4- Kearns - Alkylating Agents and Antibiotics

What are the 3 types of cell cycle non-specific anti-cancer drugs?

• alkylating agents (nitrogen mustards & nitrosoureas)- modify DNA structure

• anthracyclines- abx

• platinum-based compounds (platinum complexes)- modify DNA structure

think: “All Awesome Pharmacists”

Do each the following classes form covalent or intermolecular bonds?

• alkylating agents (nitrogen mustards & nitrosoureas)

• anthracyclines

• platinum-based compounds

• alkylating agents (nitrogen mustards & nitrosoureas)- COVALENT

• anthracyclines- INTERMOLECULAR

• platinum-based compounds- COVALENT

The efficacy of most cell-cycle nonspecific drugs are dependent on if what tumor suppressor gene is functioning?

p53

Because alkylating agents can overwhelm DNA repair mechanisms (bc of the covalent linkages) what ADR may that lead to?

2^o malignancy (like leukemia)

Are most alkylating agents prodrugs? (nitrogen mustards, nitrosoureas)

yes

Do alkylating agents have a cytotoxic or cytostatic effect?

cytotoxic

What are the general ADRs of alkylating agents? (each drug class AS WELL AS drugs will also have it’s own ADRs as well but these are just common to the entire category)

• BONE MARROW SUPPRESSION!!!!!!!!!!! (aka when fewer blood cells are made in the marrow)

• mucosal toxicity

• neurotoxicity

• reproductive toxicity

  • avoid in cancer

What is an electrophile? What is a nucleophile? Is an alkylating agent an electrophile or nucleophile? Which is DNA?

• doubt kearns will ask this but good for background

• electrophile- i think of it as “electrophillic” or electron loving—> an electrophile is electron deficient so it wants to take electrons and form bonds!!!

  • this is the alkylating agent

• nucleophile- i think of it as “nucleus loving” and it HAS electrons (electron-rich) so it wants to find a nucleus to bond to and give those electrons away

  • this is DNA

What type of bonds do alkylating agents form between an endogenous molecule and the alkyl group?

a. hydrogen

b. van der waals

c. covalent

d. ionic

c

We know DNA is a nucleophile and is made of purines and pyrimidines. Does each nitrogen in DNA have the same nucleophilicity?

no! it varies. for example, the N7 on guanine is the more nucleophilic than the N1 on cytosine

All nitrogen mustards have what functional group?

a. central amine group

b. urea group

c. transition metal electrophile

d. aromatic ring

a (pictured is an example)

(FYI: the central amine group is also called a bis-beta-haloalkylamine)

What is the goal MOA of nitrogen mustards?

DNA alkylation of GUANINE to form a cross-link

Describe the 4 step MOA of nitrogen mustards in detail:

1. the central amine group (bis-beta-haloalkylamine) forms cyclic ammonium ions called aziridinium ions

   • basically the amine group reacts with itself to form a ring

2. “1st nucleophile attack” —> the N7 on guanine (DNA) attacks the aziridinium ions to make an alkylated guanine

   • remember DNA= nucleophile, alkylating agent (in this case the azirdinium ions)= electrophile ——> these two react and form a COVALENT bond (in this case an alkylated guanine :)

3. a second cyclic aziridinium ion forms on the alkylated guanine

   • same thing as step one!!! but this time on the product from step two instead of the central amine group

4. “2nd nucleophile attack”—> the N7 on ANOTHER GUANINE attacks the alkylated guanine and that forms an INTERSTRAND CROSS LINK!!!!

   • same thing as step 2 except it’s with another guanine

SUMMARY: form a cyclic ion—> 1st nucleophile attack where guanine+ the ion form an alkylated guanine—> second cyclic ion forms —> 2nd nucleophile attack between the alkylated guanine and another guanine = RESULTS IN CROSS LINK THAT’S MESSING UP THE DNA BACKBONE!!!!!!!!!!!!!

Nitrogen mustards and nitrosoureas cause the DNA to cross link. Is this an inter or intrastrand connection?

interstrand

Nitrogen mustards CANNOT be reconstituted in _____________ or else the patient WILL DIE.

water (FYI: must be saline)

What are the class ADRs of nitrogen mustards?

(reminder each nitrogen mustards drug itself has its own additional ADRs as well)

• kearns said- “know all of these”

• BONE MARROW SUPPRESSION

• mucosal/GI toxicity

• neurotoxicity

• 2^o malignancies (like leukemia)

• reproductive toxicity

Name the drugs that are nitrogen mustards:

• mechlorethamine (mustargen)

• Cyclophosphamide (Cytoxan)

• Ifosfamide (Ifex)

Answer the following table about nitrogen mustards:

Generic Name	Brand Name	Prodrug? Yes or No	ROA	ADRs
mechlorethamine
Cyclophosphamide
Ifosfamide

What is the name of the inactive metabolite formed in Ifosfamide and Cyclophosphamide?

THE INACTIVE METABOLITE IS ACROLEIN

Acrolein is a reactive __________.

a. nucleophile

b. electrophile

b

What must Cytoxan and Ifex be administered with? Why?

MESNA— In order to neutralize the reactive electrophile ACROLEIN

Compared to Cyclophosphamide, Ifosfamide has a higher risk of _____________.

hemorrhagic cystitis (inflammation/bleeding of the bladder wall)

After the reaction at the N7 position of guanine, the cell tries to fix the damage done by nitrogen mustards using what reactions?

• deglycosylation

• ring opening

• dealkylation

What type of functional group is this? Is it lipophilic or hydrophilic?

nitrosourea- lipophillic

What is nadir? How does this apply to nitrosoureas?

• nadir= refers to the lowest point that a patient's blood cell counts reach after undergoing chemotherapy

• nitrosoureas cause myelosuppression (decrease in production of blood cells) and nadir is ~4 weeks

  • exception- steptozocin

Name the drugs that are nitrosoureas:

• Carmustine (BiCNU, Gliadel)

• Lomustine (CeeNU, Gleostine)

• Streptozocin (Zanosar)

Unlike nitrogen mustards that form 1 electrophile, how many do nitrosoureas form?

2

Explain the MOA of Nitrosoureas in detail:

1. Form 2 electrophiles—> Dianzene Hydroxide (acts on DNA) and Isocyanate (acts on Proteins)

2. Each electrophile acts differently—> 1st nucleophilic attack

   • Dianzene Hydroxide—> forms chloroethyl group that will alkylate the O6 GROUP OF GUANINE

   • Isocyanate—> N on Lys attacks Isocyanate group

3. Each electrophile acts differently —> 2nd nucleophilic attack

   • Dianzene Hydroxide—> forms crosslink w/ DNA

   • Isocyanate—> leads to protein inactivation

Answer the following table about nitrosoureas:

Generic	Brand	ROA	ADRs	What on its structure makes it unique?
Carmustine
Lomustine
Streptozocin

What is Streptozocin used for?

pancreatic islet cell carcinoma

What is the overall MOA of platinum complexes? (not the steps)

• what do they do to DNA?

• what is the result on DNA replication and protein synthesis?

• what tumor suppressor protein must be functioning?

• they COVALENTLY bind to nucleophilic sites on DNA

• inhibits DNA replication and protein synthesis

  • single and double strand breaks

  • miscording

• p53

Platinum Complexes CANNOT be administered through what kind of needles?

aluminum

Name the drugs that are platinum complexes.

• Cisplatin (Platinol)

• Carboplatin (Paraplatin)

• Oxaliplatin (Eloxatin)

What are the steps that platinum drug complexes take to cross link DNA?

1. Aquation

   • the ligands on each platinum complex drug are displaced by water

2. Form the aquo complex

   • + charged molecule

3. aquo complex reacts with nucleophilic sites on DNA and proteins

4. activated platinum complexes react with other nucleophilic site OVER AND OVER to produce crosslinked DNA

Be able to recognize the structure of the platinum complex drugs and which ligands leave during step 1 of the MOA. What is similar in all of the drugs?

• similar is a Pt molecule

Answer the following table about platinum complexes:

Generic	Brand	Admin	ADRs
Cisplatin
Carboplatin
Oxaliplatin

Which cell-cycle non-specific drug is photosenesitive and must be protected from light?

cisplatin

What is oxaliplatin co-administered with?

5-FU and leucovorin

How are anthracyclines different from tetracyclines?

aromaticity

What are the 2 major components of the structure of anthracyclines?

• 4 fused rings- A,B,C,D

• sugar group attached to D ring (L-daunosamine)

Do anthracyclines work through covalent or intermolecular bonds?

INTERMOLECULAR (VERY DIF FROM ALKYLATING AGENTS THAT USE COVALENT!!!!!!!!!!)

What specific intermolecular interaction do anthracyclines use?

pi-pi stacking

What is this picture showing?

how anthracyclines intercalate in DNA

What is the MOA of Anthracyclines?

1. effect on DNA structure

2. effect on DNA replication

3. generate what toxic substance?

4. do what to chromatin?

1. INTERCALATION disrupts helical structure

2. interferes with activity of DNA-binding enzymes

   • topoisomerase and polymerases

3. Generates FREE RADICALs = strand breaks

4. histone eviction—> disrupts chromatin

How are free radicals formed and neutralized in a normal healthy person? What do anthracyclines do to this pathway to treat cancer?

• in a normal person—> peroxides are broken down by the enzyme CATALASE to water and oxygen!!!!!!!!!

• anthracyclines—> promotes an alternative pathway called the “Fenton Pathway” to induce free radicals and cause apoptosis

Anthracyclines are given ____.

a. IV

b. oral

c. wafer

d. locally

a

For some anthracyclines, Daunorubicin and Doxorubicin a _______________formulation is available to reduce toxicity.

liposomal (FYI: liposome has hydrophillic core and hydrophobic lipid outside)

The active metabolite of anthracyclines has the ketone reduced to a ___________.

2^o alcohol

What is the MAIN TOXICITY WITH ANTHRACYCLINES AND WHY?????

CARDIOTOXICITY—> this is because cardiac tissue does NOT have catalase

Bc of the toxicity associated with anthracyclines what happens with dosing?

there are lifetime dose limits

What are some other ADRs of the anthracycline class?

• BMS

• GI

• alopecia

• derm issues

What are the brand/generic names of the anthracyclines?

• Daunorubicin (Caerubidine)

• Doxorubicin (Adriamycin)

• Epirubicin (Ellence)

• Valrubicin (Valstar)

• Idarubicin (Idadmycin)

Most of the Anthracyclines have a longer half-life (27-45 hrs), which anthracycline is an exception to this?

Valrubicin (t 1/2= 2hrs)

What type of drug is Bleomycin (Blenoxane)?

Fe++ chelating glycopeptide

Bleomycin is cell-cycle specific to which phase?

G2

Unlike the MOA of other anthracyclines, Bleomycin does not inhibit what enzyme?

topoisomerase

How is Bleomycin administered? How is it metabolized?

IV, IM, intrapleural administration, metabolized by hydrolase

With bleomycin what are the possible toxicities?

• PULMONARY TOXICITY—> fibrosis

• dermatologic toxicity

• anaphylaxis reactions