DRUG DEVELOPMENT FOR THE TREATMENT OF SOLID TUMORS
Commentary to Habilitation Work
by
MUDr. Igor Puzanov, CSc.
TABLE OF CONTENTS
INTRODUCTION..............................................................................................................2
CHAPTER 1: Drug Development for Advanced Colorectal Cancer ............................2
1.1 Development of 5-Fluorouracil and 5-FU/LV as First-line Chemotherapy ..................2
1.2 Development of Capecitabine as an Oral Alternative to 5-FU ......................................3
1.3 Development of Irinotecan as Second-Line Therapy and its Integration Into FrontLine Chemotherapy........................................................................................................4
1.4 Oxaliplatin: Initial Data on Front-Line Therapy and Demonstration of its Second-Line
Efficacy ..........................................................................................................................5
1.5 Comparison of Front-Line Combination Regimens ......................................................6
1.6 Bevacizumab ..................................................................................................................7
1.7 Cetuximab ......................................................................................................................8
CHAPTER 2: Drug Development for Advanced Renal Cell Carcinoma .....................8
2.1 VEGF-Targeted Therapy in metastatic RCC .................................................................9
2.1.1 Sorafenib .....................................................................................................................9
2.1.2 Sunitinib ....................................................................................................................10
2.1.3 Bevacizumab ............................................................................................................10
2.2 mTOR Targeted Therapy .............................................................................................11
2.2.1 Temsirolimus and Everolimus ..................................................................................11
2.3 Novel Agents Evaluated in mRCC ..............................................................................12
2.4 High-Dose Interleukin-2 Following VEGF-Targeted Therapy in mRCC ...................12
CHAPTER 3: Drug Development for the Treatment of Melanoma ...........................13
3.1 Targeting Cell Surface Receptors in Melanoma ..........................................................13
3.2 NF-κB Inactivation in the Treatment of Melanoma ....................................................14
3.3 Anti-angiogenic Agents in Metastatic Melanoma .......................................................14
3.4 Inhibition of Multiple Signaling Pathways in Melanoma ............................................15
3.5 Multitargeted Agents with Activity Against VEGFR and Other Cell Surface
Receptors............................................................................................................................15
CONCLUSIONS ..............................................................................................................15
REFERENCES .................................................................................................................17
INTRODUCTION
In the past decade, the treatment of solid tumors has seen major advances thanks
to the development of new targeted therapies based on the enhanced understanding of the
cancer signaling pathways on the molecular level. Effective treatment options are now
available for patients with progressive refractory disease who 10 years ago would be left
with best supportive care and a very poor prognosis. Although still major contributors to
cancer fatalities across the world, the management of malignancies like advanced
colorectal cancer, metastatic renal cell carcinoma and metastatic melanoma, has made
significant gains for the patients, particularly with the development of effective
antiangiogenic therapies and immunotherapies.
CHAPTER 1: Drug Development for Advanced Colorectal Cancer
The treatment options for colorectal cancer have seen exciting advances in the last
decade. For over 30 years the treatment consisted of one marginally effective drug, 5fluorouracil (5-FU), whose activity was enhanced slightly by the addition of the
biochemical modulator leucovorin (LV) (1). The number of agents approved for use in
the treatment of advanced colorectal cancer in the United States has now significantly
increased to include irinotecan, capecitabine, oxaliplatin, bevacizumab, and cetuximab.
The emergence of multiple new agents for the treatment of advanced colorectal
cancer was associated with a substantial improvement in therapeutic outcome. Analyses
of clinical trials that incorporate irinotecan, oxaliplatin, bevacizumab, and/or cetuximab
in combination with 5-FU/LV show that patients diagnosed with advanced disease today
can expect median survival times of 22 months or beyond (2–4) compared with only 11–
13 months reported in the era when 5-FU was the only drug available to treat colorectal
cancer (5). This improvement is not limited to patients treated in clinical trials. From
1974 to 1999, the five-year survival rates for Americans diagnosed with colorectal cancer
rose from 50% to 63% (6), and it is reasonable to expect that data from subsequent years,
when available, will show further improvements.
Despite these additions to the treatment armamentarium, the statistics for
colorectal cancer remain sobering. More than 146,000 new cases of colorectal cancer
were diagnosed in the United States in 2004, and more than 56,000 men and women in
the United States died from the disease, making it the third most common cause of cancer
death (after lung cancer and prostate or breast cancer) (6). Importantly, slightly more than
one-third of these people had their cancer diagnosed in an advanced stage and another
19% had distant metastases present at the time of diagnosis.
1.1. Development of 5-Fluorouracil and 5-FU/LV as First-line Chemotherapy
5-FU was first described by Heidelberger in 1957 (7). The impetus for synthesis
of fluorinated pyrimidines came from the observation that rat hepatomas use radiolabeled
uracil more avidly than nonmalignant tissues (8). The first clinical trials of single-agent
5-FU in the United States in early sixties were limited by the tools available to assess
therapeutic impact - tumor assessment by chest X ray, radionuclide scan, or physical
examination; the responses often did not have to be confirmed; and wide range of drug
2
dosages and schedules of administration. Therefore, it is not surprising that response rates
reported for single-agent 5-FU in advanced colorectal cancer ranged from 3% to 45%. In
phase III trials the response rates rarely exceeded 25%. Regardless of the exact response
rate, single-agent 5-FU treatment clearly produced tumor shrinkage, and the responding
patients experienced reduction in tumor-related symptoms. This was sufficient evidence
to earn new drug approval for 5-FU by the U.S. Food and Drug Administration (FDA) on
April 25, 1962.
With multiple new cytotoxic agents failing to demonstrate significant clinical
activity in this disease, clinical trials performed over the ensuing two decades focused on
optimization of 5-FU drug administration and biochemical modulation. The most
extensively studied biochemical modulators were LV, methotrexate, and interferon. In
1992, the Advanced Colorectal Cancer Meta-Analysis Project (1) summarized the results
of nine controlled clinical trials that compared single-agent 5-FU to LV-modulated 5-FU
in patients with previously untreated advanced colorectal cancer. The 5-FU/LV
combination was associated with a significantly higher response rate than single-agent 5FU (23% versus 11%, p < 107), but only a non-significant trend towards improved
median survival (11.5 versus 11.0 months, p = 0.57). This analysis was updated in 2004
to include 19 trials and more than 3300 patients with a median follow-up of 45 months
(9). In addition to a doubling of the objective response rate, this meta-analysis identified a
significant improvement in median survival (11.7 versus 10.5 months, p = 0.004) for
patients treated with 5-FU/LV.
The question of optimal schedule of 5-FU/LV administration – infusion versus
bolus - was solved by a meta-analysis combining the results of seven phase III trials, in
which a significant advantage for the infusional approach was found with response rate
22% vs. 14%, and median survival 12.1 vs. 11 months (p 0.04), respectively (5). A
difference in toxicity was also confirmed between the two administration schedules: 31%
of patients treated with 5-FU bolus by the daily 5 schedule reported 3/4 grade toxicities
compared with 4% treated with 5-FU CI (p < 0.0001). A greater percentage of patients
treated with 5-FU bolus experienced hematologic toxicity, while more patients receiving
5-FU infusions reported hand-foot syndrome.
1.2. Development of Capecitabine as an Oral Alternative to 5-FU
5-FU must be administered intravenously due to its unpredictable oral
bioavailability. Capecitabine is an oral prodrug that is enzymatically cleaved to release 5FU preferentially in cancer cells. The developmental strategy for capecitabine was to
demonstrate therapeutic non-inferiority compared to intravenous 5-FU and LV. The term
‘‘non-inferiority’’ was used rather than ‘‘equivalence’’ due to the fact that it is virtually
impossible to determine that two therapies are equivalent.
Two identical phase III trials were performed that randomized patients to oral
capecitabine 2500 mg/m2/day 2 weeks, every 3 weeks, or to 5-FU/LV on the daily 5
(Mayo Clinic schedule), every four weeks (10,11). Capecitabine was associated with a
higher objective response rate than 5-FU/LV (22.4% versus 13.2% by independent
review criteria, p < 0.0001) (12,13). Time to disease progression and overall survival
were virtually identical between the two treatments. Time to tumor progression (TTP)
was 4.6 months for capecitabine-treated patients and 4.7 months for 5-FU/LV-treated
3
patients (p = 0.95, progression hazard ratio = 1.0) and median survival was 12.9 months
for both (p = 0.91, death hazard ration = 1.0). Patients treated with daily bolus 5-FU/LV
were more likely to experience diarrhea, neutropenia, stomatitis, nausea, and alopecia,
while patients treated with capecitabine were more likely to experience hand–foot
syndrome and hyperbilirubinemia.
Based on its similar therapeutic efficacy to 5-FU/LV, its convenience, and its
acceptable tolerability profile, capecitabine was granted full approval by the FDA on
September 7, 2001.
1.3. Development of Irinotecan as Second-Line Therapy and its Integration Into
Front-Line Chemotherapy
Irinotecan binds the enzyme topoisomerase I, which prevents the uncoiling of
DNA during DNA synthesis and repair, leading to apoptosis (14). Irinotecan first entered
clinical trial in Japan in 1986. The results from phase I and early phase II studies began to
appear in the literature in 1990. By the time the first clinical trials were initiated in France
in 1990 and the United States in 1991, objective responses had been reported from Japan
and there was emerging recognition of the clinical potential of irinotecan (15).
There was clearly a need for another cytotoxic drug effective against advanced
colorectal cancer. Patients with progressive CRC following 5-FU had limited therapeutic
options beyond investigational agents. In the first phase II trial of irinotecan in Japan,
Shimada and colleagues reported a 27% objective response rate in a group of previously
treated and untreated patients. This prompted rapid movement of single-agent irinotecan
into phase II trials in patients with advanced colorectal cancer that had progressed
following 5-FU. Although objective response rates ranged from 11% to 27% in three
phase II trials performed in the United States, the combined data demonstrated a 15%
objective response rate, an additional 40% to 50% of patients with stable disease for at
least four months, a median survival of nine months, and a reduction in tumor-related
symptoms (14).
Following these studies, no consensus could be reached between several potential
designs for registration-directed phase III trials, which included comparison of irinotecan
to single-agent mitomycin C or BCNU or to best supportive care. Fortunately, an
alternative in the form of accelerated approval had become available, which allowed
drugs that demonstrated beneficial effects on surrogate endpoints associated with clinical
benefit to gain provisional approval based on the results of phase II trials. This provision
reflected acceptance of the fact that individuals with life-threatening illnesses such as
cancer and AIDS would be more willing to accept a greater degree of uncertainty, risk,
or side effects from a new therapy than individuals with less severe illness or for whom
effective therapies existed. The approval could be withdrawn if the confirmatory studies
failed to demonstrate clear benefit.
Using this mechanism in early 1996, irinotecan became the first new drug to be
approved for colorectal cancer in the United States in more than 30 years. Two years
later, the data from two phase III trials conducted in Europe demonstrated that irinotecan
improved survival in this setting when compared to either best supportive care or
infusional 5-FU. This enabled the FDA to convert irinotecan to full-approval status in
1999 (16,17).
4
Once a drug has been approved as a single agent in the refractory disease setting,
the next step in its development is to combine the drug with existing front-line therapy to
determine whether it improves therapeutic outcomes in that setting. Two phase III trials
evaluated the combination of irinotecan and 5-FU/LV in comparison with 5-FU/LV alone
as first-line chemotherapy for patients with advanced colorectal cancer.
One, conducted primarily in the United States, Israel, and Australia, used
irinotecan (125 mg/m2 infused over 90 minutes) added to bolus 5-FU (500 mg/m2) plus
LV (20 mg/m2) given weekly for four weeks every six weeks. This became known as the
IFL regimen (18). The other study, conducted primarily in Europe, compared irinotecan
added to infusional 5-FU administered once every two weeks (LV5FU2 or de Gramont
schedule) with the infusional 5-FU administered weekly (AIO schedule) (19). In both
studies, overall survival was prolonged when irinotecan was added to 5-FU/LV and there
were significant improvements in response rate, progression-free survival (PFS), a two-to
three-month improvement in median survival, and a 25% reduction in the death hazard
ratio. Although these improvements were associated with an increase in the frequency
and severity of adverse effects, including diarrhea, vomiting, and neutropenia, overall
quality of life was not impaired. As a result, in March of 2000, the FDA granted
expanded indication to irinotecan to include its use in the first-line treatment of advanced
colorectal cancer.
1.4. Oxaliplatin: Initial Data on Front-Line Therapy and Demonstration of its
Second-Line Efficacy
Oxaliplatin is a diaminocyclohexane platinum that is structurally and functionally
distinct from cisplatin and carboplatin. The platinum-DNA adducts formed by oxaliplatin
are bulkier and more hydrophobic and, therefore, more difficult to repair than those
formed by other platinums. Oxaliplatin entered clinical testing in 1986, but it was not
until 1990 that the single-agent maximum-tolerated dose was identified (20). In advanced
colorectal cancer, a combination of oxaliplatin with chronomodulated 5-FU and LV
resulted in a 58% response rate, a median PFS of 10 months, and a median overall
survival of 15 months in a group of 93 patients, 49% of whom had received prior
chemotherapy and/or radiotherapy (21). Over the ensuing years, similar phase II efficacy
data were reported using nonchronomodulated drug administration schedules for this
three-drug regimen.
In order to better delineate the contribution of oxaliplatin to front-line
chemotherapy, two phase III trials were undertaken in Europe in the mid-1990s using the
oxaliplatin, 5-FU, and LV combination. One compared chronomodulated 5-FU/LV to the
same regimen with oxaliplatin added (22). The other evaluated 5-FU given as a bolus and
infusion combined with LV (the so-called LV5FU2 regimen) versus that same regimen
with oxaliplatin added (23). While the addition of oxaliplatin to 5-FU/LV resulted in
more than a doubling of objective response rates and a 40% improvement in PFS, overall
survival was not significantly improved. Possible reasons offered for this therapeutic
inconsistency included the small sample size and high proportion of post study cross of
control patients to an oxaliplatin-containing second-line regimen.
The improvement in PFS, the primary endpoint for both studies, was sufficient to
garner drug approval in France in 1996 and in the European Regulatory Agency in 1999.
5
These data were brought before the U.S. Oncologic Drugs Advisory Committee in March
of 2000. At that time in the United States, overall survival was considered to be the most
important measure of efficacy, especially when the new agent was a cytotoxic compound
associated with clinically significant toxicity. No such survival advantage was seen in the
trials involving oxaliplatin. Not surprisingly, ODAC did not recommend the new drug
application for oxaliplatin for approval.
Addition of Irinotecan to the front-line therapy resulted in the lack of effective
therapeutic options for patients with progressed disease. This opened the door for the
evaluation of oxaliplatin as second-line chemotherapy.
Four hundred and sixty-three patients were randomized to 5-FU/LV administered
as the LV5FU2 regimen, single-agent oxaliplatin (85 mg/m2 every two weeks), or the
FOLFOX4 regimen (LV5FU2 plus oxaliplatin) (24). The objective response rate (RR)
was 9.9% for the FOLFOX4 group, 0% for the LV5FU2 group, and 1.3% for the
oxaliplatin monotherapy group with highly significant difference between the FOLFOX4
and LV5FU2 groups (p < 0.0001). Patients treated with FOLFOX4 also experienced a
longer time to tumor progression (TTP) than those treated with LV5FU2 (4.6 vs. 2.7
months; p < 0.0001). Based on a significant improvement in RR and TTP, the FDA
granted accelerated approval to oxaliplatin for use in combination with 5-FU/LV for the
treatment of patients with progressed advanced colorectal cancer following front-line
therapy (irinotecan, 5-FU/LV) on August 9, 2002
1.5. Comparison of Front-Line Combination Regimens
By the late 1990s, the challenges associated with multiple treatment options began
to emerge in the field of colorectal cancer. There were little comparative data available
for the various combinations involving irinotecan, oxaliplatin, and 5-FU/LV. N9741 was
originally designed to explore six combination chemotherapy regimens and compare
them to a reference standard of 5-FU/LV on a Mayo Clinic daily 5 schedule (26). Based
on emerging data on efficacy and safety, the trial was eventually truncated to just three
arms: IFL, FOLFOX4, and IROX (a combination of irinotecan and oxaliplatin). This trial
was particularly important, because IFL was the most popular first-line chemotherapy
regimen for advanced colorectal cancer in the United States, while FOLFOX4 was the
most popular regimen in Europe. IFL and FOLFOX do not differ only in terms of the
drugs contained in the regimen, but also in the way 5-FU is administered: as a weekly
bolus in IFL, and as a bolus followed by infusion in FOLFOX.
The trial demonstrated significant advantages for FOLFOX over IFL in terms of
RR (45% vs. 31%; p = 0.002), TTP (8.7 vs. 6.9 months; p = 0.0014), and median survival
(19.5 vs. 15.0 months; p = 0.0001) (26). There were no significant differences among the
groups in time to treatment discontinuation, although more patients treated with
FOLFOX discontinued therapy due to reasons other than disease progression compared
to patients on IFL. Based on the results of this trial, the approval of oxaliplatin was
expanded to include first-line treatment of advanced colorectal cancer on January 12,
2004.
6
1.6. Bevacizumab
Controlling tumor growth by inhibiting tumor angiogenesis is an attractive
concept, because the new blood vessels supplying the tumor are relatively small, leaky,
and more reliant upon angiogenic growth factors than larger, normal blood vessels. In
addition, endothelial cells were believed to lack the genetic instability of cancer cells and
considered less likely to mutate into a drug-resistant phenotype. Bevacizumab (Avastin1)
is a recombinant humanized monoclonal antibody directed against the vascular
endothelial growth factor, one of the most potent endothelial growth factors involved in
tumor-associated angiogenesis. Bevacizumab binds to vascular endothelial growth factor
before it can engage its receptor, thereby depriving the tumor of new blood vessel
formation required for further growth.
The development of bevacizumab began with a small, first-line, randomized phase
II trial in patients with metastatic colorectal cancer, comparing 5-FU/LV administered on
a weekly basis for six out of eight weeks (Roswell Park schedule) with either
bevacizumab (5 or 10 mg/kg every two weeks) or placebo (27). The results of this trial
suggested that the 5 mg/kg dose of bevacizumab could be safely combined with bolus
weekly 5-FU/LV and was associated with a very encouraging objective response rate of
40% (95% CI = 24–58%), median TTP of nine months (95% CI = 5.8–10.9 months), and
median survival of 21.5 months (range: 1.2–28.2 months). More patients in the
bevacizumab arms experienced a grade 3–4 adverse event including thrombotic events
(5%), abdominal pain (3%), and hypertension (3%).
These results prompted a large, registration-directed phase III study, designed
with three arms: IFL/bevacizumab, IFL/placebo, and 5-FU/LV (Roswell Park
schedule)/bevacizumab (4). Once IFL/bevacizumab combination was found to be
acceptably safe, the 5-FU/LV/bevacizumab arm was closed and the trial proceeded as a
two-arm study. The addition of bevacizumab to IFL significantly improved all measures
of therapeutic efficacy, including objective response rate, 44.8% versus 34.8% (p =
0.004); PFS 10.6 versus 6.2 months median (p < 0.001, HR for progression: 0.54); and
overall survival, 20.3 versus 15.6 months (p < 0.001, HR for death: 0.66). As observed in
earlier trials, the addition of bevacizumab to chemotherapy increased the rates of grade 3
hypertension, proteinuria, arterial thrombotic events, and gastrointestinal perforations.
In a smaller phase III trial with patients considered medically unfit for treatment
with IFL, the addition of bevacizumab to 5-FU/LV improved objective response rates
from 15% to 26% ( p = 0.055), PFS from 5.5 to 9.2 months ( p = 0.0002, progression HR
= 0.50), and median survival from 12.9 to 16.6 ( p = 0.16, death HR = 0.79). Similar
trends of increased toxicity were observed in this study. A pooled analysis of three
studies comparing 5-FU/LV to 5-FU/LV/bevacizumab demonstrated significant
improvements in all measures of efficacy (29).
Based on these studies, the FDA granted full approval to bevacizumab on
February 26, 2004 for use with a 5-FU-based chemotherapy regimen in the first-line
treatment of patients with metastatic colorectal cancer.
7
1.7. Cetuximab
Cetuximab is also a mouse–human chimeric IgG1 monoclonal antibody with high
affinity for EGF receptor. Unlike bevacizumab, cetuximab binds directly to the EGFR,
thereby blocking the signaling that occurs when a natural ligand binds to this receptor.
Following two small phase II trials that failed to clearly demonstrate the efficacy
of cetuximab to the FDA, a larger, randomized Phase II trial was designed to generate
definitive data required for drug registration (32). The trial was designed with a 2:1
randomization to the Irinotecan/cetuximab arm and required all patients with irinotecanrefractory disease to have EGFR-expressing tumors. A 23% objective response rate was
observed in the group treated with the Irinotecan/cetuximab combination, whereas an
11% response rate was reported in group treated with cetuximab alone (p = 0.007).
Similar trend was observed in other measures (PFS, 4.1 vs. 1.5 months; median survival,
8.6 vs. 6.9 months). A consistent correlation has been observed between intensity of skin
rash and increased likelihood of response and prolonged survival. Cetuximab-related
toxicities included acne-like skin rash and hypersensitivity reactions. The rash is
generally of cosmetic concern, but for some patients can be clinically significant. When
used in combination, cetuximab did not appear to lessen or exacerbate toxicities
associated with irinotecan. The FDA granted an accelerated approval for cetuximab on
February 12, 2004 based on this phase II data due to the beneficial outcome observed in
terms of PFS and response rate, in conjunction with tumor-related symptoms, in patients
refractory on 5-FU, Irinotecan and oxaliplatin.
CHAPTER 2: Drug Development for Advanced Renal Cell Carcinoma
Recent developments in the treatment of renal cell cancer (RCC) have generated
renewed excitement in an area of oncology where up to three years ago therapeutic
options were consistently limited and, at best, minimally effective. RCC, particularly the
clear cell subtype, represents an important example of how better understanding of
molecular pathogenesis can be successfully translated into more effective therapies. The
completion of several clinical trials with targeted agents has resulted in a shift in the
treatment paradigm of advanced RCC (34-37). However, considerable challenges remain
with both clear cell and non-clear cell subtypes of the disease, and metastatic RCC
remains a fatal disease for the majority of patients.
Over 54,000 new cases of RCC and 13,000 deaths will occur in the U.S. in 2008
and the incidence of these cancers has increased by approximately 2% per year. RCC
represents the third leading cause of death among genitourinary malignancies and the
twelfth leading cause of cancer death overall in the United States. Worldwide, the annual
mortality from RCC is over 100,000 patients (38). In the Czech Republic, 1,200 people
die annually, and the Czech Republic has one of the highest incidences of RCC in Europe
(2,800 cases).
The management of metastatic RCC has undergone a revolution in the last
decade. We came a long way from the use of debulking radical nephrectomy followed by
39, 40). More recently
8
systemic therapy targeted toward VEGF produced robust clinical effects for metastatic
RCC, leading to regulatory approval of two multikinase inhibitors - sorafenib
(Nexavar®) and sunitinib (Sutent®). In addition, a ligand-binding antibody, bevacizumab
(Avastin®) was approved in combination with IFN in Europe and is under consideration
by FDA in the US. The latest addition to our armamentarium includes temsirolimus
(Torisel®), an mTOR inhibitor with promising activity in patients with non-clear cell
RCC histologies and poor prognosis by MSKCC criteria. These advances have
collectively refined the management of metastatic RCC.
2.1. VEGF-Targeted Therapy in metastatic RCC
Inactivating mutations or methylation in the von Hippel-Lindau (VHL) gene were
observed in the majority of sporadic clear cell RCC tumors (41). Resulting constitutive
activation of the hypoxia response pathway leads to up-regulated expression of multiple
genes important for tumor angiogenesis, including VEGF and PDGF. Various strategies
have been developed to block these pathways, including antibodies that sequester VEGF,
such as bevacizumab (Avastin®), tyrosine kinase inhibitors that block the receptors for
VEGF and PDGF, such as sorafenib (Nexavar®) and sunitinib (Sutent®).
2.1.1. Sorafenib
Sorafenib is an orally bioavailable, bi-aryl urea originally identified as an
inhibitor of raf kinase, an enzyme involved in cellular proliferation that inhibits the
VEGF and PDGF receptor families (42). Sorafenib was investigated in a phase II,
randomized discontinuation trial, in which 202 patients with metastatic RCC were
evaluated. The overall tumor shrinkage rate was 71%, with a PFS advantage in the
patients receiving sorafenib (24 vs. 6 weeks, p = 0.0087) (43). A subsequent Phase III
randomized trial of sorafenib versus placebo in previously treated (cytokine-refractory)
metastatic RCC was conducted (34). Seven (2%) patients receiving the drug had an
objective response, defined by RECIST criteria. Significant advantages of sorafenib were
observed in other end points (stable disease, 78% vs. 55%; tumor shrinkage 74%; median
PFS, 24 vs. 12 weeks, P = 0.000001). PFS across all subgroups of patients receiving
sorafenib appeared to be superior to placebo, including a subset of patients who had not
received prior cytokine therapy.
The study was later modified to allow cross-over from placebo to sorafenib, and
after 6 months from cross-over the median overall survival was 19.3 months for
sorafenib-treated patients versus 15.9 months for placebo (44). A statistically significant
survival benefit was obscured by patient cross-over. Overall, sorafenib was well
tolerated, and side effects were manageable. The FDA granted approval of this agent in
December 2005 for the treatment of patients with advanced RCC.
The subsequent randomized Phase II trial evaluating sorafenib versus IFN- in
untreated metastatic RCC patients did not show sorafenib superiority to IFN in
improvement of PFS (5.6 vs. 5.7 months), although patient on sorafenib had a better
quality of life and symptom improvement. This surprising result might have been caused
by insufficient sorafenib dose (45). The original trials with sorafenib indicated that a dose
of 400 mg twice a day was well-tolerated and associated with antitumor activity.
9
Subsequent clinical trials have indicated that dose escalation up to 1600 mg/day is
feasible, and may be associated with increased antitumor activity (46).
In a trial evaluating the addition of sorafenib to IFN- therapy in untreated mRCC
patients, the treatment consisted of 8-week cycles of sorafenib 400 mg twice daily plus
10 MU of IFN- SC 3 times a week. The ORR by RECIST criteria was 42% (38% partial
response, 4% complete response). An additional 46% had stable disease for at least 1
cycle, including 8% with over 20% tumor shrinkage. Toxicities were mostly Grade ½.
Further investigation is required to demonstrate clinical benefit of this combination over
monotherapy.
2.1.2. Sunitinib
Sunitinib is an orally bioavailable inhibitor of VEGFR-2 and PDGFR-β. In two
sequentially conducted single-arm multicenter Phase II trials the activity of sunitinib was
investigated in total 169 cytokine-refractory metastatic RCC patients (48). The majority
of patients (87%) had clear cell histology and 93% of patients had undergone
cytoreductive nephrectomy. All patients had received prior cytokine-based therapy.
Patients were treated with 50 mg of sunitinib orally daily on a 4-week-on/2-week-off
cycle. The ORR was 34% and a median PFS was 8.3 months. These data led to the FDA
approval of this drug in January 2006 for the management of advanced RCC.
To evaluate the activity of sunitinib in previously untreated metastatic RCC
patients, a randomized Phase III study was undertaken (35). Previously untreated
metastatic RCC patients (n = 750) with clear cell histology were randomized 1:1 to
receive sunitinib (6-week cycles: 50 mg orally once daily for 4 weeks, followed by 2
weeks off [4/2 schedule]) or IFN- (6-week cycles: SC injection 9 MU given 3 times
weekly). The ORR was 31% versus 6% (P = 0.000001) and the median PFS was 11
versus 5 months in favor of sunitinib-treated patients (P = 0.00001). The most common
toxicities included fatigue/asthenia, diarrhea, stomatitis, dermatitis, and hypertension.
Finally, sunitinib also prolonged the OS (median 26.4 vs. 21.8 months, p=0.051) (16).
This trial has demonstrated that sunitinib is superior to IFN- in untreated advanced RCC
patients, making it one of several frontline treatment options for advanced RCC patients.
2.1.3. Bevacizumab
The clinical utility of bevacizumab in metastatic RCC was investigated in a
randomized Phase II trial, in which 116 patients with metastatic, cytokine-refractory
clear-cell RCC were randomized to receive placebo, low-dose (3 mg/kg) bevacizumab, or
high-dose (10 mg/kg) bevacizumab given intravenously every 2 weeks (51). The study
was designed to detect a two-fold TTP increase with either dose of bevacizumab versus
placebo (4.8 versus 2.5 months; P = 0.001 by log-rank test) with 10% ORR. Common
toxicity included hypertension and proteinuria, more commonly seen in the high-dose
bevacizumab arm.
The addition of an antiangiogenic agent to standard cytokines has also been
explored. Recently reported Phase III trial has evaluated bevacizumab plus IFN- versus
IFN- alone in untreated advanced RCC patients (37). The results revealed a high 30%
10
ORR and median PFS of 10.2 months for a combination arm vs. 5.6 months for IFN
(p<0.0001).
Another rational approach currently being evaluated is a simultaneous targeting of
two steps within the VEGF pathway (i.e., using a ligand binding agent with a small
tyrosine kinase inhibitor [TKI]). A Phase I/II trial evaluating the combination of
sorafenib with bevacizumab reported 53% ORR and 15.3 months PFS (52). The Eastern
Cooperative Oncology Group (ECOG) has started a randomized Phase II trial with
bevacizumab, bevacizumab/sorafenib, bevacizumab/temsirolimus or
temsirolimus/sorafenib combinations.
2.2. mTOR Targeted Therapy
Another emerging target in RCC is the enzyme mammalian target of rapamycin
(mTOR). This protein modulates a number of cellular processes, including proliferation,
nutrient uptake and metabolism, and HIF expression. Given its central role in cell
biology, the newer strategies for treating RCC now include agents that not only disrupt
VEGF or its receptor, but also mTOR.
2.2.1. Temsirolimus and Everolimus
Temsirolimus is an inhibitor of mammalian target of rapamycin (mTOR) - a
molecule implicated in multiple tumor-promoting intracellular signaling pathways,
including hypoxia-inducible factor (HIF) transcription (53). A randomized Phase III trial
was conducted in patients with poor-risk metastatic RCC as defined by existing
prognostic schema (36). Patients were equally randomized to receive IFN- up to 18 MU
SC 3 times a week, temsirolimus 25 mg IV once a week, or temsirolimus 15 mg IV once
a week plus IFN- 6 MU SC 3 times a week. Patients treated with temsirolimus had a
statistically longer survival than those treated with IFN- alone (10.9 vs. 7.3 months, P =
0.0069). There was no difference in the combination arm possibly as a result of a lower
dose of temsirolimus coupled with an increased number of patients unable to receive
temsirolimus secondary to IFN- -related toxicities. Further investigation of this agent is
planned in patients with fewer adverse risk features and in combination with VEGFtargeting therapies.
A recently reported Phase III randomized, placebo-controlled study evaluated the
activity of RAD-001 (Everolimus), an oral serine-threonine kinase inhibitor of mTOR, as
second-line therapy in advanced RCC (54). In this trial, 410 patients with metastatic
clear cell RCC were randomly assigned in a 2:1 ratio to everolimus (10 mg per day) or
placebo. The PFS was 4.0 months vs. 1.9 months on placebo (HR 0.3, 95%CI 0.22-0.40).
The PFS at 6 months was 26% on everolimus vs. 6% on placebo. Treatment-related
adverse events included mucositis, skin rash, pneumonitis, hypophosphatemia,
hyperglycemia, thrombocytopenia, anemia, and elevated liver function tests.
These studies demonstrate the importance of mTOR as a therapeutic target in RCC and
suggest a potential benefit of these agents in a broader RCC population.
11
2.3. Novel Agents Evaluated in mRCC
Several other novel agents that have shown activity in advanced RCC include
GW786034 (Pazopanib), a multitarget TKI that inhibits VEGFR-1, -2, -3, PDGFR- ,
PDGFR-β, and c-kit (55), AG013736 (Axitinib), an orally bioavailable small-molecule
TKI of VEGFR-2 and PDGFR-β (56). A Phase II single-arm, multicenter trial of
AG013736 in cytokine-refractory RCC patients (n = 52) demonstrated an ORR of 40%.
Stable disease was observed in 21 (40%) of patients with 20 of the patients experiencing
tumor shrinkage over 30%. Median TTP has not been reached with a median of 12 to 18
months of follow up for most patients. Similar to other small-molecule TKIs, most
toxicity was Grade 1 or 2, and included gastrointestinal, dermatologic, fatigue,
hypertension, and proteinuria. An additional study evaluating the activity of this agent in
sorafenib-refractory metastatic RCC patients is underway.
2.4. High-Dose Interleukin-2 Following VEGF-Targeted Therapy in mRCC
High-dose (HD) bolus interleukin-2 (IL-2) has been FDA approved for therapy of
metastatic RCC since 1992 based on its ability to induce durable responses in a small
percentage of patients (57, 58). The efficacy of HD IL-2 has subsequently been
confirmed in two separate large randomized trials (59, 60). However, due to substantial
toxicity, only specialized centers continue to offer this therapy with focus on developing
patient selection strategies to limit IL-2 therapy only to patients most likely to experience
clinical benefit (61, 62).
Since the responses to VEGF-targeted therapies are typically not complete or
durable, second line of treatment is necessary. The safety and efficacy of HD IL-2
following prior therapy with VEGF-targeted agents was explored in a retrospective
analysis of clinical outcomes of patients with mRCC and compared to the results of the
phase III Cytokine Working Group (CWG) trial that compared HD IL-2 alone to
subcutaneous IL-2 plus IFN (60). The analysis suggests that the toxicity of IL-2 therapy
may be higher in patients who have received prior VEGF-targeted therapy, compared
with the patients in the CWG trial who were untreated prior to that trial. This increase in
severe cardiovascular toxicity was limited only to patients who had received prior TKI
treatment and not to patients previously treated with bevacizumab alone. Sunitinib has
been demonstrated to reduce cardiac ejection fraction by at least 10% in 28% of patients
treated at the approved dose (63). In animal models, the mechanism of this decline in left
ventricular function appears to be direct cardiomyocyte toxicity through mitochondrial
injury. No patient treated with IL-2 following VEGF-targeted therapy experienced a
partial or complete response, which was significantly lower than the 23.2% response rate
reported for the HD IL-2 arm of the Phase III CWG trial (P=0.001). However, the clinical
significance of this result is unclear since 98% of patients in CWG trial were treatmentnaïve.
12
CHAPTER 3. Drug Development for the Treatment of Melanoma
Angiogenesis is a hallmark of melanoma progression. Antiangiogenic agents have
been infrequently tested in patients with advanced melanoma. Experience with most other
cancers suggests that combinations of antiangiogenic agents with either chemotherapy or
other targeted therapy will be needed for significant clinical benefit.
In melanoma, numerous cellular pathways important to cell proliferation,
apoptosis, or metastases have recently been shown to be activated. Activation occurs
through specific mutations (B-RAF, N-RAS, and PTEN) or changes in expression levels
of various proteins (PTEN, BCL-2, NF-κB, CDK2, and cyclin D1). Agents that block
these pathways are rapidly entering the clinical setting, including RAF inhibitors
(sorafenib), mitogen-activated protein kinase inhibitors (PD0325901), mTOR inhibitors
(CCI-779), and farnesylate transferase inhibitors (S115777) that inhibit N-RAS, and
proteosome inhibitors (PS-341) that block activation of nuclear factor-κB (NF-κB).
The evaluation of these agents alone, in combination with each other, or with
chemotherapy in patients with melanoma will be challenging. To rationally and optimally
develop these targeted agents, it will be critical to adequately test for the presence of the
presumed cellular target in tumor specimens and the effect of therapy on the proposed
target (biological response).
3.1. Targeting Cell Surface Receptors in Melanoma
Melanoma expresses a number of growth factor receptors, including EGFR,
PDGFR, and c-kit, and their expression levels changes with the disease progression (6466). Some preclinical studies suggested potential anti-melanoma effect of the inhibition
of these growth factors, which lead to cautious investigation of these inhibitors in
melanoma.
In a phase II study, patients experienced significant Grade 3 and 4 toxicity, and no
objective clinical responses were seen (67). The median TTP was 54 days and the median
OS was 200 days, with no patients being disease free at 6 months (43).
Immunohistochemical examination of the tumors revealed very low expression of c-kit,
as well as PDGFR- and PDGFR-, which did not appear to influence the clinical
outcome and it was concluded that imanitib is inactive as a single-agent therapy for
metastatic melanoma.
In a small phase II trial targeting EGFR, erlotinib was administered at its
maximum tolerated dose (150 mg/day). The treatment was well tolerated, but no
objective responses were attained, and only one patient had stable disease over 6 months.
These disappointing results maybe partially explained by the observation that in the nonsmall cell lung cancer the responses to EGFR inhibitors are not related to the surface
levels of the receptor, but rather to the activating mutations in the receptor, which are yet
to be identified in melanoma (68).
13
3.2. NF-κB Inactivation in the Treatment of Melanoma
The NF-κB-mediated gene transcription can be efficiently inactivated by using
proteasome 26S inhibitor PS-341 in vitro in melanoma, as well as in a murine xenograft
melanoma model, either alone or in combination with temozolomide (69-71). The
inhibition of the proteasome averts the breakdown of IκB, a cytosolic protein that binds
NF-κB and prevents its translocation to the nucleus.
Although a single arm phase II trial of PS-341 showed no activity in melanoma, a
small phase I trial of PS-341 in combination with temozolomide was started, in which
half of the patients had a decline in NF-κB activation in peripheral blood, 20S proteasome
inhibition in blood was 60-80 %, and 4 of 19 patients showed some tumor regression.
Immunohistochemistry of tumor biopsies obtained prior and post treatment showed
decrease in nuclear-translocated p65 NF-κB expression in two out of three samples. A
larger phase II trial of this combination in chemotherapy-naïve and pre-treated patients is
being currently initiated.
3.3. Anti-angiogenic Agents in Metastatic Melanoma
Angiogenesis is a critical step in the melanoma transformation. Serum levels of
VEGF increase with clinical stage in melanoma patients and can be predictive of worse
prognosis. In a trial evaluating the activitiy of bevacizumab alone and a combination of
bevacizumab and low-dose INF- in patients with melanoma, the combination arm
showed some promising activity and the trial was redesign to incorporate high-dose INF. Studies of bevacizumab and erlotinib have been proposed, since in vitro and in
xenograft melanoma models this combination results in a cooperative antitumor effect by
blocking VEGFR and EGFR1 pathways simultaneously (72, 73).
Another potentially worthwhile combination is chemotherapy (carboplatin +
paclitaxel) plus sorafenib as an example of antiangiogenic agent enhancing the effects of
chemotherapy. In a phase II study that evaluated the efficacy and safety of sorafenib plus
dacarbazine in patients with advanced melanoma, the median PFS was considerably
higher in the combination arm, and improvement of other clinical measures was observed
as well (PFS, TTP). While the treatment had an acceptable toxicity profile, there was no
significant difference in OS between the arms. However, these results are encouraging
and warrant further studies of this combination.
Thalimid/revlimid combination has shown important clinical effects in patients
with advanced melanoma, and although previously thought to be antiangiogenic agents,
the exact mechanism of their function remains unclear.
v3 is an integrin expressed in many cancers, including melanoma, but not in normal
melanocytes. Its expression in melanoma primary lesions increases as they progress from
the horizontal to vertical growth phase. The MEDI-522 antibody is a humanized form of
a murine antibody called LM609 that binds v3, triggering antibody-dependent cellular
cytotoxicity and potentially blocking tumor growth in mice by directly causing tumor cell
apoptosis and impairment of tumor angiogenesis (74). Preliminary results of a phase II
study of MEDI-522 alone or its combination with dacarbazine chemotherapy were
disappointing, showing some tumor response and slightly better, but still short, PFS only
in the combination arm.
14
3.4. Inhibition of Multiple Signaling Pathways in Melanoma
Many pathways are likely to contribute to melanoma resistance to cytotoxic
chemotherapy, including the PI3K/Akt pathway (75–79), MAPK pathway, and NF-κBmediated events. It has been shown that inhibition of both the MAPK pathway and NFκB in combination may produce enhanced antitumor effects (80). For example, PS-341
induces expression of an anti-apoptotic protein, Mcl-1, as a cell survival mechanism, so a
simultaneous inhibition of the MAPK pathway could depress expression of Mcl-1.
Apoptosis resistance is a hallmark of melanoma, and there are a number of new
agents in development attempting to overcome this property (71, 78, 81). IκB kinase-
inhibitor, such as BMS-345541, will block NF-κB activation more specifically and
effectively than a proteosome inhibitor (82). Inhibition of mTOR, a critical component of
the PI3K/Akt pathway, with agents such as CCI-779 (phase 2/3) and RAD001 (phase 1/2)
affords great promise (83–85). PTEN expression is either lost or the gene is mutated in a
number of melanomas, leading to activation of the PI3K/Akt pathway (77–79). Inhibition
of both RAS and RAF with the combination of R115777 (farnesylate transferase
inhibitor) and sorafenib may more effectively block the MAPK pathway than either agent
alone. Downstream from RAS are several signaling pathways, including the PI3K/Akt
pathway, that could be inhibited simultaneously with an agent such as R115777.
3.5. Multitargeted Agents with Activity Against VEGFR and Other Cell Surface
Receptors
SU011248, AG013736, and ZD6474 are all oral tyrosine kinase inhibitors that
already show promise in other cancers, including clear cell renal carcinoma (84). They
are effective inhibitors for the VEGFR2 receptor signaling but also block one or more
other receptors. Targets for both SU011248 and AG13736 include VEGFR2, PDGF, and
c-kit, whereas ZD6474 blocks both VEGFR2 and EGFR1. The ability of these agents to
inhibit multiple targets makes them of interest to investigate in patients with melanoma
alone, with chemotherapy, or with other targeted agents.
CONCLUSIONS
The emergence of five new drugs for the treatment of advanced colorectal cancer
over the past 10 years has doubled the median survival in this disease from 11 to 22
months. Effective therapies exist not only for first-line treatment, but for second-and
third-line treatment, as well. But our perspective must be tempered by the fact that very
few patients with metastatic colorectal cancer are cured, and five-year survival rates are
still less than 10%. While it is clear that further improvements are needed, it is not clear
how these new drugs for advanced colorectal cancer will be developed. It is likely that
the combination approach for the new drug development will be the most effective one in
this setting as well.
With multiple therapeutic options now available to patients with metastatic RCC,
the most appropriate sequencing of these therapies must be investigated. Sorafenib,
15
sunitinib and temsirolimus have already assumed a substantial role in the management of
advanced RCC, but their optimal usefulness is not well defined. Redundancy within
molecular pathways implicated in tumor cell growth, coupled with the ability for crosstalk
between the components of these pathways, suggests that single-target inhibition of
VEGF and its pathway may be insufficient to induce durable antitumor effects in all
patients.
The next five to ten years will offer physicians treating patients with metastatic
melanoma and the patients themselves an entirely new and different set of treatment
options to fight this disease. Deepening the understanding of melanoma genetics and
advances in anti-tumor immunity will provide new relevant targets for drug development.
Another promising treatment route for melanoma that requires further studies is using
antiangiogenic agents.
16
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