Week 1: Mechanisms of Carcinogenesis and Overview of Anticancer Drugs

What is neoplasia?

• new growth/autonomous growth of tissue

What is neoplasm?

• lesion from neoplasia

What is benign?

• lesions characterized by expansive growth, slow rate proliferation with no invasion of surrounding tissues

What is malignant?

• lesions with invasive growth, capable of metastases to tissues 

What is metastasis?

• secondary growth from primary malignant neoplasm 

What is cancer?

• Malignant neoplasm

What is carcinogen?

• physical or chemical agent that causes neoplasia 

What is genotoxic?

• carcinogen interact with DNA = mutation 

What is nongenotoxic?

• carcinogen that modify gene expression, no DNA damage 

In the stages of Carcinogenesis, what is initiation? What starts the initiation?

• Mutation 

• One cell division necessary to lock in mutation

• Genotoxic damage 

• Nonreversible 

• DNA modification 

• **Carcinogenic agent (chemicals, radiation, viruses) cause DNA damage and cell mutation

In the stages of Carcinogenesis, what is promotion? What happens?

• No direct mutation

• Multiple cell divisions necessary

• Nongenotoxic

• No direct DNA modification

• Reversible

• Clonal expansion of the initiated cell population

• Increase in cell proliferation and/or a resistance to cell apoptosis

• Activation of oncogenes by promoter agent, Oncogenes = proteins that are coded by genes 

  • Overexpression causing cell proliferation 

In the stages of Carcinogenesis, what is Progression? What happens?

• Irreversible

• Changes from preneoplasia to neoplasia 

• Mutation, chromosome rearrangement, DNA modification

• **Malignant tumor

What are the hallmarks of cancer?

• Sustained proliferative signaling = wants to go through cell cycle 

• Evading growth suppressors = cells release these suppressors but cancer cells avoid

• Inducing angiogenesis = new blood vessels

• Activating invasion and metastasis

• Resisting cell death 

• Enabling replicative immortality

• Genome instability and mutation 

• Tumor-promoting inflammation 

• Avoiding immune destruction 

• Deregulating cellular energetics 

What is the process of chemical carcinogenesis?

• Chemical initiation such as smoking causing DNA damage to normal cell 

  • We also have DNA repair but the damage is severe so repair has less equilibrium 

• We have P53 which is protein that is important in DNA regulation and when they see damage it causes apoptosis of the toxic cell

  • If we have failure of apoptosis and failure to repair cell damage → promotion (proliferation) to make pre cancer causing loss of tumor suppressor genes and genome instability = cancer 

DNA damage is a cause of what? It can also be a mechanism to do what?

• Cause of cancer and a mechanism to kill cancer cells

In the spectrum of DNA damage, what is known about single or double stranded breaks?

• Double in DNA is more significant = more opportunity for repair to go wrong vs single

In spectrum of DNA damage, what is depurination and depyrimidation?

• loss of bases (purine or pyrimidine) aka apurinic or apyrimidinic

In spectrum of DNA damage, what is DNA adduct formation and cross linking?

• Chemical moiety that reacts + attaches to purine/pyrimidine base (adduct aka adding to DNA base)

• Can occur on one strand of DNA or join 2 strands together which is crosslinking 

  • Crosslinking = chemical reacts with both strands and links them together (cannot physically separate DNA bc covalent) 

What can cause DNA damage?

• DNA damage

  • UV, x-ray, gamma ray 

  • Chemicals, Reactive O2 + N species, toxins

  • Antineoplastic drugs (DNA directed cytotoxic agents)

What are the types of chromosomal rearrangements?

• Deletion = piece of chromosome removed from double strand break, new chromosome has section deleted 

• Duplication = instead of one gene, you have 2 copies of the same gene (overexpressed)

• Insertion  

• Inversion 

• Translocation = 2 chromosomes broken but during repair, you have fusion chromosomes (brand new where pieces get attached to each other) 

• Rearrangements can make new outcomes 

  • Loss of function mutation in tumor suppressor genes

  • Gain of function in oncogenes (cause cell proliferation)

  • Creation of fusion genes (proliferation enhancement) 

What are the oncogenes?

• Oncogenes = drive growth and proliferation of the cells 

  • Genes for growth factor receptors 

    • EGFR or erbb1 → epidermal growth factor receptor 

    • HER2 or erbb2 → growth factor receptor 

  • Genes for signaling cascade proteins 

    • KRAS (codes for guanine nucleotide-proteins with GTPase activity)

    • Genes for cytoplasmic kinases BCR-ABL (codes for non-receptor tyrosine kinase

What are the tumor suppressor genes?

• Tumor suppressor genes = mutations in these genes make them inactive 

  • APC → colon/rectum carcinoma

  • BRCA1 and BRCA2 (tumor suppressor genes that are DNA repair)

    • BRCA mutations stratify breast cancer risk

  • DPC4 (pancreatic)

  • INK4 (Melanoma, lung, brain)

  • MADR2 (colon/rectum)

  • P53 (loss of function mutation here means cell can not detect DNA damage and no apoptosis → opportunity for cell growth)

  • PTEN inhibits cell proliferation (brain, melanoma, prostate) 

  • Rb (Retinoblastoma, bladder, breast)

  • VHL (renal cell carcinoma) 

What is the relationship between stimulatory and inhibitory cellular growth signals?

• Stimulatory “Go” signal = oncogenes

• Inhibitory “Stop” signal = tumor suppressor genes 

• Signals converge at cell cycle clock which decide whether cell should proliferate (depends on equilibrium on which signal has more) 

• More ligand = more activation of receptors → depends on pathway, 

  • Some mutations make receptors active even in absence of ligand causing signaling to make constant division of cells 

• Stimulatory abnormality: cell divides in the absence of external growth factors 

• Inhibitory abnormality: cell divides when it should not because inhibitory signal fails to reach nucleus because relay molecule is lost 

• MUTATION gonna activate growth signals or inhibit growth arresting signals 

How is the cell cycle regulated by CDK?

• Proliferation means cell needs to go through cell cycle 

  • Through G1, S, G2, then mitosis 

  • Cyclins and Cyclin dependent kinases 

    • Cyclins are structural proteins found to play role in regulating cell cycle by ability to regulate cyclin dependent kinases

    • CDK are enzymes that have activity dependent on the Cyclins 

    • CDK changes based on how much cyclin is around 

    • CDK phosphorylates substrates depending on cyclin amount and CDK is what allows the cell to move in different phases of the cell cycle

  • Cyclin D is master coordinator → goes up from G1 phase and remains stable then starts to decline (global master cyclin)

  • Cyclin E → peaks between G1 and S so important for a cell to transition from G1 to S (means CDK2 goes up)

  • Cyclin A is important for the cell to go through S phase and G2-M phase

  • Cyclin B is important for cell to clear the mitotic phase (M phase) 

    • Cyclin D or B won’t activate the enzyme ** recheck 

  • Cyclin D is the first that goes up, E only peaks between G1 and S so its there to facilitate G1 to S (needs Cyclin E to go via G1 to S phase)

What is a summary of CDK regulation?

• Cyclin D → G1 phase (CDK4 or CDK6)

• Cyclin E → G1 to S transition (CDK2)

• Cyclin A → G2 to M transition (CDK1) 

• Cyclin A → DNA replication machinery aka S phase (CDK2)

• Cyclin B → Mitosis (CKD 1)

What is the MOA of cell cycle inhibitors and the names of drugs?

• Palbocicilib, Ribociclib, Abemaciclib (INHIBIT CDK 4 which is cyclinD1)

• CDK 4 binds and phosphorylates Rb (retinoblastoma protein which is a tumor suppressor genes) 

  • When retinoblastoma is bound to E2F, it inhibits it, but when CDK4 phosphorylates the Rb, the Rb dissociates from E2F and the E2F translocates to nucleus and causes Gl to S to cellular proliferation 

• If we block CDK4 cells using the drugs, there is no phosphorylation of the CDK to the Rb, so no E2F activation and it is stuck in G1 phase because it needs CDK 4 (cancer cells then cannot proliferate)

What are the classes of antineoplastic drugs?

• Conventional Antineoplastic Agents

  • Kill cancer and normal cells = toxicity 

  • Causes us: Inability to fight infx, hair loss, N/V due to the fact that they kill cancer AND normal cells 

  • Alkylating agents, Antimetabolites, Antimitotic agents, Topoisomerase inhibitors, Miscellaneous DNA directed agents 

• Hormonal Agents 

  • For breast and prostate cancer 

  • SERMS, Aromatase inhibitors, antiestrogens, antiandrogens, inhibitors of steroidogenesis

• Immunotherapy

  • How can we boost immune system 

  • Immune checkpoint inhibitors  

  • MABs, Immune checkpoint inhibitors, therapeutic vaccines 

• Targeted Tx 

  • Try to target specifically to kill cancer but not harm normal cells 

  • Tyrosine Kinase Inhibitors, Signal pathway inhibitors, Differentiating agents

What are the PD mechanisms of resistance to anticancer drug effects?

• Upregulation of MDR efflux pumps (can pump out the meds/foreign chemicals)

  • Some cancers have a lot of efflux pumps so drugs cannot concentrate to damage

• Decreased cellular uptake (if the anticancer drug requires transporter for cellular uptake) by downregulating uptake transporters 

• Altered cell cycle checkpoints = cancer cells become more efficient in repairing damages causing inhibition in apoptosis 

• Increased concentration of cellular target or a mutated target (reduced binding affinity)

• Detox of reactive species of the drug by glutathione 

What is cancer mass known as?

• PK resistance is drug needs to get into cancer and concentrate there 

• Cancer mass is HETEROgenous with cancer cells having different rates of proliferation depending on presence of blood vessels and nutrient supply 

What is known about inner layers of cancer vs peripheral?

• Innermost layers of cancer are not well vascularized, vs peripheral areas that have blood supply so high proliferation rates

• Cells closer to blood supply proliferate more because that's where oxygen and nutrients are 

  • The core of cancer cells are in hypoxic conditions are less proliferative and resistant to cytotoxins and antiproliferative agents because its lower 

What is the EPR effect?

• EPR effect: enhanced penetration and retention → if you are to make the drug in a certain size, it is gonna be associated with enhanced penetration into the cancer and retention inside the cancer (AKA size requirement of liposomes and nanoparticles needed to have enhanced penetration and retention)  

• Liposomes make a comeback and certain drugs are encapsulated in form of liposomes in order to concentrate inside the cancer TO INCREASE efficacy of anticancer drugs b/c cancer has unique phenomenon of EPR 

  • Molecules of certain size (nanoparticles or liposomes) accumulate more in cancer tissues vs normal b/c blood supply of cancer cells