Abstract P1-01-03: Preclinical evidence that distant metastases occur via the lymphatic route

Cancer that metastasizes beyond the lymph nodes is almost invariably terminal. Therefore, understanding how cancer metastasizes is a critical aspect to understanding and eventually preventing cancer spreading from tissue to tissue. A major question that remains controversial is whether cancer cells that metastasize to the LNs are able to physically leave the LNs to colonize distant tissues. Moreover, whether cancer cell metastasis between different tissues involves unique genes is a question that requires further research. Using the metastatic mouse breast carcinoma line 4T1 in an LN microinjection model, we provide evidence suggesting that cancer cells can indeed metastasize and colonize distant tissues after direct implantation into the LNs. Interestingly, direct comparison of distant tissue metastatic capability comparing LN-microinjected cells and tail vein-injected cells suggests that the lymphatic route of cancer cell spreading may be a more efficient mechanism of metastasis than the hematogenous route. Moreover, our comparative transcriptome analysis results suggest that LN metastases show unique gene expression profiles relative to the primary breast tumors and distant metastases. We identified several genes that are up- or down-regulated in an LN-specific manner and thus may play a role in metastasis to the LNs and beyond. Collectively, our results suggest that LN metastases constitute an active “staging site” from which breast cancer cells can further metastasize to distant sites. Furthermore, we identify a unique set of genes that may be involved in the breast cancer metastatic process, several of which are potentially targetable using currently available inhibitors.

Citation Format: Leslie PL, Ghosh SK, Porrello A, Cooley BC, Pecot CV. Preclinical evidence that distant metastases occur via the lymphatic route [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P1-01-03.

Hypoxia-upregulated microRNA-630 targets Dicer, leading to increased tumor progression

MicroRNAs (miRNAs) are small RNA molecules that affect cellular processes by controlling gene expression. Recent studies have shown that hypoxia downregulates Drosha and Dicer, key enzymes in miRNA biogenesis, causing a decreased pool of miRNAs in cancer and resulting in increased tumor growth and metastasis. Here we demonstrate a previously unrecognized mechanism by which hypoxia downregulates Dicer. We found that miR-630, which is upregulated under hypoxic conditions, targets and downregulates Dicer expression. In an orthotopic mouse model of ovarian cancer, delivery of miR-630 using 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) nanoliposomes resulted in increased tumor growth and metastasis, and decreased Dicer expression. Treatment with the combination of anti-miR-630 and anti-vascular endothelial growth factor antibody in mice resulted in rescue of Dicer expression and significantly decreased tumor growth and metastasis. These results indicate that targeting miR-630 is a promising approach to overcome Dicer deregulation in cancer. As demonstrated in the study, use of DOPC nanoliposomes for anti-miR delivery serves as a better alternative approach to cell line-based overexpression of sense or antisense miRNAs, while avoiding potential in vitro selection effects. Findings from this study provide a new understanding of miRNA biogenesis downregulation observed under hypoxia and suggest therapeutic avenues to target this dysregulation in cancer.