Citrate-Derived Acetyl-CoA Partitioning as a Metabolic-Epigenetic Checkpoint in Cancer

Cancer metabolism is commonly interpreted through production rates, metabolite concentrations, and pathway activity. We propose that, for citrate-derived acetyl units, biological output is determined by destination as much as by supply. Citrate exported through SLC25A1 and cleaved by ATP-citrate lyase generates cytosolic acetyl-coenzyme A, but the resulting acetyl units are not assigned to a single biochemical fate. They can be captured by nuclear histone acetylation, de novo lipogenesis, sterol synthesis, redox-coupled biosynthesis, acetyl carnitine exchange, or compensatory acetate- and pyruvate-derived routes. Here we synthesize evidence from non-canonical tricarboxylic acid cycle wiring, ATP-citrate lyase-dependent histone acetylation, compartment-resolved acyl-coenzyme A pools, lipid-synthetic demand, oncogenic signaling, and alternative nuclear acetyl-coenzyme A sources. Our working hypothesis is that malignant cells may stabilize poorly differentiated states when lipogenic and redox sinks capture citrate-derived acetyl units away from lineage-regulatory chromatin. Our model is intentionally conservative. It does not claim that citrate export universally controls cancer identity. Rather, it defines a destination-resolved checkpoint that can be tested by isotope tracing, enhancer-resolved H3K27ac profiling, acetyl-source mapping, and selective weakening of competing sinks.