Inhibition of AKT-Signaling Sensitizes Soft Tissue Sarcomas (STS) and Gastrointestinal Stromal Tumors (GIST) to Doxorubicin via Targeting of Homology-Mediated DNA Repair.

Sergei Boichuk,Alexey Sabirov,Ilmira Nurgatina,Pavel Dunaev,Elena Valeeva,Firuza Bikinieva,Aida Aukhadieva,Aigul Galembikova

doi:10.3390/ijms21228842

Abstract

Activation of the phosphoinositide 3-kinase (PI3K)/Akt/mTOR pathway is well documented for a broad spectrum of human malignancies supporting their growth and progression. Accumulating evidence has also implicated AKT as a potent modulator of anti-cancer therapies via regulation of DNA damage response and repair (DDR) induced by certain chemotherapeutic agents and ionizing radiation (IR). In the present study, we examined the role of AKT signaling in regulating of Rad51 turnover and cytotoxic effects of topoisomerase II inhibitor, doxorubicin (Dox) in soft tissue sarcomas (STS) and gastrointestinal stromal tumors (GIST) in vitro. Blocking of AKT signaling (MK-2206) enhanced cytotoxic and pro-apoptotic effects of Dox in vast majority of STS and GIST cell lines. The phosphorylated form of Akt co-immunoprecipitates with Rad51 after Dox-induced DNA damage, whereas Akt inhibition interrupts this interaction and decreases Rad51 protein level by enhancing protein instability via proteasome-dependent degradation. Inhibition of Akt signaling in Dox-treated cells was associated with the increased number of γ-H2AX-positive cells, decrease of Rad51 foci formation and its colocalization with γ-H2AX foci, thereby revealing unsuccessful DDR events. This was also in consistency with an increase of tail moment (TM) and olive tail moment (OTM) in Dox-treated GIST and STS cells cultured in presence of Akt inhibitor after Dox washout. Altogether, our data illustrates that inhibition of AKT signaling is STS and GIST might potentiate the cytotoxic effect of topoisomerase II inhibitors via attenuating the homology-mediated DNA repair.

Highlights

Activation of the phosphoinositide 3-kinase (PI3K)/Akt/mTOR pathway is frequently detected in human malignancies, including gastrointestinal stromal tumors (GIST) and soft tissue sarcomas (STS)
To examine whether inhibition of AKT signaling potentiates the cytotoxic activities of Dox in STS and GIST, we performed MTS-based survival assay with a broad spectrum of cancer cell lines, including SK-LMS-1 leiomyosarcoma, RD rhabdomyosarcoma, HT-1080 fibrosarcoma, A673 Ewing’s sarcoma, U2-OS osteosarcoma, imatinib mesylate (IM)-sensitive and resistant gastrointestinal stromal tumors (e.g., GIST T-1 vs. GIST T-1R and GIST 430, respectively)
We observed that inhibition of AKT signaling potentiated cytotoxic activity of Dox and inhibited growth of the vast majority of cancer cell lines included in present study (Figure 1)

Summary

Introduction

Activation of the phosphoinositide 3-kinase (PI3K)/Akt/mTOR pathway is frequently detected in human malignancies, including gastrointestinal stromal tumors (GIST) and soft tissue sarcomas (STS) This pathway supports tumor growth and progression and is thought to be linked with resistance to the current therapeutic regimens, including certain chemotherapeutic agents, ionizing radiation (IR) and targeted-based therapies. The preclinical experiments illustrated that a long-term exposure of IM- and sunitinib (SU)-resistant cell lines to SU induces epigenetic silencing of PTEN with a consequent overactivation of the PI3K/AKT pathway [4] This correlates with a clinical data illustrating that low/negative IHC-staining for PTEN was associated with aggressive disease [5], thereby suggesting that PTEN depletion and/or silencing is associated with aggressive phenotype and resistance to RTK inhibition. Some of them have not succeeded to date [9,10], whereas the other trials to examine the novel drugs targeting the elements of this pathway are currently ongoing (NCT01991379, NCT01735968 and NCT01468688)

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Conclusion