Background: Previous paper results indicate that the activity of nm23H1 is independent of its NDPKA (Nucleoside Di Phosphate Kinase A) activity.

Materials and Methods: NDPKA/nm23 H1’s cell viability assay, standard curve for phosphate, cell phosphate analysis, cell morphological examination, etc. were performed.

Results: NDPKA’s effect on MDA-MB-231 cell growth and viability had significant correlation with phosphate content in cell media at the Yates's correction for continuity 0.00. NDPKA’s effect on MCF-07 cell growth and viability had significant correlation with phosphate content in cell media at the Yates's correction for continuity 0.00. From both cell viability MTT assay and phosphate assay data, a triangular periodic wave function was mathematically approximated as an infinite Fourier Series as an equation. There was significant difference between cell growth increase and phosphate concentration remaining after 24 hours for both MCF-07 (p=0.00) and MDA-MB-231 cell lines (p=0.00). There was significant difference between MCF-07 cell growth increase and MDA-MB-231 cell growth increase (p=0.0472). Only in case of MCF-07, significant dose-dependent change (Yates's correction for continuity 0.00) in cell growth and cell proliferation was found (In MDA-MB-231, not found).

Conclusions: Since MCF-07 cell growth increase and MDA-MB-231 cell growth increase (p=0.0472) were significantly different, it proves estrogen receptor effect on cell growth. This is how estrogen receptor (ER)-positive breast cancers generally have a better prognosis and are often responsive to anti-estrogen therapy.

Impact: MDA-MB-231 estrogen negative cells showed significantly higher phosphate content remaining after 24 hours incubation with NDPAK/nm23 H1 than MCF-07 estrogen positive cell lines. Since ER-negative breast cancers are more aggressive and unresponsive to anti-estrogens and other targeted therapies are thus urgently needed, phosphate content might act as parameter for other therapeutic targets in estrogen negative breast cancer.