REVIEW
Renal Cell Carcinoma:
Biological Features and Rationale for Molecular-targeted Therapy
Mototsugu Oya

Department of Urology, Keio University School of Medicine, Tokyo, Japan(Received for publication on April 16, 2008)(Accepted for publication on July 17, 2008)

Abstract
Cancer cells are characterized by indefinite proliferation, invasiveness and metastases.
These characteristics are usually related to one another. Namely, cancer cells that proliferate rapidly tend to invade and metastasize. Renal cell carcinoma (RCC) typically does notproliferate rapidly nor does it invade the surrounding tissues, but it does metastasize. RCC
has several peculiar characteristics that are not observed in other cancers: a relatively laterecurrence, a high frequency of paraneoplastic syndrome, hypervascularity and the spontaneous regression of metastatic lesions after the excision of the primary tumor. These clinicalobservations suggest that cytokines or growth factors are important contributors to microenvironments favoring the growth of cancer cells. Thus, the blockade of cell-to-cell communication might have some therapeutic potential. Accordingly, a popular strategy for molecular-targeted therapy for RCC targets the vasculization of RCC induced by vascular endothelial growth factor (VEGF). This review highlights the biological features of RCC that are relevant to molecular-targeted therapy. (Keio J Med 58 (1) : 1－ 11, March 2009)

Keywords: renal cell carcinoma, molecular-targeted therapy, cytokine, vascular endothelial growth
factor (VEGF)

Introductionof RCC. The U.S. Food and Drug Administration (FDA)
subsequently approved two anti-angiogenic agents,
sorafenib and sunitinib, for the treatment of metastatic
RCC. Both of these agents are small-molecule tyrosine
kinase inhibitors (TKIs). Temsirolimus, an mTOR (mammalian target of rapamycin) inhibitor, was also recently
approved by the FDA. In Japan, the government approved the use of sorafenib in January 2008 and is in theprocess of approving sunitinib. Thus, the era of molecular-targeted therapy for RCC has now begun.

With the advent of such imaging modalities as ultrasonography and computed tomography, renal cell carcinomas (RCC) are now frequently detected at an asymptomatic early-stage of carcinogenesis. These carcinomas areusually successfully treated by surgical resection. However, patients with metastatic disease either at presentation or after surgical treatment have a poor prognosis.
For these patients, immunotherapy including the administration of interferon (IFN)-α and interleukin (IL)-2 hasbeen the most common treatment option for the past 20
years. Recently, however, novel molecular findings have
led to the introduction of molecular-targeted therapy for
RCC. RCC is classified pathologically into five types,
i.e., clear cell, papillary, chromophobe, collecting duct
carcinoma and unclassified. Clear cell RCC accounts forabout 80% of all RCCs and is well known for its hypervascularity. Clinical trials using anti-angiogenic agents
proved that these agents were effective for the treatment

Peculiar Characteristics of RCC
Clinicians treating RCC patients sometimes feel that
this malignant neoplasm has characteristics that are notobserved in other cancers. Hence, patient outcome issometimes unpredictable: some patients with metastases
live longer than 5 years, and late recurrence can occur aslong as 5 or even 10 years after the initial surgery. Occasionally, RCC is accompanied by paraneoplastic syn-

Reprint request to: Mototsugu Oya, MD, Department of Urology, Keio University School of Medicine, 35 Shinanomachi, Shinjuku-ku, Tokyo 160-8582,
Japan, Tel: +81-3-5363-3824, Fax: +81-3-3225-1985, E-mail: moto-oya@sc.itc.keio.ac.jp
1

2

Oya M: Molecular-targeted therapy for Renal Cell Carcinoma

Fig. 1 VHL disease. The solid tumors are all benign tumors with hypervascularity, except for RCC.

drome, with symptoms such as fever, erythrocytosis, leukocytosis and hypercalcemia. This syndrome is causedby the secretion of cytokines or hormones from the tumor.1 Growth factors like vascular endothelial growth
factor (VEGF) and platelet-derived growth factor(PDGF) are also secreted from RCC, inducing hypervascularity. Although RCC is a solid tumor, immunotherapy(not chemotherapy) has been the standard treatment formetastatic RCC. This tumor type has been regarded as
immunogenic because spontaneous regression2 has been
observed. These characteristics of RCC can appear very
peculiar to clinicians.
Pathological Classification
RCCs comprise a heterogeneous group of tumors. The
most recent classification in 2002 (UICC3) describes fivesubtype classifications, i.e., clear cell RCC, papillary
RCC, chromophobe RCC, collecting duct carcinomas,
and unclassified RCC. This classification reflects the location within the nephron from which the tumors originate. Epithelial cells of the proximal part of the renal tubule give rise to clear cell and papillary RCC, while thecollecting tubule of the nephron gives rise to chromophobe RCC and collecting duct carcinomas. At present,
these four types of RCC are recognized as distinct entities.

Molecular Pathology of Clear Cell RCC:von Hippel-Lindau (VHL) Tumor Suppressor Gene
The most important molecular disorder in clear cell
RCC involves the VHL tumor suppressor gene. VHL
disease is a multiorgan disorder caused by an inherited
mutation of the VHL tumor suppressor gene, located on
chromosome 3p25. VHL patients present with hemangioblastomas of the retina, cerebellum, or spinal cord;
visceral cysts; and solid tumors.4 The solid tumors can
include RCC, pheochromocytomas, and pancreatic islet
cell tumors (Fig. 1). All these tumors are benign, hypervascular tumors, except for RCC. The development ofthese disorders is linked to the inactivation of the remaining wild allele in the organ tissue. Therefore, thepathology is explained by Knudson’s two-hit theory.
VHL mutation or gene silencing by promotor hypermethylation is also observed in sporadic RCC. 5, 6 In
summary, the loss of VHL tumor suppressor gene function occurs in both familial and most sporadic cases ofclear cell RCC.
The VHL tumor suppressor protein acts as the substrate recognition component of a ubiquitin E3 ligasethat targets protein degradation, including HIF-α subunits.7 The loss of VHL protein function as a result ofgene mutation leads to the constitutive expression of
HIF-α.8 To date, three HIF-α subunits, HIF-1α, HIF-2α,Keio J Med 2009; 58 (1):1－11

3

Fig. 2 VHL inactivation leads to HIF-α activation. HIF is a transcription factor that induces several genes related to hypoxia. VEGF,
PDGF, TGF-α and CAIX are representative genes induced by HIF. HRE: hypoxia response element ARNT: arylhydrocarbon receptor
nuclear translocatorand HIF-3α, have been cloned. HIF-α induces several
target genes including VEGF, PDGF, TGF-α, carbonic
anhydrase IX (CAIX) and Glut-1.9 RCC is characterized
by prominent neovasculization, probably as a result of
the overexpression of VEGF. Several reports have linked
angiogenesis and VHL mutation.1 0, 11 Angiogenesis is
the process during which new blood vessels are formed
from preexisting vessels, and this process is necessary
for tumors to receive the nutrition and oxygen that theyrequire for growth. Highly proliferative tumors are often
exposed to hypoxia, especially at their centers. HIF is
physiologically induced in these situations. In contrast,
clear cell RCC is highly angiogenic in normoxic conditions as a result of the induction of VEGF arising fromthe activation of HIF through the inactivation of pVHL
(Fig. 2).
CAIX has been implicated as a marker of RCC because CAIX is expressed in clear cell RCC, but not innormal kidney tissues. CAIX protein is a member of the
carbonic anhydrase family and plays a role in the regulation of the cell proliferation involved in hypoxia. Conceivably, this protein may be needed for tumor survival
during early carcinogenesis, when the cancers are exposed to hypoxia. Bui et al. reported that CAIX is an independent predictor of longer survival among RCC patients.1 2 However, these results were not validated by arecent report.13 Regardless of this lack of validation, thehigh frequency of positive staining for CAIX in clear
cell RCC suggests that this protein could be used as amarker for diagnosis in biopsy samples or as a marker of
early carcinogenesis.
The deregulation of the VHL-HIF pathway explains
the hypervascularity seen in RCC but not the aberrant
proliferation. Kondo et al. showed that tumor suppression by the VHL protein was overridden by an HIF-2αmutant that escaped recognition by VHL proteins. Introducing this HIF-2α mutant into cells with wild-type VHL
proteins promoted tumor growth. Therefore, HIF-2α is
considered to boost RCC proliferation.1 4 However, thedownstream target molecules of HIF-2α that are involvedin RCC carcinogenesis remain to be elucidated. Additional evidence of the crucial role of HIF in RCC tumor
growth was presented by Maranchie et al. 1 5 They
blocked the binding of VHL to HIF in RCC cells re-expressing VHL, restoring tumor growth.
Other functions of the VHL protein include cilia formation. Renal cancer cells that lack pVHL have recently
been reported to be deficient in cilia, whereas the ectopic
expression of pVHL restored cilia growth.1 6-1 8 Autosomal dominant polycystic kidney diseases (ADPKD) arecaused by mutations in proteins localized in the cilia or
centrosomes.1 9 Accordingly, in kidneys with VHL disease, premalignant cysts composed of clear cells are observed. pVHL binds to and stabilizes microtubules.2 0
Therefore, the loss of pVHL is related to cilia formation.
Indeed, in pVHL-deficient cells, the orientation of microtubule growth is disturbed, resulting in disordered
microtubule assembly. pVHL binds to microtubules and4

Oya M: Molecular-targeted therapy for Renal Cell Carcinoma

the Par3-Par6-aPKC complex to direct microtubule orientation.21 This enables the centrosome to migrate to theapical membrane. The membrane-anchored centrosome
forms the basal body of the cilium. These sequential dysfunctions cause the loss of cilia formation. Interestingly,
cilia formation is linked to the cell cycle. Differentiatedcells in G0 have cilia. In polycystic kidneys, the loss ofcilia is strongly related to an increase in the proliferationof cyst-lining epithelial cells. The deregulation of cell
cycle control that is linked to ciliary loss may be mediated by the expression of NIMA-related protein kinases
that play a role in the G2-M transition as well as in ciliary loss.2 2, 2 3 The loss of cilia followed by the aberrant
cell cycle control might be related to the early carcinogenesis of RCC.
RCC as Cytokine-producing Tumor
RCC was formerly nicknamed ‘internist’s tumor’ because most patients with RCC present with symptoms
like fever of unknown origin, hypercalcemia, and/or
erythrocytosis and are initially referred to internists fordiagnosis. The above-mentioned symptoms are collectively known as paraneoplastic syndrome, as they are
produced by the aberrant secretion of cytokines and/or
hormones. Aggressive RCC phenotypes are occasionallyassociated with inflammatory paraneoplastic syndrome,
which can be detected as an elevated serum CRP level.
Accordingly, an elevated CRP level is associated with apoor prognosis in patients with RCC.2 4, 2 5 IL-6 is also
thought to be a major causative cytokine because 50% ormore of patients with metastatic RCC have elevated IL-6
levels, which in turn are correlated with elevated CRP
levels.26, 27 IL-6 is also secreted by cancer cells and may
thus play a role in cancer development and may accelerate cancer cell growth in an autocrine or paracrine manner.2 8 Furthermore, IL-6 is an independent prognostic
factor of metastatic RCC.29
Yoshida et al. investigated the three major inflammatory cytokines, namely, IL-6, TNF-α, and IL-1β. The serum IL-6 level was strongly correlated with the presenceof metastasis and a high tumor grade.30 They established
RCC cell lines for short periods and demonstrated that
IL-6 was the only inflammatory cytokine secreted into
the supernatants of the cell lines. TNF-α and IL-1β were
not detected in the majority of the cell line supernatants,suggesting that these two cytokines are secreted from
cells other than RCCs, presumably monocytes or macrophages.
The predominant mechanism by which these cytokines
are newly synthesized involves an inducible transcriptional initiation of their respective genes. This phenomenon is governed by transcription factors that bind to theregulatory regions of the genes. Cytokine-inducible transcription factors, including NF-κB, STAT3 and C/EBP-β(NF-IL6), might contribute to the deregulated cytokine
expression observed in RCC. We previously showed thatsome RCCs contain activated NF-κB, as determined using an electrophoretic mobility shift assay (EMSA) andimmunohistochemistry.3 1 Recent reports have shownthat NF-κB activity is related to pVHL function. 3 2, 3 3Thus, NF-κB has been recognized as a therapeutic targetof RCC.3 4, 3 5 We also showed that STAT3 activation, as
determined using immunohistochemistry with a phosphorylated antibody, was associated with metastasis andthat STAT3 activation was an independent prognostic
factor.3 6 C/EBP-β is also activated in invasive phenotypes of RCC.37 The clonal selection of RCC through the
production of these cytokines, which enable autocrine orparacrine growth, may have a growth advantage, thereby
contributing to tumor development.
Importance of Cytokines and
Growth Factors to RCC Carcinogenesis
Cancer cells are characterized by indefinite proliferation, invasiveness and metastases. These characteristics
are usually related to one another. Namely, cancer cells
that proliferate rapidly tend to invade and metastasize.
RCC typically does not proliferate rapidly nor does it invade the surrounding tissues, but it does metastasize.
Late recurrence is occasionally observed in RCC, andearly-stage RCC has recurred as long as 10 years after
the initial operation. This means that small, early-stage
RCC that had metastasized at the time of the initial operation required 10 years to grow to a clinically identifiable size. Renal cancer cells seem to require the help of
surrounding cells or tissues to survive. Therefore, growth
factors or cytokines, including VEGF and IL-6, are important for the cancer cells’ ability to communicate withsurrounding cells. IL-6 works as an autocrine and/or
paracrine growth factor. Furthermore, IL-6 might act as atumor microenvironmental factor that can promote tumor-associated macrophages (TAMs), the most abundant
immunosuppressive cells in the tumor microenviroment.38
RCC is Immunogenic
but Seems to Escape Immuno-surveillance
RCC is thought to be immunogenic because spontaneous regression has been documented. Resected RCC
specimens show significant T-cell infiltration, suggesting
the immunosuppressive activity of T cells against the tumor. These observations led to the clinical use of immunotherapy, including the administration of IFN-α or IL-2,
as the standard therapy for RCC for 20 years, with objective response rates 10-20%.3 9 Other immunotherapy
options include allogenic stem cell transplantation, adoptive T-cell transfer, and vaccination using dendric cells

Keio J Med 2009; 58 (1):1－11

or heat shock protein peptide complexes. The major rationale for immunotherapy is the induction of CD8+ cytotoxic T-cells that recognize the tumor antigen and attack the cancer cells. CD4+ cells play a fundamental rolein the induction and maintenance of the effector function. However, few clinically relevant tumor-associatedantigens have been identified.40
The limited success of immunotherapies might be due
to an immune escape mechanism in RCC cells. Representative mechanisms include the loss or down-regulation of HLA class I antigens;41 the secretion of immunosuppressive cytokines like IL-10, TGF-β or VEGF; orthe lack of costimulatory factors and the overexpressionof inhibitory costimulatory factors.
Modulation of Costimulatory Molecules
The modulation of costimulatory molecules might enable the efficacy of immunotherapy to be increased. One
approach is to boost costimulatory molecules involved in
the effective T-cell response. Another approach is to inhibit costimulatory molecules that block the effective
T-cell response.
For an effective response, two signals are generally required. The first signal involves the interaction of the
T-cell receptor (TCR) and the MHC class I/II peptide
complex, whereas the second signal occurs via the costimulatory molecules. The B7 family molecules include
B7-1, B7-2 and the B7-H subfamily. Both B7-1 and B7-2
are expressed on antigen-presenting cells (APC) and interact with CD28 (for stimulation) and cytotoxic T-lymphocyte-associated protein 4 (CTLA4; for inhibition).
Indeed, a lack of B7-1 and B7-2 has been reported in
RCC.42 In contrast, the B7-H subfamily negatively regulates immune responses. The expression of B7-H1 andB7-H4 have been reported in RCC. The interaction of
B7-H1 on RCC cells with PD-1 on T-cells has been reported to induce apoptosis in activated T-cells.4 3 Notably, RCCs with B7-H1 expression have been associatedwith a poor patient outcome.44 Furthermore, the expression of PD-1 in the tumor-infiltrating T-cells is also anindicator of a poor patient prognosis.45
Role of Tumor Cytokine Microenvironment
in Immune Escape
As described above, RCC secrets various cytokinesthat might mediate immune escape. Immunosuppressive
cytokines like IL-6, IL-10, TGF-β or VEGF may act tosuppress effector T-cells. Furthermore, cytokines produced by various immune cells (TNF-α and IL-6) may
promote tumor growth in the tumor microenvironment.
Another mechanism leading to immune escape may be
the generation of regulatory T cells (Tregs) and myeloidderived suppressor cells (MDSCs), which are induced by5

soluble factors secreted from cancer cells. Tregs (CD4+,
CD25+, Foxp3+, IL7R+) are essential to the homeostasisof the immune system through their negative regulationof CD4+ and CD8+ T cell activation. RCC patients reportedly have elevated levels of Tregs in their blood,compared with the levels in healthy volunteers. During
treatment with IL-2, RCC patients with objective responses achieved a decrease in the number and frequency of Tregs, whereas an increase in Tregs was observedin patients with progressive disease.46 Thus, the manipulation of Tregs may have therapeutic potential for thetreatment of RCC.
The relevance of MDSCs to the impaired immune
function arises from the production of arginase, which
depletes arginine in the microenvironment, thereby impairing T cell proliferation. An increase in MDSCs has
been observed in RCC patients.4 7 Prostaglandin E2 isproduced by cancer cells, inducing arginase expression.
The manipulation of MDSCs also has therapeutic potential for the treatment of RCC. The blockade of prostaglandin E2 using non-steroidal anti-inflammatory drugs(NSAIDs) might boost the efficacy of immunotherapy.
Is HIF the Dominant Transcription Factor
Inducing VEGF?
Theoretically, the induction of VEGF by HIF activation is the most important mechanism of hypervascularity in RCC. However, VEGF might also be induced by
the activation of other transcription factors. Therefore,
we explored whether VEGF is dominantly induced by
HIF. We employed an siRNA knockdown method toclarify the functional role of the HIF subunits, namely
HIF-1α and HIF-2α, in VEGF transcription. 48
We used 9 RCC cell lines. The VHL gene was inactivated in 4 of the 9 cell lines because of either a frame
shift mutation or hypermethylation. All four cell lines
with VHL gene activation had either a truncated HIF-1α
protein or defective HIF-1α expression. The reduced
protein expression was caused by a low level of mRNA
expression. In the cell lines without HIF-1α expression,
VEGF expression was maintained by HIF-2α expression.
Indeed, 769P cells (lacking both HIF-1α and HIF-2α)
had a low level of VEGF expression. In these HIF-1α
defective cell lines, the knockdown of the HIF-2α gene
showed that HIF-2α regulated VEGF production, irrespective of the VHL gene mutation status. In contrast,
HIF-1α played a predominant role in VEGF secretion in
the cells expressing both wild-type HIF-1α and HIF-2α
proteins because HIF-1α knockdown resulted in marked
down-regulation of VEGF secretion. These results suggest that HIF-α is mainly responsible for the induction of
VEGF expression and that other mechanisms play aminimal role.

6

Oya M: Molecular-targeted therapy for Renal Cell Carcinoma

Fig. 3 Six methods for blocking the activity of VEGF. Transcriptional controls, trapping methods, TKI of VEGF-R and signal blockade
are possible mechanisms. At present, TKI is the most useful and widely applied clinical modality.

VEGF-targeted Therapy
HIF-mediated angiogenesis via VEGF induction could
theoretically be targeted using six different methods(Fig. 3).
1) Blocking of HIF activation: Two agents, 103D5R4 9
and NSC 644221,50 have been reported to block HIF
activation. However, the efficacy and safety of thesedrugs have not yet been evaluated in animal models.
An mTOR inhibitor has also been reported to have anindirect suppressive effect on HIF activation.51
2) anti-VEGF antibody (Ab), bevacizumab: A placebocontrolled randomized control trial for metastatic
RCC patients showed that high-dose bevacizumab
prolonged the time to progression, compared withthat in the control group. However, no significant differences in overall survival were seen. Minimal toxic
effects, like hypertension and asymptomatic proteinuria, were seen.52
3) VEGF Trap: VEGF Trap is an engineered soluble receptor made from the extracellular domains of VEGFR1 and VEGFR2. VEGF Trap binds to VEGF witha higher affinity than bevacizumab. The toxicities
seen during a phase I trial examining the subcutaneous and intravenous administration of VEGF Trap
were hypertension and proteinuria.53
4) anti-VEGFR Ab: The blockade of VEGFR-1 activation has been shown to inhibit pathologic angiogenesis and tumor growth. VEGFR-1 is also expressed inmonocyte/macrophages, and VEGF may regulate themigration of these cells.5 4 VEGFR-1 positive hematopoietic bone marrow progenitor cells may regulate
the homing of tumor cells, thus helping to form metastatic lesions.55 The blockade of VEGFR-1 may prevent the metastasis of the primary tumors. Pre-clinicalexperimental data have been obtained using humanbreast tumor xenografts. An anti-VEGFR-1 monoclonal antibody (mAb), IMC-18F1, reduced tumor cellproliferation.5 6 VEGFR-2 is the major transducer of
VEGF signals in endothelial cells, thus constituting
the major target for antiangiogenic therapy. IMC-1121
is a VEGFR-2 mAb that inhibits the VEGF-stimulated proliferation of human endothelial cells. Furthermore, IMC-1121 inhibited leukemia growth in animalmodels.5 7 hF4-3C5 is a VEGFR-3 mAb that reacts
with lymphatic endothelial cells as well as humanumbilical vein endothelial cells.58
5) TKI for VEGFR: Sorafenib and sunitinib belong tothis category. These agents are discussed later.
6) Downstream targets of VEGFR (Fig. 4): The autophosphorylation of tyrosine residues in VEGFR-2 hasbeen observed.59 The phosphorylation of Y1175 leads
to the activation of the protein kinase C (PKC) pathway. This pathway also stimulates the c-Raf-MEKMAP-kinase signal. Y1175 constitutes a binding site
for Shb, a signal adaptor for PI3K, suggesting adownstream signal cascade involving the PI3K-Akt
pathway.60 Phosphorylated Y951 binds to T-cell-spe-Keio J Med 2009; 58 (1):1－11

7

Fig. 4 Signals from VEGF-R. The PI3K-Akt pathway, Raf-MAPK pathway and ROCK pathway are the major pathways involving
activated VEGF-R.

cific adapter (TSAd), which is expressed in tumor
vessels. TSAd has a Src Homology 2 (SH2) site andassociates with Src. Src alters the cell structure to enable cell migration by modulating the actin cytoskeleton through its influence on the RhoA-ROCK pathway.6 1 Inhibitors of these signal transduction pathways might be treatment options for blocking the activity of of VEGF.
Ets-1 is a well-known downstream transcription
factor in the VEGF signal cascade. Ets-1 converts endothelial cells to an angiogenic phenotype by inducing the expression of urokinase-type plasminogen activator (uPA), matrix metalloproteinase-1 (MMP-1),
MMP-3, MMP-9 and integrin β3.6 2 Ets-1 appears to
be a key transcription factor for extracellular matrix
remodeling in angiogenesis. Indeed, endothelial cells
surrounding clear cell RCC were positive for Ets-1.63
The specific inhibition of Ets-1 to inhibit angiogenesis may be a potential therapeutic strategy for clear
cell RCC.
Anti-angiogenic Agents Currently in Use:
Sorafenib and Sunitinib
Sorafenib is an oral inhibitor of Raf kinase, which is a
crucial kinase in ras-MAP kinase signal transduction.
Sorafenib is supposed to have an anti-proliferative effecton pancreatic cancers carrying oncogenic ras mutations;however, sorafenib has not shown any anti-tumor effectin pancreatic cancer. Although MAP kinase is constitutively activated in RCC cell lines,6 4 ras mutations in
RCC are extremely rare. However, further basic studies
have revealed that sorafenib also inhibits receptor tyrosine kinases, including VEGFR2 and VEGFR3. The inhibition of ras-MAP kinases was not associated with any
growth-inhibitory effects,6 5 suggesting that sorafenib’s
underlying mechanism of activity depends on anti-angiogenesis. In a phase II randomized discontinuation trial(RDT), 202 patients were treated with 400 mg ofsorafenib twice daily during the run-in period. Seventythree patients exhibited tumor shrinkage of more than25%. Sixty-five patients with stable disease at 12 wks
were randomly assigned to a sorafenib (n = 32) or a placebo group (n = 33). The median progression-free survival period from the time of randomization was significantly longer in the sorafenib group than in the placebogroup (24 wks vs. 6 wks, p = 0.009). Adverse events included hypertension, skin reactions on the hands andfeet, and diarrhea.6 6 A subsequent randomized placebocontrolled phase 3 trial in cytokine-refractory patients
showed a statistically significant improvement in progression-free survival (PFS) from 2.2 months to 5.5
months (p < 0.01).6 7 Although the objective response
rate was 10%, 74% of the patients experienced diseasestabilization, enabling a longer PFS period.
Sunitinib is an oral receptor tyrosine kinase inhibitorwith antiangiogenic activity via the targeting of VEGFR-2, PDGFR, and KIT. Two phase 2 studies in cyto-

8

Oya M: Molecular-targeted therapy for Renal Cell Carcinoma

kine-refractory RCC patients (50 mg for 4 wks followedby 2 wks of rest) resulted in response rates of 40% and
34% among 63 and 106 patients, respectively.6 8, 6 9 Disease stabilization for more than 3 months was observedin 27% and 29% of the patients, respectively. The clinical benefit (CR+PR+SD) ratios were 67% and 63%, respectively. Adverse events included hypertension, skinreactions on the hands and feet, and diarrhea. These adverse events were also observed in the sorafenib trials. In
addition, leukopenia and thrombocytopenia were also
observed. A subsequent randomized phase 3 trial examined sunitinub versus IFN-α as a first-line therapy forclear cell RCC patients.7 0 In this study, 94% of the patients had either good or intermediate risk features according to the MSKCC risk model.7 1 The response rate
was 31% versus 6%, with a doubling of the PFS from 5
to 11 months (p < 0.001).
mTOR is Another Target for the Treatment of RCC
mTOR is a protein that was discovered during studies
to clarify the antifungal activity of rapamycin (a macrolide); rapamycin was later shown to have immunosuppressive and anti-cancer activities. mTOR constitutes
two complexes designated as mTORC1 and mTORC2.
mTORC1 has three components, (mTOR, raptor andmLST8), whereas. mTORC2 has four components,(mTOR, rictor, mSin1 and mLST8).7 2 mTORC1 regulates cell growth, ribosome biogenesis, and autophagy.
How rapamycin perturbs mTOR function is not fully understood. mTOR forms a complex with its intracellular
receptor, FKBP12, and binds directly to mTORC1, suppressing the phosphorylation of the substrates S6K1 and
4EBP1. Rapamycin also weakens the interaction between mTOR and raptor.7 3 The TSC1 (tuberous sclerosis1, hamartin)-TSC2 (tuberin) complex acts as a negative regulator. Notably, Akt directly phosphorylates andinhibits the TSC1-TSC-2 complex, eventually activating
mTORC1. The PI3K-AKT signal is activated in several
types of cancers. Therefore, the link with mTORC1 suggests a targeted therapy for cancer.
Akt is a subfamily of the serine/threonine protein kinases and is thought to play a crucial role in controllingthe balance between cell survival and apoptosis. 7 4 In
various types of human malignant tumors, including colon cancer,75 ovarian cancer,76 endometrial cancer,77 andthyroid cancer,78 high frequencies of elevated Akt activation have been demonstrated. We reported that an elevation in Akt activation in RCC was correlated with ahigher tumor grade and metastasis, resulting in a poorer
patient outcome.7 9 One of the mechanisms underlying
elevations in Akt activation has been shown to be the inactivation of the PTEN (phosphatase and tensin homologue deleted on chromosome 10) tumor suppressor
gene, which is located on 10q23.3. PTEN is a lipid phos-

phatase that dephosphorylates the 3-position of phosphatidylinositol 3,4,5-triphosphate (PIP3), a secondary messenger of phosphatidylinositol 3-kinase (PI3K).80 PTEN
antagonizes PI3K activity and negatively regulates Akt.
We reported that PTEN expression was reduced in RCC
and that this reduction was correlated with Akt activation.8 1 These observations suggest that mTORC1 might
be a target for the treatment of RCC. Indeed, clinical trials have shown temsirolimus (see below) to be effective
against RCC, and the U.S. FDA has approved this agent.
However, rapamycin analogues have not shown goodanti-tumor effects against tumors that are known to havehigh Akt activities, such as breast cancer and glioblastoma. 8 2, 8 3 Recent in vitro studies have shown thatmTORC1 inhibition induced Akt activation, possibly indicating a mechanism of resistance.8 4, 8 5 The inhibitionof PI3K signaling has also been reported to block the rapamycin-mediated activation of Akt.86 Thus, the combination of an mTOR inhibitor and a PI3K inhibitor may
be a plausible strategy for the treatment of rapamycin-resistant tumors.
Temsirolimus
Temsirolimus is an ester of rapamycin. In a phase 2
study of 111 patients with advanced refractory RCC, theresponse rate was 7% and minor responses were observed in 26%.87 A randomized phase 3 study with threearms was also performed; the 3 arms consisted of IFN-α,
temsirolimus (25 mg), and IFN-α + temsirolimus (15mg).8 8 Of note, this study was performed as a first-line
therapy and included patients regarded as having a poorrisk according to a modified MSKCC risk stratification(multiple organ metastases were added to the five risk
factors). The primary endpoint was overall survival(OS). Patients treated with temsirolimus had a median
OS of 10.9 months, versus 7.3 months for the IFN-αgroup (p = 0.007) and 8.4 for the combination group (notsignificant; NS). The response rates in this study were
low: 9%, 7%, and 11%, respectively. The adverse eventswere minor, including stomatitis, peripheral edema andrash. Patients should be carefully monitored for interstitial pneumonia and hyperglucosemia. Generally speaking, OS is the ideal study endpoint for evaluating cancer
agents. However, the response rate may also be used as asurrogate endpoint to evaluate tumor shrinkage. This
phase 3 study typically demonstrated that the response
rate does not necessarily reflect OS. Molecular-targeted
agents may have cytostatic efficacies that may be better
evaluated using PFS or the clinical benefit ratio, rather
than the response rate.
Crucial Questions
Anti-angiogenic agents are likely to be used widely forKeio J Med 2009; 58 (1):1－11

the treatment of RCC. However, several crucial questions remain unanswered. What is the refractory mechanism of RCC for anti-angiogenic agents? How can we
identify patients most likely to benefit from moleculartargeted therapy? What is the best administration sequence for these agents? Can combination therapies improve outcomes? Is there any role for immunotherapy?
If molecular-targeted agents can be used to improve theimmune microenvironment, immunotherapy might be auseful sequential therapy after molecular-targeted therapy. Further basic and clinical studies are needed to answer these questions.
References
1. Oya M, Murai M:Renal cell carcinoma: relevance of pathology.
Curr. Opin. Urol , 2003;13:445－449
2. Lokich J: Spontaneous regression of metastatic renal cancer. Case
report and literature review. Am J Clin Oncol 1997; 20:416－418
3. Sobin L H, Wittekind C:TNM classification of Malignant Tumours, 6th ed. Wiley-Liss Publications, New York, 2002;193－195
4. Kaelin WG Jr: The von hippel-lindau tumor suppressor protein:
an update. Methods Enzymol 2007; 435: 371－383
5. Shuin T, Kondo K, Torigoe S, Kishida T, Kubota Y, Hosaka M, etal.: Frequent somatic mutations and loss of heterozygosity of thevon Hippel-Lindau tumor suppressor gene in primary human renal
cell carcinomas. Cancer Res 1994; 54: 2852－2855
6. Herman J G, Latif F: Silencing of the VHL tumor-suppressor gene
by DNA methylation in renal carcinoma. Proc Natl Acad Sci USA
1994; 91: 9700－9704
7. Kamura T, Koepp DM, Conrad MN, Skowyra D, Moreland RJ, Iliopoulos O , et al.: Rbx1, a component of the VHL tumor suppressor complex and SCF ubiquitin ligase. Science 1999; 284: 657－
661
8. Maxwell PH, Wiesener MS, Chang GW, Clifford SC, Vaux EC,
Cockman ME , et al.: The tumor suppressor protein VHL targets
hypoxia-inducible factors for oxygen-dependent proteolysis. Nature 1999; 399: 271－275
9. Kaelin WG Jr: The von Hippel-Lindau gene, kidney cancer, andoxygen sensing. J Am Soc Nephrol 2003; 14: 2703－2711
10. Igarashi H, Esumi M, Ishida H, Okada K: Vascular endothelial
growth factor overexpression is correlated with von Hippel-Lindau tumor suppressor gene inactivation in patients with sporadic
renal cell carcinoma. Cancer 2002; 95: 47－53
11. Turner KJ, Moore JW, Jones A, Taylor CF, Cuthbert-Heavens D,
Han C, et al.: Expression of hypoxia-inducible factors in humanrenal cancer: relationship to angiogenesis and to the von HippelLindau gene mutation. Cancer Res 2002; 62: 2957－2961
12. Bui MHT, Seligson D, Han K, Pantuck AJ, Dorey FJ, Huang Y, etal.: Carbonic anhydrase IX is an independent predictor of survivalin advanced renal clear cell carcinoma: implications for prognosis
and therapy. Clinical Cancer Res 2003 ; 9(2):802－811
13. Leibovich BC, Sheinin Y, Lohse CM, Thompson RH, Cheville JC,
Zavada J, et al.: Carbonic anhydrase IX is not an independent predictor of outcome for patients with clear cell renal cell carcinoma.
J Clin Oncol 2007; 30: 4757－4764
14. Kondo K, Klco J, Nakamura E, Lechpammer M, Kaelin WG Jr:
Inhibition of HIF is necessary for tumor suppression by the vonHippel-Lindau protein. Cancer Cell 2002;1:237－246
15. Mranchie JK, Vasseli JR, Riss J, Bonifacio JS, Linehan WM,
Klausner RD: The contribution of VHL substrate binding and
HIF1-α to the phenotype of VHL loss in renal cell carcinoma.
Cancer Cell 2002; 1:247－255
16. Esteban MA, Harten SK, Tran MG, Maxwell PH: Formation of

9primary cilia in the renal epithelium is regulated by the von Hippel-Lindau tumor suppressor protein. J Am Soc Nephrol 2006; 17:
1801－1806
17. Lutz M, Burk RD: Primary cilium formation requires von HippelLindau gene function in renal derived cells. Cancer Res 2006; 66:
6903－6907
18. Shermer B, Ghenoiu c, Bartram M, Müller RU, Kotsis F, Höhne
M, et al.: The von Hippel-Lindau tumor suppressor protein controls ciliogenesis by orienting microtubule growth. J Cell Biol
2006; 175:547－554
19. Pazour GJ: Intraflagellar transport and clia-dependent renal disease: the ciliary hypothesis of polycystic kidney disease. J Am
Soc Nephrol 2004; 15: 2528－2536
20. Hergovich A, Lisztwan J, Barry R, Ballschmieter P, Krek W: Regulation of microtubule stability by the von Hippel-Lindau tumor
suppressor protein pVHL. Nat Cell Biol 2003; 5:64－70
21. Kuehn EW, Walz Z, Benzing T: von Hippel-Lindau: a tumor suppressor links microtubules to ciliogenesis and cancer development. Cancer Res 2007; 67: 4537－4540
22. Quarmby LM, Parker JD: Cilia and the cell cycle? J Cell Biol
2005; 169:707－710
23. O’connell MJ, Krien MJ, Hunter T: Never say never. The NIMArelated protein kinases in mitotic control. Trends Cell Biol 2003;
13:221－228
24. Ito K, Asano T, Yoshii H, Satoh A, Sumitomo M, Hayakawa M:
Impact of thrombocytosis and C-reactive protein elevation on the
prognosis for patients with renal cell carcinoma. Int J Urol 2006;
13:1365－1370
25. Karakiewicz PI, Hutterer GC, Trinh Q-D, Jeldres C, Perrotte P,
Gallina A, et al.: C-reactive protein is an informative predictor of
renal cell carcinoma-specific mortality. Cancer 2007; 110:1241－
1247
26. Tsukamoto T, Kumamoto Y, Miyao N, Masumori N, Takahashi A,
and Yanase M: Interleukin-6 in renal cell carcinoma. J Urol: 148:
1778－1781
27. Blay JK, Negrier S, Combaret V, Attali S, Goillot E, Merrouche Y,
et al.: Serum level of interleukin 6 as a prognosis factor in metastatic renal cell carcinoma. Cancer Res; 1992; 52: 3317－3322
28. Miki S, Iwano M, Miki Y, Yamamoto M, Tang B, Yokokawa K,
Sonoda T, Hirano T and Kishimoto T: FEBS Lett: 250: 607－610
29. Negrier S, Perol D, Menetrier-Caux C, Escudier B, Pallardy M,
Ravaud A, et al: Interleukin-6, interleukin-10, and vascular endothelial growth factor in metastatic renal cell carcinoma: prognostic
value of Interleukin-6. J Clin Oncol 2004; 22:2371－2378
30. Yoshida N, Ikemoto S, Narita K, Sugimura K, Wada S, Yasumoto
R, et al.: Interluekin-6, tumor necrosis factor alpha and interleukin-1 beta in patients with renal cell carcinoma. Br J Cancer 2002;
86:1396－1400
31. Oya M, Takayanagi A, Horiguchi A, Mizuno M, Ohtsubo, M,
Marumo, K, et al.: Increased nuclear factor-κB activation is related to the tumor development of renal cell carcinoma. Carcinogenesis 2003; 24, 377－384
32. An J and Rettg MB: Mechanism of von Hippel-Lindau proteinmediated suppression of nuclear factor kappa B activity. Mol Cell
Biol 2005; 25:7546－7556
33. Yang H, Minamishima YJ, Yan Q, Schlisio S, Ebert BL, Zhang X,
Zhang L, Kim WY, Olumi AF and WG Kaelin: pVHL acts as an
adaptor to promote the inhibitory phosphorylation of the NF-κB
agonist Card9 by CK2. Mol Cell 2007; 28: 15－27
34. Oya M, Ohtsubo M, Takayanagi A, Tachibana M, Shimizu N, Murai M: Constitutive activation of nuclear factor-κB prevents
TRAIL-induced apoptosis in renal cancer cells. Oncogene 2001;
20: 3888－3896
35. An J, Sun Y, Fisher M, Rettig MB: Maximal apoptosis of renal
cell carcinoma by the proteasome inhibitor bortezomib is nuclear
factor-κB dependent. Mol Cancer Ther 2004; 3: 727－736
36. Horiguchi A, Oya M, Shimada T, Uchida A, Marumo K, Murai M:

10
Activation of signal transducer and activator of transcription 3 inrenal cell carcinoma: a study of incidence and its association withpathological features and clinical outcome. J. Urol 2002; 168: 762－765
37. Oya M, Horiguchi A, Mizuno M, Marumo K, Murai M: Increased
activation of CCAAT/enhancer binding protein-β correlates with
the invasiveness of renal cell carcinoma. Clin. Cancer Res 2003;
9: 1021－1027
38. Duluc D, Delneste Y, Tan F, Moles M-P, Grimaud L, Lenoir J, etal.: Tumor-associated leukemia inhibitory factor and IL-6 skew
monocyte differentiation into tumor-associated macrophage-likecells. Blood 2007; 110: 4319－4330
39. Garcia JA, Rini BI: Recent progress in the management of advanced renal cell carcinoma. CA Cancer J Clin 2007;57:112－125
40. Gouttefangeas C, Stenzl A, Stevanovic S, Rammensee H-S: Immunotherapy of renal cell carcinoma. Cancer Immunol Immunother 2007; 56:117－128
41. Kitamura H, Honma I, Torigoe T, Asanuma H, Sato H, Tsukamoto
T: Down-regulation of HLA classI antigen is an independent prognostic factor for clear cell renal cell carcinoma. J Urol 2007; 177:
1269－1272
42. Kronfeld K, Abken H, Seliger B: B7-1 and B7-2 act differentiallyin the induction of a T cell response: their impact for a HLAmatched anti-tumor immunotherapy. Int J Cancer 2005; 117: 794－799
43. Dong H, Strome SE, Salomao DR, Tamura H, Hirano F, Flies DB,
et al.: Tumor-associated B7-1 promotes T-cell apoptosis: a potential mechanism of immune evasion. Nat Med 2002; 8: 793－800
44. Thompson RH, Kunz SM, Leibovich BC, Dong H, Lohse CM,
Webster WS, et al: Tumor B7-H1 is associated with poor prognosis in renal cell carcinoma patients with long-term follow-up.
Cancer Res 2006; 66: 3381－3385
45. Thompson RH, Dong H, Lohse CM, Leibovich BC, Blute ML,
Cheville JC, et al.: PD-1 is expressed by tumor-infiltrating immune cells and is associated with poor outcome for patients withrenal cell carcinoma. Clin Cancer Res 2007; 13:1757－1761
46. Cesana GC, DeRaffele G, Cohen S, et al: Characterization of
CD4+CD25+ regulatory T cells in patients treated with high-doseinterleukin-2 for metastatic melanoma or renal cell carcinoma. J
Clin Oncol 2006; 24: 1169－1177
47. Zea AH, Rodriguez PC, Atkins MB, Hernandez C, Signoretti S,
Zabaleta J, et al.: Arginase-producing myeloid suppressor cells inrenal cell carcinoma patients: a mechanism of tumor evasion.
Cancer Res 2005; 65: 3044－3048
48. Shinojima T, Oya M, Takayanagi A, Mizuno R, Shimizu N, Murai
M: Renal cancer cells lacking hypoxia inducible factor (HIF) 1-α
expression maintain vascular endothelial growth factor expression
through HIF 2-α. Carcinogenesis 2007; 28: 529－536
49. Tan C, de Noronha RG, Roecker AJ, Pyrzynska B, Khwaja F,
Zhang Z, Zhang H, et al.: Identification of a novel small-molecule
inhibitor of the hypoxia-inducible factor 1 pathway. Cancer Res
2005; 65:605－612
50. Creighton-Gutterige M, Cardellina JH 2nd, Stephen AG, Rapisarda
A, Uranchimeg B, Hite K, et al.: Cell type-specific, topoisomerase
II-dependent inhibition of hypoxia-inducible factor-1alpha protein
accumulation by NSC 644221. Clin Cancer Res 2007; 13:1010－
1018
51. Hudson CC, Liu M, Chiang GG, Otterness DM, Loomis DC,
Kaper F, et al.: Regulation of hypoxia-inducible factor 1 alpha expression and function by the mammalian target of rapamycin. Mol
Cell Biol 2002; 22: 7004－7014
52. Yang JC, Haworth L, Sherry RM, Hwu P, Schwartzentruber DJ,
Topalian SL, et al.: A randomized trial of bevacizumab, an antivascular endothelial growth factor antibody, for metastatic renal
cancer. N Engl J Med 2003; 349:427－434
53. Riely GJ, Miller VA: Vascular endothelial growth factor trap in
non-small cell lung cancer. Clin Cancer Res 2007; 13 :4623s－

Oya M: Molecular-targeted therapy for Renal Cell Carcinoma
4627s
54. Sawano A, Iwai S, Sakurai Y, Ito M, Shirata K, Nakahata T, et al.:Flt-1, vascular endothelial growth factor receptor 1. is a novel cellsurface marker for the lineage og monocyte-macrophages in humans. Blood 2001; 97: 785－791
55. Kaplan RN, Riba RD, Zacharoulis S, Bramley AH, Vincent L,
Costa C, et al.: VEGFR1-positive haematopoietic bone marrowprogenitors initiate the pre-metastatic Nature 2005; 438,820－827
56. WuY, Zhong Z, Huber J, Bassi R, Finnerty B, Corcoran E, et al.:Anti-vascular endothelial growth factor receptor-1 antagonist antibody as a therapeutic agent for cancer. Clin Cancer Res 2006; 12:6573－6584
57. Zhu Z, Hattori K, Zhang H, Jimenez X, Ludwig DL, Dias S, etal.: Inhibition of human leukemia in an animal model with humanantibodies directed against vascular endothelial growth factor receptor 2. Correlation between antibody affinity and biological activity. Leukemia 2003;17: 604－611
58. Persaud K, Tille J-C, Liu M, Zhu Z, Jimenez X, Pereira DS, et al.:Involvement of the VEGF receptor 3 in tubular morphogenesis
demonstrated with a human anti-human VEGFR-3 monoclonal
antibody that recognizes receptor activation by VEGF-C. J Cell
Sci 2004; 117: 2745－2756
59. Matsumoto T, Bohman S, Dixelius J, Berge T, Dimberg A, Magnusson P, et al.: VEGF receptor-2 Y951 signaling and a role forthe adapter molecule TSAd in tumor angiogenesis. EMBO J 2005;
24: 2342－2353
60. Holmqvist K, Cross MJ, Rolny R, Hagerkvist N, Rahimi T, Matsumoto L, et al.: The adaptor protein shb binds to tyrosine 1175 in
vascular endothelial growth factor (VEGF) receptor-2 and regulates VEGF-dependent cellular migration. J Biol Chem 2004;
279:22267－22275
61. Frame MC: Newest findings on the oldest oncogene; how activated src does it. J Cell Sci 2004; 117, 989－998
62. Sato Y, Kanno S, Oda N, Abe M, Ito M, Shitata K, et al.: Properties of two VEGF receptors, Flt-1 and KDR, in signal transduction. Ann NY Acad Sci 2000; 902: 201－205
63. Mikami S, Oya M, Mizuno R, Murai M, Mukai M, Okada Y: Expression of Ets-1 in human clear cell renal cell carcinomas: implications for angiogenesis. Cancer Sci 2006; 97: 875－882
64. Oka H, Chatani Y, Hoshino R, Ogawa O, Kakehi Y, Terachi T, etal.: Constitutive activation of mitogen-activated protein (MAP)kinases in human renal cell carcinoma. Cancer Res 1995; 55:
4182－4187
65. Horiguchi A, Oya M, Marumo K, Murai M: STAT3, but not ERKs
mediates IL-6-induced proliferation of renal cancer cells, ACHN
and 769P. Kidney Int 2002; 61: 926－938
66. Ratani MJ, Eisen T, Stadler WM, Flaherty KT, Kaye SB, RosnerGL, et al.: Phase II placebo-controlled randomized discontinuation trial of sorafenib in patients with metastatic renal cell carcinoma. J Clin Oncol 2006; 24:2505－2512
67. Escudier B, Eisen T, Stadler WM: Szczylik C, Oudard S, Siebels
M, et al.: Sorafenib in advanced clear-cell renal-cell carcinoma. N
Engl J Med 2007; 356: 125－134
68. Motzer RJ, Michawlson MD, Redman BG, Hudes GR, Wilding G,
Figlin RA, et al.: Activity of SU11248, a multitargeted inhibitorof vascular endothelial growth factor receptor and plateret-derived
growth factor receptor, in patients with metastatic renal cell carcinoma. J Clin Oncol 2006; 24 :16－24
69. Motzer RJ, Rini BI, Bukowsky RM, Curti BD, George DJ, Hudes
GR, et al.: Sunitinib in patients with metastatic renal cell carcinoma. JAMA 2006; 295: 2516-2524
70. Motzer RJ, Hutson TE, Pharm D, Tomczak P, Michawlson MD,
Bukowsky RM, et al: Sunitinib versus Interferon alfa in metastatic
renal-cell carcinoma. N Engl J Med 2007; 356: 115－124
71. Motzer RJ, Bacik J, Murphy BA, Russo P, Mazumdar M: Interferon-alfa as a comparative treatment for clinical trials of new therapies against advanced renal cell carcinoma. J Clin Oncol 2002; 20

Keio J Med 2009; 58 (1):1－11:289－296
72. Sabatini DM: mTOR and cancer: insights into a complex relationship. Nature Rev Cancer 2006; 6: 729－734
73. Kim DH, Sarbassov DD, Ali SM, King JE, Latek RR, ErdjumentBromage H, et al.: mTOR interacts with Raptor to form a nutrientsensitive complex that signals to the cell growth machinery. Cell
2002; 110: 163－175
74. Franke TF, Kaplan DR, Cantley LC: PI3K: downstream AKTion
blocks apoptosis. Cell 1997; 88: 435－437
75. Itoh N, Semba S, Ito M, Takeda H, Kawata S, Yamakawa M:
Phosphorylation of Akt/PKB is required for suppression of cancer
cell apoptosis and tumor progression in human colorectal carcinoma. Cancer 2002; 94: 3127－3134
76. Kurose K, Zhou XP, Araki T, Cannistra SA, Maher ER, Eng C:
Frequent loss of PTEN expression is linked to elevated phosphorylated Akt levels, but not associated with p27 and cyclin D1 expression, in primary epithelial ovarian carcinomas. Am J Pathol
2001; 158: 2097－2106
77. Kanamori Y, Kigawa J, Itamochi H, Shimada M, Takahashi M,
Kamazawa S, et al.: Correlation between loss of PTEN expression
and Akt phosphorylation in endometrial carcinoma. Clin Cancer
Res 2001; 7: 892－895
78. Ringel MD, Hayre N, Saito J, Saunier B, Schuppert F, Burch H, etal.: Overexpression and overactivation of Akt in thyroid carcinoma. Cancer Res 2001; 61: 6105－6111
79. Horiguchi A, Oya M, Uchida A, Marumo K, Murai M: Elevated
Akt activation and its impact on clinicopathological features of renal cell carcinoma. J Urol 2003; 169: 710－713
80. Maehama T, Dixon JE. The tumor suppressor, PTEN/MMAC1,
dephosphorylates the lipid second messenger, phosphatidylinositol 3,4,5-trisphosphate. J Biol Chem 1998; 273: 13375－13378

11
81. Hara S, Oya M, Mizuno R, Horiguchi A, Marumo K, Murai M:
Akt activation in renal cell carcinoma: contribution of a decreased
PTEN expression and the induction of apoptosis by an Akt inhibitor. Ann. Oncol 2005; 16: 928－933
82. Chan S, Scheulen ME, Johnston S, Mross K, Cardoso F, DittrichC, et al.: Phase II study of temsirolimus(CCI-779), a novel inhibitor of mTOR , in heavily pretreated patients with locally advanced
or metastatic breast cancer. J Clin Oncol 2005; 23: 5314－5322
83. Galanis EJ, Buckner JC, Maurer MJ, Kreisberg JI, Ballman K,
Boni J, et al.: Phase II study of temsirolimus(CCI-779), a novel
inhibitor of mTOR , in recurrent glioblastoma multiforme: a North
central Cancer Treatment Group Study. J Clin Oncol 2005; 23:5294－5304
84. Sun SY, Rosenberg LM, Wang X, Zhou Z, Yue P, Fu H, et al.: Activation of Akt and elf4E survival pathways by rapamycin inhibition. Cancer Res 2005; 65: 7052－7058
85. O’Reilly KE, Rojo F, She QB, Solit D, Mills GB, Smith D, et al.:mTOR inhibition induces upstream receptor tyrosine kinase signaling and activates Akt. Cancer Res 2006; 66: 1500－1508
86. Fan Q-W, Knight ZA, Goldenberg DD, Yu W, Mostov KE, Stokoe
D, et al.: a dual PI3 kinase/Mtor inhibitor reveals efficacy in glioma. Cancer Cell 2006; 9: 341－349
87. Atkins MB, Hidalgo M, Stadler WM, Logan TF, Dutcher JP,
Hudes GR, et al.: Randomized phase II study of multiple doselevels of CCI-779, a novel mTOR kinase inhibitor, in patientswith advanced refractory renal cell carcinoma. J Clin Oncol 2004;
22: 909－918
88. Hudes G, Carducci M, Tomczak P, Dutcher J, Figlin R, Kapoor A,
et al.: Temsirolimus, Interferon alfa, or both for advanced renalcell carcinoma. N Engl J Med 2007; 356: 2271－2281