Download Hebbel Research Day abstract

CYP3A4 promotes clonogenicity of ER+ breast cancer cells through epoxyeicosatrienoic
acid (EET) biosynthesis, but CYP3A4 effects on breast tumor growth are unknown.
Silencing of CYP3A4 in breast cancer cells suppressed EETs, promoting tumor
dormancy. In breast cancer cells, soluble epoxide hydrolase inhibition (sEHi) promoted
the mitochondrial membrane potential and increased oxygen consumption rates (OCR).
Although metformin isn’t metabolized by CYP3A4, nanodiscs revealed a metformin spinshift and a CYP3A4-metformin co-crystal enabled design of hexyl-benzyl biguanide
(HBB), a more potent (IC50=9 uM vs. 5 mM) inhibitor of CYP3A4 epoxygenase activity.
Unlike metformin, HBB potently inhibited OCR and mitochondrial membrane potential,
while sEHi and EETs reversed these effects. HBB transiently activated pyruvate kinase
M2 (PKM2), allowing synthesis of lactate, followed by inactivation of PKM2 and inhibition
of lactate. HBB also transiently activated and then inhibited mTOR. HBB (6 mg/kg/day)
halved ER+ breast tumor growth. CYP3A4 epoxygenase activity is therefore a breast
cancer therapeutic target.
Significance: Validation of cancer cell intrinsic CYP3A4 as a driver of ER+ breast
tumor growth implies that tumor growth is vulnerable to disruption of CYP3A4 functions,
including its epoxygenase activity. Identification of metformin as a disruptor of CYP3A4
epoxygenase activity enabled the design of a more potent neo-biguanide, HBB, to inhibit
epoxygenase activity and provide single agent inhibition of ER+ tumor growth. Because
of its potency, HBB improves our understanding of the mechanisms by which biguanides
inhibit breast cancer by illuminating the relationship between OCR and glycolysis and
thereby provides a therapeutic strategy to deprive cancer cells of much needed lactate
required to promote the oncogenic program.