AT7687vsVitamin B12

AT7687 is a long-acting GIP receptor antagonist designed to reduce fat storage rather than suppress appetite — a fundamentally different mechanism from every other obesity drug currently on the market or in late-stage development. The rationale is grounded in human genetics: loss-of-function variants in the GIP receptor are associated with lower body mass index and reduced cardiometabolic risk, suggesting that pharmacologically blocking GIP signalling should reproduce these protective effects.

GIP (glucose-dependent insulinotropic polypeptide) normally functions as a fat-storage signal — released from intestinal K-cells in response to food intake, it instructs adipose tissue to take up and store circulating fatty acids. By blocking the GIP receptor specifically on adipocytes, AT7687 prevents this fat-storage signal from being transmitted, leading to reduced lipid uptake into fat cells and a metabolic shift favouring fat oxidation in muscle and liver. Because the mechanism does not depend on suppressing hunger or slowing gastric emptying, the gastrointestinal side effects that limit GLP-1 drug tolerability are largely absent.

This mechanism is the conceptual mirror of MariTide (which combines GLP-1 agonism with GIP antagonism in a single molecule) — AT7687 isolates the GIP-antagonist component to test whether it can produce meaningful weight loss alone or in future combination with GLP-1 agonists. Antag Therapeutics' first-in-human Phase 1 results in 2026 showed acceptable tolerability with mild GI symptoms, plus reductions in LDL cholesterol and resting heart rate — early signals consistent with the predicted cardiometabolic benefit profile. Phase 2 trials are expected to define the magnitude of weight loss achievable in obese patients.

Vitamin B12 (cobalamin) is a large organometallic molecule with a cobalt ion at its center, coordinated within a corrin ring. It is the most structurally complex vitamin and the only one containing a metal ion. Humans cannot synthesize B12 — it is produced exclusively by certain bacteria and archaea, and enters the human diet through animal products or bacterial fermentation. Absorption requires intrinsic factor (produced by gastric parietal cells), which binds B12 in the ileum for receptor-mediated endocytosis via the cubam receptor complex.

B12 functions as a cofactor for two essential enzymes. Methionine synthase (MS) uses methylcobalamin (methylB12) to catalyze the transfer of a methyl group from methyltetrahydrofolate (methyl-THF) to homocysteine, producing methionine and regenerating tetrahydrofolate (THF). This reaction sits at the intersection of two critical pathways: methionine is converted to S-adenosylmethionine (SAM), the universal methyl donor for DNA methylation, histone modification, neurotransmitter synthesis, and hundreds of other methylation reactions; and THF regeneration is essential for folate cycling and de novo nucleotide synthesis (required for DNA replication). B12 deficiency traps folate as methyl-THF ('methyl trap'), blocking DNA synthesis and causing megaloblastic anemia — red blood cell precursors cannot replicate their DNA properly, producing abnormally large, non-functional cells.

Methylmalonyl-CoA mutase uses adenosylcobalamin (adenosylB12) in mitochondria to convert methylmalonyl-CoA to succinyl-CoA, a key step in the catabolism of odd-chain fatty acids, branched-chain amino acids, and cholesterol. Deficiency causes methylmalonic acid accumulation, which is toxic to neurons and contributes to the peripheral neuropathy, subacute combined degeneration of the spinal cord, and cognitive decline seen in B12 deficiency. The neurological damage occurs because myelin synthesis requires both SAM-dependent methylation reactions (for phospholipid synthesis) and proper fatty acid metabolism (for myelin lipid composition), both of which depend on B12. Neurological damage from severe B12 deficiency can become irreversible if not treated promptly, which is why injectable B12 (which bypasses absorption barriers) is preferred for deficiency treatment.