Pharmacology of Cancer Chemotherapy PDF - 2024

Pharmacology: Principles of Cancer Chemotherapy F.A. Fitzpatrick, PhD W7 Th: Pharmacology 19-20: Cancer Chemotherapy 1-2 - Sept 12, 9-11; Fitzpatrick - Resources & Materials W7 F: Pharmacology 21: Cancer Chemotherapy 3 - Sept. 13, 11-12; Fitzpatrick - Resources...

Pharmacology: Principles of Cancer Chemotherapy F.A. Fitzpatrick, PhD W7 Th: Pharmacology 19-20: Cancer Chemotherapy 1-2 - Sept 12, 9-11; Fitzpatrick - Resources & Materials W7 F: Pharmacology 21: Cancer Chemotherapy 3 - Sept. 13, 11-12; Fitzpatrick - Resources & Materials  Pre-Work Assignment Cell Cycle Chemotherapy The Nadir and Generalized Side Effects Nadir Cytokines - Bone Marrow Support Cell-Cycle-Specific Drugs Cell-Cycle-Nonspecific Drugs Specialized Targeted Therapies: Monoclonal Antibodies Chemo Man - Toxicity https://learn.onlinemeded.com/courses/take/pace-ps-the-cell-3- inflammation-and-neoplasia/multimedia/43805025-prime-notes General Concepts of Neoplasia Cancer Growth Log-Kill Treating Cancer https://learn.onlinemeded.com/courses/take/pace-ps-the-cell-3- inflammation-and-neoplasia/multimedia/43805028-prime-notes  Session Outcomes/Learning Objectives After completing the pre-work assignment, attending the session and studying the handout, notes and readings, a student should be able to : Learning Objective 1. Describe the phases of the cell cycle and the molecular processes that dominate each phase G1, S,G2,M and G0 Learning Objective 2. Define growth fraction and how it relates to antineoplastic treatments. Learning Objective 3 Define the log cell kill hypothesis and its clinical significance Learning Objective 4. List the various administration schedules and the routes of administration used in antineoplastic therapy. Explain why scheduling – rather than dose – is the key determinant of efficacy for cell cycle dependent drugs. Learning Objective 5. Provide the rationale for the use of drug combination therapy in cancer treatment. Learning Objective 6. Describe drug and multidrug resistance as it relates to cancer chemotherapy. Learning Objective 7. Describe serious adverse effects from cancer chemotherapy and the methods used to minimize and treat serious adverse events. Describe ‘tumor lysis syndrome’ and the rationale for using allopurinol, febuxostat or pegloticase in the management of tumor lysis syndrome. Learning Objective 8 List the major drug classes used in antineoplastic therapy, and explain their cell cycle specificities, mechanisms of action, and key toxicities. Learning Objective 9. Apply knowledge and understanding of Learning Objectives 1-8 to analyze clinically relevant scenarios. Learning Objective 1. Describe the phases of the cell cycle and the molecular processes that dominate each phase. INTRODUCTION Cancer is characterized by uncontrolled multiplication and spread of abnormal forms of the body’s own cells, illustrated by the loss of normal control mechanisms that govern cell survival, proliferation, and differentiation (often termed genetic instability). This genetic instability found within cancer cells can also lead to selection of more survivable clones through resistance to chemotherapy and radiotherapy. The invasive and metastatic nature of neoplastic cells, in combination with their genetic instability, produces symptoms and eventual death of the patient unless the neoplasm can be eradicated with treatment. There are three main approaches to treating established cancer: surgical excision, irradiation, and chemotherapy. Combination of these treatment strategies are key, as 10-15% of all cancer patients are able to be cured using chemotherapy alone while up to 50% of patients initially diagnosed can be cured with combinatorial treatment methods. Historically, cancer treatment has used cytocidal antineoplastic agents to cause lethal cytotoxicity (e.g., cell lysis). Current treatments now include agents that are also cytostatic (suppress cell growth and multiplication but do not kill cells). Ideally, antineoplastic agents would specifically target only cancer cells and leave normal, healthy cells unharmed. Unfortunately, most current antineoplastic agents do not specifically recognize neoplastic cells. In contrast, many cancer drugs affect all proliferating cells and, in turn, cause significant adverse effects. Although chemotherapy is among the primary means to treat cancer, antineoplastic agents show varying levels of effectiveness based on cancer type. In cases where cancer is difficult to treat, chemotherapy is often used as adjuvant therapy (the use of drugs following primary treatment by either surgery or radiation and often to treat metastases).  Mitosis. Cell segregates chromosomes & cytokinesis ‘Exit’ M Cell prepares G0 to divide G2 The Cell Cycle Many drugs for Organelles cancer chemotherapy G1 & cell grow are cell cycle specific DNA synthesis S as chromosomes duplicate Learning Objective 2. Define growth fraction and describe how it relates to antineoplastic treatments.  Growth Fraction & Tumor Growth Rate 1.The growth rate of most solid tumors in vivo is initially rapid, but growth rate decreases as the tumor size increases (see figure). 2.The decrease in growth rate is due to the progressive decline of nutrients and oxygen caused by inadequate vascularization in solid tumors (e.g., colon cancer) compared to disseminated tumors (e.g., leukemias). 3. As a result of inadequate nutrient supply to their interior, solid tumors have a lower growth fraction (the ratio of proliferating cells to cells in the G0 stage) than disseminated tumors. 4. In solid tumors, a higher percentage of cells at the interior are found in G0 compared to disseminated tumors. 5. As a general rule, antineoplastic drugs work best on tumors with a high growth fraction. 6. The growth fraction of indolent, slow-growing solid tumors can be increased by reducing the tumor burden through surgery or radiation, which promotes the recruitment of some of the remaining cells into active proliferation and increases their susceptibility to chemotherapeutic agents 7. Examples of human tumors with growth fractions close to 100% are Burkitt lymphoma and trophoblastic choriocarcinoma, which are readily curable by single-agent chemotherapy 8. Cancers of the lung or colon are slow-growing and have growth fractions less than 10%. Learning Objective 3 Define the log cell kill hypothesis and its clinical significance.  Treatment Regimens & Scheduling: Log-Kill Hypothesis Chemotherapy kills a fraction of tumor cells rather than an absolute number per dose. Destruction of tumor cells by chemotherapeutic agents follows first-order kinetics (a given dose of drug destroys a constant fraction of cells). The drug dose that corresponds to a three-log cell kill (i.e., 99.9% cytotoxicity) would reduce the tumor burden from 109 cells (1 billion ) to 106 cells (1 million). The major limiting factor in chemotherapy is cytotoxicity to normal tissues; only a limited log cell kill can be expected with each individual treatment (otherwise there is an increased risk of adverse events to the patient).  Learning Objective 4. List the various administration schedules and the routes of administration used in antineoplastic therapy. Explain why scheduling – rather than dose – is the key determinant of efficacy for cell cycle dependent drugs.  Schedules of Cancer Chemotherapy Drug Administration Intermittent high-dose therapy (see figure ) i) The most common form of anticancer agent administration ii) Allows recovery of normal tissues (e.g., the patient’s immune system), also affected by antineoplastic agents, and reduces the risk of serious infection iii) May be more effective with agents that are phase nonspecific (cell cycle nonspecific) Continuous infusion i) Drugs that are rapidly metabolized or excreted (or both) appear to be more effective when administered by continuous infusion ii) Antineoplastic agents that act only on one portion of the cell cycle (cell cycle specific) are also often more effective when administered by continuous infusion  Mitosis. Cell segregates chromosomes & cytokinesis ‘Exit’ M Cell prepares G0 to divide G2 The Cell Cycle Many drugs for Organelles cancer chemotherapy G1 & cell grow are cell cycle specific DNA synthesis S as chromosomes duplicate Learning Objective 1. Describe the phases of the cell cycle and the molecular processes that dominate each phase  Schedule Dependent Cancer Chemotherapy Cells in a tumor are not synchronized’ - they are distributed among G1, S, M, G2 …and G0 The duration of cells in G0 can vary dramatically in tumors, or even regions of the same tumor. An indolent, slow-growing tumor with a high proportion of cells in G0 for a substantial length of time is a ‘low growth fraction’ tumor. An aggressive, fast-growing tumor with a high proportion of cells in the cell cycle is a ‘high growth fraction’ tumor. Treatment cycle #1 Recovery 1 S S S Treatment cycle #2 S Tumor Recovery 2 Cell cycle specific drugs are schedule-dependent. The Treatment cycle #3 duration and timing of drug administration affect efficacy more than the dose.  Learning Objective 5. Provide the rationale for the use of drug combination therapy in cancer treatment  Combination Chemotherapy Combination drug chemotherapy is more successful than single drug treatment in most cancers. Advantages include the following Provides maximal cell killing within the range of tolerated toxicity Effective against a broader range of cell lines in a heterogeneous tumor population May delay or prevent the development of drug-resistant tumors\ Currently, nearly all successful cancer chemotherapy regimens use this paradigm of multiple drugs given simultaneously There are a number of principles that have been used in designing antineoplastic drug therapy 1. Each drug used in combination therapy should have some individual therapeutic activity 2. Drugs that act by different mechanisms may have additive or synergistic therapeutic effects, thus increasing log cell kill and diminishing the probability of the emergence of drug-resistant tumor cells 3. Drugs with different dose-limiting toxicities should be used in combination to avoid cumulative damage to a single organ (agents with similar dose-limiting toxicities can be combined safely only by reducing the doses of each) 4. Intensive intermittent schedules of drug treatment should allow time for recovery from the acute toxic effects of antineoplastic agents 5. Several cycles of treatment should be given (most curable tumors require at least 6-8 cycles of therapy)  Toxic Effects of Chemotherapy on Healthy Cells Key concept: Cancer chemotherapy often affects dividing normal cells – especially cells that ‘turnover’ rapidly. Not every drug affects every organ the same way or to the same extent. Thus, it is desirable to avoid multi-drug combinations that have additive or synergistic toxicities on a particular organ system. The goal is to choose chemotherapy regimens that use multi-drug combinations that distribute toxicity among different organs. The rationale governing the selection of individual drugs in regimens for combination chemotherapy: a) Distribution of dose-limiting toxicities among different organ systems b) Distribution of drug actions among different phases of the cell cycle c) Distribution of drugs among cell cycle specific mechanisms and cell cycle non-specific mechanisms.  Learning Objective 6. Describe drug resistance and multidrug resistance as it relates to cancer chemotherapy.  Chemotherapy Complications: Drug Resistance Resistance 1. Some neoplastic cells exhibit primary resistance to currently available agents (an absence of response on the first exposure) 2. Primary resistance is thought to be due to the genomic instability associated with the development of most cancers 3. Acquired resistance develops in response to exposure to a given antineoplastic agent 4. Acquired resistance is often highly specific to a single drug, or class of drugs, and is usually based on a specific change in the genetic machinery of a given tumor cell with amplification or increase expression of one or more genes 5. Examples of resistance pathways to single antineoplastic agents include the following a. Decreased drug transport into cells b. Reduced drug affinity due to mutations or alterations of the drug target c. Increased expression of an enzyme that causes drug inactivation d. Increased expression of DNA repair enzymes for drugs that damage DNA Multidrug resistance 1. A multidrug-resistant phenotype may occur in neoplastic cells that is associated with an increased expression of the MDR1 gene, which encodes a cell surface transporter glycoprotein (P-glycoprotein) 2. The P-glycoprotein pump is an ATP-dependent transporters that confers resistance to anthracyclines, vinca alkaloids, etoposide, paclitaxel, and dactinomycin 3. The P-glycoprotein transporter may be inhibited by calcium channel blockers such as verapamil  P-Glycoprotein Multi-Drug Resistance Drug A Drug B Pgp efflux pump The tumor cell expressing P-glycoprotein can emerge as the dominant component of cancer after Tumor Cells multiple rounds of treatment (recurrence) Learning Objective 7.1. Describe serious adverse effects from cancer chemotherapy and the methods used to minimize and treat serious adverse events - bone marrow toxicity & myelosuppression.  Toxicities: Cancer Chemotherapies Alopecia Mucositis Chemo-brain Dermatitis Ototoxicity Nausea/vomiting Pulmonary fibrosis Diarrhea Cardiotoxicity Cystitis Blister Sterility Nephrotoxicity Myalgia Myelosuppression Neuropathy Phlebitis Chemotherapy Complications: Toxicity & Secondary Cancers Toxicity Cancer chemotherapy drugs exert their toxic effects on both normal and tumor tissues even at optimal doses. Since antineoplastic agents target cells that are highly proliferative (high growth fraction), rapidly proliferating normal tissues are the major sites of toxicity of these agents (high growth fraction tissues include bone marrow, gastrointestinal tract, hair follicles, buccal mucosa. Many antineoplastic agents are mutagens themselves, and neoplasms may arise ten or more years after the original cancer was cured (e.g., acute nonlymphocytic leukemia). Treatment-induced tumors can occur especially after therapy with alkylating agents Common adverse effects 1. Severe vomiting, nausea, stomatitis, and alopecia occur to a lesser or greater extent during therapy with nearly all antineoplastic agents 2. Destruction of actively proliferating hematopoietic precursor cells causes myelosuppression, which can cause a predisposition to infection and impaired wound healing 3. Chemotherapy-induced myelosuppression can produce leukopenia, thrombocytopenia, and to a lesser extent, anemia Blood counts normally reach their nadir (low point) 10-14 days after treatment with recovery by day 21 and a return to normal by day 28 Key concept: Bone marrow suppression is a dose-limiting toxicity of nearly all anti-metabolites used in cancer chemotherapy A neutrophil count < 0.5 x109/L is an oncology emergency after chemotherapy  day 7-14. Patient support includes granulocyte colony-stimulating factor (G-CSF, filgrastim and PEG- filgrastim) & granulocyte-macrophage colony-stimulating factor (GM-CSF, sargramostim) to reduce the duration & degree of neutropenia. G-CSF (filgrastim) & GM-CSF (sargramostim) are effective at reducing the incidence of neutropenic fever and infectious complications in cancer patients receiving chemotherapy  Support for the Bone Marrow: Colony Stimulating Factors for Hematopoietic Progenitor Cells For the drugs listed below, know the therapeutic use and their cellular effects in the management of bone marrow toxicity by cancer chemotherapy drugs Complication Cell Deficit Drug Epoetin  Anemia Erythrocytes Darbepoetin  Filgrastim Neutropenia Neutrophils PEG filgrastim GM-CSF Sargramostim Neutrophils, Granulocytopenia Eosinophils GM-CSF Sargramostim Basophils. Thrombocytopenia Platelets IL-11 (Oprelvekin) Start filgrastim i.v., or sq daily. 24 to 72 hrs after chemo ends. PEG- filgrastim can be given once per chemotherapy cycle. Continue until clinically adequate neutrophil recovery. Avoid premature discontinuation before reaching the white blood cell nadir  Filgrastim & PEG-filgrastim stimulate neutrophil progenitors neutrophil lineage expansion Sargramostim stimulates myeloid progenitors granulocyte-monocytye progenitors Expansion of many granulocytes & monocytes  CSF & GM-CSF Clinical Complications & Adverse effects Adverse effect of G-CF colony stimulating factors - bone pain- resolves when the drug is discontinued Approximately 20% of cancer patients experienced bone pain with the administration of prophylactic daily G-CSFs (filgrastim). The reported incidence of bone pain in cancer patients undergoing peg-filgrastim prophylaxis ranged from 25% to 38%. There are four main causes of G-CSF related bone pain: bone marrow quantitative and qualitative expansion, peripheral nociceptor sensitization to nociceptive stimuli, modulation of immune function and direct effect on bone metabolism. For the prevention and treatment of bone pain occurring after or during GCSFs administration, acetaminophen and nonsteroidal anti-inflammatory agents/non- narcotic analgesics are commonly used as first-line treatment. Certain malignant cell lineages, e.g. ALL might respond to granulocyte CSF, potentially worsening the underlying condition, or triggering malignancy. Prophylactic antibacterial and antifungal agents are more commonly used during chemotherapy for AML rather than CSFs.  Learning Objective 7.2. Describe ‘tumor lysis syndrome’ and the rationale for using allopurinol, febuxostat or pegloticase in the management of tumor lysis syndrome  Chemotherapy Tumor lysis Key Concept: Chemotherapy can sometimes cause abrupt death of vast numbers of tumor cells, e.g. especially blast cells in leukemia or lymphoma. Chemicals released from dying cells can produce hyperuricemia & related life- threatening electrolyte complications. Acute nephrotoxicity produced by excessive uric acid is managed by co- administration of allopurinol (a xanthine oxidase inhibitor) with any chemotherapeutic agent when there is an K+ release Hyperkalemia anticipation that chemotherapy may cause tumor lysis syndrome. DNA release Hyperphosphatemia Nucleotides PO−2 Ca2+ imbalance (hypocalcemia) Purines uric acid Hyperuricemia  Acute renal Hyperuricemia Failure Hyperkalemia Hyperphosphatemia Precipitated interstitial urate crystals with an inflammatory response.  Drug Indication Dosing Pegloticase Hyperuricemia associated IV (uric acid with malignancy Q 2 weeks oxidase) (tumor lysis syndrome) Uric acid Pegloticase Allantoin Tumor Lysis Syndrome: Management with Pegloticase Transition Learning Objective 8 List the major drug classes used in antineoplastic therapy, including their cell cycle specificities, mechanisms of action, and key toxicities. Pyrimidine Antimetabolites Learning Objective 8.1. List the pyrimidine antimetabolites used for cancer chemotherapy. Describe their distinctive features and dose-limiting toxicity Abbreviations – Pyrimidines and Folate Antimetabolites Ara-C – cytarabine DHFU – didhydrofluorouracil 5FU – 5-fluorouracil FUMP – 5-fluorouridine monophosphate, FUDP, FUTP –…diphosphate, …triphosphate FdUMP – 5-fluorodeoxyuridine monophosphate FdUDP, FdUTP – …diphosphate, …triphosphate dNTP – deoxynucleotide triphosphate dTMP – deoxythymidine monophosphate dTDP, dTTP – …diphosphate,… triphosphate dUMP – deoxyuracil monophosphate dUDP, dUTP – …diphosphate,…triphosphate AICAR – aminoimidazole carboxamide ribonucleotide DHF – dihydrolfolate GTD – gestational trophoblastic disease (glu)n – polyglutamate HDMTX – high dose methotrexate MTX – methotrexate RFC – reduced folate carrier THF – tetrahydrofolate DHFR – dihydrofolate reductase TS – thymidylate synthase  Abbreviations - Purine Antimetabolites ALL – acute lymphoblastic leukemia AML – acute myelogenous leukemia APL – acute promyelocytic leukemia CLL – chronic lymphocytic leukemia 6-MP – 6 mercaptopurine 6-TG – 6 thioguanine NHL – Non-Hodgkin’s lymphoma CDK – cyclin dependent kinase dCK – deoxycytidine kinase GMPS – guanosine monophosphate synthetase HPRT – hypoxanthine ribosyltransferase = HGPRT HGPRT – hypoxanthine-guanosine ribosyltransferase IMPDH – inosine monophosphate dehydrogenase TPMT – thiopurine-S-methyl transferase XO – xanthine oxidase  5-Fluorouracil - Pyrimidine Antimetabolites 8.2. Describe the mechanism of action and cell cycle specificity, the mechanism of resistance, and the adverse effects of 5-fluorouracil and related fluoro-pyrimidine antimetabolites used for cancer chemotherapy  5-FU Bioactivation & Mechanisms of Action 5FU is a cell cycle specific drug acting selectively in S-phase - when DNA synthesis occurs 5FU T phosphorylase DNA T/U phosphorylase activity in T Kinase tumor tissue is greater than in FUdR normal tissue, which leads to dTTP ‘selective’ activation , and ‘selective toxicity’ of 5FU in FdUMP tumors dTDP dUMP Thymidylate dTMP Synthase  5 Fluorouracil Mechanisms of Drug Resistance Alterations in thymidylate synthase (TS) are the most common mechanism of resistance to 5FU. There is a strong inverse correlation between levels of TS activity & protein expression & sensitivity of tumors to 5FU. Cell lines and tumors with higher levels of TS are relatively resistant to 5FU. Increased TS protein content is usually associated with TS gene amplification  5FU Pharmacogenetics Affects Its Efficacy & Toxicity The DPYD gene encodes DPD, an enzyme that breaks down thymine and uracil. DPD deficiency (hereditary thymine-uraciluria or familial pyrimidinemia) is a recessive trait with variable symptoms (…from none …to seizures). 3-8% of the population may carry DPYD mutations associated with DPD deficiency. Capecitabine  The carbamate appendage makes capecitabine orally bioavailable  Cytarabine and Gemcitabine Pyrimidine Antimetabolites Learning Objective 8.3. Define the roles/contributions of cytidine deaminase in the mechanism of action/pharmacological activity / toxicity of cytarabine (Ara C) and gemcitabine Understand the roles/contributions of the following active metabolites to the mechanism of action /pharmacological activity/toxicity cytarabine and gemcitabine AraCTP – cytarabine triphosphate Gemcitabine nucleotide triphosphate  Ara-C Mechanism of Resistance Tumor (AML) response to Ara-C depends on its rate of activation versus its rate of inactivation by pyrimidine nucleotidase (PN) & cytidine deaminase (CDA) in tumor cells. CMPK dCK NDK P P P P P P PN ARA-C ARA-CMP ARA-CDP ARA-CTP Cytosine Overexpression or high deaminase cytosine deaminase enzyme activity confers tumor ARA-U ARA-UMP resistance to ARA-C inactive inactive  Ara-C Ara-CTP Active Liver & spleen contain very high levels of cytidine deaminase (CDA). These organs are a biochemical sanctuary for leukemic cells because liver & spleen Ara-U deaminate Ara-C, converting it to an inactive inactive Ara-U metabolite which has no antileukemic activity. This event probably occurs frequently when Residual Ara-C is administered in standard dose leukemia regimens. in liver & spleen sanctuary Transition Learning Objective 8 List the major drug classes used in antineoplastic therapy, including their cell cycle specificities, mechanisms of action, and key toxicities. Methotrexate Anti-Folate Drug Learning Objective 8.4. Describe the distinctive features and dose-limiting toxicity of the anti-folate drug methotrexate.  Methotrexate Anti-Folate Drug Mechanism of Action Learning Objective 8.5. Describe the mechanism of action, cell cycle specificity, mechanism of resistance, and adverse effects of methotrexate and related antifolate drugs used for cancer chemotherapy. Summarize the contributions of the following enzymes in the mechanism of action of methotrexate Dihydrofolate reductase (DHFR) polyglutamate synthase Describe the contributions of the following active metabolites to the mechanism of methotrexate MTX polyglutamate - MTX(glu)n Dihydrofolate polyglutamate – DHF(glu)n MTX is a cell cycle specific drug acting in S-phase. MTX enters cells via energy dependent transport (RFC). Competitive inhibition of DHFR is the main mechanism of action for MTX. Like folate, MTX accumulates in cells as a polyglutamate – MTX(glu)n. Inhibition of DHFR causes accumulation of DHF. DHF(glu)n inhibits DNA TS and AICAR transformylase dTTP Thymidylate dTDP Synthase dUMP dTMP MTX(Glu)n DHF(Glu)n RFC MTX N5,N 10--CHCH N ,N 5 THF THF 10 2 2 DHF Gly NADPH Serine -CH2OH THF THF DHF Reductase transferase Ser Ser NADP+  Methotrexate Anti-Folate Drug Adverse Effects Learning Objective 8.6. Describe the adverse effects of methotrexate, and the importance of dose-level and drug clearance process in the emergence of these toxicities. Methotrexate Anti-Folate Drug Adverse Effects Leucovorin Rescue Learning Objective 8.7. Explain the process of ‘leucovorin rescue’ of normal bone marrow stem cells and epithelial cells from the extreme cytotoxic adverse effect of very high dose methotrexate used in bone marrow ablation, or cancer chemotherapy.  Leucovorin (folinic acid, N5-formyl- Why doesn’t leucovorin rescue tetrahydrofolate) tumor cells? bypasses the blocked DHFR enzyme & Intracellularly, leucovorin competes best replenishes the folate pool of normal bone with free, but not polyglutamated MTX marrow stem cells and epithelial cells. It can for binding to DHFR. Compared to moderate potentially fatal myelosuppression tumor cells, less polyglutamated MTX associated with HDMTX synthesis occurs in normal gut epithelium and bone marrow. It is hypothesized that because of the lower levels of intracellular polyglutamate HDMTX MTX, leucovorin can more effectively curtail DHFR inhibition in normal as compared with malignant cells. block Leucovorin rescue Transition Learning Objective 8 List the major drug classes used in antineoplastic therapy, including their cell cycle specificities, mechanisms of action, and key toxicities. Purine Antimetabolites Learning Objective 8.8. List the purine antimetabolites used for cancer chemotherapy. Describe their distinctive features and dose-limiting toxicity.  Effects of Active Metabolites of 6-Mercaptopurine on Purine Synthesis & Cell Cycle Learning Objective 8.9. Explain the effects of active metabolites of 6-mercaptopurine on purine synthesis and salvage pathways, and on DNA and RNA integrity.  Bioactivation of 6-Mercaptopurine 6-Methyl-TIMP HGPRT in cells activates 6-MP to TIMP. Inosine ribonucleotides monophosphate dehydrogenase (IMPDH) & TMPT convert TIMP into active nucleotides. TPMT TIMP Liver 6-MP HGPRT 6-thio-inosine monophosphate Active IMPDH metabolites TXMP 6-thioxanthine monophosphate  6-Methyl TIMP is a potent inhibitor of de novo purine 6-Methyl TIMP de novo purine biosynthesis. ‘Purine starvation’ occurs in ribonucleotides Biosynthesis cells exposed to 6-MP IMP , or its precursor Azathioprine TPMT AMP GMP TIMP 6-MP HPRT 6-thioinosine RNA monophosphate HGPRT in cells activates 6- MP to TIMP. Inosine monophosphate dehydrogenase (IMPDH) & IMPDH DNA TMPT convert TIMP into active nucleotides TXMP GMPS 6-thioxanthine Kinases 6-thio-dGTP monophosphate Reductases 6-thio-GTP 6-TG Is Activated by HPRT; Inactivated by TPMT Methyl-6-TG Methyl-6-TGMP Purine starvation is negligible in cells exposed TPMT TPMT to thioguanosine (TG) because thioinosine monophosphate (TIMP) is 6-thio-GMP not produced from 6-TG. 6-TG HPRT 6-thioguanylate 6-TG nucleotide formation monophosphate & DNA damage are common to 6-MP, 6-TG, and Azathioprine Kinases Reductases RNA 6-thio-dGTP DNA 6-thio-GTP  Xanthine Oxidase: Role in 6-Mercaptopurine Bioavailability Learning Objective 8.10 Explain the clinical complications that can arise from inhibition of xanthine oxidase by other drugs, especially medications or treatment of gout. Transition  Learning Objective 8 List the major drug classes used in antineoplastic therapy, including their cell cycle specificities, mechanisms of action, and key toxicities. Antimitotic Drugs Disrupt Microtubule Stability Learning Objective 8.11.Compare and contrast the mechanism of action, typical therapeutic uses, dose-limiting toxicities and unique toxicities of separate anti-mitotic drugs belonging to the vinca alkaloid and taxane families.  (−) ‘Fraying’ end disassembly (+) continues, so Forming end microtubules shorten assembly     Sub-unit Sub-unit GTP tubulin GDP tubulin Vinca alkaloids, such as vinblastine, bind to microtubule ends. Vinca alkaloids bind to  tubulin subunit & block microtubule assembly (polymerization). Microtubules shorten/appear.  (+) forming end (−) taxanes block assembly continues. disassembly Microtubules lengthen     Sub-unit Sub-unit GTP tubulin GDP tubulin Taxanes bind to interface of  and  tubulin subunits and at the negative end of tubulin, block disassembly and over-elongate microtubules  Antimitotic Drugs M-Phase Selectivity & Adverse Effects Learning Objective 8.12. Describe how the mechanism of action of the vinca and taxane drugs makes them M-phase specific and causes peripheral neuropathy/neuritis Transition Learning Objective 8 List the major drug classes used in antineoplastic therapy, including their cell cycle specificities, mechanisms of action, and key toxicities. Topoisomerase Inhibitors That Cause DNA Strand Breaks Learning Objective 8.13.Compare and contrast the distinctions, typical therapeutic uses and dose-limiting toxicities of camptothecin and podophyllotoxin topoisomerase inhibitors. Topoisomerase Inhibitors That Cause DNA Strand Breaks Learning Objective 8.14 Align the podophyllotoxins and camptothecins with their respective targets - topoisomerase I or topoisomerase II – and explain the nature of the DNA damage inflicted by each type of drug.  Topoisomerase I Single strand cut Topoisomerase II Double strand cut Topoisomerases bind to DNA in a noncovalent fashion, and form transient cleavage complexes. In these complexes, topoisomerases I and II create single- and double- stranded breaks, respectively. In the presence of topoisomerase inhibitors, e.g. etoposide or teniposide, levels of cleavage complexes increase dramatically. Transient topoisomerase-mediated breaks become permanent double-stranded fractures, triggering events that ultimately culminate in cell death.  Super-coiled DNA Topoisomerase II Cleave - The mechanism is conceptually Unwind similar with irinotecan but it involves Topoisomerase 1 Etoposide Super-coiled LOCKED DNA Persistently Cleavable Topoisomerase II Cleave - Complex Unwind Double – strand breaks  Topoisomerase I Inhibitors – S Phase Topoisimerase II Inhibitors – S-phase or G2 Transition Anthraquinones & Bleomycin: Drugs That Cause DNA Strand Breaks by Intercalation or Oxidative Scission Learning Objective 8.15 Summarize the distinctions, typical therapeutic uses and dose-limiting toxicities of anthracycline and bleomycin antitumor antibiotic Anthraquinones & Bleomycin: Drugs That Cause DNA Strand Breaks by Intercalation or Oxidative Scission Learning Objective 8.16. Compare and contrast doxorubicin and bleomycin in terms of their unique cardio-pulmonary toxicities. Be able to identify these drugs based on scenarios related to their clinical use and toxicity.  Doxorubicin (Anthracyclines) intercalate between DNA double helix & create distortions that disrupt DNA integrity, inhibit DNA synthesis & replication – All antitumor anthracyclines are intercalating agents. Intercalation is a reversible chemical process. The distortion of DNA structure caused by intercalation of doxorubicin and related anthracyclines prevents topoisomerase enzyme from ‘sliding’ along DNA, which also blocks DNA synthesis Doxorubicin Anthracycline cardiomyocyte involves injury free radical damage to vital cell structures and subsequent cell death. Reduction of the quinone groups on the anthraquinone structure results in a semiquinone radical, before further reduction to the alcohol (e.g., doxorubicinol). Interaction of the semiquinone with oxygen generates superoxide anion (O2−). Dismutation of superoxide anion yields H2O2, which may react further with cardiac iron sources or the semiquinone to produce a reactive intermediate with the chemical characteristics of the hydroxyl radical. These reactions can proceed in either an iron-dependent or iron-independent fashion. Doxorubicin Clinical symptoms and signs (e.g., new onset of otherwise unexplained dyspnea on exertion and/or sinus tachycardia), in combination with radionuclide scans or echocardiograms at baseline, 300 mg/m2, 450 mg/m2, and each 100 mg/m2 thereafter is the best way to monitor patients for doxorubicin-induced cardiomyopathy. Concurrent and sequential use of trastuzumab (Herceptin) with anthracycline- based adjuvant chemotherapy in patients with HER2(+) positive breast cancer significantly increases risk for cardiac toxicity  Anthraquinone Adverse Effects ANTHRACYCLINE Cyp450 Cyto- DOXORUBICIN protection NADPH reductase Catalase NADH QUINONE O2 O2 − H2O2 NADP+ SEMIQUINONE Superoxide Hydrogen NAD+ Peroxide DNA Damage Cardiotoxicity – dilated cardiomyopathy, heart failure Bleomycin Mechanism of Action and Unique Toxicity  Compare Unique Toxicities Doxorubicin Bleomycin (Anthracyclines) Dyspnea, rales, dry cough, Dilated infiltrate fibrosis cardiomyopathy, heart failure THE SESSION SLIDES END HERE Questions ? F.A. Fitzpatrick, Ph.D. [email protected] Pharmacology: Principles of Cancer Chemotherapy ….continued F.A. Fitzpatrick, PhD W7 Th: Pharmacology 19-20: Cancer Chemotherapy 1-2 - Sept 12, 9-11; Fitzpatrick - Resources & Materials W7 F: Pharmacology 21: Cancer Chemotherapy 3 - Sept. 13, 11-12; Fitzpatrick - Resources & Materials  Abbreviations CCNS – cell cycle non-specific CYP – cytochrome GSH – reduced glutathione MTIC – methyltriazene imidazole carboxamide NSCL – non-small cell lung OAT – O6 alkyl guanine alkyl transferase MGMT – Methyl guanine methyl transferase  Back to the principles Learning Objective 4. List the various administration schedules and the routes of administration used in antineoplastic therapy. Explain why scheduling – rather than dose – is the key determinant of efficacy for cell cycle dependent drugs. Why do why cell cycle non-specific drugs have concentration-dependent effects, rather than schedule-dependent effects? Why does that property make these drugs an important component of chemotherapy regimens to treat indolent, slow-growing tumors with a low- growth fraction (i.e. most cells exited the cell cycle - in G0)  Mitosis. Cell segregates chromosomes & cytokinesis ‘Exit’ Cell prepares M to divide G0 G2 So far, we covered cell- cycle specific drugs. What about slow growing tumors with most tumor cells exited G1 from the cell cycle i.e. Organelles ‘low growth fraction’ & cell grow tumors ? S DNA synthesis as chromosomes duplicate  ‘DNA Damage’ Drugs Drugs That Alkylate or Cross-Link DNA Cell cycle non-specific drugs are dose-dependent (concentration dependent). The dose of drug affects efficacy more than the schedule of administration. The greater the damage to tumor cell DNA, and the more persistent the damage to tumor cell DNA then the greater the efficacy. Unfortunately, these agents have little preference for tumor cells, thus their toxicity is often a major complication. Key concept: DNA alkylation is a type of DNA damage…not all DNA damage involves alkylation. Clinically significant Alkylation alkylation reactions include inter-strand or intra-strand DNA cross-linking, DNA methylation, and DNA ethylation. Drugs in this category directly damage DNA via covalent reactions with purines or pyrimidines. This causes miscoding of DNA bases (esp. G-T pairing) and DNA strand breakage (depurination). Tumor suppressors proteins, especially p53, recognize drug-mediated damage to the genome and p53, can activate the transcription of genes that arrest the cell cycle, repair the damage or trigger apoptosis to remove the tumor cell. Tumor cells with mutant p53 tumor suppressor genes, or an impaired p53-response do not respond optimally to DNA damaging drugs.  Sensitivity & Resistance To DNA Alkylating/Cross Linking Agents DNA repair capability – Tumor sensitivity to alkylating drugs is inversely proportional to activity of repair enzymes,e.g., guanine O6-alkyl transferase (OAT), methyl guanine methyl transferase (MGMT) Multidrug resistance – if cancer cells adapt by producing more glutathione or increasing DNA repair, they will be less susceptible to other alkylating agents, especially those in the same class. Reduced glutathione is a ‘nucleophile’ which will protect cells from ‘electrophiles’ – i.e. alkylating drugs. Learning Objective 8 List the major drug classes used in antineoplastic therapy, including their cell cycle specificities, mechanisms of action, and key toxicities. DNA Alkylating Drugs Cell Cycle Non-Specific Effects Learning Objective 8.17. List the main nitrogen mustard type alkylating agents and their clinical uses. Define the roles of the cytochrome P450 enzymes in the mechanism of action / pharmacological activity and urotoxicity of cyclophosphamide & ifosfamide.  Cyclophosphamide Urotoxicity Learning Objective 8.18. Describe the mechanism of bladder toxicity from cyclophosphamide and explain the use of MESNA in the management of bladder toxicity from cyclophosphamide  Managing Urotoxicity of Nitrogen Mustards with MESNA MESNA is administered prior to nitrogen mustards to limit the hemorrhagic cystitis caused by acrolein, the urotoxic metabolite of cyclophosphamide & ifosfamide. MESNA is a sulfhydryl agent – like reduced glutathione (GSH). If given prophylactically it forms a non-toxic thiol conjugate with acrolein, thereby preventing cytotoxicity in the bladder & lessening the severity of hemorrhagic cystitis. Some patients are allergic to Non-toxic MESNA and they must be Thiol conjugate treated with antihistamines, of acrolein corticosteroids or both to manage hypersensitivity. The ‘sulfur’ smell is Acrolein objectionable & can Urotoxic metabolite aggravate nausea. Cisplatin & Related Organoplatinum Drugs Learning Objective 8.19 Describe the mechanism of action, adverse effects, therapeutic uses and dose limiting toxicities of cisplatin, oxaliplatin and carboplatin  Cisplatin use is limited by severe side effects – notably  nephrotoxicity  ototoxicity. More than 50% of cisplatin is excreted in the urine in the first 24 hours following its administration, and the concentration of cisplatin in the renal cortex is several-fold greater than that in plasma and other organs. Nephrotoxicity occurs in about 1/3 of patients undergoing cisplatin treatment. Clinically, cisplatin nephrotoxicity is often seen after 10 days of cisplatin administration and is manifested as lower glomerular filtration rate, higher serum creatinine, and reduced serum Mg2+ and K+ levels. Cisplatin is cleared by the kidney - nephrotoxicity can worsen via progressively increasing exposure Transition Learning Objective 8 List the major drug classes used in antineoplastic therapy, including their cell cycle specificities, mechanisms of action, and key toxicities. Cancer Chemotherapy Targeted Therapy & Biologicals Abl Tyrosine Kinase Inhibitors Learning Objective 8.18. List the drugs that inhibit Abl tyrosine kinase; describe their mechanism of action & adverse effects, and relate their therapeutic utility for CML, GIST, RCC to their specific molecular target.  Abbreviations ATRA – all trans retinoic acid CML – chronic myeloid leukemia EGF – epidermal growth factor EGFR – EGF receptor tyrosine kinase GF – growth factor GIST- gastrointestinal stromal tumor HCC – hepatocellular carcinoma NSCLC – non small cell lung cancer PDGF – platelet derived growth factor PDGFR – PDGF receptor tyrosine kinase RCC – renal cell carcinoma RTK – receptor tyrosine kinase TKI – tyrosine kinase inhibitor VEGF – vascular endothelial growth factor VEGFR – VEGF receptor tyrosine kinase  Cancer Chemotherapy Targeted Therapy & Biologicals Inhibitors of Oncogenic Growth Factor Receptor / Membrane Associated Tyrosine Kinase Learning Objective 8.19. List the drugs that inhibit growth factor membrane receptor tyrosine kinases and describe their mechanism of action, adverse effects and therapeutic utility for GIST, RCC, breast cancer, colorectal cancer, non-small cell lung cancer. Erlotinib Gefitinib Lapatinib Sunitinib Sorafenib  Cancer Chemotherapy Targeted Therapy & Biologicals Monoclonal Antibodies Targeting Growth Factor Membrane Receptor Tyrosine Kinase Enzyme Learning Objective 8.20. List the monoclonal antibodies that interact with growth factor membrane receptor tyrosine kinases and describe their mechanism of action, adverse effects and therapeutic utility for GIST, RCC, breast cancer, colorectal cancer, non-small cell lung cancer.  Cancer Chemotherapy Targeted Therapy & Biologicals Monoclonal Antibodies Targeting Immune Cells Learning Objective 8.20. List the antibodies that interact other oncogenic epitopes and describe their mechanism of action, adverse effects and therapeutic utility for lymphoma, leukemia and solid tumors. Rituximab Pembrolizumab  Pembrolizumab Broad Spectrum Mab for Solid Tumors: Restores T-Cell Activation Pembrolizumab binds to the PD-1 receptor (programmed-death receptor on T-cells) and blocks both immune-suppressing ligands, PD-L1 and PD-L2 (on tumor cells), from interacting with PD-1. Blockade of PD-1 restores T-cell immune response. First-line treatment of NSCLC expressing PD-L1, with no EGFR or ALK genomic tumor aberrations, and is stage III where patients are not candidates for surgical resection or definitive chemoradiation, or metastatic.  Cancer Chemotherapy Targeted Therapy & Biologicals Angiogenesis Inhibitors & Antibodies Learning Objective 8.21. Describe the process of angiogenesis and its role in tumor progression. List targeted therapies – antibodies and drugs – that inhibit angiogenesis and their clinical indications. mAb against VEGF ligand – Bevacizumab PDGF-R, VEGF-R tyrosine kinas inhibitors – Sunitinib & Sorafenib  Cancer Chemotherapy Targeted Therapy & Biologicals Differentiating Agents & Unique Drugs Learning Objective 8.21 Explain the mechanism of action and use of: i) all trans-retinoic acid. iii) asparaginase (PEG asparaginase)  Cancer Chemotherapy Learning Objective 9. Apply knowledge and understanding of Learning Objectives 1-8 to analyze clinically relevant scenarios. Clinical Correlation 1 DS is a 48-year-old woman recently diagnosed with treatment-induced acute myelogenous leukemia (AML). She was successfully treated for breast cancer 4 years prior after receiving six cycles of AC chemotherapy (doxorubicin [Adriamycin] and cyclophosphamide). Her total cumulative dose of doxorubicin was 360 mg/m2. Her current oncologist would like to begin induction chemotherapy for her AML with the goal of achieving remission. He recommends a regimen consisting of high-dose cytarabine and daunorubicin. She is otherwise in good health. Describe the pharmacology and major side effects of anthracycline agents. What special precautions should be considered when administering anthracyclines? Is this patient at risk for anthracycline-induced cardiotoxicity? How should she be monitored? Transition Clinical Correlation 2 TB is a 46-year-old woman with osteosarcoma who is admitted for treatment with very high-dose methotrexate. All of her admit laboratory values were within normal limits. She is given 1000 mL normal saline (NS) IV over 2 hours, then started on D5W with 2 amps (100 mEq) sodium bicarbonate/liter to run at 250 mL/hr. Her urine pH is checked hourly. Once her urine pH is sufficiently alkaline and her urine output is considered adequate, methotrexate is administered IV over 4 hours. Twenty-four hours after the methotrexate infusion, leucovorin “rescue” is begun. What is the pharmacology of methotrexate and what are its main side effects? What is the role of hydration in this patient? How does leucovorin work in this case and when should it be stopped? What other factors should be considered in patients receiving high-dose methotrexate? What are other antimetabolites used in cancer treatment and what are their principal side effects? Transition Clinical Correlation 3 GH is a 48-year-old woman who presents with stage III epithelial adenocarcinoma of the ovaries. She has received three cycles of cisplatin and paclitaxel, but now the cancer has progressed. Her course has been complicated by severe side effects, including numbness of her feet, persistent nausea and vomiting , severe neutropenia, and renal dysfunction (serum Cr 1.5 mg/dL). Her physician is considering switching to an alternative regimen consisting of ifosfamide and etoposide. She is reluctant due to her poor tolerability of her previous therapy. What issues should be considered when selecting an alternative regimen? Which agents caused her complications? THE SESSION SLIDES END HERE Questions ? F.A. Fitzpatrick, Ph.D. [email protected]