Endobronchial carcinogenesis in dogs

Animal models for studying lung cancer and evaluating novel intervention strategies

The pathogenesis of lung cancer progression, invasion and metastasis remains undefined. Clinically relevant laboratory models of the disease could greatly facilitate its clarification. Model systems of lung cancer that accurately reflect different biologic properties and disease stages are necessary to ensure proper experimental design of studies aimed at increasing our understanding of the disease. Such models are also essential tools to accelerate development of new therapies for lung cancer. In this review we summarize the available lung cancer model systems in use today and define both their utility and limitations.

Histogenesis of adenosquamous bronchogenic carcinoma

In our hamster lung cancer model studies, among 463 non-small-cell lung cancers (NSCLC), there were 47 adenosquamous neoplasms. In 24 of 27 lesions with diameters of less than 3.0 mm, the adenocarcinoma and the squamous cell carcinoma components arose as separate, spatially discrete lesions, but these were separate in only 7 of 20 lesions with diameters of 30 mm or greater. Co-infiltration of the components became more frequent as tumor size increased. The usual adenosquamous variety of NSCLC is likely a collision tumor, with each component possessing separate biological characteristics. Thus, future prognostically directed studies of this variety of NSCLC must recognize that these neoplasms have two components, each of which needs to assessed.

Regression of bronchial epithelial cancer in hamsters

For bronchogenic carcinoma, if and when the sequential process of carcinogenesis is reversible is fundamental to chemoprevention research. In our hamster model, focally originating non-small cell lung carcinoma (NSCLC) develops via a reproducible sequential process of carcinogenesis by 180 days after endobronchial sustained-release implants (SRIs) of 10% benzo(a)pyrene. In this study, 114 hamsters received removable 10% benzo(a)pyrene SRIs. Short-term controls were sacrificed in 3 groups at 50, 65, and 80 days after SRI placement. Three experimental groups had SRIs removed at 50, 65, and 80 days after placement, and sacrifice was delayed until 100 to 180 days later. Long-term controls retained SRIs until sacrifice at 180 or 240 days after SRI placement. All long-term controls had NSCLC. Preneoplastic change was more common in 50- and 65-day controls, as compared with hamsters with equal duration of SRI exposure whose sacrifice was delayed until 100 to 180 days after SRI removal (p < 0.05). The 56% incidence of early NSCLC in hamsters sacrificed after 80 days of SRI exposure decreased to 5% in hamsters that had delayed sacrifice after SRI removal after 80 days of exposure. At the 10% benzo(a)pyrene dose used, hamster bronchial epithelium requires more than 80 days of continuous exposure to become irreversibly committed to NSCLC uniformly. Microinvasive NSCLC in hamsters often regresses, and it is not necessarily a precursor of overt invasive cancer. The removable SRI model provides new opportunities to evaluate chemoprevention of NSCLC and the related molecular-genetic control mechanisms.

Metastatic behaviour of canine lung carcinoma in autochthonous and xenotransplant hosts

Specimens from 24 chemically induced canine non-small cell lung cancers (NSCLC) were xenotransplanted into nude mice. Twenty-one tumour lines were established in serial transplantation; four were from NSCLC that arose from orthotopically induced NSCLC in four dogs, and 17 were from NSCLC that arose heterotopically in 15 subcutaneous bronchial autografts (SBA) in seven dogs. Distant metastases developed in recipients of two orthotopic NSCLC after three and eight consecutive tumour growth cycles; no metastases have occurred after three and six growth cycles of two other orthotopic tumour lines. Recipients of eight heterotopic tumour lines developed metastases after 3-9 consecutive tumour growth cycles, while no metastases have occurred after 4-11 growth cycles in recipients of nine other heterotopic tumour lines. In three instances, both metastasizing and non-metastasizing tumour lines resulted from NSCLC that arose in different SBAs in the same dog. These findings indicate that, in the canine SBA bronchogenic cancer model as expanded by tumour xenotransplantation, those molecular events involved in both the initiation and the full progression of a single cancer may be investigated serially and concomitantly.