Viruses + Cancer
6 viruses responsible for 20% of all cancers
- HBV - HCV - HPV - EBV - KSV - HTLV-1 and HTLV-2
Human RNA Tumor viruses -- HCC -- HBV
- Hepatitis B virus (HBV) - infects hepatocytes - pleiotropic viral oncoprotein: - X protein - dysregulate cell cycle
Viruses that cause Human cancers:
- Human T-cell Leukemia Type-1 (HTLV-1 and HTLV-2) - Hepatitis C virus (HCV) - Hepatitis B virus (HBV) - Epstein Barr virus (EBV) - Kaposi's sarcoma-associated herpesvirus (KSHV) - Human Papillomavirus (HPV)
Integration of proviral DNA into host genome can result in:
- Insertional activation of expression of a c-onc when viral promoters or enhancers cause abnormal expression of unaltered c-onc - Insertional inactivation of cellular tumor suppression gene - Integration of a v-onc into host genome. V-onc may activate + transcribe oncogene product
Human DNA Tumor viruses -- Kaposi's Sarcoma
- KSHV, HHV-8 - infects B-cells - has over 90 ORFs - viral oncoproteins: - K1, vFLIP (NFkB), LANA - dysregulate cell cycle
Viruses that cause Animal cancers:
- Rous Sarcoma virus (RSV) - Feline Leukemia virus (FeLV) - Adenoviruses - Simian vacuoalting virus-40 (SV-40) - Jamestown Canyon virus (JCV) and BK virus (BKV)
Cancer Therapy
- Surgery - Radiation - Chemotherapy - Immunotherapy - Virotherapy
Designing Oncolytic Viruses
- Targeting transcription - Targeting Attachment - Exploiting IFN Defects in Cancer cells - Targeting Cellular Apoptosis
Why are adenoviruses good candidates for Gene therapy?
- b/c of mild to non-disease in humans
Causes of cancer
- carcinogens: tobacco, asbestos, or radiation 80% - viruses: human cancers, 20%
Main categories of cancer
- carcinoma - sarcoma - leukemia - lymphoma + myeloma
Techniques (assays) to determine whether or not viruses can transform cells in culture:
- focus-forming assays - soft agarose assays - reduced serum requirement
Oncogenes vs. Tumor Suppressor genes
- oncogenes result from ACTIVATION of proto-oncogenes - tumor suppressor genes cause cancer when they are INACTIVATED (turned off)
Killing Tumor with Viruses (cancer cells)
- oncolytic virus infects cancer cell - oncolytic virus able to replicate in cancer cells - cancer cells rupture to release progeny virus, which then infect nearby cancer cells to amplify the effect
Killing Tumor with Viruses (normal cells)
- oncolytic virus infects normal cell - virus inactivated or unable to replicate - no viral replication leads to healthy cells remaining unchanged
Anti-Oncogenes
- p53 gene - Retinobalastoma
Human DNA Tumor viruses -- Burkitt's Lymphoma
Epstein-Barr virus (EBV) [Human Herpes virus 4 - HHV-4] - infects B cells - pleiotropic viral oncoproteins: - EBNA-2 (c-myc) + EBNA-3C (Rb), LMP-2 - dysregulate cell cycle
Human RNA Tumor viruses -- HCC -- HCV
Hepatitis C virus (HCV) - infects hepatocytes + B cells - viral oncoprotein: - Core protein (nucleocapsid) - dysregulate cell cycle
Human DNA Tumor viruses -- Genital Warts -- HPV
Human papilloma virus (HPV) - infects epithelial cells - episome - viral oncoproteins: - E6/E7: bind Rb + p53 - dysregulate cell cycle/apoptosis
Animal DNA Tumor viruses -- Merkel Cell Carcinoma -- More Polyomaviruses
Jamestown Canyon virus (JCV), BK virus (BKV) - cause tumors in animals + 5% of AIDS patients - Merkel cell polyomavirus (MCPyV) - viral oncoprotein: - Small T antigen (PP2A)
Animal DNA Tumor viruses -- Brain Tumors -- Simian vacuolating virus-40 (SV-40)
SV-40 - Polyomavirus - infected monkey kidney cells - found in poliovirus vaccine - Pleiotropic viral oncoprotein: - Large T antigen: binds Rb and p53 - dysregulates cell cycle/apoptosis
HTLV-1
Tax is the pleiotropic viral oncoprotein - Tax modulates expression of many viral + cellular genes - dysregulates cell cycle + apoptosis
Rb
a tumor suppressor gene
p53
a tumor suppressor gene
Unique regions (U)
all for virus to insert DNA copy into hosts DNA
Radiation
low doses of radiation use to treat tumor/cancer areas
Cellular oncogene
mutated form of proto-oncogene that cause tumors
Proto-oncogenes
normal cellular genes whose products participate in cellular growth-controlling pathways. Upon mutation, gene becomes permanently turned on.
Tumor-suppressor genes
normal genes that slow down cell division, repair DNA mistakes, + involved in apoptosis. When tumor suppressor genes don't work properly, cells can grow out of control, leading to cancer.
Insertion of viral oncogene
(expression leads to abnormal protein -- hyperactive -- leads to abnormal cell growth) - result is the same
Retrovirus genome
- 2 copies of RNA genome - 7-12 kb in length - 3 main genes: gag, pol, env - Flank with unique regions (U3 and U5) - some retroviruses have additional genes: v-onc (ex: src gene in RSV) - V-onc is usually hijacked from host genome. Usually capable of inducing transformation
Immunotherapy
induce immune system to recognize + eliminate malignant tumors
Oncolytic viruses cause cancer cells to die in 4 ways:
1. As a consequence of infecting + replicating in cancer cells 2. causing cancer cells to lyse 3. inducing apoptosis of cancer cells 4. stimulating host immune system
Multisteps of Cancer
1. Cells bypass apoptosis 2. cells circumvent need for growth signals 3. cells escape immunosurveillance 4. cells (tumors) command their own blood supply 5. cells may metastasize 6. tumor suppressor genes lose function
Characteristics of cells in vivo:
1. Increase in oncogene proteins expression 2. Cells lose tumor suppression gene function 3. DNA methylation patterns altered 4. Cells divide uncontrollably 5. Increased levels of enzymes 6. Telomerase activity is reactivated 7. Avoid host immune system
Cellular targeting by genetically engineered oncolytic viruses
1. Transcription 2. Attachment 3. Cancer cell interferon defects 4. Apoptotic pathways
Transformed cells in vitro:
1. increase in # and size of nuclei 2. become immortalized 3. divide + grow rapidly 4. lack of contact of inhibition 5. anchorage-independent 6. grows independently 7. loss of cell cycle control 8. change sin membrane function + structure
Killing Tumor with Viruses (things to consider when selecting oncoolytic virus for cancer treatment)
1. not a pathogen to humans 2. no side effects 3. can be genetically manipulated 4. replicates + lyses cancer cells quickly 5. can be administered systemically 6. can eradicate tumor, leading to immunity 7. does not enter cell nucleus or recombine with host nucleic acids 8. has specificity for only tumor cells 8. is susceptible to antiviral drugs (safety) 9. virus is well characterized 10. oncolytic mechanism well characterized
Animal DNA Tumor viruses -- Tumors -- Adenovirus
Adenovirus - infects nearly all hamster cells - viral oncoproteins: - E1A/E1B: bind Rb + p53 - dysregulate cell cycle/apoptosis
Complex Retroviruses
Adult T-cell Leukemia (ATL) - HTLV-1
Oncogene
Bad gene. cells can grow out of control, which can lead to cancer.
What is cancer?
cancer cells can spread to other parts of the body through blood + lymph systems
Sarcoma
cancer that begins in bone, cartilage, fat, muscle, blood vessels, or other connective or supportive tissue. Example: Kaposi's Sarcoma (KSV)
Carcinoma
cancer that begins in skin or in tissues that line or cover internal organs exmaples: hepatocarcinoma, ovarian carinoma
Leukemia
cancer that starts in blood-forming tissue such as the BM and increase of abnormal blood cells to be produced and enter the blood. Examples: Adult T-cell leukemia (ATL) and HTVL-1 associated myelopathy (HAM).
Lymphoma + Myeloma
cancers that begin in the cells of the immune system. Example: Lymphoma (EBV)
Reduced serum requirement
certain transformed cells may grow in medium containing reduced serum or growth factors
Chemotherapy
chemical agent to selectively kill cancerous cells. many side effects
Env
codes for envelope proteins such as spikes
Pol gene
codes for reverse transcriptase
Gaga gene
encodes for matrix + core proteins
Virotherapy
experimental form of cancer therapy in which viruses are sued to target + destroy cancer cells without harming healthy cells
Viral oncogene
gene responsible for oncogenicity of a virus. v-onc in RNA - tumor inducing viruses altered cellular genes acquired via recombination with host genome
Surgery
if tumor quickly diagnosed + easily accessible for removal, patient had higher likelihood of surviving
in vitro vs. in vivo
in vitro = takes place outside organism, in petri dish or tube in vivo = takes place inside organism
Focus-forming assays
transformed cells lose contact of inhibition and form densely packed cells piling up on top of each other (foci) instead of a monolayer
Soft agarose assays
transformed cells will be able to divide and form free colonies when suspended in a methyl cellulose or agarose medium. Normal cells do not proliferate in soft agarose
Simple Retroviruses
viral integration, in or near a c-onc
Insertion of viral promoter
viral promoter with proto-oncogene cause escessive expression, through mRNA lead to protein product then to abnormal cell growth. - oncogene is highly expressed, make a lot of protein
