Gossypol suppresses telomerase activity in human leukemia cells via regulating hTERT

The potential roles of gossypol as anticancer agent: advances and future directions

Gossypol, a polyphenolic aldehyde derived from cottonseed plants, has seen a transformation in its pharmaceutical application from a male contraceptive to a candidate for cancer therapy. This shift is supported by its recognized antitumor properties, which have prompted its investigation in the treatment of various cancers and related inflammatory conditions. This review synthesizes the current understanding of gossypol as an anticancer agent, focusing on its pharmacological mechanisms, strategies to enhance its clinical efficacy, and the status of ongoing clinical evaluations.The methodological approach to this review involved a systematic search across several scientific databases including the National Center for Biotechnology Information (NCBI), PubMed/MedLine, Google Scholar, Scopus, and TRIP. Studies were meticulously chosen to cover various aspects of gossypol, from its chemical structure and natural sources to its pharmacokinetics and confirmed anticancer efficacy. Specific MeSH terms and keywords related to gossypol's antineoplastic applications guided the search strategy.Results from selected pharmacological studies indicate that gossypol inhibits the Bcl-2 family of anti-apoptotic proteins, promoting apoptosis in tumor cells. Clinical trials, particularly phase I and II, reveal gossypol's promise as an anticancer agent, demonstrating efficacy and manageable toxicity profiles. The review identifies the development of gossypol derivatives and novel carriers as avenues to enhance therapeutic outcomes and mitigate adverse effects.Conclusively, gossypol represents a promising anticancer agent with considerable therapeutic potential. However, further research is needed to refine gossypol-based therapies, explore combination treatments, and verify their effectiveness across cancer types. The ongoing clinical trials continue to support its potential, suggesting a future where gossypol could play a significant role in cancer treatment protocols.

Fighting Carcinogenesis with Plant Metabolites by Weakening Proliferative Signaling and Disabling Replicative Immortality Networks of Rapidly Dividing and Invading Cancerous Cells

BACKGROUND

Cancer, an uncontrolled multistage disease causing swift division of cells, is a leading disease with the highest mortality rate. Cellular heterogeneity, evading growth suppressors, resisting cell death, and replicative immortality drive the tumor progression by resisting the therapeutic action of existing anticancer drugs through a series of intrinsic and extrinsic cellular interactions. The innate cellular mechanisms also regulate the replication process as a fence against proliferative signaling, enabling replicative immortality through telomere dysfunction.

AREA COVERED

The conventional genotoxic drugs have several off-target and collateral side effects associated with them. Thus, the need for the therapies targeting cyclin-dependent kinases or P13K signaling pathway to expose cancer cells to immune destruction, deactivation of invasion and metastasis, and maintaining cellular energetics is imperative. Compounds with anticancer attributes isolated from plants and rich in alkaloids, terpenes, and polyphenols have proven to be less toxic and highly targetspecific, making them biologically significant. This has opened a gateway for the exploration of more novel plant molecules by signifying their role as anticancer agents in synergy and alone, making them more effective than the existing cytotoxic regimens.

EXPERT OPINION

In this context, the current review presented recent data on cancer cases around the globe, along with discussing the fundamentals of proliferative signaling and replicative immortality of cancer cells. Recent findings were also highlighted, including antiproliferative and antireplicative action of plant-derived compounds, besides explaining the need for improving drug delivery systems.

Therapeutic strategies for targeting telomerase in cancer

Telomere and telomerase play important roles in abnormal cell proliferation, metastasis, stem cell maintenance, and immortalization in various cancers. Therefore, designing of drugs targeting telomerase and telomere is of great significance. Over the past two decades, considerable knowledge regarding telomere and telomerase has been accumulated, which provides theoretical support for the design of therapeutic strategies such as telomere elongation. Therefore, the development of telomere-based therapies such as nucleoside analogs, non-nucleoside small molecules, antisense technology, ribozymes, and dominant negative human telomerase reverse transcriptase are being prioritized for eradicating a majority of tumors. While the benefits of telomere-based therapies are obvious, there is a need to address the limitations of various therapeutic strategies to improve the possibility of clinical applications. In this study, current knowledge of telomere and telomerase is discussed, and therapeutic strategies based on recent research are reviewed.

Natural Product Gossypol and its Derivatives in Precision Cancer Medicine

Gossypol, a natural product extracted from the seed, roots, and stem of cotton, was initially used as a male contraceptive but was subsequently investigated as a novel antitumor agent. This review depicts the current status of gossypol and its derivatives as novel antitumor agents as well as presents their preparation and characteristics, especially of some gossypol Schiff bases, through quantitative and structural analysis. The main attractive target sites of gossypol and its derivatives are Bcl-2 family proteins containing the anti-apoptosis proteins Bcl-2 and Bcl-XL. The molecular mechanism of gossypol analogs not only involves cell apoptosis but also autophagy, cell cycle arrest, and other abnormal cellular phenomena. Gossypol and its derivatives exert antitumor effects on different cancer types in vitro and in vivo, and demonstrate synergistic effects with other chemo- and radio- therapeutic treatments. In addition, several nanocarriers have been designed to load gossypol or its derivatives in order to expand the range of their applications and evaluate their combination effects with other anti-tumor agents. This review may serve as a reference for the rational application of gossypol analogs as anti-tumor agents.

MYC Expression and Metabolic Redox Changes in Cancer Cells: A Synergy Able to Induce Chemoresistance

Chemoresistance is due to multiple factors including the induction of a metabolic adaptation of tumor cells. In fact, in these cells, stress conditions induced by therapies stimulate a metabolic reprogramming which involves the strengthening of various pathways such as glycolysis, glutaminolysis and the pentose phosphate pathway. This metabolic reprogramming is the result of a complex network of mechanisms that, through the activation of oncogenes (i.e., MYC, HIF1, and PI3K) or the downregulation of tumor suppressors (i.e., TP53), induces an increased expression of glucose and/or glutamine transporters and of glycolytic enzymes. Therefore, in order to overcome chemoresistance, it is necessary to develop combined therapies which are able to selectively and simultaneously act on the multiple molecular targets responsible for this adaptation. This review is focused on highlighting the role of MYC in modulating the epigenetic redox changes which are crucial in the acquisition of therapy resistance.

Telomerase Inhibitors from Natural Products and Their Anticancer Potential

Telomeres and telomerase are nowadays exploring traits on targets for anticancer therapy. Telomerase is a unique reverse transcriptase enzyme, considered as a primary factor in almost all cancer cells, which is mainly responsible to regulate the telomere length. Hence, telomerase ensures the indefinite cell proliferation during malignancy—a hallmark of cancer—and this distinctive feature has provided telomerase as the preferred target for drug development in cancer therapy. Deactivation of telomerase and telomere destabilization by natural products provides an opening to succeed new targets for cancer therapy. This review aims to provide a fundamental knowledge for research on telomere, working regulation of telomerase and its various binding proteins to inhibit the telomere/telomerase complex. In addition, the review summarizes the inhibitors of the enzyme catalytic subunit and RNA component, natural products that target telomeres, and suppression of transcriptional and post-transcriptional levels. This extensive understanding of telomerase biology will provide indispensable information for enhancing the efficiency of rational anti-cancer drug design.

Apigenin overcomes drug resistance by blocking the signal transducer and activator of transcription 3 signaling in breast cancer cells

Drug resistance in chemotherapy is a serious obstacle for the successful treatment of cancer. Drug resistance is caused by various factors, including the overexpression of P-glycoprotein (P-gp, MDR1). The development of new, useful compounds that overcome drug resistance is urgent. Apigenin, a dietary flavonoid, has been reported as an anticancer drug in vivo and in vitro. In the present study, we investigated whether apigenin is able to reverse drug resistance using adriamycin-resistant breast cancer cells (MCF-7/ADR). In our experiments, apigenin significantly decreased cell growth and colony formation in MCF-7/ADR cells and parental MCF-7 cells. This growth inhibition was related to the accumulation of cells in the sub-G₀/G₁ apoptotic population and an increase in the number of apoptotic cells. Apigenin reduced the mRNA expression of multidrug resistance 1 (MDR1) and multidrug resistance-associated proteins (MRPs) in MCF-7/ADR cells. Apigenin also downregulated the expression of P-gp. Apigenin reversed drug efflux from MCF-7/ADR cells, resulting in rhodamine 123 (Rho123) accumulation. Inhibition of drug resistance by apigenin is related to the suppression of the signal transducer and activator of transcription 3 (STAT3) signaling pathway. Apigenin decreased STAT3 activation (p-STAT3) and its nuclear translocation and inhibited the secretion of VEGF and MMP-9, which are STAT3 target genes. A STAT3 inhibitor, JAK inhibitor I and an HIF-1α inhibitor decreased cell growth in MCF-7 and MCF-7/ADR cells. Taken together, these results demonstrate that apigenin can overcome drug resistance.

Broad targeting of resistance to apoptosis in cancer

Apoptosis or programmed cell death is natural way of removing aged cells from the body. Most of the anti-cancer therapies trigger apoptosis induction and related cell death networks to eliminate malignant cells. However, in cancer, de-regulated apoptotic signaling, particularly the activation of an anti-apoptotic systems, allows cancer cells to escape this program leading to uncontrolled proliferation resulting in tumor survival, therapeutic resistance and recurrence of cancer. This resistance is a complicated phenomenon that emanates from the interactions of various molecules and signaling pathways. In this comprehensive review we discuss the various factors contributing to apoptosis resistance in cancers. The key resistance targets that are discussed include (1) Bcl-2 and Mcl-1 proteins; (2) autophagy processes; (3) necrosis and necroptosis; (4) heat shock protein signaling; (5) the proteasome pathway; (6) epigenetic mechanisms; and (7) aberrant nuclear export signaling. The shortcomings of current therapeutic modalities are highlighted and a broad spectrum strategy using approaches including (a) gossypol; (b) epigallocatechin-3-gallate; (c) UMI-77 (d) triptolide and (e) selinexor that can be used to overcome cell death resistance is presented. This review provides a roadmap for the design of successful anti-cancer strategies that overcome resistance to apoptosis for better therapeutic outcome in patients with cancer.

Cryptosporidium Lactate Dehydrogenase Is Associated with the Parasitophorous Vacuole Membrane and Is a Potential Target for Developing Therapeutics

The apicomplexan, Cryptosporidium parvum, possesses a bacterial-type lactate dehydrogenase (CpLDH). This is considered to be an essential enzyme, as this parasite lacks the Krebs cycle and cytochrome-based respiration, and mainly–if not solely, relies on glycolysis to produce ATP. Here, we provide evidence that in extracellular parasites (e.g., sporozoites and merozoites), CpLDH is localized in the cytosol. However, it becomes associated with the parasitophorous vacuole membrane (PVM) during the intracellular developmental stages, suggesting involvement of the PVM in parasite energy metabolism. We characterized the biochemical features of CpLDH and observed that, at lower micromolar levels, the LDH inhibitors gossypol and FX11 could inhibit both CpLDH activity (K_i = 14.8 μM and 55.6 μM, respectively), as well as parasite growth in vitro (IC₅₀ = 11.8 μM and 39.5 μM, respectively). These observations not only reveal a new function for the poorly understood PVM structure in hosting the intracellular development of C. parvum, but also suggest LDH as a potential target for developing therapeutics against this opportunistic pathogen, for which fully effective treatments are not yet available.

Cryptosporidians are unique among the apicomplexans in regards to their parasitic life style (e.g., they are intracellular, but undergo extracytoplasmic development within a host membrane-derived structure termed parasitophorous vacuole membrane, PVM) and their metabolism (e.g., they are incapable of de novo nutrient synthesis and rely on glycolysis for the synthesis of ATP). We discovered that the Cryptosporidium parvum bacterial-type L-lactate dehydrogenase (CpLDH) enzyme is cytosolic during the parasite’s motile, extracellular, stages (sporozoites and merozoites), but becomes associated with the PVM during intracellular development, indicating the involvement of the PVM in lactate fermentation. We also observed that micromolar concentrations of the LDH inhibitors gossypol and FX11 inhibit both CpLDH activity and the growth of C. parvum in vitro, suggesting that CpLDH is a potential target for the development of anti-cryptosporidial therapeutics.

Induction of caspase-dependent extrinsic apoptosis by apigenin through inhibition of signal transducer and activator of transcription 3 (STAT3) signalling in HER2-overexpressing BT-474 breast cancer cells

Phytoestrogen intake is known to be beneficial to decrease breast cancer incidence and progression. But its molecular mechanisms of action are still unknown. The present study aimed to examine the effect of apigenin on proliferation and apoptosis in HER2-expressing breast cancer cells. In our experiments, apigenin inhibited the proliferation of BT-474 cells in a dose- and time-dependent manner. Apigenin also inhibited clonogenic survival (anchorage-dependent and -independent) of BT-474 cells in a dose-dependent manner. These growth inhibitions were accompanied with an increase in sub-G0/G1 apoptotic populations. Apigenin-induced extrinsic a caspase-dependent apoptosis up-regulating the levels of cleaved caspase-8 and cleaved caspase-3, and inducing the cleavage of poly (ADP-ribose) polymerase (PARP). Whereas, apigenin did not induce apoptosis via intrinsic mitochondrial apoptosis pathway since this compound did not decrease mitochondrial membrane potential without affecting the levels of B-cell lymphoma 2 (Bcl-2) and Bcl-2-associated X protein (BAX). Apigenin reduced the expression of phospho-JAK1, phospho-JAK2 and phospho-STAT3 and decreased signal transducer and activator of transcription 3 (STAT3) dependent luciferase reporter gene activity in BT-474 cells. Apigenin inhibited CoCl2-induced VEGF secretion and decreased the nuclear translocation of STAT3. Our study indicates that apigenin induces apoptosis through inhibition of STAT3 signalling and could serve as a useful compound to prevent or treat HER2-overexpressing breast cancer.

miR-512-5p suppresses tumor growth by targeting hTERT in telomerase positive head and neck squamous cell carcinoma in vitro and in vivo

Telomerase activation has very important implications for head and neck squamous cell carcinoma (HNSCC), but the regulatory mechanisms of telomerase in HNSCC remain unclear. In our present study, we found that miR-512-5P was markedly downregulated in telomerase-positive HNSCC cell lines. Both in vitro and in vivo assays revealed that miR-512-5P mimic attenuated HNSCC cell proliferation, and tumor growth in nude mice, which exerts its tumor suppressor function through elevated apoptosis, inhibition of the telomerase activity, decrease of telomere-binding proteins and shortening of telomere length by human telomerase reverse transcriptase (hTERT) downregulation. Furthermore, the dual-luciferase reporter gene assay results demonstrated that hTERT was a direct target of miR-512-5P. We conclude that the frequently miR-512-5P overexpression can regulate hTERT and function as a tumor suppressor in HNSCC. Therefore, miR-512-5P may serve as a potential therapeutic agent for miR-based HNSCC therapy.

Apigenin induces caspase-dependent apoptosis by inhibiting signal transducer and activator of transcription 3 signaling in HER2-overexpressing SKBR3 breast cancer cells

Phytoestrogens have been demonstrated to inhibit tumor induction; however, their molecular mechanisms of action have remained elusive. The present study aimed to investigate the effects of a phytoestrogen, apigenin, on proliferation and apoptosis of the human epidermal growth factor receptor 2 (HER2)-expressing breast cancer cell line SKBR3. Proliferation assay, MTT assay, fluorescence-activated cell sorting analysis, western blot analysis, immunocytochemistry, reverse transcription-polymerase chain reaction and ELISA assay were used in the present study. The results of the present study indicated that apigenin inhibited the proliferation of SKBR3 cells in a dose-and time-dependent manner. This inhibition of growth was accompanied by an increase in the sub-G0/G1 apoptotic population. Furthermore, apigenin enhanced the expression levels of cleaved caspase-8 and -3, and induced the cleavage of poly(adenosine diphosphate ribose) polymerase in SKBR3 cells, confirming that apigenin promotes apoptosis via a caspase-dependent pathway. Apigenin additionally reduced the expression of phosphorylated (p)-janus kinase 2 and p-signal transducer and activator of transcription 3 (STAT3), inhibited CoCl2-induced vascular endothelial growth factor (VEGF) secretion and decreased the nuclear localization of STAT3. The STAT3 inhibitor S31-201 decreased the cellular proliferation rate and reduced the expression of p-STAT3 and VEGF. Therefore, these results suggested that apigenin induced apoptosis via the inhibition of STAT3 signaling in SKBR3 cells. In conclusion, the results of the present study indicated that apigenin may be a potentially useful compound for the prevention or treatment of HER2-overexpressing breast cancer.

In vitro anti-telomerase activity of novel lycopene-loaded nanospheres in the human leukemia cell line K562

Background:

Lycopene, a plant carotenoid, has potent effects against the various types of cancer cells. To date, the effect of lycopene in the free and encapsulated forms on the telomerase activity in human leukemia cell line K562 have not been investigated. The aim of the present study was to prepare a novel lycopene-loaded nanosphere and compare its anti-telomearse activity in K562 cell line with those of free lycopene.

Materials and Methods:

The lycopene-loaded nanospheres were prepared by nanoprecipitation method. The lycopene entrapment efficacy was measured by high-performance liquid chromatography (HPLC) method. The anti-proliferation effect of the lycopene in the free and encapsulated forms in the different times (0-72 h) and the different doses (0-100 μg/ml) on K562 cell line was studied using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay. The changes of telomerase activity, following treatment with the lycopene in the free and encapsulated forms, were detected using the telomeric repeat amplification protocol-enzyme-linked immunosorbent assay.

Results:

The entrapment efficacy of lycopene was 78.5% ± 2. Treatment of the K562 cell line with lycopene, in particular in encapsulated form, resulted in a significant inhibition of the cell growth and increasing of percentage of apoptotic cells. It has also been observed that the telomerase activity in the lycopene-loaded nanospheres-treated cells was significantly inhibited in a dose and time-dependent manner.

Conclusion:

Our data suggest a novel mechanism in the anti-cancer activity of the lycopene, in particular in encapsulated form, and could be provided a basis for the future development of anti-telomerase therapies.

Gossypol increases expression of the pro-apoptotic BH3-only protein NOXA through a novel mechanism involving phospholipase A2, cytoplasmic calcium, and endoplasmic reticulum stress

Gossypol is a putative BH3 mimetic proposed to inhibit BCL2 and BCLXL based on cell-free assays. We demonstrated previously that gossypol failed to directly inhibit BCL2 in cells or induce apoptosis in chronic lymphocytic leukemia (CLL) cells or platelets, which require BCL2 or BCLXL, respectively, for survival. Here, we demonstrate that gossypol rapidly increased activity of phospholipase A2 (PLA2), which led to an increase in cytoplasmic calcium, endoplasmic reticulum (ER) stress, and up-regulation of the BH3-only protein NOXA. Pretreatment with the PLA2 inhibitor, aristolochic acid, abrogated the increase in calcium, ER stress, and NOXA. Calcium chelation also abrogated the gossypol-induced increase in calcium, ER stress, and NOXA, but not the increase in PLA2 activity, indicating that PLA2 is upstream of these events. In addition, incubating cells with the two products of PLA2 (lysophosphatidic acid and arachidonic acid) mimicked treatment with gossypol. NOXA is a pro-apoptotic protein that functions by binding the BCL2 family proteins MCL1 and BFL1. The BCL2 inhibitor ABT-199 is currently in clinical trials for CLL. Resistance to ABT-199 can occur from up-regulation of other BCL2 family proteins, and this resistance can be mimicked by culturing CLL cells on CD154(+) stroma cells. We report here that AT-101, a derivative of gossypol in clinical trials, overcomes stroma-mediated resistance to ABT-199 in primary CLL cells, suggesting that a combination of these drugs may be efficacious in the clinic.

RhoA/ROCK/PTEN signaling is involved in AT-101-mediated apoptosis in human leukemia cells in vitro and in vivo

R-(-)-gossypol acetic acid (AT-101) is a natural cottonseed product that exhibits anticancer activity. However, the molecular mechanism behind the antileukemic activity of AT-101 has not been well characterized. In this study, we investigated how AT-101 induces apoptosis in human leukemia cells. Exposure to AT-101 significantly increased apoptosis in both human leukemia cell lines and primary human leukemia cells. This increase was accompanied by the activation of caspases, cytochrome c release, Bcl2-associated X protein (Bax) translocation, myeloid cell leukemia-1 (Mcl-1) downregulation, Bcl-2-associated death promoter (Bad) dephosphorylation, Akt inactivation, and RhoA/Rho-associated coiled-coil containing protein kinase 1/phosphatase and tensin homolog (RhoA/ROCK1/PTEN) activation. RhoA, rather than caspase-3 cleavage, mediated the cleavage/activation of ROCK1 that AT-101 induced. Inhibiting RhoA and ROCK1 activation by C3 exoenzyme (C3) and Y27632, respectively, attenuated the ROCK1 cleavage/activation, PTEN activity, Akt inactivation, Mcl-1 downregulation, Bad dephosphorylation, and apoptosis mediated by AT-101. Knocking down ROCK1 expression using a ROCK1-specific siRNA also significantly abrogated AT-101-mediated apoptosis. Constitutively active Akt prevented the AT-101-induced Mcl-1 downregulation, Bad dephosphorylation, and apoptosis. Conversely, AT-101 lethality was potentiated by the phosphatidylinositol 3-kinase inhibitor LY294002. In vivo, the tumor growth inhibition caused by AT-101 was also associated with RhoA/ROCK1/PTEN activation and Akt inactivation in a mouse leukemia xenograft model. Collectively, these findings suggest that AT-101 may preferentially induce apoptosis in leukemia cells by interrupting the RhoA/ROCK1/PTEN pathway, leading to Akt inactivation, Mcl-1 downregulation, Bad dephosphorylation, and Bax translocation, which culminate in mitochondrial injury and apoptosis.

Therapeutic potential of gossypol: an overview

CONTEXT

Polyphenols are naturally occurring compounds found in fruits, vegetables, cereals, and beverages. Polyphenols occupy a unique place in biological science for their pharmacological properties. Gossypol is a polyphenolic compound that has attracted attention because of its biological effects.

OBJECTIVE

Gossypol is reported to exhibit antifertility, antioxidant, anticancer, antivirus, antiparasitic, and antimicrobial properties and lower plasma cholesterol. These are summarized with attention to the mechanisms of activity.

METHODS

This review summarizes the results of studies obtained in a comprehensive search of ScienceDirect, PubMed, Scirus, and Web of Science.

RESULTS AND CONCLUSION

The results of these studies provide a comprehensive understanding of the biological action of gossypol and its potential for the prevention of and therapy for resistant tumors and chronic human diseases such as HIV, malaria, and psoriasis.

Apigenin decreases cell viability and telomerase activity in human leukemia cell lines

Recent studies have shown that apigenin (4',5,7-trihydroxyflavone inhibits human malignant cancer cell growth through cell cycle arrest and apoptosis. However, the underlying relationship between apoptosis and telomerase activity in response to apigenin exposure is not well understood. In this study, we found that apigenin significantly induces direct cytotoxicity in human leukemia cells (U937, THP-1 and HL60) through activation of the caspase pathway. As we presumed, treatment with apigenin was found to increase the level of intracellular reactive oxygen species (ROS), whereas pretreatment with antioxidants, N-acetyl-cysteine (NAC) or glutathione (GSH), completely attenuated ROS generation. Surprisingly, these antioxidants did not promote recuperation from apigenin-induced cell death. We further showed that apigenin downregulates telomerase activity in caspase-dependent apoptosis and observed that apigenin dosing results in downregulation of telomerase activity by suppression of c-Myc-mediated telomerase reverse transcriptase (hTERT) expression. In addition, treatment of apigenin-dosed cells with the two antioxidants did not restore telomerase activity. Taken together, this data suggests that ROS is not essential for suppression of apigenin-mediated apoptosis associated with the activation of caspases and regulation of telomerase activity via suppression of hTERT. We conclude that apigenin has a direct cytotoxic effect and the loss of telomerase activity in leukemia cells.

The Bcl-2 homology domain 3 mimetic gossypol induces both Beclin 1-dependent and Beclin 1-independent cytoprotective autophagy in cancer cells

Gossypol, a natural Bcl-2 homology domain 3 mimetic compound isolated from cottonseeds, is currently being evaluated in clinical trials. Here, we provide evidence that gossypol induces autophagy followed by apoptotic cell death in both the MCF-7 human breast adenocarcinoma and HeLa cell lines. We first show that knockdown of the Bcl-2 homology domain 3-only protein Beclin 1 reduces gossypol-induced autophagy in MCF-7 cells, but not in HeLa cells. Gossypol inhibits the interaction between Beclin 1 and Bcl-2 (B-cell leukemia/lymphoma 2), antagonizes the inhibition of autophagy by Bcl-2, and hence stimulates autophagy. We then show that knockdown of Vps34 reduces gossypol-induced autophagy in both cell lines, and consistent with this, the phosphatidylinositol 3-phosphate-binding protein WIPI-1 is recruited to autophagosomal membranes. Further, Atg5 knockdown also reduces gossypol-mediated autophagy. We conclude that gossypol induces autophagy in both a canonical and a noncanonical manner. Notably, we found that gossypol-mediated apoptotic cell death was potentiated by treatment with the autophagy inhibitor wortmannin or with small interfering RNA against essential autophagy genes (Vps34, Beclin 1, and Atg5). Our findings support the notion that gossypol-induced autophagy is cytoprotective and not part of the cell death process induced by this compound.

Gossypol--a polyphenolic compound from cotton plant

Gossypol (C(30)H(30)O(8)) is a polyphenolic compound derived from the cotton plant (genus Gossypium, family Malvaceae). The presence of six phenolic hydroxyl groups and two aldehydic groups makes gossypol chemically reactive. Gossypol can undergo Schiff base formation, ozonolysis, oxidation, and methylation to form gossypol derivatives. Gossypol and its derivatives have been the target of much research due to their multifaceted biological activities including antifertility, antivirus, anticancer, antioxidant, antitrypanosomal, antimicrobial, and antimalarial activities. Because of restricted rotation of the internaphthyl bond, gossypol is a chiral compound, which has two atropisomers (i.e., (+)- and (-)-gossypol) that exhibit different levels of biological activities. This chapter covers the physiochemical properties, analyses, biological properties, and agricultural and clinical implications of gossypol.