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Sputum, widely used to study the cellular content and other microenvironmental features to understand the health of the lung, is traditionally analyzed using cytology-based methodologies. Its utility is limited because reading the slides is time-consuming and requires highly specialized personnel. Moreover, extensive debris and the presence of too many squamous epithelial cells (SECs), or cheek cells, often renders a sample inadequate for diagnosis. In contrast, flow cytometry allows for high-throughput phenotyping of cellular populations while simultaneously excluding debris and SECs. The protocol presented here describes an efficient method to dissociate sputum into a single cell suspension, antibody stain and fix cellular populations, and acquire samples on a flow cytometric platform. A gating strategy that describes the exclusion of debris, dead cells (including SECs) and cell doublets is presented here. Further, this work also explains how to analyze viable, single sputum cells based on a cluster of differentiation (CD)45 positive and negative populations to characterize hematopoietic and epithelial lineage subsets. A quality control measure is also provided by identifying lung-specific macrophages as evidence that a sample is derived from the lung and is not saliva. Finally, it has been demonstrated that this method can be applied to different cytometric platforms by providing sputum profiles from the same patient analyzed on three flow cytometers; Navios EX, LSR II, and Lyric. Furthermore, this protocol can be modified to include additional cellular markers of interest. A method to analyze an entire sputum sample on a flow cytometric platform is presented here that makes sputum amenable for developing high-throughput diagnostics of lung disease.

Cellular uptake of vitamin B

Designing effective therapies with selective toxicity in cancer cells is a priority of cancer research. Porphyrins are known to selectively accumulate in cancerous tissue, a feature that has been exploited in cancer diagnostics and therapeutics. The porphyrin TCPP is used in the CyPath® Lung test for diagnosis of lung cancer. During efforts to elucidate the mechanism by which TCPP selectively accumulates in cancer cells, we discovered that simultaneous knockdown of two LDLR-family receptors, CD320 and LRP2, was selectively cytotoxic to cancer cells and not to normal cells. CD320 is a receptor that internalizes the complex of cobalamin (Vitamin B12)/transcobalamin II. LRP2 is a receptor strongly expressed in the kidney which also internalizes the cobalamin/transcobalamin II complex, in addition to more than 50 other ligands. Cobalamin is the catalytic cofactor for the enzymes methionine synthase and methylmalonyl CoA mutase, which play direct and indirect roles in folate metabolism, nucleotide biosynthesis, DNA methylation, and metabolism of fatty acids and amino acids, which suggests that cobalamin deprivation might be particularly deleterious to metabolically active cancer cells. We designed siRNAs to effectively silence CD320 and LRP2 protein expression and transfected these siRNAs into normal and cancer cell lines using commercial transfection reagents. Effective gene knockdown (up to 90%) was confirmed by western blotting. Simultaneous siRNA knockdown of CD320 and LRP2 in normal fibroblasts did not affect their cell proliferation, as measured by the Cell Titer-GLO assay. However, knockdown of CD320 and LRP2 in cancer cell lines derived from diverse tissues (lung, breast, prostate, brain, and skin cancers) inhibited cell proliferation or killed the cells by up to 80%. Interestingly, in some cell lines, when either CD320 or LRP2 were silenced individually, a concurrent increase in protein expression of the other receptor was observed, suggesting that CD320 and LRP2 compensate for each other's function; hence, silencing both receptors is required for optimal cell killing. Ongoing studies will test the hypothesis that cobalamin deficiency is a mechanism for the selective cytotoxicity observed in cancer cells. Further studies include in vivo animal studies to study the effects on CD320 and LRP2 knockdown on human tumor xenograft models. In summary, we have found that inhibiting CD320 and LRP2 expression strongly and selectively inhibits cancer cell growth, leading to a promising therapeutic strategy for diverse cancers. Citation Format: David J. Elzi, William Bauta, Shao-Chiang Lai, Trisha Das, Shweta Mogare, Vivienne I. Rebel. Simultaneous knockdown of CD320 and LRP2 receptors is selectively toxic to cancer cells but not normal cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1223.

Cellular uptake of vitamin B12 (cobalamin, Cbl) is mediated by a cell surface receptor (TCblR/CD320) that binds transcobalamin (TC) saturated with Cbl. TC is secreted by the vascular endothelium, has a relatively short half-life, binds Cbl with high affinity and presents the vitamin to the receptor for cellular uptake. Here we show binding and internalization of the TC-Cbl complex along with its’ receptor (TCblR) in several human cell lines. The expression of TCblR is linked to the cell cycle with highest expression in actively proliferating cells. Upon binding TC-Cbl, the receptors appear to segregate on the plasma membrane and are internalized over the course of 30–60 min. Subsequently, the receptors appear to be destroyed along with the TC, which results in the release of free Cbl in the lysosome. The appearance of TCblR on the cell surface is limited to newly synthesized protein without contribution from recycling of the receptor. Therefore, Cbl uptake into cells is fully dependent on the expression of newly synthesized TCblR that is up-regulated in actively proliferating cells. The cell cycle-associated up-regulation of TCblR in cancers provides a route for targeted drug delivery.

Thyroid transcription factor 1 (TTF-1 or NKX2-1) is a transcription factor of fundamental importance in driving lung maturation and morphogenesis. In the last decade, scientists began to appreciate the functional roles of TTF-1 in lung tumorigenesis. This movement was triggered by the discoveries of genetic alterations of TTF-1 in the form of gene amplification in lung cancer. Many downstream target genes of TTF-1 relevant to the lung cancer biology of TTF-1 have been documented. One of the most surprising findings was that TTF-1 may exhibit either pro- or antitumorigenic activities, an outcome with the complexity exceeding the original anticipation purely based on the fact that TTF-1 undergoes gene amplification in lung cancer. In the coming decade, we believe, we will witness additional surprises as the research exploring the cancer roles of TTF-1 progresses.

Thyroid transcription factor 1 (TTF-1 or NKX2-1) is a transcription factor of fundamental importance in driving lung maturation and morphogenesis. In the last decade, scientists began to appreciate the functional roles of TTF-1 in lung tumorigenesis. This movement was triggered by the discoveries of genetic alterations of TTF-1 in the form of gene amplification in lung cancer. Many downstream target genes of TTF-1 relevant to the lung cancer biology of TTF-1 have been documented. One of the most surprising findings was that TTF-1 may exhibit either pro- or antitumorigenic activities, an outcome with the complexity exceeding the original anticipation purely based on the fact that TTF-1 undergoes gene amplification in lung cancer. In the coming decade, we believe, we will witness additional surprises as the research exploring the cancer roles of TTF-1 progresses.

Through both gain- and loss-of-TTF-1 expression strategies, we show that TTF-1 positively regulates vascular endothelial growth factor (VEGF) and that the VEGF promoter element contains multiple TTF-1-responsive sequences. The major signaling receptor for VEGF, i.e VEGFR2, also appears to be under a direct and positive regulation of TTF-1. The TTF-1-dependent upregulation of VEGF was moderately sensitive to rapamycin, implicating a partial involvement of mammalian target of rapamycin (mTOR). However, hypoxia did not further increase the secreted VEGF level of the TTF-1+ lung cancer cells. The TTF-1-induced VEGF upregulation occurs in both compartments (exosomes and exosome-depleted media (EDM)) of the conditioned media. Surprisingly, the EDM of TTF-1+ lung cancer cells (designated EDM-TTF-1+) displayed an anti-angiogenic activity in the endothelial cell tube formation assay. Mechanistic studies suggest that the increased granulocyte-macrophage colony-stimulating factor (GM-CSF) level in the EDM-TTF-1+ conferred the antiangiogenic activities. In human lung cancer, the expression of TTF-1 and GM-CSF exhibits a statistically significant and positive correlation. In summary, this study provides evidence that TTF-1 may reprogram lung cancer secreted proteome into an antiangiogenic state, offering a novel basis to account for the long-standing observation of favorable prognosis associated with TTF-1+ lung adenocarcinomas.