R-(-)-gossypol (AT-101) activates programmed cell death in multiple myeloma cells

The Role of t(11;14) in Tailoring Treatment Decisions in Multiple Myeloma

Multiple myeloma (MM) represents a hematological neoplasia with an uncontrolled proliferation of malignant plasma cells and complex cytogenetic abnormalities. t(11;14) has emerged as a crucial genetic aberration and is one of the most common primary translocations in MM. Patients harboring t(11;14) represent a distinctive subgroup with a clinical profile that differs from t(11;14)-negative MM risk categories. One of the key features linked with t(11;14) is the BCL2 dependency, indicating vulnerability to BCL2 inhibition. BCL2 inhibitors, such as venetoclax, demonstrated impressive efficacy alone or in combination with other anti-myeloma drugs in patients with RRMM accompanied by t(11;14) and BCL2 overexpression. Therefore, t(11;14) plays a key role in both risk stratification and informed decision making towards a tailored therapy. In this review, we highlight the biology of t(11;14) in MM cells, summarize the current evolving role of t(11;14) in the era of novel agents and novel targeted therapies, illuminate current efficacy and safety data of BCL2-based treatment options and explore the future prospects of individualized precision medicine for this special subgroup of patients with MM.

Molecular docking analysis of MCL-1 inhibitors for breast cancer management

Myeloid leukemia 1 (MCL-1), a BCL-2 protein family member, acts as an anti-apoptotic protein by interacting with pro-apoptotic BCL-2 proteins. Its overexpression is frequently observed in numerous cancer types including breast cancer, and is closely linked to the initiation and progression of tumors as well as poor prognosis and resistance to therapeutic interventions. Here, a database of 3402 chemicals with established therapeutic activity against various diseases was chosen and systematically screened against the MCL-1 protein. Visual inspection and binding energy analysis revealed that the compounds OSU-03012, Raltitrexed, Ostarine (MK-2866), Dovitinib (TKI-258), and Varespladib (LY315920) had strong binding affinity for the MCL-1 protein. Notably, their binding affinity was higher than that of the control compounds. These compounds exhibited strong interactions with critical amino acid residues of the MCL-1 protein. Furthermore, these compounds shared several common amino acid residue interactions with the control compounds. These findings suggest that these compounds may be useful as MCL-1 inhibitors in the treatment of breast cancer. However, additional experimental validation is required to confirm these findings.

Genome-wide identification of terpenoid synthase family genes in Gossypium hirsutum and functional dissection of its subfamily cadinene synthase A in gossypol synthesis

Plant terpenoid synthase (TPS) family genes participate in metabolite synthesis, hormones, gossypol, etc. Here, we genome-widely identified TPS family genes in 12 land plant species. Four hundred and thirty TPS-related genes were divided into seven subfamilies. The TPS-c in Bryophytes was suggested to be the earliest subfamily, followed by the TPS-e/f and TPS-h presence in ferns. TPS-a, the largest number of genes, was derived from monocotyledonous and dicotyledonous plants. Collinearity analysis showed that 38 out of the 76 TPS genes in G. hirsutum were collinear within G. arboreum and G. raimondii. Twenty-one GhTPS-a genes belong to the cadinene synthase (GhCDN) subfamily and were divided into five groups, A, B, C, D, and E. The special cis-elements in the promoters of 12 GhCDN-A genes suggested that the JA and ethylene signaling pathways may be involved in their expression regulation. When 12 GhCDN-A genes were simultaneously silenced through virus-induced gene silencing, the glandular color of GhCDN-A-silenced plants was lighter than that of the control, supported by a gossypol content decrease based on HPLC testing, suggesting that GhCDN-A subgroup genes participate in gossypol synthesis. According to RNA-seq analysis, gossypol synthesis-related genes and disease-resistant genes in the glandular variety exhibited upregulated expression compared to the glandless variety, whereas hormone signaling-related genes were downregulated. All in all, these results revealed plant TPS gene evolution rules and dissected the TPS subfamily, GhCDN-A, function in gossypol synthesis in cotton.

AT-101 Enhances the Antitumor Activity of Lenalidomide in Patients with Multiple Myeloma

Bcl-2 and Mcl-1 proteins play a role in multiple myeloma (MM) cell survival, for which targeted inhibitors are being developed. AT-101 is an oral drug, which disrupts Bcl-2 and Mcl-1 function, impedes mitochondrial bioenergetic processes and induces apoptosis in MM cells. When combined with lenalidomide and dexamethasone (Rd), AT-101 significantly reduced tumor burden in an in vivo xenograft model of MM. These data provided rationale for a phase I/II study to establish the effective dose of AT-101 in combination with Rd (ARd regimen) in relapsed/refractory MM. A total of 10 patients were enrolled, most with high-risk cytogenetics (80%) and prior stem cell transplant (70%). Three patients were lenalidomide-refractory, 2 were bortezomib-refractory and 3 were daratumumab-refractory. The ARd combination was well tolerated with most common grade 3/4 adverse events being cytopenia's. The overall response rate was 40% and clinical benefit rate was 90%. The median progression free survival was 14.9 months (95% CI 7.1-NE). Patients responsive to ARd showed a decrease in Bcl-2:Bim or Mcl-1:Noxa protein complexes, increased CD8+ T and NK cells and depletion of T and B-regulatory cells. The ARd regimen demonstrated an acceptable safety profile and promising efficacy in patients with relapsed/refractory MM prompting further investigation in additional patients.

Gossypol and Its Natural Derivatives: Multitargeted Phytochemicals as Potential Drug Candidates for Oncologic Diseases

Despite the vast amounts of research and remarkable discoveries that have been made in recent decades, cancer remains a leading cause of death and a major public health concern worldwide. Gossypol, a natural polyphenolic compound derived from the seeds, roots, and stems of cotton (Gossypium hirsutum L.), was first used as a male contraceptive agent. Due to its diverse biological properties, including antifertility, antiviral, antioxidant, antibacterial, antimalarial, and most notably antitumor activities, gossypol has been the subject of numerous studies. Nevertheless, no systematic review has been performed that analyzes the antineoplastic potential of gossypol and related natural compounds in an organ-specific manner while delineating the molecular mechanisms of action. Hence, we have performed an extensive literature search for anticancer properties of gossypol and their natural derivatives against various types of cancer cells utilizing PubMed, ScienceDirect, Google Scholar, and Scopus. The sources, distribution, chemical structure, and toxicity of gossypol and its constituents are briefly reviewed. Based on emerging evidence, gossypol and related compounds exhibit significant antineoplastic effects against various cancer types through the modulation of different cancer hallmarks and signaling pathways. Additionally, the synergistic activity of gossypol and its derivatives with chemotherapeutic agents has been observed. Our evaluation of the current literature suggests the potential of gossypol and its derivatives as multitargeting drug candidates to combat multiple human malignancies.

Updates in the Use of BCL-2-Family Small Molecule Inhibitors for the Treatment of Relapsed/Refractory Multiple Myeloma

Despite considerable advances in the treatment of multiple myeloma over the past decade, progression of disease is inevitable, and patients ultimately succumb to relapsed and refractory disease. Efficacious therapeutic regimens that target the key biological pathways that are essential for malignant plasma cell survival are necessary in the efforts to improve patient survival outcomes. The Bcl-2 family of proteins comprise oncogenes that promote myeloma cell survival by conferring resistance to apoptosis. These proteins are frequently upregulated in myeloma cells, thus making them attractive therapeutic targets. Several small molecule inhibitors of Bcl-2-family proteins are currently in clinical development for the treatment of relapsed/refractory multiple myeloma. Venetoclax, a Bcl-2-specific inhibitor, has generated the most clinical data and has shown promising results in patients with multiple myeloma harboring the t (11;14) translocation. Venetoclax has shown efficacy when combined with anti-CD38 monoclonal antibodies, immunomodulatory drugs, and proteasome inhibitors. Several other Bcl-2 inhibitors are in clinical development, as are inhibitors of Mcl-1, a Bcl-2-family oncoprotein that is perhaps more critical for myeloma cell survival than Bcl-2. This review will summarize the latest clinical data regarding the clinical development of Bcl-2-family protein inhibitors in the treatment of relapsed/refractory multiple myeloma.

Structure, properties of gossypol and its derivatives-from physiological activities to drug discovery and drug design

Covering up to 2022Gossypol is a polyphenolic compound isolated from cottonseed. There are two optical enantiomers of gossypol, (-)-gossypol and (+)-gossypol. Gossypol exists as three different tautomers, aldehyde, ketone and lactol. Gossypol is toxic and provides a protective mechanism for cotton plants against pests. Gossypol was used as a male contraceptive in China in the 1970s. It was eventually abandoned due to noticeable side effects, disruption of potassium uptake and incomplete reversibility. Gossypol has gained considerable research interest due to its attractive biological activities, especially antitumor and antivirus. Gossypol derivatives are prepared by a structural modification to reduce toxicity and improve their therapeutic effect. This review depicts the bioactivity and regulation mechanisms of gossypol and its derivatives as drug lead compounds, with emphasis on its antitumor mechanism. The design and synthesis of pharmacologically active derivatives based on the structure of gossypol, such as gossypol Schiff bases, apogossypol, gossypolone, are thoroughly discussed. This review aims to serve as a reference for gossypol-based drug discovery and drug design.

An Overview of Cotton Gland Development and Its Transcriptional Regulation

Cotton refers to species in the genus Gossypium that bear spinnable seed coat fibers. A total of 50 species in the genus Gossypium have been described to date. Of these, only four species, viz. Gossypium, hirsutum, G. barbadense, G. arboretum, and G. herbaceum are cultivated; the rest are wild. The black dot-like structures on the surfaces of cotton organs or tissues, such as the leaves, stem, calyx, bracts, and boll surface, are called gossypol glands or pigment glands, which store terpenoid aldehydes, including gossypol. The cotton (Gossypium hirsutum) pigment gland is a distinctive structure that stores gossypol and its derivatives. It provides an ideal system for studying cell differentiation and organogenesis. However, only a few genes involved in the process of gland formation have been identified to date, and the molecular mechanisms underlying gland initiation remain unclear. The terpenoid aldehydes in the lysigenous glands of Gossypium species are important secondary phytoalexins (with gossypol being the most important) and one of the main defenses of plants against pests and diseases. Here, we review recent research on the development of gossypol glands in Gossypium species, the regulation of the terpenoid aldehyde biosynthesis pathway, discoveries from genetic engineering studies, and future research directions.

Root Illumination Promotes Seedling Growth and Inhibits Gossypol Biosynthesis in Upland Cotton

Gossypol, a terpenoid compound mainly synthesized in the cotton roots, acts as a phytoalexin in protecting the plants from biotic stress. Roots are critical for both the secondary metabolism and the growth of the plant. Light plays an important role in plant growth and material metabolism, however, the effect of root illumination (RI) on the cotton seedling growth and gossypol metabolism remains unclear. In the present study, the cotton genetic standard line TM-1 and four pairs of near-isogenic lines (NILs) were used as materials to study the impact of RI on cotton seedlings. Results showed that, compared with the cotton seedlings cultivated without RI, the photosynthetic rate, leaf area, and dry weight of roots and leaves were significantly increased, while the gossypol content in leaves and roots was significantly reduced in seedlings cultivated with RI. GO and KEGG enrichment analysis of the differentially expressed genes (DEGs) with and without RI both indicated that photosynthesis and terpenoid biosynthesis-related GO terms and pathways were significantly enriched, the expression profile confirmed that RI positively regulated the photosynthesis system and negatively affected the gossypol biosynthesis pathway in roots. This study revealed the effects of RI on seedlings' growth and gossypol biosynthesis in upland cotton, and provided important insights for the engineering of cotton with low gossypol accumulation.

Cyclic RGD-Decorated Liposomal Gossypol AT-101 Targeting for Enhanced Antitumor Effect

Introduction

(-)-Gossypol (AT-101), the (-)-enantiomer of the natural compound gossypol, has shown significant inhibitory effects on various types of cancers such as osteosarcoma, myeloma, glioma, lung cancer, and prostate cancer. However, the clinical application of (-)-gossypol was often hindered by its evident side effects and the low bioavailability via oral administration, which necessitated the development of suitable (-)-gossypol preparations to settle the problems. In this study, injectable cyclic RGD (cRGD)-decorated liposome (cRGD-LP) was prepared for tumor-targeted delivery of (-)-gossypol.

Methods

The cRGD-LP was prepared based on cRGD-modified lipids. For comparison, a non-cRGD-containing liposome (LP) with a similar chemical composition to cRGD-LP was specially designed. The physicochemical properties of (-)-gossypol-loaded cRGD-LP (Gos/cRGD-LP) were investigated in terms of the drug loading efficiency, particle size, morphology, drug release, and so on. The inhibitory effect of Gos/cRGD-LP on the proliferation of tumor cells in vitro was evaluated using different cell lines. The biodistribution of cRGD-LP in vivo was investigated via the near-infrared (NIR) fluorescence imaging technique. The antitumor effect of Gos/cRGD-LP in vivo was evaluated in PC-3 tumor-bearing nude mice.

Results

Gos/cRGD-LP had an average particle size of about 62 nm with a narrow size distribution, drug loading efficiency of over 90%, and sustained drug release for over 96 h. The results of NIR fluorescence imaging demonstrated the enhanced tumor targeting of cRGD-LP in vivo. Moreover, Gos/cRGD-LP showed a significantly enhanced inhibitory effect on PC-3 tumors in mice, with a tumor inhibition rate of over 74% and good biocompatibility.

Conclusion

The incorporation of cRGD could significantly enhance the tumor-targeting effect of the liposomes and improve the antitumor effect of the liposomal (-)-gossypol in vivo, which indicated the potential of Gos/cRGD-LP that warrants further investigation for clinical applications of this single-isomer drug.

Susceptibility of multiple myeloma to B-cell lymphoma 2 family inhibitors

Multiple myeloma (MM) is a biologically complex hematological disorder defined by the clonal proliferation of malignant plasma cells producing excessive monoclonal immunoglobulin that interacts with components of the bone marrow microenvironment, resulting in the major clinical features of MM. Despite the development of numerous protocols to treat MM patients, this cancer remains currently incurable; due in part to the emergence of resistant clones, highlighting the unmet need for innovative therapeutic approaches. Accumulating evidence suggests that the survival of MM molecular subgroups depends on the expression profiles of specific subsets of anti-apoptotic B-cell lymphoma (BCL)-2 family members. This review summarizes the mechanisms underlying the anti-myeloma activities of the potent BCL-2 family protein inhibitors, individually or in combination with conventional therapeutic options, and provides an overview of the strong rationale to clinically investigate such interventions for MM therapy.

Promising Anti-Mitochondrial Agents for Overcoming Acquired Drug Resistance in Multiple Myeloma

Multiple myeloma (MM) remains an incurable tumor due to the high rate of relapse that still occurs. Acquired drug resistance represents the most challenging obstacle to the extension of survival and several studies have been conducted to understand the mechanisms of this phenomenon. Mitochondrial pathways have been extensively investigated, demonstrating that cancer cells become resistant to drugs by reprogramming their metabolic assessment. MM cells acquire resistance to proteasome inhibitors (PIs), activating protection programs, such as a reduction in oxidative stress, down-regulating pro-apoptotic, and up-regulating anti-apoptotic signals. Knowledge of the mechanisms through which tumor cells escape control of the immune system and acquire resistance to drugs has led to the creation of new compounds that can restore the response by leading to cell death. In this scenario, based on all literature data available, our review represents the first collection of anti-mitochondrial compounds able to overcome drug resistance in MM. Caspase-independent mechanisms, mainly based on increased oxidative stress, result from 2-methoxyestradiol, Artesunate, ascorbic acid, Dihydroartemisinin, Evodiamine, b-AP15, VLX1570, Erw-ASNase, and TAK-242. Other agents restore PIs' efficacy through caspase-dependent tools, such as CDDO-Im, NOXA-inhibitors, FTY720, GCS-100, LBH589, a derivative of ellipticine, AT-101, KD5170, SMAC-mimetics, glutaminase-1 (GLS1)-inhibitors, and thenoyltrifluoroacetone. Each of these substances improved the efficacy rates when employed in combination with the most frequently used antimyeloma drugs.

Targeting Mitochondrial Apoptosis to Overcome Treatment Resistance in Cancer

Deregulated cellular apoptosis is a hallmark of cancer and chemotherapy resistance. The B-cell lymphoma 2 (BCL-2) protein family members are sentinel molecules that regulate the mitochondrial apoptosis machinery and arbitrate cell fate through a delicate balance between pro- and anti-apoptotic factors. The recognition of the anti-apoptotic BCL2 gene as an oncogenic driver in hematological malignancies has directed attention toward unraveling the biological significance of each of the BCL-2 superfamily members in cancer progression and garnered interest in the targeting of apoptosis in cancer therapy. Accordingly, the approval of venetoclax (ABT-199), a small molecule BCL-2 inhibitor, in patients with chronic lymphocytic leukemia and acute myeloid leukemia has become the proverbial torchbearer for novel candidate drug approaches selectively targeting the BCL-2 superfamily. Despite the inspiring advances in this field, much remains to be learned regarding the optimal therapeutic context for BCL-2 targeting. Functional assays, such as through BH3 profiling, may facilitate prediction of treatment response, development of drug resistance and shed light on rational combinations of BCL-2 inhibitors with other branches of cancer therapy. This review summarizes the pathological roles of the BCL-2 family members in cancer, discusses the current landscape of their targeting in clinical practice, and highlights the potential for future therapeutic inroads in this important area.

Gossypol induces apoptosis of multiple myeloma cells through the JUN-JNK pathway

Multiple myeloma (MM) is one of the most common hematologic neoplastic diseases. Gossypol was once used as a male contraceptive but is considered a novel antitumor agent. This study aimed to reveal the gossypol-induced apoptosis mechanism and its hub genes. Gossypol-induced MM cell apoptosis is concentration- and time-dependent. Of a total of 532 differentially expressed genes, 273 genes were upregulated and 259 genes were downregulated in gossypol-treated MM cells. Through KEGG and WGCNA analyses, the apoptosis-associated module was identified, and JUN was identified as the hub gene. The expression of the JUN protein product c-Jun was downregulated in MM cell lines compared to that in normal plasma cells. High-risk MM patients had a lower expression of JUN. High-expression JUN group patients had a lower risk of death. JUN overexpression in MM cells induced potent cell death and growth inhibition by a caspase-dependent apoptotic mechanism. DR5 is one of the upstream receptors of the JNK pathway, and shRNA knockdown of DR5 can partially reverse gossypol-induced apoptosis. A total of 1017 genes were coexpressed with JUN in MM patients. These genes are mainly involved in other JNK-associated signaling pathways, such as the IL6, EGF and PDGF signaling pathways. In conclusion, JUN is identified as the hub gene in gossypol-induced apoptosis, and gossypol can activate caspase-dependent apoptosis through the JNK pathway by targeting c-Jun and other JNK-associated pathways. DR5 and IL6 are also involved in this mechanism.

Cotton roots are the major source of gossypol biosynthesis and accumulation

BACKGROUND

Gossypol is a specific secondary metabolite in Gossypium species. It not only plays a critical role in development and self-protection of cotton plants, but also can be used as important anti-cancer and male contraceptive compound. However, due to the toxicity of gossypol for human beings and monogastric animals, the consumption of cottonseeds was limited. To date, little is known about the gossypol metabolism in cotton plants.

RESULTS

In this study, we found that cotyledon was the primary source of gossypol at the seed germination stage. But thereafter, it was mainly originated from developing roots. Grafting between glanded and glandless cotton as well as sunflower rootstocks and cotton scion revealed that gossypol was mainly synthesized in the root systems of cotton plants. And both glanded and glandless cotton roots had the ability of gossypol biosynthesis. But the pigment glands, the main storage of gossypol, had indirect effects on gossypol biosynthesis. In vitro culture of root and rootless seedling confirmed the strong gossypol biosynthesis ability in root system and the relatively weak gossypol biosynthesis ability in other organs of the seedling. Expression profiling of the key genes involved in the gossypol biosynthetic pathway also supported the root as the major organ of gossypol biosynthesis.

CONCLUSIONS

Our study provide evidence that the cotton root system is the major source of gossypol in both glanded and glandless cottons, while other organs have a relatively weak ability to synthesize gossypol. Gossypol biosynthesis is not directed related to the expression of pigment glands, but the presence of pigment glands is essential for gossypol accumulation. These findings can not only clarify the complex regulation network of gossypol metabolism, but it could also accelerate the crop breeding process with enhanced commercial values.

A phase I study of AT-101, a BH3 mimetic, in combination with paclitaxel and carboplatin in solid tumors

Background AT-101 is a BH3 mimetic that inhibits the heterodimerization of Bcl-2, Bcl-xL, Bcl-W, and Mcl-1 with pro-apoptotic proteins, thereby lowering the threshold for apoptosis. This phase I trial investigated the MTD of AT-101 in combination with paclitaxel and carboplatin in patients with advanced solid tumors. Methods Patients were treated with AT-101 (40 mg) every 12 h on days 1, 2 and 3 of each cycle combined with varying dose levels (DL) of paclitaxel and carboplatin [DL1: paclitaxel (150 mg/m²) and carboplatin (AUC 5) on day 1 of each cycle; DL2: paclitaxel (175 mg/m²) and carboplatin (AUC 6) on day 1 of each cycle]. Secondary objectives included characterizing toxicity, efficacy, pharmacokinetics, and pharmacodynamics of the combination. Results Twenty-four patients were treated across two DLs with a planned expansion cohort. The most common tumor type was prostate (N = 11). Two patients experienced DLTs: grade 3 abdominal pain at DL1 and grade 3 ALT increase at DL2; however, the MTD was not determined. Moderate hematologic toxicity was observed. One CR was seen in a patient with esophageal cancer and 4 patients achieved PRs (1 NSCLC, 3 prostate). PD studies did not yield statistically significant decreases in Bcl-2 and caspase 3 protein levels, or increased apoptotic activity induced by AT-101. Conclusion The combination of AT-101 at 40 mg every 12 h on days 1, 2 and 3 combined with paclitaxel and carboplatin was safe and tolerable. Based on the modest clinical efficacy seen in this trial, this combination will not be further investigated. Clinical Trial Registration: NCT00891072, CTEP#: 8016.

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.

Mitosis inhibitors in anticancer therapy: When blocking the exit becomes a solution

Current microtubule-targeting agents (MTAs) remain amongst the most important antimitotic drugs used against a broad range of malignancies. By perturbing spindle assembly, MTAs activate the spindle assembly checkpoint (SAC), which induces mitotic arrest and subsequent apoptosis. However, besides toxic side effects and resistance, mitotic slippage and failure in triggering apoptosis in various cancer cells are limiting factors of MTAs efficacy. Alternative strategies to target mitosis without affecting microtubules have, thus, led to the identification of small molecules, such as those that target spindle Kinesins, Aurora and Polo-like kinases. Unfortunately, these so-called second-generation of antimitotics, encompassing mitotic blockers and mitotic drivers, have failed in clinical trials. Our recent understanding regarding the mechanisms of cell death during a mitotic arrest pointed out apoptosis as the main variable, providing an opportunity to control the cell fates and influence the effectiveness of antimitotics. Here, we provide an overview on the second-generation of antimitotics, and discuss possible strategies that exploit SAC activity, mitotic slippage/exit and apoptosis induction, in order to improve the efficacy of anticancer strategies that target mitosis.

Piperlongumine Induces Apoptosis in Human Melanoma Cells Via Reactive Oxygen Species Mediated Mitochondria Disruption

Malignant melanoma is a devastating skin cancer due to its severe drug resistance and prompt metastasis. Piperlongumine is an anti-inflammation and tumor-suppressing natural product with defined structure. While numerous studies revealed exceptional inhibitory effects of piperlongumine on several carcinomas, few investigations were performed on melanoma. Therefore, the present study investigated the anti-tumor effects of piperlongumine on human melanoma cells in vitro, and explored the mechanisms of action. Results from cytotoxicity and proliferation studies demonstrated that piperlongumine inhibited cell growth in melanoma cell lines A375, A875, and B16-F10 in a dose- and time-dependent manner. Flow cytometric analysis showed that piperlongumine obstructed cell cycle progression at G2/M phase and induced apoptosis in A375 cells. Mechanistic investigations illustrated that piperlongumine promoted reactive oxygen species production and decreased mitochondrial membrane potential. In addition, piperlongumine was reported to interfere with the expression of p21, p27, cleaved caspases-3, Bax, Bcl-2, and p-Jun N-terminal kinase (JNK), which are typical regulators associated with cell proliferation, intrinsic apoptosis, and JNKs pathway. Taken together, these results strongly suggested that piperlongumine inhibits cell growth and induces apoptosis in human melanoma cells via ROS mediated mitochondria disruption and JNKs pathway, and piperlongumine may exert promising potential for patients suffering from malignant melanoma.

Smac mimetic LCL161 overcomes protective ER stress induced by obatoclax, synergistically causing cell death in multiple myeloma

Bcl2 and IAP families are anti-apoptotic proteins deregulated in multiple myeloma (MM) cells. Pharmacological inhibition of each of these families has shown significant activity only in subgroups of MM patients. Here, we have examined a broad-spectrum Bcl2 family inhibitor Obatoclax (OBX) in combination with a Smac mimetic LCL161 in MM cell lines and patient cells. LCL161/OBX combination induced synergistic cytotoxicity and anti-proliferative effects on a broad range of human MM cell lines. The cytotoxicity was mediated through inhibition of the IAPs, activation of caspases and up regulation of the pro-apoptotic proteins Bid, Bim, Puma and Noxa by the drug combination. In addition, we observed that OBX caused ER stress and activated the Unfolded Protein Response (UPR) leading to drug resistance. LCL161, however inhibited spliced Xbp-1, a pro-survival factor. In addition, we observed that OBX increased GRP78 localization to the cell surface, which then induced PI3K dependent Akt activation and resistance to cell death. LCL161 was able to block OBX induced Akt activation contributing to synergistic cell death. Our results support clinical evaluation of this combination strategy in relapsed refractory MM patients.

Apoptosis signaling and BCL-2 pathways provide opportunities for novel targeted therapeutic strategies in hematologic malignances

Apoptosis is an essential biological process involved in tissue homeostasis and immunity. Aberrations of the two main apoptotic pathways, extrinsic and intrinsic, have been identified in hematological malignancies; many of these aberrations are associated with pathogenesis, prognosis and resistance to standard chemotherapeutic agents. Targeting components of the apoptotic pathways, especially the chief regulatory BCL-2 family in the intrinsic pathway, has proved to be a promising therapeutic approach for patients with hematological malignances, with the expectation of enhanced efficacy and reduced adverse events. Continuous investigations regarding the biological importance of each of the BCL-2 family components and the clinical rationale to achieve optimal therapeutic outcomes, using either monotherapy or in combination with other targeted agents, have generated inspiring progress in the field. Genomic, epigenomic and biological analyses including BH3 profiling facilitate effective evaluation of treatment response, cancer recurrence and drug resistance. In this review, we summarize the biological features of each of the components in the BCL-2 apoptotic pathways, analyze the regulatory mechanisms and the pivotal roles of BCL-2 family members in the pathogenesis of major types of hematologic malignances, and evaluate the potential of apoptosis- and BCL-2-targeted strategies as effective approaches in anti-cancer therapies.

Killing Two Cells with One Stone: Pharmacologic BCL-2 Family Targeting for Cancer Cell Death and Immune Modulation

A crucial component of regulating organismal homeostasis is maintaining proper cell number and eliminating damaged or potentially malignant cells. Apoptosis, or programed cell death, is the mechanism responsible for this equilibrium. The intrinsic apoptotic pathway is also especially important in the development and maintenance of the immune system. Apoptosis is essential for proper positive and negative selection during B- and T-cell development and for efficient contraction of expanded lymphocytes following an immune response. Tight regulation of the apoptotic pathway is critical, as excessive cell death can lead to immunodeficiency while apoptotic resistance can lead to aberrant lymphoproliferation and autoimmune disease. Dysregulation of cell death is implicated in a wide range of hematological malignancies, and targeting various components of the apoptotic machinery in these cases is an attractive chemotherapeutic strategy. A wide array of compounds has been developed with the purpose of reactivating the intrinsic apoptotic pathway. These compounds, termed BH3 mimetics are garnering considerable attention as they gain greater clinical oncologic significance. As their use expands, it will be imperative to understand the effects these compounds have on immune homeostasis. Uncovering their potential immunomodulatory activity may allow for administration of BH3 mimetics for direct tumor cell killing as well as novel therapies for a wide range of immune-based directives. This review will summarize the major proteins involved in the intrinsic apoptotic pathway and define their roles in normal immune development and disease. Clinical and preclinical BH3 mimetics are described within the context of what is currently known about their ability to affect immune function. Prospects for future antitumor immune amplification and immune modulation are then proposed.

Treatment Strategies that Enhance the Efficacy and Selectivity of Mitochondria-Targeted Anticancer Agents

Nearly a century has passed since Otto Warburg first observed high rates of aerobic glycolysis in a variety of tumor cell types and suggested that this phenomenon might be due to an impaired mitochondrial respiratory capacity in these cells. Subsequently, much has been written about the role of mitochondria in the initiation and/or progression of various forms of cancer, and the possibility of exploiting differences in mitochondrial structure and function between normal and malignant cells as targets for cancer chemotherapy. A number of mitochondria-targeted compounds have shown efficacy in selective cancer cell killing in pre-clinical and early clinical testing, including those that induce mitochondria permeability transition and apoptosis, metabolic inhibitors, and ROS regulators. To date, however, none has exhibited the standards for high selectivity and efficacy and low toxicity necessary to progress beyond phase III clinical trials and be used as a viable, single modality treatment option for human cancers. This review explores alternative treatment strategies that have been shown to enhance the efficacy and selectivity of mitochondria-targeted anticancer agents in vitro and in vivo, and may yet fulfill the clinical promise of exploiting the mitochondrion as a target for cancer chemotherapy.

Proteomic analysis of gossypol induces necrosis in multiple myeloma cells

Gossypol is a phenolic aldehyde extracted from plants and is known to be an antitumor agent to induce cancer cell apoptosis. In the present study, multiple myeloma cells were treated with gossypol, which resulted in an increase of cellular reactive oxygen species (ROS) and cell necrosis. Quantitative proteomic analysis was carried out to identify differentially expressed proteins between untreated and gossypol-treated cells. Proteomic analysis identified 4330 proteins, in which 202 proteins are upregulated and 383 proteins are downregulated in gossypol-treated cells as compared to the untreated cells. Importantly, proteomic and western blot analysis showed that apoptosis regulators BAK and Bax were upregulated in gossypol-treated cells, indicating that Bcl-2 associated death pathway was activated. Similarly, gossypol also induced upregulations of DNA mismatch repair proteins and DNA replication licensing factor, suggesting that gossypol caused significant DNA damage. Furthermore, upregulations of HLA class I and class II histocompatibility antigens and beta-2-microglobulin were observed in gossypol-treated cells, indicating that gossypol has a novel function to activate cellular immune responses. Our data demonstrate that the execution of necrosis is a complex process involving ROS, DNA damage, and Bcl-2 family proteins. Gossypol-activated immune responses are a potential new approach for multiple myeloma chemotherapy.

The investigational agent MLN2238 induces apoptosis and is cytotoxic to CLL cells in vitro, as a single agent and in combination with other drugs

Chronic lymphocytic leukaemia (CLL) is the most common haematological malignancy in the U.S. The course of the disease has been shown to be negatively impacted by increased levels of BCL2. Strategies to downregulate BCL2 and shift the balance towards cellular demise are actively being explored. Therefore, we examined whether the investigational agent MLN2238 could inhibit the proteasomal machinery and induce CLL cell death while also downregulating BCL2. MLN2238-induced cell death was studied in peripheral blood mononuclear cells from 28 CLL patients. MLN2238 produced a dose-dependent reduction in BCL2 and CLL cell viability with maximum cell death observed at a 50 nmol/l concentration by 48 h. Annexin-V staining, PARP1 and caspase-3 cleavage along with an increase in mitochondrial membrane permeability were noted after cells were treated with MLN2238; however, apoptosis was only partially blocked by the pan-caspase inhibitor z-VAD.fmk. Furthermore, we observed enhanced anti-CLL effects in tumour cells treated with either a combination of MLN2238 and the BH3 mimetic AT-101 or MLN2238 and fludarabine. Together, our data suggest the potential for proteasome inhibitor based therapy in CLL and the rationale design of drug combination strategies based on CLL biology.

AT-101 downregulates BCL2 and MCL1 and potentiates the cytotoxic effects of lenalidomide and dexamethasone in preclinical models of multiple myeloma and Waldenström macroglobulinaemia

Multiple myeloma, the second most common haematological malignancy in the U.S., is currently incurable. Disruption of the intrinsic apoptotic pathway by BCL2 and MCL1 upregulation is observed in >80% of myeloma cases and is associated with an aggressive clinical course. Remarkably, there is no approved drug with the ability to target BCL2 or MCL1. Thus, we investigated the anti-tumour effects of a pan-BCL2 inhibitor, AT-101, which has high binding specificity for BCL2 and MCL1 in preclinical models of plasma cell cancers (Multiple myeloma and Waldenström macroglobulinaemia). Gene expression and immunoblot analysis of six plasma cell cancer models showed upregulation of BCL2 family members. AT-101 was able to downregulate BCL2 and MCL1 in all plasma cell cancer models and induced apoptotic cell death in a caspase-dependent manner by altering mitochondrial membrane permeability. This cytotoxic effect and BCL2 downregulation were further potentiated when AT-101 was combined with lenalidomide/dexamethasone (LDA). NanoString nCounter mRNA quantification and Ingenuity Pathways Analysis revealed differential changes in the CCNA2, FRZB, FYN, IRF1, PTPN11 genes in LDA-treated cells. In summary, we describe for the first time the cellular and molecular events associated with the use of AT-101 in combination with lenalidomide/dexamethasone in preclinical models of plasma cell malignancy.

Small molecule inhibitors of bcl-2 family proteins for pancreatic cancer therapy

Pancreatic cancer (PC) has a complex etiology and displays a wide range of cellular escape pathways that allow it to resist different treatment modalities. Crucial signaling molecules that function downstream of the survival pathways, particularly at points where several of these pathways crosstalk, provide valuable targets for the development of novel anti-cancer drugs. Bcl-2 family member proteins are anti-apoptotic molecules that are known to be overexpressed in most cancers including PC. The anti-apoptotic machinery has been linked to the observed resistance developed to chemotherapy and radiation and therefore is important from the targeted drug development point of view. Over the past ten years, our group has extensively studied a series of small molecule inhibitors of Bcl-2 against PC and provide solid preclinical platform for testing such novel drugs in the clinic. This review examines the efficacy, potency, and function of several small molecule inhibitor drugs targeted to the Bcl-2 family of proteins and their preclinical progress against PC. This article further focuses on compounds that have been studied the most and also discusses the anti-cancer potential of newer class of Bcl-2 drugs.

A novel benzothiazole derivative YLT322 induces apoptosis via the mitochondrial apoptosis pathway in vitro with anti-tumor activity in solid malignancies

Benzothiazole derivatives are known for various biological activities, and their potency in cancer therapy has received considerable attention in recent years. YLT322, a novel synthesized benzothiazole derivative, exhibits potent anti-tumor activity via inducing apoptosis both in vitro and in vivo. In this study, we found that YLT322 showed growth inhibition against a broad spectrum of human cancer cells and induced apoptosis of HepG2 cells in a dose- and time-dependent manner. The occurrence of its apoptosis was associated with activation of caspases-3 and -9, but not caspase-8. YLT322 increased the expression of Bax, decreased the expression of Bcl-2, and induced the release of cytochrome c which activates the mitochondrial apoptotic pathway. The down-regulation of phosphorylated p42/44 MAPK and phosphorylated Akt was also observed. Moreover, YLT322 suppressed the growth of established tumors in xenograft models in mice without obvious side effects. Histological and immunohistochemical analyses revealed an increase in TUNEL and caspase-3-positive cells and a decrease in Ki67-positive cells upon YLT322. These results suggest that YLT322 may be a potential candidate for cancer therapy.

Natural Bcl-2 inhibitor (-)- gossypol induces protective autophagy via reactive oxygen species-high mobility group box 1 pathway in Burkitt lymphoma

(-)- Gossypol, a natural inhibitor of anti-apoptotic Bcl-2 proteins, has presented an effective anti-tumor activity in numerous preclinical trials. More and more evidence in vivo and in vitro validates that (-)- gossypol can dramatically suppress cell proliferation and induce cell death in hematological malignancies. However, the detailed mechanisms are not well known. In the present study, we showed that treatment with (-)- gossypol stimulated reactive oxygen species (ROS) generation and induced autophagy in Burkitt lymphoma cells. Antioxidant N-acetyl-cysteine (NAC) pretreatment attenuated (-)- gossypol-induced autophagy. Furthermore, (-)- gossypol treatment increased the translocation of high mobility group box 1 (HMGB1) from nuclei to cytoplasm, which can be suppressed by NAC pretreatment. NAC pretreatment also dramatically enhanced (-)- gossypol-induced apoptosis and total cell death. These results indicate that (-)- gossypol induces a protective autophagy in Burkitt lymphoma cells, partly due to ROS induction and cytosolic translocation of HMGB1. Antioxidants may serve as potent chemosensitizers to enhance cell death through blocking (-)- gossypol-induced autophagy.

Gossypol decreases tumor necrosis factor-α-induced intercellular adhesion molecule-1 expression via suppression of NF-κB activity

Gossypol is a yellowish polyphenolic compound originally from cotton plant, which has been shown to exert a potential for anti-cancer and anti-inflammatory effects. However, its molecular mechanism is not thoroughly understood on breast cancer cells known to highly express intercellular adhesion molecule-1 (ICAM-1) for their adhesion and metastasis. This study aims to investigate the effect of gossypol on tumor necrosis factor (TNF)-α-stimulated ICAM-1 via nuclear factor-kappa B (NF-κB) activity. Gossypol was shown to inhibit TNF-α-induced ICAM-1 expression and U937 cell adhesion to MDA-MB-231 and MCF-7 cells. Additionally, TNF-α-induced MDA-MB-231 cell invasion was blocked in the presence of gossypol. Chromatin immunoprecipitation analysis demonstrated that gossypol blocks NF-κB binding on the ICAM-1 promoter regions. Additionally, TNF-α-induced NF-κB activation was completely suppressed in the presence of gossypol. Gossypol did not directly suppress the binding of NF-κB to the DNA but rather inhibited the nuclear translocation of p65 and p50 via phosphorylation and degradation of IκB. We also found that gossypol suppresses NF-κB activation induced by a wide variety of agents, including taxol, okadaic acid, and phorbol myristate acetate. Taken together, gossypol effectively inhibited TNF-α-induced ICAM-1 expression via the suppression of NF-κB activation and in vitro adhesion and invasion in human breast cancer cells.

Small-molecule inhibitors reveal a new function for Bcl-2 as a proangiogenic signaling molecule

Cancer has a complex etiology and displays a wide range of cellular escape pathways that allow it to circumvent treatment. Signaling molecules functionally downstream of the circumvented pathways, and particularly at checkpoints where several of these pathways intersect, provide valuable targets for the development of novel anti-cancer drugs. Bcl-2, a pro-survival signaling molecule, is one such protein. This review examines the efficacy, potency, and function of several small molecule inhibitor drugs targeted to the Bcl-2 family of proteins. The review focuses on the compounds with most available data within the literature and discusses both the anti-cancer and the recently unveiled anti-angiogenic potential of this new class of drugs.

AT-101 (R-(-)-gossypol acetic acid) enhances the effectiveness of androgen deprivation therapy in the VCaP prostate cancer model

Prostate cancer remains a leading cause of cancer death in American men. Androgen deprivation therapy (ADT) is the most common treatment for advanced prostate cancer patients; however, ADT fails in nearly all cases resulting in castration resistant or androgen-insensitive (AI) disease. In many cases, this progression results from dysregulation of the pro-survival Bcl-2 family proteins. Inhibition of pro-survival Bcl-2 family proteins, therefore, may be an effective strategy to delay the onset of AI disease. Gossypol, a small molecule inhibitor of pro-survival Bcl-2 family proteins, has been demonstrated to inhibit AI prostate cancer growth. The apoptotic effect of gossypol, however, has been demonstrated to be attenuated by the presence of androgen in a prostate cancer xenograft mouse model (Vertebral Cancer of Prostate [VCaP]) treated with AT-101 (R-(-)-gossypol acetic acid). This study was undertaken to better understand the in vitro effects of androgen receptor (AR) on AT-101-induced apoptosis. VCaP cells treated with AT-101 demonstrated an increase in apoptosis and downregulation of Bcl-2 pro-survival proteins. Upon AR activation in combination with AT-101 treatment, apoptosis is reduced, cell survival increases, and caspase activation is attenuated. Akt and X inhibitor of apoptosis (XIAP) are downregulated in the presence of AT-101, and AR stimulation rescues protein expression. Combination treatment of bicalutamide and AT-101 increases apoptosis by reducing the expression of these pro-survival proteins. These data suggest that combination therapy of AT-101 and ADT may further delay the onset of AI disease, resulting in prolonged progression-free survival of prostate cancer patients.

A novel water-soluble gossypol derivative increases chemotherapeutic sensitivity and promotes growth inhibition in colon cancer

Compound 1 ((-)-gossypol) has been long known as a chemical anticancer agent. With its low water solubility and toxicity, it is not widely used as a commercial drug. To overcome these disadvantages, several novel derivatives of gossypol were designed, synthesized, and analyzed. One of the derivatives, compound 7 (6-aminopenicillanic acid sodium-gossypolone), was identified with great water solubility and anticancer property, suggested by inducing a dramatically decrease in Bcl-2 and Bcl-xL protein expression level found in vitro and growth inhibition of murine colon tumor in vivo. Furthermore, it was also recognized with less toxicity than compound 1 in vivo and significantly increased chemotherapeutic sensitivity against colon cancer in combination with traditional chemotherapeutic agent 5-fluorouracil. Therefore, it is concluded that compound 7 is superior to parent compound 1, and further preclinical studies of compound 7 is necessary for colon cancer therapy.

AT-101, a pan-Bcl-2 inhibitor, leads to radiosensitization of non-small cell lung cancer

INTRODUCTION

Radiotherapy has a central role in the treatment of lung cancer. However, its effectiveness is often limited, in part, because of the defects in key apoptosis regulators, such as Bcl-2 family members, that contribute to cancer ability to evade apoptosis. In this study, we tested AT-101, a pan-Bcl-2 inhibitor, as a potential radiosensitizer in lung cancer.

METHODS AND RESULTS

Clonogenic assays were used to determine the radiosensitivity of multiple lung cancer cell lines. On the basis of their relative response to radiotherapy, lung cancer cells were stratified into two groups, and a representative cell line of each group was selected for more in-depth study: A549 (resistant) and HCC2429 (sensitive). The expression levels of antiapoptotic (Bcl-2, Bcl-XL, and Mcl-1) and proapoptotic (Bax, Bak, and Bid) Bcl-2 proteins were determined for each group. Although the levels of Bcl-2 and Mcl-1 were low for both groups, Bcl-XL expression was dramatically higher in A549, whereas almost not detected in HCC2429. The levels of Bax/Bak were 40% higher in HCC2429 compared with A549. When administered alone, AT-101 resulted in increased apoptosis in concentration-dependent manner against both groups, with enhanced activity in HCC2429 even at lower concentration. Furthermore, AT-101 promoted radiosensitivity of A549 and HCC2429 cells (p < 0.005). Consistent with 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay findings, A549 cells required increased AT-101 dose to achieve a similar cytoxicity to HCC2429 cells.

CONCLUSIONS

These investigations suggest that the Bcl-2 family may serve as effective therapeutic targets in lung cancer. Further clinical studies are warranted to assess the potential of AT-101 as an agent that enhances the therapeutic ratio of radiotherapy in lung cancer.

Current and emerging treatments for chronic lymphocytic leukaemia

Chronic lymphocytic leukaemia (CLL) is the most common adult leukaemia in Europe and North America. The disease is characterized by proliferation and accumulation of small CD5+ B cells in blood, lymph nodes, spleen, liver and bone marrow. The natural clinical course of CLL is highly variable, and chemotherapy is usually not indicated in early and stable disease. However, patients with progressive and more advanced CLL require treatment. For many years, chlorambucil with or without corticosteroids was used in previously untreated patients with CLL. More recently, purine nucleoside analogues (PNAs) [fludarabine, cladribine and pentostatin] have been included in treatment approaches for this disease, and chlorambucil is no longer the leading standard everywhere. Currently, this drug is rather recommended for the treatment of older, unfit patients with co-morbidities, especially in European countries. Significantly higher overall response (OR) and complete response (CR) rates in patients treated initially with PNAs than in those treated with chlorambucil or cyclophosphamide-based combination regimens have been confirmed in randomized, prospective, multicentre trials. Moreover, PNAs administered in combination with cyclophosphamide produce higher response rates, including CR and molecular CR, compared with PNA as monotherapy. Recent reports suggest that the administration of monoclonal antibodies (mAbs) can significantly improve the course of CLL. At present, two mAbs have the most important clinical value in patients with CLL. The first is rituximab, a human mouse antibody that targets CD20 antigens, and the second is alemtuzumab, a humanized form of a rat antibody active against CD52. Several recent reports suggest that in patients with CLL, rituximab combined with a PNA can increase the OR and CR rates compared with PNA or rituximab alone, with acceptable toxicity. In randomized trials, the combination of rituximab with fludarabine and cyclophosphamide (FC-R regimen) demonstrated higher rates of OR, CR and progression-free survival in patients with previously untreated and relapsed or refractory CLL than fludarabine plus cyclophosphamide (FC regimen). Several reports have confirmed significant activity with alemtuzumab in relapsed or refractory CLL, as well as in previously untreated patients. Recently, several new agents have been investigated and have shown promise in treating patients with CLL. These treatments include new mAbs, agents targeting the antiapoptotic bcl-2 family of proteins and receptors involved in mediating survival signals from the microenvironment, antisense oligonucleotides and other agents. The most promising are new mAbs directed against the CD20 molecule, lumiliximab and anti-CD40 mAbs. Oblimersen, alvocidib (flavopiridol) and lenalidomide are also being evaluated both in preclinical studies and in early clinical trials. In recent years, a significant improvement in haematopoietic stem cell transplantation (HSCT) procedures in patients with high-risk CLL has been observed. However, the exact role of HSCT, autologous or allogeneic, in the standard management of CLL patients is still undefined.

Small-molecule Bcl-2 antagonists as targeted therapy in oncology

Dynamic protein–protein interactions between proapoptotic and pro-survival Bcl-2 family members regulate outer-mitochondrial membrane permeabilization and cytochrome c release, key events in the path to apoptosis. Their relative levels often dictate the fate of a cell following an apoptotic stimulus. However, in cancer cells, the pro-survival Bcl-2 family members are frequently upregulated, thereby creating a constitutive block to apoptosis and resulting in continued cell survival under conditions that normally result in cell death. Because many chemotherapeutics used to treat cancer also trigger apoptosis, this upregulation of pro-survival members also contributes to resistance to conventional cancer therapies. Strategies that inactivate pro-survival Bcl-2 family members therefore suggest a means by which this downstream block in apoptosis can be alleviated, resulting in the selective killing of malignant cells. Here, we outline the progress of three small-molecule Bcl-2 antagonists that have advanced into clinical evaluation.

Glucocorticoid-induced apoptosis of healthy and malignant lymphocytes

Glucocorticoids exert a wide range of physiological effects, including the induction of apoptosis in lymphocytes. The progression of glucocorticoid-induced apoptosis is a multi-component process requiring contributions from both genomic and cytoplasmic signaling events. There is significant evidence indicating that the transactivation activity of the glucocorticoid receptor is required for the initiation of glucocorticoid-induced apoptosis. However, the rapid cytoplasmic effects of glucocorticoids may also contribute to the glucocorticoid-induced apoptosis-signaling pathway. Endogenous glucocorticoids shape the T-cell repertoire through both the induction of apoptosis by neglect during thymocyte maturation and the antagonism of T-cell receptor (TCR)-induced apoptosis during positive selection. Owing to their ability to induce apoptosis in lymphocytes, synthetic glucocorticoids are widely used in the treatment of haematological malignancies. Glucocorticoid chemotherapy is limited, however, by the emergence of glucocorticoid resistance. The development of novel therapies designed to overcome glucocorticoid resistance will dramatically improve the efficacy of glucocorticoid therapy in the treatment of haematological malignancies.

AT-101, a small molecule inhibitor of anti-apoptotic Bcl-2 family members, activates the SAPK/JNK pathway and enhances radiation-induced apoptosis

Background

Gossypol, a naturally occurring polyphenolic compound has been identified as a small molecule inhibitor of anti-apoptotic Bcl-2 family proteins. It induces apoptosis in a wide range of tumor cell lines and enhances chemotherapy- and radiation-induced cytotoxicity both in vitro and in vivo. Bcl-2 and related proteins are important inhibitors of apoptosis and frequently overexpressed in human tumors. Increased levels of these proteins confer radio- and chemoresistance and may be associated with poor prognosis. Consequently, inhibition of the anti-apoptotic functions of Bcl-2 family members represents a promising strategy to overcome resistance to anticancer therapies.

Methods

We tested the effect of (-)-gossypol, also denominated as AT-101, radiation and the combination of both on apoptosis induction in human leukemic cells, Jurkat T and U937. Because activation of the SAPK/JNK pathway is important for apoptosis induction by many different stress stimuli, and Bcl-X_L is known to inhibit activation of SAPK/JNK, we also investigated the role of this signaling cascade in AT-101-induced apoptosis using a pharmacologic and genetic approach.

Results

AT-101 induced apoptosis in a time- and dose-dependent fashion, with ED₅₀ values of 1.9 and 2.4 μM in Jurkat T and U937 cells, respectively. Isobolographic analysis revealed a synergistic interaction between AT-101 and radiation, which also appeared to be sequence-dependent. Like radiation, AT-101 activated SAPK/JNK which was blocked by the kinase inhibitor SP600125. In cells overexpressing a dominant-negative mutant of c-Jun, AT-101-induced apoptosis was significantly reduced.

Conclusion

Our data show that AT-101 strongly enhances radiation-induced apoptosis in human leukemic cells and indicate a requirement for the SAPK/JNK pathway in AT-101-induced apoptosis. This type of apoptosis modulation may overcome treatment resistance and lead to the development of new effective combination therapies.

An open-label, multicenter, phase I/II study of single-agent AT-101 in men with castrate-resistant prostate cancer

PURPOSE

AT-101 binds and inhibits the antiapoptotic function of Bcl-2, Bcl-xL, Mcl-1, and Bcl-w and is a potent stimulator of proapoptotic proteins. In this multi-institution phase I/II trial, we evaluated the safety and efficacy of single-agent AT-101, in men with chemotherapy naïve, castrate-resistant prostate cancer (CRPC).

EXPERIMENTAL DESIGN

Patients with progressive CRPC were to be treated with escalating doses of AT-101 on a continuous daily basis until the maximally tolerated dose was achieved. At the recommended phase 2 dose, an additional 21 patients were planned to assess for preliminary evidence of efficacy.

RESULTS

Twenty-three patients were enrolled. The phase I starting dose was 30 mg/day on a continuous basis; however, ongoing trials with AT-101 showed increased gastrointestinal toxicity with this daily schedule when given for repetitive cycles. As a result, the phase II starting dose was chosen to be 30 mg/day for 21 of 28 days. The most frequent observed adverse events (any grade) were diarrhea (43.5%), fatigue (34.8%), nausea (21.7%), anorexia (21.7%), and small intestinal obstruction (21.7%). Due to the high incidence of grade 3 small intestinal obstruction (n = 5; 21.7%), a reduction in dose to 20 mg/day for 21 of 28 days was mandated for all patients. Two patients had a confirmed > or =50% posttherapy prostate-specific antigen decline. No objective responses (Response Evaluation Criteria in Solid Tumors) were observed.

CONCLUSION

AT-101 administered at 20 mg/day for 21 of 28 days was well-tolerated. Evidence of single-agent clinical activity was observed with prostate-specific antigen declines in some patients. Further investigation of AT-101 in prostate cancer is warranted and trials combining AT-101 with androgen deprivation, as well as with docetaxel chemotherapy are ongoing.

Mechanisms regulating the susceptibility of hematopoietic malignancies to glucocorticoid-induced apoptosis

Glucocorticoids (GCs) are commonly used in the treatment of hematopoietic malignancies owing to their ability to induce apoptosis of these cancerous cells. Whereas some types of lymphoma and leukemia respond well to this drug, others are resistant. Also, GC-resistance gradually develops upon repeated treatments ultimately leading to refractory relapsed disease. Understanding the mechanisms regulating GC-induced apoptosis is therefore uttermost important for designing novel treatment strategies that overcome GC-resistance. This review discusses updated data describing the complex regulation of the cell's susceptibility to apoptosis triggered by GCs. We address both the genomic and nongenomic effects involved in promoting the apoptotic signals as well as the resistance mechanisms opposing these signals. Eventually we address potential strategies of clinical relevance that sensitize GC-resistant lymphoma and leukemia cells to this drug. The major target is the nongenomic signal transduction machinery where the interplay between protein kinases determines the cell fate. Shifting the balance of the kinome towards a state where Glycogen synthase kinase 3alpha (GSK3alpha) is kept active, favors an apoptotic response. Accumulating data show that it is possible to therapeutically modulate GC-resistance in patients, thereby improving the response to GC therapy.

Regulation of antiapoptotic MCL-1 function by gossypol: mechanistic insights from in vitro reconstituted systems

Small-molecule drugs that induce apoptosis in tumor cells by activation of the BCL-2-regulated mitochondrial outer membrane permeabilization (MOMP) pathway hold promise for rational anticancer therapies. Accumulating evidence indicates that the natural product gossypol and its derivatives can kill tumor cells by targeting antiapoptotic BCL-2 family members in such a manner as to trigger MOMP. However, due to the inherent complexity of the cellular apoptotic network, the precise mechanisms by which interactions between gossypol and individual BCL-2 family members lead to MOMP remain poorly understood. Here, we used simplified systems bearing physiological relevance to examine the impact of gossypol on the function of MCL-1, a key determinant for survival of various human malignancies that has become a highly attractive target for anticancer drug design. First, using a reconstituted liposomal system that recapitulates basic aspects of the BCL-2-regulated MOMP pathway, we demonstrate that MCL-1 inhibits BAX permeabilizing function via a "dual-interaction" mechanism, while submicromolar concentrations of gossypol reverse MCL-1-mediated inhibition of functional BAX activation. Solution-based studies showed that gossypol competes with BAX/BID BH3 ligands for binding to MCL-1 hydrophobic groove, thereby providing with a mechanistic explanation for how gossypol restores BAX permeabilizing function in the presence of MCL-1. By contrast, no evidence was found indicating that gossypol transforms MCL-1 into a BAX-like pore-forming molecule. Altogether, our findings validate MCL-1 as a direct target of gossypol, and highlight that making this antiapoptotic protein unable to inhibit BAX-driven MOMP may represent one important mechanism by which gossypol exerts its cytotoxic effect in selected cancer cells.