v-Ha-ras oncogene insertion: a model for tumor progression of human small cell lung cancer

Small Cell Lung Cancer-An Update on Chemotherapy Resistance

OPINION STATEMENT

Compared to other types of lung cancer, small cell lung cancer (SCLC) exhibits aggressive characteristics that promote drug resistance. Despite platinum-etoposide chemotherapy combined with immunotherapy being the current standard treatment, the rapid development of drug resistance has led to unsatisfactory clinical outcomes. This review focuses on the mechanisms contributing to the chemotherapy resistance phenotype in SCLC, such as increased intra-tumoral heterogeneity, alterations in the tumor microenvironment, changes in cellular metabolism, and dysregulation of apoptotic pathways. A comprehensive understanding of these drug resistance mechanisms in SCLC is imperative for ushering in a new era in cancer research, which will promise revolutionary advancements in cancer diagnosis and treatment methodologies.

YAP drives fate conversion and chemoresistance of small cell lung cancer

Small cell lung cancer (SCLC) has a high degree of plasticity and is characterized by a remarkable response to chemotherapy followed by the development of resistance. Here, we use a mouse SCLC model to show that intratumoral heterogeneity of SCLC is progressively established during SCLC tumorigenesis. YAP/TAZ and Notch are required for the generation of non-neuroendocrine (Non-NE) SCLC tumor cells, but not for the initiation of SCLC. YAP signals through Notch-dependent and Notch-independent pathways to promote the fate conversion of SCLC from NE to Non-NE tumor cells by inducing Rest expression. In addition, YAP activation enhances the chemoresistance in NE SCLC tumor cells, while the inactivation of YAP in Non-NE SCLC tumor cells switches cell death induced by chemotherapy drugs from apoptosis to pyroptosis. Our study demonstrates that YAP plays critical roles in the establishment of intratumoral heterogeneity and highlights the potential of targeting YAP for chemoresistant SCLC.

Extracellular signal-regulated kinase mediates chromatin rewiring and lineage transformation in lung cancer

Lineage transformation between lung cancer subtypes is a poorly understood phenomenon associated with resistance to treatment and poor patient outcomes. Here, we aimed to model this transition to define underlying biological mechanisms and identify potential avenues for therapeutic intervention. Small cell lung cancer (SCLC) is neuroendocrine in identity and, in contrast to non-SCLC (NSCLC), rarely contains mutations that drive the MAPK pathway. Likewise, NSCLCs that transform to SCLC concomitantly with development of therapy resistance downregulate MAPK signaling, suggesting an inverse relationship between pathway activation and lineage state. To test this, we activated MAPK in SCLC through conditional expression of mutant KRAS or EGFR, which revealed suppression of the neuroendocrine differentiation program via ERK. We found that ERK induces the expression of ETS factors that mediate transformation into a NSCLC-like state. ATAC-seq demonstrated ERK-driven changes in chromatin accessibility at putative regulatory regions and global chromatin rewiring at neuroendocrine and ETS transcriptional targets. Further, ERK-mediated induction of ETS factors as well as suppression of neuroendocrine differentiation were dependent on histone acetyltransferase activities of CBP/p300. Overall, we describe how the ERK-CBP/p300-ETS axis promotes a lineage shift between neuroendocrine and non-neuroendocrine lung cancer phenotypes and provide rationale for the disruption of this program during transformation-driven resistance to targeted therapy.

Genomic and pathological heterogeneity in clinically diagnosed small cell lung cancer in never/light smokers identifies therapeutically targetable alterations

Small-cell lung cancer (SCLC) occurs infrequently in never/former light smokers. We sought to study this rare clinical subset through next-generation sequencing (NGS) and by characterizing a representative patient-derived model. We performed targeted NGS, as well as comprehensive pathological evaluation, in 11 never/former light smokers with clinically diagnosed SCLC. We established a patient-derived model from one such patient (DFCI168) harboring an NRAS^Q61K mutation and characterized the sensitivity of this model to MEK and TORC1/2 inhibitors. Despite the clinical diagnosis of SCLC, the majority (8/11) of cases were either of nonpulmonary origin or of mixed histology and included atypical carcinoid (n = 1), mixed non-small-cell lung carcinoma and SCLC (n = 4), unspecified poorly differentiated carcinoma (n = 1), or small-cell carcinoma from different origins (n = 2). RB1 and TP53 mutations were found in four and five cases, respectively. Predicted driver mutations were detected in EGFR (n = 2), NRAS (n = 1), KRAS (n = 1), BRCA1 (n = 1), and ATM (n = 1), and one case harbored a TMPRSS2-ERG fusion. DFCI168 (NRAS^Q61K ) exhibited marked sensitivity to MEK inhibitors in vitro and in vivo. The combination of MEK and mTORC1/2 inhibitors synergized to prevent compensatory mTOR activation, resulting in prolonged growth inhibition in this model and in three other NRAS mutant lung cancer cell lines. SCLC in never/former light smokers is rare and is potentially a distinct disease entity comprised of oncogenic driver mutation-harboring carcinomas morphologically and/or clinically mimicking SCLC. Comprehensive pathologic review integrated with genomic profiling is critical in refining the diagnosis and in identifying potential therapeutic options.

Small cell lung cancer tumors and preclinical models display heterogeneity of neuroendocrine phenotypes

Background

Small cell lung cancer (SCLC) is a deadly, high grade neuroendocrine (NE) tumor without recognized morphologic heterogeneity. However, over 30 years ago we described a SCLC subtype with "variant" morphology which did not express some NE markers and exhibited more aggressive growth.

Methods

To quantitate NE properties of SCLCs, we developed a 50-gene expression-based NE score that could be applied to human SCLC tumors and cell lines, and genetically engineered mouse (GEM) models. We identified high and low NE subtypes of SCLC in all of our sample types, and characterized their properties.

Results

We found that 16% of human SCLC tumors and 10% of SCLC cell lines were of the low NE subtype, as well as cell lines from the GEM model. High NE SCLC lines grew as non-adherent floating aggregates or spheroids while Low NE lines had morphologic features of the variant subtype and grew as loosely attached cells. While the high NE subtype expressed one of the NE lineage master transcription factors ASCL1 or NEUROD1, together with NKX2-1, the entire range of NE markers, and lacked expression of the neuronal and NE repressor REST, the low NE subtype had lost expression of most NE markers, ASCL1, NEUROD1 and NKX2-1 and expressed REST. The low NE subtype had undergone epithelial mesenchymal transition (EMT) and had activated the Notch, Hippo and TGFβ pathways and MYC oncogene . Importantly, the high and low NE group of SCLC lines had similar gene expression profiles as their SCLC tumor counterparts.

Conclusions

SCLC tumors and cell lines can exhibit distinct inter-tumor heterogeneity with respect to expression of NE features. Loss of NE expression results in major alterations in morphology, growth characteristics, and molecular properties. These findings have major clinical implications as the two subtypes are predicted to have very different responses to targeted therapies.

Expression of the coxsackie adenovirus receptor in neuroendocrine lung cancers and its implications for oncolytic adenoviral infection

Coxsackie adenovirus receptor (CAR) is the primary receptor to which oncolytic adenoviruses have to bind for internalization and viral replication. A total of 171 neuroendocrine lung tumors in form of multitissue arrays have been analyzed resulting in a positivity of 112 cases (65.5%). Immunostaining correlated statistically significant with histopathology and development of recurrence. The subtype small cell lung cancer (SCLC) showed the highest CAR expression (77.6%), moreover the CAR level was correlated to the disease-free survival. Further, high CAR expression level in SCLC cell lines was found in vitro and in vivo when cell lines had been transplanted into immunodeficient mice. A correlation between CAR expression in the primary tumors and metastases development in the tumor model underlined the clinical relevance. Cell lines with high CAR level showed a high infectivity when infected with a replication-deficient adenovirus. Low levels of CAR expression in SCLC could be upregulated with Trichostatin A, a histone deacetylase inhibitor. As a result of the unaltered poor prognosis of SCLC and its high CAR expression it seems to be the perfect candidate for oncolytic therapy. With our clinically relevant tumor model, we show that xenograft experiments are warrant to test the efficiency of oncolytic adenoviral therapy.

Definition of genetic events directing the development of distinct types of brain tumors from postnatal neural stem/progenitor cells

Although brain tumors are classified and treated based upon their histology, the molecular factors involved in the development of various tumor types remain unknown. In this study, we show that the type and order of genetic events directs the development of gliomas, central nervous system primitive neuroectodermal tumors, and atypical teratoid/rhabdoid-like tumors from postnatal mouse neural stem/progenitor cells (NSC/NPC). We found that the overexpression of specific genes led to the development of these three different brain tumors from NSC/NPCs, and manipulation of the order of genetic events was able to convert one established tumor type into another. In addition, loss of the nuclear chromatin-remodeling factor SMARCB1 in rhabdoid tumors led to increased phosphorylation of eIF2α, a central cytoplasmic unfolded protein response (UPR) component, suggesting a role for the UPR in these tumors. Consistent with this, application of the proteasome inhibitor bortezomib led to an increase in apoptosis of human cells with reduced SMARCB1 levels. Taken together, our findings indicate that the order of genetic events determines the phenotypes of brain tumors derived from a common precursor cell pool, and suggest that the UPR may represent a therapeutic target in atypical teratoid/rhabdoid tumors.

A functional role for tumor cell heterogeneity in a mouse model of small cell lung cancer

Small cell lung cancer (SCLC) is the lung neoplasia with the poorest prognosis, due to its high metastatic potential and chemoresistance upon relapse. Using the previously described mouse model for SCLC, we found that the tumors are often composed of phenotypically different cells with either a neuroendocrine or a mesenchymal marker profile. These cells had a common origin because they shared specific genomic aberrations. The transition from neuroendocrine to mesenchymal phenotype could be achieved by the ectopic expression of oncogenic Ras(V12). Crosstalk between mesenchymal and neuroendocrine cells strongly influenced their behavior. When engrafted as a mixed population, the mesenchymal cells endowed the neuroendocrine cells with metastatic capacity, illustrating the potential relevance of tumor cell heterogeneity in dictating tumor properties.

Regulation of the NRSF/REST gene by methylation and CREB affects the cellular phenotype of small-cell lung cancer

The neuron-restrictive silencer factor/RE1-silencing transcription factor (NRSF/REST) is a negative regulator of gene expression restricting the expression of neuronal genes to the nervous system. NRSF/REST is highly expressed in non-neuronal tissues like the lung. In previous work, we identified small-cell lung cancer (SCLC) cell lines with no detectable NRSF/REST expression that, as a consequence, expressed neuronal markers like L1-cell adhesion molecule (L1-CAM) and neural cell adhesion molecule (NCAM). The loss of NRSF/REST expression was linked to malignant progression; however, its mechanistic role remained elusive. Here, we show that NRSF/REST itself, rather than one of its regulated genes, acts like a classic tumour suppressor, being in part regulated by methylation. In SCLCs, NRSF/REST is positively regulated by CREB, with an NRSF/REST promoter fragment showing cell type specificity. Downstream, NRSF/REST directly regulates AKT2, in which NRSF/REST loss leads to an epidermal growth factor-mediated de-regulation of AKT-Serine473 phosphorylation, important for cellular proliferation and survival. Assaying anchorage-independent growth, we observed that with reduced NRSF/REST expression, proliferation was significantly enhanced, whereas NRSF/REST rescue decreased the potential of cells to grow anchorage independently. Our observations support the fact that NRSF/REST may act as an important modulator of malignant progression in SCLC.

p66(Shc) restrains Ras hyperactivation and suppresses metastatic behavior

Normal tissue cells survive and proliferate only while anchored to solid substrate. Conversely, transformed cells both survive and proliferate following detachment, having lost attachment context through unclear mechanisms. p66(Shc) is a focal adhesion-associated protein that reports cell attachment through a RhoA-dependent mechanosensory test. We find that human small cell lung cancer (SCLC) cells and mouse Lewis lung carcinoma (LLC), which display aggressive metastatic behavior, lack both p66(Shc) and retinoblastoma (pRB) and bypass anoikis. Re-expression of p66(Shc) in these cells restores anoikis and provides striking protection from metastasis by LLC cells in vivo. Notably, knockdown of p66(Shc) in normal epithelial cells leads to unrestrained Ras activation, preventing anoikis through downstream suppression of RhoA but blocking proliferation in a pRB-dependent manner, thus mimicking oncogenic Ras. Conversely, LLC and SCLC cells display constitutive Ras activation necessary to bypass anoikis, which is reversed by re-expression of p66(Shc). p66(Shc) therefore coordinates Ras-dependent control of proliferation and anchorage sensation, which can be defeated in the evolution of highly metastatic tumors by combined loss of both p66(Shc) and pRB.

Critical role of G(alpha)12 and G(alpha)13 for human small cell lung cancer cell proliferation in vitro and tumor growth in vivo

PURPOSE

In small cell lung cancer cells (SCLC), various autocrine stimuli lead to the parallel activation of G(q/11) and G(12/13) proteins. Although the contribution of the G(q/11)-phospholipase C-beta cascade to mitogenic effects in SCLC cells is well established, the relevance of G(12/13) signaling is still elusive. In other tumor entities, G(12/13) activation promotes invasiveness without affecting cellular proliferation. Here, we investigate the role of G(12/13)-dependent signaling in SCLC.

EXPERIMENTAL DESIGN

We used small hairpin RNA-mediated targeting of G(alpha)(12), G(alpha)(13), or both in H69 and H209 cells and analyzed the effects of G(alpha)(12) and/or G(alpha)(13) knockdown on tumor cells in vitro, tumor growth in vivo, and mitogen-activated protein kinase (MAPK) activation.

RESULTS

Lentiviral expression of small hairpin RNAs resulted in robust and specific G(alpha)(12) and G(alpha)(13) knockdown as well as markedly inhibited proliferation, colony formation, and bradykinin-promoted stimulation of cell growth. Analyzing the activation status of all three major MAPK families revealed nonredundant functions of G(alpha)(12) and G(alpha)(13) in SCLC and a marked p42/p44 activation upon G(alpha)(12)/G(alpha)(13) knockdown. In a s.c. tumor xenograft mouse model, G(alpha)(12) or G(alpha)(13) downregulation led to decreased tumor growth due to reduced tumor cell proliferation. More importantly, G(alpha)(12)/G(alpha)(13) double knockdown completely abolished H69 tumorigenicity in mice.

CONCLUSIONS

G(alpha)(12) and G(alpha)13) exert a complex pattern of nonredundant effects in SCLC, and in contrast to other tumor types, SCLC cell proliferation in vitro and tumorigenicity in vivo critically depend on G(12/13) signaling. Due to the complete abolishment of tumorgenicity in our study, RNAi-mediated double knockdown may provide a promising new avenue in SCLC treatment.

Pathogenesis of lung cancer: 100 year report

Over the past 100 years, our understanding of the pathogenesis of lung cancer has advanced impressively. Environmental carcinogens and a gene locus determining susceptibility have been identified. The pathology of lung cancer has been classified into categories with major clinical implications. The cellular and molecular genetic changes underlying lung cancer have become better understood over the past 25 years, but the stepwise progression of respiratory epithelium from normal to neoplastic is not yet well demarcated, limiting abilities to advance early detection and chemoprevention. The translation of improved understanding of dominant signal transduction pathways in lung cancer to rationally designed therapeutic strategies has had recent successes, demonstrating a proof of principle for targeted therapy in lung cancer. Improvement in overall patient outcomes has been stubbornly slow and will require concerted efforts.

Immunomodulatory functions of the diffuse neuroendocrine system: implications for bronchopulmonary dysplasia

Pulmonary neuroendocrine (NE) cells are believed to be the precursor of NE lung carcinomas, including well-differentiated (carcinoids) and moderately/poorly differentiated (atypical carcinoids and small-cell carcinomas, SCLCs) subtypes. In early studies, we determined mechanisms by which NE cell-derived peptides such as bombesin-like peptide (BLP) promote normal fetal lung development. Postnatally, BLP may normally regulate perinatal adaptation of the pulmonary circulation. However, elevated BLP levels in premature infants shortly after birth predict which infants are at high risk for developing bronchopulmonary dysplasia (BPD, chronic lung disease of newborns). An anti-BLP blocking antibody abrogates clinical and pathological evidence of lung injury in two baboon models of BPD. These observations indicate that BLP mediates lung injury in BPD, supporting a role for BLP as pro-inflammatory cytokines. We have directly tested the effects of BLP on eliciting inflammatory cell infiltrates in vivo. Surprisingly, mast cells are the major responding cell population. These data suggest that the diffuse NE system may be a newly recognized component of innate immunity in multiple organ systems. We speculate that overproduction of NE cell-derived peptides such as BLP may be responsible for a variety of chronic inflammatory disorders.

Modeling human lung cancer in mice: similarities and shortcomings

Lung cancer kills more Americans yearly than any other neoplastic process. Mortality rates have changed little over the past several decades, despite improvements in surgical techniques, radiation therapy and chemotherapy. The identification of mutations in oncogenes and tumor suppressor genes in human lung tumor specimens, including K-ras, p53, p16INK4a and Rb, offers molecular explanations for tumor development and resistance to therapy. Mouse models of human lung cancer may advance our understanding of this disease. The examination of mice which develop lung cancer either spontaneously or due to carcinogen exposure, and the creation of mouse strains harboring the specific genetic mutations found in human lung cancer are among strategies being pursued.

A phase II study of all-trans-retinoic acid plus cisplatin and etoposide in patients with extensive stage small cell lung carcinoma: an Eastern Cooperative Oncology Group Study

BACKGROUND

The dysregulation of both myc gene expression and retinoid signaling pathways commonly occurs in small cell lung carcinoma (SCLC). Because preclinical data showed that all-trans-retinoic acid (RA) inhibited SCLC growth, altered myc expression, and blocked transition to a treatment-resistant phenotype, a Phase II trial was designed to determine the effects of the combination of RA, cisplatin, and etoposide in patients with SCLC.

METHODS

Patients with untreated, extensive stage SCLC were treated with up to 8 cycles of cisplatin, 60 mg/m2, intravenously (i.v.) on Day 1 and etoposide, 120 mg/m2, i.v. on Days 1-3 in addition to up to 1 year of oral RA, 150 mg/m2/day.

RESULTS

Of 22 assessable patients 1 had a complete response and 9 had a partial response, for an overall response rate of 45% (95% confidence interval, 24-68%). The median survival was 10.9 months and the 1-year survival was 41%. The median duration of chemotherapy was 6 cycles and the median duration of RA treatment was 2.8 months. Thirteen patients discontinued RA prematurely due to toxicity and only 4 responders were receiving RA at the time of recurrence. Toxicity-limiting RA treatment mainly was comprised of mucocutaneous changes and headaches.

CONCLUSIONS

RA at a dose of 150 mg/m2/day was tolerated poorly in combination with cisplatin plus etoposide, leading to early discontinuation of RA in the majority of patients. The hematologic toxicity, response rate, and survival were similar to those associated with cisplatin and etoposide in prior trials. Further studies with more active and less toxic agents will be required to determine the role of retinoids in the treatment of SCLC.

Expression of mRNA for gastrin-releasing peptide receptor by human bronchial epithelial cells. Association with prolonged tobacco exposure and responsiveness to bombesin-like peptides

Bombesin-like peptides (BLPs) are important regulators of lung development and may also act as autocrine growth factors in lung tumors. We have previously demonstrated expression of mRNA for the three BLP receptor subtypes (neuromedin B [NMB]) receptor, gastrin-releasing peptide [GRP] receptor, and bombesin receptor subtype 3 [BRS-3]) in human non-small cell lung carcinoma (NSCLC) cell lines and bronchial biopsies using the reverse transcription-polymerase chain reaction (RT-PCR; DeMichele, et al. Am. J. Respir. Cell Mol. Biol. 1994; 11:66-74). We have also previously found that growth responses to BLPs could be elicited in some, but not all, cultures of human bronchial epithelial (HBE) cells (Siegfried, et al. Anat. Rec. 1993; 236:241-247). In this report, we utilized RT-PCR to demonstrate mRNA expression of BLP receptor subtypes in cultured HBE cells and also assessed the response of these cultures to BLPs in proliferation assays. The pattern of mRNA expression was correlated with proliferative response, and the results were also analyzed in relation to smoking history and pulmonary function of the subjects studied. Our results suggest that expression of mRNA for the GRP receptor is associated with a long smoking history (> 25 pack-years [PY], p = 0.02). This association was related to past tobacco exposure, regardless of whether the subjects were still active smokers at the time of tissue procurement. Responsiveness to GRP and NMB in proliferation assays was also found only in those HBE cultures with expression of mRNA for at least one of the known receptors for BLPs, and there was a significant association between expression of mRNA for the GRP receptor and proliferative response to both GRP and NMB (p = 0.048). HBE cultures from subjects with a greater than 25 PY smoking history were also more likely to respond to BLPs in the proliferation assays than cells from subjects with less than a 25 PY history (10 of 16 versus 1 of 7, p = 0.06). Cultures of HBE cells from four of the five subjects with severe obstructive lung disease gave a positive response to GRP and NMB in proliferation assays, compared to five of fifteen without severe obstructive lung disease, but this difference was not significant (p = 0.13). These results suggest there is an increased likelihood of expression of the GRP receptor mRNA in the respiratory epithelium of some individuals with a history of prolonged tobacco exposure, and that expression of the GRP receptor mRNA is accompanied by responsiveness to the mitogenic effects of BLPs. These effects appear to persist after smoking cessation.

Rapid ras-oncogene-mediated transformation maintains steroidogenic differentiation in adrenocortical parenchymal cells

While its action as a transforming agent is well known, expression of the ras oncogene may also alter tissue-specific differentiation. We have been examining the relationship of transformation and differentiation in steroidogenic cells of the rat. Infection of adrenocortical zona glomerulosa (GLOM) cells with the v-Ki ras containing Kirsten murine sarcoma virus did not induce focus formation. Instead, diffuse cellular multilayers formed from which loosely adherent, refractile cells emerged. After selective passaging these refractile cells, designated KiGLOM, were morphologically transformed, had reduced serum requirements for growth, greatly increased saturation densities, and they rapidly formed tumours in immunosuppressed hosts. In addition, under conditions where normal cells were no longer steroidogenic (ie. after passaging), KiGLOM cells expressed the steroid-specific cholesterol side chain cleavage cytochrome P-450scc and they produced significant, albeit reduced, amounts of corticosterone in comparison with primary GLOM cultures. Additionally, trophic hormone treatment increased steroid production in Ki-GLOM cells and this increase was partially reversed by lovastatin, a pharmacological inhibitor of ras p21 function. Thus, after a morphological selection that removed normal neighbours, v-Ki ras infected cells transformed rapidly while remaining steroidogenic. These results, combined with previous reports of steroidogenic v-Ki ras transformed adrenocortical fibroblasts and ovarian granulosa cells suggest that the ability of the ras oncogene to co-opt signal transduction pathways associated with both growth and differentiation is a common feature of the steroidogenic phenotype.

Molecular events in lung cancer

The observation that genes contributing to the process of malignant transformation are altered forms of genes normally present in eukaryotic cells initiated many of the advances that have increased our understanding of lung carcinogenesis at the molecular level. The gene families implicated in carcinogenesis include dominant oncogenes and tumor suppressor genes. Proto-oncogenes (normal homologue of the oncogene) participate in critical cell functions, including signal transduction and transcription. Only a single mutant allele is required for malignant transformation. Primary modifications in the dominant oncogenes that confer gain of transforming function include point mutations, amplification, translocations, and rearrangements. A second recently described gene family is the tumor suppressor genes. Tumor suppressor genes appear to require homozygous loss of function either by mutation, deletion, or a combination of these. Some tumor suppressor genes appear to play a role in the governance of proliferation by regulation of transcription. The identification of specific genes that contribute to the development of the cancer cell presents an opportunity to use these genes and their products as prevention and treatment targets.

Differentiation markers for lung-cancer sub-types. A comparative study of their expression in vivo and in vitro

Cell lines representing the major sub-types of lung cancer have proved to be useful tools to study the molecular and cellular biology of these malignancies, provided that they are well established and well characterized. Antibodies directed against constituents of different cellular compartments can detect the type and degree of differentiation in lung cancer and derived cell lines. Antibodies can detect cell-surface adhesion molecules, such as NCAM, cadherins and integrins. NCAM antibodies are able to differentiate between small-cell lung cancer (SCLC) and non-SCLC, both in cell lines and in tumours. In addition, a spectrum of other membrane proteins, expressed in solid tumours, such as epidermal-growth-factor receptor and carcino-embryonic antigen, are retained in cell lines. Cytoplasmic intermediate filament proteins appear to be generally retained in lung-cancer cell lines, their combinations being the same as in solid SCLC, adenocarcinomas and squamous-cell carcinomas. Nuclear expression of lamins is comparable in tumours and in their corresponding cell lines and can be used to differentiate between SCLC and non-SCLC: A-type lamins, which are present in non-SCLC, are absent in most SCLC.

Human T-cell leukemia virus-1-positive cell line established from a patient with small cell lung cancer

A stable cell line, KHM-3S, was established from a patient with small cell lung cancer (SCLC), who had a high serum level of soluble interleukin 2 receptors (sIL2-R) and was seropositive for human T cell leukemia virus (HTLV)-1. KHM-3S cells were positive for IL2-R (Tac) and NKH-1, but negative for other lymphocytic markers such as OKT 11, OKT 4, OKT 8, T cell receptor (WT 31), B 1, and B 4. Moreover, the KHM-3S cells were negative for leukocyte common antigen and strongly positive for neuron-specific enolase (NSE). Secretion of sIL2-R and NSE by the KHM-3S line was detected by an enzyme-linked immunosorbent assay. Rearrangement of the T cell receptor gene and monoclonal HTLV-1 integration were found by Southern blot analysis of KHM-3S DNA. However, Northern blot analysis showed no T cell receptor mRNA. KHM-3S may be useful for studies on the role of HTLV-1 in carcinogenesis and IL2-R expression in SCLC.

Malignant epithelial cells in primary human lung carcinomas coexpress in vivo platelet-derived growth factor (PDGF) and PDGF receptor mRNAs and their protein products

Lung cancer represents one of the major human carcinomas with the highest degree of mortality. Epidemiologic studies have linked this disease to "chronic injury," largely induced by cigarette smoking. In the present studies, we demonstrate the in vivo expression of platelet-derived growth factor (PDGF) and PDGF receptor (PDGF-R) beta mRNAs and their respective protein products in malignant epithelial cells of primary human lung carcinomas. In contrast, nonmalignant epithelial cells in control, normal lung tissue specimen did not express PDGF and PDGF-R mRNAs and did not produce their respective protein products. Epithelial cells in lung specimen from patients with idiopathic pulmonary fibrosis expressed only PDGF mRNA but not PDGF-R beta mRNA. These findings of the inappropriate coexpression of a potent mitogen, PDGF, and its receptor in lung cancer epithelial cells suggest the presence of a powerful in vivo mechanism contributing to the self-stimulation and unregulated growth of lung cancer tumor cells.

Modulation of neuroendocrine surface antigens in oncogene-activated small cell lung cancer lines

Small cell lung cancer (SCLC) manifests a number of neuroendocrine differentiation features and antigenic characteristics that distinguish the tumour from non-small cell lung cancer (NSCLC). Several surface antigens on SCLC cells, identified by clusters of monoclonal antibodies (MAbs), distinguish SCLC and other neuroendocrine tumours of NSCLC. Stable transfection of the c-myc proto-oncogene has been reported to confer upon classic SCLC cells the growth properties and morphology of the variant subtype of SCLC (SCLC-v). Furthermore, insertion of the v-Ha-ras oncogene into such SCLC-v cells has been found to induce features typical of NSCLC. We have used classic SCLC cells transfected with c-myc, or co-transformed with c-myc and v-Ha-ras, to examine the expression of characteristics SCLC cluster antigens. Flow cytometric assays reveal that SCLC cells co-transformed with c-myc and v-Ha-ras oncogenes down-modulate SC-1, SC-2 and SC-5A surface antigens to levels approaching, in some cases, those seen with NSCLC cells. The SC-4 surface antigen is not modulated by activation of these oncogenes. These findings support clinical and laboratory observations that important transitions can occur between subtypes of human lung cancer cells, and that these shifts may play a role in the clinical progression of lung cancer.

Gene amplification in human lung cancer. The myc family genes and other proto-oncogenes and growth factor genes

The development of human lung cancer may require multiple genetic deletions affecting a number of chromosomes, e.g., 1, 3, 11, 13, and 17. These genetic aberrations may induce the activation of proto-oncogenes (c-jun, ras, c-raf1) and the loss of tumor suppressor genes (p53). Some of the activated proto-oncogenes and tumor suppressor genes are more selectively expressed or absent in small-cell lung cancer (L-myc, c-myb, c-scr, Rb gene) or non-small-cell lung cancer (c-erbB-2, c-sis, c-fes). These genes may thus be of importance for selection of differentiation pathway. The c-myc oncogene is frequently amplified in small-cell lung cancer cell lines in a much higher frequency than in vivo. This indicates that c-myc seems to be related to tumor progression and a relatively late event in the lung cancer development. The uncontrolled production of multiple growth factors has been identified in human lung cancer cell lines. These factors can promote and inhibit the proliferation via paracrine and autocrine loops via specific receptors. The products from some of the activated proto-oncogenes (c-sis, c-erbB-2) are sequences homologous to a certain growth factor (PDGF) and a receptor (EGF) identified in lung cancer. The production and action of these growth factors may be of major importance for further activation of proto-oncogenes via intracellular signal transduction and specific oncogenic activation leading to further tumor progression.

v-rasH induces non-small cell phenotype, with associated growth factors and receptors, in a small cell lung cancer cell line

Small cell lung cancer (SCLC) tumor progression can involve partial or complete conversion to a more treatment-resistant non-small cell (NSCLC) phenotype. In a cell culture model of this phenomenon, we have previously demonstrated that insertion of the viral Harvey ras gene (v-Ha-ras) into SCLC cell lines with amplification and overexpression of the c-myc gene induced many NSCLC phenotypic features. We now report that the v-Ha-ras gene can also induce morphologic, biochemical, and growth characteristics consistent with the NSCLC phenotype in an N-myc amplified SCLC cell line, NCI-H249. We show that v-Ha-ras has novel effects on these cells, abrogating an SCLC-specific growth requirement for gastrin-releasing peptide, and inducing mRNA expression of three NSCLC-associated growth factors and receptors, platelet-derived growth factor B chain, transforming growth factor-alpha (TGF-alpha), and epidermal growth factor receptor (EGF-R). TGF-alpha secretion and EGF-R also appear, consistent with the induction of an autocrine loop previously shown to be growth stimulatory for NSCLC in culture. These data suggest that N-myc and v-Ha-ras represent functional classes of genes that may complement each other in bringing about the phenotypic alterations seen during SCLC tumor progression, and suggest that such alterations might include the appearance of growth factors and receptors of potential importance for the growth of the tumor and its surrounding stroma.

Dominant oncogenes and tumor suppressor genes in the pathogenesis of lung cancer

An understanding of the molecular pathogenesis of lung cancer has evolved from classic cytogenetic studies and the use of restriction fragment length polymorphisms to encompass the definition of specific genetic abnormalities associated with this disease. Activation of the dominant class of oncogenes is frequent, with involvement of the ras and myc families of genes being the best defined. Several examples of inactivation at specific loci exist and have been related to the presence of tumor suppressor genes, most notably the retinoblastoma gene, p53, and a putative gene located on the short arm of chromosome 3. As our understanding of the nature and interactions between these numerous genetic events evolves, new opportunities for early diagnosis, prevention, and treatment will arise.

Cooperation of c-raf-1 and c-myc protooncogenes in the neoplastic transformation of simian virus 40 large tumor antigen-immortalized human bronchial epithelial cells

Overexpression of c-raf-1 and the myc family of protooncogenes is primarily associated with small cell carcinoma, which accounts for approximately 25% of human lung cancer. To determine the functional significance of the c-raf-1 and/or c-myc gene expression in lung carcinogenesis and to delineate the relationship between protooncogene expression and tumor phenotype, we introduced both protooncogenes, alone or in combination, into human bronchial epithelial cells. Two retroviral recombinants, pZip-raf and pZip-myc, containing the complete coding sequences of the human c-raf-1 and murine c-myc genes, respectively, were constructed and transfected into simian virus 40 large tumor antigen-immortalized bronchial epithelial cells (BEAS-2B); this was followed by selection for G418 resistance. BEAS-2B cells expressing both the transfected c-raf-1 and c-myc sequences formed large cell carcinomas in athymic nude mice with a latency of 4-21 weeks, whereas either pZip-raf- or pZip-myc-transfected cells were nontumorigenic after 12 months. Cell lines established from tumors (designated RMT) revealed the presence of the cotransfected c-raf-1 and c-myc sequences and expressed morphological, chromosomal, and isoenzyme markers, which identified BEAS-2B cells as the progenitor line of the tumors. A significant increase in the mRNA levels of neuron-specific enolase was detected in BEAS-2B cells containing both the c-raf-1 and c-myc genes and derived tumor cell lines. The data demonstrate that the concomitant expression of the c-raf and c-myc protooncogenes causes neoplastic transformation of human bronchial epithelial cells resulting in large cell carcinomas with certain neuroendocrine markers. The presented model system should be useful in studies of molecular events involved in multistage lung carcinogenesis.

ras mutations in human leukemia and related disorders

The clinical association of an increased incidence of acute myelogenous leukemia (AML) with previous chemoradiotherapy, the detection of specific karyotypic changes in these secondary (therapy-induced) cases of AML and the discovery of increasing levels of oncogene-specific RNA in leukemia cells suggest that one potential site of action of environmental agents might be the proto-oncogenes in human hematopoietic stem cells. The location of human proto-oncogenes at the sites of chromosome breaks and/or translocations in cells from some patients with leukemia or lymphoma is a striking observation. These data stimulated research into the mechanism of activation of specific oncogenes that change the biology of human hematopoietic cells. Recent investigations have focused upon several areas that might alter cell biology including: 1) translocation and/or inversion of chromosome fragments containing a proto-oncogene to a location where other gene sequences can stimulate oncogene activation, 2) replication of copy number of proto-oncogenes or increased transcriptional activity and 3) point mutation in proto-oncogenes leading to a structurally altered protein. The third area of research has recently received significant attention with respect to the potential role of three ras genes (c-Harvey-ras, c-Kirsten-ras and N-ras) in human leukemias and myelodysplastic syndromes. Recent studies have proposed a model for leukemogenic transformation of human hematopoietic cells by the product of a mutated ras oncogene. Mutations at codons 12, 13 or 61 of the first exon of its 4.7 Kb of DNA (for c-Ha-ras) have been described. Other data revealing an absence of such mutations in the ras genes of many human leukemias and the absence of detectable transcription of ras genes in many alkylating agent-associated cases of AML, suggest that while ras mutations may be involved in some settings, there are probably multiple genetic pathways to leukemogenic transformation of human hematopoietic cells.

Insertion of the v-Ha-ras oncogene induces differentiation of calcitonin-producing human small cell lung cancer

Human small cell lung cancers (SCLC) and cell lines derived therefrom are phenotypically heterogeneous concerning neuroendocrine differentiation. Unlike most SCLC tumors and cell lines that express poorly differentiated neuroendocrine phenotypes, the SCLC cell line DMS 53 exhibits mature endocrine differentiation features, including unusually high expression of the gene for the peptide hormone, calcitonin (CT). We now report that introduction of the viral Harvey ras (v-rasH) oncogene into DMS 53 cells via retroviral infection, with resultant constitutive expression, results in increased features of neuroendocrine differentiation. 7-10 d after infection the cells demonstrated altered morphology, increased CT secretion, increased CT gene expression, markedly diminished cellular proliferation, and nearly abolished methylcellulose cloning efficiency. This response of DMS 53 cells to v-rasH is unlike the tumor progression effects we have previously observed in other SCLC lines. Significantly, the differentiation response that follows expression of the virally introduced v-rasH oncogene in DMS 53 cells is similar to that of neoplastic neuroendocrine cell lines derived from adrenal pheochromocytes and thyroid C cells. The effects of constitutive v-rasH expression in DMS 53 SCLC cells and other neuroendocrine cell lines suggest an important role for rasH or related genes in neuroendocrine differentiation.

Oncogene expression in cell lines derived from rat tracheal implants exposed in vivo to 7,12-dimethylbenz[a]anthracene

Expression of four oncogenes and two keratin genes was determined in rat tracheal epithelial cell lines derived from tracheal implants exposed in vivo to 7,12-dimethylbenz[a]anthracene. Cell lines were grouped into four stages of neoplastic progression based on phenotypic markers in order to correlate oncogene expression with stage of malignancy. Northern analysis of RNA revealed a significantly enhanced expression of the c-myc oncogene in the most tumorigenic or tumor-derived cell lines, whereas preneoplastic cells expressed approximately five-fold less transcript. Southern analysis of tracheal cell DNA did not demonstrate amplification of the c-myc gene in any of the positive cell lines. In contrast to c-myc, other oncogenes such as ras and fos were expressed in all cell lines, as well as in control cell cultures, to a similar extent. Patterns of differentiation were examined in these epithelial cell lines by determining the expression of two distinct keratin genes, KA-1 and KB-2. Both malignant and preneoplastic cells expressed the KB-2 gene at variably high levels, whereas the expression of the KA-1 keratin was barely detectable in any of the cell lines. The stage-specific expression of the c-myc oncogene in these tracheal cell lines suggests a correlation between the regulation of certain oncogenes and neoplastic progression in this model of respiratory carcinogenesis.