Blockade of Tumor Cell Transforming Growth Factor-βs Enhances Cell Cycle Progression and Sensitizes Human Breast Carcinoma Cells to Cytotoxic Chemotherapy

Abstract

We have examined the effect of neutralizing TGF-β antibodies on cisplatin-mediated cytotoxicity against MDA-231 human breast tumor cell spheroids. These tridimensionalin vitrosystems have been shown to recapitulate the drug sensitivity pattern of tumor cellsin vivo.MDA-231 tumor cell spheroids exhibit higher protein levels of the cyclin-dependent kinase (Cdk) inhibitors p21 and p27 and >10-fold lower Cdk2 activity compared to adherent cell monolayers, as well as pRb hypophosphorylation, a predominant G1 population, and a cisplatin 1-h IC50of approximately 100 μM. Treatment of MDA-231 cells in monolayer with cisplatin for 1 h, subsequently grown as spheroids, increased steady-state TGF-β1 mRNA levels, secretion of active TGF-β, cellular Cdk2 activity, pRb phosphorylation, and p21 protein levels, while downregulating p27. Accumulation of cells in G2M and progression into S were noted 48 h after treatment with 100 μM cisplatin. We tested whether drug-induced upregulation of TGF-β1 and p21, perhaps by preventing cell cycle progression, were protective mechanisms against drug-mediated toxicity by using neutralizing anti-TGF-β antibodies. Anti-TGF-β antibodies diminished the induction of p21, enhanced the activation of Cdk2, and facilitated progression into S and G2M following cisplatin treatment. This resulted in a >twofold enhancement of drug-induced DNA fragmentation and a shift in the cisplatin 1-h IC50from 100 to <10 μM. These data suggest that tumor cell TGF-β1 may protect from DNA damage and that postchemotherapy administration of TGF-β inhibitors may facilitate progression beyond G1/S, potentially increasing the efficacy of cytotoxic chemotherapy.