Defective autophagy in multidrug resistant cells may lead to growth inhibition by BH3-mimetic gossypol

Triangular Relationship between p53, Autophagy, and Chemotherapy Resistance

Chemotherapy and radiation often induce a number of cellular responses, such as apoptosis, autophagy, and senescence. One of the major regulators of these processes is p53, an essential tumor suppressor that is often mutated or lost in many cancer types and implicated in early tumorigenesis. Gain of function (GOF) p53 mutations have been implicated in increased susceptibility to drug resistance, by compromising wildtype anti-tumor functions of p53 or modulating key p53 processes that confer chemotherapy resistance, such as autophagy. Autophagy, a cellular survival mechanism, is initially induced in response to chemotherapy and radiotherapy, and its cytoprotective nature became the spearhead of a number of clinical trials aimed to sensitize patients to chemotherapy. However, increased pre-clinical studies have exemplified the multifunctional role of autophagy. Additionally, compartmental localization of p53 can modulate induction or inhibition of autophagy and may play a role in autophagic function. The duality in p53 function and its effects on autophagic function are generally not considered in clinical trial design or clinical therapeutics; however, ample pre-clinical studies suggest they play a role in tumor responses to therapy and drug resistance. Further inquiry into the interconnection between autophagy and p53, and its effects on chemotherapeutic responses may provide beneficial insights on multidrug resistance and novel treatment regimens for chemosensitization.

A progressive reduction in autophagic capacity contributes to induction of replicative senescence in Hs68 cells

Autophagy has been implicated in delayed aging and extended longevity. Here, we aimed to study the possible effects of autophagy during the progression of replicative senescence, which is one of the major features of aging. Human foreskin fibroblasts, Hs68 cells, at an initial passage of 15 were serially cultured for several months until they reached cellular senescence. A decrease in cell proliferation was observed during the progression of senescence. Induction of replicative senescence in aged cells (at passage 40) was confirmed by senescence-associated β-galactosidase (SA-β-gal) activity that represents a sensitive and reliable marker for quantifying senescent cells. We detected a significantly increased percentage (%) of SA-β-gal-positive cells at passage 40 (63%) when compared with the younger SA-β-gal-positive cells at passage 15 (0.5%). Notably, the gradual decrease in basal autophagy coincided with replicative senescence induction. However, despite decreased basal autophagic activity in senescent cells, autophagy inducers could induce autophagy in senescent cells. RT-PCR analysis of 11 autophagy-related genes revealed that the decreased basal autophagy in senescent cells might be due to the downregulation of autophagy-regulatory proteins, but not autophagy machinery components. Moreover, the senescence phenotype was not induced in the cells in which rapamycin was added to the culture to continuously induce autophagy from passage 29 until passage 40. Together, our findings suggest that reduced basal autophagy levels due to downregulation of autophagy-regulatory proteins may be the mechanism underlying replicative senescence in Hs68 cells.

An efficient nanomaterial-based electrochemical biosensor for sensitive recognition of drug-resistant leukemia cells

A novel electrochemical cytosensor was developed for the fast and high-sensitivity recognition of drug-resistant leukemia K562/ADM cells based on the P-glycoprotein (P-gp) expression level on a cell membrane. The nanocomposite interface of the gold nanoparticles/polyaniline nanofibers (AuNPs/PANI-NF) was chosen to design the biosensor for electrochemical detection. Au/PANI-NF-based cytosensors coated with anti-P-glycoprotein (anti-P-gp) molecules could provide a biomimetic interface for the immunosensing of cell surface P-glycoprotein, and thus could capture the over-expression P-gp cells. Transmission electron microscopy (TEM) indicated that the gold nanoparticles were uniformly anchored along the structure of the PANI-NF surface, displaying fibrillar morphology with a diameter of ∼70 nm, and atomic force microscopy (AFM) further presented the morphology of the nanocomposite film. Owing to the high affinity of anti-P-gp for leukemia K562/ADM cells of the propounded sensing platform, the proposed biosensor exhibited excellent analytical performance for leukemia K562/ADM cells, ranging from 1.6 × 10(2) to 1.6 × 10(6) cells per mL with a detection limit of 80 cells per mL. Recovery experiments indicated that the sensitivity reported here is suitable for practical application. The cell surface P-gp expression level was analysed by flow cytometric experiments, which confirmed the above recognized result. This strategy is also a cost-effective and convenient operation, implying great promise for the sensitive recognition of cancer cells and cell surface receptors; thus, it is helpful in cancer diagnosis.

Gossypol sensitizes the antitumor activity of 5-FU through down-regulation of thymidylate synthase in human colon carcinoma cells

PURPOSE

5-Fluorouracil (5-FU) is the basic chemotherapeutic agent used to treat colon cancer. However, the sensitivity of colon cancer cells to 5-FU is limited. Gossypol is a polyphenolic extract of cottonseeds. The purpose of this study was to investigate the activities and related mechanism of gossypol alone or in combination with 5-FU against human colon carcinoma cells.

METHODS

The IC50 of gossypol or/and 5-FU in vitro was tested by 3-(4,5-dimethyl thiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay, and the drug interaction was analyzed using the CalcuSyn method. Cell apoptosis was determined using presidium iodide staining and flow cytometric analysis. Western blotting was used to determine the expression of proteins. Transient transfection method was used to silence protein.

RESULTS

The IC₅₀ at 48 h of gossypol in colon cancer cells was 26.11 ± 1.04 μmol/L in HT-29 cells, 14.11 ± 1.08 μmol/L in HCT116 cells, and 21.83 ± 1.05 μmol/L in RKO cells. When gossypol was combined with 5-FU, a synergistic cytotoxic effect was observed in HT-29 cells, HCT116 cells, and RKO cells compared with treatment with gossypol or 5-FU alone. The Western blotting results indicated that gossypol down-regulated thymidylate synthase (TS) rather than thymidine phosphorylase protein expression. Furthermore, the mTOR/p70S6K1 signaling pathway was inhibited in gossypol-treated colon cancer cells, and consequently, cyclin D1 expression was decreased, suggesting an additional mechanism of the observed antiproliferative synergistic interactions. All the observation was confirmed by silencing TS and inactivating the mTOR/p70S6K1 signaling pathway by rapamycin, both of which increased the chemo-sensitizing efficacy of 5-FU.

CONCLUSIONS

These findings suggest that gossypol-mediated down-regulation of TS, cyclin D1, and the mTOR/p70S6K1 signaling pathways enhances the anti-tumor effect of 5-FU. Ultimately, our data exposed a new action for gossypol as an enhancer of 5-FU-induced cell growth suppression.

Nanomaterial-induced autophagy: a new reversal MDR tool in cancer therapy?

Most of the therapeutic strategies to counteract cancer imply killing of malignant cells. The most exploited cell death mechanism in cancer therapies is apoptosis, but recently, a lot of papers report that other mechanisms, mainly autophagy, could represent a new line of attack in the fight against cancer. One of the limitations for the effectiveness of the approved clinical treatments is the phenomenon of multidrug resistance (MDR) which enables the cancer cells to develop resistance to therapy, especially for chemotherapy. The MDR mechanisms include (a) decreased uptake of drug, (b) reduced intracellular drug concentration by efflux pumps, (c) altered cell cycle checkpoints, (d) altered drug targets, (e) increased metabolism of drugs, (f) induced emergency response genes to impair apoptotic pathway, and (g) altered drug detoxification. Great efforts have been made to reverse MDR. Currently, autophagy and nanosized drug delivery systems (DDSs) belonging to nanomaterials (NMs) provide alternative strategies to circumvent MDR. Nanosized DDSs are very promising tools to accumulate chemotherapeutics at targeting sites and control temporal and spatial drug release into tumor cells. On the other hand, autophagy could overrule drug resistance upon its activation by ensuring cell death via switching its prosurvival role to a prodeath one or by mediating the occurrence of cell death, i.e., apoptosis or necrosis. Likewise, the autophagy inhibition could counteract MDR by sensitizing the cells to anticancer molecules, i.e., Src family tyrosine kinase (SFK) inhibitors or 5-fluorouracil. Noteworthy, autophagy has been recently indicated to be a common cellular response to NMs, corroborating the fascinating idea of the exploitation of NM-induced autophagy in nanomedicine therapy. This review focuses on recently published literature about the relationship between MDR reversal and NMs or autophagy pointing to hypothesize a pivotal role of autophagy modulation induced by NMs in counteracting MDR.

Crosstalk between apoptosis and autophagy: molecular mechanisms and therapeutic strategies in cancer

Both apoptosis and autophagy are highly conserved processes that besides their role in the maintenance of the organismal and cellular homeostasis serve as a main target of tumor therapeutics. Although their important roles in the modulation of tumor therapeutic strategies have been widely reported, the molecular actions of both apoptosis and autophagy are counteracted by cancer protective mechanisms. While apoptosis is a tightly regulated process that is implicated in the removal of damaged or unwanted cells, autophagy is a cellular catabolic pathway that is involved in lysosomal degradation and recycling of proteins and organelles, and thereby is considered an important survival/protective mechanism for cancer cells in response to metabolic stress or chemotherapy. Although the relationship between autophagy and cell death is very complicated and has not been characterized in detail, the molecular mechanisms that control this relationship are considered to be a relevant target for the development of a therapeutic strategy for tumor treatment. In this review, we focus on the molecular mechanisms of apoptosis, autophagy, and those of the crosstalk between apoptosis and autophagy in order to provide insight into the molecular mechanisms that may be essential for the balance between cell survival and death as well as their role as targets for the development of novel therapeutic approaches.