Principles Of Anti-cancer Drug Therapy Flashcards
What is the goal of chemo in vet species?
Palliation/ control rather than cure
What should be considered throughout chemo?
QoL
When is chemotherapy indicated?
Disseminated disease for chemo-sensitive tumours (e.g. lymphoma)
Adjuvant therapy following sx for highly metastatic tumours (e.g. high grade MCT)
Following incomplete resection
Neo-adjuvant chemo (shrink prior to sx)
Chemosensitive tumours not amenable to sx or XRT
What chemo-sensitive tumours can cause disseminative disease?
Lymphoma
Leukaemia / myeloma
Disseminated MCT
Disseminated histiocytic sarcoma
When should chemotherapy NOT be used?
Sx or XRT more effective
What are the potential routes of administration for chemo drugs?
oral IV SC intra-cavitary Intra-lesional (not common)
When might intra-cavity chemotherapy be indicated?
Mesothelioma (cells lining the body cavity)
What cells do most anti-cancer drugs target?
Actively dividing cells
How is mitotic index related to the efficacy of chemo?
Tumours with a high mitotic index are more likely to be sensitive
Cells in G0 are relatively resistant
Describe the typical growth of tumours
Log phase of growth
Plateau phase of growth
During what phase of growth is it best to use chemo?
What is the problem with this clinically?
Log phase of growth
Tend to be detected clinically in the plateau phase
Following surgery, when should chemo be started if it is indicated?
Why?
As soon as the surgical wound has healed
Need rapidly dividing cells to heal the wound - will be targeted by cytotoxic drugs
How do you quantify the effect of a cytotoxic drug?
A given dose kills a fixed percentage of cells
Each treatment reduces numbers by a percentage
What is the MTD?
Maximum tolerated dose
Why should you give cytotoxic drugs at pulse dose intervals?
Why should you not leave intervals too long?
Allow normal tissues to recover in between doses
DON’t want tumour to regrow
How is toxicity related to the size of an animal?
Toxicity often relates more to body surface area than body weight
How do combination protocols compare to using a single agent?
MORE EFFECTIVE
What considerations need to be made when devising combination protocols?
Use drugs which:
Are effective as a single agent
Have different modes of action and don’t interfere with each other
Ideally act at different stages of the cell cycle
Don’t have overlapping toxicities
What is the COP protocol?
Cyclophosphamide
O - vincristine
Prednisolone
What is the CHOP protocol?
Cyclophosphamide
H- Doxorubicin
O - vincristine
Prednisolone
What is the LOPP protocol?
Lomusine
O- vincristine
Procarbazine
Prednisolone
What can the COP, CHOP and LOPP protocols be used to treat?
Lymphoma
What are the phases of chemotherapy?
Induction
Maintenance (only in some protocols)
Re-induction
Rescue
Which is the most intense phase of chemo?
Induction
What is the rescue phase?
Switch to different drugs if the current protocol is not effective
What is metronomic chemotherapy?
NSAID plus low dose alkylating agent (cyclophosphamide or chlorambucil)
What are RTKIs?
Receptor Tyrosine Kinase inhibitors
Interfere with aberrant cell-signalling in cancer cells
What factors affect the success of chemotherapy?
Tumour cell type
Drug distribution
Development of resistance
How can tumour cell type affect success of chemotherapy?
Some have intrinsic resistance e.g. many carcinomas, malignant melanoma
How can drug distribution be compromised?
Blood supply to neoplasm
Barriers to diffusion e.g. BBB
How can tumours develop resistance?
Tumours are genetically unstable
Drug exposure selects for resistant cells
Describe a mechanism for drug resistance.
Multi-drug resistance pump - MDR1 gene
Can be upregulated resulting in Doxorubicin and vincristine being pumped OUT
What shouldn’t be used to pre-treat lymphomas before chemo?
Why?
Pred
Glucocorticoids can cause MDR1 upregulation
How are alkylating agents cytotoxic?
Cross-link DNA and cause strand breakage
Interfere with DNA replication and transcription
When in the cell cycle do alkylating agents act?
ALL THE TIME
Which cytotoxic drugs are alkylating agents?
Cyclophosphamide
Chlorambucil
Lomustine
Melphalan
What alkylating agents are indicated for lymphoma?
Cyclophosphamide
Chlorambucil
Lomustine
Which alkylating agent is indicated for sarcomas?
Cyclophosphamide
What is Melphalan indicated for?
Myeloma
Which alkylating agent is indicated for brain tumours?
Lomustine
How are mitotic spindle inhibitors cytotoxic?
Binds to tubulin, interferes with mitotic spindle formation
METAPHASE ARREST
At what phase of the cell cycle do mitotic spindle inhibitors act?
G2/M
Give examples of mitotic spindle inhibitors.
Vincristine
Vinblastine
Vinorelbine
When is vinblastine indicated?
high grade MCT
What are anti-metabolites?
Mimic normal substrates in DNA / RNA synthesis
- inhibit enzymes or make metabolites non-functional
What phase of the cell cycle do anti-metabolites affect?
S phase
Give examples of anti-metabolites
Cytosine arabinoside Methotrexate 5-fluorouracil Gemcytabine Hydroxycarbamide
Which anti-metabolite can penetrate the CNS
Cytosine arabinoside
How do platinum compounds work?
Cross-link DNA
Which platinum compound is the one thats typically used?
Carboplatin
Which stage of the cell cycle do platinum compounds work?
CELL CYCLE NON-SPECIFIC
Which cytotoxic drugs are cell cycle non-specific?
Alkylating agents
Platinum compounds
Anti-tumour antibiotics
Give examples of anti-tumour antibiotics
Doxorubicin, epirubicin
Mitoxantrone
Actinomycin - D
How is doxorubicin cytotoxic ?
Free radical formation, damages DNA directly
Why might prednisolone be indicated for patients with neoplasms?
Causes apoptosis of lymphoid/ mast cells
Lymphoma (?), mast cell tumours
Why can L-asparaginase be used as an anti-cancer tx?
Breaks down L-asparagine
Neoplastic lymphoid cells are dependent on an external supply of L-asparagine
Inhibits protein synthesis of neoplastic cells
What is a benefit of using L-asparaginase ?
It isn’t myelosuppressive
When might L-asparaginase be indicated?
Lymphoma
Where would you expect to find a transitional cell carcinoma?
Bladder
Why isn’t L-asparaginase myelosuppressive?
Normal body cells aren’t dependent on an external L-asparagine supply
What might you pre-treat a patient recieving L-asparaginase with?
Why?
Anti-histamines
Possible anaphylactic reaction - indicated if using more than once
How can NSAIDs be beneficial in cancer tx?
Anti-angiogenic
Promote apoptosis
Anti-inflammatory, analgesic
Effects on stromal cells
When might you use NSAIDs in cancer tx?
TCC
Prostate carcinoma
CARCINOMAS
How does metronomic therapy work?
Acts on tumour microenvironment
Anti-angiogenic
Immunomodulatory - decreases T-regs
Why is metronomic therapy useful?
Useful even in drug-resistant cancers
Tumours with low MI can be susceptible e.g. HSA, TCC,
What receptor tyrosine kinase inhibitors are indicated for mast cell tumours?
Masitinib and toceranib
Why are RTK inhibitors effective against mast cells?
KIT mutation
- constitutive activation of KIT receptor
Inhibitors stop activation and prevent downstream signalling
What patient factor can increase the toxicity of chemo drugs?
Hepatic or renal function impaired
Give an example of a drug that is both activated and metabolised by the liver.
Cyclophosphamide
Which normal tissues are susceptible to damage by cytotoxic drugs?
Bone marrow
GIT (crypts)
What is the nadir?
The lowest point
When would you expect the nadir of neutropenia to be?
About a week after a dose
When would you expect the nadir of thrombocytopenia to be?
Platelet nadir - around 10 days post tx
How can you assess myelosuppression?
Monitor CBC frequently
Check neutrophil nadir and before administering next dose
When should you consider prophylactic antibiotics?
If very low counts <0.75 x10^9
What should you do if a chemo patient presents as sick/febrile with a neutropenia?
Give IV antibiotics and fluid s
If a patient is consistently neutropenic, what should you do?
Lower doses
How could you symptomatically treat a chemo patient presenting with vomiting?
- Bland diet
- anti-emetic - Maropitant, Odansetron, Metoclopramide
- gastroprotectant - Omeprazole, sucralfate
How could you symptomatically treat a chemo patient presenting with diarrhoea?
Bland diet
Pro-kolin (probiotic)
+/- metronidazole
IVFT
Sympto tx - loperamide, sulphasalazine
How could you symptomatically treat a chemo patient presenting with anorexia?
Antiemetics if nauseous
Appetite stimulants (e.g. cyproheptadine, mirtazapine)
Feeding tubes for temporary support
Analgesia if in pain
When might hair loss be associated with chemo tx?
If in growth phase of hair + whiskers as they grow continuously
Can be marked in poodles, bichons, some terriers
How can doxorubicin injury be prevented?
Place catheter cleanly
Firmly tape in
Flush with saline
How can you treat doxorubicin injury?
Ice (keeps it local),
Dexrazotane (antidote - free radical scavenger)
How could you treat vincristine injury?
Hot compresses
Hylauronidase (helps it disperse)
What specific toxicities are associated with Doxorubicin?
CARDIOTOXICITY
GI (Colitis) Mast cell degranulation Perivascular Pigment changes Cats - nephrotoxic
What cardiac effects are associated with doxorubicin?
Dysrhythmias
DCM
What doxorubicin side effect is only seen in cats?
Nephrotoxicity - still can give but monitor renal function
What specific toxicities are associated with cyclophosphamide?
Haemorrhagic cystitis
Why does cyclophosphamide cause a haemorrhagic cystitis?
ACROLEIN is a metabolite
How can you prevent haemorrhagic cystitis developing in patients treated with cyclophosphamide?
Monitor, Free access to water Opportunity to urinate Avoid prolonged courses FUROSEMIDE
How can you treat haemorrhagic cystitis which has developed after cyclophosphamide treatment?
Analgesia
Oxybutinin - antispasmodic
GAGs - to coat bladder
DMSO
What specific toxicities are vincristine associated with?
Peripheral neuropathies
Ileus - abdo pain - especially in cats
Constipation
Skin sloughs if perivascular injection
What could you give to help with some of the side effects associated with vincristine?
Prokinetics - metaclopramide/ ranitidine
What side effects are associated with LOMUSTINE?
How can you monitor this?
What could you give?
HEPATOTOXIC
Monitor ALT
Give SAMe
Which platinum drug gives fewer side effects?
What side effects may still be present
Carboplatin
Nausea via CRTZ
What side effects are associated with RTKIs?
MAIN - GI diarrhoea
Weight loss Myelosuppression Proteinuria Hypertension Muscle cramps Depigmentation
What cytotoxic drugs should you NEVER give to cats?
Cisplatin
5 - FU (5-fluorouracil)
What breeds are associated with the MDR1 mutation?
Herding breeds: Collies Shelters Australian Shepherds LH Whippets
What is the effect of the MDR1 mutation?
Drug excretion via kidneys or into bile
Increased toxicity of some drugs
What cytotoxic drugs shouldn’t be given to patients with the MDR1 mutation?
Why?
Vincristine
Doxorubicin
Act as substrates for the pump
How could you determine if a patient has the MDR1 mutation?
PCR test