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Abnormal N6-methyladenosine (m6A) modification is closely associated with the occurrence, development, progression and prognosis of cancer, and aberrant m6A regulators have been identified as novel anticancer drug targets. Both traditional medicine-related approaches and modern drug discovery platforms have been used in an attempt to develop m6A-targeted drugs. Here, we provide an update of the latest findings on m6A modification and the critical roles of m6A modification in cancer progression, and we summarize rational sources for the discovery of m6A-targeted anticancer agents from traditional medicines and computer-based chemosynthetic compounds. This review highlights the potential agents targeting m6A modification for cancer treatment and proposes the advantage of artificial intelligence (AI) in the discovery of m6A-targeting anticancer drugs. Graphical abstract Three stages of m6A-targeting anticancer drug discovery: traditional medicine-based natural products, modern chemical modification or synthesis, and artificial intelligence (AI)-assisted approaches for the future.

Hepatocellular carcinoma (HCC) is a deadly form of cancer without effective chemotherapy so far. Currently, only sorafenib, a multitargeted tyrosine kinase inhibitor, slightly improves survival in HCC patients. In searching for natural anti-HCC components from toad venom, which is frequently used in the treatment of liver cancer in traditional Chinese medicine, we discovered that arenobufagin, a bufadienolide from toad venom, had potent antineoplastic activity against HCC HepG2 cells as well as corresponding multidrug-resistant HepG2/ADM cells. We found that arenobufagin induced mitochondria-mediated apoptosis in HCC cells, with decreasing mitochondrial potential, as well as increasing Bax/Bcl-2 expression ratio, Bax translocation from cytosol to mitochondria. Arenobufagin also induced autophagy in HepG2/ADM cells. Autophagy-specific inhibitors (3-methyladenine, chloroquine and bafilomycin A1) or Beclin1 and Atg 5 small interfering RNAs (siRNAs) enhanced arenobufagin-induced apoptosis, indicating that arenobufagin-mediated autophagy may protect HepG2/ADM cells from undergoing apoptotic cell death. In addition, we observed the inhibition of phosphatidylinositol 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) pathway by arenobufagin. Interestingly, inhibition of mTOR by rapamycin or siRNA duplexes augmented arenobufagin-induced apoptosis and autophagy. Finally, arenobufagin inhibited the growth of HepG2/ADM xenograft tumors, which were associated with poly (ADP-ribose) polymerase cleavage, light chain 3-II activation and mTOR inhibition. In summary, we first demonstrated the antineoplastic effect of arenobufagin on HCC cells both in vitro and in vivo. We elucidated the underlying antineoplastic mechanisms of arenobufagin that involve cross talk between apoptosis and autophagy via inhibition of the PI3K/Akt/mTOR pathway. This study may provide a rationale for future clinical application using arenobufagin as a chemotherapeutic agent for HCC.

The paradoxical coexistence of spontaneous tumor antigen-specific immune response with progressive disease in cancer patients need to dissect the molecular pathways involved in tumor-induced T-cell dysfunction or exhaustion. Programmed cell death 1 (PD-1) has been identified as a marker of exhausted T cells in chronic disease states, and blockade of PD-1-PD-L1 interactions has been shown to partially restore T-cell function. We have found that T-cell immunoglobulin mucin (Tim) 3 is expressed on CD8+ tumor-infiltrating lymphocytes (TILs) isolated from patients with colorectal cancer. All T-cell immunoglobulin mucin 3 (Tim-3+) TILs coexpress PD-1, and Tim-3+ PD-1+ CD8+ TILs represent the predominant fraction of Tcells infiltrating tumors. Tim-3+PD-1+ CD8+ TILs exhibit the most severe exhausted phenotype as defined by failure to produce cytokines, such as interferon-γ, tumor necrosis factor-α, and interleukin-2. We further find that combined targeting of the Tim-3 and PD-1 pathways increased the frequencies of not only interferon-γ and tumor necrosis factor-α but also frequencies of proliferating tumor antigen-specific CD8+ T cells than targeting either pathway alone. A concomitant decrease in regulatory T cells and enhanced killing in a cytotoxicity assay was observed. Collectively, our findings support the use of Tim-3-Tim-3L blockade together with PD-1-PD-L1 blockade to reverse tumor-induced T-cell exhaustion/dysfunction in patients with colorectal cancer.