DNA Methyltransferase 3B-Mediated Intratumoral Heterogeneity and Therapeutic Targeting in Breast Cancer Recurrence and Metastasis.

The mechanisms of how cancer cells are selected and evolve to establish distant metastatic colonies remain unclear. Tumor heterogeneity and lack of biomarkers are some of the most difficult challenges in cancer biology and treatment. Here using mouse models for triple-negative breast cancer (TNBC) metastasis, we report heterogeneous expression of DNA methyltransferase 3B (DNMT3B) in both mouse and human primary tumors. High levels of DNMT3B were correlated with poor clinical outcomes in multiple human breast cancer datasets. Mechanistically, clonal cells with high DNMT3B (DNMT3BH) showed higher vimentin (VIM) expression and displayed enhanced epithelial-to-mesenchymal transition capacity. Deletion of VIM diminished the metastatic phenotype of DNMT3BH cells. Importantly, in preclinical mouse models in which the primary tumors were surgically removed, perioperative targeting of DNMT3B in combination with chemotherapy markedly suppressed tumor recurrence and metastasis. Our studies identify DNMT3B-mediated transcription regulation as an important mediator of tumor heterogeneity and show that DNMT3B is critical for tumor invasion and metastasis, reinforcing its potential as a target for treating metastatic disease. IMPLICATIONS: Our findings of transcriptome changes mediated by DNMT3B provide new mechanistic insight for intratumor heterogeneity and chemoresistance, and therapeutic targeting of DNMT3B in combination with chemotherapy offer additional treatment options for metastatic disease especially for patients with TNBC.

Induction of DNMT3B by PGE2 and IL6 at Distant Metastatic Sites Promotes Epigenetic Modification and Breast Cancer Colonization.

Current cancer treatments are largely based on the genetic characterization of primary tumors and are ineffective for metastatic disease. Here we report that DNA methyltransferase 3B (DNMT3B) is induced at distant metastatic sites and mediates epigenetic reprogramming of metastatic tumor cells. Multiomics analysis and spontaneous metastatic mouse models revealed that DNMT3B alters multiple pathways including STAT3, NFκB, PI3K/Akt, ß-catenin, and Notch signaling, which are critical for cancer cell survival, apoptosis, proliferation, invasion, and colonization. PGE2 and IL6 were identified as critical inflammatory mediators in DNMT3B induction. DNMT3B expression levels positively correlated with human metastatic progression. Targeting IL6 or COX-2 reduced DNMT3B induction and improved chemo or PD1 therapy. We propose a novel mechanism linking the metastatic microenvironment with epigenetic alterations that occur at distant sites. These results caution against the "Achilles heel" in cancer therapies based on primary tumor characterization and suggests targeting DNMT3B induction as new option for treating metastatic disease. SIGNIFICANCE: These findings reveal that DNMT3B epigenetically regulates multiple pro-oncogenic signaling pathways via the inflammatory microenvironment at distant sites, cautioning the clinical approach basing current therapies on genetic characterization of primary tumors.

Molecular species of PC and PE formed during castor oil biosynthesis.

As part of a program to elucidate castor oil biosynthesis, we have identified 36 molecular species of PC and 35 molecular species of PE isolated from castor microsomes after incubations with [14C]-labeled FA. The six [14C]FA studied were ricinoleate, stearate, oleate, linoleate, linolenate, and palmitate, which were the only FA identified in castor microsomal incubations. The incorporation of each of the six FA into PC was better than that into PE. The [14C]FA were incorporated almost exclusively into the sn-2 position of both PC and PE. The incorporation of [14C]stearate and [14C]palmitate into 2-acyl-PC was slower compared to the other four [14C]FA. The incorporation does not show any selectivity for the various lysoPC molecular species. The level of incorporation of [14C]FA in PC was in the order of: oleate > linolenate > palmitate > linoleate > stearate > ricinoleate, and in PE: linoleate > linolenate > oleate > palmitate > stearate > ricinoleate. In general, at the sn-1 position of both PC and PE, linoleate was the most abundant FA, palmitate was the next, and oleate, linolenate, stearate, and ricinoleate were minor FA. The activities of oleoyl-12-hydroxylase, oleoyl-12-desaturase seem unaffected by the FA at the sn-1 position of 2-oleoyl-PC. The FA in the sn-1 position of PC does not significantly affect the activity of phospholipase A2, whereas ricinoleate is preferentially removed from the sn-2 position of PC. The results show that (i) [14C]oleate is most actively incorporated to form 2-oleoyl-PC, the immediate substrate of oleoyl-12-hydroxylase; (ii) 2-ricinoleoyl-PC is formed mostly by the hydroxylation of 2-oleoyl-PC, not from the incorporation of ricinoleate into 2-ricinoleoyl-PC; and (iii) 2-oleoyl-PE is less actively formed than 2-oleoyl-PC.