Recent Updates on the Efficacy of Mitocans in Photo/Radio-Therapy for Targeting Metabolism in Chemo/Radio-Resistant Cancers: Nanotherapeutics

Conventional therapeutic modalities against the cancers such as surgery, chemotherapy (CT) and radiotherapy (RT) have limited efficacy due to drug resistance, and adverse effects. Recent developments in nanoscience emphasized novel approaches to overcome the aforementioned limitations and subsequently improve overall clinical outcomes in cancer patients. Photodynamic therapy (PDT), photothermal therapy (PTT), and radiodynamic therapy (RDT) can be used as cancer treatments due to their high selectivity, low drug resistance, and low toxicity. Mitocans are the therapeutic molecules that can produce anti-cancer effects by modulating mitochondria functions and they have significant implications in cancer therapy. Mitochondria- targeted therapy is a promising strategy in cancer treatment as these organelles play a crucial function in the regulation of apoptosis and metabolism in tumor cells and are more vulnerable to hyperthermia and oxidative damage. The aim of this review is used to explore the targeting efficacy of mitocans in the nanotherapeutic formulation when combined with therapies like PDT, PTT, RDT. We searched several databases include Pubmed, relemed, scopus, google scholar, Embase and collected the related information to the efficacy of mitocans in nanotherapeutics when combined with photo-radiotherapy to target chemo/radio-resisant tumor cells. In this review, we vividly described research reports pertinent to the selective delivery of chemotherapy molecules into specific sub-organelles which can significantly improve the efficiency of cancer treatment by targeting tumor cell metabolism. Furthermore, the rational design, functionalization and application of various mitochondrial targeting units, including organic phosphine/sulfur salts, quaternary ammonium salts, transition metal complexes, and mitochondria-targeted cancer therapy such as PDT, PTT, RDT, and others were summarized. Mainly, the efficacy of these modalities against mtDNA and additional nanotherapeutic strategies with photosensitizers, or radiotherapy to target mitochondrial metabolism in tumor cells with chemo/radio-resistance were delineated. This review can benefit nanotechnologists, oncologists, and radiation oncologists to develop rational designs and application of novel mitochondrial targeting drugs mainly to target metabolism in chemo/radio-resistant cancer cells in cancer therapy.

Converting bile acids into mitocans

Cholic acid (1, CD), deoxycholic (3, DCA), chenodeoxycholic acid (5, CDCA), ursodeoxycholic acid (7, UDCA), and lithocholic acid (9, LCA) were acetylated and converted into their piperazinyl spacered rhodamine B conjugates 16-20. While the parent bile acids showed almost no cytotoxic effects for several human tumor cell lines, the piperazinyl amides were cytostatic but an even superior effect was observed for the rhodamine B conjugates. Extra staining experiments showed these compounds as mitocans; they led to a cell arrest in the G1 phase.

Straightforward access to novel mitochondriotropics derived from 2-arylethanol as potent and selective antiproliferative agents

The necessity for developing novel cytostatic agents with improved activities and reduced side-effects to tackle cancer prompted us to investigate mitochondria-targeted compounds, an approach that is gaining attention for the selective transportation of cytotoxic agents. We envisioned the possibility of conjugating a phenethyl alcohol motif, decorated with a series of phenol-based substituents on the aryl moiety, with a triphenyl phosphonium scaffold (a mitochondria-directed vector), through a hydrocarbon chain of different lengths. Thus, such compounds that incorporate the phenethyl skeleton can be considered as masked phenolic compounds derived from relevant natural counterparts found in olive tree (e.g. tyrosol, hydroxytyrosol). Title compounds exhibited very strong in vitro antiproliferative activities against the panel of six human tumor cell lines tested, with GI₅₀ values ranging from the nanomolar (0.026 ± 0.010 μM for 36) to the submicromolar range in most of the cases; this represents an improvement of up to 350-fold compared to classical chemotherapeutic agents, like 5-fluorouracil or cisplatin. Interestingly, decrease in the linker length led to an increase of GI₅₀ values against non-tumor cells, thus allowing a remarkable improvement of selectivity (SI up to 269). The very promising antiproliferative activities prompted us to further investigate their behaviour against multidrug resistant cell lines (MDR). The results indicated a reduced sensitivity of the multidrug resistant cells to compounds, probably due to P-gp-mediated efflux of these antiproliferative agents. Interestingly, activities were completely restored to the same levels by co-administration of tariquidar, a well-known inhibitor of P-gp. Flow cytometry analysis on sensitive cell lines revealed a decrease in the percentage of cells in G1 phase accompanied by increase in S and G2/M phases. In addition, a significant increase in subG1 area, was observed. These results are compatible with the necrotic and apoptotic cell death detected in the Annexin V assay, and with the depolarization of the mitochondria membrane. Thus, the new mitochondriotropic agents reported herein can be considered as promising antiproliferative agents, endowed with remarkable potency and selectivity, including MDR cells, upon co-administration with a pump-efflux inhibitor.

Mitochondrial metabolism as a target for acute myeloid leukemia treatment

Acute myeloid leukemias (AML) are a group of aggressive hematologic malignancies resulting from acquired genetic mutations in hematopoietic stem cells that affect patients of all ages. Despite decades of research, standard chemotherapy still remains ineffective for some AML subtypes and is often inappropriate for older patients or those with comorbidities. Recently, a number of studies have identified unique mitochondrial alterations that lead to metabolic vulnerabilities in AML cells that may present viable treatment targets. These include mtDNA, dependency on oxidative phosphorylation, mitochondrial metabolism, and pro-survival signaling, as well as reactive oxygen species generation and mitochondrial dynamics. Moreover, some mitochondria-targeting chemotherapeutics and their combinations with other compounds have been FDA-approved for AML treatment. Here, we review recent studies that illuminate the effects of drugs and synergistic drug combinations that target diverse biomolecules and metabolic pathways related to mitochondria and their promise in experimental studies, clinical trials, and existing chemotherapeutic regimens.

Sweet as honey, bitter as bile: Mitochondriotoxic peptides and other therapeutic proteins isolated from animal tissues, for dealing with mitochondrial apoptosis

Mitochondria are subcellular organelles involved in cell metabolism and cell life-cycle. Their role in apoptosis regulation makes them an interesting target of new drugs for dealing with cancer or rare diseases. Several peptides and proteins isolated from animal and plant sources are known for their therapeutic properties and have been tested on cancer cell-lines and xenograft murine models, highlighting their ability in inducing cell-death by triggering mitochondrial apoptosis. Some of those molecules have been even approved as drugs. Conversely, many other bioactive compounds are still under investigation for their proapoptotic properties. In this review we report about a group of peptides, isolated from animal venoms, with potential therapeutic properties related to their ability in triggering mitochondrial apoptosis. This class of compounds is known with different names, such as mitochondriotoxins or mitocans.

Mitochondria-Targeted Agents: Mitochondriotropics, Mitochondriotoxics, and Mitocans

Mitochondria, the powerhouse of the cell, have been known for many years for their central role in the energy metabolism; however, extensive progress has been made and to date substantial evidence demonstrates that mitochondria play a critical role not only in the cell bioenergetics but also in the entire cell metabolome. Mitochondria are also involved in the intracellular redox poise, the regulation of calcium homeostasis, and the generation of reactive oxygen species (ROS), which are crucial for the control of a variety of signaling pathways. Additionally, they are essential for the mitochondrial-mediated apoptosis process. Thus, it is not surprising that disruptions of mitochondrial functions can lead or be associated with human pathologies. Because of diseases like diabetes, Alzheimer, Parkinson's, cancer, and ischemic disease are being increasingly linked to mitochondrial dysfunctions, the interest in mitochondria as a prime pharmacological target has dramatically risen over the last decades and as a consequence a large number of agents, which could potentially impact or modulate mitochondrial functions, are currently under investigation. Based on their site of action, these agents can be classified as mitochondria-targeted and non-mitochondria-targeted agents. As a result of the continuous search for new agents and the design of potential therapeutic agents to treat mitochondrial diseases, terms like mitochondriotropics, mitochondriotoxics, mitocancerotropics, and mitocans have emerged to describe those agents with high affinity to mitochondria that exert a therapeutic or deleterious effect on these organelles. In this chapter, mitochondria-targeted agents and some strategies to deliver agents to and/or into mitochondria will be reviewed.

Indoleamine-2,3-dioxygenase elevated in tumor-initiating cells is suppressed by mitocans

Tumor-initiating cells (TICs) often survive therapy and give rise to second-line tumors. We tested the plausibility of sphere cultures as models of TICs. Microarray data and microRNA data analysis confirmed the validity of spheres as models of TICs for breast and prostate cancer as well as mesothelioma cell lines. Microarray data analysis revealed the Trp pathway as the only pathway upregulated significantly in all types of studied TICs, with increased levels of indoleamine-2,3-dioxygenase-1 (IDO1), the rate-limiting enzyme of Trp metabolism along the kynurenine pathway. All types of TICs also expressed higher levels of the Trp uptake system consisting of CD98 and LAT1 with functional consequences. IDO1 expression was regulated via both transcriptional and posttranscriptional mechanisms, depending on the cancer type. Serial transplantation of TICs in mice resulted in gradually increased IDO1. Mitocans, represented by α-tocopheryl succinate and mitochondrially targeted vitamin E succinate (MitoVES), suppressed IDO1 in TICs. MitoVES suppressed IDO1 in TICs with functional mitochondrial complex II, involving transcriptional and posttranscriptional mechanisms. IDO1 increase and its suppression by VE analogues were replicated in TICs from primary human glioblastomas. Our work indicates that IDO1 is increased in TICs and that mitocans suppress the protein.