Selective Mitochondrial Uptake of MKT-077 Can Suppress Medullary Thyroid Carcinoma Cell SurvivalIn VitroandIn Vivo

Abstract

BackgroundMedullary thyroid carcinoma (MTC) is a neuroendocrine tumor mainly caused by mutations in the rearranged during transfection (RET) proto-oncogene. Not all patients with progressive MTC respond to current therapy inhibiting RET, demanding additional therapeutic strategies. We recently demonstrated that disrupting mitochondrial metabolism using a mitochondria-targeted agent or by depleting a mitochondrial chaperone effectively suppressed human MTC cells in culture and in mouse xenografts by inducing apoptosis and RET downregulation. These observations led us to hypothesize that mitochondria are potential therapeutic targets for MTC. This study further tests this hypothesis using1-ethyl-2-[[3-ethyl-5-(3-methylbenzothiazolin-2-yliden)]-4-oxothiazolidin-2-ylidenemethyl] pyridinium chloride (MKT-077), a water-soluble rhodocyanine dye analogue, which can selectively accumulate in mitochondria.MethodsThe effects of MKT-077 on cell proliferation, survival, expression of RET and tumor protein 53 (TP53), and mitochondrial activity were determined in the human MTC lines in culture and in mouse xenografts.ResultsMKT-077 induced cell cycle arrest in TT and MZ-CRC-1. Intriguingly, MKT-077 also induced RET downregulation and strong cell death responses in TT cells, but not in MZ-CRC-1 cells. This discrepancy was mainly due to the difference between the capacities of these cell lines to retain MKT-077 in mitochondria. The cytotoxicity of MKT-077 in TT cells was mainly attributed to oxidative stress while being independent of TP53. MKT-077 also effectively suppressed tumor growth of TT xenografts.ConclusionMKT-077 can suppress cell survival of certain MTC subtypes by accumulating in mitochondria and interfering with mitochondrial activity although it can also suppress cell proliferation via other mechanisms. These results consistently support the hypothesis that mitochondrial targeting has therapeutic potential for MTC.

Vandetanib and cabozantinib potentiate mitochondria-targeted agents to suppress medullary thyroid carcinoma cells

“…Indeed, we previously demonstrated that perturbing mitochondrial bioenergetics and redox balance using the mitochondria-targeted superoxide dismutase mimetic, Mito-CP (triphenyl-phosphonium-carboxy-proxyl), or by targeting a key mitochondrial chaperone such as HSPA9 (GRP75/mortalin) can effectively suppress human MTC cells in culture and in mouse xenografts. [15][16][17] These observations strongly suggested the significance of mitochondria for MTC cell survival and proliferation, leading us to further evaluate the potential of mitochondria as a target for MTC therapy.…”

“…We asked whether mitochondria are involved because (i) mitochondrial activity can be regulated by RTKs 30 and (ii) mitochondria have a key role for MTC cell survival and proliferation. [15][16][17] We thus determined whether vandetanib and cabozantinib affected Dc m , an indicator of mitochondrial activity, in parental and the drug-resistant MTC cells using the Dc msensitive dye, TMRE.…”

<p>Subcellular Performance of Nanoparticles in Cancer Therapy</p>

“…Accordingly, it is highly feasible to achieve mitochondrial targeting by lipophilic architectures with delocalized cations. 148 Owing to the high-density phospholipids yielding high membrane potential (constant negative charge), mitochondria are highly selective for the entry of some of the common lipophilic structures, including TPP, 93,156 rhodamine 123 (Rh123), 157,158 flupirtine, 159 and MKT-077, [160][161][162] which could be selectively retained in the mitochondria. Amongst them, TPP holds a better balance of lipophilicity and charge with a large area of three benzene moieties in its chemical structure, which can be efficiently used for mitochondrial targeting of nanoparticles by immobilizing it over various inorganic nanoparticles 94 such as cerium and ferromagnetic particles or polymer, drug-polymer block system.…”

Suppression of B-RafV600E melanoma cell survival by targeting mitochondria using triphenyl-phosphonium-conjugated nitroxide or ubiquinone

“…For flow cytometric measurement, TMRE-treated cells were collected by trypsinization and resuspended in PBS containing 0.1% bovine serum albumin, and analyzed by flow cytometry (PE channel, 575 nm), as previously described. 20,21 Data from 20,000 cells were analyzed using FCS Express software (De Novo Software).…”

“…Cells were incubated with culture medium containing 1 mM carboxy-H 2 DCFDA at 37 C for 1 h. After medium change, cells were incubated in dark for 2 h, trypsinized, and resuspended in PBS before analysis by flow cytometry (FITC channel, 525 nm), as previously described. 20,21 Data from 20,000 cells were analyzed using FCS Express software (De Novo Software).…”