Background: Success of neoadjuvant chemotherapy (NACT) varies by intrinsic subtype of a patient’s breast cancer (e.g., Normal-like, Luminal A/B, HER2-enriched, Triple Negative). The metabolic rate of a given tumor is implicated in response to chemotherapies, as many act by killing rapidly dividing cells. Metabolic dis-regulation opens avenues for cancer cells to exploit environmental niches arising in the tumor microenvironment (TME). Focusing on the role the TME plays in defining cancer behavior, we undertook a theoretical investigation to uncover how metabolic cross-feeding affects subtype behavior and patient response.
Methods: An in silico analysis of cross-feeding variability arising from metabolic differences breast cancers was undertaken. TME community models consisting of fatty, glandular, and cancerous tissues’ metabolic behaviors were created. Expression levels of metabolic enzymes for 1222 community patients in TCGA BRCA were used to create models. Models were used in 3D simulations of tumors for 300 patients from the TCIA (Clark et al., J. Digital Imaging, 2013). Cross-feeding trends within each intrinsic subtype were analyzed.
Results: Predicted TME metabolic capabilities were compared to literature: LA/LB had lower amino acid consumption than TNBC/HER2+ for asparagine, glutamine (Glu), tryptophan, phenylalanine (van Geldermolsen et al. Oncogone 2016; Furuya et al. Cancer Sci. 2012). Additionally, TNBC tumors produced Glu which was consumed by adipose tissue (Cao et al. BMC Cancer, 2014), TNBC produced methionine and proline (Kanaan et al. Can. Gen. Prot. 2014), and TNBC/HER2+ cancers consumed high density lipoprotein produced by adipose (Balabum et al. Cancer Met. 2017). The simulations revealed novel cross-feeding behaviors. In general, TNBC/HER2+ relied on glucose as the primary energy source, while LA/LB relied on the amino acids alanine, glycine and Glu. TNBC/HER2+ cancers produced high levels of lactate which was consumed by adipose tissues. Uniquely, glycine produced by cancer was consumed by fat in TNBC cancers Several environmental niches were induced in the healthy tissue by the presence of the cancer; for example, ornithine was predicted to be cross-fed from fatty to glandular tissues in TNBC/HER2+ cancers, and glutamate and inosine from glandular to fatty tissues in HER2+ cancers.
Conclusions: Metabolic niches provide opportunities for cancer subtypes. These results suggest that metabolic pathway usage can lead to difference in growth, cross-feeding, and drug efficacy.