Clinical Pharmacology and Targeted Therapies Flashcards
(108 cards)
Mechanism of therapeutic action of radiation?
- Interacts with intracellular components
- Direct effects on DNA (25-75% of cells killed)
- Indirect: ionizing water creating free hydroxyl radicals that damage
- Lethal damage from accumulation of DSB in DNA
- Sub-lethal damage from limited DSB, SSB, cross-links or base damage
Factors affecting radiation sensitivity?
- Cellular
- Cell type
- Growth and replicative activity
- Cell cycle phase at the time of exposure
- Genetic mutations in oncogenes and tumour suppressor genes - Microenvironment
- Vascularity
- Oxygenation
- Necrosis - Underlying radiation hypersensitivity
- Ataxia telangiectasia
- Nijmegen breakage syndrome - Concomitant medications (radiation sensitizer; also increased toxicity)
- Doxorubicin, dactinomycin, gemcitabine
What is a Gray? How many rad in 1 gray?
- The amount of radiation depositing 1 joule of energy in 1 kilogram
- 1 Gy=100 rad
- 1 rad=0.01 Gy or 1 centiGray (cGy)
Typical total dose of radiation? How much per fraction? Why in fractions?
- 10.8 (e.g. Wilms)-65 (e.g. head and neck)
- 1.5-2 Gy fractions
- Fractionation balances tumour lethality and normal tissue injury and exploits the cell cycle of the cancer cell
Advantage of proton therapy?
Plateau dose distribution - deposits 90-100% of the dose at the point they stop in the tissue (Bragg peak); avoids an exit dose, may decrease normal tissue toxicity
Cranial irradiation for ALL includes _______ and _____.
- Posterior half of eye
- C2
Flank irradiation for Wilms Tumour includes ________.
Whole vertebral body
Irradiation for tumour spillage and peritoneal metastases includes _________.
The pelvis
Whole lung irradiation may not be able to avoid _______.
The thyroid gland
Spinal irradiation includes _______ and extends to _____.
- Thecal sac
- S3
What is MIBG? How does it work? What cancers is it used in?
- 131-Meta-iodobenylguanidine
- Delivers beta particles via neuroendocrine transporter
- Neuroblastoma and pheochromocytoma
What enzymes involved in catabolism of mercaptopurine or thiopurines in general have clinically significant polymorphisms?
- Thiopurine methyl transferase (TPMT) - catabolism of mercaptopurine - increased toxicity (neutropenia) from mercaptopurine. 1/300 people deficient
- NUDIT-15 - polymorphisms associated with thiopurine intolerance
What enzyme involved in irinotecan metabolism can have clinically significant polymorphisms?
- UDP-glucuronosyl-transerase 1A1 (Gilberts Disease)
- Polymorphism in promoter of UGT1A1 associated with increased neutropenia in adults receiving bolus doses of inrotecan
- Effect on diarrhea in protracted dosing in children is unclear
What super family of drug metabolizing enzymes are responsible for 70-80% of all phase 1 drug metabolism? Which enzyme specifically responsible for 50% of phase 1 drug metabolism?
- Cytochrome P450
- CYP3A
Drug interactions based on inhibition of CYP3A4 include _____ and _____.
Fluconazole and vincristine
Strategies to circumvent the blood brain barrier and examples of drugs?
- High-dose chemotherapy
- Methotrexate, cytarabine - Drugs with penetrate the BBB based on lipophilicity, molecular weight, degree of ionization, plasma concentration of free drug (protein binding)
- Nitrosoureas, thiotepa, topotecan - Disruption of the BBB
- Osmotic, radiation, vasoactive compounds - Regional chemotherapy
- Intra-carotid chemotherapy (cisplatin, methotrexate)
- Intrathecal injection (methotrexate, cytarabine)
- Intratumoral (carmustine)
- Convection enhanced delivery
CSF is a fixed volume that reaches ____ of adult volume by age ___ years. Why is IT chemo dose based on age?
- 80%, 3 years
- Study 1977, 1983: IT MTX dosing based on BSA, children <18 months had higher rate of isolated CNS relapse (being underdosed).
Volume of CSF is _____.
CSF is produced in the ______ and _____of ______ at a rate of _______.
Flow is via ______ synchronized with _____.
- 135-150ml
- Produced in choroid plexus and ependyma of ventricles at a rate of 0.35-0.4ml/min.
- Flow via pulsatile motion synchronized with cardiac systole.
Dosing of intrathecal MTX and Cytarabine?
MTX: <1 yo: 6mg 1 yo: 8mg 2 y o: 10 mg >/=3 y o : 12 mg
Cytarabine: <1 yo : 15mg 1 y o: 30 mg 2 y o: 50 mg >/=3 y o : 70mg
Definition of chemotherapy? Definition of cytotoxic therapy? Definition of molecularly targeted therapy?
- Chemotherapy: drugs administered to treat cancer
- Cytotoxic therapy: refers to ability to directly kill cancer cells through non-specific mechanisms of action such as induction of DNA damage and apoptosis that result in cell death. Is non-selective (both cancer and rapidly dividing normal cells are affected; usually myelosuppressive (except vincristine). Can target cytotoxic drugs to cell surface antigens using antibody drug conjugates
- Molecularly targeted therapy: refer to drugs that interfere with pathways critical to oncogenic phenotype of cancer cells. Greater selectivity for cancer cells alters the side effect profile (have class effect toxicities). Are non-myelosuppressive or minimally myelosuppressive.
What is the Goldie-Coldman hypothesis?
- Cancer cells mutate and become resistant to therapy at a rate that depends on the cancer’s inherent genetic instability
- The probability that a cancer contains a resistance clone is dependent on the mutation rate and size of the tumour
- Even when the tumour burden is low, there is likely to be at least one drug resistant clone
Three basic principles of chemotherapy for cancer in children?
- Combination therapy
- Adjuvant chemotherapy
- Dose intensity
Definition of adjuvant chemotherapy? 2 Examples?
- Administration of chemotherapy when disease burden is minimal but risk of recurrence is high
- -Continuation of systemic therapy after local control in localized cancer e.g. 1987 Osteosarcoma: improved 3 y EFS when chemo administered after complete resection of localized tumour (20% surgery alone vs. 65% surgery + chemo)
- -Maintenance therapy: ALL - MTX, 6MP; RMS: vinorelbine +cyclophosphamide (2019)
Definition of neoadjuvant chemotherapy? Advantages?
- Administration of systemic chemotherapy prior to definitive local control
- -Reduces tumour burden at primary site prior to definitive local therapy (surgery/radiation)
- -Controls disease not amenable to local therapy (metastases)
- -Assesses the sensitivity of the tumour to chemotherapy by measuring tumour response