Exam 3 Flashcards
Cancer is:
• a disease of uncontrolled cell proliferation
• the accumulation of mutations that activate proto-oncogenes and inactivate tumor suppressor genes
• cell growth becomes uncoupled from the hormonal and metabolic conditions that normally maintain homeostasis
Colorectal cancer gene alterations
(normal epithelium) Loss of APC—> (hyper proliferative epithelium, early adenoma) activation of Ras—> (intermediate adenoma) loss of tumor suppressor gene—> (late adenoma) loss of p53 activity—> (carcinoma) additional alterations—> metastases
Which cancers have the fewest mutations, and are driven by only single changes typically?
• blood cancers
• pediatric cancers
Causes of DNA mutations:
• DNA replication errors, chromosome segregation errors
• chemical damage to DNA
• oxidative stress, pathological and physiological
• radiation
• virus infection
• infidelity in DNA repair
Proto-oncogenes normally function to:
Promote cell proliferation, and physiologically there expression an activity are tightly regulated
What are the types of mutations that convert proto-oncogenes to oncogenes?
• point mutation
• gene rearrangement
• gene amplification
Single base changes within a coding sequence leading to overactive enzymes, or enzymes with different substrates/products
- Phosphatidylinositol-4,5-bisphosphate-3-kinase (PI3K) activating mutations in breast cancer
- Isocitrate dehydrogenase (IDH2) mutations in glioblastoma
Example of mutations in promoters that cause hyperactive expression of genes
• telomerase (TERT) promoter activating mutations in urothelial cancer
The fusion of chromosomes 9 and 22
• chronic myelogenous leukemia
• Proto oncogene becoming activated through rearrangements of short DNA fragments or large pieces of chromosomes— more common in blood cancer
What gene is amplified in human breast cancer?
• Cyclin D1
• increases their copy number and expression amount
Tumor suppressor gene RB1
• retinoblastoma protein (Rb) encoded tumor suppressor gene
• it’s normal function is to bind and inactivate E2F transcription factors
• when myogenic signal increases cyclin D1, Rb is phosphorylated, and that releases E2F causing increased transcription of genes that promote DNA replication
For a tumor suppressor to become inactivated:
Both alleles must be lost
What is the most frequently mutated tumor suppressor in human cancers?
p53 encoded by TP53 gene
• it’s normal function is to respond to DNA damage by halting the replication fork, initiating DNA repair, arresting the cell cycle at G1-S checkpoint, and increasing apoptosis
Log kill model
• assumes that cancer cells have the same rate in proliferation at all stages of disease
• example: if a given drug can reduce cancer burden from 10^10 to 10^7, I can also reduce the cancer burden from 10^18 to 10^15, and so on
What does debulking the tumor do?
This is a surgical procedure before chemotherapy in order to lower the tumor burden and decrease the number of chemotherapy cycles required
Gompertzian growth model
• human tumors follow this rather than a logarithmic growth
• early stages of tumorigenesis: Cancer cell proliferation is limited by the ability of the vasculature and supply of oxygen/nutrients
• later stage of tumorigenesis: Cancer cell proliferation is limited by the accumulation of lethal mutations
• the cell cycle is most active right in the middle, during the angiogenic switch
G1 phase:
• a checkpoint, in which signals from the extracellular environment, are integrated into a decision whether to proliferate or not (40% of time)
S phase
• when genomic DNA is duplicated (DNA synthesis) (39% of time)
G2 phase
• a checkpoint in which the integrity of DNA replication is assessed
• synthesis of cellular components for mitosis (19% of time)
M phase
• mitosis, in which replicated, chromosomes, segregate, and the cell divides into two daughter cells (2% of time)
G0 phase
• Quiescent, or non-replicative state
• metabolism still occurs, but replication and division is not active
Cell cycle specific drugs
• cytotoxic chemotherapy drugs. Their target only exists for a discreet period In the cell cycle.
• Taxane/paclitaxel
• 5-fluorouracil
Taxane/paclitaxel
Cell cycle specific drug that stabilizes mitotic spindles in the M phase, preventing division into two daughter cells
5-fluorouracil
Cell cycle specific chemotherapy that inhibits thymidine synthase, an enzyme expressed during S phase