Term
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Definition
in a phase (G1, S, G2, or M) preparing for or part of cell division
G0 is not part of the cell cycle (the cell is not preparing for cell division or in the process of cell division)
[image]
M phase starts after G2 (4N) and ends before G1 (2N) phase
M phase includes the 5 stages of nuclear division (mitosis) as well as cytoplasmic division (cytokinesis)
the cell cycle consists of 4 distinct phases:
G1: preparing for S phase; the cell is producing proteins and enzymes that are needed during DNA replication
S phase - the cell is duplicating chromosomes by action of DNA polymerase and other enzymes
G2: the cell, with duplicated chromosomes (4N), prepares for mitosis
M phase: consists of mitosis (separation of chromosome pairs, division of nucleus) and cytokinesis (division of cell cytoplasm); after M phase the cell may go directly into G1 or enter G0
G0: cells are not in or preparing for mitosis, cytokinesis or DNA synthesis; the cells in G0 are called quiescent; time in G0 depends on the cell type
M phase = mitosis and cytokinesis
dynamic instability required
microtubule inhibitors stop cell cycle in mitosis (metaphase arrest)
the M phase includes both mitosis (separation of duplicated chromosomes) and cytokinesis (division of cell cyclplasm)
mitosis occurs before cytokinesis
drugs that bind microtubules (vinca alkaloids, taxanes, epothilones) act in M phase (specifically mitosis)
in the presence of these drugs the cell arrests in mitosis (often in metaphase)
dynamic instability of microtubules is required for search and capture of duplicated chromosomes
microtubule motors then move chromosomes into daughter cell compartments |
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Term
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Definition
segregation of duplicate chromosomes into daughter cells
during mitosis the cell condenses the duplicated chromosomes and then separates the duplicated chromosomes into the 2 compartments that will become the daughter cells
mitosis is not synonymous with M phase
mitosis is part of M phase |
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Term
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Definition
part of mitosis when chromosomes are aligned between daughter cells
before separation by microtubule-mediated transport
microtubule inhibitors often cause cell cycle arrest in metaphase |
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Term
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Definition
| includes both mitosis (nuclear division) and cytoplasmic division (cytokinesis) |
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Term
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Definition
relaxes (unwinds) DNA and prevents DNA knotting
these are enzymes that are especially important during the last half of S phase
opening of the helix (during replication) causes tighter winding of DNA (topoisomerases unwind/relax DNA helix during replication)
also during end of S phase 2 DNA helices may become tangle/knotted (topoisomerases untangle DNA helices)
these enzymes regulate DNA topology |
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Term
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Definition
essential for mitosis and other cell processes
composed of polymerized protein dimers (one alpha and one beta subunit)
microtubules have many functions including intracellular transport, coordination of cell motility, and mitosis |
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Term
| dynamic instability of microtubules |
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Definition
alternating phases of growth and shortening
the plus ends of microtubules alternate between periods of growth (polymerization) and shortening (de-polymerization) in seemingly random fashion |
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Term
| action of natural products and antibiotics in the cell cycle |
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Definition
[image]
A. INHIBITORS OF MICROTUBULES
interfere with mitosis
act in M phase
B. ANTITUMOR ANTIBIOTICS
damage DNA mainly in G2
C. TOPOISOMERASE INHIBITORS
interfere with DNA unwinding, unknotting, and ligation (includes some antibiotics)
acts near S-G2 interface
some drugs have dual mechanisms |
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Term
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Definition
[image]
1) ENZYME BINDS DNA
the DNA double helix is twisted (wound), the topoisomerase enzyme binds
2) HELIX IS CUT AND FREE TO UNWIND (OTHER STRAND PASSES THROUGH CUT)
the enzyme cuts one of the DNA strands (tyrosine is the catalytic residue that hydrolyzes the phosphodiester bond)
the cut helix is free to unwind (one strand passes through cut) and relaxes
3) CUT IS LIGATED
FUNCTION IS TO RELAX HELIX DURING REPLICATION AND TRANSCRIPTION |
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Term
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Definition
[image]
1) ENZYME BINDS HELIX B
2) BOTH STRANDS IN HELIX B ARE CUT AND HELIX A PASSES THROUGH CUT
3) CUTS IN HELIX B ARE LIGATED
FUNCTION IS TO UNTANGLE AND UNLINK 2 DNA HELICES |
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Term
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Definition
certain anti cancer drugs (vinca alkaloids, taxanes, epothilones) bind microtubules resulting in terference with mitosis
dividing cell:
chromosomes are separated by a microtubule-dependent transport mechanism
cytokinesis occurs through a contractile ring formed by actin
before the chromosomes can be segregated, microtubules must caprues the chromosomes (dynamic instability is essential)
microtubule polymerization:
[image]
microtubules grow (requiring GTP hydrolysis) through addition of heterodimers (alpha-tubulin + beta-tubulin)
the plus end (+) is where tubulin heterodimers are added
drugs that bind microtubules cause depolymerization or polymerization which interferes with the process of mitosis (interferes with dynamic instability
[image]
vinca alkaloids and taxanes bind at different sites:
vinca alkaloids bind the beta subunit (sitve V) near the GTP binding site and cause microtubule shortening (depolymerization)
taxanes and epothilones bind at a different area of the beta subunit (site T) and cuase microtubule to grow (polymerization)
these effects on microtubule polymerization interfere with mitosis |
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Term
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Definition
vinca alkaloids: vinblastin, vincristine, vinorelbine
taxanes: paclitaxel, docetaxel
epothilones: ixabepilone
eribulin mesylate |
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Term
| vinblastine, vincristine, and vinorelbine |
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Definition
vinca alkaloids
mechanism:
1) BIND TO BETA SUBUNIT OF TUBULIN HETERODIMER
near the GTP binding site
2) MICROTUBULE DEPOLYMERIZATION
these drugs cause shortening (depolymerization) of microtubules
low concentrations can stabilize microtubule polymer
3) METAPHASE DISRUPTED, NO CHROMOSOME ALIGNMENT
the cell cycle disrupted in mitosis, particularly in metaphase
duplicated chromosomes cannot align properly at division plane
drug resistance:
EFFLUX TRANSPORT (P-GLYCOPROTEIN)
cancer cells may transport drug to extracellular space via p-glycoprotein and other members of MDRP (multi drug resistance protein) family
TUBULIN MUTATION
mutations in the beta subunit can decrease drug affinity
EFFECT OF VERAPAMIL:
verapamily increases sensitivity of drug resistance cancer cells to vinca alkaloids (once study found increased intracellular concentration of vinca alkaloid in presence of verapamil) |
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Term
| toxicity of vinca alkaloids: vinblastin, vincristine, and vinorelbine |
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Definition
NEUROTOXIC SYMPTOMS
an important function of microtubules is axon transport
there are motors that bind microtubules and carry cargo along the axon
these drugs also interfere with axon transport resulting in numbness and tingling of extremities, reduced tendon reflex, and motor weakness
LEUKOPENIA (NADIR 7-10 DAYS)
INAPPROPRIATE SECRETION OF ADH (RARE)
rarely hyponatremia may occur from increased production of ADH
other considerations:
intrathecal administration fatal |
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Term
| MOA of taxanes: paclitaxel and docetaxel |
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Definition
1) BIND BETA SUBUNIT OF TUBULIN DIMER
similar to vinca alkaloids taxanes bind to the beta subunit of tubulin, but at a different site
2) MICROTUBULE POLYMERIZATION (OPPOSITE OF VINCA ALKALOIDS)
3) CELLS ARREST IN MITOSIS
cancer cell arrest in mitosis (metaphase) and enter apoptosis |
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Term
| drug resistance to taxanes - paclitaxel and docetaxel |
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Definition
mechanism similar to vinca alkaloids (P-glycoprotein)
also, increased anti-apoptosis factors P53 INDEPENDENT
similar mechanism as vinca alkaloids with additional increased expression of factors that protect against cell apoptosis (resistant cell express survivin and aurora kinase that promote completion of mitosis)
these factors (survivin, aurora) where observed in cell line experiments treated with taxanes (clinical importance is uncertain)
taxane resistance independent of functional p53 |
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Term
| toxicity of taxanes - paclitaxel and docetaxel |
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Definition
NEUROPATHY (DOCETAXEL < PACLITAXEL)
peripheral neuropathy and asthenia (feeling of muscle weakness) is more severe with paclitaxel
NEUTROPENIA
with paclitaxel, neutropenia nadir usually occurs 8-11 days after a dose and then reverses by 15-21 days
usually docetaxel causes more severe, but shorter duration of neutropenia
other considerations:
LOW WATER SOLUBILITY and HYPERSENSITIVITY TO VEHICLE
low water solubility requires ethanol or castor oil vehicle for administration
ABRAXANE - advanced breast cancer
abraxane is a formulation of paclitaxel bound to albumin particles
albumin formulation does not require lipophilic vehicle
that that the nanoscale particles of abraxane exploit the enhance permeability and retention commonly found in tumors |
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Term
| MOA of epothilones - ixabepilone |
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Definition
indicated for breast cancer; indicated when taxanes are ineffective
1) BINDS NEAR TAXANE SITE
2) PROMOTES POLYMERIZATION
like taxanes, stabilizes microtubules (causes polymerization) |
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Term
| toxicity of epothilones - ixabepilone |
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Definition
peripheral neuropathy limits treatment
myelosuppression
LITTLE CROSS RESISTANCE WITH TAXANES |
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Term
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Definition
used for metastatic breast cancer
1) INTERFERES WITH MICROTUBULES POLYMERIZATION
2) BLOCKS MITOSIS |
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Term
| toxicity of eribulin mesylate |
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Definition
neutropenia
peripheral neuropathy
asthenia
QT interval prolongation |
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Term
| topoisomerase inhibitors and DNA damage |
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Definition
camptothecins: topotecan, irinotecan
antibiotics: caunorubicin, doxorubicin, epirubicin, idarubicin
epipodophyllotoxins: etoposide, teniposide |
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Term
| MOA of camptothecins: topotecan and irinotecan |
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Definition
1) BINDS TOPOISOMERASE I
topoisomerase I makes a cut in one strand of the DNA helix which allows the DNA to unwind (rotate) to relieve torsion stress
2) INHIBITS LIGATION OF DNA STRAND
after the stress if relieved the DNA strand is ligated (mended)
camptothecins bind topoisomerase I and prevent ligation
3) APOPTOSIS TRIGGERED IN S-G2 PHASE
during replication the DNA (at the point of the cut) becomes completely broken (double strand break)
the cells with double strand breaks enter apoptosis in S phase
[image]
the "winding problem" that arises during DNA replication
during DNA replication strands of the helix must be separated as illustrated above
the separation of strands causes winding of the helix as indicated by the broad circular arrow
the winding must be relieved by topoisomerase I
the enzyme cuts a single strand and relieves winding
broad white arrow indicates movement of DNA polymerase toward replication fork
camptothecins prevent ligation and consequently cause breakage of both strands of DNA as replication fork approaches the single cut |
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Term
| resistance to camptothecins - topotecan and irinotecan |
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Definition
DRUG EFFLUX
drug may be removed from the tumor cell (via P-glycoprotein or multi drug resistance transporters)
DRUG TARGET MUTATION
mutations in topoisomerase may arise |
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Term
| toxicity of camptothecins - topotecan and irinotecan |
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Definition
NEUTROPENIA (TOPOTECAN > IRINOTECAN)
primary concern
SEVERE DIARRHEA (EARLY AND LATE; IRINOTECAN > TOPOTECAN)
in patients with hematological malignancies diarrhea may be dose limiting
early and late diarrhea occur by different mechanisms
severe diarrhea may limit treatment with irinotecan
other considerations:
irinotecan is a prodrug - converted to SN-38 (active) primarily by carboxylesterases in the liver; SN-38 inhibits topoisomerase I with much higher potency compared to parent drug; SN-38 is inactivated by glucuronidation by uridine glucuronosyltransferases (UGTs); polymorphisms of these enzymes (for example Gilbert's syndrome, autosomal dominant inheritance) are associated with less glucuronidation and more GI epithelial toxicity (diarrhea); UGTs also conjugate bilirubin
a correlation exists between basline unconjugated bilirubin and irinotecan toxicity
irinotecan (parent form) has some acetylcholinesterase inhibition activity
metabolism and toxicity of irinotecan:
[image]
severe diarrhea is a common side effect of irinotecan (neutropenia is also a major concern):
1) irinotecan is converted to sN-38 by action of hepatic carboxylesterase; SN-38 is toxic to blood cells and epithelial cells
2) SN-38 is conjugated with glucuronic acid catalyzed by the enzyme uridine diphosphate glucuronosyltransferase (UGT) to inactive SN-38G; sequence polymorphisms in UGT determine severity of diarrhea
3) polymorphisms in genes for UGT resulting in lower catalytic activity (Gilbert's syndrome which occurs in about 10% of general population) are associated with increased toxicity (higher SN-38 concentration toxic to blood cells and GI epithelium)
4) SN-38G can be excreted in feces or converted back to SN-38 by bacterial glucuronidase
accumulation of SN-38 in intestinal epithelial cells
[image]
routes of SN-38 entry into GI epithelial cells occur from both apical side and the basolateral side
apical exposure of SN-38 is generated from cleavage of SN-38 glucuronide (SN-38G) by bacterial beta-glucuronidase
transport of SN-38 into epithelial cells occurs by passive diffusion (indicated by the dashed arrows) and active transport processes
efflux of unconjugated and conjugated SN-38 into the lumen and blood occurs through P-glycoprotein, MRP2 and MRP1
any reduction in glucuronidation (Gilbert's syndrome or other gene polymorphisms) will lead to an accumulation of unconjugated (toxic) SN-38
conjugation of SN-38 in liver is also important |
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Term
| MOA of anthracycline antibiotics - daunorubicin, doxorubicin, epirubicin, and idarubicin |
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Definition
the antracycline antibiotics work through 3 main mechanisms that trigger apoptosis:
1) DNA INTERCALATION
these drugs can intercalate between base pair stacks causing disruption of replication and transcription
2) BINDS TOPOISOMERASE II AND INHIBITS LIGATION
topoisomerase II cuts both strands of the DNA helix and allows passage of another DNA helix through the cuts
a trimolecular (tripartite) complex is formed (drug-DNA-topoisomerase II) that interferes with DNA ligation step
3) FREE RADICAL GENERATION
the drug-DNA interaction generates hydroxyl radicals and hydrogen peroxide which can directly damage (oxidize) DNA bases |
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Term
| drug resistance to antracycline antibiotics - daunorubicin, doxorubicin, epirubicin, and idarubicin |
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Definition
| efflux, topoisomerase II mutation, increased DNA repair |
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Term
| toxicity of antracycline antibiotics - daunorubicin, doxorubicin, epirubicin, and idarubicin |
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Definition
myelosuppression
CARDIAC
drug bind ferrous Fe
hydrogen peroxide generates hydroxyl radical
cardiac myocyte damage -> heart failure
a serious concern with use of antracycline antibiotics is cardiotoxicity
these drugs bind to ferrous iron which can catalyze generation of hydroxyl radical from hydrogen peroxide
normally catalase will convert hydrogen peroxide to water and oxygen, but it is though that cardiac muscle has less catalase
congestive heart failure caused by anthracycline antibiotics does not respond to digoxin treatment
cardiotoxic mechanism of antracyclines:
[image]
myocytes in heart tissue are more sensitive (high iron content, high mitochondrial oxidative respiration, low catalase) to oxidative stress generated by anthracycline antibiotics:
1) iron can bind antibiotic when the antibiotic is DNA intercalated and catalyze local generation of hydroxyl radical from hydrogen peroxide
2) generation of free radicals may occur inside the myocyte mitochondira independent
3) free radical derived from oxygen (ODFR, oxygen derived free radicals) damage lipids, protein, and DNA causing cell death (cardiotoxicity)
exogenous administered antioxidants and endogenous free radical scavengers (catalase, super oxide dismutase) are protective against antracycline damage |
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Term
| MOA of dactinomycin (actinomycin) |
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Definition
intercalates between guanine-cytosine base pair stacks
the planar ring system of this drug intercalates between guanine-cytosine base pair stacks and the amino acid chains insert along the minor groove of DNA forming a very stable drug-DNA interaction
[image]
transcription and replication blocked (RNA polymerase more sensitive)
dactinomycin also causes single strand breaks possibly through generation of free radicals
topoisomerase II inhibition may be possible |
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Term
| dactinomycin (actinomycin) toxicity |
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Definition
bone marrow suppression
mucosal
hyperpigmentation of skin (x-ray)
irradiation can worsen GI symptoms and bone marrow suppression
skin reactions can occur with dactinomycin weeks after irradation or x-ray
extravasation concern |
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Term
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Definition
1) DNA BINDING
bleomycins position in a DNA groove and intercalate
2) FORMS COMPLEX WITH FERROUS FE
the DNA bound drugs binds ferrous iron then iron is oxidized to ferric state
3) FREE RADICAL GENERATION AND STRAND BREAKS
ferric iron catalyzes production of free radicals which can break glycosidic and phophodiester bonds
4) CYCLE ARREST IN G2 PHASE |
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Term
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Definition
little myelosuppression
bleomycins have little myelosuppressive effect compared to other anticancer drugs
PULMONARY FIBROSIS (HYDROLASE IMPORTANT)
10% incidence
toxicity may depend on hydrolase (enzyme inactivates bleomycins) which is low in skin and lungs
cutaneous effects
hyperpigmentation, hyperkeratosis (increased keratin production resulting in skin thickening), erythema
effect of bleomycin on lung tissue:
the accumulated collagen restricts gas exchange, leading to death of the afflicted individual
bleomycins have a very high affinity for Cu
the mechanism for causing pulmonary fibrosis is speculative
it is thought that bleomycins may complex with copper in the lung and then activate Cu-dependent inflammatory factors resulting in lung tissue damage
the damaged tissue is replaced by extracellular matrix proteins such as collagen (most likely produced by fibroblast cells)
fibrosis decreases lung compliance, increases work or breathing and decreases gas exchange
susceptibility to bleomycin induced pulmonary fibrosis is dependent on prior environmental exposure and genetic factors (hydrolase gene polymorphisms)
gas exchange must occur through epithelial cells of the alveolus, the interstitial space, and endothelial cells of capillaries surrounding the alveolus
many different cell types are involved in the process of fibrotic tissue accumulation in the interstitial space
the fibrotic material in the interstitial space is produced largely by fibroblasts as a result stimulation from many different factors
matrix accumulation in the interstitial space interferes with lung compliance and gas exchange |
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Term
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Definition
metabolites alkylate DNA
hydroxyl radical damage
mitomycin requires metabolism for activation of alkylating activity of adenine and guanine bases
free radical damage can cause strand breaks |
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Term
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Definition
myelosuppression
pulmonary fibrosis
HEMOLYTIC UREMIC SYNDROME (HUS)
HUS is characterized by a triad of 3 processes (microangiopathic hemolytic anemia, thrombocytopenia, and acute renal failure)
HUS is commonly caused by infectious disease (E. coli is a well known example) and sometimes chemotherapeutic agents (mitomycin is most common)
endothelial damage in arterioles and capillaries is most likely the initiating factor
small clots and platelet aggregations form in small blood vessels
platelets may be consumed causing thrombocytopenia
the small clots and endothelial cell lesions cause methanical destruction of RBCs (microangiopathic hemolytic anemia)
obstruction of blood vessels in kidneys leads to acute renal failure |
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Term
| MOA of epipodophyllotoxins - etoposide and teniposide |
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Definition
1) DRUG BINDS TOPOISOMERASE II
2) PREVENTS LIGATION
3) CYCLE ARREST IN S AND G2 PHASE
free radical generation may also be important |
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Term
| resistance to epipodophyllotoxins - etoposide and teniposide |
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Definition
| increased drug efflux (P-glycoprotein), topoisomerase mutation, p53 mutation (tumor suppressor gene - without functional p53 the cells are resistant to apoptosis) |
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Term
| epipodophyllotoxins (etoposide and teniposide) toxicity |
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Definition
myelosuppression dose limiting
these drugs have typical toxicity profile (leukopenia, GI disturbances, alopecia)
bone marrow suppression can be severe
increased risk of toxicity associated with low serum albumin such as in hepatic disease (albumin capacity is saturated so more free drug available)
other considerations:
HIGH ALBUMIN BINDING (SATURABLE)
associated with DEVELOPMENT OF LEUKEMIA (mixed lineage leukemia (MLL) gene rearragement
onset of leukemia is 1-3 years after epipodophyllotoxin use compared to 4-5 year interval after alkylating agent use
development of leukemia in etoposide treated patients is associated with rearrangement in the mixed lineage (sometimes calls myeloid-lymphoid) leukemima (MLL) gene
the gene product (a histone methyltransferase) normally controls proliferation of bone marrow stem cells
the rearrangement of MML associated with etoposide use caused hyperproliferation of stem cells resulting in leukemia |
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Term
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Definition
1) CERTAIN LYMPHOID MALIGNANCIES REQUIRE EXOGENOUS ASPARAGINE
particularly acute lymphocytic leukemia cannot synthesize asparagine
these tumor cells are dependent on plasma asparagine for growth
2) NORMAL CELLS SYNTHESIZE ASPARAGINE
3) ASPARAGINASE HYDROLYZES ASPARAGINE
the asparaginase hydrolyzes asparagine to aspartic acid and ammonia, thus lowering plasma asparagine
the tumor cells tend to die in G1 phase |
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Term
| resistance to L-asparaginase |
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Definition
asparagine synthesis by tumor cells or by nearby cells
the resistant tumor cells produce the enzyme asparagin synthetase |
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Term
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Definition
1) LITTLE EFFECT ON BONE MARROW OR GI
as expected the side effect profile of this drug is unlike the cytotoxic anticancer drugs
2) HYPERSENSITIVITY REACTION, ANTIBODY PRODUCTION
over repeated dose patients may develop serious hypersensitivity reaction (type I, anaphylactic reaction)
circulating anti-asparaginase antibodies is associated with much shorter t1/2
3) DECREASED PROTEIN C AND S AND ALBUMIN
normal tissues are also affected by treatment with this enzyme
caused by deficiency of asparagine, the liver may produce less albumin or less clotting factors (especially protein S and protein C)
protein C and S are factors that prevent activation of the coagulation cascade by degrading pro-coagulation factors
loss of C and S will promote formation of clots (thrombosis)
[image]
protein S and C degrade factors VIII and V thereby controlling coagulation |
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