17a Parasites (Malaria) Duncan

Question 1

What microorganism causes Malaria?

Answer 1

Plasmodium spp.

Question 2

What is the primary form of Plasmodium in Asia?

Answer 2

Plasmodium vivax. Causes Benign tertian malaria

Question 3

What is the primary form of Plasmodium in Africa?

Answer 3

Plasmodium falciparum. Malignant tertian malaria (most severe type, fatal)

Question 4

What is the major group that Plasmodium is placed in?

Answer 4

Apicomplexans

Question 5

What is the Plasmodium life cycle?

Answer 5

Mosquito bites human. Young Plasmodium transferred to human and travels to liver where it develops further (tissue schizont). Final liver stage (merozoite) is released, infects RBCs. Development is completed in RBCs, where they then lyse and release infectious Merozoites (which can infect more RBCs or re-infect liver cells). Some of the released forms develop into gametes

Question 6

What is the primary focus of therapy for anti-malarial agents?

Answer 6

RBCs. Agents that target this step are called Schizonticides

Question 7

What do Quinines require?

Answer 7

An intact quinoline ring and the secondary alcohol are required. The R groups can be varied; a specific chain is not required

Question 8

What is the main 4-Aminoquinoline?

Answer 8

Chloroquine

Question 9

What does the structure of Chloroquine (4-Aminoquinoline) look like?

Answer 9

1) Secondary amine at C4. 2) Tertiary amine at terminus of C4 amino side chain. 3) Chlorine at C7. 4) C-C chain length in side chain (4 C’s between the N’s)

Question 10

What is the main 9-Aminoacridine used?

Answer 10

Quinacrine (Withdrawn)

Question 11

What does the structure of Quinacrine (9-Aminoacridine) look like?

Answer 11

1) Structurally related to 4-Aminoquinolines (has a third ring). 2) More toxic, hence not used

Question 12

What is the main 8-Aminoquinoline used?

Answer 12

Primaquine

Question 13

What does the structure of Primaquine (8-Aminoquinoline) look like?

Answer 13

1) Secondary amine at C8. 2) Primary, secondary or tertiary amine at terminus of C8 side chain. 3) Methoxy at C6. 4) C-C chain length in side chain can vary

Question 14

What is a major theory on how 4-Aminoquinolines work?

Answer 14

Plasmodium “digests” hemoglobin to obtain energy. The process results in the release ofheme, which is toxic. Plasmodium polymerize heme, which de-toxifies it (Polymerized form is called “hemozoin”). Chloroquine (and related 4-aminoquinolines) inhibit heme polymerization by binding directly to heme. Heme accumulates, preventing parasite development

Question 15

What is a new theory on how Aminoquinolines work?

Answer 15

Chloroquine and primaquine bind tightly to the RBC enzyme quinone reductase, and inhibit its activity. Quinone reductase reduces oxidative stress; when it’s inhibited, oxidative stress increases, to which Plasmodium are especially sensitive

Question 16

What is 4-Aminoquinoline sensitivity like?

Answer 16

Heme polymerase enzyme unique to Plasmodium. Aminoquinolines are concentrated in parasite’s food vacuole (entry as N-deprotonated forms, but gain H in the acidic food vacuole which restricts exit)

Question 17

What is 4-Aminoquinoline resistance like?

Answer 17

Resistance is common. Resistant strains frequently increase efflux (sometimes can be overcome by Ca channel blockers). Resistance associated with mutations in the PfCRT gene (encodes Chloroquine transporter, that regulates drug accumulation levels). K76T mutation: either blocks uptake, or increases export

Question 18

What are the general characteristics of Artemisinins?

Answer 18

Rapid action, no evidence of significant side effects. Provides a new, effective option for “drug-resistant” or severe strains of Plasmodium

Question 19

What is this a structure of?

Answer 19

Artemisinin

Question 20

What is the MOA of Artemisinins?

Answer 20

1) Iron-catalyzed cleavage of the endoperoxide bond. 2) Rearrangement to form carbon-based free radicals. 3) Destruction of biopolymers - e.g. proteins, RNA, DNA. Recent studies specifically pinpoint SERCA Ca-pump PfATP6 as target. 5) Information implicates heme (required for hemoglobin formation in RBCs) in generation of reactive intermediates (this may be because heme contains iron, and can act through the pathway shown)

Question 21

What are the SAR features of Artemisinins?

Answer 21

1) Activity requires endoperoxide (heme digestion releases Fe that catalyzes activation/conversion). 2) Modification of keto in naturally-occurring form increases potency (primary variant that is currently used: artemether). 3) Artesunate: succinate derivative, increased water solubility

Question 22

What is Halofantrine?

Answer 22

Phenanthrene methanols have some anti-malarial activity. Progenitor of lumefantrine. Not recommended d/t erratic activity, potenially lethal cardiotoxicity

Question 23

What is Lumefantrine and Coartem (Riamet)?

Answer 23

Lumefantrine is a superior “derivative” of halofantrine. Used in combination with artemether in the formulation called Coartem (Riamet) (Novartis). Interferes with heme polymerase

Question 24

What drug is currently the WHO recommended malaria treatment for areas where significant chloroquine resistance occurs?

Answer 24

Lumefantrine and Coartem (Riamet) (Novartis)

Question 25

What is Mefloquine?

Answer 25

1) Structurally similar to Quinine (Quinolone ring, secondary alcohol at C4, side chain extends into complex ring). 2) No rationale for the CF3. Initially very effective, now many strains are resistant

Question 26

What are some anti-malarial agents that affect folic acid synthesis?

Answer 26

Sulfonamides and sulfones. Pyrimidines (Pyrimethamine). Combination of sulfadoxine with pyrimethamine (Fansidar) significantly increases efficacy. Biguanides (Cycloguanil, Proguanil (frequently used prodrug form)

Question 27

What is Atovaquone?

Answer 27

Lipophilic compound similar to ubiquinone. Interferes with mitochondrial functions involving ubiquinone (cytochrome c reductase mutations lead to resistance). Useful in drug-resistant malaria. Combination with Proguanil (Malarone) significantly increases efficacy

Question 28

How do Tetracycline and Doxycycline attack Malaria?

Answer 28

Inhibit protein translocation by interfereing with the Apicoplast