Increased uptake of [¹²³I]meta-iodobenzylguanidine, [¹⁸F]fluorodopamine, and [³H]norepinephrine in mouse pheochromocytoma cells and tumors after treatment with the histone deacetylase inhibitors.

[¹³¹I]meta-iodobenzylguanidine ([¹³¹I]MIBG) is the most commonly used treatment for metastatic pheochromocytoma and paraganglioma. It enters the chromaffin cells via the membrane norepinephrine transporter; however, its success has been modest. We studied the ability of histone deacetylase (HDAC) inhibitors to enhance [¹²³I]MIBG uptake by tumors in a mouse metastatic pheochromocytoma model. HDAC inhibitors are known to arrest growth, induce differentiation and apoptosis in various cancer cells, and further inhibit tumor growth. We report the in vitro and in vivo effects of two HDAC inhibitors, romidepsin and trichostatin A, on the uptake of [(3)H]norepinephrine, [¹²³I]MIBG, and [(18)F]fluorodopamine in a mouse model of metastatic pheochromocytoma. The effects of both inhibitors on norepinephrine transporter activity were assessed in mouse pheochromocytoma (MPC) cells by using the transporter-blocking agent desipramine and the vesicular-blocking agent reserpine. HDAC inhibitors increased [(3)H]norepinephrine, [¹²³I]MIBG, and [(18)F]fluorodopamine uptake through the norepinephrine transporter in MPC cells. In vivo, inhibitor treatment resulted in significantly increased uptake of [(18)F]fluorodopamine positron emission tomography (PET) in pheochromocytoma liver metastases (19.1 ± 3.2% injected dose per gram of tumor (%ID/g) compared to liver metastases in pretreatment scans 5.9 ± 0.6%; P<0.001). Biodistribution analysis after inhibitors treatment confirmed the PET results. The uptake of [(123)I]MIBG was significantly increased in liver metastases 9.5 ± 1.1% compared to 3.19 ± 0.4% in untreated control liver metastases (P<0.05). We found that HDAC inhibitors caused an increase in the amount of norepinephrine transporter expressed in tumors. HDAC inhibitors may enhance the therapeutic efficacy of [(131)I]MIBG treatment in patients with advanced malignant pheochromocytoma and paraganglioma.