Neoplasia Part 3 Flashcards
what is a major etiology of cancers?
Carcinogens
Cancer results from accumulation of ______ including genes that regulate apoptosis and senescence
multiple mutations
what are 3 types of Carcinogenic Agents?
-Chemicals
-Radiant energy
-Microbial agents
T/F the different types of Carcinogenic Agents may act together or alone to elicit genetic alterations leading to neoplasia
true
what are the 3 groups of carcinogenic chemicals?
-direct acting
-indirect acting
-natural products
what occurs with direct acting carcinogenic chemicals?
No metabolic conversion to be
carcinogenic
what is an example of direct acting carcinogenic chemicals?
Chemotherapeutic drugs (alkylating agents- cyclophosphamide)
what occurs with indirect acting carcinogenic chemicals?
Require metabolic conversion to ultimate carcinogen by cytochrome p-450 enzymes (which are unique among individuals)
what are two examples of indirect acting carcinogenic chemicals?
-Polycyclic hydrocarbons: benzo[a]pyrene in smoked tobacco, smoked fish/meat
-Aromatic amines and azo dyes: β naphthylamine –> bladder cancer in aniline dye and rubber industry
what are some Natural Products that act as carcinogenic chemicals? (2)
-Aflatoxin B1: produced by Aspergillus on improperly stored grains/nuts→ hepatocellular CA
-Nitrites: preservatives-form nitrosamines
what is the Mechanism of Action for carcinogenic chemicals?
Chemical carcinogens are mutagenic (initiators):
- Contain highly reactive electrophile groups, which form adducts (covalently bound) with
nucleophiles (principally DNA)
- In subsequent transcription or DNA replication, if the adduct is not repaired, it predisposes to mutations, strand breaks etc.
what genes are common targets for the adduct formation that occurs with carcinogenic chemicals? (2)
-Oncogenes (RAS)
-tumor suppressor genes (p53)
T/F DNA adduct formation alone is sufficient for the carcinogenesis process to proceed.
FALSE (it is not, just an initiating event)
how do Promoters correlated with tumors?
-Do not cause mutations (not initiators), so alone are not tumorigenic
-INSTEAD: Induce cell proliferation of mutated cells → new mutations that can lead to cancer formation
what are examples of chemicals that are Promoters of cancer formation (not initiators)? (2)
-phorbol esters: used in cancer research
-estrogen: promoter in patients with breast and endometrial cancer
how does radiation cause cancer? (2)
-Causes double-stranded DNA breaks, translocations, point
mutations
-UV radiation forms pyrimidine dimers (thymine-thymine) which
normally are fixed by nucleotide excision repair pathways
what is the only RNA/retrovirus that can cause cancer in humans?
Human T-cell leukemia virus-1 (HTLV-1)
what are 4 DNA viruses that can cause cancer in humans?
-Human papilloma virus (HPV)
-Epstein-Barr virus (EBV)
-Kaposi sarcoma herpesvirus (HHV-8)
-Hepatitis B virus (HBV)
where is HTLV-1 endemic?
Japan and Caribbean
how does HTLV-1 cause cancer?
CD4+ T cell tropism
How is HTLV-1 transmitted?
through intercourse, blood and breast milk
what cancer is associated with HTLV-1?
leukemia (3-5% after long latency)
what protein in HTLV-1 drives cancer formation?
Tax protein
there are >150 types of HPV. how are the different types categorized?
-low-risk (e.g. 6,11)
-high risk (e.g. 16,18,31,33)
what can low-risk HPV (e.g. 6,11) cause?
-squamous papillomas
-genital warts, condyloma acuminatum
what can high risk HPV (e.g. 16,18,31,33) cause?
-cervical/anogenital cancer
-associated with ~70% of oropharyngeal cancers*
what are the 2 different proteins of HPV oncogenesis?
-Early viral protein E7
-Early viral protein E6
how does Early viral protein E7 work in HPV oncogenesis? (3)
-Binds RB protein and displaces E2F, promoting progression
-Inactivates CDKIs
-Activates cyclins
how does Early viral protein E6 work in HPV oncogenesis? (2)
-Binds and mediates degradation of p53 and BAX (pro-apoptotic factor)
-Activates telomerase
summarize what happens during HPV oncogenesis?
E6 and E7 activate growth, stimulate loss of growth inhibition, inhibit apoptosis, and combat senescence
what cancers is EBV implicated in? (4)
-Burkitt lymphoma (African type)
-B-cell lymphoma in
immunosuppressed pts
Hepatitis B and C and associated with 75-80% of what cancers?
hepatocellular carcinomas
describe how the HBV Pathogenesis that can lead to cancer (2)
-Chronic inflammation with hepatocyte death
→ regeneration and genomic damage
-Activated immune cells make ROS (mutagenic) → NF-κB pathway activation which blocks apoptosis and allows accumulation of mutations (no viral oncoproteins)