Abstract
<p>A human adenosquamous carcinoma of the cervix (HASCC) xenograft contains two morphologically distinct subpopulations. The presence of adenoid and squamous epithelial elements was confirmed by histologic and ultrastructural analysis. Culturing in soft agar resulted in three morphologically distinct colony types. These were: Type A: grape-cluster like colonies, Type B: refractile colonies and Type C: loosely associated colonies. Time lapse photography followed colony development and revealed no interconversion between colony types in primary explants. Subculturing of type A colonies however, did result in either A or B type morphology. The data suggests that A and B subpopulations represent differing stages of differentiation within the same cell type. The C subpopulation retains distinct morphology and growth characteristics suggesting an overall A/B versus C polyclonal heterogeneity in HASCC tumors.The growth environment differentially influenced subpopulation survival. Under reduced oxygen tension (5%) the plating efficiency was enhanced over that seen in parallel cultures under 20% oxygen. A and C type colonies were enhanced 2-3 fold and 3-5 fold, respectively. B type colonies showed no change or slight increases (1-2 fold).Variation in the nutritional matrix altered the ratio of A:B:C type colonies. The presence of serum resulted in dominance of C type colonies (>90%). Its absence was associated with the prevalence of A type colonies (>60%).HASCC subpopulations responded differentially to anticancer agents. Continuous exposure to Ara-C, ADR and Mito-C produced marked cytotoxicity and overlapping dose response profiles. Divergence in subpopulation drug response occurred with HU and cis-PLT and was most marked at lower drug concentrations. The highest drug concentrations tended to select for A type colonies in 5 of 6 drugs tested.Based on the results shown here, measurement of total colony formation in clinical tumors may obscure the dynamic changes induced within individual subpopulations. Physiologic (e.g. oxygen), nutritional (e.g. serum) and cytotoxic (chemotherapeutic drugs) factors alter the balance of surviving heterogeneous tumor subpopulations. Future efforts to define the role of environmental selection of drug resistant subpopulations, such as the A type in HASCC tumors, may improve our understanding of human tumor biology and drug resistance.</p>