EXAM #2: ANTINEOPLASTIC AGENTS Flashcards
What are the three major cell cycle checkpoints?
G1/S
G2/M
Metaphase/Anaphase
What are the specific criteria necessary to proceed through the G1/S checkpoint?
1) Cell nutrition, size, and environment must be favorable for replication
2) DNA must be intact
This check ensures the cell is prepared for DNA replication and to enter S-phase.
What are the specific criteria necessary to proceed through the G2/M checkpoint?
DNA must be completely replicated
This is the checkpoint that ensures the cell is ready to enter mitosis.
What are the specific criteria necessary to proceed through the metaphase/anaphase checkpoint?
1) DNA intact must be intact
2) Chromosomes must be attached to the mitotic spindle
This check ensure that the cell is ready for chromatid separation and is prepared for cytokinesis.
What are the three mechanisms of oncogene formation?
First, an oncogene is a mutated form of a normal gene that supported cellular proliferation i.e. “proto-oncogenes”
1) Point mutations
2) Chromosomal translocation
3) Proto-oncogene duplication/ amplification
How can point mutations lead to the development of an oncogene?
- Change in an amino acid regulatory region in the proto-oncogene product
- Amino acid change that makes the proto-oncogene resistant to degradation
How do chromosomal translocations result in oncogenes? Give an example.
Chromosomal translocation that causes the fusion of two genes, the product of which is the “fusion gene”
E.g. “Philadelphia” chromosome (9 x 22) ABL and BCR in CML
What is a major oncogene that is found in roughly 30% of all cancers?
Ras
Ras in involved in cell signaling/ GPCR signaling; mutations leave Ras permanently turned on.
Define first order killing of cancer cells i.e. what is the cell kill hypothesis?
This is the chemotheraputic elimination of a FIXED percentage of cancer cells.
This is first order kinetics*
What are the four goals of cancer drug therapy?
1) Curative intent
2) Adjuvant therapy
3) Neoadjuvant therapy
4) Palliation
List the general characteristics of chemotheraputic drug therapy.
- Drugs are cytotoxic and only PARTIALLY selective
- Low TI
Thus, adverse effects are common.
What are the general mechanisms of resistance to chemotherapeutic agents?
1) Genetic instability
2) Drug efflux pumps/ mutated drug transporters
3) DNA damage repair
4) Cell death inhibition
5) Drug inactivation
- Up-regulation of enzymes that metabolize drugs
6) Drug target alteration
7) Epithelial-Mesenchymal Transition
What types of tumors are easiest to treat with chemotherapy?
Tumors that are RAPIDLY growing
Define curative intent.
Drug therapy is intended to CURE the disease
Define adjuvant therapy.
- Drug given AFTER primary treatment e.g. surgery
- Prevent recurrence
Define neoadjuvant therapy.
Drug given FIRST to SHRINK tumor, making it amenable to surgery
Define palliative therapy.
Therapy intended to relieve symptoms and improve quality of life.
Do most cancers follow the cell-kill hypothesis? Why or why not?
NO
B/c of the cytotoxicity of chemotherapeutic, it is not possible to dose patients in a manner necessary to achieve 1st order kill.
What is a drug efflux pump?
A cellular transporter than “pumps” drugs out
E.g. MDR-2
What is Epithelial- Mesenchymal Transition (EMT)?
- Cell loses adhesive properties and becomes motile
- Changes can also cause drug resistance
What are the three general cytotoxic mechanisms to kill cancer cells?
1) Perturb normal DNA replication
2) Perturb mitosis
3) Starve cells of amino acids
What are the three targeted mechanisms to kill cancer cells?
1) Perturb hormone and growth factor signaling
2) Inhibit blood supply to tumor e.g. VEGF
3) Target activating proteins
What are cell-cycle non-specific drugs?
DNA alkylating agents that kill cells in ANY stage
Preferentially kill replicating cells
What are the S-phase specific drugs?
DNA synthesis inhibitors
What is the mechanism of action of the “antimetabolites?”
Inhibiting de novo nucleotide biosynthesis and generally target cells in S-phase
What is the function of ribonucleotide reductase?
Turning ribonucleotides into deoxyribnucleotides
What is the mechanism of action of methotrexate?
- Anti-metabolite that targets s-phase
- Inhibition of dihydrofolate reductase i.e. the enyzme that makes THF from dihydrofolate
- THF is crucial in the action of thymidylate synthetase (dUMP–>dTMP), which is required for DNA synthesis
Essentially, inhibiting DNA synthesis by preventing the action of folate
Why can extremely high does of Methotrexate be administered to pateints?
Leucovorin rescue (folinic acid)
Leucovorin is a reduced form of folic acid. Administration within the proper window can allow for nearly fatal doses of methotrexate do be administered (hopefully targeting cancerous/ rapidly dividing cell), followed by Leucovorin rescue to prevent harmful toxic effects of such a high dose to normal tissue.
What are the mechanisms of Methotrexate resistance?
1) Impaired transport
2) Altered DHFR (isozyme) that decrease the affinity of methotrexate’s target
3) Elevated DHFR expression
DHFR= dihydrofolate reductase
What are the unique toxicities seen with Methotrexate?
- Interstitial pneumonitis
- Nephrotoxicity
What is the mechanism of action of 5-fluorouracil?
- Pyrimidine analog
- Anti-metabolite that targets s-phase
- 5-FU is metabolized:
1) 5dUMP, which INHIBITS THYMIDYLATE SYNTHASE and prevents DNA synthesis
2) FUTP that is falsely incorporated into RNA
3) FdUTP that is falsely incorporated into DNA
False incorporation causes defects in RNA/DNA function and sturucture leading to cell death.*
What are the unique adverse effects seen with 5-FU administration?
Oral and GI ulcers
What is Capecitabine?
- Antimetabolite
- Targets S-phase
This Prodrug of 5-FU that can be given orally; same mechanism of action as 5-FU (inhibition of thymidylate synthase etc.
What is Cytarabine used to treat?
This is the most important antimetabolite for AML
It is only used to treat HEMATOLOGIC MALIGNANCIES*
What is the mechanism of action of Cytarabine?
- Pyrimidine analog/ anti-metabolite
- Targets cells in S-phase
1) Cytarabine or Ara-C is transported into the cell and converted to Ara-CMP by DEOXYCYTIDINE KINASE
2) Ara-CMP is converted to Ara-dCTP
3) Ara-dCTP is incorporated into DNA and inhibits DNA synthesis
What is the specific toxicity that is associated with Cytarabine?
Cerebellar Syndrome
*****Note that inactivation of Ara-C required CYTIDINE DEAMINASE; there are low levels of this enzyme in the brain, making brain more susceptible to adverse effects of drug.
What are the symptoms of Cerebellar Syndrome?
1) Dysarthria
2) Nystagumus
3) Ataxia
What are the major mechanisms of cytarabine resistance?
1) Loss of DEOXYCYTIDINE KINASE
2) Inability of tumor cells to transport Ara-C into cells
3) Cytidine demainase upregulation
What is the mechanism of action of Gemcitabine?
- Pyrimidine analog/ anti-metabolite that targets S-phase
1) Converted to active form by DEOXYCYTIDINE KINASE, like Cytarabine
1) Incorporated into DNA–inhibits DNA synthesis
3) Inhibits RIBONUCLEOTIDE REDUCTASE, which also inhibits DNA synthesis
What are the mechanisms of Gemcitabine resistance?
1) Reduced activity of DEOXYCYTIDINE KINASE
2) Increased production of deoxycytidine b/c of inhibitive effect on deoxycytidine kinase
What is the mechanism of action of 6-MP and 6-TG?
- Purine analogs/ antimetabolites that inhibit s-phase of the cell cycle
1) Activated by HGPRT into thio-IMP and thio-GMP respectively
2) thio-IMP converted into thio-GMP
3) thio-GMP blocks BOTH SALVAGE and DE NOVO purine synthesis i.e. inhibits DNA replication
What is the common mechanism of resistance in 6-MP and 6-TG?
Decreased HGPRT activity
What enzymes inactivates 6-MP? Why is this important?
Thiopurine methyltransferase (TPMT)
Polymorphism causes reduced TPMT activity that can lead to life-threatening toxicity and need for lower doses
What is the mechanism of action of Fludarabine?
- Purine analog/ antimetabolite that targets cells in s-phase
1) Activated by DEOXYCYTIDINE KINASE and incorporated into DNA and RNA
2) Inhibits RIBONUCLEOTIDE REDUCTASE and DNA POLYMERASE
3 Inhibits RNA function and mRNA translation
What is the common mechanism of Fludarabine resistance?
Decreased of DEOXYCYTIDINE KINASE