Targeted therapy against chemoresistant colorectal cancers: Inhibition of p38α modulates the effect of cisplatin in vitro and in vivo through the tumor suppressor FoxO3A

Chemoresistance is a major obstacle to effective therapy against colorectal cancer (CRC) and may lead to deadly consequences. The metabolism of CRC cells depends highly on the p38 MAPK pathway, whose involvement in maintaining a chemoresistant behavior is currently being investigated. Our previous studies revealed that p38a is the main p38 isoform in CRC cells. Here we show that p38a pharmacolog- ical inhibition combined with cisplatin administration decreases colony formation and viability of cancer cells and strongly increases Bax-dependent apoptotic cell death by activating the tumor suppressor pro- tein FoxO3A. Our results indicate that FoxO3A activation up-regulates transcription of its target genes (p21, PTEN, Bim and GADD45), which forces both chemosensitive and chemoresistant CRC cells to undergo apoptosis. Additionally, we found that FoxO3A is required for apoptotic cell death induction, as confirmed by RNA interference experiments. In animal models xenografted with chemoresistant HT29 cells, we further confirmed that the p38-targeted dual therapy strategy produced an increase in apoptosis in cancer tissue leading to tumor regression. Our study uncovers a major role for the p38- FoxO3A axis in chemoresistance, thereby suggesting a new therapeutic approach for CRC treatment; moreover, our results indicate that Bax status may be used as a predictive biomarker

po 243 uncoupling foxo3a mitochondrial and nuclear functions in cancer cells undergoing metabolic stress and chemotherapy

Introduction While aberrant cancer cell growth is frequently associated with altered biochemical metabolism, normal mitochondrial functions are usually preserved and necessary for full malignant transformation. The transcription factor FoxO3A is a key determinant of cancer cell homeostasis, playing a dual role in survival/death response. We recently described a novel mitochondrial arm of the AMPK-FoxO3A axis in normal cells upon nutrient shortage. Material and methods After extensive characterisation of mitochondrial FoxO3A function in vitro in several cell lines and tumours, we generated FoxO3A-knockout cancer cells with the CRISPR/Cas9 system and reconstituted FoxO3A expression with wild-type or mutant vectors. Results and discussions Here we show that in metabolically stressed cancer cells, FoxO3A is recruited to the mitochondria through activation of MEK/ERK and AMPK which phosphorylate serine 12 and 30, respectively, on FoxO3A N-terminal domain. Subsequently, FoxO3A is imported and cleaved to reach mitochondrial DNA, where it activates expression of the mitochondrial genome to support mitochondrial metabolism and cell survival. Using FoxO3A-/- cancer cells generated with the CRISPR/Cas9 genome editing system and reconstituted with FoxO3A mutants being impaired in their nuclear or mitochondrial subcellular localization, we show that mitochondrial FoxO3A promotes survival in response to metabolic stress. In cancer cells treated with chemotherapeutic agents, accumulation of FoxO3A into the mitochondria promoted survival in a MEK/ERK-dependent manner, while mitochondrial FoxO3A was required for apoptosis induction by metformin. Conclusion Elucidation of FoxO3A mitochondrial vs. nuclear functions in cancer cell homeostasis might help devise novel personalised therapeutic strategies to selectively disable FoxO3A pro-survival activity and manipulate cellular metabolism to counteract cancer initiation and progression

po 161 the ampk and mek erk signalling pathways regulate mitochondrial foxo3a import through phosphorylation of serine 12 and serine 30

Introduction FoxO3A is a well-known tumour suppressor transcription factor involved in the regulation of various metabolic and cell-death/survival genes. Its activity is finely modulated through specific post-translational modifications functioning as a 'molecular FoxO code'. Recently, we described a novel mitochondrial arm of the AMPK-FoxO3A axis in normal cells upon nutrient shortage. Here, we show that the MEK/ERK and AMPK pathways induce FoxO3A mitochondrial accumulation in cancer cells upon metabolic stress or chemotherapy treatment. Material and methods We performed an extensive in vitro characterisation of the cleaved intra-mitochondrial form of FoxO3A, by analysing mitoplasts purified from several cancer cell lines and tumours. Then, after an in silico preliminary analysis, we generated FoxO3A mutants to identify the key residues required for its mitochondrial accumulation and we extended our in vitro analysis to define the involved kinases. Therefore, to dissect the impact of the MEK/ERK and AMPK pathways on FoxO3A mitochondrial import and functions, we expressed the previously generated mutants in FoxO3A-knockout cancer cell lines obtained by using the CRISPR-Cas9 genome editing system. Results and discussions In metabolically stressed cancer cells, activation of the MEK/ERK and AMPK pathways is required to phosphorylate, respectively, S12 and S30 on FoxO3A N-terminal domain, and promote FoxO3A mitochondrial translocation. Once into the mitochondria, FoxO3A is cleaved by MPPs (mitochondrial processing peptidases) to reach and bind to mitochondrial DNA in complex with TFAM, SIRT3 and mtRNAPol, activating its expression and supporting mitochondrial metabolism and cancer cell survival. Intriguingly, cancer cells treated with chemotherapeutic drugs only require the MEK/ERK pathway to accumulate FoxO3A into the mitochondria, through S12 phosphorylation, and promote resistance and cell survival. Finally, mitochondrial FoxO3A recruitment is necessary for metformin-induced apoptosis. Conclusion The interplay between the MEK/ERK and AMPK pathways, which converge on the N-terminal domain of FoxO3A to eventually increase the expression of mitochondrial-encoded core subunits of the OXPHOS machinery, drives cancer cells towards survival or death. Further elucidation of the FoxO3A 'mitochondrial code' will be instrumental to devise personalised therapeutic strategies to selectively disable FoxO3A pro-survival activity

p38α MAPK pathway: A key factor in colorectal cancer therapy and chemoresistance

Colorectal cancer (CRC) remains one of the most common malignancies in the world. Although surgical resection combined with adjuvant therapy is effective at the early stages of the disease, resistance to conventional therapies is frequently observed in advanced stages, where treatments become ineffective. Resistance to cisplatin, irinotecan and 5-fluorouracil chemotherapy has been shown to involve mitogen-activated protein kinase (MAPK) signaling and recent studies identified p38α MAPK as a mediator of resistance to various agents in CRC patients. Studies published in the last decade showed a dual role for the p38α pathway in mammals. Its role as a negative regulator of proliferation has been reported in both normal (including cardiomyocytes, hepatocytes, fibroblasts, hematopoietic and lung cells) and cancer cells (colon, prostate, breast, lung tumor cells). This function is mediated by the negative regulation of cell cycle progression and the transduction of some apoptotic stimuli. However, despite its anti-proliferative and tumor suppressor activity in some tissues, the p38α pathway may also acquire an oncogenic role involving cancer related-processes such as cell metabolism, invasion, inflammation and angiogenesis. In this review, we summarize current knowledge about the predominant role of the p38α MAPK pathway in CRC development and chemoresistance. In our view, this might help establish the therapeutic potential of the targeted manipulation of this pathway in clinical settings