Transcript Cancer Therapeutics: Drug Agents which alter programmed cell death

Cancer Therapeutics: Drug
Agents which alter
programmed cell death
Afshin Farzam-Shareqi,
Jason S. Lam, Kelvin Deng, Andrew Ly
PHM142 Fall 2016
Instructor: Dr. Jeffrey Henderson
Outline of Presentation
Programmed cell death is the regulated death of cells. PCD prevents overproliferation of cells and ensures proper organism survival. There are two forms of
PCD: apoptosis and autophagy.
1) Intrinsic and extrinsic apoptosis
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Normal functioning pathway
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Drug targets for cancer
2) Autophagy
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Normal function and regulation of autophagy
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Cancer therapies
Challenges of current cancer therapeutics
Apoptosis
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Functions in tissues to maintain
homeostasis and balance cell death and
growth
Cell membrane blebbing, cell shrinkage,
chromatin condensation, nucleosomal
fragmentation leading to death
Many chemotherapeutic drugs induce
apoptosis by altering components of
pathways
Two apoptotic signaling pathways:
○ Intrinsic (mitochondria-mediated)
○ Extrinsic
http://render.fineartamerica.com/images/rendered/medium/greeting-card/imagesmedium-5/hela-cell-apoptosis-sem-thomas-deerinck-ncmir.jpg
Intrinsic Pathway
● Activated by intracellular stress (e.g. DNA damage,
ROS)
● Stress stabilizes tumor suppressor p53
○ Interacts with Bcl-2 family proteins that regulate
mitochondrial outer membrane permeability
(MOMP)
● Antiapoptotic bcl-2 protein inhibition allows
dimerization of Bax and Bak (proapoptotic Bcl-2
proteins), increasing MOMP
http://www.nature.com/nrd/journal/v7/n12/fig_tab/
nrd2637_F1.html
Intrinsic Pathway
● Cytochrome C efflux from mitochondria
● Pro-caspase 9 activation via apoptosome formation
○ Cytochrome C binds Apaf-1(Apoptotic protease
activating factor 1) which then recruits procaspase 9 and activates it
● Activation of effector caspases 3, 6, and 7 by
caspase 9
● Cellular degradation initialized
● Effector caspases can be inhibited by IAPs
(Inhibitors of Apoptosis Proteins)
http://www.nature.com/nrd/journal/v7/n12/fig_tab/
nrd2637_F1.html
Intrinsic Pathway Drug Targets
● Common causes of tumorigenesis are p53 and bcl-2
mutations
● Result in decreased activation of intrinsic pathway;
reduced apoptosis leading to dysregulated cell growth
● Types of chemotherapeutics:
○ Antiapoptotic Bcl-2 antisense oligonucleotides (1)
○ Proapoptotic Bcl-2 mimetics (2)
○ Antiapoptotic bcl-2 inhibitors (3)
○ IAP inhibitors (4)
○ IAP antisense oligonucleotides (5)
○ Direct caspase activating agents (6)
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1,3
4,5
6
http://www.nature.com/nrd/journal/v7/n12/fig_tab/
nrd2637_F1.html
Venetoclax
● Approved by the FDA April 2016
(Venclexta)
● Used to treat chronic lymphocytic
leukemia due to deletion of 17p
○ Overexpression of Bcl-2 in these
cells which increases tumor cell
survival
● Selective inhibitor of Bcl-2
(antiapoptotic)
● Allows increased Bax, Bak
dimerization
● Increased intrinsic pathway apoptosis
in tumor cells
https://en.wikipedia.org/wiki/Vene
toclax#/media/File:Venetoclax.sv
g
http://www.nature.com/nrd/journal/v7/n12/fig_tab/
nrd2637_F1.html
Extrinsic pathway for the activation of caspase
cascades
● Extrinsic pathway involves an extracellular ligand binding to receptors on cell
surface
● These ligands, called tumor necrosis factors (TNFs), are cytokines or
transmembrane proteins on the surfaces of lymphocytes that bind to tumor
necrosis factor receptors (TNFRs) on the surfaces of cells
● Examples of ligands: Fas, TNF-related apoptosis-inducing ligand (TRAIL),
TNF-alpha
● The extrinsic pathway involves:
1. Assembly of DISC - the death inducing signalling complex
2. Cleavage of procaspases to form activated caspases
Extrinsic Pathway - formation of the DISC
• In this example: the Fas ligand,
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https://upload.wikimedia.org/wikipedia/commons/6/60/Fas-signalling.svg
expressed on T lymphocytes, binds
to the Fas receptor on the cell
surface
Upon activation of the Fas receptor, a
Fas-associated death domaincontaining protein (FADD) is
recruited
Inactivated procaspase 8 is recruited
and bound to FADD
Together, these structures form the
death-induced signaling complex
(DISC)
Extrinsic Pathway, Cleavage of
Procaspases
• The procaspase undergoes cleavage
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into activated caspases
The activation of caspase 8 induces
apoptosis of cells categorized as
Type I cells
In Type II cells, the caspase interacts
with the protein Bid, which
subsequently activates Bax and Bak
in the intrinsic mitochondrial pathway.
This amplifies the levels of caspases,
leading to apoptosis.
http://www.nature.com/nrd/journal/v7/n12/fig_tab/
nrd2637_F1.html
Bortezomib
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Bortezomib (VELCADE) - a proteasome inhibitor, prevents the degradation of proapoptotic proteins, like p53
Study explored how the drug could increase sensitivity of TNF ligand (TRAIL) binding to
TNF receptor
Studies suggested that Bortezomib increased death receptor expression on the
membrane, increased recruitment of caspase 8 to the DISC, increasing apoptosis
http://www.arasto.com/index.php/2016-03-10-21-15-47/2016-04-16-05-44-52/bortezomib
Phenoxodiol
● Shown to safely and effectively treat multiple cancers types including
ovarian and prostate.
● Effective in cells resistant to conventional chemotherapy like paclitaxel and
carboplatin
● Activates both the intrinsic and extrinsic pathways
● Intrinsic: Facilitates the cleavage of caspase-9 into the active p36 form
● Extrinsic: Reduces expression of FLIP, an apoptotic blocker that competes
with caspase-8 in DISC binding
● Reduces the expression and increases the cleavage of XIAP
● Results in an increased sensitivity to Fas-mediated apoptosis
Atezolizumab
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Recently FDA-approved to treat urothelial
carcinoma and non-small lung cancer
● Tumour cells have increased expression of
PD-L1 which binds to receptors on T cells
and suppresses T-cell activity
● Atezolizumab (Tecentriq) is a monoclonal
antibody that binds to PD-L1 and blocks its
interactions with the T-cell receptors
● As a result, T cells become more active
● Increased tumour apoptosis
http://www.cell.com/trends/molecular-medicine/fulltext/S1471-4914(14)00183-X
Autophagy
The double edged sword in cancer therapeutics
https://encrypted-tbn3.gstatic.com/images?q=tbn:ANd9GcTX941i12KoHLwpTtVEbbT9O0lGeX1x1CLC3PVLjJCnc8ewEhVR
Autophagy
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Maintains metabolic homeostasis under stress
Purpose is to recycle molecules such as amino acids and other
constituents to increase energy efficiency by reusing materials
Also used as damage control to remove non-functioning
proteins,organelles and genomic damage that can lead to diseases
such as cancer
Lysosome-dependent process that degrades cargoes from molecules
to organelles
Autophagy mechanism
Role in cancer therapeutics
https://swedishgarden.files.wordpress.com/2011/12/rebel-double-edgedsword1.jpg
● When induced, can play both prodeath and prosurvival role which can
either:
○ Contribute to anticancer efficacy of chemotherapy (contribute to death when apoptotic
machinery is defective)
○ Contribute to drug resistance of chemotherapy
● Dependent on cancer type, stress signals, mutations, and genetic alterations
● Anti-tumor prior to tumorigenesis; promotes tumor once established
● Protect tumors that are dormant from chemotherapy → leads to relapse
● Most cancer models try to inhibit rather than induce autophagy
Inhibitors of Autophagy
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Chloroquine (CQ) and its derivative hydroxychloroquine (HCQ) inhibits
autophagy by blocking autophagosome fusion and degradation
When CQ/HCQ is used in conjunction with antineoplastic agents, it increases
tumor cell killing
Pretreating cancer cells with HCQ then adding chemotherapeutic drugs
overcame chemotherapeutic resistance
Chloroquine
http://content.answcdn.com/main/content/img/oxford/oxfordBiochemistry/0198529171.chloroquine.
1.jpg
Hydroxychloroquine
http://quod.lib.umich.edu/cgi/i/image/api/image/medchem1ic:287:HYDROXYCHLOROQUINE.TIF/full/512,250/0/nati
ve.jpg
Challenges of chemotherapy & future directions
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Chemotherapy resistance
Too toxic, intolerable
Goals
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Targeting multiple pathways to overcome resistance
Develop less toxic chemotherapeutics
Management of side effects/coping
Keep tumors from going into dormancy → prevents relapse
Summary
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Two types of programmed cell death: apoptosis (intrinsic + extrinsic) and autophagy -> dysfunctional
regulation can lead to cancer.
The intrinsic apoptotic pathway is regulated primarily by p53, the Bcl-2 family of proteins (pro and
antiapoptotic), and IAPs. P53 induces an increase in Bcl-2-mediated mitochondrial outer membrane
permeability resulting in effector caspase activation.
The extrinsic pathway involves the binding of a tumor necrosis factor ligand onto a TNF-receptor on
the surface of the cell membrane. This initiates formation of the death-induced signalling complex
(DISC) and the activation of caspases, which can induce apoptosis. Bortezomib prevents the
breakdown of p53, improves death-receptor expression, and improves DISC formation.
Chemotherapeutics like phenoxodiol can target both the intrinsic and extrinsic pathways
Chemotherapeutics like atezolizumab can increase T-cell activity to increase induction of apoptosis
in cancer cells
Autophagy has both prosurvival and prodeath mechanism
In cancer therapeutics, autophagy is a tumor suppressor prior to tumorigenesis, and plays a role in
chemotherapy resistance in established tumors
References
Aguero MF, Venero M, Brown DM, Smulson ME, Espinoza LA. Phenoxodiol inhibits growth of metastatic prostate cancer cells. The Prostate. 2010;70(11):12111221. doi:10.1002/pros.21156.
Ashkenazi A. Directing cancer cells to self-destruct with pro-apoptotic receptor agonists. Nature Reviews Drug Discovery. 2008;7(12):1001-1012.
doi:10.1038/nrd2637
Bortezomib - DrugBank. Bortezomib - DrugBank. https://www.drugbank.ca/drugs/DB00188. Accessed November 20, 2016.
FDA Approved Drugs for Oncology. FDA Approved Drugs in Oncology | CenterWatch. https://www.centerwatch.com/drug-information/fda-approveddrugs/therapeutic-area/12/oncology. Accessed November 15, 2016.
Glick D, Barth S, Macleod KF. Autophagy: cellular and molecular mechanisms. The Journal of Pathology. 2010;221(1):3-12. doi:10.1002/path.2697.
Kamsteeg M, Rutherford T, Sapi E, et al. Phenoxodiol – an isoflavone analog – induces apoptosis in chemoresistant ovarian cancer cells. Oncogene.
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Mowers EE, Sharifi MN, Macleod KF. Autophagy in cancer metastasis. Oncogene. September 2016. doi:10.1038/onc.2016.333.
Nigata S. Fas Ligand-Induced Apoptosis. Fas Ligand-Induced Apoptosis - Annual Review of Genetics, 33(1):29.
http://www.annualreviews.org/doi/abs/10.1146/annurev.genet.33.1.29. Published December 1999. Accessed November 16, 2016.
References
Ozpolat B, Benbrook D. Targeting autophagy in cancer management – strategies and developments. Cancer Management and Research. September 2015:291.
doi:10.2147/cmar.s34859.
Rebecca VW, Amaravadi RK. Emerging strategies to effectively target autophagy in cancer. Oncogene. 2015;35(1):1-11. doi:10.1038/onc.2015.99.
Reyjal J, Cormier K, Turcotte S. Autophagy and Cell Death to Target Cancer Cells: Exploiting Synthetic Lethality as Cancer Therapies. Advances in Experimental
Medicine and Biology Tumor Microenvironment and Cellular Stress. October 2013:167-188. doi:10.1007/978-1-4614-5915-6_8.
Tecentriq (atezolizumab). Tecentriq New FDA Drug Approval | CenterWatch. https://www.centerwatch.com/drug-information/fda-approveddrugs/drug/100149/tecentriq-atezolizumab. Published May 2016. Accessed November 16, 2016.
Sayers TJ. Targeting the extrinsic apoptosis signaling pathway for cancer therapy. National Center for Biotechnology Information.
https://www.ncbi.nlm.nih.gov/pubmed/21626033. Published April 6, 2011. Accessed November 22, 2016
Sui X, Chen R, Wang Z, et al. Autophagy and chemotherapy resistance: a promising therapeutic target for cancer treatment. Cell Death and Disease. 2013;4(10).
doi:10.1038/cddis.2013.350.
Venetoclax. http://reference.medscape.com/drug/venclexta-venetoclax-1000078#10. Accessed November 15, 2016.
Zong W-X, Ricci SM. Chemotherapeutic Approaches for Targeting Cell Death Pathways. Oncologist. 2011;11(4):342-357. doi:10.1634/theoncologist.11-4-342.
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