Is Hydrogen Sulfide a Concern During Treatment of Lung Adenocarcinoma With Ammonium Tetrathiomolybdate?

Ammonium tetrathiomolybdate (ATTM) has been used in breast cancer therapy for copper chelation, as elevated copper promotes tumor growth. ATTM is also an identified H(2)S donor and endogenous H(2)S facilitates VitB(12)-induced S-adenosylmethionine (SAM) generation, which have been confirmed in m(6)A methylation and lung cancer development. The m(6)A modification was recently shown to participate in lung adenocarcinoma (LUAD) progression. These conflicting analyses of ATTM's anticancer vs. H(2)S's carcinogenesis suggest that H(2)S should not be ignored during LUAD's treatment with ATTM. This study was aimed to explore ATTM's effects on LUAD cells and mechanisms associated with H(2)S and m(6)A. It was found that treatment with ATTM inhibited cell growth at high concentrations, while enhanced cell growth at low concentrations in three LUAD cell lines (A549, HCC827, and PC9). However, another copper chelator triethylenetetramine, without H(2)S releasing activity, was not found to induce cell growth. Low ATTM concentrations also elevated m(6)A content in A549 cells. Analysis of differentially expressed genes in TCGA cohort indicated that m(6)A writer METTL3 and reader YTHDF1 were upregulated while eraser FTO was downregulated in LUAD tissues, consistent with the findings of protein expression in patient tissues. ATTM treatment of A549 cells significantly increased METTL3/14 and YTHDF1 while decreased FTO expression. Furthermore, inhibition of m(6)A with shMETTL3 RNA significantly attenuated eukaryotic translation initiation factor (eIF) expressions in A549 cells. Correlation analysis indicated that small nuclear ribonucleic protein PRPF6 was positively expressed with YTHDF1 in LUAD tissues. Knockdown of YTHDF1 partially blocked both basal and ATTM-induced PRPF6 expression, as well as A549 cell growth. Lastly, ATTM treatment not only raised intracellular H(2)S content but also upregulated H(2)S-producing enzymes. Exogenous H(2)S application mimicked ATTM's aforementioned effects, but the effects could be weakened by zinc-induced H(2)S scavenging. Collectively, H(2)S impedes ATTM-induced anticancer effects through YTHDF1-dependent PRPF6 m(6)A methylation in lung adenocarcinoma cells.