Abstract
Background
Re‐expression of the imprinted tumor suppressor gene DIRAS family GTPase 3 (DIRAS3) (aplysia ras homology member I [ARHI]) induces autophagy and tumor dormancy in ovarian cancer xenografts, but drives autophagic cancer cell death in cell culture. The current study explored the tumor and host factors required to prevent autophagic cancer cell death in xenografts and the use of antibodies against those factors or their receptors to eliminate dormant autophagic ovarian cancer cells.
Methods
Survival factors (insulinlike growth factor 1 [IGF‐1], vascular endothelial growth factor [VEGF], and interleukin 8 [IL‐8]) were detected with growth factor arrays and measured using enzyme‐linked immunoadsorbent assay analysis. Phosphorylation of protein kinase B (AKT), phosphorylation of extracellular signal‐regulated kinase (ERK), nuclear localization of translocation factor EB (TFEB) or forkhead box O3a (FOXo3a), and expression of microtubule‐associated proteins 1A/1B light chain 3B (MAPLC3B; LC3B) were examined using Western blot analysis. The effect of treatment with antibodies against survival factors or their receptors was studied using DIRAS3‐induced dormant xenograft models.
Results
Ovarian cancer cells grown subcutaneously in nude mice exhibited higher levels of phosphorylated ERK/AKT activity and lower levels of nuclear TFEB/FOXo3a, MAPLC3B, and autophagy compared with cells grown in culture. Induction of autophagy and dormancy with DIRAS3 was associated with decreased ERK/AKT signaling. The addition of VEGF, IGF‐1, and IL‐8 weakened the inhibitory effect of DIRAS3 on ERK/AKT activity and reduced DIRAS3‐mediated TFEB or FOXo3a nuclear localization and MAPLC3B expression in ovarian cancer cells. Treatment with antibodies against VEGF, IL‐8, and IGF receptor inhibited the growth of dormant xenografts, thereby prolonging survival from 99 to >220 days (P < .05) and curing a percentage of mice.
Conclusions
Treatment with a combination of anti‐VEGF, anti–IL‐8, and anti‐IGF receptor antibodies prevented the outgrowth of dormant cells and prolonged survival in a preclinical model.
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