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