Acquired resistance to MEK1/2 inhibitors (MEKi) arises through amplification of BRAF V600E or KRAS G13D to reinstate ERK1/2 signalling. Here we show that BRAF V600E amplification and MEKi resistance are reversible following drug withdrawal. Cells with BRAF V600E amplification are addicted to MEKi to maintain a precise level of ERK1/2 signalling that is optimal for cell proliferation and survival, and tumour growth in vivo. Robust ERK1/2 activation following MEKi withdrawal drives a p57 KIP2 -dependent G1 cell cycle arrest and senescence or expression of NOXA and cell death, selecting against those cells with amplified BRAF V600E . p57 KIP2 expression is required for loss of BRAF V600E amplification and reversal of MEKi resistance. Thus, BRAF V600E amplification confers a selective disadvantage during drug withdrawal, validating intermittent dosing to forestall resistance. In contrast, resistance driven by KRAS G13D amplification is not reversible; rather ERK1/2 hyperactivation drives ZEB1-dependent epithelial-to-mesenchymal transition and chemoresistance, arguing strongly against the use of drug holidays in cases of KRAS G13D amplification.
Alterations of mitochondrial metabolism and genomic instability have been implicated in tumorigenesis in multiple tissues. High-grade glioma (HGG), one of the most lethal human neoplasms, displays genetic modifications of Krebs cycle components as well as electron transport chain (ETC) alterations. Furthermore, the p53 tumor suppressor, which has emerged as a key regulator of mitochondrial respiration at the expense of glycolysis, is genetically inactivated in a large proportion of HGG cases. Therefore, it is becoming evident that genetic modifications can affect cell metabolism in HGG; however, it is currently unclear whether mitochondrial metabolism alterations could vice versa promote genomic instability as a mechanism for neoplastic transformation. Here, we show that, in neural progenitor/stem cells (NPCs), which can act as HGG cell of origin, inhibition of mitochondrial metabolism leads to p53 genetic inactivation. Impairment of respiration via inhibition of complex I or decreased mitochondrial DNA copy number leads to p53 genetic loss and a glycolytic switch. p53 genetic inactivation in ETC-impaired neural stem cells is caused by increased reactive oxygen species and associated oxidative DNA damage. ETC-impaired cells display a marked growth advantage in the presence or absence of oncogenic RAS, and form undifferentiated tumors when transplanted into the mouse brain. Finally, p53 mutations correlated with alterations in ETC subunit composition and activity in primary glioma-initiating neural stem cells. Together, these findings provide previously unidentified insights into the relationship between mitochondria, genomic stability, and tumor suppressive control, with implications for our understanding of brain cancer pathogenesis.
Resistance to therapy is an enduring challenge in cancer care. Here we interrogate this critical unmet need using high grade serous ovarian cancer (HGSC) as a disease model. We have generated a unique panel of platinum-resistant HGSC models and shown that they share multiple transcriptomic features with relapsed human HGSC. Moreover, they evolve diverse in vivo phenotypes reflecting the human disease. We previously characterised copy number signatures in HGSC that correlate with patient survival and now provide the first evidence that these signatures undergo recurrent alterations during platinum therapy. Furthermore, specific, resistance-associated signature change is associated with functionally relevant gene expression differences. For example, reduced signature 3 (BRCA1/2-related homologous recombination deficiency) is associated with increased expression of homologous recombination repair genes (Rad51C, Rad51D, BRCA1) and DNA recombination pathway enrichment. Our mechanistic examination therefore provides new and clinically relevant insights into the genomic evolution of platinum-resistant cancers.
High-grade serous cancer (HGSC) accounts for ~67% of all ovarian cancer deaths. Although initially sensitive to platinum chemotherapy, resistance is inevitable and there is an unmet clinical need for novel therapies that can circumvent this event. We performed a drug screen with 1177 FDA-approved drugs and identified the hydroxyquinoline drug, chloroxine. In extensive validation experiments, chloroxine restored sensitivity to both cisplatin and carboplatin, demonstrating broad synergy in our range of experimental models of platinum-resistant HGSC. Synergy was independent of chloroxine’s predicted ionophore activity and did not relate to platinum uptake as measured by atomic absorption spectroscopy. Further mechanistic investigation revealed that chloroxine overrides DNA damage tolerance in platinum-resistant HGSC. Co-treatment with carboplatin and chloroxine (but not either drug alone) caused an increase in γH2AX expression, followed by a reduction in platinum-induced RAD51 foci. Moreover, this unrepaired DNA damage was associated with p53 stabilisation, cell cycle re-entry and triggering of caspase 3/7-mediated cell death. Finally, in our platinum-resistant, intraperitoneal in vivo model, treatment with carboplatin alone resulted in a transient tumour response followed by tumour regrowth. In contrast, treatment with chloroxine and carboplatin combined, was able to maintain tumour volume at baseline for over 4 months. In conclusion, our novel results show that chloroxine facilitates platinum-induced DNA damage to restore platinum sensitivity in HGSC. Since chloroxine is already licensed, this exciting combination therapy could now be rapidly translated for patient benefit.
Oncolytic viruses are being tested in clinical trials, including in women with ovarian cancer. We use a drug-repurposing approach to identify existing drugs that enhance the activity of oncolytic adenoviruses. This reveals that carvedilol, a β-arrestin-biased β-blocker, synergises with both wild-type adenovirus and the E1A-CR2-deleted oncolytic adenovirus, dl922-947. Synergy is not due to β-adrenergic blockade but is dependent on β-arrestins and is reversed by β-arrestin CRISPR gene editing. Co-treatment with dl922-947 and carvedilol causes increased viral DNA replication, greater viral protein expression and higher titres of infectious viral particles. Carvedilol also enhances viral efficacy in orthotopic, intraperitoneal murine models, achieving more rapid tumour clearance than virus alone. Increased anti-cancer activity is associated with an intratumoural inflammatory cell infiltrate and systemic cytokine release. In summary, carvedilol augments the activity of oncolytic adenoviruses via β-arrestins to re-wire cytokine networks and innate immunity and could therefore improve oncolytic viruses for cancer patient treatment.
Background: High grade serous ovarian cancer (HGSOC) is the most common ovarian cancer subtype. Although it is initially responsive to platinum-containing chemotherapy, the emergence of chemo-resistant cells is inevitable. Most women with HGSOC die of platinum-resistant cancer, and the five-year overall survival for ovarian cancer has changed little in recent decades. The aim of this project is to identify and validate existing, licensed drugs that selectively target resistant cancer cells in combination with cisplatin or carboplatin. Methods: Established chemo-sensitive HGSOC cell lines Ovcar4, COV318 and OVSAHO were passaged in vitro with increasing doses of either Cisplatin or Carboplatin to achieve a 5-10 fold difference in IC50 in resistant compared to sensitive parental cells, reflecting the chemo-resistance commonly found in patient tumor samples. We screened a library of 1170 FDA-approved drugs in Ovcar4 and carboplatin-resistant Ovcar4 (Ov4Carbo) cell lines and viability was analyzed using Cell Titre Glow (CTG). Ovcar4 or Ov4Carbo cells were injected and intraperitoneal tumor growth was assessed in female CD1 nude mice as in vivo model to assess the effects of drug combinations. Results: Using a high throughput drug screen, we identified Chloroxine as one of the top hits that re-sensitized resistant Ov4Carbo cells to Carboplatin. We have further validated Chloroxine in the platinum sensitive/resistant cell pairs in our novel HGSOC cell line panel (Ovcar4/Ov4Cis; Ov4CarboRFP; Ov4Carbo single cell clone 7 and COV318/Cov318Cis). Previous literature has identified kappa-type opioid receptor, OPRK1 as a potential binding target for Chloroxine. We found that the OPRK1 agonist, U50488 reproduced the synergy with Carboplatin in resistant Ov4Carbo cells, as observed with Chloroxine. Additionally, OPRK1 antagonist, nor- Binaltorphimine (nor-BNI) reduced the combined effects of Chloroxine and Carboplatin in Ov4Carbo cells suggesting that Chloroxine acts via OPRK1 receptor. We have tested Ovcar4, Ov4Carbo and Ov4Cis in vivo and found that all formed tumors in the peritoneum of nude mice and sequential bioluminescent readings correlated with survival. We are currently testing the effects of Chloroxine or OPRK1 agonist, U50488 in combination with Carboplatin in our in-vivo models. Conclusion: We have identified Chloroxine, an FDA-approved clinical drug that combines synergistically with carboplatin or cisplatin to induce cell death in chemo-resistant cell lines. We expect that understanding the mechanism of this synergy will provide novel insights into the pathophysiology of chemotherapy resistance in high grade serous ovarian cancer. In addition, as the pharmacokinetics and toxicity profiles of these FDA-approved drugs have already been established, this ‘repurposing’ of commonly used drugs will allow for a faster bench-to-bedside translation. Citation Format: Jayeta Saxena, Francesco Nicolini, Michelle Lockley. Reversing chemoresistance in high grade serous ovarian cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3801.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.