ID1 and ID3 regulate the self-renewal capacity of human colon cancer-initiating cells through p21

ID proteins regulate diverse aspects of cancer progression and provide novel therapeutic opportunities

The inhibitor of differentiation (ID) proteins are helix-loop-helix transcriptional repressors with established roles in stem cell self-renewal, lineage commitment, and niche interactions. While deregulated expression of ID proteins in cancer was identified more than a decade ago, emerging evidence has revealed a central role for ID proteins in neoplastic progression of multiple tumor types that often mirrors their function in physiological stem and progenitor cells. ID proteins are required for the maintenance of cancer stem cells, self-renewal, and proliferation in a range of malignancies. Furthermore, ID proteins promote metastatic dissemination through their role in remodeling the tumor microenvironment and by promoting tumor-associated endothelial progenitor cell proliferation and mobilization. Here, we discuss the latest findings in this area and the clinical opportunities that they provide.

Inhibitor of DNA-binding protein 1 knockdown arrests the growth of colorectal cancer cells and suppresses hepatic metastasis in vivo

Inhibitor of DNA-binding protein 1 (ID1) is commonly abnormally overexpressed in colorectal cancer (CRC); yet, the functional significance of ID1 in the growth and invasive properties of CRC cells remains largely unclear. The present study investigated the effects of ID1 downregulation on the cell growth and metastatic features of CRC. Using lentiviral shRNA infection, stable ID1-knockdown (KD) HCT116 and SW620 cells, human metastatic CRC cell lines, were created. In vitro, the migration/invasion capacity of the ID1-KD CRC cells was assessed by a wound healing assay. The activities of MMP2 and MMP-9 were measured by gelatin zymography. The expression of CXC chemokine receptor 4 (CXCR4), PCNA and survivin were determined by immunoblot analysis and qRT-PCR. The effects of ID1 knockdown on tumor growth and hepatic metastasis were demonstrated by a xenograft study in mice. The results showed evident decreases in proliferation, migration and invasion and an increased apoptosis rate in the ID1-KD CRC cells. Similarly, ID1 knockdown significantly decreased mRNA and protein levels of PCNA, survivin, CXCR4, MMP2 and MMP9. Overexpression of CXCR4 antagonized the negative effect on the migration and invasion abilities of the ID1-KD cells. As compared with the control, ID1 knockdown prevented tumor growth and profoundly suppressed hepatic metastasis in vivo. The present study demonstrated the significance of ID1 in colon cancer progression, and its effect on tumor invasiveness and metastatic properties may be partly dependent on CXCR4.

A microRNA-operated switch of asymmetric-to-symmetric cancer stem cell divisions

Defective asymmetric cell divisions of stem and progenitor cells are associated with tumorigenesis by a largely unknown mechanism. A signalling axis involving Snail, microRNA-146a and Numb is now shown to regulate the switch between symmetric and asymmetric cell division in colorectal cancer stem cells.

P21 and CD166 as predictive markers of poor response and outcome after fluorouracil-based chemoradiotherapy for the patients with rectal cancer

Background

Pre-operative chemoradiotherapy (CRT) is the standard treatment in clinical stage T3/4 or node positive rectal cancer. However, there are no established biomarkers that can predict the pathological response and clinical outcome to CRT.

Methods

Immunohistochemical staining was performed in tissue arrays constructed from core tissue specimens taken before treatment and from operative specimens from 112 patients who received 5-FU based pre-operative CRT and surgery. Expression of Ki67, TS, BAX, EpCAM, p53, p21, EGFR, CD44, CD133, CD166, HIF1α and ALDH1 were assessed and correlated with tumor regression grades and disease free survival.

Results

Of the 112 patients (M/F 74/38, median age: 62), 20 (17.9%) patients achieved pathologic complete remission (pCR). In analyzing the associations between marker expressions and tumor regression grades, high p21 expression at the pretreatment biopsy was significantly associated with non-pCR (p = 0.022) and poor disease free survival (median DFS - low vs high p21: 75.8 vs 58.1 months, p = 0.002). In the multivariate analysis, high p21 expression level at the pre-treatment biopsy was significantly associated with poor DFS (p = 0.001, HR 6.14; 95% CI 2.03, 18.55). High CD166 expression level at the pretreatment biopsy was also associated with poor DFS (p = 0.003; HR 5.61; 95% CI 1.81, 17.35).

Conclusion

These show high p21 and CD166 expression at the pretreatment biopsy were associated with tumor regression and poor prognosis in patients treated with 5-FU based CRT. Larger, prospective and functional studies are warranted to determine the role of p21 and CD166 as predictive biomarker of response to CRT.

Id proteins regulate capillary repair and perivascular cell proliferation following ischemia-reperfusion injury

Acute kidney injury (AKI) results in microvascular damage that if not normally repaired, may lead to fibrosis. The Id1 and 3 proteins have a critical role in promoting angiogenesis during development, tumor growth and wound repair by functioning as dominant negative regulators of bHLH transcription factors. The goal of this study was to determine if Id proteins regulate microvascular repair and remodeling and if increased Id1 expression results in decreased capillary loss following AKI. The effect of changes in Id expression in vivo was examined using Id1−/−, Id3RFP/+ (Id1/Id3 KO) and Tek (Tie2)-rtTA, TRE-lacz/TRE Id1 (TRE Id1) mice with doxycycline inducible endothelial Id1 and β-galactosidase expression. Id1 and 3 were co-localized in endothelial cells in normal adult kidneys and protein levels were increased at day 3 following ischemia-reperfusion injury (IRI) and contralateral nephrectomy. Id1/Id3 KO mice had decreased baseline capillary density and pericyte coverage and increased tubular damage following IRI but decreased interstitial cell proliferation and fibrosis compared with WT littermates. No compensatory increase in kidney size occurred in KO mice resulting in increased creatinine compared with WT and TRE Id1 mice. TRE Id1 mice had no capillary rarefaction within 1 week following IRI in comparison with WT littermates. TRE Id1 mice had increased proliferation of PDGFRβ positive interstitial cells and medullary collagen deposition and developed capillary rarefaction and albuminuria at later time points. These differences were associated with increased Angiopoietin 1 (Ang1) and decreased Ang2 expression in TRE Id1 mice. Examination of gene expression in microvascular cells isolated from WT, Id1/Id3 KO and TRE Id1 mice showed increased Ang1 and αSMA in Id1 overexpressing cells and decreased pericyte markers in cells from KO mice. These results suggest that increased Id levels following AKI result in microvascular remodeling associated with increased fibrosis.

The ID proteins: master regulators of cancer stem cells and tumour aggressiveness

Inhibitor of DNA binding (ID) proteins are transcriptional regulators that control the timing of cell fate determination and differentiation in stem and progenitor cells during normal development and adult life. ID genes are frequently deregulated in many types of human neoplasms, and they endow cancer cells with biological features that are hijacked from normal stem cells. The ability of ID proteins to function as central 'hubs' for the coordination of multiple cancer hallmarks has established these transcriptional regulators as therapeutic targets and biomarkers in specific types of human tumours.

Cervical cancer cells with positive Sox2 expression exhibit the properties of cancer stem cells

Background

Although Sox2 expression has been found in several types of cancer, it has not yet been used to identify or isolate CSCs in somatic carcinoma.

Methods

SiHa and C33A cells stably transfected with a plasmid containing human Sox2 transcriptional elements driving the enhanced green fluorescent protein (EGFP) reporter were sorted into the Sox2-positive and the Sox2-negative populations by FACS, and Sox2 expression was detected by western blot and immunohistochemistry. The differentiation, self-renewal and tumor formation abilities, as well as the expression of the stemness and the EMT related genes of the Sox2-positive and the Sox2-negative cervical cancer cells were characterized in vitro and in vivo.

Results

A pSox2/EGFP system was used to separate the Sox2-positive and the Sox2-negative cells from cervical cancer cell lines, SiHa and C33A cells. Compared with the Sox2-negative cells, the Sox2-positive SiHa and C33A cells exhibited greater capacities for self-renewal, differentiation and tumor formation. Furthermore, Sox2-positive SiHa and C33A cells expressed higher levels of stemness-related genes, such as Sox2/Bmi-1/Oct4/ALDH1, and EMT-related genes, such as vimentin/snail/β-catenin. Taken together, all these results indicated that cells expressing endogenous Sox2 are CSCs in cervical carcinomas.

Conclusion

This study is the first to establish a functional link between endogenous Sox2 expression and CSCs in cervical carcinomas. Additionally, this study demonstrated that it is feasible to develop a tool to isolate CSCs from somatic tumors based on the expression of the endogenous nuclear protein Sox2 instead of cell surface markers.

MET signaling in colon cancer stem-like cells blunts the therapeutic response to EGFR inhibitors

Metastatic colorectal cancer remains largely incurable, although in a subset of patients, survival is prolonged by new targeting agents such as anti-EGF receptor (anti-EGFR) antibodies. This disease is believed to be supported by a subpopulation of stem-like cells termed colon cancer-initiating cell (CCIC), which may also confer therapeutic resistance. However, how CCICs respond to EGFR inhibition has not been fully characterized. To explore this question, we systematically generated CCICs through spheroid cultures of patient-derived xenografts of metastatic colorectal cancer. These cultures, termed "xenospheres," were capable of long-term self-propagation in vitro and phenocopied the original patient tumors in vivo, thus operationally defining CCICs. Xenosphere CCICs retained the genetic determinants for EGFR therapeutic response in vitro and in xenografts; like the original tumors, xenospheres harboring a mutated KRAS gene were resistant to EGFR therapy, whereas those harboring wild-type RAS pathway genes (RAS(wt)) were sensitive. Notably, the effects of EGFR inhibition in sensitive CCICs could be counteracted by cytokines secreted by cancer-associated fibroblasts. In particular, we found that the MET receptor ligand hepatocyte growth factor (HGF) was especially active in supporting in vitro CCIC proliferation and resistance to EGFR inhibition. Ectopic production of human HGF in CCIC xenografts rendered the xenografts susceptible to MET inhibition, which sensitized the response to EGFR therapy. By showing that RAS(wt) CCICs rely on both EGFR and MET signaling, our results offer a strong preclinical proof-of-concept for concurrent targeting of these two pathways in the clinical setting.

The role of microRNAs in the regulation of cancer stem cells

Cancer stem cells (CSCs) have been reported in many human tumors and are proposed to drive tumor initiation and progression. CSCs share a variety of biological properties with normal somatic stem cells such as the capacity for self-renewal, the propagation of differentiated progeny, and the expression of specific cell surface markers and stem cell genes. However, CSCs differ from normal stem cells in their chemoresistance and tumorigenic and metastatic activities. Despite their potential clinical importance, the regulation of CSCs at the molecular level is not well-understood. MicroRNAs (miRNAs) are a class of endogenous non-coding RNAs that play an important role in the regulation of several cellular, physiological, and developmental processes. Aberrant miRNA expression is associated with many human diseases including cancer. miRNAs have been implicated in the regulation of CSC properties; therefore, a better understanding of the modulation of CSC gene expression by miRNAs could aid the identification of promising biomarkers and therapeutic targets. In the present review, we summarize the major findings on the regulation of CSCs by miRNAs and discuss recent advances that have improved our understanding of the regulation of CSCs by miRNA networks and may lead to the development of miRNA therapeutics specifically targeting CSCs.

Id proteins: small molecules, mighty regulators

The family of inhibitor of differentiation (Id) proteins is a group of evolutionarily conserved molecules, which play important regulatory roles in organisms ranging from Drosophila to humans. Id proteins are small polypeptides harboring a helix-loop-helix (HLH) motif, which are best known to mediate dimerization with other basic HLH proteins, primarily E proteins. Because Id proteins do not possess the basic amino acids adjacent to the HLH motif necessary for DNA binding, Id proteins inhibit the function of E protein homodimers, as well as heterodimers between E proteins and tissue-specific bHLH proteins. However, Id proteins have also been shown to have E protein-independent functions. The Id genes are broadly but differentially expressed in a variety of cell types. Transcription of the Id genes is controlled by transcription factors such as C/EBPβ and Egr as well as by signaling pathways triggered by different stimuli, which include bone morphogenic proteins, cytokines, and ligands of T cell receptors. In general, Id proteins are capable of inhibiting the differentiation of progenitors of different cell types, promoting cell-cycle progression, delaying cellular senescence, and facilitating cell migration. These properties of Id proteins enable them to play significant roles in stem cell maintenance, vasculogenesis, tumorigenesis and metastasis, the development of the immune system, and energy metabolism. In this review, we intend to highlight the current understanding of the function of Id proteins and discuss gaps in our knowledge about the mechanisms whereby Id proteins exert their diverse effects in multiple cellular processes.

Self-renewal as a therapeutic target in human colorectal cancer

Tumor recurrence following treatment remains a major clinical challenge. Evidence from xenograft models and human trials indicates selective enrichment of cancer-initiating cells (CICs) in tumors that survive therapy. Together with recent reports showing that CIC gene signatures influence patient survival, these studies predict that targeting self-renewal, the key 'stemness' property unique to CICs, may represent a new paradigm in cancer therapy. Here we demonstrate that tumor formation and, more specifically, human colorectal CIC function are dependent on the canonical self-renewal regulator BMI-1. Downregulation of BMI-1 inhibits the ability of colorectal CICs to self-renew, resulting in the abrogation of their tumorigenic potential. Treatment of primary colorectal cancer xenografts with a small-molecule BMI-1 inhibitor resulted in colorectal CIC loss with long-term and irreversible impairment of tumor growth. Targeting the BMI-1-related self-renewal machinery provides the basis for a new therapeutic approach in the treatment of colorectal cancer.

Small-molecule inhibitors of USP1 target ID1 degradation in leukemic cells

Inhibitor of DNA binding 1 (ID1) transcription factor is essential for the proliferation and progression of many cancer types, including leukemia. However, the ID1 protein has not yet been therapeutically targeted in leukemia. ID1 is normally polyubiquitinated and degraded by the proteasome. Recently, it has been shown that USP1, a ubiquitin-specific protease, deubiquitinates ID1 and rescues it from proteasome degradation. Inhibition of USP1 therefore offers a new avenue to target ID1 in cancer. Here, using a ubiquitin-rhodamine-based high-throughput screening, we identified small-molecule inhibitors of USP1 and investigated their therapeutic potential for leukemia. These inhibitors blocked the deubiquitinating enzyme activity of USP1 in vitro in a dose-dependent manner with an IC50 in the high nanomolar range. USP1 inhibitors promoted the degradation of ID1 and, concurrently, inhibited the growth of leukemic cell lines in a dose-dependent manner. A known USP1 inhibitor, pimozide, also promoted ID1 degradation and inhibited growth of leukemic cells. In addition, the growth of primary acute myelogenous leukemia (AML) patient-derived leukemic cells was inhibited by a USP1 inhibitor. Collectively, these results indicate that the novel small-molecule inhibitors of USP1 promote ID1 degradation and are cytotoxic to leukemic cells. The identification of USP1 inhibitors therefore opens up a new approach for leukemia therapy.

Small molecule antagonist of the bone morphogenetic protein type I receptors suppresses growth and expression of Id1 and Id3 in lung cancer cells expressing Oct4 or nestin

Background

Bone morphogenetic proteins (BMP) are embryonic morphogens that are aberrantly expressed in lung cancer. BMPs mediate cell fate decisions and self-renewal of stem cells, through transcription regulation of inhibitor of differentiation protein/DNA binding proteins (Id1-3). Inhibition of BMP signaling decreases growth and induces cell death of lung cancer cells lines by downregulating the expression of Id proteins. It is not known whether the BMP signaling cascade regulates growth and the expression of Id proteins of lung cancer cells expressing the stem cell markers Oct4 and/or nestin.

Methods

Lung cancer cells expressing Oct4 or nestin were isolated from lung cancer cell lines by stably transfecting the Oct4 promoter or nestin promoter expression vectors that induce expression of the green fluorescent protein reporter.

Results

Our studies suggest that lung cancer cells expressing Oct4 or nestin are different cell populations. Microarray and quantitative RT-PCR demonstrated that the expression of specific stem cell markers were different between isolated Oct4 and nestin cells. Both the Oct4 and nestin populations were more tumorigenic than controls but histologically they were quite different. The isolated Oct4 and nestin cells also responded differently to inhibition of BMP signaling. Blockade of BMP signaling with the BMP receptor antagonist DMH2 caused significant growth inhibition of both the Oct4 and nestin cell populations but only increased cell death in the nestin population. DMH2 also induced the expression of nestin in the Oct4 population but not in the nestin cells. We also show that BMP signaling is an important regulator of Id1 and Id3 in both the Oct4 and nestin cell populations. Furthermore, we show that NeuN is frequently expressed in NSCLC and provide evidence suggesting that Oct4 cells give rise to cancer cells expressing nestin and/or NeuN.

Conclusion

These studies show that although biologically different, BMP signaling is growth promoting in cancer cells expressing Oct4 or nestin. Inhibition of BMP signaling decreases expression of Id proteins and suppresses growth of cancer cells expressing Oct4 or Nestin. Small molecule antagonists of the BMP type I receptors represent potential novel drugs to target the population of cancer cells expressing stem cell markers.

Serum regulation of Id1 expression by a BMP pathway and BMP responsive element

Immediate early genes (IEGs) are expressed upon re-entry of quiescent cells into the cell cycle following serum stimulation. These genes are involved in growth control and differentiation and hence their expression is tightly controlled. Many IEGs are regulated through Serum Response Elements (SREs) in their promoters, which bind Serum Response Factor (SRF). However, many other IEGs do not have SREs in their promoters and their serum regulation is poorly understood. We have identified SRF-independent IEGs in SRF-depleted fibroblasts. One of these, Id1, was examined more closely. We mapped a serum responsive element in the Id1 promoter and find that it is identical to a BMP responsive element (BRE). The Id1 BRE is necessary and sufficient for the serum regulation of Id1. Inhibition of the BMP pathway by siRNA depletion of Smad 4, treatment with the BMP antagonist noggin, or the BMP receptor inhibitor dorsomorphin blocked serum induction of Id1. Further, BMP2 is sufficient to induce Id1 expression. Given reports that SRC inhibitors can block Id1 expression, we tested the SRC inhibitor, AZD0530, and found that it inhibits the serum activation of Id1. Surprisingly, this inhibition is independent of SRC or its family members. Rather, we show that AZD0530 directly inhibits the BMP type I receptors. Serum induction of the Id1 related gene Id3 also required the BMP pathway. Given these and other findings we conclude that the Id family of IEGs is regulated by BMPs in serum through similar BREs. This represents a second pathway for serum regulation of IEGs.

The secretome of colon cancer stem cells contains drug-metabolizing enzymes

Drug-resistant cancer stem cells (CSCs) have been implicated in tumor recurrence following chemotherapy. However, the contribution of CSCs to drug-resistance in colorectal cancer is unclear and CSC-intrinsic drug-resistance mechanisms are ill-defined. Here, we address these issues by proteomic analysis of the secretomes of CSCs and isogenic differentiated tumor cells (DTCs) isolated from three distinct metastasized colon tumors. Mass spectrometry-based proteomics identified 1254 unique proteins in the conditioned media of the paired CSC and DTC cultures. Ingenuity Pathway Analysis revealed that proteins governing 'Cell Death' were most significantly enriched in the CSC secretome. The vast majority of these (37/43) promote cell survival. The CSC secretome is also characterized by a pro-survival Nrf2 antioxidant signature. Interestingly, proteome-maintenance networks are highly enriched in the CSC secretome. CSCs also secrete high levels of drug-metabolizing enzymes, including aldehyde dehydrogenase 1 (ALDH1A1) and bleomycin hydrolase (BLMH). We show that these enzymes cause extracellular detoxification of maphosphamide and bleomycin respectively. We conclude that colorectal CSCs are characterized by extensive survival and anti-oxidant networks, which are likely to contribute to CSC-intrinsic drug-resistance. In addition, CSCs may modulate drug responses in nearby tumor cells by detoxifying chemotherapeutic drugs in the extracellular space.

BIOLOGICAL SIGNIFICANCE

Cancer stem cells are thought to play an important role in mediating drug resistance and tumor recurrence following chemotherapy. Therefore, it is important to identify the factors that are secreted by them. Our results provide novel insights into the pathways that govern the intrinsic resistance of CSCs to chemotherapy and, furthermore, demonstrate that they can also inactivate chemotherapeutic drugs in the extracellular space. A better understanding of the pathways that govern drug resistance in CSCs may help in developing effective CSC-targeting drugs.

A dynein motor attachment complex regulates TGFß/Smad3 signaling

Our previous results have demonstrated that km23-2 has functions in TGFß signaling that are distinct from those for km23-1. In the current report, we demonstrate that blockade of km23-2 decreased TGFß activation of the human Smad7 promoter Smad7-Luc, an endogenous Smad3-target promoter. Luminescence-based mammalian interaction mapping (LUMIER) analyses showed that TGFß stimulated the interaction of km23-2 preferentially with Smad3, relative to that with Smad2. Size exclusion chromatography experiments revealed that km23-2 and Smad3 were recruited into the same complex after TGFß treatment. Moreover, in the presence of TGFß, but not in the absence, km23-2 was present in early endosomes with the TGFß receptors (TßRs) and Smad3. Collectively, our data indicate that km23-2 is a critical signaling intermediate in a Smad3-dependent TGFß signaling pathway. We also provide evidence of the novel finding that TGFß stimulates the rapid recruitment of the km23-2 dimer to the dynein intermediate chain (DIC) of the dynein complex, whereas a kinase-deficient form of TßRII prevented this interaction. Finally, we demonstrate for the first time that TGFß stimulated not only assembly of the dynein motor attachment complex, but also triggered the tethering of the km23-2-Smad3 cargo to the other dynein components. Thus, our data demonstrate a novel function for km23-2 as a motor receptor to recruit Smad3 to the dynein complex for intracellular transport, thereby mediating Smad3-dependent TGFß signaling.

A microRNA miR-34a-regulated bimodal switch targets Notch in colon cancer stem cells

microRNAs regulate developmental cell-fate decisions, tissue homeostasis, and oncogenesis in distinct ways relative to proteins. Here, we show that the tumor suppressor microRNA miR-34a is a cell-fate determinant in early-stage dividing colon cancer stem cells (CCSCs). In pair-cell assays, miR-34a distributes at high levels in differentiating progeny, whereas low levels of miR-34a demarcate self-renewing CCSCs. Moreover, miR-34a loss of function and gain of function alter the balance between self-renewal versus differentiation both in vitro and in vivo. Mechanistically, miR-34a sequesters Notch1 mRNA to generate a sharp threshold response where a bimodal Notch signal specifies the choice between self-renewal and differentiation. In contrast, the canonical cell-fate determinant Numb regulates Notch levels in a continuously graded manner. Altogether, our findings highlight a unique microRNA-regulated mechanism that converts noisy input into a toggle switch for robust cell-fate decisions in CCSCs.

Molecular culprits generating brain tumor stem cells

Despite current advances in multimodality therapies, such as surgery, radiotherapy, and chemotherapy, the outcome for patients with high-grade glioma remains fatal. Understanding how glioma cells resist various therapies may provide opportunities for developing new therapies. Accumulating evidence suggests that the main obstacle for successfully treating high-grade glioma is the existence of brain tumor stem cells (BTSCs), which share a number of cellular properties with adult stem cells, such as self-renewal and multipotent differentiation capabilities. Owing to their resistance to standard therapy coupled with their infiltrative nature, BTSCs are a primary cause of tumor recurrence post-therapy. Therefore, BTSCs are thought to be the main glioma cells representing a novel therapeutic target and should be eliminated to obtain successful treatment outcomes.

Variable clonal repopulation dynamics influence chemotherapy response in colorectal cancer

Intratumoral heterogeneity arises through the evolution of genetically diverse subclones during tumor progression. However, it remains unknown whether cells within single genetic clones are functionally equivalent. By combining DNA copy number alteration (CNA) profiling, sequencing, and lentiviral lineage tracking, we followed the repopulation dynamics of 150 single lentivirus-marked lineages from 10 human colorectal cancers through serial xenograft passages in mice. CNA and mutational analysis distinguished individual clones and showed that clones remained stable upon serial transplantation. Despite this stability, the proliferation, persistence, and chemotherapy tolerance of lentivirally marked lineages were variable within each clone. Chemotherapy promoted the dominance of previously minor or dormant lineages. Thus, apart from genetic diversity, tumor cells display inherent functional variability in tumor propagation potential, which contributes to both cancer growth and therapy tolerance.

Id1 and Id3 co-expression correlates with clinical outcome in stage III-N2 non-small cell lung cancer patients treated with definitive chemoradiotherapy

Background

Inhibitor of DNA binding 1 (Id1) and 3 (Id3) genes have been related with the inhibition of cell differentiation, cell growth promotion and tumor metastasis. Recently, Id1 has been identified as an independent prognostic factor in patients with lung adenocarcinoma, regardless of the stage. Furthermore, Id1 may confer resistance to treatment (both, radiotherapy and chemotherapy).

Methods

We have studied, using monoclonal antibodies for immunohistochemistry, the Id1 and Id3 tumor epithelial expression in 17 patients with stage III-N2 non-small cell lung cancer (NSCLC) treated with definitive chemoradiotherapy.

Results

Id1 expression is observed in 82.4% of the tumors, whereas Id3 expression is present in 41.2% of the samples. Interestingly, Id1 and Id3 expression are mutually correlated (R = 0.579, p = 0.015). In a subgroup analysis of patients with the most locally advanced disease (T4N2 stage), co-expression of Id1 and Id3 showed to be related with a worse overall survival (45 vs 6 months, p = 0.002). A trend towards significance for a worse progression free survival (30 vs 1 months, p = 0.219) and a lower response rate to the treatment (RR = 50% vs 87.5%, p = 0.07) were also observed.

Conclusions

A correlation between Id1 and Id3 protein expression is observed. Id1 and Id3 co-expression seems associated with a poor clinical outcome in patients with locally advanced NSCLC treated with definitive chemoradiotherapy.