The natural compound forskolin synergizes with dexamethasone to induce cell death in myeloma cells via BIM

Forskolin affects proliferation, migration and Paclitaxel-mediated cytotoxicity in non-small-cell lung cancer cell lines via adenylyl cyclase/cAMP axis

Non-Small-Cell Lung Cancer (NSCLC) is considered one of the most frequently diagnosed cancers and the leading cause of cancer-related deaths worldwide. Despite the undoubted therapeutic advances that have occurred in clinical practice over time, due to its high degree in both heterogeneity and resistance, NSCLC remains largely incurable. As a natural cAMP elevating agent, Forskolin has shown anti-cancer properties in different tumor types, thus supposing its possible usage in treating malignancies. In this study, we investigated the Forskolin outcome in H1299 and A549 NSCLC cell lines, either alone or in combination with Paclitaxel. We proved that Forskolin impairs cell growth and migration ability of these cells, concurrently. Albeit with a different extent between H1299 and A549, changes in cell-cycle progression and epithelial-mesenchymal markers were observed in response to Forskolin administration. Interestingly, comparable cell growth impairment was also obtained with the cAMP phosphodiesterase inhibitor IBMX, while the employment of adenylyl cyclase inhibitor SQ22536 counteracted, at least in part, the Forskolin-mediated anticancer effects. Besides as a single agent, we also demonstrated that Forskolin strongly enhances Paclitaxel-induced cytotoxicity, affecting cell death mainly via apoptosis induction. Notably, H89-mediated protein kinase A (PKA) inhibition further deteriorated the combination outcome. Altogether, our data designate Forskolin as a possible anticancer molecule in NSCLC, and recognize the adenylyl cyclase/cAMP axis as one of the pathways involved in. Although achieved at preclinical stage, our findings encourage the design of future studies aimed at further exploring the Forskolin employment in NSCLC treatment.

Protein Kinase A-Mediated Effects of Protein Kinase C Partial Agonist 5-(Hydroxymethyl)Isophthalate 1a3 in Colorectal Cancer Cells

Colorectal cancer is the third most commonly occurring cancer in men and the second in women. The global burden of colorectal cancer is projected to increase to over 2 million new cases with over 1 million deaths within the next 10 years, and there is a great need for new compounds with novel mechanisms of action. Our group has developed protein kinase C (PKC)-modulating isophthalic acid derivatives that induce cytotoxicity toward human cervical and prostate cancer cell lines. In this study, we investigated the effects of 5-(hydroxymethyl)isophthalate 1a3 (HMI-1a3) on colorectal cancer cell lines (Caco-2, Colo205, and HT29). HMI-1a3 inhibited cell proliferation, decreased cell viability, and induced an apoptotic response in all studied cell lines. These effects, however, were independent of PKC. Using serine/threonine kinome profiling and pharmacological kinase inhibitors, we identified activation of the cAMP/PKA pathway as a new mechanism of action for HMI-1a3-induced anticancer activity in colorectal cancer cell lines. Our current results strengthen the hypothesis for HMI-1a3 as a potential anticancer agent against various malignancies. SIGNIFICANCE STATEMENT: Colorectal cancer (CRC) is a common solid organ malignancy. This study demonstrates that the protein kinase C (PKC)-C1 domain-targeted isophthalatic acid derivative 5-(hydroxymethyl)isophthalate 1a3 (HMI-1a3) has anticancer activity on CRC cell lines independently of PKC. We identified PKA activation as a mechanism of HMI-1a3-induced anticancer effects. The results reveal a new anticancer mechanism of action for the partial PKC agonist HMI-1a3 and thus provide new insights for the development of PKC and PKA modulators for cancer therapy.

Cdc25C/cdc2/cyclin B, raf/MEK/ERK and PERK/eIF2α/CHOP pathways are involved in forskolin-induced growth inhibition of MM.1S cells by G2/M arrest and mitochondrion-dependent apoptosis

Multiple myeloma (MM) remains an incurable hematological malignancy characterized by proliferation and accumulation of plasma cells in the bone marrow. Innovative and effective therapeutic approaches that are able to improve the outcome and the survival of MM sufferers, especially the identification of novel natural compounds and investigation of their anti-MM mechanisms, are needed. Here, we investigated the effects and the potential mechanisms against MM of forskolin, a diterpene derived from the medicinal plant Coleus forskohlii, in MM cell line MM.1S. CCK-8 assay showed that forskolin significantly inhibited MM.1S cells viability in a time- and dose-dependent manner. Furthermore, we demonstrated that forskolin induced G2/M phase arrest with a remarkable increase of p-cdc25c, p-cdc2, and a decrease of cyclin B1, indicating the suppression of cdc25C/cdc2/cyclin B pathway. Moreover, we found that forskolin induced mitochondrion-dependent apoptosis which was accompanied by the increase of pro-apoptotic proteins Bax, Bad, Bim and Bid, the decrease of anti-apoptotic proteins Bcl-2 and Bcl-xl, the changes of the mitochondrial membrane potential (MMP) and increase of cleaved caspase-9, cleaved caspase-3 and cleaved PARP. Of note, we demonstrated that forskolin induced a decrease of p-C-Raf, p-MEK, p-ERK1/2 and p-p90Rsk, and an increase of p-PERK, p-eIF2α and CHOP, which indicated that the inhibition of Raf/MEK/ERK pathway and activation of PERK/eIF2α/CHOP pathway were involved, at least partially, in forskolin-induced MM.1S cells apoptosis. These findings confirm the anti-MM action of forskolin and extend the understanding of its anti-MM mechanism in MM.1S cells, as well as reinforcing the evidence for forskolin as a natural chemotherapeutic compound against MM.

Epithelial-to-Mesenchymal Transition Is Not a Major Modulating Factor in the Cytotoxic Response to Natural Products in Cancer Cell Lines

Numerous natural products exhibit antiproliferative activity against cancer cells by modulating various biological pathways. In this study, we investigated the potential use of eight natural compounds (apigenin, curcumin, epigallocatechin gallate, fisetin, forskolin, procyanidin B2, resveratrol, urolithin A) and two repurposed agents (fulvestrant and metformin) as chemotherapy enhancers and mesenchymal-to-epithelial (MET) inducers of cancer cells. Screening of these compounds in various colon, breast, and pancreatic cancer cell lines revealed anti-cancer activity for all compounds, with curcumin being the most effective among these in all cell lines. Although some of the natural products were able to induce MET in some cancer cell lines, the MET induction was not related to increased synergy with either 5-FU, irinotecan, gemcitabine, or gefitinib. When synergy was observed, for example with curcumin and irinotecan, this was unrelated to MET induction, as assessed by changes in E-cadherin and vimentin expression. Our results show that MET induction is compound and cell line specific, and that MET is not necessarily related to enhanced chemosensitivity.

Multiple Myeloma Inhibitory Activity of Plant Natural Products

A literature search on plant natural products with antimyeloma activity until the end of 2020 resulted in 92 compounds with effects on at least one human myeloma cell line. Compounds were divided in different compound classes and both their structure-activity-relationships as well as eventual correlations with the pathways described for Multiple Myeloma were discussed. Each of the major compound classes in this review (alkaloids, phenolics, terpenes) revealed interesting candidates, such as dioncophyllines, a group of naphtylisoquinoline alkaloids, which showed pronounced and selective induction of apoptosis when substituted in position 7 of the isoquinoline moiety. Interestingly, out of the phenolic compound class, two of the most noteworthy constituents belong to the relatively small subclass of xanthones, rendering this group a good starting point for possible further drug development. The class of terpenoids also provides noteworthy constituents, such as the highly oxygenated diterpenoid oridonin, which exhibited antiproliferative effects equal to those of bortezomib on RPMI8226 cells. Moreover, triterpenoids containing a lactone ring and/or quinone-like substructures, e.g., bruceantin, whitaferin A, withanolide F, celastrol, and pristimerin, displayed remarkable activity, with the latter two compounds acting as inhibitors of both NF-κB and proteasome chymotrypsin-like activity.

Reprogramming Cancer Stem-like Cells with Nanoforskolin Enhances the Efficacy of Paclitaxel in Targeting Breast Cancer

Cancer stem-like cells (CSCs) have emerged as an important target for breast cancer therapy owing to their self-renewability, proliferation, and elevated chemoresistance properties. Here, we present a strategy of eliminating CSCs by differentiation therapy where "forced differentiation" reprograms CSCs so that they lose their intrinsic properties and become susceptible for conventional chemotherapeutic drugs. In this study, we report that a conventional chemotherapeutic paclitaxel enhances the stemness of CSCs, while a phytochemical forskolin being essentially nontoxic to CSCs possesses the intrinsic ability to reprogram them. To achieve simultaneous targeting of CSCs and bulk tumor cells, we used a co-delivery system where liquid crystal nanoparticles (LCN) were co-encapsulated with both paclitaxel and forskolin. LCN showed higher uptake, retention, and penetration potential in CSCs overcoming their high drug efflux property. Moreover, LCN improved the pharmacokinetic parameters of forskolin, which otherwise had very low retention and bioavailability. Forskolin-loaded LCN forced CSCs to exit from their mesenchymal state, which reduced their stemness and chemosensitized them while inhibiting E-cadherin-mediated survival and tumor-initiating potential as well as reversing paclitaxel-induced stemness. We further showed that upon administration of paclitaxel and forskolin co-loaded LCN to an orthotropic xenograft mouse model, the nanomedicine showed enhanced passive tumor targeting capability with very potent antitumor activity that eradicated small solid tumor in a single dose and showed no sign of tumor relapse or systemic toxicity over a long period. Overall, these findings give a proof of concept that co-delivery of forskolin and paclitaxel in a single nanoformulation can achieve overall tumor targeting where forskolin can efficiently reprogram/differentiate CSCs and paclitaxel can induce cytotoxicity in both differentiated CSCs and bulk tumor cells simultaneously. Hence, this study can provide a nanoformulation that can offer an efficient strategy for cancer therapy.

Latest perspectives on glucocorticoid-induced apoptosis and resistance in lymphoid malignancies

Glucocorticoids are essential drugs in the treatment protocols of lymphoid malignancies. These steroidal hormones trigger apoptosis of the malignant cells by binding to the glucocorticoid receptor (GR), which is a member of the nuclear receptor superfamily. Long term glucocorticoid treatment is limited by two major problems: the development of glucocorticoid-related side effects, which hampers patient quality of life, and the emergence of glucocorticoid resistance, which is a gradual process that is inevitable in many patients. This emphasizes the need to reevaluate and optimize the widespread use of glucocorticoids in lymphoid malignancies. To achieve this goal, a deep understanding of the mechanisms governing glucocorticoid responsiveness is required, yet, a recent comprehensive overview is currently lacking. In this review, we examine how glucocorticoids mediate apoptosis by detailing GR's genomic and non-genomic action mechanisms in lymphoid malignancies. We continue with a discussion of the glucocorticoid-related problems and how these are intertwined with one another. We further zoom in on glucocorticoid resistance by critically analyzing the plethora of proposed mechanisms and highlighting therapeutic opportunities that emerge from these studies. In conclusion, early detection of glucocorticoid resistance in patients remains an important challenge as this would result in a timelier treatment reorientation and reduced glucocorticoid-instigated side effects.

Blame the signaling: Role of cAMP for the resolution of inflammation

A complex intracellular signaling governs different cellular responses in inflammation. Extracellular stimuli are sensed, amplified, and transduced through a dynamic cellular network of messengers converting the first signal into a proper response: production of specific mediators, cell activation, survival, or death. Several overlapping pathways are coordinated to ensure specific and timely induction of inflammation to neutralize potential harms to the tissue. Ideally, the inflammatory response must be controlled and self-limited. Resolution of inflammation is an active process that culminates with termination of inflammation and restoration of tissue homeostasis. Comparably to the onset of inflammation, resolution responses are triggered by coordinated intracellular signaling pathways that transduce the message to the nucleus. However, the key messengers and pathways involved in signaling transduction for resolution are still poorly understood in comparison to the inflammatory network. cAMP has long been recognized as an inducer of anti-inflammatory responses and cAMP-dependent pathways have been extensively exploited pharmacologically to treat inflammatory diseases. Recently, cAMP has been pointed out as coordinator of key steps of resolution of inflammation. Here, we summarize the evidence for the role of cAMP at inducing important features of resolution of inflammation.

Cytochrome P450 enzymes: A driving force of plant diterpene diversity

In plant terpene biosynthesis, oxidation of the hydrocarbon backbone produced by terpene synthases is typically carried out by cytochrome P450 oxygenases (CYPs). The modifications introduced by CYPs include hydroxylations, sequential oxidations at one position and ring rearrangements and closures. These reactions significantly expand the structural diversity of terpenoids, but also provide anchoring points for further decorations by various transferases. In recent years, there has been a significant increase in reports of CYPs involved in plant terpene pathways. Plant diterpenes represent an important class of metabolites that includes hormones and a number of industrially relevant compounds such as pharmaceutical, aroma or food ingredients. In this review, we provide a comprehensive survey on CYPs reported to be involved in plant diterpene biosynthesis to date. A phylogenetic analysis showed that only few CYP clans are represented in diterpene biosynthesis, namely CYP71, CYP85 and CYP72. Remarkably few CYP families and subfamilies within those clans are involved, indicating specific expansion of these clades in plant diterpene biosynthesis. Nonetheless, the evolutionary trajectory of CYPs of specialized diterpene biosynthesis is diverse. Some are recently derived from gibberellin biosynthesis, while others have a more ancient history with recent expansions in specific plant families. Among diterpenoids, labdane-related diterpenoids represent a dominant class. The availability of CYPs from diverse plant species able to catalyze oxidations in specific regions of the labdane-related backbones provides opportunities for combinatorial biosynthesis to produce novel diterpene compounds that can be screened for biological activities of interest.

Forskolin exerts anticancer roles in non-Hodgkin's lymphomas via regulating Axin/β-catenin signaling pathway

Background

Non-Hodgkin’s lymphomas (NHLs) account for 85% of lymphomas, which are characterized by high-degree malignancy, rapid progress, and even invasion into central nervous system in pediatric patients. Although the cure rate of pediatric NHL has improved, some patients have still underwent recurrence or death. This study focuses on the effects and mechanism of forskolin on the progression of NHL, aiming to find efficient therapy methods for pediatric NHL.

Methods

MTT, flow cytometry and mice tumor bearing experiments were used to evaluate the effects of forskolin on NHL cell proliferation, apoptosis and tumorigenesis. Western blotting and RT-PCR assays were used to detect protein and mRNA expression. Immunohistochemistry technology was recruited to analyze Ki-67 expression in tumor tissues.

Results

Forskolin significantly increased the expression of cleaved caspase-3/9 in both NHL Toledo and NK-92 cell lines, and inhibited cell growth. Besides, forskolin obviously reduced the expression of β-catenin protein, promoted its ubiquitination, enhanced its transportation from nuclear to cytoplasm, as well as decreased the expression of its downstream oncogenes c-myc and cyclin D1 through upregulating Axin expression and stability and inhibiting Axin ubiquitination. Moreover, forskolin enhanced the effects of SP600125, an inhibitor of c-Jun N-terminal kinase signaling on cell apoptosis promotion and tumorigenesis inhibition via Axin-induced β-catenin signaling repression.

Conclusion

The current study clarifies that forskolin can inhibit the progression of NHL through Axin-mediated inhibition of β-catenin signaling. Moreover, forskolin improves the effects of SP600125 on cell apoptosis enhancement and tumorigenesis inhibition of NHL cells. These findings provide theoretical foundation of serving forskolin as a new effective therapeutic drug for pediatric NHL.

Isoforskolin and forskolin attenuate lipopolysaccharide-induced inflammation through TLR4/MyD88/NF-κB cascades in human mononuclear leukocytes

The principal active component of isoforskolin (ISOF) is from the plant Coleus forskohlii, native to China, which has attracted much attention for its biological effects. We hypothesize that ISOF and forskolin (FSK) pretreatment attenuates inflammation induced by lipopolysaccharide (LPS) related to toll‐like receptor 4 (TLR4), myeloid differentiation factor 88 (MyD88), and nuclear factor kappa B (NF‐κB) signaling. Mononuclear leukocytes (MLs) from healthy donors' blood samples were separated by using density gradient centrifugation. Protein levels of TLR4, MyD88, and NF‐κB were detected using western blot and inflammatory cytokines interleukin (IL) 1β, IL‐2, IL‐6, IL‐21, IL‐23, tumor necrosis factor (TNF) α, and TNF‐β were tested by enzyme‐linked immunosorbent assay and Quantibody array in MLs. Our results showed that LPS augmented the protein levels of TLR4, MyD88, and NF‐κB in MLs and the production of IL‐1β, IL‐2, IL‐6, IL‐21, IL‐23, TNF‐α, and TNF‐β in supernatants of MLs. Despite treatment with ISOF and FSK prior to LPS, the protein levels of TLR4, MyD88, NF‐κB, IL‐1β, IL‐2, IL‐6, IL‐21, IL‐23, TNF‐α, and TNF‐β in MLs were apparently decreased. roflumilast (RF) and dexamethasone (DM) had a similar effect on MLs with ISOF and FSK. Our results, for the first time, have shown that ISOF and FSK attenuate inflammation in MLs induced by LPS through down‐regulating protein levels of IL‐1β and TNF‐α, in which TLR4/MyD88/NF‐κB signal pathway could be involved.

Forskolin Sensitizes Human Acute Myeloid Leukemia Cells to H3K27me2/3 Demethylases GSKJ4 Inhibitor via Protein Kinase A

Acute myeloid leukemia (AML) is an aggressive hematological malignancy occurring very often in older adults, with poor prognosis depending on both rapid disease progression and drug resistance occurrence. Therefore, new therapeutic approaches are demanded. Epigenetic marks play a relevant role in AML. GSKJ4 is a novel inhibitor of the histone demethylases JMJD3 and UTX. To note GSKJ4 has been recently shown to act as a potent small molecule inhibitor of the proliferation in many cancer cell types. On the other hand, forskolin, a natural cAMP raising compound, used for a long time in traditional medicine and considered safe also in recent studies, is emerging as a very interesting molecule for possible use in cancer therapy. Here, we investigate the effects of forskolin on the sensitivity of human leukemia U937 cells to GSKJ4 through flow cytometry-based assays (cell-cycle progression and cell death), cell number counting, and immunoblotting experiments. We provide evidence that forskolin markedly potentiates GSKJ4-induced antiproliferative effects by apoptotic cell death induction, accompanied by a dramatic BCL2 protein down-regulation as well as caspase 3 activation and PARP protein cleavage. Comparable effects are observed with the phosphodiesterase inhibitor IBMX and 8-Br-cAMP analogous, but not by using 8-pCPT-2'-O-Me-cAMP Epac activator. Moreover, the forskolin-induced enhancement of sensitivity to GSKJ4 is counteracted by pre-treatment with Protein Kinase A (PKA) inhibitors. Altogether, our data strongly suggest that forskolin sensitizes U937 cells to GSKJ4 inhibitor via a cAMP/PKA-mediated mechanism. Our findings provide initial evidence of anticancer activity induced by forskolin/GSKJ4 combination in leukemia cells and underline the potential for use of forskolin and GSKJ4 in the development of innovative and effective therapeutic approaches for AML treatment.

Forskolin improves sensitivity to doxorubicin of triple negative breast cancer cells via Protein Kinase A-mediated ERK1/2 inhibition

Triple negative breast cancer (TNBC) is an invasive, metastatic, highly aggressive tumor. Cytotoxic chemotherapy represents the current treatment for TNBC. However, relapse and chemo-resistance are very frequent. Therefore, new therapeutic approaches that are able to increase the sensitivity to cytotoxic drugs are needed. Forskolin, a natural cAMP elevating agent, has been used for several centuries in medicine and its safeness has also been demonstrated in modern studies. Recently, forskolin is emerging as a possible novel molecule for cancer therapy. Here, we investigate the effects of forskolin on the sensitivity of MDA-MB-231 and MDA-MB-468 TNBC cells to doxorubicin through MTT assay, flow cytometry-based assays (cell-cycle progression and cell death), cell number counting and immunoblotting experiments. We demonstrate that forskolin strongly enhances doxorubicin-induced antiproliferative effects by cell death induction. Similar effects are observed with IBMX and isoproterenol cAMP elevating agents and 8-Br-cAMP analog, but not by using 8-pCPT-2'-O-Me-cAMP Epac activator. It is important to note that the forskolin-induced potentiation of sensitivity to doxorubicin is accompanied by a strong inhibition of ERK1/2 phosphorylation, is mimicked by ERK inhibitor PD98059 and is prevented by pre-treatment with Protein Kinase A (PKA) and adenylate cyclase inhibitors. Altogether, our data indicate that forskolin sensitizes TNBC cells to doxorubicin via a mechanism depending on the cAMP/PKA-mediated ERK inhibition. Our findings sustain the evidence of anticancer activity mediated by forskolin and encourage the design of future in-vivo/clinical studies in order to explore forskolin as a doxorubicin sensitizer for possible use in TNBC patients.

Active enhancer and chromatin accessibility landscapes chart the regulatory network of primary multiple myeloma

Multiple myeloma (MM) is an aggressive cancer that originates from antibody-secreting plasma cells. Although genetically and transcriptionally well characterized, the aberrant gene regulatory networks that underpin this disease remain poorly understood. Here, we mapped regulatory elements, open chromatin, and transcription factor (TF) footprints in primary MM cells. In comparison with normal antibody-secreting cells, MM cells displayed consistent changes in enhancer activity that are connected to superenhancer (SE)-mediated deregulation of TF genes. MM cells also displayed widespread decompaction of heterochromatin that was associated with activation of regulatory elements and in a major subset of patients' deregulation of the cyclic adenosine monophosphate pathway. Finally, building SE-associated TF-based regulatory networks allowed identification of several novel TFs that are central to MM biology. Taken together, these findings significantly add to our understanding of the aberrant gene regulatory network that underpins MM.

1,2,3,4,6-Penta-O-Galloyl-Beta-D-Glucopyranoside Inhibits Proliferation of Multiple Myeloma Cells Accompanied with Suppression of MYC Expression

Multiple myeloma (MM) still remains an incurable disease, therefore discovery of novel drugs boosts the therapeutics for MM. The natural compound 1,2,3,4,6-Penta-O-galloyl-beta-D-glucopyranoside (PGG) has been shown to exhibit antitumor activities against various cancer cells. Here, we aim to evaluate antitumor effects of PGG on MM cell lines. PGG inhibited the growth of three different MM cell lines in a dose- and time-dependent manner. Cell cycle analysis revealed that PGG treatment caused cell cycle arrest in G1 phase. It also induced apoptosis which was indicated by significant increases of Annexin V positive cells, caspase 3/7 activity, and cleaved caspase 3 expression in PGG treated MM cell. Since MYC is frequently hyperactivated in MM and inhibition of MYC leads to MM cell death. We further demonstrated that PGG decreased MYC expression in protein and mRNA levels and reversed the mRNA expression of MYC target genes such as p21, p27, and cyclin D2. In addition, PGG also reduced protein expression of DEPTOR which is commonly overexpressed in MM. Unexpectedly, PGG antagonized the cytotoxic effect of bortezomib in the combination treatment. However, PGG treatment sensitized MM cells to another proteasome inhibitor MG132 induced cytotoxicity. Moreover, MYC inhibitor JQ1 enhanced the cytotoxic effect of bortezomib on MM cells. Our findings raised concerns about the combinatory use of bortezomib with particular types of chemicals. The evidence also provide useful insights into the combination of MYC and proteasome-inhibitors for MM therapy. Finally, PGG has a therapeutic potential for treatment of MM and further development is mandatory.

cAMP induces cell apoptosis in multiple myeloma and overcomes bortezomib resistance

The acquired resistance to bortezomib represents a major obstacle for multiple myeloma (MM) treatment. Studies revealed that the treatment with cyclic adenosine monophosphate (cAMP) may be a promising strategy for MM therapy. Therefore, the present study aimed to explore the mechanism of action of cAMP in MM cells. Our results showed that 8-CPT-cAMP and bortezomib synergistically induced growth inhibition and apoptosis in MM bortezomib-resistant cell lines and primary MM cells, in which protein kinase A (PKA) activation was involved. Furthermore, 8-CPT-cAMP induced the degradation of cyclinD1 and downregulation of myeloid cell leukemia-1 (Mcl-1). Moreover, 8-CPT-cAMP enhanced endoplasmic reticulum stress caused by bortezomib. A synergy between bortezomib and cAMP was also revealed in a murine MOPC315 xenograft model, which was evidenced by the significantly inhibited tumor growth and the improved multiple cancer-related parameters by the combination of the cAMP-elevating compound forskolin and bortezomib. Taken together, this study suggests that the treatment with cAMP may be a promising strategy for enhancing the therapeutic efficacy of bortezomib in MM treatment.

GPER promotes tamoxifen-resistance in ER+ breast cancer cells by reduced Bim proteins through MAPK/Erk-TRIM2 signaling axis

Tamoxifen resistance is a major clinical challenge in breast cancer treatment. Our previous studies find that GPER and its down-stream signaling play a pivotal role in the development of tamoxifen (TAM) resistance. cDNA array analysis indicated a set of genes associated with cell apoptosis are aberrant in GPER activated and TAM-resistant MCF-7R cells compared with TAM-sensitive MCF-7 cells. Among these genes, Bim (also named BCL2-L11), a member of the BH3-only pro-apoptotic protein family is significantly decreased, and TRIM RING finger protein TRIM2 (a ubiquitin ligase) is highly expressed in MCF-7R. To understand the mechanism of TAM-resistance in GPER activated ER+ breast cancer, the function of TRIM2 and Bim inducing cell apoptosis was studied. By using immunohistochemical and western blot analysis, there is an adverse correlation between TRIM2 and Bim in TAM-resistant breast tumor tissues and MCF-7R cells. Knockdown Bim in TAM-sensitive MCF-7 cells or overexpression of Bim in TAM-resistant MCF-7 cells significantly changed its sensibility to TAM through altering the levels of cleaved PARP and caspase-3. Activation of GPER and its downstream signaling MAPK/ERK, not PI3K/AKT, led to enhanced TRIM2 protein levels and affected the binding between TRIM2 and Bim which resulted in a reduced Bim in TAM-resistant breast cancer cells. Thus, the present study provides a novel insight to TAM-resistance in ER-positive breast cancer cells.

The Natural cAMP Elevating Compound Forskolin in Cancer Therapy: Is It Time?

Cancer is a major public health problem and the second leading cause of mortality around the world. Although continuous advances in the science of oncology and cancer research are now leading to improved outcomes for many cancer patients, novel cancer treatment options are strongly demanded. Naturally occurring compounds from a variety of vegetables, fruits, and medicinal plants have been shown to exhibit various anticancer properties in a number of in vitro and in vivo studies and represent an attractive research area for the development of new therapeutic strategies to fight cancer. Forskolin is a diterpene produced by the roots of the Indian plant Coleus forskohlii. The natural compound forskolin has been used for centuries in traditional medicine and its safety has also been documented in conventional modern medicine. Forskolin directly activates the adenylate cyclase enzyme, that generates cAMP from ATP, thus, raising intracellular cAMP levels. Notably, cAMP signaling, through the PKA-dependent and/or -independent pathways, is very relevant to cancer and its targeting has shown a number of antitumor effects, including the induction of mesenchymal-to-epithelial transition, inhibition of cell growth and migration and enhancement of sensitivity to conventional antitumor drugs in cancer cells. Here, we describe some features of cAMP signaling that are relevant to cancer biology and address the state of the art concerning the natural cAMP elevating compound forskolin and its perspectives as an effective anticancer agent. J. Cell. Physiol. 232: 922-927, 2017. © 2016 Wiley Periodicals, Inc.