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NAC and Cancer

NAC was shown to increase tumor growth in mice

This is a consequence of the fact cancer uptakes a lot of things more preferentially than normal cells.

For instance, glucose uptake preference by overexpressing preferential insulin receptor

Insulin receptor isoform A favors tumor progression in human hepatocellular carcinoma by increasing stem/progenitor cell features.

  • Hepatocellular carcinoma (HCC) is one of the most common and deadly neoplasms. Insulin receptor (IR) exists in two isoforms, IR-A and IR-B, the latter being predominantly expressed in normal adult hepatocytes while IR-A is overexpressed in HCC to the detriment of IR-B .... IR-A overexpression promoted gene programs related to stemness, inflammation and cell movement
  • cancer cells express outcompeting insulin receptors, seemingly causing a preferential (over normal cells) uptake of glucose. Good reason to burn fat.

For this particular issue with cystein, tumors over express gamma-glutamyl transpeptidase in their cell membrane, which allows them to preferentially grab glutahtione (which NAC converts to) from the blood stream:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4388159/
GGT in tumors is expressed over the entire cell membrane and provides tumors with access to additional cysteine and cystine from reduced and oxidized glutathione in the blood and interstitial fluid. Cysteine is rate-limiting for glutathione synthesis in cells under oxidative stress.