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Cellular heterogeneity is an integral part of cancer development and progression. Progression can be associated with emergence of cells that exhibit high phenotypic plasticity (including "de-differentiation" to primitive developmental states), and aggressive behavioral properties (including high tumorigenic potentials). We observed that many biomarkers that are used to identify Cancer Stem Cells (CSC) can label cell subsets in an advanced clinical stage of lung cancer (malignant pleural effusions, or MPE). Thus, CSC-biomarkers may be useful for live sorting functionally distinct cell subsets from individual tumors, which may enable investigators to hone in on the molecular basis for functional heterogeneity. We demonstrate that the CD44(hi) (CD44-high) cancer cell subsets display higher clonal, colony forming potential than CD44(lo) cells (n=3) and are also tumorigenic (n=2/2) when transplanted in mouse xenograft model. The CD44(hi) subsets express different levels of embryonal (de-differentiation) markers or chromatin regulators. In archived lung cancer tissues, ALDH markers co-localize more with CD44 in squamous cell carcinoma (n=5/7) than Adeno Carcinoma (n=1/12). MPE cancer cells and a lung cancer cell line (NCI-H-2122) exhibit chromosomal abnormalities and 1p36 deletion (n=3/3). Since miR-34a maps to the 1p36 deletion site, low miR-34a expression levels were detected in these cells. The colony forming efficiency of CD44(hi) cells, characteristic property of CSC, can be inhibited by mir-34a replacement in these samples. In addition the highly tumorigenic CD44(hi) cells are enriched for cells in the G2 phase of cell cycle.

Malignant Pleural Effusions (MPE) may be useful as a model to study hierarchical progression of cancer and/or intratumoral heterogeneity. To strengthen the rationale for developing the MPE-model for these purposes, we set out to find evidence for the presence of cancer stem cells (CSC) in MPE and demonstrate an ability to sustain intratumoral heterogeneity in MPE-primary cultures. Our studies show that candidate lung CSC-expression signatures (PTEN, OCT4, hTERT, Bmi1, EZH2 and SUZ12) are evident in cell pellets isolated from MPE, and MPE-cytopathology also labels candidate-CSC (CD44, cMET, MDR-1, ALDH) subpopulations. Moreover, in primary cultures that use MPE as the source of both tumor cells and the tumor microenvironment (TME), candidate CSC are maintained over time. This allows us to live-sort candidate CSC-fractions from the MPE-tumor mix on the basis of surface markers (CD44, c-MET, uPAR, MDR-1) or differences in xenobiotic metabolism (ALDH). Thus, MPE-primary cultures provide an avenue to extract candidate CSC populations from individual (isogenic) MPE-tumors. This will allow us to test whether these cells can be discriminated in functional bioassays. Tumor heterogeneity in MPE-primary cultures is evidenced by variable immunolabeling, differences in colony-morphology, and differences in proliferation rates of cell subpopulations. Collectively, these data justify the ongoing development of the MPE-model for the investigation of intratumoral heterogeneity, tumor-TME interactions, and phenotypic validation of candidate lung CSC, in addition to providing direction for the pre-clinical development of rational therapeutics.