Inhibitory effects of nitric oxide on invasion of human cancer cells

Citation:
Wang, F., Zhang, R., Xia, T., Hsu, E., Cai, Y., Gu, Z., Hankinson, O. Inhibitory effects of nitric oxide on invasion of human cancer cells (2007). Cancer Letters, 257 (2), pp. 274-282.
PMID: 17869411

Summary:
This paper talks about testing whether or not NO had an inhibitory effect on cancer cell invasion and also exploring the mechanism of the inhibition. In particular, they explored the effect of NO on HIF-1, which is involved in the transcription of many genes linked to cell proliferation, angiogenesis, and metastasis. HIF-1 often overexpressed in human cancers as a result of hypoxia at the tumor site and genetic mutations; and its overexpression has been associated with patient morality in many studies.

For their experiments, the group used prostate cancer cell line PC-3M and bladder cancer cell line T24 cells as their strains and performed invasion assays using Matrigel invasion chambers. The cells were seeded in the Matrigel chambers both under normal conditions and also after hypoxia treatments , during which the chambers were placed in an airtight cell culture incubator maintained with low levels of oxygen for 24 hours and then cultured under normal conditions afterwards for another 24 hours.

In their experiments, sodium nitroprusside (SNP) was used as a nitric oxide donor. In addition to invasion assays, immunoblotting techniques were used to detect HIF-1 protein levels and cell proliferation rates were measured for cultures treated with SNP alone and with SNP and a NO scavenger PTIO together, as well as other controls. From the experiments, hypoxia conditions increased cell proliferation and invasion as well as higher levels of HIF-1. Their results also showed that SNP strongly inhibited the invasion of the cells. In the presence of a NO scavenger), the effect of SNP on invasion was negated, which suggests that invasion is dependent on how much NO is released. From the immunoblotting assays, it was shown that SNP inhibits the expression of HIF-1 for the two strains at 100uM.

The group has concluded that the inhibitory effect of NO is related to inhibiting HIF-1. However, they do no believe that this is the only mechanism since some of their results could not be explained fully. They also hypothesize that NO inhibits the function of mitochondria and that mitochondria inhibitors reduces the invasion of cancer cells.

Significance:
In clinical applications, hypoxia is associated with cancer cell resistance to chemotherapy, metastasis and patient mortality. Since most cancer related deaths are a result of uncontrollable metastasis of tumor cells, mechanisms by which cancer cells invasion can be inhibited would be useful in predicting and designing drugs that target the mobility of cancer cells. The discovery of the inhibitory effects of nitric oxide on cancer cell invasion suggests that NO donors may be effective cancer chemotherapeutic agents. Since its mechanism for inhibiting cancer cell motility is related to inhibiting HIF-1, other ways of down-regulating the effect of HIF-1 in cancer cells or reducing hypoxia at cancer sites can also be explored for their therapeutic potential.