Faculty Bibliography

INTRODUCTION: Human bronchioloalveolar carcinoma (BAC) is a disease with an evolving definition. "Pure" BAC, characterized by a bronchioloalveolar growth pattern and no evidence of stromal, vascular, or pleural invasion, represents only 2 to 6% of non-small cell lung cancer (NSCLC) cases, but up to 20% of NSCLC cases may contain elements of BAC. This imprecise definition makes it difficult to perform epidemiologic analyses or to generate accurate animal models. However, because BAC appears to behave clinically differently from adenocarcinoma, a better understanding of this disease entity is imperative. METHODS/RESULTS: At the BAC Consensus Conference in 2004, our committee discussed issues relevant to BAC epidemiology, pathogenesis, and preclinical models. CONCLUSIONS: Elucidation of molecular events involved in BAC tumorigenesis will allow for more precise epidemiologic studies and improved animal models, which will enable development of more effective treatments against the disease.

Activating mutations in the kinase domain of the epidermal growth factor receptor (EGFR) in nonsmall cell lung cancers (NSCLCs) correlate with responsiveness to EGFR kinase inhibitors. In vitro cell culture studies have demonstrated that EGFR kinase domain mutants but not wild type (wt) EGFR are transforming and essential for cancer cell survival. We and others have recently demonstrated that the induction of EGFR kinase domain mutants specifically in murine lung epithelium in vivo led to development of adenocarcinoma with bronchioloalveolar carcinoma (BAC) features. These tumors depend completely on the sustained expression of EGFR kinase domain mutants for tumor maintenance. The murine tumors with EGFR kinase domain mutations are sensitive to EGFR targeted therapy similarly to NSCLC patients whose tumors harbor EGFR mutations. In contrast, initial results suggest that overexpression of wt EGFR in murine lungs does not seem to be transforming. We therefore divide EGFR targeted therapy in NSCLC patients into two parts: "EGFR mutant targeted therapy" and "wt EGFR targeted therapy". The "EGFR mutant targeted therapy" targets the oncogene essential for tumor initiation and maintenance and is frequently correlated with effective clinical outcome. In contrast, "wt EGFR targeted therapy" likely targets the proto-oncogene product wt EGFR, which is not directly involved in tumor initiation and maintenance, and in these cases, the response has been considerably less dramatic.

Loss of p53 tumor suppressor facilitates acquisition of telomerase activity. In fact, both p53 inactivation and telomerase activation are frequently found in human cancers. p53 inactivation, however, eliminates or attenuates the biological responses to telomerase inhibition and the eventual telomere erosion. We show that telomere erosion can increase the susceptibility to radiation, irrespective of p53 status. Both telomerase inhibition and critically shortened telomere with significant change of chromosomal end-to-end fusion were essential for the enhancement of radiosensitivity. The enhancement was correlated with greater formation of multinucleated cells. p53 inactivation did not eliminate the observed generation of chromosomal fusion and multinucleation, and the resulting increased susceptibility to radiation, as opposed to the previously proved role of p53 in mediating cellular responses to telomere dysfunction. The present findings suggest the importance of chromosomal end fusion in modulating radiosensitivity rather than p53 DNA damage signaling. Thus, the suggested anticancer radiotherapeutic strategy combined with telomerase inhibition could clinically be applicable to cancers, irrespective of p53 status.

Human lung cancer is responsible for approximately 30% of all cancer deaths worldwide with >160,000 deaths in the United States alone annually. Recent advances in the identification of novel mutations relevant to lung cancer from a myriad of genomic studies might translate into meaningful diagnostic and therapeutic progress. Towards this end, a genetic model animal system that can validate the oncogenic roles of these mutations in vivo would facilitate the understanding of the pathogenesis of lung cancer as well as provide ideal preclinical models for targeted therapy testing. The mouse is a promising model system, as complex human genetic traits causal to lung cancer, from inherited polymorphisms to somatic mutations, can be recapitulated in its genome via genetic manipulation. We present here a brief overview of the existing mouse models of lung cancers and the challenges and opportunities for building the next generation of lung cancer mouse models.

Mutation-specific cancer therapy has shown promising clinical efficacy. In non-small-cell lung cancer (NSCLC), the presence of mutations in the epidermal growth factor receptor (EGFR) tyrosine kinase correlates with clinical response to small-molecule tyrosine kinase inhibitors. Here, we show that cells harboring the G776insV_G/C mutation in the related ERBB2 tyrosine kinase (also known as HER2 or Neu), present in a small percentage of NSCLCs, are sensitive to HKI-272, an irreversible dual-specific kinase inhibitor targeting both EGFR and ERBB2. In the ERBB2-mutant NCI-H1781 cell line, HKI-272 treatment inhibited proliferation by induction of G(1) arrest and apoptotic cell death. Furthermore, HKI-272 abrogated autophosphorylation of both ERBB2 and EGFR. Finally, Ba/F3 murine pro-B cells, engineered to express mutant ERBB2, became independent of interleukin-3 and sensitive to HKI-272. Thus, the subset of NSCLC patients with tumors carrying the ERBB2 G776insV_G/C mutation may benefit from treatment with HKI-272.

The sensitivity of conventional DNA sequencing in tumor biopsies is limited by stromal contamination and by genetic heterogeneity within the cancer. Here, we show that microreactor-based pyrosequencing can detect rare cancer-associated sequence variations by independent and parallel sampling of multiple representatives of a given DNA fragment. This technology can thereby facilitate accurate molecular diagnosis of heterogeneous cancer specimens and enable patient selection for targeted cancer therapies.

To understand the role of human epidermal growth factor receptor (hEGFR) kinase domain mutations in lung tumorigenesis and response to EGFR-targeted therapies, we generated bitransgenic mice with inducible expression in type II pneumocytes of two common hEGFR mutants seen in human lung cancer. Both bitransgenic lines developed lung adenocarcinoma after sustained hEGFR mutant expression, confirming their oncogenic potential. Maintenance of these lung tumors was dependent on continued expression of the EGFR mutants. Treatment with small molecule inhibitors (erlotinib or HKI-272) as well as prolonged treatment with a humanized anti-hEGFR antibody (cetuximab) led to dramatic tumor regression. These data suggest that persistent EGFR signaling is required for tumor maintenance in human lung adenocarcinomas expressing EGFR mutants.

The tyrosine kinase inhibitors gefitinib (Iressa) and erlotinib (Tarceva) have shown anti-tumor activity in the treatment of non-small cell lung cancer (NSCLC). Dramatic and durable responses have occurred in NSCLC tumors with mutations in the tyrosine kinase domain of the epidermal growth factor receptor (EGFR). In contrast, these inhibitors have shown limited efficacy in glioblastoma, where a distinct EGFR mutation, the variant III (vIII) in-frame deletion of exons 2-7, is commonly found. In this study, we determined that EGFRvIII mutation was present in 5% (3/56) of analyzed human lung squamous cell carcinoma (SCC) but was not present in human lung adenocarcinoma (0/123). We analyzed the role of the EGFRvIII mutation in lung tumorigenesis and its response to tyrosine kinase inhibition. Tissue-specific expression of EGFRvIII in the murine lung led to the development of NSCLC. Most importantly, these lung tumors depend on EGFRvIII expression for maintenance. Treatment with an irreversible EGFR inhibitor, HKI-272, dramatically reduced the size of these EGFRvIII-driven murine tumors in 1 week. Similarly, Ba/F3 cells transformed with the EGFRvIII mutant were relatively resistant to gefitinib and erlotinib in vitro but proved sensitive to HKI-272. These findings suggest a therapeutic strategy for cancers harboring the EGFRvIII mutation.

BACKGROUND: Little is known about the biological mechanisms underlying the excess medical morbidity and mortality associated with mood disorders. Substantial evidence supports abnormalities in stress-related biological systems in depression. Accelerated telomere shortening may reflect stress-related oxidative damage to cells and accelerated aging, and severe psychosocial stress has been linked to telomere shortening. We propose that chronic stress associated with mood disorders may contribute to excess vulnerability for diseases of aging such as cardiovascular disease and possibly some cancers through accelerated organismal aging. METHODS: Telomere length was measured by Southern Analysis in 44 individuals with chronic mood disorders and 44 nonpsychiatrically ill age-matched control subjects. RESULTS: Telomere length was significantly shorter in those with mood disorders, representing as much as 10 years of accelerated aging. CONCLUSIONS: These results provide preliminary evidence that mood disorders are associated with accelerated aging and may suggest a novel mechanism for mood disorder-associated morbidity and mortality.