RRM2 and neoplasm: The results of our in vitro experiments showed that HDS significantly reduced dNTP levels in H929 and ARP-1 cells, and excessive exogenous supplementation of dNTPs can partially inhibit the anti-tumor effect of HDS, suggesting that HDS exerted an anti-MM effect via the inhibition of RNR activity through targeting its subunit RRM2 and consequently depletion pool of dNTPs.