Chemo flash cards - SS/LC
what is the role of RAD51
associates with BRCA2
ATPase that forms a nucleoprotein filament on single-stranded DNA
RAD51 binds ssDNA leading to invasion of homologous dsDNA for homologous DNA repair
Describe the process of nucleotide excision repair (NER)
Large complex of > 24 subunits
requires:
- sig chang of Watson crick structure
- chemically change base
1. recognition of problem
2. cleavage on both sides ( dual incision 5’ and 3’ ) of the DNA lesion ~25 - 30 nucleotides
3. damaged sequence dissociate in an ATP-dependent manner and become bound to replication protein A (RPA). Proliferating Cell Nuclear Antigen (PCNA) binds DNA and gap is filled in by DNA polymerase (y or E or k)
4. ligases seal the nicks and complete NER
Formula for clearance
dose = auc x Cl
why are heterocyclic amines carcinogenic
- A chemical that is formed when meat, poultry, or fish is cooked at high temperatures, such as frying, broiling, and barbecuing
- (CYP) cytochrome P450 oxidation
- ring oxidation -> detox amino oxidation -> followed by acetylation or sulfation to form direct-acting reactive mutagens that attack key elements in DNA
topotecan generase pk
and what is it
Topotecan (Hycamtin), a semisynthetic water-soluble derivative of camptothecin, is a potent inhibitor of DNA topoisomerase I in vitro and has demonstrated encouraging antitumour activity in a wide variety of tumours, including ovarian cancer and small cell lung cancer.
- given IV admin
- lactone ring -> rapid hydrolysis to carboxylate (undergo renal excretion) - non enzymatic and less active
- minor metabolite - n- desmonyl
- further metabolism into UGT mediated glucuronide product (reversible)
anthracyclines and apoptosis
- increased interaction of FAS Rw/FASL cascade activation
- anthracyclines increase cytochrome c release independent of DNA damage
- increase p53 -> p21 (G1 arrest), increase Cyclin G (G2/m arrest), increase BAX
Doxo and NfkB
key to response to cell damage and stress and DNA
increase in resistance in cells - associated with superoxide dismutase increase
Why is gemcitabine not given as a prolonged infusion?
Myelosuppression increases with length of infusion
describe BER
- glycosylases recognize abnormal base and cleave covalent bond to deoxyribose
- sugar cleavage endonuclease ape on 5’
- APlyase cleaves on 3’ - liberation of sugar
- dna polymerase base repair
- ligase
what are major proteins that localize for dsb repair
MRE, RAD50, NBS1 -> ATM
Ku70, Ku80 -> DNA pk
s phase dna check point
ATM -> NBS1 -> SMC1 -> S phase
ATM/ATR -> CHK2 CHk1 blocks CBC25A from phosphorylating cyclin A CDK2 -> stops s phase
BER action - what occurs/
cleavage og bond linking a modified base to deoxyribose sugar
endogenous DNA damage - ROS, depurination
what occurs during ner
excision of entire nucleotide including base and sugar
exogenous damage - chemicals, UV
what abnormality is most commonly cause by UV damage
pyrimidine dimers - intrastrand
60% are TT - weak mutagen
30 % are CT
10% CC - most significant mutagenic potential
what drug should vincas not be given with due to increase toxicity
erythromycin
itraconazole
other cyp3A inhibitors
MTD doxo in horse
75 mg/m2
mechanism of chemo resistance; dec affinity of a drug
- tubule - taxanes, vincas
- topo i - topotecan, Irinotecan
- topo ii - anthracyclines, Epipodophyllotoxin -etoposides
- DHFR - mitoxantron
- thymidylate synthase - 5fu
what drug can increase microtubule formation and thus dec neurotoxicity
glutamine - anecdotal
what drug does vincas increase the efficacy of
methotrexate - inc accumulation in cells due to vInca blocking drug efflux
BSA formula
10.1 x Wt(kg) ^ 2/3 / 1000 - dog
10 x wt (kg) ^ 2/3 / 1000
27 kg = 1 m2 ( same dose)
how to vinca interact with lspar
decrease hepatic clearance of vincas
vinblastine metabolism
binds to proteins extensively
so more sequestration in tissues
vincristine metabolism
bind proteins extensively
cyp450 and cyp 3A
increased clearance with phenytoin and carbamazepine due to increase cyp3A
why does vincristine target platelets
high tubular concentration
what tissue accumulates vcristine
spleen
also liver heart kidney muscle
where is pGp normally over expressed
renal tubules, colonic mucosa, adrenal medullar, other epithelium
other than MDR1 what protein can results in vinca resistance
MRP1
also methotrexate resistance
increased MAP Microtubule-associated proteins expression which stabilize MT
MAP Microtubule-associated proteins (MAPs)
promote microtubule assembly and stability in neuronal axonal chambers
how do vincas enter the cell
simple diffusion
how to vincas produce neurotoxicity
major proposed mech - MT loss, MAP hindrances, change in MT dynamics in axons
neurons are enriched in a = b tubular
** axonal degeneration and dec transport due to dec MT function**
randing vinca tubulin binding affinity
vincristine>vinb> vinorelbine > vinflunine
aside from microtubule effect what 2 other mechanisms contribute to vinca function
- change in angiogenesis
- radio sensitization due to G2/m phase blocking
actinomycin d resistance
P170 glycoprotein transporter
what’s the difference between dynein and kinesin
dynein -> gtpases, retrograde motor protein but can be bidirectional
kinesis -> atpases , unidirectional motor protein anterograde> retrograde
how are tubulin subunits organized
- a -b end in helix
- a at slow growing - end -> MTOC = deployment
- b at + end with net elongation = polymerization
- y tubular - scaffold for association into microtubules - caps the - end
explain process of microtubule elongation
each tubulin has 2 GTP
- a = non exchangable
- b can be exchanged fro gdp
when tubulin - gtp binds microtubule -> undergoes b subunit hydrolysis
the gtp is non exchange able until the b subunit dissociates from the microtubule
gtp hydrolysis lags behind polymerase - > GTP cap => stabilizes and promotes further assembly
required for growth
ifosphamide metabolism
ifosfamide x cyp3A -> 4 hydroxyifosphamide -> aldophosphamide
-> isophosphoramide mustard = acrolein
-> chloroacetaldehyde
hydroxylation is slower than cytoxan - longer t1/2
facts about cytoxan/ifosphamide met/pk
dose dependent, non linear
* induces its own metabolism = decreases the t1/2 if given on consecutive days
what does acrolein cause
SHC
06G adducts
what product of chlorambucil metabolism has alkylating activity
phenyl acetic acid mustard
why is there an increased the risk of SHC with ifosfamide
slower activation rate = prolonged exposure to acrolein
what are special consideration with high dose ifosfamide or cytoxan
ifosfamide: tubular damage, falcon acidosis, metabolic encephalopathy
cytoxan: SIADH -> water retention
what is the shared structure feature of non classical alkylating agents
** N-methyl group**
no bifunctional activity
progress metabolize to active intermediates
- procure, DTIC, temozolamide
major metabolite of DTIC
5-aminoimidazole-4-carboxamide (AIC)
formed int he liver by cap enzymes and some tumor cells
TMZ metabolism
- pH dependent
- stable when acidic -> MTIC if pH >7
- MTIC stable in basic -> degrade at pH <7
- spontaneous conversion by effect of h20 and electro + C4 of TMZ -> ring opening
-> C)2 released -> MTIC (methylating agent)
-> degrades methyldiazonium cation -> DNA methylation via methyl group donation
methydiazonium -> RNA or AIC (final degradation product) -> renal excretion
lesions produced by TMZ
most common
most critical
- N7 methylation of guanine
- 03 position
- 06 position - 06 most impt = dec AGT = sensitive to cell death
O6-Alklyguanine-DNA alkyltransferase (AGT) is an important DNA repair protein that protects cells from mutagenesis and toxicity arising from alkylating agents
Tmax
time to reach Cmax
cytoxan in the dog vs cat
dog - P450 enzyme - best cytoxan
cats - 4OHCP doesnt metabolize as rapidly -> can tolerate higher doses
what clearance parameters coorelate with BSA
- CO
- liver volumes
NOT GFR
what are lymph prevalence in blood? LN?
CD4
- Blood 50-60%
- LN 50-60%
CD8
- Blood 20 - 25%
- LN 15-20%
B
- Blood 10 - 15 %
- LN 20 - 25%
NK
- Blood 10%
- LN rare
what enzyme is responsible for cytoxan activation
CYP450
CYP2B**
liposome encapsulation
enhanced tissue distribution
pegylated (polyethylene glycol) -> extends plasma t1/2 of the drug and restricts distribution
unknown idi it improved cardiotoxicity
mitoxantrone moa
binds nucleic acids and inhibits DNA/RNA
intercalation GC preference
dec ability to undergo electron reduction
topoisomerase II inhibition - ssbreaks
dec cardiotoxicity (poss d/t dec ROS)
paciltaxel disposition
cyp450 in liver
taxanes - other chemo interactions
inc doxo cardiotoxicity
increase thymidine phosphorylase -> inc fluoropyrimidine prodrug Capecitabine activity , a precursor of 5-FU
what is the concern of using cimetidine with either taxanes or vincas
dec p450 metabolism -> increased toxicity
taxmen toxicity
paclitaxal
1. hypersensitivity
2. neurotoxicity - mild
3. cardiac rythme disturbance bradycardia
docetaxel
1. fluid retention d/t inc cap permeability - can dec by premeding with Benadryl
2. hypersensitivity
3. rash
4. neuro toxicity
what are Epothilones
Epothilones are a class of potential cancer drugs. Like taxanes, they prevent cancer cells from dividing by interfering with tubulin
** evade MDR*
what drug is formulated in castor oil (other than paclitaxel) and causes severe hypersensitivity
ixabepilone
what is KSP (EgS)
specific kinesin that establishes mitotic spindle bipolarity
drugs - Ispinesib blocks ATPase
what is CENP-E
kinesin protein that plays a role in chromosome movement early in division
N7meG base excision repair
BER
N7MeG - recognized by MPG -> PAR endonucleaosome -> PARP -> recruitment of POIb, XRCCI, DNA ligase _> survival
methoxyamine blocks PARP -> ds DNA breaks -> cytotoxic
what is the most common alkylation lesion
N3meA
N7me G
> 80%
how does PI3k/AKT confer resistance and inhibit apoptosis
Phosphorylation of BH3 Bad Bax and Bio -> dec ability to hold mitochondria open
phosphorylation of cascade 9 -> dec activity of executioner caspase 3
cytoxan metabolism
met by cyp450 -> alkylating and cytotoxic metabolites
- oxidation of ring adjacent to nitrogen to produce 4-hydroxycyclophosphamide + aldophosphamide
- ALDH -> detox carboxyphsophamide ( won’t enter cells d/t anionic for
- spontaneous elimination
-> phsophoramide mustard -> DNA cross linking
-> acrolein
alkylation of targets of:
1. bysulfan
2. mustargen
3. nitrogen mustards
4. melphelan
5. nitrosoureas
6. non classical methylators
N7 most electro negative -> most susceptible
- & 2. N7 guanine
- N7 guanine and N1 adenine
- guanine /adenine N3
- & 6. O6 guanine
what are procarb/dacarbazine
mono or bifunctional
mono functional
what are the two roles of intracellular resistance to alkylation agents
- increased sulfhydryl (glutathione)
- inc GST activity
- inc ALDH activity -> aldophosphamide -> inactive carboxyphosphamide (inactive form of cytoxan)
what are some mechanisms of GSH related tumor cell resistance
- inc inactivation by direct conjugation to GSH
- GSH dependent denitrosation of nitrosureas
- scavenging for reactive organic peroxidase
- quenching of chloroethylated - DNA mono adducts
what is the importance of ALDH in alkylation
converts activated cytoxan to inactive carboxyphosphamide
how does gemcitabine evade normal DNA repair
extra nucleotide added after dFdCTP
Incorporation of dFdCTP into DNA is most likely the major mechanism by which gemcitabine causes cell death. After incorporation of gemcitabine nucleotide on the end of the elongating DNA strand, one more deoxynucleotide is added and thereafter, the DNA polymerases are unable to proceed.
gemcitabine metabolism
dFdCTP blocks DNA polymerase and dna synthesis see diagram
when is gemcitabine active
NOT confined to S phase kills cells nor in log growth
maybe d/t
1 competition with DCTP for polymerase
2 dFDCDP blocks ribonucleatide reductase = deoxycytidine depletion
3 dFdCTP incorporation into DNA -> strand termination
how does gemcitibine enter the cell
active nucleoside transporters
busulfan MOA
SN2
reacts with thiol groups of AA
N7 guanine
cytotoxicity - adenine -> guanine cross linking
BCNU alkylation reaction
BCNU hydrolysis -> 2 chlorophyl carbonium (electrophile) = alkylation of G,C,A
-> Cl displaced by e- ion nitrogen on complimentary DNA strand - cross linking
DNA protein cross links also possible by initiating chlorethylation and amino or sulfhydryl group
nitrosurea MOA
- chloro ethyl groups transfers to the O-6 methyl of guanine on DNA - alkylating
- carbamylation of nucleophile
carmustine, temo, DTIC-> lipophilic and penetrate CNS
only cross resistance with other alkylating agent
N7 alkylation -> cross linking
BCNU hydrolysis -> 2chloroethyl groups -> inc alkylation
what is an isocyanate and what’s the relevance
product of spontaneous break down of methyl and chloroethyl nitrosureas
responsible for some tox with nitrosurea tx
Carbamylation (carbamoylation) is a post-translational modification resulting from the nonenzymatic reaction between isocyanic acid and free functional groups of proteins, in particular with the free amino groups
alters structural and functional properties of proteins and results in faster aging of proteins
nucleophile selectivity preference for nitrogen mustards
- phosphate oxygens
- base oxygen
- purine amino groups
- protein amino groups
- sulfide atoms of methionine
- thiol group s
doxo resistance - most impt transporter
- p170 (atp dept ABC)
- inc MDR1 via inc FOXO3A
doxo and TGF-B
inhibition of TGFB signaling
blocks HIF1a expression
doxo and PI3K/AKT
- in tumor cells and inc phosphorylation AKT
- in the heart doxo = dec AKT/ERK phosphorylation -> inc apoptosis
inhibited by dexrazoxane
doxo changes signal transduction
- PKC inhibition @ high doses
- @ lower doses - increased Phosphoinositides and phsophatidyl closure => accumulation of DAG & IP3 & 2x PKC activity => inc protein cross links +/- inc topo II
doxo membrane perturbations
- binds to phospholipids (cardiolymphatics)
- change fluidity of tumor cell plasma membranes and mitochondria
- cytotoxic w/o even entering the cell
- inc EGFR - blocks transferrin reductase, increase iron-dependent protein oxidation in RBC
2 e- reduction of anthracyclines
formation of unstable quinone methide -> loss of daunosamine sugar and formation of deoxyglycose (LESS CYTOTOXIC)
may be means to dec tissue reactions
cardiac toxicity of anthracyclines
- dec catalase activity and high mitochondrial myoglobin content -> inc activation
- sensitivity of cardiac glutathione peroxidase to free radical attack
- increased release of iron
1. abstract iron from ferritin
2. semiquinone (free radical) -> release Fe under hypoxic conditions
**doxorubicinol production by carbonyl reductase 3 ***
IRP1 is critical to iron homeostasis
dexrazoxane moa
Fe2+ chelator in urinary clearance
prevents doxo induced lipid peroxidation and cardiac toxicity
prodrug -> ICRF198 -> Fe binding
enhanced in cardiac myocytes
what is one electron reduction
- @ quinone oxygen of chromophore
- central to cardiac toxicity
- react w/ o2 -> superoxide
- activates reactive compounds that cause widespread damage in all intracellular components
- catalyzed by NO synthase -> superoxide production + dec NO
effects of anthracyclines on DNA
- intercalation -> dGdC regions flanked by A:T pairs. Potentiated by methylation.
- planar ring: intercalates
- side chain: H+ bonding
- sugar: minor groove binding
- critical for BP recognition*
- TOPO II -> cleavable complex stabilization
- trapping intermediated and prevent resealing
- specific regions: 3’ adenine @ break site
- inhibition of catalysis
- helicase - inhibition via helices stabilization
- ROS generation -> DNA and mitochondrial damage
what is the consensus sequence for doxo affinity and intercalation
5’-TCA
what do anthracyclines do once entering the cell
bind 2OS proteasome -> inc ubiquitin system -> enter nucleus through ATP dependent pore system -> proteasome -> DNA (higher affinity)
why do anthrocyclines accumulate in cells
rapid association with membranes
avid DNA binding
intracellular storage in compartments
how do anthrocycluines enter the cell
passive diffusion of un-ionized drug
daunorubicin uptake faster (less polar)
pH dependent fxna nd uptake
what is the basic anthracycline structure
4 planar rings
danosamine sugar is D ring
quinone and hydroxyquinone on B+ C rings
- redox potential and free radical generation
doxo - single OH on C14??
epirubisin epimeric 4’ subunit on danosamine sugar
how may lspar change drug clearance
decrease serum albumin and dec binding
accelerated clearance
what chemo drug is contraindicated with lspar d/t dec efficacy
methotrexate
lspar block protein synthesis
dec protein synthesis means block entrance into the s phase - dec cytotoxic effects
why might lspar cause clotting abnormalities
dec synthesis of AT III
particularly problematic in CNS
does lspar penetrate CNS
yes but concentration falls rapidly
what is benefit of pegylated Lspar
dec immunogenicity
inc T1/2
how does lspar work
lspar -> aspartic aci and ammonia
how is asparagine normally synthesized
- transamination of l-aspartic acid
- amine groups donated by glutamine
catalyzed by l-asparagine synthetase (tumor cells lack this)
what drugs have toxicity based on BSA calculation in small dogs
doxo
cisplatin
carbo
melphalan
what type of mutation results from 06 methyguanine
G-> A transition
means of methylation repair
MGMT (O6 MG)
AlkB ( oxidizes methyl groups attached to bases _> shead as formaldehyde
yondelis “Trabectedin”
- DNA alklyation
- inhibition of gene transcription
FDA approved for liposarcoma and leiomyosarcoma in people
mitomycin c moa
- crosslinks in DNA and induces mono functional alkylation
- DNA replicaiton inhibitor
cross links = most lethal
monofxn = most common interaction
HCl -> N6 adenine
reductively activated -> N217guanine
dactinomycin moa
binding ss and dsDNA -> potent inhibition of DNA and RNA + protein synthesis
what happens with you dose obese dogs on ideal body weight
underdose them
carbo dosing in cats
dose = auc x (GFR x 2.6) x Kg (wt)
endocrine effects of vincas
SIADH
vinorelbine dose in dogs and cats
dog - 15 mg/m2
cat - 11.5 mg/m2
dose limiting tox - neutropenia, v, nephrotoxicity
with what chemo drugs is carbo synergistic
drugs that decrease intracellular pyrimidine precursors
5FU and Gemcitabine
means of cisplatin resistance
- change in cellular accumulation
- cytosolic inactivation
- change in dna repair
- change in apoptosis - inc dna damage tolerance
platinum renal toxicity mechanism
primary distal tubule damage
mg/ca loss is common and should be monitored
what should you never use in a patient receiving carbo to potential minimize renal toxicity
FUROSEMIDE - dec in total h20 leads to inc drug exposure and inc toxicity
okay to use mannitol bc inc flow
what neoplasia have platinum been causative agents
AML - cisplatin and carbo
when in the cell cycle are topo I and ii inhibitors active
topo I - require active replication, S phase
Camptothecin
topo II - less cell cycle specific-> deplete s phase cells via g2 arrest
what’s th most well known topo1 inhibitor class
Camptothecin
topotecan, irinotecan
how does etoposide interact with radiation
it is a radiosensitizer
- change response of dna repair genes
- dec topo i/ii expressoin
how ar eetoposide and teniposide eliminated
etoposide - renal and non renal - can cause azotemia dec dose if azotemia seen
tenoposide - non renal
what happens with topo II sensitivity as topo enzyme increases
inc top2 = inc sensitivity to topo inihibition
moa topII inihbitors
stabilize DNA cleavage component d/t inhibition of dna regulation
( inihibts ds break)
when are topII concentrations highest during the cell cycle
end of s phase - headed to separate chromatin loops
top2a - linked to proliferative state and ki67
top2b- constant throughout the cell cycle
- top 2a inc 2-3 x during g2/M
what part of the alpha folate structure affords DMFR inhibition
- 2,4-diamino
+ charge added to structures of folates -> N10 bridge
change 5-8N position
what is the general structure of folic acid and alpha folate
FA; pteridine ring (2,4 diamino inhibits DMFR) + p amino benzoic acid + glutamic residue (1-6)
Methotrexate: truncated glutamyl
how does folate enter the cell
folate receptor (FR), reduced folate carrier (RFC1) and proton-coupled folate transporter (PCFT) , pH sensitive transporter (intestines, some tumors, most tissue)
which folate proteins are present in membrane and share folate binding site
alpha
beta
less efficient (dec capacity) for reduced folates and Methotrexate
what is the most important transporter for methotrexate
reduced folate carrier system RFC1
what is different about methotrexate and piritrexim
piritrexim dont require transport
they are lipid soluble
what is the effect of low folate conditions
increased toxicity d/t folate receptor up regulation.
what are most important drug efflux pumps for methotrexate
MRP1/2/3
BCRP
how may lspar change methotrexate
dec effect d/t amino acid deprivation and growth arrest
what are the effects of polyglutamation
- inc intracellular accumulation
- selective intracellular retention = inc t1/2
- inc folate affinity for folate dependent enzymes
methotrexate also polyglutamated -> inc tox
inc retention in cells
inc inhibition of folate dept enzymes -> slower dissociation
Tumor lysis bw
increased K, P, decreased Ca – metabolic acidosis low HCO3
how do folates normaly exist within cells
poly glutamates form
directed by FPGS -> adds < 8 glutamic group in y linkage
figs - correlated with rate of cell growth inversely with concentration of intra cellular folates
high levels = dec max polyglut
what is an important determinant of optimal max binding to DMFR
NADPH concentration
co-substrate for DMFR
NADPH does not promote mix binding
under what condition is methotrexate INeffective
1 high concentration of dihydrofolate (a competitive substrate)
2. neutral pH
under these you need a higher concentration of Mtx to except effect
an excess of free unbound max is required for DMFR inhibition
Aminopterin
original alpha folate
4 amino analog of folic acid
why is FR system not as effective for methotrexate transport vs endogenous folate
- inc affinity for reduce folates and folic acid
- max PG 75x affinity vs mono glutamate
other ara- c functions
- inhibition of neonucleotide reductase
- formation of are cap choline - inhibit synthesis of membrane glycoproteins
- diff of leukemic cells
- ceramide formation -> apoptosis
- DAG induction -> PKC
5FU metabolism
what is a 2nd MOA in vivo of hydroxy urea
- change to NO -> ribonucleotide reductase inhibitor
- acceleration of loss of double minute chromosomes
which are extrachromosomal circular DNA fragments frequently found in brain tumors
ribonucleotide reductase structure
1 subunits: m1 + m2
m1: diphosphate binding site and allosteric triphosphate reg sites
- stable throughout the cell cycle except very decreased in G0
m2: Fe2+ and free radical attached to tyrosine
- peak in s-phase
hydroxy urea target - chelates iron and inactivates m2 tyrosine
* s phase selective*
how does hydroxyurea interact with other chemo
- inc cytotoxicity of purine/pyrimidine analogs by dec dcompetitive pools of triphophates
Hydroxyurea and fluorouracil (5-FU) have shown synergistic activity in vitro in g1/s phase
Both drugs also act as radiosensitizers
dec deoxynbonucleaotide pools -> dec dna repair after alkylation/RT damage
dog/ cat doses of
1. ara c
2. 5 aza
3. gemcitibine
- dog - 300 mg/m2/d up to 600 over 2-4 d
cat - 10mg/m2 every 12 hours SQ - 0.2mg/kg q 24h SQ on day 1-5 of 25 d or
0.1 mg/kg every 24 hours SQ d 1-5 every 14 days - dog - 350 - 400 mg/m2 weekly x 5 weeks for HCA
800mg/m2 weekly for tcc
original dose 675mg/m2 q 14 d
lymphoma rescue - 400 mg/m3
cat 0 10mg/m2/min
sig difference between gemcitabine and ara-c
- dFDCTP biophasic elimination
- inc RNR inhibition
- dFfC (gemcitabine) - . dec dNTPS d/t RNR inhibition
nitrogen mustard moa
- choline lost
- B carbon -> nitrogen nucleophile - > aziridinium moiety (reactive)
- nucleophile -> alkylated product
- 2ndary fn - 2nf aziridinium 2 alkylation = cross linking
what is unique about nitrosurea
no carbamoylating activity
what is the natural cofactor of Thymidylate Synthase rxn
5-10-CH-2FH4 (or polyglutamases) bings fdUMp/dump
Thymidylate synthase (TS) catalyzes the conversion of deoxyuridine monophosphate (dUMP) to thymidylate (TMP), in a reductive methylation that involves the transfer of a carbon atom from the cofactor 5,10-methylenetetrahydrofolate to the 5 position of the pyrimidine ring
why were cytoxan and ifosfamide created as prodrugs
hope that high concentrations of phosphamidase in epithelial tumors would selectively activate
what is required for function of top II
- Mg2+
- ATP
ccnu moa and pharacology
- spontaneous met to alkylating + carboxylating compounds
- chloroethyl group 06 guanine -> cross linking
only Cl group - monofuncional
metabolites have increase alkylating ability and dec carbamylating ability
how to alkylating agent enter the cell
lipid soluble (passive) - ccnu bcnu chlorambucil
mustargen - via choline transport
melphalan - active transport systems show with cell line
what favors glutathione conjugation
GST presence -> offer catalysis
what is an important mech of resistance to chlorambucil
increased gut dept MRP1/2 efflux
alkyl guanine DNA alkyltransferase repair AGT
O6 -meG -> AGT -> survival (can be ubiquinated)
or
O6-meG -> MSH2/6-> DNA break/toxicity
encoded by MGMT
what are 2 branches of DNA damage-debt S phase check point
- phosphorylation of SMC1 - cohesion + by ATM/ATR
- ATR (chk1)/ATM(chk2) complexes -> turnover of CDC25A removes the inhibitory phosphorylation in CDK2 and blocks replication initiation
cytotoxic mech of TMZ
- failure of mar to find complement for methyl guanine
- g2/m arrest via chk1 kinase activation -> phosphorylation of CDC25 phosphatase -> dephosphorylation of CDK2 - blocking cell replication
*p53 independant
what is the primary met of doxo
how is it formed
doxorubianol - greatest cardiotoxicity
created by carbonyl reductase 3
taxanes -> inc CR3 -> inc alcohol ( humans will have inc BAC)
taxanes and other chemo drugs
doxo excretion
50% biliary - parent + metabolite
<10% urinary
what determines pK of doxo
tissue binding
75% protein bound in plasma
higher binding for dna vs plasma
how is innotecan pk unique among campothecans
must be converted by carboxyl esterase converting enzyme -> SN-38 (metabolite thought to be responsible for activity and toxicity)
NS38 detox via UGT IAI -SN 38G
innothecan is a p450 substrate
what determines
Cmax
Cmin
Cavg
accumulation factor
Tmax
Max/min/avg - t1/2, tauc, dose
accumulation factor - how high at steady state - t 1/2 and tauc
Max dept on K and t 1/2
what neutrophil cutoff is associated with increased duration and ST in LSA
<3000
what enemy form metabolite doxorubianol in dogs
Aldo - keto reductase
how do you calculate dox exposure without full course sampling
AUC = 46.9 + 0.63 (C5min) + 1.96 (C45min) + 6.63 ( c60min)
5, 45, 60 min sampling
what’s the relevance of protein binding for carbo
it inactivates it
vinc general structure
asymmetric structure of dihydroindole nucleus ( vindoline) linked to indole nucleus (Catharanthine)
vcr and vbl identical except R1 of nitrogen of vindolene nucleus
when do vincas bind
vinca domain of microtubules ( not soluble tubulin like colchicine)
2 sites
1. high affinity - change treadmilling, no change in microtubule mass
- enhance - end instability
- inhibit + end instability
- low affinity ( high concentraiton of vinca -> depolymerization
what protein plays a critical role in vina driven destabilization
MAPs
1. stabilize longitudinal dimers as they splay apart
2. may help destabilize microtubules
describe the basic structure of the platinum agents
divalent inorganic complexes
h20 soluble and readily activated by h2O displacement of Cl/carboxyl groups
complex leaving groups of carbo+ oxiplatin -> dec reactivity in aqueous solution, dec renal toxicity
what proteins aim to repair platinum adducts
NER pathway
ERCC1, XPA, etc
how is apoptosis altered with platinum agents
mmr complex and p53
etoposide metabolism
main metabolite - etoposide glucuronide
when is top2 phosphorylation the highest
correlates with cellular need for enzyme
- s phase -> peak @ G2
primary enzyme - casein kinase II
what happens to topo 2 when DNA is bound
closed confirmation ->
tyrosine of each monomer attacks DNA PDE bond 4 bases apart on the G duplex -> linked 5’ ends while 3’ re hydrolyzed
t sement passes through the gap
ATP hydrolysis -> open and release
what is a prominent and general feature of top mediated DNA breaks
type 1 enzyme (1,3) -> ss dna breaks
type 2 enzyme (2a,b) _> ds dna breaks
- DNA cleavage by topoisomerases is a **transesterification reaction, in which a tyrosine residue(s) of the enzymes forms a transient covalent bond with phosphates of the DNA backbone
top1 - linked to the 3’ terminus of dna
top 2 - each enzyme molecule of homodimer -> linked to 5’ terminus each on each of the cleaved dna strands
what product of 2e- reduction - anthracycline metabolized to ?
7 deoxyaglycone
7 hydroxyaglycone
treatment of SHC
oxybutynin (0.2–0.3 mg/kg PO q8–12 h), and/or pentosan polysulfate sodium (20 mg/kg PO twice weekly for 5 weeks, then once weekly for 12 weeks). In extreme cases, intravesicular dimethyl sulfoxide (DMSO) or dilute formalin, or surgery can be considered
