Selective Mitochondrial Uptake of MKT-077 Can Suppress Medullary Thyroid Carcinoma Cell Survival In Vitro and In Vivo

Analogs of the Heat Shock Protein 70 Inhibitor MKT-077 Suppress Medullary Thyroid Carcinoma Cells

Medullary thyroid carcinoma (MTC) is a neuroendocrine tumor mainly caused by mutations in the RET proto-oncogene. We previously demonstrated that depletion of the mitochondrial molecular chaperone, mortalin, can effectively suppress human MTC cells in culture and in mouse xenografts, by disrupting mitochondrial bioenergetics and subsequently inducing apoptosis and RET downregulation. Similar effects were induced by MKT-077, a water-soluble rhodocyanine dye analog known to inhibit mortalin, but with notable toxicity in animals. These observations led us to evaluate recently developed MKT-077 analogs that exhibited higher selectivity to HSP70 proteins and improved bioavailability. We validated the MTC cell-suppressive effects of mortalin depletion in three-dimensional cultures of the human MTC lines, TT, and MZ-CRC-1, and then evaluated different MKT-077 analogs in two- and three-dimensional cell cultures, to show that the MKT-077 analogs, JG-98 and JG-194, effectively and consistently inhibited propagation of TT and MZ-CRC-1 cells in these cultures. Of note, these compounds also effectively suppressed the viability of TT and MZ-CRC-1 progenies resistant to vandetanib and cabozantinib. Moreover, JG-231, an analog with improved microsomal stability, consistently suppressed TT and MZ-CRC-1 xenografts in mice. These data suggest that mortalin inhibition may have therapeutic potential for MTC.

Immunoexpression of HSPA9 and CUL2 in prostatic tissue and adenocarcinoma

CUL2 plays a crucial role in proteolysis by preserving the balance between normal growth and uncontrolled proliferation. HSPA9 safeguards the integrity of protein interactions and supports cellular homeostasis. In carcinomas, HSPA9 and CUL2 appear to protect neoplastic cells from internal and external damage. In prostate tumors they are apparently associated with increased risk of unfavorable outcomes, but information remains scarce. In this study we evaluated CUL2 and HSPA9 expression in neoplastic and non-neoplastic prostate tissue and Gleason pattern 3 and 4 adenocarcinoma to identify associations with ISUP prognostic groups and postoperative disease progression. The records of 636 radical prostatectomy patients were reviewed retrospectively and microarrays were mounted with paraffin-embedded adenocarcinoma and non-neoplastic tissue. We evaluated the ability of HSPA9 and CUL2 to predict postoperative PSA outcomes, response to adjuvant/salvage therapy and systemic disease. HSPA9 and CUL2 were diffusely expressed. HSPA9 expression was associated with increased risk of high-grade adenocarcinoma, while HSPA9 and CUL2 were associated with biochemical failure after salvage therapy. In conclusion, HSPA9 and CUL2 were highly expressed in prostate tissue, especially in neoplastic cells. HSPA9 and CUL2-positive Gleason pattern 3 adenocarcinoma was more likely to be associated with Gleason pattern 4 or 5, while HSPA9 and CUL2-positive Gleason pattern 4 adenocarcinoma was less likely to belong to ISUP groups 1 and 2. Staining for HSPA9 and CUL2 can help identify patients at increased risk of recurrence after salvage therapy.

Effect of F16-Betulin Conjugate on Mitochondrial Membranes and Its Role in Cell Death Initiation

This work demonstrates the effects of a newly synthesized conjugate of the plant triterpenoid betulin and the penetrating cation F16 used for mitochondrial targeting. The resulting F16-betulin conjugate revealed a mitochondria-targeted effect, decreasing the mitochondrial potential and inducing superoxide overproduction in rat thymocytes in vitro. It has been suggested that this may cause the cytotoxic effect of the conjugate, which significantly exceeds the effectiveness of its precursors, betulin and F16. Using isolated rat liver mitochondria, we found that the F16-betulin conjugate has a surface-active effect on mitochondrial membranes, causing organelle aggregation. This effect of the derivative resulted in a dose-dependent decrease in mitochondrial transmembrane potential, as well as suppression of respiration and oxidative phosphorylation, especially in the case of nicotinamide adenine dinucleotide (NAD)-fueled organelles. In addition, the F16-betulin conjugate caused an increase in H₂O₂ generation by mitochondria fueled with glutamate and malate. These effects of the derivative can presumably be due to the powerful suppression of the redox activity of complex I of the mitochondrial electron transport chain. The paper discusses how the mitochondria-targeted effects of the F16-betulin conjugate may be related to its cytotoxic effects.

Emerging insights into mitochondria-specific targeting and drug delivering strategies: Recent milestones and therapeutic implications

Mitochondria are a major intracellular organelle for drug targeting due to its functional roles in cellular metabolism and cell signaling for proliferation and cell death. Mitochondria-targeted treatment strategy could be promising to improve the therapeutic efficacy of cancer while minimizing the adverse side effects. Over the last decades, several studies have explored and focused on mitochondrial functions, which has led to the emergence of mitochondria-specific therapies. Molecules in the mitochondria are considered to be prime targets, and a wide range of molecular strategies have been designed for targeting mitochondria compared with that of the cytosol. In this review, we focused on the molecular mechanisms of mitochondria-specific ligand targeting and selective drug action strategies for targeting mitochondria, including those premised on mitochondrial targeting of signal peptides (MTS), cell-penetrating peptides (CPPs), and use of lipophilic cations. Furthermore, most research has concentrated on specific conjugation of ligands to therapeutic molecules to enhance their effectiveness. There are several variations for the ideal design and development for mitochondrial-targeted drugs, such as selecting a suitable ligand and linker targets. However, some challenges related to drug solubility and selectivity could be resolved using the nanocarrier system. Nanoparticles yield excellent advantages for targeting and transmitting therapeutic drugs, and they offer elegant platforms for mitochondria-specific drug delivery. We explain many of the advanced and proven strategies for multifunctional mitochondria-specific targets, which should contribute to achieving better anticancer therapies in a promising future.

Growth Inhibitory Signaling of the Raf/MEK/ERK Pathway

In response to extracellular stimuli, the Raf/MEK/extracellular signal-regulated kinase (ERK) pathway regulates diverse cellular processes. While mainly known as a mitogenic signaling pathway, the Raf/MEK/ERK pathway can mediate not only cell proliferation and survival but also cell cycle arrest and death in different cell types. Growing evidence suggests that the cell fate toward these paradoxical physiological outputs may be determined not only at downstream effector levels but also at the pathway level, which involves the magnitude of pathway activity, spatial-temporal regulation, and non-canonical functions of the molecular switches in this pathway. This review discusses recent updates on the molecular mechanisms underlying the pathway-mediated growth inhibitory signaling, with a major focus on the regulation mediated at the pathway level.

Resveratrol Reduces Kidney Injury in a Rat Model of Uremia and is Associated with Increased Expression of Heat Shock Protein 70 (Hsp70)

BACKGROUND This study aimed to investigate the effects of resveratrol on kidney function in a rat model of uremia and the expression of heat shock proteins. MATERIAL AND METHODS The rat model of uremia was developed by 5/6 nephrectomy of Sprague-Dawley rats. The Hsp70 inhibitor MKT-077, a rhodacyanine dye, was used. The study groups included rats with sham surgery (the sham group), the rat model of uremia (the model group), the solvent-treated control group (the control group), the rat model treated with resveratrol group (the resveratrol group), the rat model treated with MKT-077 (the MKT-077 group), and the resveratrol+MKT-077 group. Kidney tissues were studied histologically. Renal cell apoptosis was detected by the TUNEL method. Expression of p53, Bax, and Bcl-2 mRNA and protein were detected by quantitative reverse transcription-polymerase chain reaction (qRT-PCR) and immunohistochemistry, respectively. RESULTS Compared with the sham group, the expression levels of heat shock proteins Hsp70, Hsp90, Hsp27, Hsp25, Hsp40, and Hsp60 in the kidney of the rat model group increased to different degrees. Compared with the model group, the Hsp70 levels in the resveratrol group were significantly increased (p<0.05). Compared with the model group, treatment with MKT-077 reduced the survival rate of rats, which was increased following resveratrol treatment. Compared with the resveratrol group, renal function in the resveratrol+MKT-077 group was significantly reduced (p<0.05). CONCLUSIONS In a rat model of uremia, resveratrol reduced renal injury and improved both renal function and survival, which were associated with increased expression of Hsp70.

Subcellular Performance of Nanoparticles in Cancer Therapy

With the advent of nanotechnology, various modes of traditional treatment strategies have been transformed extensively owing to the advantageous morphological, physiochemical, and functional attributes of nano-sized materials, which are of particular interest in diverse biomedical applications, such as diagnostics, sensing, imaging, and drug delivery. Despite their success in delivering therapeutic agents, several traditional nanocarriers often end up with deprived selectivity and undesired therapeutic outcome, which significantly limit their clinical applicability. Further advancements in terms of improved selectivity to exhibit desired therapeutic outcome toward ablating cancer cells have been predominantly made focusing on the precise entry of nanoparticles into tumor cells via targeting ligands, and subsequent delivery of therapeutic cargo in response to specific biological or external stimuli. However, there is enough room intracellularly, where diverse small-sized nanomaterials can accumulate and significantly exert potentially specific mechanisms of antitumor effects toward activation of precise cancer cell death pathways that can be explored. In this review, we aim to summarize the intracellular pathways of nanoparticles, highlighting the principles and state of their destructive effects in the subcellular structures as well as the current limitations of conventional therapeutic approaches. Next, we give an overview of subcellular performances and the fate of internalized nanoparticles under various organelle circumstances, particularly endosome or lysosome, mitochondria, nucleus, endoplasmic reticulum, and Golgi apparatus, by comprehensively emphasizing the unique mechanisms with a series of interesting reports. Moreover, intracellular transformation of the internalized nanoparticles, prominent outcome and potential affluence of these interdependent subcellular components in cancer therapy are emphasized. Finally, we conclude with perspectives with a focus on the contemporary challenges in their clinical applicability.

A BAG's life: Every connection matters in cancer

The members of the BCL-2 associated athanogene (BAG) family participate in the regulation of a variety of interrelated physiological processes, such as autophagy, apoptosis, and protein homeostasis. Under normal circumstances, the six BAG members described in mammals (BAG1-6) principally assist the 70 kDa heat-shock protein (HSP70) in protein folding; however, their role as oncogenes is becoming increasingly evident. Deregulation of the BAG multigene family has been associated with cell transformation, tumor recurrence, and drug resistance. In addition to BAG overexpression, BAG members are also involved in many oncogenic protein-protein interactions (PPIs). As such, either the inhibition of overloading BAGs or of specific BAG-client protein interactions could have paramount therapeutic value. In this review, we will examine the role of each BAG family member in different malignancies, focusing on their modular structure, which enables interaction with a variety of proteins to exert their pro-tumorigenic role. Lastly, critical remarks on the unmet needs for proposing effective BAG inhibitors will be pointed out.

Heat Shock Proteins (HSPs): A Novel Target for Cancer Metastasis Prevention

Background:

Heat shock proteins (HSPs) are predominant molecular chaperones which are actively involved in the protein folding; which is essential in protecting the structure and functioning of proteins during various stress conditions. Though HSPs have important physiological roles, they have been well known for their roles in various pathogenic conditions such as carcinogenesis; however, limited literature has consolidated its potential as an anti-metastatic drug target.

Objectives:

The present review outlines the role of different HSPs on cancer progression and metastasis; possible role of HSP inhibitors as anti-neoplastic agents is also discussed.

Methods:

The data were collected from PubMed/Medline and other reputed journal databases. The literature that was too old and had no significant role to the review was then omitted.

Results:

Despite their strong physiological functions, HSPs are considered as good markers for cancer prognosis and diagnosis. They have control over survival, proliferation and progression events of cancer including drug resistance, metastasis, and angiogenesis. Since, neoplastic cells are more dependent on HSPs for survival and proliferation, the selectivity and specificity of HSP-targeted cancer drugs remain high. This has made various HSPs potential clinical and experimental targets for cancer prevention. An array of HSP inhibitors has been in trials and many others are in experimental conditions as anticancer and anti-metastatic agents. Several natural products are also being investigated for their efficacy for anticancer and anti-metastatic agents by modulating HSPs.

Conclusion:

Apart from their role as an anticancer drug target, HSPs have shown to be promising targets for the prevention of cancer progression. Extensive studies are required for the use of these molecules as anti-metastatic agents. Further studies in this line may yield specific and effective antimetastatic agents.

Mortalin (GRP75/HSPA9) Promotes Survival and Proliferation of Thyroid Carcinoma Cells

We previously reported that upregulation of mortalin (HSPA9/GRP75), the mitochondrial HSP70 chaperone, facilitates tumor cell proliferation and survival in human medullary thyroid carcinoma (MTC), proposing mortalin as a novel therapeutic target for MTC. In this report, we show that mortalin is also upregulated in other thyroid tumor types, including papillary thyroid carcinoma (PTC), follicular thyroid carcinoma (FTC), and anaplastic thyroid carcinoma (ATC), and that mortalin depletion can effectively induce growth arrest and cell death in human PTC (TPC-1), FTC (FTC133), and ATC (8505C and C643) cells in culture. Intriguingly, mortalin depletion induced varied effects on cell cycle arrest (G0/G1 phase arrest in TPC-1 and C643, G2/M phase arrest in 8505C, and mild G2/M phase arrest with increased sub-G0/G1 population in FTC133) and on the levels of TP53, E2F-1, p21^CIP1, p27^KIP1, and poly (ADP-ribose) polymerase cleavage in these cells, suggesting that thyroid tumor cells respond to mortalin depletion in a cell type-specific manner. In these cells, we also determined the efficacy of triphenyl-phosphonium-carboxy-proxyl (Mito-CP) because this mitochondria-targeted metabolism interfering agent exhibited similar tumor suppressive effects as mortalin depletion in MTC cells. Indeed, Mito-CP also induced robust caspase-dependent apoptosis in PTC and ATC cell lines in vitro, exhibiting IC₅₀ lower than PLX4032 in 8505C cells and IC₅₀ lower than vandetanib and cabozantinib in TPC-1 cells. Intriguingly, Mito-CP-induced cell death was partially rescued by mortalin overexpression, suggesting that Mito-CP may inactivate a mechanism that requires mortalin function. These findings support the significance of mortalin and mitochondrial activity in a broad spectrum of thyroid cancer.

Mitochondrial autophagosomes as a mechanism of drug resistance in breast carcinoma

We have previously described the process by which mitochondria donate their membranes for the formation of autophagosomes, and in this study we show that the same process could be involved in drug sequestration and exocytosis resulting in multidrug-resistant cancerous cells. We examine the implications of mitochondrial vesicle formation of mitoautophagosomes (MAPS) in response to the cytotoxic drug MKT-077, which targets mortalin, in a drug-resistant breast carcinoma cell line overexpressing P-glycoprotein (P-gp). The breast cancer cell line MCF-7Adr is derived from MCF-7, but differs from its ancestral line in tolerance of MKT-077-induced mitochondrial toxicity. Our ultrastructural observations suggest that autophagy in the MCF-7Adr cells entails regional sequestration of MKT077 in multilamellar LC3-labeled MAPS, which then separate from their mitochondria, and fuse with or engulf each other. MAPS appeared to be migrating through the cytoplasm and fusing with the plasma membrane, thus carrying out exocytotic secretion. This mechanism, which seems ineffective in the ancestral cell line, provides a resistance mechanism for MKT-077 by enhancing the efflux process of the cells. After 8 hr of MKT-077 exposure, a fraction of the resistant cells appeared viable and contained larger number of smaller sized mitochondria. Mitoautophagosomes, therefore, provide a potentially novel model for multidrug resistance in cancerous cells and may contribute to the P-gp efflux process.

Targeted Therapy for Medullary Thyroid Cancer: A Review

Medullary thyroid cancers (MTCs) constitute between 2 and 5% of all thyroid cancers. The 10-year overall survival (OS) rate of patients with localized disease is around 95% while that of patients with regional stage disease is about 75%. Only 20% of patients with distant metastases at diagnosis survive 10 years which is significantly lower than for differentiated thyroid cancers. Cases with regional metastases at presentation have high recurrence rates. Adjuvant external radiation confers local control but not improved OS. The management of residual, recurrent, or metastatic disease till a few years ago was re-surgery with local measures such as radiation. Chemotherapy was used with marginal benefit. The development of targeted therapy has brought in a major advantage in management of such patients. Two drugs—vandetanib and cabozantinib—have been approved for use in progressive or metastatic MTC. In addition, several drugs acting on other steps of the molecular pathway are being investigated with promising results. Targeted radionuclide therapy also provides an effective treatment option with good quality of life. This review covers the rationale of targeted therapy for MTC, present treatment options, drugs and methods under investigation, as well as an outline of the adverse effects and their management.

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

Although the FDA-approved receptor tyrosine kinases inhibitors, vandetanib and cabozantinib, are used to treat surgically inoperable progressive medullary thyroid carcinoma (MTC), not all patients are responsive while the disease sometimes progresses after an initial response. To better understand MTC drug resistance at molecular and biochemical levels, we have generated drug-resistant subpopulations of the human MTC cell lines, TT and MZ-CRC-1, via prolonged exposure to vandetanib and cabozantinib. These drug-resistant progenies exhibited substantial cross-resistance to vandetanib and cabozantinib, suggesting that these inhibitors may invoke an overlapping resistance mechanism(s) in MTC cells. Of note, vandetanib and cabozantinib increased mitochondrial membrane potential (Δψ_m) in drug-naïve as well as drug-resistant cells but only drug-naïve cells exhibited substantially altered oxygen consumption and extracellular acidification rates. Therefore, these inhibitors appear to cause a bioenergetics stress to which drug-resistant MTC cells are more tolerant. Given the ability of vandetanib and cabozantinib to increase Δψ_m, we hypothesized that these inhibitors can augment growth inhibitory effects of mitochondria-targeted carboxy-proxyl and ubiquinone by increasing their Δψ_m-dependent uptake/retention in MTC cells. Indeed, our in vitro and mouse xenograft data strongly support this possibility.

Mitochondria chaperone GRP75 moonlighting as a cell cycle controller to derail endocytosis provides an opportunity for nanomicrosphere intracellular delivery

Understanding how cancer cells regulate endocytosis during the cell cycle could lead us to capitalize this event pharmacologically. Although certain endocytosis pathways are attenuated during mitosis, the endocytosis shift and regulation during the cell cycle have not been well clarified. The conventional concept of glucose-regulated proteins (GRPs) as protein folding chaperones was updated by discoveries that translocated GRPs assume moonlighting functions that modify the immune response, regulate viral release, and control intracellular trafficking. In this study, GRP75, a mitochondria matrix chaperone, was discovered to be highly expressed in mitotic cancer cells. Using synchronized cell models and the GRP75 gene knockdown and ectopic overexpression strategy, we showed that: (1) clathrin-mediated endocytosis (CME) was inhibited whereas clathrin-independent endocytosis (CIE) was unchanged or even up-regulated in the cell cycle M-phase; (2) GRP75 inhibited CME but promoted CIE in the M-phase, which is largely due to its high expression in cancer cell mitochondria; (3) GRP75 targeting by its small molecular inhibitor MKT-077 enhanced cell cycle G1 phase-privileged CME, which provides an opportunity for intracellular delivery of nanomicrospheres sized from 40 nm to 100 nm. Together, our results revealed that GRP75 moonlights as a cell cycle controller and endocytosis regulator in cancer cells, and thus has potential as a novel interference target for nanoparticle drugs delivery into dormant cancer cells.

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

Most BRAF-mutated melanomas initially responsive to the FDA-approved inhibitors preferentially targeting B-Raf mutated in Val600 residue eventually relapse, requiring additional therapeutic modalities. Recent studies report the significance of metabolic reprograming in mitochondria for maintenance of BRAF-mutated melanomas and for development of their drug resistance to B-Raf inhibitors, providing a rationale for targeting mitochondria as a potential therapeutic strategy for melanoma. We therefore determined whether mitochondria-targeted metabolism-interfering agents can effectively suppress human B-Raf^V600E melanoma cell lines and their dabrafenib/PLX4032-resistant progenies using mitochondria-targeted carboxy-proxyl (Mito-CP) and ubiquinone (Mito-Q). These agents exhibited comparable efficacy to PLX4032 in suppressing SK-MEL28, A375, and RPMI-7951 cells in vitro. As determined in SK-MEL28 and A375 cells, Mito-CP induced apoptotic cell death mediated by mitochondrial membrane depolarization and subsequent oxidative stress, which PLX4032 could not induce. Of note, Mito-CP also effectively suppressed PLX4032-resistant progenies of SK-MEL28 and A375. Moreover, when orally administered, Mito-CP suppressed SK-MEL28 xenografts in mice as effectively as PLX4032 without serious adverse effects. These data demonstrate that mitochondria-targeted agents have therapeutic potential to effectively suppress BRAF-mutated melanomas via an effect(s) distinct from those of B-Raf inhibitors.