Cancer 1

Question 1

Cancer Biology

Answer 1

• cancer is a group of more than 100 diseases
• second leading cause of death
• more than 1 million new cases each year

Question 2

Pancreatic Cancer Stats

Answer 2

• estimated new cases 45,220
• estimated deaths 38,460
• the number of new cases and estimated deaths are both still going up

Question 3

Molecular Basis of Cancer

Answer 3

• cancer is a genetic disease, but other epigenetic changes also occur
• it is characterized by abnormal cellular growth and reduced cell death
• nonlethal genetic damage (or mutations) - acquired e.g. chemicals, radiation, viruses or inherited in the germ line
• targets of genetic damage (or mutations)- growth promoting protooncogenes, growth inhibiting tumor suppressor genes, genes that regulate apoptosis or cell death, genes that repair damaged DNA

Question 4

Adenoma Carcinoma Sequence in Colorectal Carcinogenesis

Answer 4

• Normal colon- germline (inherited) or somatic (acquired) mutations of cancer suppressor genes (first hit), APC at 5q21, mismatch repair genes, MSH2 at 2p22
• mucosa at risk- methylation abnormalities, inactivation of normal alleles (second hit), APC, B-calenin, MSH2
• adenomas- protooncogene mutation, K-ras at 12p12 and then homozygous loss of additional cancer suppressor genes- p53 at 17p13 LOH at 18q21
• carcinoma- additional mutations, gross chromosomal alterations- many genes

Question 5

Clonal Evolution of Tumors and Tumor Heterogeneity

Answer 5

• all tumors arise from a single transformed clone
• new subclones arise from the descendants of the original clone during continuous growth
• new subclones differ from the original clone in many respects- more aggressive, metastatic and acquire the ability to evade host defense

Question 6

Clonal Evolution vs Cancer Stem Cells?

Answer 6

• cancer stem cells: a sub population of cells with ability to self-renew and differentiate-have cancer initiating potential
• several issues unclear
• origin of cancer stem cells?

Question 7

Rate of Tumor Growth

Answer 7

• it takes about 30 population doublings to 10^9 cells
• in the case of a solid tumor, these many cells weigh about 1 gm, which would be the smallest clinically detectable mass
• ten more doublings would give to 10^12 and a massage of about 1kg
• one kg is the maximal solid tumor mass that is compatible with life
• it would take 90 days to generate a mass of 1gm of 30 population doubles and a cell cycle time of 3 days
• there is actually a long latent peroid before a tumor can be detected in clinic
• when a solid tumor is clinically detected, it has already completed a major portion of its life cycle
• once clincally detectable, the average volume-doubling time could be 2 to 3 months for some tumors such as lung and colon cancers

Question 8

Approaches to Cancer Treatment

Answer 8

• conventional chemotherapy- conventional chemotherapeutic agents currently in use
• molecular targeted therapy

Question 9

Conventional chemotherapy agents

Answer 9

• Alkylating Agents- Cyclophosphamide, Melphalen, Carmustine
• Antimetabolites- 5-fluorouracil, Gemcitabine, 6-mercaptopurine
• Natural Products- Vincristine, Paclitazel, Etoposide, Doxorubicin, Interferon-alpha
• Miscellaneous Agents- Cisplatin, Carboplatin, Hydroxyurea, Mitoxantrone
• Hormones and Antagonists- Prednisone, Hydorxyprogesterone, Estradiol, Tamoxifen, Flutamide

Question 10

Molecular Targeted Therapy

Answer 10

• rational molecular-based approaches in the discovery, design and utility of anticancer agents
• anticancer drugs recently approved by the FDA
• investigational drugs currently in clinical trials

Question 11

Cell Cycle and Apoptosis

Answer 11

• anticancer agents mediate their effects by inducing cell cycle arrest and/or cell death (apoptosis)
• certain drugs act in specific phase of the cell cycle while others are phase nonspecific
• a better understanding of cell-cycle kinetics and apoptosis is essential for effective utility of anticancer agents

Question 12

Cell Cycle Control

Answer 12

• cell cycle is divided into 4 phases: G1, S, G2, and M
• a normal somatic cell may spend: 6-12 hours in G1, 6-8 hours in S, 3-4 hours in G2, 1 hour in M (timing could vary depending on cell type)
• GO- post mitotic cells exit the cell cycle and enter into a non-proliferative phase e.g. terminally differentiated nerve cells, or some cells that enter temporarily into Go for weeks, months or years and later re-enter the cycle

Question 13

Two Major Types of Proteins that Control the Cell Cycle

Answer 13

• cyclins: the regulatory proteins e.g cyclins A, B, D, E

- cyclin-dependent kinases (Cdks): the catalytic proteins- Cdks 1,2,4, or 6

Question 14

How does cyclins and Cdks function?

Answer 14

• cyclin-cdk function as heterodimers that phosphorylate target proteins
• Cdks no kinase activity unless associated with a cyclin
• cyclin determines which proteins to be phosphorylated by the cyclin-Cdk complex

Question 15

Cyclin and CDk complexes

Answer 15

• each Cdk can associate with different cyclins
• different cyclin-Cdk complexes function in different phases of the cell cycle
• Cdk4-cyclin D in G1phase
• Cdk2-cyclin A in S phase
• Cdk1-cyclin B in G2/M

Question 16

Rb-E2F Pathway: progression from G1 to S phase

Answer 16

• cyclin D/Cdk4, cyclin D/Cdk6 and Cyclin E/Cdk2 phosphorylate the retinoblastoma protein
• hypophosphorylated Rb is bound to E2F family of transcription facotrs
• hyperphosphorylation of Rb results in the release of E2F
• E2F activates the transcription of genes whose products control progression from G1 to S phase

Question 17

Progression from S phase to G phase

Answer 17

-involves Cyclin A/Cdk2 but the targets remain unknown

Question 18

Progression from G2 to M phase

Answer 18

-involves Cyclin B/Cdk1 and there are several target proteins

Question 19

Checkpoint Concept

Answer 19

• mechanisms that control cell cycle progression implement checkpoints to ensure that each stage of the cell cycle is properly completeted before the next stage is initiated
• G1 arrest, S-phase arrest, G2 arrest, M arrest
• if DNA is damaged, cells will arrest in G1 or G2, no progress to S or M phases respectively
• if DNA is not properly replicated, S phase arrest and no progress to G2
• if improper spindle formation, M phase arrest

Question 20

p53 and cell cycle arrest

Answer 20

• anticancer drugs- activate p53
• activate p21 which leads to G1 or G2 Arrest
• activate 14-3-3 leads to G2 arrest
• tumors with p53 mutations; lack of G1 and/or G2 checkpoints. Altered sensitivity to anticancer drugs. Decisions about tumor response to chemotherapy

Question 21

Pathways of Cell Death (Apoptosis)

Answer 21

• cell death or cell suicide is also known as apoptosis
• it is a physiological process but can be induced e.g. by anticancer drugs
• a well controlled process that leads to cell death via a series of well-defined morphological, molecular and biochemical changes

Question 22

Morphological Changes in Apoptosis

Answer 22

• cell shrinkage
• cell shape changes
• cytoplasmic condensation
• alterations in nuclear envelop and nuclear shrinkage
• nuclear chromatin condensation and fragmentation
• cell membrane blebbing
• formation of apoptotic bodies
• cell detachment
• phagocytosis of apoptotic bodies

Question 23

Molecular and Biochemical changes in apoptosis

Answer 23

• activation of proteases: caspases and serine proteases
• proteolysis: cleavage of important proteins involved in cell structure and function
• DNA fragmentation: nucleases
• loss of mitochondrial membrane potential
• cytochrome C release from mitochondrial into cytosol
• other changes

Question 24

Caspases

Answer 24

• integral component of apoptotic machinery
• 14 caspases have been identified but 11 as well-studied
• they are cystein proteases and exist as inactive pro-enzymes named pro-caspases
• activated in response to apoptotic insults e.g. anticancer drug treatment
• they recognize specific cleavage sites within proteins (including caspases)

Question 25

How Caspases are utilized in mediating apoptosis

Answer 25

• they are utilized in cascade as Caspase Cascade
• for example, upstream initiator caspases (caspase 8 or 9( cleave and activate downstream effector (executioner) caspases such as 3, 6 and 7

Question 26

Two major apoptotic pathway

Answer 26

• death receptor-dependent pathway

- mitochondrial pathway

Question 27

Anticancer Drug Resistance

Answer 27

-resistance to anticancer drugs: intrinsic or acquired

Question 28

Intrinstic Resistance

Answer 28

• dysregulation of one or both apoptotic pathways due to: inactivation of apoptosis promoting genes/proteins (mutations, deletions or epigenetic mechanisms
• hyperactivity of survival or anti-apoptotic genes/proteins (such dysregulation in apoptotic/survival pathways, common in many cancer types, confers upon cancer cells in the intrinsic survival advantage and resistance to anticancer drugs “double whammy”)
• host factors: poor absorption or rapid metabolism or excretion ofdrugs: low serum levels. Delivery failure eg bulky tumors or high molecular mass of drugs such as monoclonal antibodies

Question 29

Acquired Resistance

Answer 29

• acquired drug resistance due to dysregulation of one or both apoptotic pathways during chemo
• many anticancer drugs induce DNA damage. During the course of chemotherapy, many cancer cells acquire the ability to rapidly and efficently repair DNA damage. Consequence: reduced apoptosis
• gene amplification: amplification of genes triggering overproduction of proteins that make anticancer drugs ineffective
• increased expression of energy-dependent efflux pumps that confer multidrugresistance by ejecting drugs out of cells. Transporters of the ATP-binding cassette (ABC) family e.g. p-glycoprotein also known as p-gp or multidrug transporter, MRP1 through MRP6 (multidrug ressitance associated protein) and some other less well characterized transporters
• decreased drug uptake because the protein molecules that facilitate drug transport inside the cells stop working
• dysregulation in drug metabolism: some drugs are normally metabolized into active metabolites inside the cells but cancer cells can acquire mechanisms to block drug activation
• acquistion of mechanisms by the cancer cells to inactivate drugs

Question 30

Anticancer Drug Toxicities-

Answer 30

• most anticancer drugs affect rapidly dividing normal and malignant cells; consequently the toxicities are associated with bone marrow, intestinal epithelium etc.
• acute toxicities are generally dose limiting

Question 31

Toxic Effect on Hematopoietic System

Answer 31

• bone marrow suppression
• suppression of all blood elements can occur
• myelosuppression- leukopenia
• G-CSF (granulocyte colony-stimulating factor) is now given to shorten the period of Leukopenia

Question 32

Toxic Effect on Dividing Mucosal Cells

Answer 32

• oral mucosal ulceration

- intestinal denudation

Question 33

Toxic effect on hair follicles-

Answer 33

-alopecia

Question 34

Toxic Effect on Reproductive System

Answer 34

• permanent Amenorrhea (females)

- azoospermia (males)

Question 35

Delayed Toxicities

Answer 35

• organ damage (heart, lungs, kidneys or liver)
• pulmonary fibrosis
• endothelial damage giving rise to venooclusive disease of liver
• nephrotoxicity giving rise to renal failure
• neurotoxicities giving rise to seizures, paralysis and coma
• major organ damage can be avoided by strict adherence to the treatment protocols
• secondary neoplasia: most alkylating agents are leukemogenic
• some drugs have specific acute effect on major organs: for example, cyclophosphamide releases nephrotoxic and urotoxic metabolite that causes hemorrhagic cystitis, anthracycline antibiotics such as doxorubicin cause dose-related cardiac toxicity