High sensitivity to peripheral blood lymphocytes and low HLA-class I antigen expression of small cell lung cancer cell lines with diverse chemo-radiosensitivity

Small cell lung cancer: will recent progress lead to improved outcomes?

Small cell lung cancer (SCLC) is an aggressive neuroendocrine malignancy with a unique natural history characterized by a short doubling time, high growth fraction, and early development of widespread metastases. Although a chemotherapy- and radiation-sensitive disease, SCLC typically recurs rapidly after primary treatment, with only 6% of patients surviving 5 years from diagnosis. This disease has been notable for the absence of major improvements in its treatment: Nearly four decades after the introduction of a platinum-etoposide doublet, therapeutic options have remained virtually unchanged, with correspondingly little improvement in survival rates. Here, we summarize specific barriers and challenges inherent to SCLC research and care that have limited progress in novel therapeutic development to date. We discuss recent progress in basic and translational research, especially in the development of mouse models, which will provide insights into the patterns of metastasis and resistance in SCLC. Opportunities in clinical research aimed at exploiting SCLC biology are reviewed, with an emphasis on ongoing trials. SCLC has been described as a recalcitrant cancer, for which there is an urgent need for accelerated progress. The NCI convened a panel of laboratory and clinical investigators interested in SCLC with a goal of defining consensus recommendations to accelerate progress in the treatment of SCLC, which we summarize here.

Immunomodifiers in combination with conventional chemotherapy in small cell lung cancer: a phase II, randomized study

PURPOSE

To evaluate the effect of immunotherapy on response, survival, and certain immune markers in patients with small cell lung cancer (SCLC) who are receiving chemotherapy.

PATIENTS AND METHODS

Patients with SCLC (n = 164) were assigned to receive either chemotherapy alone (group A) or a combination of chemotherapy and immunotherapy as follows: interferon α (IFN-α; 3 million IU) 3 times per week (group B); IFN-γ (3 million IU) 3 times per week (group C); and IFN-α and IFN-γ (1.5 million IU of each) 3 times per week (group D). Chemotherapy was the same for all groups and consisted of eight cycles with carboplatin 5.5 mg/m(2) intravenously on day 1, ifosfamide 3.5 mg/m(2) intravenously on day 1, and etoposide 200 mg/m(2) total dose taken orally on days 1 through 3, every 28 days. Patients completing chemotherapy were restaged, and those who were found to have limited disease received primary site and prophylactic cranial irradiation. Immunotherapy was continued throughout these treatments and during the follow-up period. Blood was taken before each course of chemotherapy and during follow-up to measure CD3+ lymphocytes, CD3+CD4+ lymphocytes, CD3+CD8+ lymphocytes, natural killer cells, and natural killer T cells.

RESULTS

Differences in response and survival were not significantly different when all patients were considered. However, among patients with limited disease, Kaplan-Meier analysis disclosed a survival benefit for group B (P , 0.05). The analysis of immunologic measurements revealed that the improvement of immune markers was always accompanied by clinical improvement, whereas deterioration of all markers was accompanied by disease progression (result not statistically significant except for group C; P , 0.05).

CONCLUSION

Among cytokines used in the study, only IFN-α seems to confer a survival benefit to patients with SCLC with limited disease. However, immunotherapy remains a challenge in the treatment of lung neoplasms and should be further explored.

HER2 as therapeutic target for overcoming ATP-binding cassette transporter-mediated chemoresistance in small cell lung cancer

Small cell lung cancer (SCLC) easily acquires multidrug resistance after successful initial therapy. Overexpression of ATP-binding cassette (ABC) transporters is important for the multidrug resistance. Among them, ABCB1 and ABCG2 are known to be upregulated in chemoresistant SCLC cells. We found that human epidermal growth factor receptor 2 (HER2) expressions are also upregulated in chemoresistant SBC-3/ETP, SBC-3/SN-38, and SBC-3/CDDP cells, compared with chemosensitive SBC-3 cells. Lapatinib, a tyrosine kinase inhibitor of HER2, could not suppress proliferation of these HER2-positive SCLC cells alone but successfully restored chemosensitivity to etoposide and SN-38 with a clinically applicable concentration. The reversal effect of lapatinib was thought to be caused by inhibition of drug efflux pump functions of ABC transporters, although lapatinib itself has been reported to be a substrate for them. Moreover, knocking down of HER2 by an short interfering RNA weakened the effect of lapatinib on ABCB1, indicating the involvement of HER2 in the inhibitory mechanisms. Notably, we showed that caveolin-1 and Src play key roles in modulating ABCB1 function via HER2 inactivation. In SBC-3/ETP cells, dephosphorylation of HER2 by lapatinib activates Src and successively leads to increased caveolin-1 phosphorylation. Through this process, caveolin-1 dissociates from HER2 and strengthens association with ABCB1, and finally impairs the pump functions. Furthermore, we showed that treatment by lapatinib in combination with etoposide or irinotecan significantly suppresses the growth of subcutaneous SBC-3/ETP and SBC-3/SN-38 tumors in mice, respectively. Collectively, these results indicate that combination therapy with lapatinib and cytotoxic agents could conquer ABC transporter-mediated chemoresistance especially in HER2-positive SCLC.

Expression of tetraspanins in human lung cancer cells: frequent downregulation of CD9 and its contribution to cell motility in small cell lung cancer

Small cell lung cancer (SCLC) invades locally and metastasizes distantly extremely early when compared with nonsmall cell lung cancer (NSCLC). The underlying molecular mechanisms, however, have not been elucidated. Accumulating evidence suggests that downregulation of several members of tetraspanins is associated with progression of solid tumors, thus indicating poor prognosis. Here we screened 30 lung cancer cell lines for expression of tetraspanins, CD9, CD63, CD81, CD82, CD151, and NAG-2. Flow cytometry revealed that, among these proteins, CD9 is broadly expressed in NSCLC lines, but is absent or highly reduced in most SCLC lines (P<0.0001). Using the Boyden chamber and videomicroscopic cell motility assays, we showed that stable transfection of CD9 into an SCLC line, OS3-R5, reduced cell motility on fibronectin. Furthermore, by transient transfection of green fluorescent protein (GFP)-tagged CD9 into three other SCLC lines, we observed that SCLC cells expressing GFP-CD9 were uniformly less motile than untransfected cells. CD9 or GFP-CD9 was associated with beta1 integrins and distributed at the tumor cell periphery and cell-cell contacts, suggesting that CD9 modifies beta1 integrin function to reduce motility. These findings suggest that low expression of CD9 may contribute to the highly invasive and metastatic phenotype of SCLC.

Lack of class II transactivator causes severe deficiency of HLA-DR expression in small cell lung cancer

Small cell lung cancer (SCLC) is characteristically not associated with tumour-infiltrating lymphocytes. Since SCLC has been reported to show marked reduction of class I HLA, the reduced expression has been considered a means of escaping anti-cancer immunity. However, HLA-DR expressed in cancer cells is now known to contribute to anti-cancer immunity. To clarify the difference in HLA-DR expression between SCLC and non-small cell lung cancer (NSCLC), and the mechanism, the expression and the cis- and trans-acting factors involved were investigated. HLA-DR was not immunohistochemically detected in any SCLC and could not be induced by interferon gamma (IFN-gamma) in any SCLC cell line, whereas HLA-DR was expressed to varying degrees and was easily induced in NSCLC. SCLC cell lines lacked class II transactivator (CIITA) even after IFN-gamma induction, whereas NSCLC cell lines expressed CIITA. The other class II HLA-specific transcription factors were expressed and genomic DNA of HLA-DR, including the promoter, was conserved well both in SCLC and in NSCLC cell lines. CIITA transfection improved the expression of HLA-DR in SCLC. In conclusion, the lack of CIITA results in severe deficiency of HLA-DR expression in SCLC. Since CIITA has also been reported to induce class I HLA, CIITA transfection might make it possible to establish effective anti-cancer immunotherapy against SCLC through the up-regulation of class I and class II HLA.

Complementary DNA sequence encoding the major neural cell adhesion molecule isoform in a human small cell lung cancer cell line

The neural cell adhesion molecule (N-CAM), a member of the immunoglobulin gene super-family mediating homophilic cell-cell adhesion in a neuroendocrine system, is preferentially expressed in human small cell lung cancer (SCLC). Immunoprecipitation of a panel of SCLC cell lines by monoclonal antibodies (mAbs) specific for N-CAM detects mainly the 145-kDa isoform. This result was correlated with Northern blotting where a single 6.2-kb mRNA was detected in nine SCLC cell lines. To determine cDNA sequence encoding the N-CAM isoform, we selected several cDNA clones encoding N-CAM isolated from OS2-R, a SCLC cell line established in our laboratory. Based on the analysis of the full-length cDNA obtained from two clones, the sequence of this 145-kDa isoform was shown to be essentially identical to that of the 140-kDa N-CAM isoform of neuroblastoma except for a single base pair changed at position 1620 without changing amino acid encoded.