Guanine　O-6-alkylating　agents　are　widely　used　as　first-line　chemotherapeutic　drugs　due　to　their　ability　to　induce　cytotoxic　DNA　damage.　However,　a　major　hurdle　in　their　effectiveness　is　the　emergence　of　chemoresistance,　largely　attributed　to　the　DNA　repair　pathway　mediated　by　O-6-methylguanine-DNA　methyltransferase　(MGMT).　MGMT　plays　an　important　role　in　removing　the　alkyl　groups　from　lethal　O-6-alkylguanine　(O-6-AlkylG)　adducts　formed　by　chemotherapeutic　alkylating　agents.　By　doing　so,　MGMT　enables　tumor　cells　to　evade　apoptosis　and　develop　drug　resistance　toward　DNA　alkylating　agents.　Although　covalent　inhibitors　of　MGMT,　such　as　O(6)benzylguanine　(O-6-BG)　and　O-6-(4-bromothenyl)guanine　(O-6-4-BTG　or　lomeguatrib),　have　been　explored　in　clinical　settings,　their　utility　is　limited　due　to　severe　delayed　hematological　toxicity　observed　in　most　patients　when　combined　with　alkylating　agents.　Therefore,　there　is　an　urgent　need　to　identify　new　targets　and　unravel　the　underlying　molecular　mechanisms　and　to　develop　alternative　therapeutic　strategies　that　can　overcome　MGMTmediated　tumor　resistance.　In　this　context,　the　regulation　of　MGMT　expression　via　interfering　the　specific　cell　signaling　pathways　(e.g.,　Wnt/beta-catenin,　NF-kappa　B,　Hedgehog,　PI3K/AKT/mTOR,　JAK/STAT)　emerges　as　a　promising　strategy　for　overcoming　tumor　resistance,　and　ultimately　enhancing　the　efficacy　of　DNA　alkylating　agents　in　chemotherapy.