound I selectively and potently inhibited the kinase activity of RON and c-Met with IC(50)s of 9 and 4 nmol/L, respectively. Compound I inhibited hepatocyte growth factor-mediated and macrophage-stimulating protein-mediated signaling and cell migration in a dose-dependent manner. Compound I was tested in vivo in xenograft models that either were dependent on c-Met or expressed a constitutively active form of RON (RONDelta160 in HT-29). Compound I caused complete tumor growth inhibition in NIH3T3 TPR-Met and U-87 MG xenografts but showed only partial inhibition in HT-29 xenografts. The effect of compound I in HT-29 xenografts is consistent with the expression of the activating b-Raf V600E mutation, which activates the mitogen-activated protein kinase pathway downstream of RON. Importantly, tumor growth inhibition correlated with the inhibition of c-Met-dependent and RON-dependent signaling in tumors. Taken together, our results suggest that a small-molecule dual inhibitor of RON/c-Met has the potential to inhibit tumor growth and could therefore be useful for the treatment of patients with cancers where RON and/or c-Met are activated.

Therapeutic targeting of human hepatocyte growth factor with a single neutralizing monoclonal antibody reduces lung tumorigenesis

The hepatocyte growth factor (HGF)/c-Met signaling pathway is involved in lung tumor growth and progression, and agents that target this pathway have clinical potential for lung cancer treatment. L2G7, a single potent anti-human HGF neutralizing monoclonal antibody, showed profound inhibition of human HGF-induced phosphorylated mitogen-activated protein kinase induction, wound healing, and invasion in lung tumor cells in vitro. Transgenic mice that overexpress human HGF in the airways were used to study the therapeutic efficacy of L2G7 for lung cancer prevention. Mice were treated with the tobacco carcinogen, nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone, over 4 weeks. Beginning at week 3, i.p. treatment with 100 mug L2G7 or isotype-matched antibody control, 5G8, was initiated and continued through week 15. The mean number of tumors per mouse in the L2G7-treated group was significantly lower than in the control group (1.58 versus 3.19; P = 0.0005). Proliferative index was decreased by 48% (P = 0.013) in tumors from L2G7-treated mice versus 5G8-treated mice, whereas extent of apoptosis was increased in these same tumors by 5-fold (P = 0.0013). Phosphorylated mitogen-activated protein kinase expression was also significantly decreased by 84% in tumors from L2G7-treated mice versus 5G8-treated mice (P = 0.0003). Tumors that arose in HGF transgenic animals despite L2G7 treatment were more likely to contain mutant K-ras, suggesting that targeting the HGF/c-Met pathway may not be as effective if downstream signaling is activated by a K-ras mutation. These preclinical results show that blocking the HGF/c-Met interaction with a single monoclonal antibody delivered systemically can have profound inhibitory effects on development of lung tumors.

MetMAb, the one-armed 5D5 anti-c-Met antibody, inhibits orthotopic pancreatic tumor growth and improves survival

The hepatocyte growth factor (HGF) and its receptor, c-Met, have been implicated in driving proliferation, invasion, and poor prognosis in pancreatic cancer. Here, we investigated the expression of HGF and c-Met in primary pancreatic cancers and described in vitro and in vivo models in which MetMAb, a monovalent antibody against c-Met, was evaluated. First, expression of HGF and MET mRNA was analyzed in 59 primary pancreatic cancers and 51 normal samples, showing that both factors are highly expressed in pancreatic cancer. We next examined HGF responsiveness in pancreatic cancer lines to select lines that proliferate in response to HGF. Based on these studies, two lines were selected for further in vivo model development: BxPC-3 (c-Met(+), HGF(-)) and KP4 (c-Met(+), HGF(+)) cells. As BxPC-3 cells are responsive to exogenous HGF, s.c. tumor xenografts were grown in a paracrine manner with purified human HGF provided by osmotic pumps, wherein MetMAb treatment significantly inhibited tumor growth. KP4 cells are autocrine for HGF and c-Met, and MetMAb strongly inhibited s.c. tumor growth. To better model pancreatic cancer and to enable long-term survival studies, an orthotopic model of KP4 was established. MetMAb significantly inhibited orthotopic KP4 tumor growth in 4-week studies monitored by ultrasound and also improved survival in 90-day studies. MetMAb significantly reduced c-Met phosphorylation in orthotopic KP4 tumors with a concomitant decrease in Ki-67 staining. These data suggest that the HGF/c-Met axis plays an important role in the progression of pancreatic cancer and that targeting c-Met therein may have therapeutic value.

MET as a target for treatment of chest tumors

The receptor tyrosine kinase MET has been studied of a large variety of human cancers, including lung and mesothelioma. The MET receptor and its ligand HGF (hepatocyte growth factor) play important roles in cell growth, survival and migration, and dysregulation of the HGF-MET pathway leads to oncogenic changes including tumor proliferation, angiogenesis and metastasis. In small cell lung cancer (SCLC), non-small cell lung cancer (NSCLC), and malignant pleural mesothelioma (MPM), MET is dysregulated via overexpression, constitutive activation, gene amplification, ligand-dependent activation, mutation or epigenetic mechanisms. New drugs targeted against MET and HGF are currently being investigated in vitro and in vivo, with promising results. These drugs function at a variety of steps within the HGF-MET pathway, including MET expression at the RNA or protein level, the ligand-receptor interaction, and tyrosine kinase function. This paper will review the structure, function, mechanisms of tumorigenesis, and potential for therapeutic inhibition of the MET receptor in lung cancer and mesothelioma.

Drug development against metastasis-related genes and their pathways: a rationale for cancer therapy

It is well recognized that the majority of cancer related deaths is caused by metastatic diseases. Therefore, there is an urgent need for the development of therapeutic intervention specifically targeted to the metastatic process. In the last decade, significant progress has been made in this research field, and many new concepts have emerged that shed light on the molecular mechanism of metastasis cascade which is often portrayed as a succession of six distinct steps; localized invasion, intravasation, translocation, extravasation, micrometastasis and colonization. Successful metastasis is dependent on the balance and complex interplay of both the metastasis promoters and suppressors in each step. Therefore, the basic strategy of our interventions is aimed at either blocking the promoters or potentiating the suppressors in this disease process. Toward this goal, various kinds of antibodies and small molecules have been designed. These include agents that block the ligand-recepter interaction of metastasis promoters (HGF/c-Met), antagonize the metastasis-promoting enzymes (AMF, uPA and MMP) and inhibit the transcriptional activity of metastasis promoter (beta-Catenin). On the other hand, the intriguing roles of metastasis suppressors and their signal pathways have been extensively studied and various attempts have been made to potentiate these factors. Small molecules have been developed to restore the expression or mimic the function of metastasis-suppressor genes such as NM23, E-cadherin, Kiss-1, MKK4 and NDRG1, and some of them are under clinical trials. This review summarizes our current understanding of the molecular pathway of tumor metastasis and discusses strategies and recent development of anti-metastatic drugs.

Drug development of MET inhibitors: targeting oncogene addiction and expedience

The MET tyrosine kinase stimulates cell scattering, invasion, protection from apoptosis and angiogenesis, thereby acting as a powerful expedient for cancer dissemination. MET can also be genetically selected for the long-term maintenance of the primary transformed phenotype, and some tumours appear to be dependent on (or 'addicted' to) sustained MET activity for their growth and survival. Because of its dual role as an adjuvant, pro-metastatic gene for some tumour types and as a necessary oncogene for others, MET is a versatile candidate for targeted therapeutic intervention. Here we discuss recent progress in the development of molecules that inhibit MET function and consider their application in a subset of human tumours that are potentially responsive to MET-targeted therapies.

Transcriptional regulation of the hepatocyte growth factor gene by pyrrolidine dithiocarbamate

Hepatocyte growth factor (HGF) mediates cancer cell invasion and metastasis. This study characterised the down-regulation of HGF expression by pyrrolidine dithiocarbamate (PDTC), which markedly reduced HGF mRNA expression and protein production in MRC-5 cells. Reporter gene studies revealed that PDTC inhibited HGF gene transcription and that the response element is located in the region -75 to +42 bp flanking the transcription initiation site. Electrophoretic mobility shift assay identified three specific protein complexes binding in this region, which were abrogated by exposure of cells to PDTC. PDTC deserves further investigation as a novel therapeutic agent for HGF-driven cancers.

c-Met targeted therapy of cholangiocarcinoma

Cholangiocarcinoma continues to be a challenging disease to treat. Systemic therapy is used in unresectable disease, disease progression after surgery, and in the palliative setting. Unfortunately, results of multiple phase II trials have rarely yielded positive results. As data on the molecular carcinogenesis of cholangiocarcinoma is developing, we are more able to understand the disease process and can use this understanding to create unique targeted therapies. We reviewed the role of c-Met/hepatocyte growth factor (HGF) in the development of cholangiocarcinoma. Furthermore, we explored the use of the c-Met guided cascade as a target to treat cholangiocarcinoma. We reviewed the current use and options for future development of c-Met agents to treat this disease.

A high affinity hepatocyte growth factor-binding site in the immunoglobulin-like region of Met

Hepatocyte growth factor (HGF) and its high affinity receptor, the tyrosine kinase Met, play a key role in embryo development and tumor invasion. Both HGF and Met are established targets for cancer therapy. However, the mechanism of their interaction is complex and remains elusive. HGF is secreted as a monomeric precursor (pro-HGF) that binds to but does not activate Met. Mature HGF is a α/β heterodimer containing a high affinity Met-binding site in the α-chain (HGF-α) and a low affinity Met-binding site in the β-chain (HGF-β). The extracellular portion of Met contains a semaphorin (Sema) domain, a cysteine-rich hinge (plexin-semaphorin-integrin), and four immunoglobulin-like domains (immunoglobulin-like regions in plexins and transcription factors (IPT) 1-4). HGF-β binds to Sema through a low affinity contact. The domain of Met responsible for high affinity binding to HGF-α has not been identified yet. Here we show that this long sought after binding site lies in the immunoglobulin-like region of Met and more precisely in IPT 3 and 4. We also show that IPT 3 and 4 are sufficient to transmit the signal for kinase activation to the cytoplasm, although the lack of Sema makes the receptor equally sensitive to mature HGF and pro-HGF. Finally, we provide evidence that soluble Met-derived proteins containing either the low affinity or high affinity HGF-binding site antagonize HGF-induced invasive growth both in vitro and in xenografts. These data suggest that the immunoglobulin-like region of Met cooperates with the Sema domain in binding to HGF and in controlling Met kinase activity. Although the IPT-HGF-α interaction provides binding strength, the Sema-HGF-β contact confers selective sensitivity to the active form of the ligand.

MicroRNA miR-199a* regulates the MET proto-oncogene and the downstream extracellular signal-regulated kinase 2 (ERK2)

MicroRNAs (miRNAs) constitute a class of small noncoding RNAs that play important roles in a variety of biological processes including development, apoptosis, proliferation, and differentiation. Here we show that the expression of miR-199a and miR-199a* (miR-199a/a*), which are processed from the same precursor, is confined to fibroblast cells among cultured cell lines. The fibroblast-specific expression pattern correlated well with methylation patterns: gene loci on chromosome 1 and 19 were fully methylated in all examined cell lines but unmethylated in fibroblasts. Transfection of miR-199a and/or -199a* mimetics into several cancer cell lines caused prominent apoptosis with miR-199a* being more pro-apoptotic. The mechanism underlying apoptosis induced by miR-199a was caspase-dependent, whereas a caspase-independent pathway was involved in apoptosis induced by miR-199a* in A549 cells. By employing microarray and immunoblotting analyses, we identified the MET proto-oncogene as a target of miR-199a*. Studies with a luciferase reporter fused to the 3'-untranslated region of the MET gene demonstrated miR-199a*-mediated down-regulation of luciferase activity through a binding site of miR-199a*. Interestingly, extracellular signal-regulated kinase 2 (ERK2) was also down-regulated by miR-199a*. Coordinated down-regulation of both MET and its downstream effector ERK2 by miR-199a* may be effective in inhibiting not only cell proliferation but also motility and invasive capabilities of tumor cells.

Liver regeneration and tumor stimulation--a review of cytokine and angiogenic factors

Liver resection for metastatic (colorectal carcinoma) tumors is often followed by a significant incidence of tumor recurrence. Cellular and molecular changes resulting from hepatectomy and the subsequent liver regeneration process may influence the kinetics of tumor growth and contribute to recurrence. Clinical and experimental evidence suggests that factors involved in liver regeneration may also stimulate the growth of occult tumors and the reactivation of dormant micrometastases. An understanding of the underlying changes may enable alternative strategies to minimize tumor recurrence and improve patient survival after hepatectomy.

The Met tyrosine kinase receptor in development and cancer

Met is a tyrosine kinase receptor, encoded by an oncogene, whose crucial role has been elucidated during the last two decades. The complex biological program triggered by Met has been dissected and its biological relevance in both physiology and pathology has been proven. Met supports a morphogenetic program, known as invasive growth, taking place both during embryogenesis and adulthood. In tumors Met is often aberrantly activated, giving rise to the pathological counterpart of the invasive growth program: cancer progression towards metastasis. Several approaches have been recently developed to interfere with the tumorigenic and metastatic processes triggered by Met.

Showering c-MET-dependent cancers with drugs

The receptor tyrosine kinase, c-MET and its ligand hepatocyte growth factor/scatter factor (HGF/SF) have become leading candidates for targeted cancer therapies. Inappropriate c-MET signaling through autocrine, paracrine, amplification, and mutational activation occurs in virtually all types of solid tumors (http://www.vai.org/met), contributing to one or a combination of proliferative, invasive, survival, or angiogenic cancer phenotypes. c-MET and HGF/SF participate in all stages of malignant progression and represent promising drug targets in a variety of cancer types, including carcinomas, sarcomas, and brain tumors. While many are in pre-clinical testing, a few inhibitors have entered clinical trials. With hundreds of thousands of potential responding cancers that express c-MET, the interest in this molecule as a drug target is not surprising. However, the cognate c-MET diagnostic tests lag behind. In addition, despite the great enthusiasm based on response rates in phase I trials, there is a need for caution. It is almost without question that combination therapies with c-MET-HGF/SF inhibitors will be required for most cancers to achieve a cytotoxic tumor response.

Clinical correlations and prognostic relevance of HGF, VEGF AND FGF expression in Brazilian patients with non-Hodgkin lymphoma

The aims of this study were to correlate HGF, VEGF and FGF serum levels and microvessel density (MVD) with cell origin, biological behavior, tumor load and prognosis in NHL. Eighty-seven consecutive previously untreated NHL patients had serum samples collected; 37 (42%) of them also had serum follow-up samples; the control group was composed of 10 healthy blood donors. Cytokine serum levels were determined by ELISA, and MVD was measured by CD34 staining in paraffin blocks. HGF mean serum level was significantly higher in both early and advanced NHL stages when compared with the control group. HGF was also significantly higher in aggressive and indolent NHL when compared with the control group. Also, mean serum level of HGF in aggressive NHL was significantly higher than in indolent NHL. Regarding International Prognostic Index (IPI), HGF mean serum level at diagnosis was significantly higher for patients with IPI >2 when compared to IPI <or=2. Sequential analyses of HGF, VEGF and FGF serum levels in NHL showed that serum HGF and VEGF levels decreased significantly after 6 months of treatment completion. Our findings suggest that HGF serum level is associated with tumor load and aggressiveness, and response to treatment results in a decrease in HGF serum levels in NHL patients.

Transcription-dependent epidermal growth factor receptor activation by hepatocyte growth factor

The mechanisms and biological implications of coordinated receptor tyrosine kinase coactivation remain poorly appreciated. Epidermal growth factor receptor (EGFR) and c-Met are frequently coexpressed in cancers, including those associated with hepatocyte growth factor (HGF) overexpression, such as malignant astrocytoma. In a previous analysis of the HGF-induced transcriptome, we found that two EGFR agonists, transforming growth factor-alpha and heparin-binding epidermal growth factor-like growth factor (HB-EGF), are prominently up-regulated by HGF in human glioma cells. We now report that stimulating human glioblastoma cells with recombinant HGF induces biologically relevant EGFR activation. EGFR phosphorylation at Tyr(845) and Tyr(1068) increased 6 to 24 h after cell stimulation with HGF and temporally coincided with the induction of transforming growth factor-alpha (~5-fold) and HB-EGF (~23-fold) expression. Tyr(845) and Tyr(1068) phosphorylation, in response to HGF, was inhibited by cycloheximide and actinomycin D, consistent with a requirement for DNA transcription and RNA translation. Specifically, blocking HB-EGF binding to EGFR with the antagonist CRM197 inhibited HGF-induced EGFR phosphorylation by 60% to 80% and inhibited HGF-induced S-G(2)-M transition. CRM197 also inhibited HGF-induced anchorage-dependent cell proliferation but had no effect on HGF-mediated cytoprotection. These findings establish that EGFR can be activated with functional consequences by HGF as a result of EGFR ligand expression. This transcription-dependent cross-talk between the HGF receptor c-Met and EGFR expands our understanding of receptor tyrosine kinase signaling networks and may have considerable consequences for oncogenic mechanisms and cancer therapeutics.

Oncogene addiction: setting the stage for molecularly targeted cancer therapy

In pugilistic parlance, the one-two punch is a devastating combination of blows, with the first punch setting the stage and the second delivering the knock-out. This analogy can be extended to molecularly targeted cancer therapies, with oncogene addiction serving to set the stage for tumor cell killing by a targeted therapeutic agent. While in vitro and in vivo examples abound documenting the existence of this phenomenon, the mechanistic underpinnings that govern oncogene addiction are just beginning to emerge. Our current inability to fully exploit this weakness of cancer cells stems from an incomplete understanding of oncogene addiction, which nonetheless represents one of the rare chinks in the formidable armor of cancer cells.

Molecular cancer therapy: can our expectation be MET?

Altered regulation of tyrosine kinase receptors (RTKs) is frequent in solid tumours and it is often associated with the acquisition of an aggressive phenotype. Thus, therapies targeting these receptors have been proposed as molecular approaches to treat human cancers. The MET proto-oncogene, encoding the tyrosine kinase receptor for hepatocyte growth factor (HGF), controls genetic programmes leading to cell growth, invasion and protection from apoptosis. Germ-line mutations of MET in patients affected by hereditary papillary renal carcinomas (HPRC) have provided strong genetic evidences for its role in human malignancies; moreover, constitutive activation of this receptor, as a consequence of different mechanisms such as over-expression, autocrine stimulation or point mutations, is frequent in sporadic cancers. Several strategies to block the activation of MET are under development, such as the use of tyrosine kinase inhibitors or monoclonal antibodies and some of these compounds have already been used in clinical trials. In this review, we will discuss the molecular mechanisms underlying MET involvement in tumourigenesis and present pre-clinical and clinical data obtained with compounds aimed at targeting MET in the frame of cancer therapy.

AMG 102, a fully human anti-hepatocyte growth factor/scatter factor neutralizing antibody, enhances the efficacy of temozolomide or docetaxel in U-87 MG cells and xenografts

PURPOSE

Hepatocyte growth factor (HGF/SF) and its receptor c-Met have previously been shown to be up-regulated in multiple human cancers, including glioblastoma multiforme. To better understand if AMG 102, a fully human, anti-HGF/SF-neutralizing antibody, could be incorporated into current clinical practice, AMG 102 was tested preclinically in combination with temozolomide or docetaxel to determine if enhanced efficacy was observed compared with AMG 102 alone.

EXPERIMENTAL DESIGN

The effects of AMG 102 were tested for antiproliferative activity in combination with temozolomide or docetaxel on U-87 MG cells in vitro and for antitumor activity in a U-87 MG xenograft model in vivo. Apoptotic activity was also measured for AMG 102 and docetaxel combined in vitro.

RESULTS

Treatment with temozolomide combined with AMG 102 resulted in increased inhibition of cell growth in vitro compared with treatment with either single agent alone. In U-87 MG xenografts in vivo, AMG 102 combined with temozolomide or docetaxel significantly increased the inhibitory effect on tumor growth when compared with treatment with either agent alone (P < 0.0001 and P < 0.015, respectively). In vitro, docetaxel alone induced both caspase-3/7 activity as well as poly(ADP)ribose polymerase and caspase-7 cleavage in U-87 MG cells; these events were enhanced when used in combination with AMG 102. Importantly, there was no evidence of interference between AMG 102 and either temozolomide or docetaxel in vitro or in vivo.

CONCLUSION

These studies support testing of AMG 102 in combination with temozolomide or docetaxel. Such combinations may represent promising, novel clinical therapeutic strategies for cancers that are dependent on the HGF/SF/SF:c-Met pathway in the oncology setting.

Inhibition of angiogenesis and invasion in malignant gliomas

Malignant gliomas confer a dismal prognosis. As the molecular events that underlie tumor angiogenesis are elucidated, angiogenesis inhibition is emerging as a promising therapy for recurrent and newly diagnosed tumors. Data from animal studies suggest that angiogenesis inhibition may promote an invasive phenotype in tumor cells. This may represent an important mechanism of resistance to antiangiogenic therapies. Recent studies have begun to clarify the mechanisms by which glioma cells detach from the tumor mass, remodel the extracellular matrix and infiltrate normal brain. An array of potential therapeutic targets exists. Combination therapy with antiangiogenic and novel anti-invasion agents is a promising approach that may produce a synergistic antitumor effect and a survival benefit for patients with these devastating tumors.

From XenoMouse technology to panitumumab, the first fully human antibody product from transgenic mice

Therapeutic monoclonal antibodies have shown limited efficacy and safety owing to immunogenicity of mouse sequences in humans. Among the approaches developed to overcome these hurdles were transgenic mice genetically engineered with a 'humanized' humoral immune system. One such transgenic system, the XenoMouse, has succeeded in recapitulating the human antibody response in mice, by introducing nearly the entire human immunoglobulin loci into the germ line of mice with inactivated mouse antibody machinery. XenoMouse strains have been used to generate numerous high-affinity, fully human antibodies to targets in multiple disease indications, many of which are progressing in clinical development. However, validation of the technology has awaited the recent regulatory approval of panitumumab (Vectibix), a fully human antibody directed against epidermal growth factor receptor (EGFR), as treatment for people with advanced colorectal cancer. The successful development of panitumumab represents a milestone for mice engineered with a human humoral immune system and their future applications.

Human monoclonal antibodies from transgenic mice

Since the 1986 regulatory approval of muromonomab-CD3, a mouse monoclonal antibody (MAb) directed against the T cell CD3epsilon antigen, MAbs have become an increasingly important class of therapeutic compounds in a variety of disease areas ranging from cancer and autoimmune indications to infectious and cardiac diseases. However, the pathway to the present acceptance of therapeutic MAbs within the pharmaceutical industry has not been smooth. A major hurdle for antibody therapeutics has been the inherent immunogenicity of the most readily available MAbs, those derived from rodents. A variety of technologies have been successfully employed to engineer MAbs with reduced immunogenicity. Implementation of these antibody engineering technologies involves in vitro optimization of lead molecules to generate a clinical candidate. An alternative technology, involving the engineering of strains of mice to produce human instead of mouse antibodies, has been emerging and evolving for the past two decades. Now, with the 2006 US regulatory approval of panitumumab, a fully human antibody directed against the epidermal growth factor receptor, transgenic mice expressing human antibody repertoires join chimerization, CDR grafting, and phage display technologies, as a commercially validated antibody drug discovery platform. With dozens of additional transgenic mouse-derived human MAbs now in clinical development, this new drug discovery platform appears to be firmly established within the pharmaceutical industry.

Identification of a met-binding peptide from a phage display library

PURPOSE

Aberrant c-Met expression has been implicated in most types of human cancer. We are developing Met-directed imaging and therapeutic agents.

EXPERIMENTAL DESIGN

To seek peptides that bind specifically to receptor Met, the Met-expressing cell lines S114 and SK-LMS-1 were used for biopanning with a random peptide phage display library. Competition ELISA, fluorescence-activated cell sorting analysis, an internalization assay, and a cell proliferation assay were used to characterize a Met-binding peptide in vitro. To evaluate the utility of the peptide as a diagnostic agent in vivo, 125I-labeled peptide was injected i.v. into nude mice bearing s.c. xenografts of the Met-expressing and hepatocyte growth factor (HGF)/scatter factor-expressing SK-LMS-1/HGF, and total body scintigrams were obtained between 1 and 24 h postinjection.

RESULTS

One Met-binding peptide (YLFSVHWPPLKA), designated Met-pep1, reacts with Met on the cell surface and competes with HGF/scatter factor binding to Met in a dose-dependent manner. Met-pep1 is internalized by Met-expressing cells after receptor binding. Met-pep1 inhibits human leiomyosarcoma SK-LMS-1 cell proliferation in vitro. In SK-LMS-1 mouse xenografts, tumor-associated activity was imaged as early as 1 h postinjection and remained visible in some animals as late as 24 h postinjection.

CONCLUSIONS

Met-pep1 specifically interacts with Met: it is internalized by Met-expressing cells and inhibits tumor cell proliferation in vitro; it is a potential diagnostic agent for tumor imaging.

Recent discoveries in the genetics of melanoma and their therapeutic implications

The incidence of cutaneous malignant melanoma, tumors arising from melanocytes, has increased markedly over the past few years in many countries. Although early melanoma is curable through surgical excision, the prognosis of advanced melanoma is very poor, this tumor being resistant to current therapies. Thus there is a need for new therapies to improve the treatment of advanced melanoma. This review provides an overview of recent discoveries in the genetics of melanoma which could offer new therapeutic opportunities.

c-Met inhibitors with novel binding mode show activity against several hereditary papillary renal cell carcinoma-related mutations

c-Met is a receptor tyrosine kinase often deregulated in human cancers, thus making it an attractive drug target. One mechanism by which c-Met deregulation leads to cancer is through gain-of-function mutations. Therefore, small molecules capable of targeting these mutations could offer therapeutic benefits for affected patients. SU11274 was recently described and reported to inhibit the activity of the wild-type and some mutant forms of c-Met, whereas other mutants are resistant to inhibition. We identified a novel series of c-Met small molecule inhibitors that are active against multiple mutants previously identified in hereditary papillary renal cell carcinoma patients. AM7 is active against wild-type c-Met as well as several mutants, inhibits c-Met-mediated signaling in MKN-45 and U-87 MG cells, and inhibits tumor growth in these two models grown as xenografts. The crystal structures of AM7 and SU11274 bound to unphosphorylated c-Met have been determined. The AM7 structure reveals a novel binding mode compared with other published c-Met inhibitors and SU11274. The molecule binds the kinase linker and then extends into a new hydrophobic binding site. This binding site is created by a significant movement of the C-helix and so represents an inactive conformation of the c-Met kinase. Thus, our results demonstrate that it is possible to identify and design inhibitors that will likely be active against mutants found in different cancers.

Signaling pathways involved in cyclooxygenase-2 induction by hepatocyte growth factor in non small-cell lung cancer

Many studies have suggested a role for the hepatocyte growth factor (HGF)/c-Met pathway in tumorigenesis. Some actions of HGF are believed to be mediated by cyclooxygenase-2 (COX-2), resulting in the production of prostaglandin E2 (PGE(2)). We examined four c-Met-positive non-small-cell lung cancer (NSCLC) cell lines for effects of HGF on COX-2. HGF increased COX-2 protein expression 3-fold over basal levels. Induction of COX-2 occurred through both the extracellular signal-regulated kinase 1/2 and p38 pathways. HGF treatment caused activation of the activator protein-1, CCAAT/enhancer-binding protein, and cAMP response element-binding protein transcription factors, and COX-2 induction was blocked by actinomycin D. The half-life of COX-2 mRNA was also increased by HGF. HGF stimulation resulted in a 4-fold increase in PGE(2) secretion, and treatment of NSCLC cells with exogenous PGE(2) significantly increased cell proliferation. The addition of PGE(2) to NSCLC cells also led to rapid phosphorylation of c-Met in the absence of HGF, which was blocked by epidermal growth factor receptor (EGFR) inhibition. EGFR ligands were released in response to PGE(2). This suggests that secretion of PGE(2) induced by HGF/c-Met pathway activation can further activate the c-Met pathway via EGFR in a reinforcing loop that is independent of HGF. HGF and PGE(2) each significantly stimulated invasion in NSCLC cells. Cells transiently transfected with c-Met antisense plasmid showed a significant decrease in HGF- or PGE(2)-induced invasion. PGE(2)-induced invasion was EGFR-dependent, confirming a link between PGE(2), EGFR, and c-Met. Targeting of both the HGF/c-Met and PGE(2) pathways with a neutralizing antibody to HGF and celecoxib resulted in enhanced anti-invasion effects in response to HGF.

Downstream signalling and specific inhibition of c-MET/HGF pathway in small cell lung cancer: implications for tumour invasion

The c-MET receptor can be overexpressed, amplified, or mutated in solid tumours including small cell lung cancer (SCLC). In c-MET-overexpressing SCLC cell line NCI-H69, hepatocyte growth factor (HGF) dramatically induced c-MET phosphorylation at phosphoepitopes pY1230/1234/1235 (catalytic tyrosine kinase), pY1003 (juxtamembrane), and also of paxillin at pY31 (CRKL-binding site). We utilised a global proteomics phosphoantibody array approach to identify further c-MET/HGF signal transduction intermediates in SCLC. Strong HGF induction of specific phosphorylation sites in phosphoproteins involved in c-MET/HGF signal transduction was detected, namely adducin-alpha [S724], adducin-gamma [S662], CREB [S133], ERK1 [T185/Y187], ERK1/2 [T202/Y204], ERK2 [T185/Y187], MAPKK (MEK) 1/2 [S221/S225], MAPKK (MEK) 3/6 [S189/S207], RB [S612], RB1 [S780], JNK [T183/Y185], STAT3 [S727], focal adhesion kinase (FAK) [Y576/S722/S910], p38alpha-MAPK [T180/Y182], and AKT1[S473] and [T308]. Conversely, inhibition of phosphorylation by HGF in protein kinase C (PKC), protein kinase R (PKR), and also CDK1 was identified. Phosphoantibody-based immunohistochemical analysis of SCLC tumour tissue and microarray established the role of c-MET in SCLC biology. This supports a role of c-MET activation in tumour invasive front in the tumour progression and invasion involving FAK and AKT downstream. The c-MET serves as an attractive therapeutic target in SCLC, as shown through small interfering RNA (siRNA) and selective prototype c-MET inhibitor SU11274, inhibiting the phosphorylation of c-MET itself and its downstream molecules such as AKT, S6 kinase, and ERK1/2. Investigation of mechanisms of invasion and, ultimately, metastasis in SCLC would be very useful with these signal transduction molecules.

The therapeutic potential of hepatocyte growth factor to sensitize ovarian cancer cells to cisplatin and paclitaxel in vivo

PURPOSE

Advanced ovarian cancers are initially responsive to combinatorial chemotherapy with platinum drugs and taxanes but, in most cases, develop drug resistance. We recently showed that, in vitro, hepatocyte growth factor (HGF) enhances death of human ovarian cancer cell lines treated with cisplatin (CDDP) and paclitaxel. The present study addresses whether in vivo HGF makes ovarian carcinoma cells more responsive to these chemotherapeutics.

EXPERIMENTAL DESIGN

Using Lentiviral vectors carrying the HGF transgene, we transduced SK-OV-3 and NIH:OVCAR-3 ovarian carcinoma cell lines to obtain stable autocrine and paracrine HGF receptor activation. In vitro, we assayed growth, motility, invasiveness, and the response to CDDP and paclitaxel of the HGF-secreting bulk unselected cell populations. In vivo, we tested the cytotoxic effects of the drugs versus s.c. tumors formed by the wild-type and HGF-secreting cells in immunocompromised mice. Tumor-bearing mice were treated with CDDP (i.p.) and paclitaxel (i.v.), combined in different schedules and doses.

RESULTS

In vitro, HGF-secreting cells did not show altered proliferation rates and survival but were strongly sensitized to the death triggered by CDDP and paclitaxel, alone or in combination. In vivo, we found a therapeutic window in which autocrine/paracrine HGF made tumors sensitive to low doses of the drugs, which were ineffective on their own.

CONCLUSIONS

These data provide the proof-of-concept that in vivo gene therapy with HGF might be competent in sensitizing ovarian cancer cells to conventional chemotherapy.

Novel xenograft model expressing human hepatocyte growth factor shows ligand-dependent growth of c-Met-expressing tumors

c-Met, a receptor tyrosine kinase responsible for cellular migration, invasion, and proliferation, is overexpressed in human cancers. Although ligand-independent c-Met activation has been described, the majority of tumors are ligand dependent and rely on binding of hepatocyte growth factor (HGF) for receptor activation. Both receptor and ligand are attractive therapeutic targets; however, preclinical models are limited because murine HGF does not activate human c-Met. The goal of this study was to develop a xenograft model in which human HGF (hHGF) is produced in a controllable fashion in the mouse. Severe combined immunodeficient mice were treated with adenovirus encoding the hHGF transgene (Ad-hHGF) via tail vein injection, and transgene expression was determined by the presence of hHGF mRNA in mouse tissue and hHGF in serum. Ad-hHGF administration to severe combined immunodeficient mice resulted in hHGF production that was (a) dependent on quantity of virus delivered; (b) biologically active, resulting in liver hypertrophy; and (c) sustainable over 40 days. In this model, the ligand-dependent human tumor cell line SW1417 showed enhanced tumor growth, whereas the ligand-independent cell lines SW480 and GTL-16 showed no augmented tumor growth. This novel xenograft model is ideal for investigating c-Met/HGF-dependent human tumor progression and for evaluating c-Met targeted therapy.

Mice with GFAP-targeted loss of neurofibromin demonstrate increased axonal MET expression with aging

Neurofibromatosis 1 (NF1) is a common genetic disease that predisposes patients to peripheral nerve tumors and central nervous system (CNS) abnormalities including low-grade astrocytomas and cognitive disabilities. Using mice with glial fibrillary acidic protein (GFAP)-targeted Nf1 loss (Nf1(GFAP)CKO mice), we found that Nf1(-/-) astrocytes proliferate faster and are more invasive than wild-type astrocytes. In light of our previous finding that aberrant expression of the MET receptor tyrosine kinase contributes to the invasiveness of human NF1-associated malignant peripheral nerve sheath tumors, we sought to determine whether MET expression is aberrant in the brains of Nf1 mutant mice. We found that Nf1(-/-) astrocytes express slightly more MET than wild-type cells in vitro, but do not express elevated MET in situ. However, fiber tracts containing myelinated axons in the hippocampus, midbrain, cerebral cortex, and cerebellum express higher than normal levels of MET in older (> or =6 months) Nf1(GFAP)CKO mice. Both Nf1(GFAP)CKO and wild-type astrocytes induced MET expression in neurites of wild-type hippocampal neurons in vitro, suggesting that astrocyte-derived signals may induce MET in Nf1 mutant mice. Because the Nf1 gene product functions as a RAS GTPase, we examined MET expression in the brains of mice with GFAP-targeted constitutively active forms of RAS. MET was elevated in axonal fiber tracts in mice with active K-RAS but not H-RAS. Collectively, these data suggest that loss of Nf1 in either astrocytes or GFAP(+) neural progenitor cells results in increased axonal MET expression, which may contribute to the CNS abnormalities in children and adults with NF1.

Pharmacokinetics and safety of a fully human hepatocyte growth factor antibody, AMG 102, in cynomolgus monkeys

PURPOSE

AMG 102, a fully human monoclonal antibody that binds to hepatocyte growth factor (HGF), is a potential cancer therapeutic agent because of its ability to disrupt HGF/c-Met signaling pathways which have been implicated in most tumor types. To support a phase 1 study, the pharmacokinetic and safety profile of AMG 102 was assessed in cynomolgus monkeys.

MATERIALS AND METHODS

Serum concentration-time data from single- (i.v. and s.c.) and repeated-dose (i.v.) studies of up to 13 weeks were used for pharmacokinetic analysis. Safety was assessed in a single-dose safety pharmacology study with i.v. doses of 0 (vehicle), 25, 100, or 300 mg/kg and a 4-week toxicity study with once weekly i.v. doses of 0 (vehicle), 5, 25, or 100 mg/kg.

RESULTS

AMG 102 exhibited linear pharmacokinetics over a 600-fold dose range (0.5 to 300 mg/kg) with a mean terminal half-life of 5.6 days after i.v. dosing. Clearance and volume of distribution at steady state were 1.22 ml/h and 198.3 ml, respectively. Estimated bioavailability was 72% for s.c. administration. Antibody response to AMG 102 was observed in a small percentage of monkeys. No treatment-related cardiovascular, respiratory, or CNS changes were observed. Administration of AMG 102 for 4 weeks was well tolerated at doses up to 100 mg/kg. Potential treatment-related effects were limited to minimal/moderate gastric mucosa hemorrhage in the mid- and high-dose groups.

CONCLUSIONS

The nonclinical pharmacokinetic and safety profile of AMG 102 effectively supports clinical investigation.

Fast, hungry and unstable: finding the Achilles' heel of small-cell lung cancer

Over 95% of patients with small-cell lung cancer (SCLC) die within five years of diagnosis. The standard of care and the dismal prognosis for this disease have not changed significantly over the past 25 years. Some of the characteristics of SCLC that have defined it as a particularly virulent form of cancer -- rapid proliferation, excessive metabolic and angiogenic dependence, apoptotic imbalance and genetic instability -- are now being pursued as tumor-specific targets for intervention both in preclinical and early phase clinical studies. Here, we summarize areas of ongoing anti-cancer drug development, including classes of agents that target essential pathways regulating proliferation, angiogenesis, apoptotic resistance, chromosomal and protein stability, and cell-cell and cell-matrix interaction.

Identification of the genes for kidney cancer: opportunity for disease-specific targeted therapeutics

Recent advances in understanding the kidney cancer gene pathways has provided the foundation for the development of targeted therapeutic approaches for patients with this disease. Kidney cancer is not a single disease; it includes a number of different types of renal cancers, each with different histologic features, a different clinical course, a different response to therapy, and different genes causing the defects. Most of what is known about the genetic basis of kidney cancer has been learned from study of the inherited forms of kidney cancer: von Hippel Lindau (VHL gene), hereditary papillary renal carcinoma (c-Met gene), Birt Hogg Dubé (BHD gene), and hereditary leiomyomatosis renal cell cancer (fumarate hydratase gene). These Mendelian single-gene syndromes provide a unique opportunity to evaluate the effectiveness of agents that target the VHL, c-Met, BHD, and fumarate hydratase pathways.

Emerging monoclonal antibody therapies for malignant gliomas

An improved understanding of the molecular characteristics of gliomas has led to the recognition of potential antigen targets and monoclonal antibody (mAb) therapies for these challenging tumors. The design of glioma mAbs--including species, construct, immunoglobulin isotype and conjugate--affects their delivery, efficacy and toxicities. mAbs that are under study for glioma therapy include some mAbs that are currently approved for use in the treatment of other cancers, as well as novel molecules. Although the greatest experience so far is with locally administered, radiolabeled mAbs, systemic unconjugated mAbs are being studied increasingly for glioma treatment. Previous experience with mAbs in other malignancies may provide guidance for their use in the treatment of CNS malignancies.

A neutralizable epitope is induced on HGF upon its interaction with its receptor cMet

A new conformational neutralizable epitope is created on heptocyte growth factor (HGF), when it interacts with its receptor, cMet. By immunizing rabbits with HGF-cMet complex, we successfully generated a monoclonal antibody (SFN68) that inhibits HGF-cMet interaction, and blocks the biological function mediated by HGF. To define the epitope, we screened out an epitope-mimicking peptide, KSLSRHDHIHHH, from a phage display of combinatorial peptide library. In molecular mimicry this peptide bound to cMet and inhibited HGF-cMet interaction. No humoral response was induced to this epitope-mimicking peptide when immunization was done with HGF alone.

c-Met ectodomain shedding rate correlates with malignant potential

PURPOSE

Many proteins are proteolytically released from the cell surface by a process known as ectodomain shedding. Shedding occurs under normal physiologic conditions and can be increased in certain pathologies. Among the many receptors for which ectodomain shedding has been shown is c-Met, the hepatocyte growth factor (HGF) receptor tyrosine kinase. HGF stimulates mitogenesis, motogenesis, and morphogenesis in a variety of cellular targets during development, homeostasis, and tissue regeneration. Inappropriate HGF signaling resulting in unregulated cell proliferation, motility, and invasion occurs in several human malignancies. This can occur through paracrine signaling, autocrine loop formation, receptor mutation, gene amplification, or gene rearrangement, accompanied frequently with overexpression of ligand and/or receptor proteins. We hypothesized that c-Met overexpression in cancer might result in increased ectodomain shedding, and that its measure could be a useful biomarker of tumor progression.

EXPERIMENTAL DESIGN

We developed a sensitive electrochemiluminescent immunoassay to quantitate c-Met protein in cell lysates, culture supernatants, and biological samples.

RESULTS

A survey of cultured cell models of oncogenic transformation revealed significant direct correlations (P < 0.001, t test or ANOVA) between malignant potential and the rate of c-Met ectodomain shedding that was independent of steady-state receptor expression level. Moreover, weekly plasma and urine samples from mice harboring s.c. human tumor xenografts (n = 4 per group) displayed soluble human c-Met levels that were measurable before tumors became palpable and that correlated directly with tumor volume (R2 > 0.92, linear regression).

CONCLUSIONS

For a variety of human cancers, c-Met ectodomain shedding may provide a reliable and practical indicator of malignant potential and overall tumor burden.

The MET receptor tyrosine kinase in invasion and metastasis

Various cytokines and soluble growth factors upon interaction with their membrane receptors are responsible for inducing cellular proliferation, differentiation, movement, and protection from anoikis (a planned suicide activated by normal cells in absence of attachment to neighboring cells or extracellular matrix (EMC)). Among those soluble factors a major position is exerted by hepatocyte growth factor (HGF) together with its receptor MET and macrophage-stimulating protein (MSP) in cooperation with its receptor RON.

Treatment outcome for metastatic papillary renal cell carcinoma patients

BACKGROUND

Most clinical trial reports in metastatic renal cell carcinoma (RCC) do not distinguish between histologic subtypes, making it difficult to assess specific treatment efficacy. The current retrospective study sought to define clinical features and outcome data for metastatic papillary RCC.

METHODS

Clinical features, treatment outcome, and survival were evaluated in 38 patients with metastatic papillary RCC who underwent clinical evaluation at Memorial Sloan-Kettering Cancer Center (MSKCC) between 1985 and 2005. Twenty-three of 513 individuals were identified from a clinical trial database, 14 of 1895 from a surgery database, and 1 of 357 from a pathology database. A literature review of systemic therapy in metastatic papillary RCC was performed.

RESULTS

Among the 38 patients, 30 had been treated at MSKCC with various systemic therapies, including cytokines. Twelve therapies resulted in stable disease, 30 in initial progression of disease, and 1 in an unknown response. One patient had a partial response to sunitinib, a novel multitargeted tyrosine kinase inhibitor. The median overall survival time for the entire study group was 8 months (95% confidence interval, 5-12). A literature review on treatment of metastatic papillary RCC produced 4 reports, confirming a lack of efficacy for systemic therapy.

CONCLUSIONS

A resistance to systemic therapy characterizes patients with metastatic papillary RCC. Further understanding of the genetics and molecular biology and subtypes involved may provide the basis for more effective agents. Treatment with targeted therapies or other experimental agents is warranted.