Therapeutic Potential of Leelamine, a Novel Inhibitor of Androgen Receptor and Castration-Resistant Prostate Cancer

Targeting the N-terminal domain of the androgen receptor: The effective approach in therapy of CRPC

The androgen receptor (AR) is dominant in prostate cancer (PCa) pathology. Current therapeutic agents for advanced PCa include androgen synthesis inhibitors and AR antagonists that bind to the hormone binding pocket (HBP) at the ligand binding domain (LBD). However, AR amplification, AR splice variants (AR-Vs) expression, and intra-tumoral de novo synthesis of androgens result in the reactivation of AR signalling. The AR N-terminal domain (NTD) plays an essential role in AR transcriptional activity. The AR inhibitor targeting NTD could potentially block the activation of both full-length AR and AR-Vs, thus overcoming major resistance mechanisms to current treatments. This review discusses the progress of research in various NTD inhibitors and provides new insight into the development of AR-NTD inhibitors.

The Crucial Role of AR-V7 in Enzalutamide-Resistance of Castration-Resistant Prostate Cancer

Simple Summary

Androgen receptor splice variant 7 (AR-V7) has always been considered a key driver for triggering enzalutamide resistance of castration-resistant prostate cancer (CRPC). In recent years, both the homeostasis of AR-V7 protein and AR-V7’s relationship with LncRNAs have gained great attention with in-depth studies. Starting from protein stability and LncRNA, the paper discusses and summarizes the mechanisms and drugs that affect the CRPC patients’ sensitivity to enzalutamide by regulating the protein or transcriptional stability of AR-V7, hoping to provide therapeutic ideas for subsequent research to break through the CRPC therapeutic bottleneck.

Abstract

Prostate cancer (PCa) has the second highest incidence of malignancies occurring in men worldwide. The first-line therapy of PCa is androgen deprivation therapy (ADT). Nonetheless, most patients progress to castration-resistant prostate cancer (CRPC) after being treated by ADT. As a second-generation androgen receptor (AR) antagonist, enzalutamide (ENZ) is the current mainstay of new endocrine therapies for CRPC in clinical use. However, almost all patients develop resistance during AR antagonist therapy due to various mechanisms. At present, ENZ resistance (ENZR) has become challenging in the clinical treatment of CRPC. AR splice variant 7 (AR-V7) refers to a ligand-independent and constitutively active variant of the AR and is considered a key driver of ENZR in CRPC. In this review, we summarize the mechanisms and biological behaviors of AR-V7 in ENZR of CRPC to contribute novel insights for CRPC therapy.

Potential Application of Leelamine as a Novel Regulator of Chemokine-Induced Epithelial-to-Mesenchymal Transition in Breast Cancer Cells

CXCR7 and CXCR4 are G protein-coupled receptors (GPCRs) that can be stimulated by CXCL12 in various human cancers. CXCR7/4–CXCL12 binding can initiate activation of multiple pathways including JAK/STAT and manganese superoxide dismutase (MnSOD) signaling, and initiate epithelial–mesenchymal transition (EMT) process. It is established that cancer cell invasion and migration are caused because of these events. In particular, the EMT process is an important process that can determine the prognosis for cancer. Since the antitumor effect of leelamine (LEE) has been reported in various previous studies, here, we have evaluated the influence of LEE on the CXCR7/4 signaling axis and EMT processes. We first found that LEE suppressed expression of CXCR7 and CXCR4 both at the protein and mRNA levels, and showed inhibitory effects on these chemokines even after stimulation by CXCL12 ligand. In addition, LEE also reduced the level of MnSOD and inhibited the EMT process to attenuate the invasion and migration of breast cancer cells. In addition, phosphorylation of the JAK/STAT pathway, which acts down-stream of these chemokines, was also abrogated by LEE. It was also confirmed that LEE can induce an imbalance of GSH/GSSG and increases ROS, thereby resulting in antitumor activity. Thus, we establish that targeting CXCR7/4 in breast cancer cells can not only inhibit the invasion and migration of cancer cells but also can affect JAK/STAT, EMT process, and production of ROS. Overall, the findings suggest that LEE can function as a novel agent affecting the breast cancer.

Leelamine Exerts Antineoplastic Effects in Association with Modulating Mitogen‑Activated Protein Kinase Signaling Cascade

Mitogen‑activated protein kinase (MAPK) pathway is a prominent signaling cascade that modulates cell proliferation, apoptosis, stress response, drug resistance, immune response, and cell motility. Activation of MAPK by various small molecules/natural compounds has been demonstrated to induce apoptosis in cancer cells. Herein, the effect of leelamine (LEE, a triterpene derived from bark of pine trees) on the activation of MAPK in hepatocellular carcinoma (HCC) and breast cancer (BC) cells was investigated. LEE induced potent cytotoxicity of HCC (HepG2 and HCCLM3) and BC (MDA-MB-231 and MCF7) cells over normal counterparts (MCF10A). LEE significantly enhanced the phosphorylation of p38 and JNK MAPKs in a dose-dependent fashion and it did not affect the phosphorylation of ERK in HCC and BC cells. The apoptosis-driving effect of LEE was further demonstrated by cleavage of procaspase-3/Bid and suppression of prosurvival proteins (Bcl-xL and XIAP). Furthermore, LEE also reduced the SDF1-induced-migration and -invasion of HCC and BC cells. Taken together, the data demonstrated that LEE promotes apoptosis and induces an anti-motility effect by activating p38 and JNK MAPKs in HCC and BC cells.

Leelamine Modulates STAT5 Pathway Causing Both Autophagy and Apoptosis in Chronic Myelogenous Leukemia Cells

Simple Summary

Autophagy is a cellular mechanism that is essential for removing misfolded proteins and damaged organelles. Moreover, the aberrant activation of signal transducer and activator of transcription 5 (STAT5), which can regulate cellular survival and homeostasis, has been often observed in different malignancies. In this study, we demonstrate that leelamine inhibits the STAT5 phosphorylation while inducing autophagy as well as apoptosis in chronic myeloid leukemia cells. Leelamine induces autophagy by stimulating the expression of Atg7, beclin-1, and the production of autophagosomes, which leads to substantial inhibition of STAT5 activation.

Abstract

Leelamine (LEE) has recently attracted significant attention for its growth inhibitory effects against melanoma, breast cancer, and prostate cancer cells; however, its impact on hematological malignancies remains unclear. Here, we first investigate the cytotoxic effects of LEE on several human chronic myeloid leukemia (CML) cells. We noted that LEE stimulated both apoptosis and autophagy in CML cells. In addition, the constitutive activation of signal transducer and activator of transcription 5 (STAT5) was suppressed substantially upon LEE treatment. Moreover, STAT5 knockdown with small interfering RNA (siRNA) increased LEE-induced apoptosis as well as autophagy and affected the levels of various oncogenic proteins. Thus, the targeted mitigation of STAT5 activation by LEE can contribute to its diverse anticancer effects by enhancing two distinct cell death pathways.

Chiral Quaternary Ammoniums Derived from Dehydroabietylamine: Synthesis and Application to Alkynylation of Isatin Derivatives Catalyzed by Silver

Abietic acid and its derivatives have broadly been used in fine chemicals and are renewable resources. Its inherent chiral rigid tricyclic phenanthrene skeleton is unique. Its utilities in asymmetric catalysis remain to be explored. A series new amide-type chiral quaternary ammoniums bearing dehydroabietylamine were designed, and prepared by two convenient steps. Acylation of dehydroabietylamine with bromoacetyl chloride afforded amide holding bromoacetyl group in higher yields using triethyl amine as base. Subsequent quaternization reaction gave the desired amide-type chiral quaternary ammoniums. The new chiral quaternary ammoniums can be used as phase-transfer catalyst (PTC) for the transition metal-catalysed alkynylation of isatin derivatives.

Natural Products Induce Lysosomal Membrane Permeabilization as an Anticancer Strategy

Cancer is a global health and economic issue. The majority of anticancer therapies become ineffective due to frequent genomic turnover and chemoresistance. Furthermore, chemotherapy and radiation are non-specific, killing all rapidly dividing cells including healthy cells. In this review, we examine the ability of some natural products to induce lysosomal-mediated cell death in neoplastic cells as a way to kill them more specifically than conventional therapies. This list is by no means exhaustive. We postulate mechanisms to explain lysosomal membrane permeabilization and its role in triggering cell death in cancer cells.

Leelamine suppresses cMyc expression in prostate cancer cells in vitro and inhibits prostate carcinogenesis in vivo

Aim

Leelamine (LLM) inhibits growth of human prostate cancer cells but the underlying mechanism is not fully understood. The present study was undertaken to determine the effect of LLM on cMyc, which is overexpressed in a subset of human prostate cancers.

Methods

The effect of LLM on cMyc expression and activity was determined by western blotting/confocal microscopy and luciferase reporter assay, respectively. A transgenic mouse model of prostate cancer (Hi-Myc) was used to determine chemopreventive efficacy of LLM.

Results

Exposure of androgen sensitive (LNCaP) and castration-resistant (22Rv1) human prostate cancer cells to LLM resulted in downregulation of protein and mRNA levels of cMyc. Overexpression of cMyc partially attenuated LLM-mediated inhibition of colony formation, cell viability, and cell migration in 22Rv1 and/or PC-3 cells. LLM treatment decreased protein levels of cMyc targets (e.g., lactate dehydrogenase), however, overexpression of cMyc did not attenuate these effects. A trend for a decrease in expression level of cMyc protein was discernible in 22Rv1 xenografts from LLM-treated mice compared with control mice. The LLM treatment (10 mg/kg body weight, 5 times/week) was well-tolerated by Hi-Myc transgenic mice. The incidence of high-grade prostatic intraepithelial neoplasia, adenocarcinoma in situ, and microinvasion was lower in LLM-treated Hi-Myc mice but the difference was not statistically significant.

Conclusion

The present study reveals that LLM inhibits cMyc expression in human prostate cancer cells in vitro but concentrations higher than 10 mg/kg may be required to achieve chemoprevention of prostate cancer.

Blockage of the JAK/STAT3 signaling pathway in multiple myeloma by leelamine

BACKGROUND

Leelamine (LEE) is a lipophilic diterpene amine phytochemical, which can be naturally extracted from pine's bark trees. It has been extensively studied recently for its promising chemopreventive and anti-cancer effects against various cancers such as that of prostate and breast.

HYPOTHESIS

We examined the potential impact of LEE in affecting the activation of signal transducer and activator of transcription 3 (STAT3) and promoting apoptosis in human multiple myeloma (MM) cells.

METHODS

We evaluated the effect of LEE on STAT3 signaling pathway in MM cells by using Western blot analysis and reverse transcription polymerase chain reaction (RT-PCR). Thereafter, apoptosis was evaluated using cell cycle analysis and Annexin V assay.

RESULTS

We noted that LEE could attenuate the phosphorylation of STAT3 and other up-stream signaling molecules such as JAK1, JAK2, and Src activation in U266 and MM.1S cells. It also diminished STAT3 translocation into the nucleus and enhanced the expression of protein-tyrosine phosphatase epsilon (PTPε). Additionally, LEE caused cell cycle arrest and synergistically augmented the apoptotic actions of bortezomib against MM cells.

CONCLUSIONS

Our data indicates that LEE could block STAT3 signaling cascade linked to tumorigenesis and can be used in combination with approved anti-cancer agents in attenuating MM growth and survival.

Improving Strategies in the Development of Protein-Downregulation-Based Antiandrogens

The androgen receptor (AR) plays a crucial role in the occurrence and development of prostate cancer (PCa), and its signaling pathway remains active in castration-resistant prostate cancer (CRPC) patients. The resistance against antiandrogen drugs in current clinical use is a major challenge for the treatment of PCa, and thus the development of new generations of antiandrogens is under high demand. Recently, strategies for downregulating the AR have attracted significant attention, given its potential in the discovery and development of new antiandrogens, including G-quadruplex stabilizers, ROR-γ inhibitors, AR-targeting proteolysis targeting chimeras (PROTACs), and other selective AR degraders (SARDs), which are able to overcome current resistance mechanisms such as acquired AR mutations, the expression of AR variable splices, or overexpression of AR. This review summarizes the various strategies for downregulating the AR protein, at either the mRNA or protein level, thus providing new ideas for the development of promising antiandrogen drugs.

Androgen receptor variant-driven prostate cancer II: advances in laboratory investigations

Background:

The androgen receptor (AR) is a key prostate cancer drug target. Suppression of AR signaling mediated by the full-length AR (AR-FL) is the therapeutic goal of all existing AR-directed therapies. AR-targeting agents impart therapeutic benefit, but lead to AR aberrations that underlie disease progression and therapeutic resistance. Among the AR aberrations specific to castration-resistant prostate cancer (CRPC), AR variants (AR-Vs) have emerged as important indicators of disease progression and therapeutic resistance.

Methods:

We conducted a systemic review of the literature focusing on recent laboratory studies on AR-Vs following our last review article published in 2016. Topics ranged from measurement and detection, molecular origin, regulation, genomic function, and preclinical therapeutic targeting of AR-Vs. We provide expert opinions and perspectives on these topics.

Results:

Transcript sequences for 22 AR-Vs have been reported in the literature. Different AR-Vs may arise through different mechanisms, and can be regulated by splicing factors and dictated by genomic rearrangements, but a low-androgen environment is a prerequisite for generation of AR-Vs. The unique transcript structures allowed development of in-situ and in-solution measurement and detection methods, including mRNA and protein detection, in both tissue and blood specimens. AR variant-7 (AR-V7) remains the main measurement target and the most extensively characterized AR-V. Although AR-V7 co-exists with AR-FL, genomic functions mediated by AR-V7 do not require the presence of AR-FL. The distinct cistromes and transcriptional programs directed by AR-V7 and their co-regulators are consistent with genomic features of progressive disease in a low-androgen environment. Preclinical development of AR-V-directed agents currently focuses on suppression of mRNA expression and protein degradation as well as targeting of the amino-terminal domain.

Conclusions:

Current literature continues to support AR-Vs as biomarkers and therapeutic targets in prostate cancer. Laboratory investigations reveal both challenges and opportunities in targeting AR-Vs to overcome resistance to current AR-directed therapies.

Targeting Cancer Lysosomes with Good Old Cationic Amphiphilic Drugs

Being originally discovered as cellular recycling bins, lysosomes are today recognized as versatile signaling organelles that control a wide range of cellular functions that are essential not only for the well-being of normal cells but also for malignant transformation and cancer progression. In addition to their core functions in waste disposal and recycling of macromolecules and energy, lysosomes serve as an indispensable support system for malignant phenotype by promoting cell growth, cytoprotective autophagy, drug resistance, pH homeostasis, invasion, metastasis, and genomic integrity. On the other hand, malignant transformation reduces the stability of lysosomal membranes rendering cancer cells sensitive to lysosome-dependent cell death. Notably, many clinically approved cationic amphiphilic drugs widely used for the treatment of other diseases accumulate in lysosomes, interfere with their cancer-promoting and cancer-supporting functions and destabilize their membranes thereby opening intriguing possibilities for cancer therapy. Here, we review the emerging evidence that supports the supplementation of current cancer therapies with lysosome-targeting cationic amphiphilic drugs.

Leelamine Is a Novel Lipogenesis Inhibitor in Prostate Cancer Cells In Vitro and In Vivo

Increased de novo synthesis of fatty acids is implicated in the pathogenesis of human prostate cancer, but a safe and effective clinical inhibitor of this metabolic pathway is still lacking. We have shown previously that leelamine (LLM) suppresses transcriptional activity of androgen receptor, which is known to regulate fatty acid synthesis. Therefore, the current study was designed to investigate the effect of LLM on fatty acid synthesis. Exposure of 22Rv1, LNCaP, and PC-3 prostate cancer cells, but not RWPE-1 normal prostate epithelial cell line, to LLM resulted in a decrease in intracellular levels of neutral lipids or total free fatty acids. LLM was superior to another fatty acid synthesis inhibitor (cerulenin) for suppression of total free fatty acid levels. LLM treatment downregulated protein and/or mRNA expression of key fatty acid synthesis enzymes, including ATP citrate lyase, acetyl-CoA carboxylase 1, fatty acid synthase, and sterol regulatory element-binding protein 1 (SREBP1) in each cell line. Consistent with these in vitro findings, we also observed a significant decrease in ATP citrate lyase and SREBP1 protein expression as well as number of neutral lipid droplets in vivo in 22Rv1 tumor sections of LLM-treated mice when compared with that of controls. LLM-mediated suppression of intracellular levels of total free fatty acids and neutral lipids was partly attenuated by overexpression of SREBP1. In conclusion, these results indicate that LLM is a novel inhibitor of SREBP1-regulated fatty acid/lipid synthesis in prostate cancer cells that is not affected by androgen receptor status.

A Brief Overview of the Antitumoral Actions of Leelamine

For the last couple of decades, natural products, either applied singly or in conjunction with other cancer therapies including chemotherapy and radiotherapy, have allowed us to combat different types of human cancers through the inhibition of their initiation and progression. The principal sources of these useful compounds are isolated from plants that were described in traditional medicines for their curative potential. Leelamine, derived from the bark of pine trees, was previously reported as having a weak agonistic effect on cannabinoid receptors and limited inhibitory effects on pyruvate dehydrogenase kinases (PDKs). It has been reported to possess a strong lysosomotropic property; this feature enables its assembly inside the acidic compartments within a cell, such as lysosomes, which may eventually hinder endocytosis. In this review, we briefly highlight the varied antineoplastic actions of leelamine that have found implications in pharmacological research, and the numerous intracellular targets affected by this agent that can effectively negate the oncogenic process.

Advances in Rosin-Based Chemicals: The Latest Recipes, Applications and Future Trends

A comprehensive review of the publications about rosin-based chemicals has been compiled. Rosin, or colophony, is a natural, abundant, cheap and non-toxic raw material which can be easily modified to obtain numerous useful products, which makes it an excellent subject of innovative research, attracting growing interest in recent years. The last extensive review in this research area was published in 2008, so the current article contains the most promising, repeatable achievements in synthesis of rosin-derived chemicals, published in scientific literature from 2008 to 2018. The first part of the review includes low/medium molecule weight compounds: Especially intermediates, resins, monomers, curing agents, surfactants, medications and biocides. The second part is about macromolecules: mainly elastomers, polymers for biomedical applications, coatings, adhesives, surfactants, sorbents, organosilicons and polysaccharides. In conclusion, a critical evaluation of the publications in terms of data completeness has been carried out with an indication of the most promising directions of rosin-based chemicals development.