Lecture 4 - Topoisomerase Inhibitors and Microtubule Inhibitors PDF
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This lecture covers topoisomerase inhibitors and microtubule inhibitors, focusing on their roles in DNA replication and transcription, as well as their applications in cancer therapy. The lecture details the mechanisms and actions of these inhibitors.
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2023-02-26 DNA “Cutters” Topoisomerases inhibitors Camptothecin and derivatives Anthracyclines Podophyllotoxin derivatives DNA Topoisomerases Important in DNA replication and RNA transcription – Type I topoisomerases change the degree...
2023-02-26 DNA “Cutters” Topoisomerases inhibitors Camptothecin and derivatives Anthracyclines Podophyllotoxin derivatives DNA Topoisomerases Important in DNA replication and RNA transcription – Type I topoisomerases change the degree of supercoiling of DNA by causing ss breaks and re-ligation Subtypes IA-III (top3A) 1A-IIIβ (top3B), 1B (top1) – Type II topoisomerases cause ds breaks. Subtypes II (top2A), IIβ (top2B) Topoisomerases are generally present at elevated levels in tumors upregulated > - chemotherapeutic target Resolution of the molecular structures of topoisomerases has opened new avenues for drug development in this area The targets of the currently marketed cancer chemotherapeutic agents are topoisomerase I, IIα, and IIβ. 1 2023-02-26 inhibit the last step > - strand break + No religation Topoisomerase Inhibitors 1. “Topoisomerase poisons” -inhibit the re-ligation step and locks enzyme into a “cleavage complex” - enhance the rate of cleavage 2. Competitive inhibition of the ATP binding site – only Type II topoisomerases – prevents ATP- hydrolysis drive enzymatic action (novobiocin; coumermycin) 3. Inhibitors of DNA-topoisomerase binding (aclaruibicin; suramin) 4. Inhibit ATP hydrolysis and DNA release at the last step (dexrazoxane) – Type II Pommier Nature Reviews Cancer 6, 789–802 (October 2006) | doi:10.1038/nrc1977 A B C Topo IB inhibitors D SS cutters E Camptothecin prevents religation Forms a stable ternary complex with the topo I-DNA complex – Intercalation between the -1 and +1 DNA base pairs in the protein-DNA cleavage complex. Additional hydrophobic and electrostatic interactions stabilize the binding of the poison and prevent DNA re-ligation by the topoisomerase Causes DNA strand breaks which results in apoptosis Remarkable activity in preclinical trials – Low solubility in aqueous environments – Adverse drug reactions Isolated from the bark and stem of Camptotheca acuminata (Camptotheca, Happy tree), a tree native to China used as a cancer treatment in Traditional Chinese Medicine Camptotheca acuminata 2 2023-02-26 Substitution of the A ring increases solubility while retaining cytoxicity A B C D Camptothecin E circled = substituted Irinotecan and topotecan: semisynthetic analogues of camptothecin – Irinotecan = colon cancer – FOLFIRI (5- FluOrouracil, Leucovorin, and IRInotecan) Topotecan – Topotecan = ovarian and lung cancer Irinotecan (CPT-11) Metabolism metabolised by CYP3A4 to active compound chemotherapeutically active UDP glucuronosyltransferase 3 2023-02-26 Prodrug activation Irinotecan is converted to an active metabolite (SN-38) by carboxylesterase. – SN-38 is 1000 times more active than irinotecan itself – Down-regulation of carboxylesterase → resistance SN38 is metabolized to an inactive form via glucoronidation by UGT1A1. – There is a reduced function variant of UGT1A1 in ~10% of Caucasians → poor metabolism of Irinotecan → Irinotecan toxicity, as it cannot be excreted from the body in its SN-38 form. more adverse effects – On the other hand, increased expression of UGT1A1 can lead to resistance to Irinotecan ↓ ↑ metabolism Cytochrome p450 Irinotecan (CPT-11) is also inactivated by P450s (Cyp3A4) increased expression of either Cyp3A4 or UGT1A1 can lead to resistance to this drug. 4 2023-02-26 Anthracyclins: antitumor antibiotics Doxorubicin (adriamycin) main & ones Daunorubicin Doxorubicin ( Adriamycin ) – Solid O OH solid tumors tumors COCH 2 R 4 leukemias – Leukemia OH lymphomas – Lymphoma R1 O OH O R2 O Idarubicin CH 3 – AML (Acute Myeloid Leukemia) R3 Epirubicin NH 2 DNA-intercalating – Breast cancer topoII inhibitors Valrubicin – Bladder cancer Anthracyclins – Mechanisms of Action Inhibition of topoisomerase II (subtype-independent) causing DNA strand breakage Intercalative binding to DNA – Partial unwinding of DNA – Much of the DNA is organized and folded into chromatin and maybe protected from this type of damage G 2 M S Cell Cycle Free radical formation + heart damage Nonspecific – Generation of OH. and O2- > - strand breakage ↓ Go DNA strand breaks G1 Cell membrane damage can form in healthy cells too 5 2023-02-26 Toxicity of Anthracyclins ∗Myelosuppression ∗Mucositis (GI irritation) Cardiac toxicity (acute arrhythmias and delayed cardiomyopathies) – delayed cardiotoxicity is related to a patient's cumulative lifetime dose if cancer returns >higherdo not a second time - – Mechanism not entirely known J cardiac toxicity Superoxide radicals, hydrogen peroxide Disruption of calcium and iron levels in cells Preventing/limiting cardiotoxicity also an antioxidant Dexrazoxane (also a topo II inhibitor) – FDA approved – indicated to reduce adverse cardiac effects in women on doxorubicin who have already received a total dose of over 300 mg/m2 – may be due to its iron chelating activity (antioxidant) also an antioxidant Co-admin of carvedilol (adrenoceptor blocker) – also antioxidant in cardiac tissue Use of anthraquinones (mitoxantron, pixantrone) – act like anthracycline drugs but with fewer adverse effects/toxicities ↳ intercalated into the ONA 6 2023-02-26 Resistance to Anthracyclins ↑ ABCs ↓ activation ↳ phase 2 metab. downregulated enzymes ↓ upregulated ↑ DNA repair enzymes (biggest contributor to resistance) 7 2023-02-26 Podophyllotoxin derivatives Semi-synthetic glycoside derivatives of podophyllotoxin – Etoposide – Teniposide better cell accumulation Podophyllum peltatum (May-apple) Etoposide (VP-16) Non-intercalating inhibitor of topo II Formation of a stabilized ternary complex – Etoposide-topo II-DNA Single and double strand breaks in DNA G2 M S Cell Cycle PhaseSpecific (lateS/earlyG2) Go G1 8 2023-02-26 Etoposide – Clinical Use Testicular cancer Lung cancer Acute myeloid leukemia ∗Myelosuppression Etoposide Resistance Enhanced efflux ABCs Decreased binding to topoisomerase II - ↳ varies based on topoisomerase isoforms Increased glutathione conjugation phase 2 metabolism 9 2023-02-26 Antimicrotubular agents Vinca alkaloids – Vinblastine – Vincristine Taxanes – Paclitaxel – Docetaxel Microtubules Play a role in cellular structural support – Component of the cytoskeleton dynamic structures Important roles in: – Formation and function of mitotic spindles – Axonal transport of organelles 10 2023-02-26 (+) end Anti-microtubule agents interfere with formation and function of microtubules stabilizers destabilizers (-) end Vinca Alkaloids: Catharathus roseus Vincristine (VCR) Vinblastine (VLB) R VCR = CHO VLB + CH3 H 3COOC 11 2023-02-26 VCR and VLB Bind to tubulin at the end of microtubules and to tubulin dimers Blocks assembly of microtubules (Destabilizer) – Causes dissolution of mitotic spindles – Inhibit organelle transport nerves Especially mitochondria in neural cells G2 M ↳ S Ge Is phase specific Cell Cycle (G1/S) phase specific Go G1 Clinical Activity Vincristine – Acute lymphoblastic leukemia (ALL) – Hodgkin's lymphoma – Pediatric solid tumors ∗Peripheral neuropathy PLT z Vinblastine – Hodgkin's lymphoma – Non-small cell lung cancer ∗ Myelosuppression OLT 12 2023-02-26 Resistance ABCs upregulated PACLITAXEL (Taxol) O from the Western yew, Taxus brevifolia H 3C O O OH O CH3 3 13 2023-02-26 PACLITAXEL (Taxol) O ovarian and breast cancer lung cancer G2 Binds to tubulin enhancing its M binds to tubulin, S polymerization enhancing (Stabilizer) the polymerization of tubulin Cell Cycle PhaseSpecific (G2/M) – Discrete bundles of stable microtubules – Inhibition of cell replication Go G1 DOCETAXEL (Taxotere) (CH ovarian cancer breast cancer lower dose needed Higher affinity for tubulin binding site than paclitaxel ∗MYELOSUPPRESSION (neutropenia) OLT hypersensitivity reactions 14 2023-02-26 Noscapine Isoquinoline alkaloid found in opium latex sigma opioid receptor agonist. Used as a non-sedating antitussive in various countries - available OTC in Canada can be used orally. Under investigation for use in the treatment of several cancers, particularly for prostate cancer (at doses 100-fold higher than those effective as an antitussive) Fewer side effects than other microtubule disruptors (nausea and abdominal discomfort) Not as good a substrate for efflux transporters 15