A novel series of pyrazole-platinum(II) complexes as potential anti-cancer agents that induce cell cycle arrest and apoptosis in breast cancer cells

Six novel compounds of platinum(II) with pyrazole derivatives PtPz1–PtPz6 were synthesised and characterised (PtPz1 - [Pt₂N-hydroksymethyl-3,5-dimethylpyrazole₄(berenil)₂]Cl₄; PtPz2 - [Pt₂3,5-dimethylpyrazole₄(berenil)₂]Cl₄; PtPz3 - [Pt₂3,4-dimethylpyrazole₄(berenil)₂]Cl₄; PtPz4 - [Pt₂pyrazole₄(berenil)₂]Cl₄; PtPz5- [Pt₂5-methylpyrazole₄(berenil)₂]Cl₄; PtPz6 - [Pt₂N-ethylpyrazole₄(berenil)₂]Cl₄). The cytotoxic activity of these complexes against MCF-7 and MDA-MB-231 breast cancer cell lines was determined using the MTT assay. Evaluation of apoptosis induction was done with the Annexin V-fluorescein isothiocyanate/propidium iodide assay. In addition, using a flow cytometer, we determined the influence of test compounds on the cell cycle and caspase-3, -8, and -9 activity. The obtained results of caspase activity were confirmed by cell imaging. Moreover, using the flow cytometer, the effects of the test compounds on mitochondrial potential change were assessed. The test results showed that novel pyrazole-platinum(II) complexes exhibited stronger anti-proliferative activity against two breast cancer cell lines than reference cisplatin. Compounds PtPz1, PtPz2, and PtPz3 with methyl substituents at the pyrazole ring showed stronger activity than pyrazole or ethylpyrazole containing complexes. Studies have shown that inhibition of cell survival occurs by arresting the G1 cell cycle and inducing apoptosis. Our analysis associated with the response of MCF-7 and MDA-MB-231 cells to treatment with PtPz1–PtPz6 showed that it leads the cells through the external and intrinsic (mitochondrial) apoptotic pathway via indirect DNA damage.     

Wogonin and related natural flavones are inhibitors of CDK9 that induce apoptosis in cancer cells by transcriptional suppression of Mcl-1

The wogonin-containing herb Scutellaria baicalensis has successfully been used for curing various diseases in traditional Chinese medicine. Wogonin has been shown to induce apoptosis in different cancer cells and to suppress growth of human cancer xenografts in vivo. However, its direct targets remain unknown. In this study, we demonstrate for the first time that wogonin and structurally related natural flavones, for example, apigenin, chrysin and luteolin, are inhibitors of cyclin-dependent kinase 9 (CDK9) and block phosphorylation of the carboxy-terminal domain of RNA polymerase II at Ser². This effect leads to reduced RNA synthesis and subsequently rapid downregulation of the short-lived anti-apoptotic protein myeloid cell leukemia 1 (Mcl-1) resulting in apoptosis induction in cancer cells. We show that genetic inhibition of Mcl-1 or CDK9 expression by siRNA is sufficient to mimic flavone-induced apoptosis. Pull-down and in silico docking studies demonstrate that wogonin directly binds to CDK9, presumably to the ATP-binding pocket. In contrast, wogonin does not inhibit CDK2, CDK4 and CDK6 at doses that inhibit CDK9 activity. Furthermore, we show that wogonin preferentially inhibits CDK9 in malignant compared with normal lymphocytes. Thus, our study reveals a new mechanism of anti-cancer action of natural flavones and supports CDK9 as a therapeutic target in oncology.     

Selective amino acid restriction targets mitochondria to induce apoptosis of androgen-independent prostate cancer cells

Relative specific amino acid dependency is one of the metabolic abnormalities of cancer cells, and restriction of specific amino acids induces apoptosis of prostate cancer cells. This study shows that restriction of tyrosine and phenylalanine (Tyr/Phe), glutamine (Gln), or methionine (Met), modulates Raf and Akt survival pathways and affects the function of mitochondria in DU145 and PC3, in vitro. These three restrictions inhibit energy production (ATP synthesis) and induce generation of reactive oxygen species (ROS). Restriction of Tyr/Phe or Met in DU145 and Met in PC3 reduces mitochondrial membrane potential (DeltaPsim) and induces caspase-dependent and -independent apoptosis. In DU145, Tyr/Phe or Met restriction reduces activity of Akt, mitochondrial distribution of phosphorylated Raf and apoptosis inducing factor (AIF), and increases mitochondrial distribution of Bak. Mitochondrial Bcl-XL is increased in Tyr/Phe-restricted but decreased in Met-restricted cells. Under Tyr/Phe or Met restriction, reduced mitochondrial Raf does not inactivate the pro-apoptotic function of Bak. Tyr/Phe restriction also inhibits Bcl-2 and Met restriction inhibits Bcl-XL in mitochondria. These comprehensive actions damage the integrity of the mitochondria and induce apoptosis of DU145. In PC3, apoptosis induced by Met restriction was not associated with alterations in intracellular distribution of Raf, Bcl-2 family proteins, or AIF. All of the amino acid restrictions inhibited Akt activity in this cell line. We conclude that specific amino acid restriction differentially interferes with homeostasis/balance between the Raf and Akt survival pathways and with the interaction of Raf and Bcl-2 family proteins in mitochondria to induce apoptosis of DU145 and PC3 cells.     

Human amniotic epithelial cells induce apoptosis of cancer cells: a new anti-tumor therapeutic strategy

Background aimsAmniotic membrane (AM), the innermost layer of human placenta, is composed of a single layer of epithelial cells, a basement membrane and an avascular stroma. The AM has many functions and properties, among which angiogenic modulatory and immunoregulatory effects are applicable in cancer therapy. Because these functions belong to amniotic epithelial cells, in this study we compared the anti-cancer effect of amniotic epithelial cells and the whole AM.MethodsThe effect of the AM and the amniotic epithelial cells on cancer cell apoptosis was evaluated by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium assay, terminal deoxynucleotidyl transferase dUTP nick end labeling assay and immunocytochemistry. The effect of the AM on angiogenesis in conditions both with and without epithelial cells was also evaluated using rat aortic ring assay.ResultsThere was a decrease in cancer cell viability after adding either AM or amniotic epithelial cell supernatant to cancer cells. A significant increase in caspase-3 and caspase-8 expression in cancer cells treated with amniotic epithelial cell supernatant was observed. The recorded media also demonstrated the possible induction of apoptosis in cancer cells treated with the amniotic epithelial cell supernatant. In the aorta ring assay, the AM showed an anti-angiogenic effect in the presence of its epithelial cells; however, this effect was altered to initiate angiogenesis when amniotic epithelial cells were removed from the AM.ConclusionsThese results suggest that amniotic epithelial cells, with their anti-angiogenic effect and induction of apoptosis, are candidates for cancer therapeutic agents in the near future.     

ZnO nanomaterials target mitochondrial apoptosis and mitochondrial autophagy pathways in cancer cells

In recent years, the application of engineering nanomaterials has significantly contributed to the development of various biomedical fields. Zinc oxide nanomaterials (ZnO NMts) have gained wide popularity due to their biocompatibility, unique physical and chemical properties, stability, and cost-effectiveness for large-scale production. They have emerged as potential materials for anticancer applications. This article provides a comprehensive review of the synthesis methods of ZnO NMts and highlights the advantages of combining ZnO NMts with anticancer drugs as a nano platform for cancer treatment. Additionally, the article briefly explains the mechanism of action of ZnO NMts in tumor cells, focusing on the mitochondrial pathways that target cell apoptosis and autophagy. It is observed that these pathways are primarily influenced by reactive oxygen species generated through oxidative stress. The article discusses the promising prospects of ZnO NMts combined with anticancer drugs in the field of cancer medicine and emphasizes the need for further in-depth research on the mitochondrial apoptosis and mitochondrial autophagy pathways.     

A natural product enhances apoptosis via mitochondria/caspase-mediated pathway in HeLa cells

Cervical cancer is the fourth most lethal human malignancy and the leading cause of death among females around the world. Many antitumor agents have microbial origins. 5′-epi-SPA-6952A is a new 24-membered macrolide isolated from the cultured broth of Streptomyces diastatochromogenes. Therefore, we studied the activity and molecular mechanism of 5′-epi-SPA-6952A in human cervical carcinoma HeLa cell. The results showed that 5′-epi-SPA-6952A significantly inhibited cell proliferation and migration. In addition, 5′-epi-SPA-6952A obviously increased the production of intracellular reactive oxygen species and DNA damage in HeLa cells. Moreover, nuclear shrinkage of cells, decrease in mitochondrial membrane potential, and upregulation of Bax/Bcl-2 ratio resulted in the release of cytochrome c, and activation of caspase-9/3 was observed in HeLa cells treated with 5′-epi-SPA-6952A, which means it enhanced the intrinsic mitochondrial apoptosis. Besides, DNA-damage associated proteins poly (ADP-ribose) polymerase (PARP) and p53 were also studied, and the expressions of cleaved-PARP and p53 were drastically increased in HeLa cells treated with 5′-epi-SPA-6952A. Furthermore, we confirmed that 5′-epi-SPA-6952A affected the survival of HeLa cells by blocking cell cycle progression in the G1 phase. Taken together, the results shows that 5′-epi-SPA-6952A significantly inhibited HeLa cells proliferation via intrinsic mitochondrial apoptosis, cell cycle arrest, and blocking cell migration.     

Loss of cardiolipin in palmitate-treated GL15 glioblastoma cells favors cytochrome c release from mitochondria leading to apoptosis

Unlike oleate and linoleate, palmitate induced mitochondrial apoptosis in GL15 glioblastoma cells. Decrease in membrane potential in a subpopulation of mitochondria of palmitate-treated cells was revealed using the 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazolylcarbocyanine iodide probe. The diminished ability to reduce a tetrazolium salt indicated an impairment of mitochondrial function. Up to 50% cytochrome c (cyt c ) was detached from the inner mitochondrial membrane and released outside mitochondria in palmitate-treated cells, whereas no release was detected after oleate and linoleate treatments. Cyt c release into the cytosol was followed by caspase 3 activation. Released cyt c and caspase 3 activity were not affected by neutral and acid sphingomyelinase inhibitors and by the inhibitor of serine palmitoyltransferase cycloserine, indicating that apoptosis was independent of the ceramide pathway, nor the mitochondrial pro-apoptotic AIF or Bcl-2/Bax factors appeared to be involved in the effect. Utilization of palmitate by GL15 cells altered phospholipid composition. Cardiolipin (CL), the lipid involved in cyt c interaction with the inner mitochondrial membrane, was decreased and highly saturated. This produced an imbalance in hydrophilic/hydrophobic interactions underlying the anchorage of cyt c , by weakening the hydrophobic component and facilitating detachment of the protein and activation of downstream processes. The primary role of CL was explored by supplying GL15 with exogenous CL through a fusion process of CL liposomes with cell plasma membrane. Fused CL moved to mitochondria, as detected by nonylacridine orange probe. Enrichment of mitochondrial membranes with CL prior to palmitate treatment of cells caused decreased cyt c release and caspase 3 activity.     

Organopalladium compound 7b targets mitochondrial thiols and induces caspase-dependent apoptosis in human myeloid leukemia cells

The advances in the treatment of chronic myeloid leukemia (CML) during the last years were also accompanied by the development of evading strategies by tumor cells, resulting in chemotherapy resistance in some patients. Patented organopalladium compounds derived from the reaction of N,N-dimethyl-1-phenethylamine (dmpa) with [1,2-ethanebis(diphenylphosphine)] (dppe) exhibited a potent antitumor activity in vivo and in vitro in melanoma cells. We showed here that the cyclopalladated derivative [Pd₂(R₍₊₎)C², N-dmpa)₂(μ-dppe)Cl₂], named compound 7b, was highly effective to promote cell death in the K562 human leukemia cells and its mechanisms of action were investigated. It was shown that compound 7b was able to promote exclusively apoptotic cell death in K562 cells associated to cytochrome c release and caspase 3 activation. This cytotoxic effect was not observed in normal peripheral mononuclear blood cells. The compound 7b-induced intrinsic apoptotic pathway was triggered by the protein thiol oxidation that resulted in the dissipation of the mitochondrial transmembrane potential. The preventive effect of the dithiothreitol on the compound 7b-induced cell death and all downstream events associated to apoptosis confirmed that death signal was elicited by the thiol oxidation. These findings contribute to the elucidation of the palladacycle 7b-induced cell death mechanism and present this compound as a promising drug in the CML antitumor chemotherapy.     

Pristimerin induces apoptosis by targeting the proteasome in prostate cancer cells

Pristimerin is a natural product derived from the Celastraceae and Hippocrateaceae families that were used as folk medicines for anti inflammation in ancient times. Although it has been shown that pristimerin induces apoptosis in breast cancer cells, the involved mechanism of action is unknown. The purpose of the current study is to investigate the primary target of pristimerin in human cancer cells, using prostate cancer cells as a working model. Nucleophilic susceptibility and in silico docking studies show that C6 of pristimerin is highly susceptible towards a nucleophilic attack by the hydroxyl group of N-terminal threonine of the proteasomal chymotrypsin subunit. Consistently, pristimerin potently inhibits the chymotrypsin-like activity of a purified rabbit 20S proteasome (IC50 2.2 micromol/L) and human prostate cancer 26S proteasome (IC50 3.0 micromol/L). The accumulation of ubiquitinated proteins and three proteasome target proteins, Bax, p27 and I kappa B-alpha, in androgen receptor (AR)-negative PC-3 prostate cancer cells supports the conclusion that proteasome inhibition by pristimerin is physiologically functional. This observed proteasome inhibition subsequently led to the induction of apoptotic cell death in a dose- and kinetic-dependent manner. Furthermore, in AR-positive, androgen-dependent LNCaP and AR-positive, androgen-independent C4-2B prostate cancer cells, proteasome inhibition by pristimerin results in suppression of AR protein prior to apoptosis. Our data demonstrate, for the first time, that the proteasome is a primary target of pristimerin in prostate cancer cells and inhibition of the proteasomal chymotrypsin-like activity by pristimerin is responsible for its cancer cell death-inducing property.     

Breast cancer cells induce osteoblast apoptosis: a possible contributor to bone degradation

Breast cancer cells exhibit a predilection for metastasis to bone. There, the metastases usually bring about bone loss with accompanying pain and loss of function. One way that breast cancer cells disrupt the normal pattern of bone remodeling is by activating osteoclasts, the bone degrading cells. Nevertheless, targeting the osteoclasts does not cure the disease or result in bone repair. These observations indicate that osteoblast function also may be compromised. The objective of this study was to investigate the interaction of metastatic breast cancer cells with osteoblasts. Human metastatic breast cancer cells, MDA-MB-435 or MDA-MB-231, or their conditioned media were co-cultured with a human osteoblast line hFOB1.19. The breast cancer cells caused an increase in the prevalence of apoptotic osteoblasts. Apoptotic osteoblasts detected by the TUNEL assay or by caspase activity increased approximately two to fivefold. This increase was not seen with non-metastatic MDA-MB-468 cells. In an investigation of the mechanism, it was determined that the hFOB1.19 cells expressed fas and that fas was functional. Likewise the hFOB1.19 cells were susceptible to TNF-alpha, but this cytokine was not detected in the conditioned medium of the breast cancer cells. This study indicates that osteoblasts are the target of breast cancer cell-induced apoptosis, but fas/fas-ligand and TNF-alpha, two common initiators of cell death, are probably not involved in this aspect of the metastases/bone cell axis. There are several mechanisms that remain to be explored in order to determine how breast cancer cells bring about osteoblast apoptosis. Even though the specific initiator of apoptosis remains to be identified, the results of this study suggest that the mechanism is likely to be novel.     

Silibinin induced apoptosis of human epidermal cancer A431 cells by promoting mitochondrial NOS

The antitumor effects of silibinin are of increasing interest, though its mechanism is not yet clear. The goal of this study was to clarify the mechanism of silibinin-induced cell death in the A431 human epidermoid carcinoma cell line. We used a cell viability assay, flow cytometry, nitric oxide (NO) assay, and western blotting to examine relationships between silibinin, NO generation and apoptosis in A431 cells. Silibinin inhibited A431 cell growth in a dose-dependent manner, inducing mitochondrial damage, and apoptosis at a high dose. At the same time, high dose silibinin increased NO levels in A431 cells and the endothelial nitric oxide synthase (eNOS) inhibitor NG-nitro-L-arginine methylester (L-NAME) attenuated silibinin-induced cell growth inhibition. By western blotting, silibinin caused increased eNOS phosphorylation in the mitochondria. The AMP-activated protein kinase inhibitor compound C significantly decreased p-eNOS expression, while blocking eNOS did not affect p-AMPK levels, suggested that AMPK acted upstream of eNOS. This study showed that silibinin increased NO levels in A431 cells by activating the AMPK–eNOS pathway, leading to mitochondrial dysfunction and apoptosis. In this mechanism of action, mitochondrial eNOS played an important role. The results provided new understanding of the functions of intracellular NO.     

Indomethacin and juglone inhibit inflammatory molecules to induce apoptosis in colon cancer cells

Colorectal cancer (CRC) is the third most common fatal cancer. Indomethacin, a nonsteroidal anti‐inflammatory drug, is known to reduce the occurrence of CRC. This study evaluated the potential anticolon cancer effects of juglone (5‐hydroxy‐1,4‐naphthoquinone) in combination with indomethacin. Human colon adenocarcinoma cells (HT29) were subjected to treatment with indomethacin, juglone, and a combination of both. Morphological analysis, cell cycle regulation, and dual staining using acridine orange and ethidium bromide in control and treated cells revealed the apoptotic potential of these compounds. Bcl2 and inflammatory molecules (tumor necrosis factor‐α, nuclear factor kappa B, and Cox‐2) were found to be decreased with a concomitant increase in the expression of proapoptotic molecules (Bad, Bax, cytochrome c, and PUMA) as a result of the molecular regulation of Wnt, Notch, and peroxisome proliferator‐activated receptor‐γ signaling. Treatment with juglone was not as effective as with indomethacin; however, a combination of both was shown to be more effective, suggesting that juglone may be considered for therapeutic intervention of colon cancer.     

Abrus abrin derived peptides induce apoptosis by targeting mitochondria in HeLa cells

In our previous study, Abrus abrin derived peptide fraction (ABP) with molecular weight in range of 600-1500 Da was shown to have potent antitumor activity in Dalton's lymphoma (DL) tumor bearing mice. The purpose of this study was to elucidate the mechanism of mitochondrial apoptosis induced by the peptide fraction. ABP was found to have selective antiproliferative activity (10 ng-100 ng/ml) on several tumor cell lines in vitro without having any cytotoxic effect on normal cell lines with a dose of 1000 ng/ml. Analysis of the growth inhibitory mechanism in HeLa cells revealed DNA fragmentation with appearance of the sub G₀/G₁ peak indicative of apoptosis. Further investigation results showed that the apoptotic machinery of HeLa induced by ABP was associated with the release of reactive oxygen species, a drop in mitochondrial transmembrane potential, upregulation of Bax, downregulation of Bcl-2, and activation of caspase-3. The peptide fraction was found to target mitochondria of HeLa cells as observed by confocal microscopy. This peptide fraction offers a source of mitochondria penetrating peptides which might have therapeutic induction of apoptosis in cancer cells.     

Myostatin induces mitochondrial metabolic alteration and typical apoptosis in cancer cells

Myostatin, a member of the transforming growth factor-β superfamily, regulates the glucose metabolism of muscle cells, while dysregulated myostatin activity is associated with a number of metabolic disorders, including muscle cachexia, obesity and type II diabetes. We observed that myostatin induced significant mitochondrial metabolic alterations and prolonged exposure of myostatin induced mitochondria-dependent apoptosis in cancer cells addicted to glycolysis. To address the underlying mechanism, we found that the protein levels of Hexokinase II (HKII) and voltage-dependent anion channel 1 (VDAC1), two key regulators of glucose metabolisms as well as metabolic stress-induced apoptosis, were negatively correlated. In particular, VDAC1 was dramatically upregulated in cells that are sensitive to myostatin treatment whereas HKII was downregulated and dissociated from mitochondria. Myostatin promoted the translocation of Bax from cytosol to mitochondria, and knockdown of VDAC1 inhibited myostatin-induced Bax translocation and apoptosis. These apoptotic changes can be partially rescued by repletion of ATP, or by ectopic expression of HKII, suggesting that perturbation of mitochondrial metabolism is causally linked with subsequent apoptosis. Our findings reveal novel function of myostatin in regulating mitochondrial metabolism and apoptosis in cancer cells.     

A novel Osmium-based compound targets the mitochondria and triggers ROS-dependent apoptosis in colon carcinoma

Engagement of the mitochondrial-death amplification pathway is an essential component in chemotherapeutic execution of cancer cells. Therefore, identification of mitochondria-targeting agents has become an attractive avenue for novel drug discovery. Here, we report the anticancer activity of a novel Osmium-based organometallic compound (hereafter named Os) on different colorectal carcinoma cell lines. HCT116 cell line was highly sensitive to Os and displayed characteristic features of autophagy and apoptosis; however, inhibition of autophagy did not rescue cell death unlike the pan-caspase inhibitor z-VAD-fmk. Furthermore, Os significantly altered mitochondrial morphology, disrupted electron transport flux, decreased mitochondrial transmembrane potential and ATP levels, and triggered a significant increase in reactive oxygen species (ROS) production. Interestingly, the sensitivity of cell lines to Os was linked to its ability to induce mitochondrial ROS production (HCT116 and RKO) as HT29 and SW620 cell lines that failed to show an increase in ROS were resistant to the death-inducing activity of Os. Finally, intra-peritoneal injections of Os significantly inhibited tumor formation in a murine model of HCT116 carcinogenesis, and pretreatment with Os significantly enhanced tumor cell sensitivity to cisplatin and doxorubicin. These data highlight the mitochondria-targeting activity of this novel compound with potent anticancer effect in vitro and in vivo, which could have potential implications for strategic therapeutic drug design.     

Human papillomavirus (HPV) 16 E6 sensitizes cells to atractyloside-induced apoptosis: Role of p53, ICE-like proteases and the mitochondrial permeability transition

Infection of cervical epithelial cells with certain high risk HPV genotypes is thought to play an etiologic role in the development of cervical cancer. In particular, HPV type 16 and 18 early protein 6 (E6) is thought to contribute to epithelial transformation by binding to the tumor suppressor protein p53, targeting it for rapid proteolysis, resulting in loss of its cell cycle arrest and apoptosis-inducing activities. Recent data indicate that factors responsible for triggering apoptosis reside in the cytoplasm of cells, and not in the nucleus. In particular, the findings that mitochondria are required in certain cell-free models for induction of apoptosis and that bcl-2 is localized to mitochondria have focused attention on the role of the mitochondrial membrane permeability transition (MPT) in apoptosis. Here we present data to indicate that HPV 16 E6 expression sensitizes cells to MPT-induced apoptosis. We also report that HPV 16 E6 sensitization of cells to MPT-induced apoptosis occurs only in the presence of wildtype (wt) p53 expression. The extent of apoptosis induced by atractyloside (an inducer of the MPT) in normal, temperature-sensitive (ts) p53, and HPV-16 E6 transfected J2-3T3 cells, and the HPV expressing cervical carcinoma cell lines SiHa, Hela and CaSki was determined. C33A cells, which express mutant p53 but not HPV, were also exposed to atractyloside in the presence or absence of HPV 16 E6 expression. Dose-dependent apoptosis induced by atractyloside in normal J2-3T3 cells and cervical carcinoma cells was measured by loss of cell viability, nuclear fragmentation and DNA laddering. The sensitivity of cells to atractyloside-induced apoptosis was found to be: HPV 16 E6-J2-3T3 > CaSki > normal-J2-3T3 cells ≈ ts p53-J2-3T3 ≈ vector-J2-3T3 cells > Hela > SiHa > C33A ≈ C33A 16 E6. Cyclosporin A (CsA), an inhibitor of the MPT, and ICE-I, a protease inhibitor, provided protection against atractyloside-induced apoptosis. These findings indicate that: 1) high risk HPV 16 E6 protein is capable of sensitizing cells to apoptosis; 2) HPV 16 E6 sensitization of cells to atractyloside-induced apoptosis occurs in a p53-dependent fashion; 3) the target of HPV 16 E6 sensitization of cells to atractyloside-induced apoptosis is the mitochondria; and 4) HPV 16 E6 sensitization of cells to atroctycoside-induced apoptosis involves an ICE-like protease-sensitive mechanism, regulating the onset of the MPT. These findings constitute the first evidence that mitochondria play a role in HPV 16 E6 modulation of apoptosis. J. Cell. Biochem. 66:245-255. © 1997 Wiley-Liss, Inc.     

The cationic cell-penetrating KT2 peptide promotes cell membrane defects and apoptosis with autophagy inhibition in human HCT 116 colon cancer cells

The anticancer activity of cationic antimicrobial peptides (AMPs) has become more interesting because some AMPs have selective recognition against cancer cells. However, their antitumor properties and underlying mechanisms in cancer cells have not been clearly understood. In this study, we evaluated the effects of KT2 (lysine/tryptophan-rich AMP) on the cellular uptake and internalization mechanism, cell viability, surface charge of the cell membrane, membrane integrity, apoptotic cell death, and autophagy in human HCT 116 colon cancer cells. We found that KT2 interacted with the cell membrane of HCT 116 cells and was internalized into HCT 116 cells via clathrin-mediated and caveolae-mediated endocytosis mechanisms. The interaction of KT2 with cells caused cell membrane structure change, elevated membrane permeability, and KT2 also affected the lipid component. The results of atomic force microscopy showed cellular membrane defects of KT2-treated cells. The internalized KT2 induced nuclear condensation and apoptotic cell death. It elevated the apoptotic factor levels including those of cytochrome c and apoptosis-inducing factor. Furthermore, KT2 inhibited autophagy by the suppression of autophagy-related 5, autophagy-related 7, autophagy-related 16 like 1, and Beclin-1 proteins. In conclusion, these results revealed the cytotoxicity of cationic KT2 against HCT 116 cells and may help to clarify the interactions between cationic AMPs and cancer cells.