Inositol / AST Cancer Research Results

Inositol — Inositol is a naturally occurring six-carbon cyclitol (sugar alcohol-like carbohydrate), with myo-inositol being the predominant biologically active stereoisomer in humans and the form most commonly used as an oral supplement. It is formally classified as a nutrient/metabolic signaling molecule rather than an established anticancer drug; common abbreviations include MI, myo-Ins, and Ins. Myo-inositol is obtained from foods and is also synthesized endogenously from glucose-6-phosphate through ISYNA1-dependent metabolism. It is a precursor for phosphatidylinositol and phosphoinositide second-messenger systems. Myo-inositol should be distinguished from inositol hexaphosphate (IP6/phytic acid), which has substantially more preclinical anticancer literature and is listed separately in this database.

Primary mechanisms (ranked):

1. Suppression or normalization of PI3K/Akt-associated oncogenic signaling in responsive tumor and premalignant-cell contexts.
2. Suppression of IL-6/STAT3-associated inflammatory tumor signaling and modulation of the tumor immune microenvironment, including macrophage phenotype.
3. Activation of the miR-125a-5p/IP6K1 tumor-suppressive axis, reducing migration, epithelial-mesenchymal transition and metastatic potential in responsive breast-cancer models.
4. Antiproliferative and pro-differentiation effects with remodeling of cell-cycle, cytoskeletal and apoptosis-associated proteins.
5. Metabolic modulation involving insulin signaling, glucose metabolism, AMPK and phosphoinositide signaling; effects are strongly tumor- and metabolic-context dependent.

Bioavailability / PK relevance: Myo-inositol is orally absorbed through sodium-dependent inositol transport systems, with human serum concentrations peaking approximately 1.5–3 hours after oral administration. A 100 mg/kg oral dose produced an estimated peak serum concentration of about 100 µM in a small human kinetic study. Bioavailability varies with formulation and can be reduced by competing D-chiro-inositol and some sugars/transporter substrates. Renal elimination is important. High-dose oncology studies have used approximately 18 g/day; gastrointestinal intolerance becomes dose-limiting at higher doses.

In-vitro vs systemic exposure relevance: Exposure is concentration-driven. A recent DU-145 prostate-cancer study reported an approximate myo-inositol IC50 of 0.06 mg/mL after 72 hours, equivalent to about 330 µM; this is several-fold above the approximately 100 µM peak serum concentration observed after a 100 mg/kg oral human dose, although substantially higher oral doses have been used clinically. Some mechanistic experiments use still higher concentrations, so direct systemic translation of in-vitro cytotoxicity should be interpreted cautiously. Chemopreventive and signaling effects may occur below directly cytotoxic concentrations.

Clinical evidence status: RCT-level chemoprevention evidence but no demonstrated anticancer efficacy. A randomized double-blind phase IIb trial used myo-inositol 9 g twice daily for six months in smokers with bronchial dysplasia. It did not significantly improve the primary dysplasia-response endpoint versus placebo, although BAL IL-6 decreased and responders showed reduced airway PI3K-activation signatures. Earlier phase I work established approximately 18 g/day as a tolerated dose and suggested lesion-regression activity. Myo-inositol is therefore best classified as an experimental chemopreventive/metabolic adjunct rather than an established cancer treatment.

Inositol Cancer-Relevant Mechanisms