Chemo/Targeted Flashcards
What effects does mCTX have on STS?
decreased blood vessel density, depleted Tregs (immunomodulatory)
What kind of T cells are Tregs?
CD4+
What is rosiglitazone?
peroxisome proliferator-activated receptor gamma (PPARγ) agonist and antidiabetic agent in humans
What supportive care medication decreases permeability of the BBB? (Chabner)
corticosteroids
What are two ways antifolates inhibit DNA biosynthesis?
- partial depletion of reduced-folate substrates
2. direct inhibition of folate-dependent enzymes
What does methotrexate inhibit?
dihydrofolate reductase (DHFR) - results in depletion of reduced folates
How is methotrexate transported into the cell?
reduced folate carrier system
What are 5 mechanisms of resistance to methotrexate?
- decreased transport into cell
- increased efflux by MDR1, MRP1, 2, 3, BCRP
- decreased intracellular polyglutamation
- decreased binding to DHFR (due to mutation)
- gene amplification of DHFR
- changes in level/affinity for thymidine synthase
How does L-spar affect methotrexate?
blocks activity (through AA deprivation)
How do NSAIDs affect methotrexate?
decrease renal clearance, increase toxicity
How does methotrexate affect 5-FU and Cytosar?
increases activity
How is MTX metabolized?
- converted to poly glutamates within cells (by follypolyglutamyl synthetase); polyglutamated MTX retained intracellularly
- metabolized in liver
How is MTX excreted?
excreted as intact drug in urine - dose reduce with CKD!!
What is leucovorin?
source of reduced folate - used 24-36h after high dose MTX; decreases/prevents toxicity via competition
What PK parameter determines efficacy of MTX? What other drugs follow this principle?
DURATION of exposure above threshold concentration
same for cytosar, vincas, taxanes
Is MTX cell-cycle specific?
Yes - S-phase
What is the MOA of 5-FU?
5-FU converted to FdUMP which acts to inhibit thymidylate synthase (responsible for conversion of dUMP to dTMP (a precursor of dTTP))
Other MOA:
- also converted to FUTP and incorporates in RNA
- also converted to FdUTP and incorporates in DNA
How is 5-FU transported into the cell?
shares facilitated transport with uracil, adenine, hypoxanthine
What are 5 mechanisms of resistance to 5-FU?
- decreased uptake (mutations in nucleoside transporters)
- increased efflux
- decreased activation
- increased activation by DPD
- mutations of thymidylate synthase
How do cimetidine and IFNalpha affect 5-FU?
decreased clearance
How does 5-FU interact with radiation?
radio sensitization through decrease in dTTP pools – inhibits DNA repair
5-FU inhibits metabolism of which two drugs?
warfarin, phenytoin
How does leucovorin affect 5-FU?
provides increased intracellular folates which augments inhibition of thymidylate synthase
(benefit seen in clinical trials but toxicity enhanced)
What important enzyme is involved in 5-FU metabolism? What happens if you’re deficient in this enzyme?
Dihydropyrimidine dehydrogenase - initial rate-limiting step in 5-FU catabolism
- DPD deficiency in people causes severe toxicity
What important 5-FU enzyme has been evaluated in cats? What were the findings? (Saba 2013)
DPD
23% had value associated with decreased DPD activity (based on human studies)
Measured U:UH2
How is 5-FU eliminated?
90% by catabolism/anabolism
<10% excreted in urine and lungs (urea, CO2)
How does toxicity differ between CRI and bolus of 5-FU?
CRI = mucositis Bolus = myelosuppression
What are the toxic and fatal doses of 5-FU in dogs?
> 20 mg/kg = neurotoxicity
>43 mg/kg = fatal
What toxicities does capecitabine cause in dogs?
corneal and neurotoxicity
What does bevacizumab target?
VEGF-A ligand
humanized mAb
What does trastuzumab target?
HER-2
humanized mAb
What is cytosar an analog of?
deoxycytidine (precursor of dCTP)
What is the rate-limiting step of cytosar metabolism?
Deoxycytidine kinase enzyme converts Ara-C to Ara-CMP
What is the active form/metabolite of cytosar?
Ara-CTP
What is the MOA of cytosar?
Inhibition of DNA polymerase-alpha
Ara-C becomes incorporated into DNA to cause DNA chain termination and induction of apoptosis
How is cytosar transported into the cell?
carrier-mediated process via nucleoside transporters
What are mechanisms of resistance to cytosar?
- decreased activation by deoxycytidine kinase
- increased activation by deaminases (produces inactive metabolite Ara-U)
- decreased drug uptake (mutation in nucleoside transporters)
Is cytosar cell cycle specific?
Yes (S-phase)
What PK parameter determines efficacy of cytosar?
duration of exposure (correlates with cell kill)
this is also the case for MTX, vincas, taxanes
What is the role of cytosar in canine stage V LSA? (Marconato VCO 2008)
dogs with bone marrow involvement treated with CHOPL and Cytosar - MST 243d (vs. 72.5 with CHOPL alone); dogs received both EPO and Neupogen
What is the metabolism for gemicitabine? (apparently less important than cytosar and Cytoxan)
dFdc is phosphorylated by deoxycytidine kinase to dFdCMP –> dFdCDP –> dFdCTP
Where is gemcitabine inactivated?
Inactivated by deaminases in the LIVER (reduce dose for liver dysfunction)
What is the MOA of gemcitabine? (two things)
- dFdCTP is incorporated in to DNA and causes termination of chain elongation and inhibits DNA repair
- dFdCDP inhibits ribonucleotide reductase (results in decreased deoxyribonucleotide pools necessary for DNA synthesis)
How is gemcitabie transported into the cell?
carrier-mediated transport via nucleoside transporters
Name 4 mechanisms of resistance to gemcitabine.
- decreased activation by deoxycytidine kinase
- increased activation by deaminases
- increased expression of ribonucleotide reductase
- decreased drug uptake (mutation in nucleoside transporters)
What is the mechanism of radiosensitization with gemcitabine?
inhibition of ribonucleotide reductase (results in decreased deoxyribonucleotide pools necessary for DNA synthesis)
What was the RR with gem/carbo for carcinomas? % GI toxicity? (Dominguez 2009)
RR 13% (prostatic carcinoma had a CR, GI ACA and tongue SCC had PR)
73% GI toxicity (usually mild)
What responses were seen with gem/carbo for feline carcinomas? What was toxicity? (Martinez-Ruzafa 2009)
1 CR, 1 PR
33.3% neutropenia, 16.7% thrombocytopenia, 16.7% GI dox (similar to any chemo protocol)
What were the results of a phase 1 study with gemcitabine in dogs? MTD, DLT, detectable in urine, tumor responses? (Marconato JVIM 2015)
MTD 900 mg/m2 (weekly)
DLT neutropenia
Tumor responses in TCC, mammary, primary lung
What is the MOA of 5-azacytidine and decitabine?
Inhibit DNA methyltransferase to inhibit DNA methylation and promote expression of suppressed genes
Also incorporated into DNA +/- RNA
What is 6-MP? What is it a structural analog of?
Guanine analog
Hypoxanthine
How is 6-MP metabolized?
Activated intracellularly by HGPRT (hypoxanthine guanine phosphoribosyl transferase) to TIMP – metabolized to thioguanine nucleotides which are the active products
How is 6-MP catabolized?
By xanthine oxidase and TPMT (thiopurine methyltransferase)
Why is genetic screening for TPMT (thiopurine methyltransferase) important in humans?
low activity can result in decreased drug metabolism and increased toxicity
What is the MOA of 6-MP?
incorporation of thioguanine metabolites into DNA - causes miscoding, results in apoptosis via MMR
(secondary MOA - also inhibits purine synthesis, incorporation into RNA)
What drug interaction is seen with 6-MP and allopurinol?
concurrent use causes inhibition of XO which increases 6-MP activity
What is the metabolism of 6-TG (thioguanine)?
activated to TGMP (6-thioguanylic acid) by HGPRT (hypoxanthine guanine phosphoribosyl transferase)
How is 6-TG catabolized?
By TPMT (NOT XO)
What is the MOA of 6-TG?
incorporates TGMP into DNA, triggers apoptotic with MMR
What were the results of 6-TG and zebularine with canine malignant lymphoid cells? (Flesner BMC Vet Res 2014)
- Down-regulate DNMT1 and globally demethylate canine malignant lymphoid cells
- dose-dependent decrease in cell survival was also observed (apoptosis)
What is azathioprine’s metabolism and MOA similar to?
6-MP
What is zebularine?
nucleoside analog of cytidine, also inhibits DNA methylation
What are the uses of allopurinol?
prevention of hyperuricemia and uric acid nephropathy
NOT NEEDED in dogs, hyperuricemia not a problem - different pathway
What electrolyte abnormalities are seen in TLS?
increased K, increased PO4, decreased Ca
increased uric acid (due to cell destruction with release of purines from degraded DNA) - can cause renal failure due to precipitation of urate crystals in distal renal tubules
What is the MOA of allopurinol?
inhibition of xanthine oxidase (to inhibit conversion of xanthine and hypoxanthine to uric acid)
Name two important drug interactions with allopurinol.
Increases half-life of 6-mercaptopurine and azathioprine
How does rasburicase treat TLS?
recombinant urate oxidase (aka uricase - most mammals have this enzyme but humans don’t) that converts uric acid to allantoin
Why doesn’t uric acid accumulation occur in dogs with TLS?
Dogs (other than Dalmatians and English Bulldogs) oxidize uric acid to allantoin in the liver via uricase, prevents hyperuricemia.
In humans, allopurinol is indicated because purines (released from damaged cells) are catabolized by the liver through oxidation of hypoxanthine and xanthine to produce uric acid.
What is the main MOA of hydroxyurea?
inhibition of ribonucleotide reductase (rate-limiting enzyme in de novo synthesis of deoxyribonucleotide triphosphate)
How does hydroxyurea enter cells?
passive diffusion
Is hydroxyurea cell-cycle specific?
Yes, S-phase
How is hydroxyurea excreted?
renal excretion - decrease dose with renal dysfunction
What is the main MOR to hydroxyurea?
increased ribonucleotide reductase activity
How does hydroxyurea affect the activity of anti-metabolites?
increases their activity by reducing competitive pools of physiologic triphosphates
Which drugs should be avoided or dose reduced in patients with azotemia? (5)
cisplatin etoposide carboplatin bleomycin methotrexate
Which drugs should be avoided or dose reduced in patients with hepatic dysfunction/hyperbilirubinemia? (8)
paclitaxel etoposide vincristine vinblastine vinorelbine docetaxel mitoxantrone doxorubicin
Which cancers have shown a PR to piroxicam as single agent? (Knapp 1992, also Eichstadt 2016)
TCC, TVT, SCC, mammary carcinoma
What cell cycle phase transition is blocked by gemcitabine?
G1 to S phase
What is the active form of gemcitabine (once it gets into cell)?
dFdCTP
What enzyme regulates the rate limiting step of gemcitabine metabolism?
deoxycytidine kinase (dCK)
What rate of gemcitabine administration is recommended in cats to achieve target plasma concentration (TPC)? (Garnett, Rodriguez 2016)
Fixed dose-rate between 2.5-5 mg/m2 per minute.
What two things does folate depletion interfere with?
nucleotide synthesis and DNA methylation
What happens when dTMP synthesis is inhibited in conditions of low folate?
Uracil is incorporated in to the DNA instead
Both uracil disincorporation and DNA strand breaks are observed in folate-deficient humans
Why does cyclophosphamide spare platelets?
May be due to increased aldehyde dehydrogenase in stem cells - inactivates CTX
What is the active form of CTX?
phosphoramide mustard
What drug type is particularly teratogenic?
antimetabolites
What are the targets of masitinib?
KIT, PDGFR, Lyn
What is bevacizumab?
Humanized IgG1 mAb against VEGF
treats colorectal cancer
What is cetuximab?
chimeric IgG1 mAb against EGFR
treats colorectal cancer
What is the difference in MOA between low and high doses of vinca alkaloids?
High - bind to low affinity sites (sides of microtubules), leads to tubular depolymerization and reduced microtubule mass; inhibits assembly
Low - binds to high affinity sites (end of microtubules) - disrupts dynamic processes but microtubule mass not affected
How are vincas transported into the cell?
passive diffusion
What is the most important determinant of cytotoxicity of the vinca alkaloids?
duration of exposure above a critical threshold
Two main mechanisms of resistance to vincas and taxanes?
- increased drug efflux
- alterations in tubules that confer hyperstability
How do you dose vinc in patient with hepatic dysfunction?
At UMN:
If t.bili >2.0 – Decrease by 75%
If t.bili 0.6 – 1.9 – Decrease by 50%
What are 3 cytochrome p450 inducers? How do they affect vincas?
phenobarbital, phenytoin, rifampin, steroids
decreased VCR efficacy because increased metabolism
What are 3 cytochrome p450 inhibitors and how do they affect vincas?
erythromycin, ketoconazole, cimetidine
increase VCR toxicity because decreased metabolism
What are DLTs of vincas?
VCR: peripheral neuropathy
VBL, VRL, VFL, VDS: neutropenia
What endocrine toxicity is possible with vincas?
SIADH (hyponatremia, seizures)
also caused by CTX, cisplatin, thiazides, morphine, pulmonary/CNS infections
What is the proposed MOA for vinc’s ability to increase circulating PLT?
causes endoreduplication (replication of genome in absence of cell division) of megakaryocytes
MOA of taxanes? Where do they bind?
inhibit depolymerization (disassembly) of tubulin bind interior of microtubules
Would you expect a tumor resistant to vinc and DOX to respond to paclitaxel?
No - MDR1 resistance
How does paclitaxel interact with DOX? Cisplatin?
DOX - reduced clearance, increased cardiotox
CIS - given before paclitaxel reduces clearance of paclitaxel
What is the incidence of hypersensitivity in dogs treated with IV paclitaxel? How does Paccal Vet avoid this?
64% HS (Poirier JVIM 2004)
Paccal Vet is water soluble and does not have the Cremophor EL
(pretreat with steroids and H1/H2 blockers for paclitaxel)
What is the MTD of oral docetaxel in dogs and cats?
Dogs - 1.625 mg/kg with 5 mg/kg CSA q2 weeks
Cats - 1.75 mg/kg with 5 mg/kg CSA
(2.25 mg/kg in cats if IV)
- can achieve therapeutic plasma concentration at lower dose with CSA
MOA of epothilone B? MTD and DLT of epothilone B in dogs?
inhibits tubulin depolymerization
MTD 2.76 mg/m2 IV weekly
DLT was GI
Is there cross-resistance in taxanes?
No
not affected by over expression of MDR1
What drugs are nitrogen mustards? (alkylating agents)
mustargen, melphalan, chlorambucil, CTX, ifosfamide, bendamustine
What drugs are nitrosureas? (alkylating agents)
CCNU, BCNU, streptozotocin