Pharmacology Lecture 6 - Cancer drugs

Most common type of cancer

breast (followed by prostate, lung, colon)

Most common type of cancer that results in death

lung (colon, pancreas, breast)

________________ is an important process in the body as it promotes the removal of unwanted cells.​

- Failure of cells to die can lead to many diseases.​

cell death

Why do cells die?

​- To remove excess cells​

- To create a structure (e.g., outer layer of the new skin)​

- When cells are damaged by toxins or radiation​

- When cells are infected by viruses​

​

How do cells die?

several ways, Apoptosis, Necrosis, etc.​

___________supply much of the cell’s ATP

mitochondria

how mitochondrial dysfunction can contribute to cell death

- Severe mitochondrial dysfunction can reduce ATP​

- Ion pups can fail​

- This contributes to cell death.​

Ototoxic drug exposure – sensory/non-sensory cell stress – mitochondrial dysfunction – cell death mechanism activated – cell death (comment done)​

done

What is apoptosis?

the mechanism that each day some 10 billion cells are intentionally removed from the human body (programmed / regulated cell death)​

Apoptosis depends on a cascade of proteases called ___________

caspases

Two main pathways activate the caspases:​

- The death receptor pathway: outside cell factor/receptor family initiates the death receptor pathway. The main initiator is caspase 8.​

- The mitochondrial pathway is activated by internal factors such as DNA damage, which results in transcription of gene p53 from the mitochondrion. The P53 protein activates initiator caspase 9.

(caspase 8 or 9 to 3)​

In undamaged cells, ____________continuously activate antiapoptotic mechanisms.​

- Withdrawal of ____________ causes cell death through the mitochondrial pathway. ​

survival factors (cytokines, hormone)

impaired apoptosis is implicated in many conditions including chronic neurodegenerative disease and typically involves ___________ and ______________

cell shrinkage and nuclear fragmentation

Necrosis

uncontrolled cell death after injury

the death of passive cell process (irreversible).​

- This can be from infection, injury, radiation, chemical reaction or a lack of blood supply. ​

- Necrosis triggers the inflammatory response (e.g., cochlear implants)​

process of necrosis

severe injury – ATP depletion – Ion pumps fail – Sodium/potassium pump malfunction - Water accumulation – Swelling and eventual rupture (=Necrotic death) (aka cell swelling and rupture of plasma membrane)​

slide 8!!!! (esp last 5 rows)

done

typical causes of apoptosis

Development, DNA damage, oxidative stress, removal of abnormal cells​

typical causes of necrosis

Ischemia, severe trauma, toxins, infection, extreme oxidative stress​

For apoptosis, cell size ________

shrinks

For necrosis, cell size ______

swells

for apoptosis, what happens to cell membrane?

remains intact until late stages

for necrosis, what happens to cell membrane?

membrane ruptures

ROS acronym

reactive oxygen species

___ is generated as by-products of cellular metabolism, primarily in the mitochondria.​

ROS

ROS production can be triggered by

dysfunctional mitochondrial oxidative phosphorylation and increases or decreases in ROS-related enzymes.

oxidative stress

an imbalance between production of oxidants or ROS, and their elimination by protective mechanisms or antioxidants.​

T or F: The accumulation of ROS and subsequent apoptosis induction is an important contributor to several diseases and aging (e.g., presbycusis).​

true

too much ROS —→ ?

oxidative stress → damage to DNA, proteins, lipids, mitochondria​

too little ROS —→ ?

can also be undesirable because ROS are used for normal cell signaling and immune defense​

JNK Signal Transduction Pathway

a stress-response enzyme pathway that changes protein activity and gene expression. ​

T or f: • DNA damage or oxidative stress can activate the JNK pathway, resulting in mitochondrial apoptosis.​

true

T or F: JNK is an enzyme and once response pathway is activated it leads to apoptosis

true

T or F: Increasing the intracellular concentration of calcium (Ca2+) is lethal to cells.​

true

T or F: Increasing Ca2+ results in a rise in Ca2+ uptake by mitochondria and can induce an increase in ROS production and pore formation which results in apoptosis​​

true

T or F: Calcium overload impairs mitochondrial function and ATP production​

true

T or F: Calcium is needed to release glutamate however if level of CA gets too high, it's bad and causes cell death

true

main side effects of chemotherapeutics

ototoxicity, neurotoxicity, and nephrotoxicity.

T or F: Chemotherapeutics induced hearing loss is typically SNHL and may be permanent and progressive.

true

side effects of cancer treatment slide 12

done

nephrotoxicity

kidney malfunction

chemotherapy agents chart slide 13

done

T or F: Radiation to the area of the ear (for head and neck cancers) is often associated with a chronic, progressive hearing loss

true

T or F: The radiation-induced hearing loss is usually delayed: with no hearing loss in the first couple of months post treatment, but as much as 50%hearing loss by one year

true

direct effects of radiation on hair and nerve cells

Direct damaged is caused to mitochondrial (mtDNA) and nuclear DNA(nDNA).​

indirect effects of radiation on hair and nerve cells

Indirect damage is due to the formation of reactive oxygen species (ROS)and reactive nitrogen species (RNS).​

Possible adverse effects of radiation to the ear (3)

1) Ear canal necrosis,

2) Osteonecrosis otitis media, and

3) Stiffness of the ossicular chain and otosclerosis​

radiation effects on mouse cochlea

Outer hair cell loss, reduced synaptic ribbons, decreased spiral ganglion neuron density, demonstrating injury to both sensory and neural cochlear structures.

high freuqencies worsened​

two transporters are main gates to cochlear fluid spaces​

CTR1, OCT2

(the putative cisplatin transporters copper-like transport-1 (CTR1) and organic cation transporter-2(OCT2) are expressed by cells in the stria vascularis)

entry of chemotherapeutics into fluid space of IE (cisplatin)

Systemically administered cisplatin can enter the perilymphatic space from the bloodstream ​

CTR1, OCT2

Systemic inflammation and noise, associated with vasodilation of the blood vessels in the stria vascularis, enhance uptake drugs

• Cisplatin may enters hair cells (across the cell membrane) via passive diffusion

• Uptake of cisplatin is most dependent on mechanically gated transmembrane channel-like protein-1 (TMC1) channels. ​

• Cellular uptake of cisplatin can be enhanced by putative cisplatin transporters (i.e., CTR1 and OCT2) on apical surface of the hair cell

Mechanisms of Chemotherapeutic Induced Ototoxicity​

Cisplatin affects many other intracellular pathways and binds to hundreds of proteins that could potentially dysregulate cells and lead to cell death

Unfortunately, regulated necrosis and potential pathways associated with cell death are still unclear in thefield of cell biology.​

Cisplatin increases the generation of reactive oxygen species (ROS) by either stimulating enzyme system linked to this process or by inactivating antioxidant systems. The increased oxidative stress is induction of inflammatory processes in the inner ear.

…slide 18-19

Possible mechanisms: Exposure to cisplatin – Uptake by stria vascularis, cochlear fluids and hair cells –Transport through CTR1, OCT2, and TMC1 proteins – Inside the cells (e.g., hair cells (and neurons)),

1) Overload of ROS – Reduction in antioxidant enzymes – Apoptosis of the hair cells, supporting cells, stria vascularis, and nerves – Cell death & Ototoxicity​

2) Activation of NOX3 – Increased ROS generation – Increased Ca2+ influx into the cells causing apoptosis –Cell death & Ototoxicity​

3) Activation of the transient receptor potential Vallinoid 1 channel (TRPV1) in the cells – Increased Ca2+influx into the cell – NOX3 dependent generation of ROS – Activation of the transcription factor, signal transducer and activator of transcription 1 (STAT1) – Cell death & Ototoxicity​​​

T or F: The incidence of chemotherapeutic induced auditory and vestibular dysfunction ranges from 11% to 62%.​

true

Ototoxicity is highly dependent on ​

different doses, duration of treatment, and different age groups

T or F: children show greater risk for developing inner ear problems than adults (e.g., affecting early speech development and hampering social integration). ​

true

T or F: Systemically administered cisplatin initially/predominantly leads to OHC death in the basal turn of the cochlea before affecting hair cells at more apical turn.

true

slide 22 idk

done

T or F: here are a fewer reports of cisplatin induced vestibular dysfunction due to 1) lack of reliable assessment tools and 2) possible vestibular compensation.

true

Otoprotectants (approaches to treat cisplatin ototoxicity)

- Development of drugs which specifically block entry of drugs into hair cells and other cells in the inner ear without affecting entry into cancer cells.​

- Some drugs that have a high affinity for cisplatin and provides a risk for interference with therapeutic effects Thus, suggest to administer the otoprotectants ~6 hours before or after chemotherapeutic drugs to reduce ototoxicity.​

• The use of antioxidant agents such as vitamin C, vitamin E, thiols(e.g., GSH) are protective in preclinical studies (Rybak et al, 2000;Kalkanis et al, 2004).​

• The use of anti-inflammatory agents activates the pro-inflammatory mechanisms associated with cisplatin treatment in the cochlea.​

• Since ROS plays a critical role in cisplatin-induced ototoxicity, its inhibition could ameliorate ototoxicity.​

describe FDA approved drug for reducing ototoxicity

Fennec Pharmaceuticals Inc. (Durham, NC) developed a drugs (chemical name: sodium thiosulfate, generic name: PEDMARK) to reduce ototoxicity in pediatric patients.​

- Mechanism) The drug is an antioxidant and an inhibitor of intracellular oxidative stress.​

- Half-life (t1/2) is 20 to 50 minutes. (when to deliver second dose)​

- Excretion) After administration (IV), ~50% of the administered drug was excreted in urine and > 95% of the dose excreted in urine occurs within the first 4 hours after administration.​

T or F: Monitoring for ototoxicity after the completion of cancer therapy is required.​

true

Importance of OAE monitoring

the hearing toxicity begins in the outer hair cells​

T or F: Cisplatin is retained within the inner ear for months to years in mouse and human

true

For patients with a history of treatment with chemotherapy, an auditory assessment is recommended usually every

1-2 years