Serum protein profiling reveals baseline and pharmacodynamic biomarker signatures associated with clinical outcome in mCRC patients treated with chemotherapy ± cediranib.

BACKGROUND: This study evaluated soluble serum proteins as biomarkers to subset patients with metastatic colorectal cancer (mCRC) treated with chemotherapy±cediranib, a vascular endothelial growth factor (VEGF) signalling inhibitor (VEGFi). Exploring biomarkers at pre- and on-treatment may identify patient subgroups showing clinical benefit on cediranib combination. METHODS: Two hundred and seven serum proteins were analysed in 588 mCRC patients at pre- and on-treatment with chemotherapy (FOLFOX/CAPOX)±cediranib 20 mg. Patients were enrolled in the phase III trial HORIZON II. We correlated baseline biomarker signatures and pharmacodynamic (PD) biomarkers with PFS and OS. RESULTS: We identified a baseline signature (BS) of 47 biomarkers that included VEGFA, VEGFD, VEGFR2, VEGFR3 and TIE-2, which defined two distinct subgroups of patients. Patients treated with chemotherapy plus cediranib who had 'high' BS had shorter PFS (HR=1.82, P=0.003) than patients with 'low' BS. This BS did not correlate with PFS of the patients treated with chemotherapy plus placebo. In addition, we identified a profile of 16 PD proteins on treatment associated with PFS (HR=0.58, P<0.001) and OS (HR=0.52, P<0.001) in patients treated with chemotherapy plus cediranib. This PD profile did not correlate with PFS and OS in patients treated with chemotherapy plus placebo. CONCLUSIONS: Serum proteins may represent relevant biomarkers to predict the outcome of patients treated with VEGFi-based therapies. We report a BS and PD biomarkers that may identify mCRC patients showing increased benefit of combining cediranib with chemotherapy. These exploratory findings need to be validated in future prospective studies.

Prognostic/predictive value of 207 serum factors in colorectal cancer treated with cediranib and/or chemotherapy.

BACKGROUND: The prognostic and predictive value of multiple serum biomarkers was evaluated using samples from a randomised phase III study (HORIZON II) investigating chemotherapy with or without cediranib in metastatic colorectal cancer (mCRC). METHODS: Baseline levels of 207 protein markers were measured in serum samples from 582 HORIZON II (FOLFOX/XELOX plus cediranib 20 mg (n=330) or placebo (n=252)) patients. Median baseline values of each biomarker were used to categorise patients as high or low. Markers were then assessed for their association with efficacy, defined by progression-free survival (PFS) and overall survival (OS). A generalised boosted regression model identified markers of particular interest. RESULTS: Correlation of protein levels with PFS and OS suggested that multiple factors had a prognostic value, independent of treatment arm, including IL-6, IL-8, C-reactive protein (CRP), ICAM-1 and carcinoembryonic antigen (CEA). Among the angiogenesis regulators, low levels of vascular endothelial growth factor (VEGF), VEGF-D, VEGFR-1, VEGFR-3, NRP1 and Tie-2 correlated with better outcome. CONCLUSION: This large data set generated using serum samples from mCRC patients treated with chemotherapy and VEGF inhibitors, defines baseline characteristics for 207 serum proteins. Multiple prognostic factors were identified that could be disease related or predict which patients derive most benefit from 5-fluorouracil (5-FU)-based chemotherapy, meriting further exploration in prospective studies.

Prognostic and predictive value of VEGF, sVEGFR-2 and CEA in mCRC studies comparing cediranib, bevacizumab and chemotherapy.

BACKGROUND: The prognostic/predictive value of potential vascular endothelial growth factor (VEGF) signalling biomarkers was evaluated retrospectively using samples from two randomized Phase III studies (HORIZON II and III) investigating cediranib in metastatic colorectal cancer (mCRC). METHODS: Baseline levels of VEGF, soluble VEGF receptor-2 (sVEGFR-2) and carcinoembryonic antigen (CEA) were measured in plasma/serum samples collected from patients participating in HORIZON II (n=860; FOLFOX/XELOX plus cediranib 20 mg (n=502) or placebo (n=358)) and HORIZON III (n=1422; mFOLFOX6 plus cediranib 20 mg (n=709) or bevacizumab (n=713)). Median biomarker baseline levels determined cutoff values for the patient subgroups. RESULTS: Baseline data were available for 88-97% of patients/study (>2000 patients). In both the studies, high baseline VEGF and CEA were associated with worse outcomes for progression-free survival (PFS) and overall survival (OS) independent of treatment (HORIZON II OS: VEGF, hazard ratio (HR)=1.35 (95% confidence interval (CI): 1.12-1.63); CEA, HR=1.63 (1.36-1.96); HORIZON III OS: VEGF, HR=1.32 (1.12-1.54); CEA, HR=1.50 (1.29-1.76)). sVEGFR-2 was not prognostic for PFS/OS. Baseline VEGF and CEA were not predictive for PFS/OS outcome to cediranib treatment; low sVEGFR-2 was associated with a trend towards improved cediranib effect in HORIZON II. CONCLUSION: Baseline VEGF and CEA levels were treatment-independent prognostic biomarkers for PFS and OS in both the studies.

Bax and adenine nucleotide translocator cooperate in the mitochondrial control of apoptosis.

The proapoptotic Bax protein induces cell death by acting on mitochondria. Bax binds to the permeability transition pore complex (PTPC), a composite proteaceous channel that is involved in the regulation of mitochondrial membrane permeability. Immunodepletion of Bax from PTPC or purification of PTPC from Bax-deficient mice yielded a PTPC that could not permeabilize membranes in response to atractyloside, a proapoptotic ligand of the adenine nucleotide translocator (ANT). Bax and ANT coimmunoprecipitated and interacted in the yeast two-hybrid system. Ectopic expression of Bax induced cell death in wild-type but not in ANT-deficient yeast. Recombinant Bax and purified ANT, but neither of them alone, efficiently formed atractyloside-responsive channels in artificial membranes. Hence, the proapoptotic molecule Bax and the constitutive mitochondrial protein ANT cooperate within the PTPC to increase mitochondrial membrane permeability and to trigger cell death.

Bax- and Bak-induced cell death in the fission yeast Schizosaccharomyces pombe.

The effects of the expression of the human Bcl-2 family proteins Bax, Bak, Bcl-2, and Bcl-XL were examined in the fission yeast Schizosaccharomyces pombe and compared with Bax-induced cell death in mammalian cells. Expression of the proapoptotic proteins Bax and Bak conferred a lethal phenotype in this yeast, which was strongly suppressed by coexpression of the anti-apoptotic protein Bcl-XL. Bcl-2 also partially abrogated Bax-mediated cytotoxicity in S. pombe, whereas a mutant of Bcl-2 (Gly145Ala) that fails to heterodimerize with Bax or block apoptosis in mammalian cells was inactive. However, other features distinguished Bax- and Bak-induced death in S. pombe from animal cell apoptosis. Electron microscopic analysis of S. pombe cells dying in response to Bax or Bak expression demonstrated massive cytosolic vacuolization and multifocal nuclear chromatin condensation, thus distinguishing this form of cell death from the classical morphological features of apoptosis seen in animal cells. Unlike Bax-induced apoptosis in 293 cells that led to the induction of interleukin-1 beta-converting enzyme (ICE)/CED-3-like protease activity, Bax- and Bak-induced cell death in S. pombe was accompanied neither by internucleosomal DNA fragmentation nor by activation of proteases with specificities similar to the ICE/CED-3 family. In addition, the baculovirus protease inhibitor p35, which is a potent inhibitor of ICE/CED-3 family proteases and a blocker of apoptosis in animal cells, failed to prevent cell death induction by Bax or Bak in fission yeast, whereas p35 inhibited Bax-induced cell death in mammalian cells. Taken together, these findings suggest that Bcl-2 family proteins may retain an evolutionarily conserved ability to regulate cell survival and death but also indicate differences in the downstream events that are activated by overexpression of Bax or Bak in divergent cell types.

Transforming growth factor beta-treated normal fibroblasts eliminate transformed fibroblasts by induction of apoptosis.

Transforming growth factor beta (TGF-beta) induces normal fibroblasts to perform an inhibitory effect directed against transformed cells (P. Höfler, I. Wehrle, and G. Bauer, Int. J. Cancer, 54: 125-130, 1993). Coculture of normal fibroblasts with transformed cells, either resistant to G 418 or expressing Mx antigen detectable by specific immunofluorescence, allowed discrimination between three theoretical mechanisms of inhibition: irreversible inhibition of proliferation; reversion to the nontransformed phenotype; or elimination of transformed cells. Our data demonstrate that normal fibroblasts treated with TGF-beta are able to eliminate transformed cells by induction of apoptosis. Sensitivity against TGF-beta-induced elimination seems to be a general feature of in vitro-transformed cell lines. TGF-beta-induced elimination of transformed fibroblasts by their untransformed counterparts is proposed as a potential potent control point in carcinogenesis, which may lead to the suppression of transformed cells.

Bcl-2 family proteins and mitochondria.

The Bcl-2 family of proteins plays a pivotal role in regulating cell life and death. Many of these proteins reside in the outer mitochondrial membrane, oriented towards the cytosol. Cytoprotective Bcl-2 family proteins such as Bcl-2 and Bcl-XL prevent mitochondrial permeability transition pore opening and release of apoptogenic proteins from mitochondria under many circumstances that would otherwise result in either apoptosis or necrosis. In contrast, some pro-apoptotic members of this family such as Bax can induce these destructive changes in mitochondria in both mammalian cells and when expressed exogenously in yeast. The mechanisms by which Bcl-2 family proteins control cell life and death remain elusive, but may include both the ability to form ion channels or pores in membranes and physical interactions with a variety of proteins implicated in apoptosis regulation.

Defective Bax activation in Hodgkin B-cell lines confers resistance to staurosporine-induced apoptosis.

Deregulated apoptosis represents an important hallmark of tumor cells. Here we investigated the induction of cell death signaling pathways in cell lines previously established from patients with Hodgkin's disease. Our data show that Hodgkin's disease derived B-cell lines uniformly proved resistant to staurosporine, a protein kinase C inhibitor that preferentially stimulates the mitochondrial apoptotic pathway. Contrary to control cell lines, staurosporine failed to induce cytochrome c release from mitochondria in Hodgkin derived B-cells. Correspondingly, activation of caspases was not observed in these cells. In staurosporine-treated Hodgkin cells Bax remained in its inactive state, indicating that these cell lines have a defect in this crucial step in apoptotic signaling upstream of the mitochondria. Our results suggest that the failure to activate Bax might represent a common defect of Hodgkin tumor cells of the B-cell lineage.

Interference of bcl-2 with intercellular control of carcinogenesis.

Induction of apoptosis in transformed fibroblasts by surrounding normal cells has been discussed as a potent early control step in carcinogenesis. According to this hypothesis, tumor progression should require resistance of transformed cells against this TGF-beta-triggered control mechanism. Here we show that Bcl-2, a protein involved in inhibition of apoptosis, can protect transformed cells from induction of apoptosis by surrounding cells. Rather than acting on the transformation process itself, Bcl-2 may thus represent an efficient modulator of carcinogenesis at an intercellular level.

Reactive oxygen species as mediators of the transformed phenotype.

Reactive oxygen species (ROS) are known to be involved in different pro- and anticarcinogenic mechanisms. However, their influence on the maintenance of the transformed phenotype has not been studied so far. Here we show that the anchorage-independent growth of transformed murine fibroblasts is inhibited by antioxidants and radical scavengers in a concentration-dependent and reversible manner. These agents also reduce TGF-beta-dependent stimulation of colony formation in soft agar, pointing to their specific interference with TGF-beta-triggered signal chains involved in the maintenance of the transformed state.

Reactive oxygen species act at both TGF-beta-dependent and -independent steps during induction of apoptosis of transformed cells by normal cells.

We have recently shown that TGF-beta-treated normal fibroblasts can induce apoptosis of transformed cells. The overall process was inhibited by antioxidants and radical scavengers, pointing to a role of reactive oxygen species (ROS). To define the ROS-dependent steps precisely, our experimental system was dissected into three phases. During phase I, TGF-beta 1 induced production and release of apoptosis-inducing signal molecules by normal cells. In phase II, these signal molecules were transferred between normal and transformed cells. During phase III, transformed cells went into apoptosis. The use of antibody directed against TGF-beta revealed that TGF-beta was required only during phase I. Application of radical scavengers and antioxidants at defined phases revealed that reactive oxygen species are involved specifically with biochemical processes induced by TGF-beta in normal cells and early in signal transfer between normal cells and transformed cells. These data therefore point to a functional role of reactive oxygen species both for the TGF-beta 1-induced signal pathway in normal cells and for the induction of apoptosis in transformed cells.

Catechol interferes with TGF-beta-induced elimination of transformed cells by normal cells: implications for the survival of transformed cells during carcinogenesis.

We have recently shown that TGF-beta-treated normal fibroblasts are able to induce apoptosis of transformed fibroblasts, leading to their elimination. Here we describe a test system that allows the quantitative analysis of the elimination of G418-resistant transformed cells by TGF-beta-treated normal cells. This assay system was used to screen for substances that interfere with the elimination of transformed cells. Catechol and hydroquinone, but not resorcinol, were found to represent potent antagonists of TGF-beta-induced elimination of transformed cells by normal cells. Protection of transformed cells from negative effects derived from their cellular environment defines a hitherto unrecognized crucial mechanism for the survival of transformed cells. The protective effect of catechol as seen in this experimental system may act in concert with its co-carcinogenic and promoting activities during carcinogenesis.

Methods of assaying Bcl-2 and Bax family proteins in yeast.

Bcl-2 family proteins play an evolutionarily conserved role in regulating the life and death of the cell. Certain proapoptotic members of the Bcl-2 family, Bax and Bak, have intrinsic cytotoxic activities in that they not only induce or sensitize mammalian cells to undergo apoptosis but also display a lethal phenotype when ectopically expressed in two yeast species Saccharomyces cerevisiae and Schizosaccharomyces pombe. Furthermore, the antiapoptotic Bcl-2 and Bcl-XL proteins can protect yeast against Bax-mediated lethality, suggesting that the death-regulatory functions of these Bcl-2 family proteins are well preserved in yeast. These observations provide the opportunity to study the function of Bcl-2 family proteins in genetically tractable yeast and to apply classical yeast genetics and functional cloning approaches to the dissection of programmed cell death pathway regulated by Bcl-2 family proteins. We describe here methods used in our laboratory to express and to study the functions of Bcl-2 family proteins in both the budding yeast S. cerevisiae and the fission yeast S. pombe.

Bax directly induces release of cytochrome c from isolated mitochondria.

Bax is a pro-apoptotic member of the Bcl-2 protein family that resides in the outer mitochondrial membrane. It is controversial whether Bax promotes cell death directly through its putative function as a channel protein versus indirectly by inhibiting cellular regulators of the cell death proteases (caspases). We show here that addition of submicromolar amounts of recombinant Bax protein to isolated mitochondria can induce cytochrome c (Cyt c) release, whereas a peptide representing the Bax BH3 domain was inactive. When placed into purified cytosol, neither mitochondria nor Bax individually induced proteolytic processing and activation of caspases. In contrast, the combination of Bax and mitochondria triggered release of Cyt c from mitochondria and induced caspase activation in cytosols. Supernatants from Bax-treated mitochondria also induced caspase processing and activation. Recombinant Bcl-XL protein abrogated Bax-induced release of Cyt c from isolated mitochondria and prevented caspase activation. In contrast, the broad-specificity caspase inhibitor benzyloxycarbonyl-valinyl-alaninyl-aspartyl-(0-methyl)- fluoromethylketone (zVAD-fmk) and the caspase-inhibiting protein X-IAP had no effect on Bax-induced release of Cyt c from mitochondria in vitro but prevented the subsequent activation of caspases in cytosolic extracts. Unlike Ca2+, a classical inducer of mitochondrial permeability transition, Bax did not induce swelling of mitochondria in vitro. Because the organellar swelling caused by permeability transition causes outer membrane rupture, the findings, therefore, dissociate these two events, implying that Bax uses an alternative mechanism for triggering release of Cyt c from mitochondria.

Pro-caspase-3 is a major physiologic target of caspase-8.

The apoptotic signal triggered by ligation of members of the death receptor family is promoted by sequential activation of caspase zymogens. We show here that in a purified system, the initiator caspases-8 and -10 directly process the executioner pro-caspase-3 with activation rates (kcat/Km) of 8.7 x 10(5) and 2.8 x 10(5) M-1 s-1, respectively. These rates are of sufficient magnitude to indicate direct processing in vivo. Differentially processed forms of caspase-3 that accumulate during its activation have similar rates of activation, activities, and specificities. The pattern and rate of caspase-8 induced activation of pro-caspase-3 in cytosolic extracts was the same as in a purified system. Moreover, immunodepletion of a putative intermediary in the pathway to activation, pro-caspase-9, was without consequence. Taken together these data demonstrate that the initiator caspase-8 can directly activate pro-caspase-3 without the requirement for an accelerator. The in vitro data thus help to deconvolute previous in vivo transfection studies which have debated the role of a direct versus indirect transmission of the apoptotic signal generated by ligation of death receptors.