Intratumor lactate levels reflect HER2 addiction status in HER2-positive breast cancer.

Despite different molecular tumor profiles indicate that human epidermal growth factor receptor 2 (HER2) messenger RNA (mRNA) levels mirror HER2 addiction and trastuzumab benefit in HER2-positive breast cancer (BC), the identification of noninvasive clinical predictors of trastuzumab sensitivity remains an unmet clinical need. In the current study, we investigated whether intratumor lactate levels reflect HER2 addiction and, in turn, trastuzumab susceptibility. Accordingly, the gene expression profiles of transgenic murine BC cell lines expressing the human d16HER2 variant (HER2-addicted) or human full-length HER2 (WTHER2; HER2-nonaddicted) revealed a significant enrichment of glycolysis-related gene pathways in HER2-addicted cells. We studied the metabolic content of 22 human HER2-positive BC by quantitative nuclear magnetic resonance spectroscopy and found that those cases with higher lactate levels were characterized by higher HER2 transcript levels. Moreover, gene expression analyses of HER2-positive BC samples from a TCGA data set revealed a significant enrichment in glycolysis-related pathways in high/HER2-addicted tumors. These data were confirmed by metabolic analyses of human HER2-positive BC cell lines with high or low HER2 transcript levels, which revealed significantly more active glycolytic metabolism in high HER2 transcript than in low HER2 transcript cells. Overall, our results provide evidence for noninvasive intratumor lactate detection as a potential metabolic biomarker of HER2 addiction and trastuzumab response suggesting the possibility to use in vivo imaging to assess lactate levels and, in turn, select HER2-positive BC patients who are more likely to benefit from anti-HER2 treatments.

Phenethyl isothiocyanate hampers growth and progression of HER2-positive breast and ovarian carcinoma by targeting their stem cell compartment.

PURPOSE: Isothiocyanates elicit anticancer effects by targeting cancer stem cells (CSCs). Here, we tested the antitumor activity of phenethyl-isothiocyanate (PEITC), either alone or in combination with trastuzumab, in HER2-positive tumor models. METHODS: We assessed the in vitro anticancer activity of PEITC, alone or combined with trastuzumab, in HER2-positive BT474, SKBR3, HCC1954 and SKOV3 cancer cells by measuring their sphere forming efficiency (SFE). The expression of the human/rodent CSC biomarkers aldehyde-dehydrogenase (ALDH) and CD29High/CD24+/Sca1Low was evaluated by cytofluorimetric analysis. The expression of wild type HER2 (WTHER2), its splice variant d16HER2 and NOTCH was analysed by quantitative RT-PCR and Western blotting. The in vivo activity of PEITC and trastuzumab was evaluated in mice orthotopically implanted with MI6 tumor cells transgenic for the human d16HER2 splice isoform. Magnetic resonance imaging/spectroscopy and immunohistochemistry were used to assess morpho-functional and metabolic profiles of treated versus untreated mice. RESULTS: We found that PEITC significantly impaired the SFE of HER2-positive human cancer cells by decreasing their ALDH-positive compartments. The anti-CSC activity of PEITC was demonstrated by a reduced expression/activation of established cancer-stemness biomarkers. Similar results were obtained with MI6 cells, where PEITC, alone or in combination with trastuzumab, significantly inhibited their SFE. We also found that PEITC hampered the in vivo growth of MI6 nodules by inducing hemorrhagic and necrotic intra-tumor areas and, in combination with trastuzumab, by significantly reducing spontaneous tumor development in d16HER2 transgenic mice. CONCLUSIONS: Our results indicate that PEITC targets HER2-positive CSCs and that its combination with trastuzumab may pave the way for a novel therapeutic strategy for HER2-positive tumors.