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Genome-wide synthetic lethal screen unveils novel CAIX-NFS1/xCT axis as a targetable vulnerability in hypoxic solid
Shawn C Chafe1, Frederick S Vizeacoumar2, Geetha Venkateswaran1
1Department of Integrative Oncology, BC Cancer Research Institute, Vancouver, BC V5Z 1L3, Canada.
Abstract:
The metabolic mechanisms involved in the survival of tumor cells within the hypoxic niche remain unclear. We carried out a synthetic lethal CRISPR screen to identify survival mechanisms governed by the tumor hypoxia-induced pH regulator carbonic anhydrase IX (CAIX). We identified a redox homeostasis network containing the iron-sulfur cluster enzyme, NFS1. Depletion of NFS1 or blocking cyst(e)ine availability by inhibiting xCT, while targeting CAIX, enhanced ferroptosis and significantly inhibited tumor growth. Suppression of CAIX activity acidified intracellular pH, increased cellular reactive oxygen species accumulation, and induced susceptibility to alterations in iron homeostasis. Mechanistically, inhibiting bicarbonate production by CAIX or sodium-driven bicarbonate transport, while targeting xCT, decreased adenosine 5'-monophosphate-activated protein kinase activation and increased acetyl-coenzyme A carboxylase 1 activation. Thus, an alkaline intracellular pH plays a critical role in suppressing ferroptosis, a finding that may lead to the development of innovative therapeutic strategies for solid tumors to overcome hypoxia- and acidosis-mediated tumor progression and therapeutic resistance.
Insights
Tumor cells survive in low-oxygen (hypoxic) environments by regulating pH. Targeting carbonic anhydrase IX (CAIX) and a redox network enzyme (NFS1) triggers cell death (ferroptosis), inhibiting tumor growth.
Area of Science:
- Oncology
- Cell Biology
- Biochemistry
Background:
- Tumor cells in hypoxic niches utilize specific metabolic pathways for survival.
- Carbonic anhydrase IX (CAIX) is a key regulator of tumor pH under hypoxia.
- Mechanisms of tumor cell survival in hypoxic and acidic microenvironments are not fully understood.
Purpose of the Study:
- To identify survival mechanisms of tumor cells in hypoxic niches regulated by CAIX.
- To investigate the role of a redox homeostasis network in tumor cell survival.
- To explore novel therapeutic strategies targeting hypoxia- and acidosis-mediated tumor progression.
Main Methods:
- Synthetic lethal CRISPR screening was employed to identify CAIX-governed survival pathways.
- NFS1 (an iron-sulfur cluster enzyme) and xCT (cyst(e)ine transporter) were investigated.
- Intracellular pH, reactive oxygen species, iron homeostasis, and metabolic enzyme activity were measured.
Main Results:
- A redox homeostasis network involving NFS1 was identified as crucial for tumor cell survival.
- Simultaneous targeting of CAIX and NFS1 or xCT significantly inhibited tumor growth by enhancing ferroptosis.
- Suppression of CAIX activity led to intracellular acidification, increased reactive oxygen species, and iron dysregulation.
- Inhibition of bicarbonate production and xCT decreased AMPK activation and increased ACC1 activation, indicating a role for alkaline pH in suppressing ferroptosis.
Conclusions:
- Alkaline intracellular pH is critical for suppressing ferroptosis in tumor cells.
- Targeting CAIX and the identified redox network presents a potential therapeutic strategy for solid tumors.
- These findings offer insights into overcoming hypoxia- and acidosis-mediated therapeutic resistance in cancer.
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