Trametinib Thwarts Activation of Survival Pathways Induced by Pro-ferroptotic Drug Conjugate ACXT-3102 Resulting in Enhanced Pancreatic Cancer Cell Death

Abstract Ferroptosis has recently been described as an iron-dependent subroutine of programmed cell death. Cancers driven by oncogenic Ras mutations, such as pancreatic ductal adenocarcinoma, are particularly vulnerable to ferroptosis and are thus promising candidates for antineoplastic drugs targeting this unique form of programmed cell death. Our group has developed a cancer-specific drug conjugate (ACXT-3102), consisting of a proapoptotic sigma-2 ligand as a delivery moiety (SV119), linked to an inhibitor of the cystine antiporter xCT (dm-erastin), an established inducer of ferroptosis. We hypothesized that ACXT-3102 would trigger apoptosis and ferroptosis via its discrete chemical components, representing a new approach to clinical therapy for pancreatic ductal adenocarcinoma. In vitro cell viability assays corroborated our earlier findings that ACXT-3102 is a potent inducer of cancer cell death. The sigma-2 delivery component of ACXT-3102 induced canonical markers of apoptosis, including cleaved caspase-3/7 and PARP, whereas the dm-erastin cargo component induced canonical markers of ferroptosis, including lipid peroxidation and consumption of glutathione peroxidase 4. These changes resulted in the accumulation of reactive oxygen species. Subsequently, we found that ACXT-3102–mediated cell death was accompanied by the activation of MAPK/ERK signaling, presumably via the reactive oxygen species–dependent degradation of dual-specificity phosphatase 6, a negative regulator of MAPK/ERK phosphorylation. We suspected that this was a compensatory reaction and that ACXT-3102–induced cancer cell death would be augmented by inhibition of MAPK/ERK signaling. We successfully combined ACXT-3102 with trametinib (MEK inhibitor) to enhance the overall efficacy of treatment in vitro and in vivo, presumably by targeting ACXT-3102–induced upregulation of MAPK/ERK.