Bladderwrack extract inhibits LDHA a potential drug target for pancreatic cancer

Bladderwrack (fucus vesiculosus) (figure 1) is a seaweed which was the original source of iodine [1]. A recent study has found that an extract of bladderwrack significantly inhibits the enzyme LDHA [2]. LDHA plays a key role in cancer metabolism and in pancreatic cancer it is often overexpressed [3, 4] and is required for pancreatic cancer cell tumourigenicity in mouse xenograft models [3].

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Figure 1: Bladderwrack. Photo taken by Hans Kylberg. No changes were made. Creative Commons Attribution 2.0 Generic.

LDHA inhibition is associated with the generation of reactive oxygen species (ROS) and the apoptosis of cancer cells [5]. Interestingly lysosomal cell death (LCD) is also promoted by ROS and the possibility that bladderwrack extract could promote LCD should be investigated. There is the possibility that the extract could synergise with drugs that promote LCD such as chloroquine [6]. It will of course be important to isolate the precise compound that inhibits LDHA from the bladderwrack extract.

Refs

  1. Fucus Vesiculosus’. Wikipedia, the Free Encyclopedia, 8 February 2016. https://en.wikipedia.org/w/index.php?title=Fucus_vesiculosus&oldid=703897180.
  2. Deiab, S., E. Mazzio, S. Messeha, N. Mack, and K. F. A. Soliman. ‘High-Throughput Screening to Identify Plant Derived Human LDH-A Inhibitors’. European Journal of Medicinal Plants 3, no. 4 (2013): 603. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3903096/.
  3. Rong, Yefei, Wenchuan Wu, Xiaoling Ni, Tiantao Kuang, Dayong Jin, Dansong Wang, and Wenhui Lou. ‘Lactate Dehydrogenase A Is Overexpressed in Pancreatic Cancer and Promotes the Growth of Pancreatic Cancer Cells’. Tumour Biology: The Journal of the International Society for Oncodevelopmental Biology and Medicine 34, no. 3 (June 2013): 1523–30. doi:10.1007/s13277-013-0679-1.
  4. Pan, Sheng, Ru Chen, Tyler Stevens, Mary P. Bronner, Damon May, Yasuko Tamura, Martin W. McIntosh, and Teresa A. Brentnall. ‘Proteomics Portrait of Archival Lesions of Chronic Pancreatitis’. Edited by Jörg D. Hoheisel. PLoS ONE 6, no. 11 (23 November 2011): e27574. doi:10.1371/journal.pone.0027574.
  5. Valvona, Cara J., Helen L. Fillmore, Peter B. Nunn, and Geoffrey J. Pilkington. ‘The Regulation and Function of Lactate Dehydrogenase A: Therapeutic Potential in Brain Tumor: Regulation and Function of Lactate Dehydrogenase A’. Brain Pathology 26, no. 1 (January 2016): 3–17. doi:10.1111/bpa.12299.
  6. King, M A, I G Ganley, and V Flemington. ‘Inhibition of Cholesterol Metabolism Underlies Synergy between mTOR Pathway Inhibition and Chloroquine in Bladder Cancer Cells’. Oncogene, 8 February 2016. doi:10.1038/onc.2015.511.
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Hybrid insulin peptides – the trigger for type I diabetes?

Type I diabetes is an autoimmune disease of unknown etiology against pancreatic ß cells which is distinct from type II diabetes which is largely triggered by lack of exercise and obesity. Great progress has been made developing targeted gene and cell therapies to reverse type I diabetes. However these therapies have a limited duration of effect due to the return of the pre-existing autoimmune disease which triggered the symptoms of diabetes in the first place (see here). This makes basic research into the underlying autoimmune disease extremely important. Hybrid insulin peptides have just been discovered in a mouse model of type I diabetes [1]. These may provide the elusive drug target required to prevent the underlying autoimmune disease.

Hybrid insulin peptides (HIPs) are a covalent linkage between the protein pro-insulin and other proteins present in the ß cell. The covalent junction is an antigen for T-cells which then attack the ß cells.  It has been found that antibodies from the blood of people with type I diabetes recognise the mouse HIPs suggesting that a human equivalent exists [1]. Clearly the next steps will be to isolate these human HIPs and determine the exact mechanism of their generation which could involve the proteasome [2]. This could reveal a druggable target to eliminate the underlying autoimmune disease. The question remains as to whether HIP generation is a universal trigger of type I diabetes or just one of several mechanisms in which autoimmunity is generated. This caveat aside the identification of HIPs are an extremely exciting development that could remove the last barrier to a cure for type I diabetes – the autoimmune reaction.

Refs

  1. Delong, Thomas, Timothy A. Wiles, Rocky L. Baker, Brenda Bradley, Gene Barbour, Richard Reisdorph, Michael Armstrong, et al. ‘Pathogenic CD4 T Cells in Type 1 Diabetes Recognize Epitopes Formed by Peptide Fusion’. Science 351, no. 6274 (11 February 2016): 711–14. doi:10.1126/science.aad2791.
  2. Vigneron N, Stroobant V, Chapiro J, Ooms A, Degiovanni G, Morel S, van der Bruggen P, Boon T, Van den Eynde BJ. An antigenic peptide produced by peptide splicing in the proteasome. Science. 2004 Apr 23;304(5670):587-90. PubMed PMID: 15001714.

Possible synergy between nimbolide and chloroquine as pancreatic cancer therapeutics?

Nimbolide is a phytochemical extracted from the leaves and flowers of the neem tree (Azadirachta indica) native to India. When applied to pancreatic cancer cell lines in vitro it was found to increase the production of reactive oxygen species (ROS) and lead to apoptosis. In a pancreatic cancer cell line mouse xenograft model nimbolide was found to inhibit the phosphorylation of the AKT pathway of the pancreatic cancer cells and lead to a significant decrease in tumour volume [1]. These effects were found to be independent of autophagy induction. These are promising preclinical results. Furthermore nimbolide’s inhibition of the AKT pathway suggests a possible synergistic combination with chloroquine which was recently found to promote lysosomal cell death [2].

Chloroquine has been shown to promote the cell death of KRAS activated cancers such as pancreatic cancer independently of autophagy (see here). A recent paper has shown that in bladder cancer inhibition of the AKT pathway in combination with chloroquine is synergistic due to the enhancement of chloroquine mediated lysosomal cell death [2]. In pancreatic cancer nimbolide appears to inhibit the AKT pathway raising the possibility that chloroquine will synergise with nimbolide via enhanced lysosomal cell death. Figure 5d of ref [2] is not inconsistent with this. This would be an interesting avenue of future research.

Refs

  1. Subramani, Ramadevi, Elizabeth Gonzalez, Arunkumar Arumugam, Sushmita Nandy, Viviana Gonzalez, Joshua Medel, Fernando Camacho, et al. ‘Nimbolide Inhibits Pancreatic Cancer Growth and Metastasis through ROS-Mediated Apoptosis and Inhibition of Epithelial-to-Mesenchymal Transition’. Scientific Reports 6 (25 January 2016): 19819. doi:10.1038/srep19819.
  2. King, M A, I G Ganley, and V Flemington. ‘Inhibition of Cholesterol Metabolism Underlies Synergy between mTOR Pathway Inhibition and Chloroquine in Bladder Cancer Cells’. Oncogene, 8 February 2016. doi:10.1038/onc.2015.511.

 

PRMT5 a promising synthetic lethal drug target for an estimated 30% of pancreatic cancers

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PRMT5 is a type II protein arginine methyltransferase. It is expressed in a number of cancers including pancreatic IPMN [1] and PDAC (GEO database). It is expressed by all 44 pancreatic cancer cell lines in the cancer cell line encyclopedia (CCLE- figure 1). In leukaemia and lymphoma cells it has been shown that PRMT5 suppresses the transcription of the RB family of tumour suppressors [2].

 CCLE
Figure 1: Comparison of PRMT5, MTAP and CDKN2A mRNA expression in 44 pancreatic cancer cell lines (data source CCLE). RMA = robust multiarray average (mRNA expression).

5-Methylthioadenosine phosphorylase (MTAP) is a key enzyme in the methionine salvage pathway [3]. The MTAP gene is located next to the tumour suppressor CDKN2A and its expression is often lost as a result of CDKN2A deletion during cancer progression. Indeed 30% of the pancreatic cancer cell lines in the CCLE have MTAP deletion associated with loss of CDKN2A expression (figure 1). MTAP-deleted cells accumulate the metabolite methylthioadenosine (MTA), which has been found to inhibit PRMT5 methyltransferase activity [3].

In cancer cells PRMT5 expression and activity prevents programmed cell death from occurring. Cancer cells express high levels of PRMT5 (figure 1) such that MTAP deletion does not fully inhibit PRMT5’s activity. However the cancer cells are sensitive to further drug inhibition of PRMT5 compared to normal cells due to inhibition of PRMT5 by MTA. If PRMT5 is fully inhibited tumour suppressor proteins such as the RB family are able to trigger cancer cell death. This makes PRMT5 an excellent target for drug development.

PRMT5 is required in normal tissues for instance it is essential for sustaining normal adult hematopoiesis [4]. However due to MTAP deletion cancer cells are more sensitive to PRMT5 inhibition than normal cells so it should be possible to optimise PRMT5 drug dosing such that it is fully inhibited in cancer but only partially in normal cells. This would be much better than traditional chemotherapeutics which are fully toxic to both normal and cancer cells. PRMT5 is a promising synthetic lethal drug target for roughly 30% of pancreatic cancers (figure 1).

Refs

  1. Sato, Norihiro, Noriyoshi Fukushima, Anirban Maitra, Christine A. Iacobuzio-Donahue, N. Tjarda van Heek, John L. Cameron, Charles J. Yeo, Ralph H. Hruban, and Michael Goggins. ‘Gene Expression Profiling Identifies Genes Associated with Invasive Intraductal Papillary Mucinous Neoplasms of the Pancreas’. The American Journal of Pathology 164, no. 3 (2004): 903–14. Article – Pubmed Central.
  2. Wang, L., S. Pal, and S. Sif. ‘Protein Arginine Methyltransferase 5 Suppresses the Transcription of the RB Family of Tumor Suppressors in Leukemia and Lymphoma Cells’. Molecular and Cellular Biology 28, no. 20 (15 October 2008): 6262–77. doi:10.1128/MCB.00923-08.
  3. Mavrakis, Konstantinos J., E. Robert McDonald, Michael R. Schlabach, Eric Billy, Gregory R. Hoffman, Antoine deWeck, David A. Ruddy, et al. ‘Disordered Methionine Metabolism in MTAP/CDKN2A Deleted Cancers Leads to Dependence on PRMT5’. Science, 11 February 2016, aad5944. doi:10.1126/science.aad5944.
  4. Liu, Fan, Guoyan Cheng, Pierre-Jacques Hamard, Sarah Greenblatt, Lan Wang, Na Man, Fabiana Perna, et al. ‘Arginine Methyltransferase PRMT5 Is Essential for Sustaining Normal Adult Hematopoiesis’. Journal of Clinical Investigation 125, no. 9 (1 September 2015): 3532–44. doi:10.1172/JCI81749.

Mul-1867 a new compound with potential as a broad range topical antimicrobial agent

Mul-1867 (poly-N1-hydrazino(imino)-methyl-1,6-hexanediamine) is a member of the polymeric guanidine family developed by TGV-Therapeutics [1]. It lyses the cell membrane of both gram-positive and gram-negative bacteria including antibiotic resistant strains such as MRSA. It is also effective against biofilms making it attractive as a topical agent.

Mul-1867 could have applications in dentistry, otolaryngology, surgery and gynecology as well as preventing hospital acquired infections. It may be that it is suitable for incorporation into medical devices to prevent biofilm development. However all these developments will require clinical testing.

Refs

  1. Tetz, George, and Victor Tetz. ‘In Vitro Antimicrobial Activity of a Novel Compound, Mul-1867, against Clinically Important Bacteria’. Antimicrobial Resistance and Infection Control 4, no. 1 (December 2015). doi:10.1186/s13756-015-0088-x.

The TRP superfamily

Members of the transient receptor potential (TRP) superfamily are cation channels that depolarise cells by allowing cations to flow into the cytoplasm down their electrochemical gradients either from extracellular sources or from the endoplasmic reticulum (ER) [1, 2]. The cation selectivity varies between TRPs [3]. In neurons transmembrane voltage (Vm) dictates action potential propagation, and muscle contraction [1]. In non-excitable cells Vm is a component of the electrochemical gradient which drives calcium entry through plasma membrane channels and controls the gating of voltage-dependent Ca2+, K+, and Cl channels [1]. Only two TRP channels are impermeable to Ca2+ [3]. Elevated cytoplasmic Ca2+ activates various signalling pathways leading to neurotransmitter release, cell proliferation, gene transcription, and apoptosis to name but a few [4].

The TRP superfamily comprises over 30 members and can be divided into seven families, six of which have human members [4]. The three largest families are TRPM, TRPV and TRPC. There are four smaller families consisting of TRPML, TRPP, TRPA and TRPN which is not expressed in mammals [4]. The human TRPM family comprises eight members that are genetically and functionally diverse and takes its name from Melastatin (TRPM1) which is used as a prognostic marker for melanoma metastasis [1]. TRPMs have diverse functional properties such as controlling Mg2+ entry, modulating the membrane potential, and sensing cold and menthol in sensory neurons [5]. The TRPV family comprises six members. The vanilloid receptor (TRPV1), the founding member is activated by a variety of signals including vanilloid compounds such as capsaicin, noxious signals, hypotonic cell swelling and heat. All TRPVs are activated by heat and may therefore function in thermosensation [4]. The mammalian TRPC family has seven members designated TRPC1-7 and are known to control neuronal growth cone guidance [1].

Refs

  1. Ramsey, I.S. Delling, M. Clapham, D.E. 2006. An introduction to TRP channels. Annual review of physiology. 68:619-647.
  2. Turner, H. Fleig, A. Stokes, A. Kinet, J.P. Penner, R. 2003. Discrimination of intracellular calcium store subcompartments using TRPV1 (transient receptor potential channel, vanilloid subfamily member 1) release channel activity. The biochemical journal. 371:341-350.
  3. Owsianik G, Talavera K, Voets T, Nilius B. 2006. Permeation and selectivity of TRP channels. Annual review of physiology. 68:685-717.
  4. Pedersen, S.F. Owsianik, G. Nilius, B. 2005. TRP channels: an overview. Cell Calcium. 38:233-252.
  5. Trebak, M. 2006. Canonical transient receptor potential channels in disease: targets for novel drug therapy? Drug discovery today. 11:924-930.

Polyphenon E a promising Chinese/ green tea extract for cancer therapy

Polyphenon E is the trademarked name (by Mitsui Norin Co., Ltd.) of the catechin epigallocatechin-3-gallate abundant in green/ Chinese tea. It is in multiple clinical trials for cancer and other diseases [1]. Notably it has shown an effect in early stage chronic lymphocytic leukemia (CLL) and hormone receptor negative breast cancer with possible but unconfirmed mechanisms involving down-regulation of vascular endothelial growth factor. [2, 3].

It is known that polyphenon E reduces the proliferation of pancreatic cancer cell lines. In the pancreatic cancer cell line MIA PaCa-2 polyphenon E was shown to alter the metabolic profile of the cells in a manner similar to the LDHA inhibitor oxamate [4]. This suggests that LDHA and cancer metabolism could be the target of polyphenon E in pancreatic cancer, however confirmatory studies are required that directly demonstrate this.

Polyphenon E represents a potential drug where clinical evidence of effect in many diseases has been found before the basic mechanism of action has been determined. Moving forward it will be very important to pinpoint the molecular targets of polyphenon E as these may be novel, provide new insight into disease biology, and ultimately provide a rationale for the development of even more potent drugs to modulate those targets.

You never know the year of the monkey might not be so unlucky!

Refs

  1. ‘Search of: Polyphenon – List Results – ClinicalTrials.gov’. Accessed 10 February 2016. https://www.clinicaltrials.gov/ct2/results?term=polyphenon&pg=1.
  2. Shanafelt, Tait D., Timothy G. Call, Clive S. Zent, Jose F. Leis, Betsy LaPlant, Deborah A. Bowen, Michelle Roos, et al. ‘Phase 2 Trial of Daily, Oral Polyphenon E in Patients with Asymptomatic, Rai Stage 0 to II Chronic Lymphocytic Leukemia: EGCG for CLL’. Cancer 119, no. 2 (15 January 2013): 363–70. doi:10.1002/cncr.27719.
  3. Crew, K. D., P. Brown, H. Greenlee, T. B. Bevers, B. Arun, C. Hudis, H. L. McArthur, et al. ‘Phase IB Randomized, Double-Blinded, Placebo-Controlled, Dose Escalation Study of Polyphenon E in Women with Hormone Receptor-Negative Breast Cancer’. Cancer Prevention Research 5, no. 9 (1 September 2012): 1144–54. doi:10.1158/1940-6207.CAPR-12-0117.
  4. Lu, Qing-Yi, Lifeng Zhang, Jennifer K. Yee, Vay-Liang W. Go, and Wai-Nang Lee. ‘Metabolic Consequences of LDHA Inhibition by Epigallocatechin Gallate and Oxamate in MIA PaCa-2 Pancreatic Cancer Cells’. Metabolomics : Official Journal of the Metabolomic Society 11, no. 1 (February 2015): 71–80. doi:10.1007/s11306-014-0672-8.