Cancer Chemotherapy Principles & Cytotoxic Drugs

The Plant Alkaloids Class (5 drugs to know) Which subclass do these belong to? -Vinblastine -Vincristine -Paclitaxel -Etoposide -Irinotecan

-Vinblastine (Vinca alkaloid)...CCS -Vincristine (Vinca alkaloid)...CCS -Paclitaxel (Taxene)...CCS -Etoposide (Epipodophyllotoxin)...CCS -Irinotecan (Camptothecan)...CCS and CCNS

Platinum compounds (subclass of the alkylating agents) in general What are the two platinum compounds discussed?

-administered via IV -enter cancer cells by diffusion and active transport -mechanism of action similar to cyclophosphamide (cross link G bases on opposite DNA strands; interstrand crosslinking) -they are CCNS drugs just like cyclophosphamide... also have prominent activity during the S phase of the cell cycle Platinum compounds: 1. cisplatin 2. oxaliplatin

Benefits of Adjuvant Cytotoxic Chemo?

-answer primarily depends on type, stage, grade of cancer, and the end point used to define "benefit" such as 5 year survival or 10 year progression free -clear benefits of 10-15% for "chemo sensitive cancers" -lower benefits of 1-2% for non chemo sensitive cancers like colon or lung -all depends on risk (of drug) vs benefit weighing

*DRUG TWELVE: Doxorubicin (anthracyclines)* Where does the drug come from? Which cancers does it treat? Mechanism of action? How administered? Toxicities? Resistance?

Doxorubucin is isolated from Streptomyces bacteria. A very popular cytotoxic drug. CCNS! Treats: Hodgkin's and non-Hodgkin's lymphoma, breast, ovarian and bladder cancer Mechanism: A. DNA intercalation that indirectly interferes with DNA and RNA poly activity B. inhibits topoismerase II C. generates semiquinone and *oxygen free radicals via iron* dependent processes; leads to DNA scission --> *this is why it can cause cardiotoxicities* Administered by IV *Toxicities: reversible acute arrhythmias and heart conduction abnormalities; dose limiting toxicity is irreversible, chronic cardiomyopathies* Resistance: due to increased MDR1 expression; also increased glutathione peroxidase activite; also resistance rendering mutations to topo II

*DRUG TEN: Etoposide (epipodophyllotoxins)* Where does the drug come from? Which cancers does it treat? Mechanism of action? How administered? Toxicities? Resistance?

Etoposide is a semi-synthetic derivative of the podophyllotoxin from the mayapple root. Cancers treated: testicular cancer, non small cell and small cell lung carcinoma, AML, ALL, Hodgkin's and non-Hodgkin's lymphomas\ Mechanism: Blocks tumor cells in the late S-G2 phase of the cell cycle through inhibition of *topoisomerase II.* DNA strand is strained and breaks. Administered by IV or orally Toxicities: myelosuppression is dose-limiting, alopecia Resistance: due to increased MDR1 gene expression

Patterns of Chemo toxicity in normal tissues - General patterns dose limiting toxicity

General patterns: the organ system that displays the most *major toxicity* is the GI system across the board. The organ system that dictates the *dose limiting toxicity* is typically the heme/bone marrow. *alkylating agents overall are carcinogenic. They kill tumor cells, but tend to modify normal cells. So patient will be cured of initial cancer but then may develop another. *Alkylating agents are also associated with reproductive system toxicity* Because anticancer drugs target - proliferating cells, common sites for toxicity are normal tissues that have a high growth fraction: hair follicles, blood/bone marrow, GI. Dose limiting toxicity - each cytotoxic drug is associated with a particular organ that effectively limits the max dose of the drug that can be given to the patient.

MOPP Combo Therapy for Treating Hodgkins Lymphoma

M - Mustargen (nitrogen mustard) O - oncovin (mitotic spindle poison) P - procarbazine (alkylating agent) P - prednisone (steroid) *together, the combo is 78% effective! Also can add a targeted monoclonal antibody that prevents growth called Avastin!

Cancer stem cell (CSC) properties

➢ Cancer Stem Cells (CSCs) comprise a unique subpopulation of neoplastic cells within the tumor. CSCs have the following properties: i. highly tumorigenic in nude mouse model; in contrast, bulk of cancer cells in tumor are non-CSCs and not tumorigenic ii. undergo asymmetric cell division: leads to 1 CSC and 1 'daughter' cancer cell iii. relatively resistant to standard chemotherapy (linked to slow replication) iv. relatively resistant to radiation (linked to functional loss of tumor suppressor gene p53)

Cancer Stem Cell (CSC) chemotherapy

➢ Conventional anti-cancer treatments can often transiently shrink tumors by targeting tumor bulk, but these therapies *fail to target and kill CSCs* leading to treatment failure, relapse, and ultimately death --> cancer stem cells survive and just keep making more daughter cells. Why are CSCs not targeted well? Because they divide very infrequently! ➢ In order to overcome therapy failure, there needs to be development of drugs directly targeting CSCs --> these drugs will truly eradicate the cancer and keep it from coming back

*DRUG SIX: Fluorouracil (5-FU)* What cancers does it treat? How is it administered? Toxicities? Resistances to it?

-5-FU treats colon cancer, breast cancer, gastroesophageal cancer, hepatocellular cancer and pancreatic cancer -administered parenterally; given topically for skin cancer -toxicity = bone marrow again is the dose-limiting toxicity. Also causes diarrhea, nausea, vomiting, neurotoxicity -resistance - typically due to amplification of the TS gene *Interesting: Capecitabine: drug that is converted to 5-FU; the final enzyme in this process is TS

The Alkylating Agents Class (3 drugs to know) Which subclass do these belong to? -Cyclophosphamide: -Cisplatin -Oxaliplatin Special note about these three drugs?

-Cyclophosphamide: nitrogen mustard -Cisplatin: platinum compound -Oxaliplatin: platinum compound these three drugs are all CCNS drugs, but have their greatest anticancer activity in the S phase of rapidly dividing cells ALKYLATING AGENTS WORK BY INHIBITING GENE TRANSCRIPTION, LEADING TO APOPTOSIS OF THE CANCER CELLS

The Anticancer Antibiotics Class (2 drugs to know) Which subclass do these belong to? -Doxorubicin -Bleomycin Overall mechanism of anticancer antibiotics

-Doxorubicin: anthracyclines (CCNS) -Bleomycin: no specific class, unique in that its the only one that is CCS As a class, these antibiotics act by inserting themselves between base pairs of DNA (intercalating), thus changing DNA configuration. Leads to breakage or interference with enzymes like topoisomerases, DNA poly, RNA poly

*DRUG FOUR: METHOTREXATE (MTX)* What is its mechanism of action? Does it cause a toxic substance to build up?

-MTX binds with high affinity to dihydrofolate reductase (in its active site), preventing the reduction of THF (reformation of THF from DHF) and thus all the nice things THF is a cofactor for (biosynthesis) are not made ...intracellular deficiency of THF. Interruption of DNA, RNA and protein synthesis! -MTX also causes a build up of the toxic inhibitory substrate, DHF polyglutamate!

*DRUG FOUR: METHOTREXATE (MTX)* What cancers does it treat? How is it administered? Drug interactions to note? Toxicity?

-MTX is used in breast cancer, head and neck cancer, bladder cancer, Burkitt's and non-Hodgkin's lymphomas, childhood acute lymphoblastic leukemia, lung cancer, and osteogenic sarcomas. It is also used to treat psoriasis and arthritis -administered orally, by IV, or by IM. *IT is poorly transported across the BBB...so must be given intrathecally --> into the CSF to treat brain cancer* -drug interactions: penicillin, NSAIDs, cephalosporins prevent renal excretion of MTX -toxicity: myelosuppression is dose limiting!! Also causes severe GI disturbances, renal toxicity due to crystallization

The Antimetabolites Class (3 drugs to know) Which subclass do these belong to? -Methotrexate -Mercaptopurine -Flurouracil Special note about these three drugs?

-Methotrexate: Folic acid analog -Mercaptopurine (6-MP): Purine analog -Flurouracil: Pyrimidine Special notes: -these drugs are CCS drugs - target drugs that are growing rapidly -bone marrow suppression/myelosuppresion is typically the dose-limiting toxicity for this whole class of drugs!

*DRUG ONE: CYCLOPHOSPHAMIDE* List: -class of the drug -what cancer(s) it treats -how it is administered/any relative other notes -toxicity and any deviations from the toxicity -major mode of resistance against the drug -describe the major biochemical mechanisms by which drug-resistant tumor cells differ from susceptible tumor cells -likelihood of specificity -mechanism of cyclophosphamide

-class: alkylating agent; a nitrogen mustard -treats: lymphomas, leukemias, multiple myeloma, breast and ovarian carcinoma, small cell lung cancer; some autoimmune diseases -administered by/other notes: orally, IV, or IM; found in many combination treatment regimens -toxicity: it is a *myelosuppressant - decreases activity of bone marrow* and this immune suppression is very important for dose-limiting toxicity; acrolein formation (next card). Nausea, vomiting and alopecia are common on this drug -specificity: cyclophosphamide is CCNS --> can target nondividing cells -mechanism: *bifunctional DNA alkylating agent - alkylate guanine residues and produce interstrand crosslinks*

Principles of Combination Chemo Regimens - 1965

-major breakthrough -propose combining cytotoxic drugs with different mechanisms of action...cancer cells may mutate to become resistant to one drug, but it is much more difficult to develop resistance to multiple drugs with different mechanisms of action

Achievement of therapeutic effect in cancer cells and minimization of adverse effects in non cancer cells typically requires combinations of drugs with different: (3)

-mechanisms of action -dose limiting toxicities -mechanisms of resistance

More about nitrogen mustards:

-mustard gas was first used in WWI as chemical warfare --> caused blistering of the skin and lungs -autopsy of soldiers revealed the drug affected bone marrow and thus may be useful in hematologic cancers (leukemia and lymphoma)!!! -this data was lost but eventually the same conclusion was stumbled upon again.

*DRUG SEVEN AND EIGHT: Vinblastine and Vincristine (the vinca alkaloids)* Where do these drugs come from? Mechanism of action? How administered? Resistance? Are there differences in clinical activity and safety between vinblastine and vincristine?

-plant alkaloids derived from the periwinkle plant vinca rosa Mechanism: 1. bind to beta-tubulin and prevent polymerization of microtubules 2. *depolymerization of microtubules still occurs*, thus blocking mitotic spindle formation during the M phase of the cell cycle 3. Resulting mitotic arrest at metaphase interferes with chromosome segregation --> tumor cell death -both administered via IV -resistance due to increased MDR1 expression -despite close structural similarities, vinblastine and vincristine DO have very different clinical activity

Antimetabolites General Mechanism of Action Why are cancer cells more sensitive to these drugs than normal cells? These drugs have selectivity!!

-they are structurally similar to endogenous molecules (folic acid - MTX, purine - mercaptopurine, and pyrimidine - fluorouracil) and thus they serve as antagonists of biosynthetic pathways -there are some difference between cancer cells and normal cells that render the cancer cells more sensitive!! 1) cancers with a *high growth fraction* have overall higher metabolism than normal tissues (exceptions are hair follicles, GI tract, bone marrow) 2) higher levels of certain key enzymes are found in cancer cells (like thymidine phosphorylase)

*DRUG FIVE: MERCAPTOPURINE (6-MP)* What cancers does it treat? How is it administered? Toxicities? Drug interactions? (1 very important one) What does mercaptopurine resistance result from?

-treats acute lymphoblastic leukemia (ALL) and acute myelogenous leukemia (AML) ... remember these drugs are myelosuppresants -administered orally -bone marrow suppression is the major dose limiting toxicity. GI disturbances include anorexia, vomiting and nausea -drug interaction with *allopurinol, a purine analog* which inhibits mercaptopurine metabolism by *xanthine oxidase* in the liver --> leads to toxic buildup of 6-MP/mercaptopurine. If you need to use allopurinol at the same time (to treat hyperuricemia - excess uric acid in blood), need to reduce mercaptopurine dose. *ALLOPURINOL MIMICS HYPOXANTHINE*

*DRUG TWO: CISPLATIN*

-used in combo regimens to treat testicular, ovarian, bladder, non-small cell lung and small cell lung cancers -the dose limiting toxicity is cumulative, non-reversible damage to *renal tubules* --> to prevent this, need to stay hydrated and give a diuresis (mannitol) - to produce a lot of urine and flush out the drug -it is also "oxotoxic" - can cause tinnitus and *hearing loss* -it is a moderate myelosuppressant -cross links G bases on opposite DNA strands by alkylating the G bases... also makes these guanines want to pair with thymine --> wrong base pair combo

*DRUG THREE: OXALOPLATIN* can you use oxaloplatin in cancer cells that are resistant to drug two, cisplatin?

-used in metastatic colon cancer as part of the FOLF*OX* regimen -cancer cells that are resistant (in vitro) to cisplatin on the basis of DNA mismatch repair enzyme defects (mutator phenotypes) CAN BE GIVEN OXALOPLATIN ---> the oxaloplatin can kill these cells! Clinical proof not there yet. -dose limiting toxicity again, similar to cisplatin, is RENAL (nephrotoxicity). It is also a myelosuppressant (so that can cause toxicity), and peripheral neuropathies can result

Mechanisms of alkylating agents:

1) Alkylate DNA at N7 position of guanine (major action) - Other bases are alkylated to lesser degree - Alkylation of phosphate backbone of DNA, and proteins associated with DNA 2) Mono-functional alkylating agents (contains 1 reactive group): - Alkylated guanine has *abnormal base-pairing with thymine* during DNA replication. Can lead to protein miscoding and apoptosis 3) Many alkylating agents are bi-functional (2 reactive groups), leading to cross-linking of DNA - Cross-linking involves covalent attachment of alkylating agent to guanine bases on opposite strands of the DNA duplex - The damaged DNA elicits DNA repair mechanisms (NER or BER), but repair proves too difficult thus activating apoptosis in cancer cell - Damage caused by bi-functional agents more difficult to repair than mono-functional agents

Alkylating agents discussed

1. Cyclophosphamide (a nitrogen mustard) 2. Cisplatin (a platinum compound) 3. Oxaloplatin (a platinum compound) 4. touched on nitrosoureas (but not on drug list)

six established cancer treatment modalities (top 2 are non drug related)

1. Surgery - local therapy involving surgical removal of entire tumor, or removal of as much of a tumor as possible (debulking). Debulking may increase the chance that chemotherapy will kill remaining cancer cells (adjuvant therapy) 2. Radiotherapy - local therapy involving the use of high-energy radiation in the form of x-rays, gamma rays, neutrons, or protons to kill cancer cells and shrink tumors 3. Chemotherapy - systemic treatment with drugs that kill cancer cells by inhibiting certain biochemical pathways 4. Endocrine therapy - synthetic hormones, antagonists or SERMs (e.g. *tamoxifen* is a SERM) may be given to a patient in order to block the body's natural hormones, thereby slowing/stopping the growth of cancers (such as prostate & breast cancers). 5. Monoclonal antibodies (MABs)/Biologics - use of Ab's (e.g. *Herceptin®, Avastin*) targeting specific cell surface proteins or secreted proteins involved in cancer cell signaling --> example: target the HER2 receptors! 6. Small molecule inhibitors - inhibitors that target non-receptor tyrosine kinases (e.g. *Gleevac* for bcr/abl translocation), and receptor tyrosine kinases (*gefitinib* for mutant EGFR) to impede intracellular signaling

Cell cycle nonspecific drugs! Drug classes that do this: 1. alkylating agents and their platinum analogs 2. antibiotics (except bleomycin) 3. camptothecans AT HIGH CONCENTRATION ONLY Are these drugs still affective at killing tumor cells that are actively dividing?

1. alkylating agents and their platinum analogs - cross link DNA 2. antibiotics (except bleomycin) - intercalate DNA 3. camptothecans AT HIGH CONCENTRATION ONLY - inhibit topoisomerase I -These drugs are capable pf exerting their actions on cancer cells that are cycling OR in the resting state (G0) -The greatest killing activity of these drugs is still seen with RAPIDLY dividing cancer cells, however, they are also effective at killing non dividing cancer cells

6 classes that cytotoxic drugs can be divided into

1. antimetabolites (nucleotide level - inhibit nucleotide synthesis, purine ring synthesis...MTX) 2. alkylating agents (DNA level - cross link DNA) 3. camptothecins and epipodophyllotoxins (DNA level - inhibit DNA uncoiling; produce torsional stress) 4. antibiotics (DNA level - intercalate DNA) 5. mitotic poisons (protein level - interfere with mitotic spindle apparatus; inhibit microtubule function) 6. protein synthesis inhibitors (protein level)

Which cell cycle(s) do the following *cell cycle specific (CCS) drug classes effect? 1. antimetabolites 2. epipodophyllotoxins and camptothecans 3. antibiotics 4. mitotic poisons Which types of cancers are most sensitive to CCS drugs?

1. antimetabolites - S phase 2. epipodophyllotoxins and camptothecans - S and G2 phase 3. antibiotics - G2 (ex: *bleomycin*... a cell cycle specific antibiotic - not typical!) 4. mitotic poisons - mitosis rapidly growing cancers are most sensitive to cell cycle-specific (CCS) chemotherapeutic drugs. Cancers with high growth fraction (high % of cells dividing; low % in Go) respond well to CCS drugs. High growth fraction cancers (e.g. > 70%) include acuteleukemias and aggressive high-grade lymphomas (Hodgkin's). Low growth fraction cancers (e.g. < 10%) such as slow-growing adenocarcinomas tend to respond only modestly to CCS drugs.

*DRUG FOUR: METHOTREXATE (MTX)* Resistance to methotrexate? What is the role of polyglutamate additions in the normal action of this drug and why does its loss cause resistance?

1. decreased drug transport due to impaired expression of the folate carrier protein/MTX transporter 2. decreased polyglutamate addition to MTX --> polyglutamate tails are added to MTX by *folylpolyglutamate synthase* when MTX gets inside cells so that it cannot escape... decreased addition of this tail (as some cancer cells have a mutation to do) prevents drug from doing its job because it doesn't stay in the cell 3. amplification of DHFR gene --> harder to knock down its activity 4. mutant DHFR protein that doesnt like to bind MTX 5. MDR1 expression may confer resistance too

Why are combination chemotherapy regimens so effective/ what are the principles of combination chemotherapy regimens?

1. drugs with different mechanisms of action should be combined >difficult for cancers to develop resistance to multiple drugs with different mechanisms of action >such combinations tend to have additive or synergistic cytotoxic effects on cancer 2. drugs targeting different populations of cancer cells should be combined - ex: combine CCS drug to target actively replicating cells with a CCNS drug to target quiescent cells 3. drugs with *different organ toxicities* should be combined, so full therapeutic doses of each drug can be used 4. Drugs associated with different patterns of resistance should be used to minimize cross-resistance. Concurrently employ drug combos where each drug is susceptible to a different mode of resistance (ex: avoid drug combos in which all agents are susceptible to MDR-1 mediated resistance) 5. identify drug combos that allow for the *shortest possible treatment free period* ...want recovery of normal tissues but not enough time for recovery of cancer cells

Resistance to alkylating agents

1. increased capacity of cancer cell to repair the DNA lesions created 2. decreased transport of the alkylating drug into the cancer cell 3. increased production of glutathione and glutathione-associated proteins *which conjugate the alkylating agent - making it nontoxic* 4. increased glutathione-S-transferase activity, which catalyzes that conjugation reaction

The two types of alkylating agents

1. monofunctional = each molecule can covalently modify a single site on the DNA 2. bifunctional = 2 sites, so can covalently modify two different sites on the DNA and form *a cross link*... this molecule will be SYMMETRICAL! Can also define alkylating agents by their leaving group (ex: sulfonate molecule, Cl) *note: the platinum analog alkylating agents actually contain a platinum molecule (Pt)

Cytotoxic Chemotherapy Modalities Against Cancer

1. primary induction chemotherapy: drug is the primary treatment in those with *advanced solid cancer or metastatic disease* for which no alternative treatment exists. Serves as a palliative measure to improve quality and length of life - not a cure. 2. neoadjuvant chemotherapy: drug first to reduce tumor size; surgery or radiation second to get rid of tumor 3. adjuvant chemotherapy: surgery or radiation first to remove tumor and lower risk of cancer reoccurrence. (chemo is given to erradiacte any microscopic/occult metastases). Ex: breast, colorectal

*DRUG ONE: CYCLOPHOSPHAMIDE* Why is the liver protected from the acrolein formed by cyclophosphamide, while that compound causes bleeding of the bladder and death in tumor cells?

Because the liver has high levels of p450 enzymes and high levels of aldehyde oxidase!

The death rates for heart disease and stroke have steadily declined from the 1970s - 2002. Why hasnt cancer? What was the slight downward trend from 1991-2002 attributed to?

Because there are so many types of cancers... also, sequencing the human genome has not yet been as promising as once hoped Slight downward trend attributed to increased cancer screening, more targeted therapies, and a reduction in tobacco use. 1971 - nixon announces war on cancer, gives 200 million to cancer research 2003- NCI directors challenge to cure cancer by 2015

*DRUG THIRTEEN: Bleomycin (anthracyclines)* Where does the drug come from? Which cancers does it treat? Mechanism of action? How administered? Toxicities? Resistance?

Bleomycin is a copper-chelating glycopeptide isolated from Streptomyces. CCS!!!!!! Treats: Testicular carcinoma, squamous cell carcinoma, Hodgkin's and non-Hodgkin's lymphomas Mechanism: Intercalation, scission and fragmentation of DNA due to a redox reaction mediated by a *DNA-bleomycin-Fe(II) complex.* Tumor cells accumulate in the G2 phase of the cell cycle. Administered parenterally Toxicity: *dose limiting pulmonary fibrosis that may be fatal because lungs have a low level of bleomycin hydrolase.* Also produces skin toxicity; acute anaphylactic-like reaction leading to hypotension and cardiovascular collapse in 1% of lymphoma patients Resistance: would be due to increased levels of bleomycin hydrolase in tumor cells and increased DNA repair activity

On this graph: pay special attention to the toxicity of Cisplatin, doxorubicin, and bleomycin

Cisplatin (alkylating agent): GI exhibits major toxicity, renal is the dose limiting toxicity Doxorubicin (antibiotic): GI and hematologic both exhibit major toxicity; cardiac is the dose limiting toxicity Bleomycin (antibiotic): GI and hematologic both exhibit major toxicity; lung is the dose limiting toxicity!

*DRUG FOUR: METHOTREXATE (MTX)* What drug is given to rescue normal cells from the actions of MTX? Why are cancer cells not rescued?

Drug = leucovorin (folinic acid) >can be converted to THF by healthy cells >won't rescue cancer cells because they cannot take it up or the cancer cells lack the machinery to make it into THF

*DRUG ELEVEN: Irinotecan (camptothecins)* Where does the drug come from? Which cancers does it treat? Mechanism of action? How administered? Toxicities? Resistance?

Irinotecan comes from the Camptotheca tree. IT IS A PRO DRUG (metabolized by the liver enzyme *carboxylesterase* to the active metabolite. Cancers treated: metastatic colon cancer Mechanism of action: inhibits *topoisomerase I.* DNA strand is strained and breaks. It is a CCS at low concentrations, and a CCNS at high concentrations. Adminstered orally Toxicity: myelosuppression and diarrhea are dose-limiting toxicities Resistance: due to increased MDR1 gene expression

*DRUG FOUR: METHOTREXATE (MTX)* Which analog is this? Other key notes? What enzyme does it interfere with?

MTX is a folic acid analog. *its the most popular cytotoxic drug!* -folate is an essential vitamin, which is reduced to THF by *dihydrofolate reductase (DHFR)* -THF is metabolically converted to *THF cofactors* like 5-10 methylene THF and 10-formyl THF -these THF cofactors are key methyl donors for de novo synthesis of thymidylate (dTMP), purine bases, and the AAs serine and *methionine*

Top 3 male cancer related deaths Top 3 female cancer related deaths

Male: lung, colorectal, prostate Female: lung, breast, colorectal

Top 3 male cancer cases diagnosed Top 3 female cancer cases diagnosed

Male: prostate, lung, colorectal Female: breast, lung, colorectal

WHAT IS THE TYPICAL SOURCE OF CYTOTOXIC COMPOUNDS THAT ARE TRANSPORTED BY MDRI?

Naturally occurring cytotoxic compounds!! ex: vinblastine comes from vinca rosea (a flower)

*DRUG ONE: CYCLOPHOSPHAMIDE* List: -metabolism of cyclophosphamide -major mode of resistance against the drug -describe the major biochemical mechanisms by which drug-resistant tumor cells differ from susceptible tumor cells

Overall goal: Some cyclophosphamide enters tumor cells, alters their DNA, and leads to apoptosis. Cyclophosphamide is a prodrug!! It is metabolized by liver cytochrome p450 oxidase into its active metabolite (4-hydroxycyclephosphamide). From there it can be converted by another liver enzyme to an inactive metabolite OR it can undergo a rearrangement to aldophosphamide (another active metabolite). Aldophosphamide is then 1. converted to an inactivate metabolite. This is what happens in liver cells, cells with high levels of the enzyme *aldehyde oxidase.* This enzyme is *low in tumor cells*, so they must go with the second option... 2. aldophsophamide is made into acrolein (cytotoxic, need to give MESNA) and then converted to phosphoramide mustard (also cytotoxic)

The POMP regimen for children with acute lymphoblastic leukemia (ALL)

P = purinethol (antimetabolite) O = oncovin (mitotic spindle poison) M = MTX (anti metabolite) P = prednisone (steroid)

*DRUG NINE: Paclitaxel (taxenes)* Where does the drug come from? Which cancers does it treat? Mechanism of action? How administered? Toxicities? Resistance?

Paclitxel comes from alkaloid esters derived from the bark of the yew tree Cancers treated: ovarian, breast, bladder, non-small cell lung cancers Mechanism of action: 1. binds with high affinity to beta-tubulin and stabilizes microtubules formation 2. *stabilizes depolymerization* of microtubules 3. cells are blocked at the G2/M phase because they are unable to form a normal mitotic spindle apparatus -Administered by IV -Toxicities: myelosuppression AND peripheral neuropathies are dose limiting -Resistance: due to increased MDR1 expression

*DRUG FIVE: MERCAPTOPURINE (6-MP)* Which analog is this? What is its mechanism of action?

Purine analog Mechanism: 1. Mercaptopurine (6-MP) is metabolized by HGPRT enzyme to the active metabolite TIMP (thio-IMP) 2. TIMP takes the place of the endogenous IMP (which is normally used to make dGMP --> dGTP) and makes thio-dGTP. If this is incorporated into the DNA, it will damage it! 3. thio-dGTP can be incorporated into the RNA, causing damage too! (or can halt RNA synthesis) 4. TIMP will also prevent the formation of the normal AMP and GMP, preventing formation dAMP and dGMP for DNA synthesis.

*DRUG FIVE: MERCAPTOPURINE (6-MP)* More detail on the allopurinol interaction

Purines are typically released from necrotizing cells and sent to the liver to be metabolized to hypoxanthine. Hypoxanthine is then made into uric acid by *xanthine oxidase (XO),* causing gout if theres too much of it. Allopurinol is a structural isomer of *hypoxanthine,* and acts as an inhibitor of XO. This prevents the production of uric acid. Issue though - allopurinol also inhibits the breakdown of 6-MP (because 6-MP is broken down by xanthine oxidase too).

*DRUG SIX: Fluorouracil (5-FU)* Which analog is this? Note important details about 5-FU Mechanism of action

Pyrimidine analog 5-FU is an analog of uracil. IT IS A PRODRUG that is converted into the active metabolites 5-FUMP, 5-FUTP, 5-FdUMP and 5-FdUTP. Mechanism of action: A. 5-FUMP is converted to 5-UTP and incorporated into RNA --> RNA damage B. 5-fDUMP is converted to 5-FdUTP and incorporated into DNA --> DNA damage C. 5-FdUMP eliminates thymidylate synthase (TS), and enzyme required for de novo pyrimidine synthase --> thus inhibits cancer cell replication!

Tumor log-kill graph - for NON SOLID TUMORS What shape do these untreated cells take on graph of time vs number of cells? What do the peaks represent? What are the different phases of the graph?

Shape = logarithmic note: peak= where drug was administered time between peaks = interval between treatments Phases: INDUCTION, CONSOLIDATION & MAINTENANCE CHEMO (for disseminated cancers, such as the acute leukemias) i. Induction phase - Initial high dose chemo ii. Consolidation - Continuation of high dose chemo (months) iii.Maintenance - Low dose chemo may be continued long after all clinical evidence of cancer has disappeared (months)

TRANSITION TO CYTOTOXIC DRUGS PORTION

TRANSITION TO CYTOTOXIC DRUGS PORTION

*DRUG FIVE: MERCAPTOPURINE (6-MP)* What role does purine salvage play?

The purine salvage pathway converts 6-MP to thioinosine monophosphate (TIMP). TIMP is converted to Thio-dGTP in a de novo pathway, and Thio-dGTP is readily incorporated into DNA during replication of leukemic cells. Incorporation leads to lethal DNA lesions and death/lysis of cancer cells.

Which reaction mechanism do nitrogen mustards (subclass of alkylating agents) use?

They alkylate guanine residues in the DNA. They form an *ethyleneimonium ion and then a carbonium ion* which reacts with N7 of guanine, producing an alkylated purine. Alkylation of a second guanine would result in cross linking of the DNA strand --> inhibiting DNA transcription and gene transcription; also causes strand breaks

Nitrosoureas (subclass of the alkylating agents) - not on drug list, but their advantage is:

They are highly lipid soluble and thus they can cross the BBB and treat brain tumors. Non-cross resistant with other subclasses of alkylating agents! Renal toxicity

Mechanisms of drug resistance: Types of resistance Resistance due to resistance rendering mutations

Types: 1. primary resistance - cells do not respond to initial chemotherapy 2. acquired - develops as a consequence of chemotherapy; initially cancer responds but chemotherapy leads to clonal selection of resistant cells Resistance due to resistance rendering mutations: - cancer cells have an inherent mutator phenotype (accelerated mutation rate in these cells vs normal due to mutations in DNA repair or DNA poly) - frequency of mutations in normal cells thought to 10-30 mutations per division; in cancer cells thought to be 1000-10000s per division --- *NOTE: high tumor burdens accumulate more mutations so need to catch early*

*DRUG ONE: CYCLOPHOSPHAMIDE* The metabolite acrolein (after metabolism of cyclophosphamide) What is it and how to prevent its effects?

When cyclophosphamide is metabolized, the metabolite *acrolein* is formed. This is very toxic to the bladder - causes hemorrhagic cystitis (bleeding of the bladder). So need to prophylactically give patients the drug *MESNA (mercaptoethane sulfonate)* which neutralizes the extreme acidity of acrolein in the urine --> protecting the bladder.

Tumor growth and log-kill hypothesis

for cancers like leukemias that grow exponentially, the log kill hypothesis proposes that the killing action of CCS drugs follows first order kinetics: a given dose kills a *constant proportion* of cancer cells, not a constant number magnitude of cancer cell kill is a logarithmic function! *3 log kill dose would reduce the cancer cell load from 10^9 to 10^6!*

Consequences of resistance-rendering mutations

i. UPREGULATION OF DRUG RESISTANCE TRANSPORTERS. *Up-regulation of drug resistance transporters like MDR1!!*. For example, multidrug resistant transporter MDR1 (gene for P-glycoprotein), multidrug resistant-associated proteins (MRP1 - MRP9), breast cancer resistance protein (BCRP) ii. DOWN REGULATION OF CHEMO DRUG TRANSPORTER. Down-regulation of the methotrexate transporter, a.k.a. reduced folate carrier protein) iii. Increased expression of DNA repair enzymes in the cancer cell (e.g. nucleotide excision repair enzymes) iv. Increased expression of enzymes that produce "trapping" metabolites (e.g. thiols, glutathione) within resistant cells

Tumor log-kill graph for SOLID TUMORS What shape do these tumors show on the graph of time vs number of cells? What is the trend of these graphs? What procedure/treatment must be done to get these tumors to behave logarithmically?

shape = sigmoidal (ex shown on graph is of drug *gompertzian*) TREND: GROWTH RATE DECLINES AS TUMOR EXPANDS SO....the most rapid growth occurs at small tumor volumes, and large tumors have many cells that are not dividing due to lack of nutrients. This makes them potentially less sensitive to chemo drugs. *these tumors (solid tumors) do not obey log-kill kinetics!!!! NEED TO DEBULK FIRST in order to get a log kill trend (which the cells at the middle of the tumor will obey)--> use adjuvant therapy*

*DRUG SEVEN: Vinblastine* Which cancers does it treat? Toxicities?

vinBBBBlastine (part of ABVD regimen) Treats: BBBBreast cancer, hodgkin's and non-hodgkins lymphoma, testicular tumors Toxicities: bone marrow suppression (dose limiting toxicity), anorexia, vomiting, diarrhea, alopecia

*DRUG EIGHT: Vincristine* Which cancers does it treat? Toxicities?

vinCCCCristine (part of POMP, MOPP regimens) Treats: CCCChiidhood leukemias, CCCChildhood tumors (Wilm's tumor, neuroblastoma, Hodgkin's disease, Ewing's sarcoma) Toxicities: peripheral neuropathy with paresthesia/prickly sensation (dose limiting toxicity), muscle weakness. Has a very narrow sparing effect