(3/5) Jaki Lecture: Malaria Malaria Epidemiology

- Mortality fluctuations: From 1980 to 2004, the morality rate continued to climb. After the peak in 2004, it has been decreasing in prevalence thanks to private donors (such as Bill Gates) investing in malaria management.

- Vector: Female Anopheles Mosquito “Anopheles” = Useless, in greek. Which most of us can agree with - Infective Agent: A single-celled parasitic protozoan of the plasmodium type. There are 5 that can cause malaria. Protozoan Pathology Characterization

P. falciparum M. tropica “the most deadly parasitic human disease”. This is the most severe form of malaria, often leading to meningitis or cerebral bleeding. Fulminating disease, q36-48h

P. vivax M. tertiana Prone to Relapse. Q48h P. ovale M. tertiana Prone to Relapse, q48h P. malariae M. quartana Q72h. This is a more mild form of disease P. knowlesi *NEW Zoonotic. Previously only in macaque monkeys, genetic changes have altered its infectivity

to now target humans. This leads to severe disease, relatable to P. falciparum Pathophysiology ~ Life Cycle The parasite has two distinct phases of its life, alternating between the human host & mosquito vector

- Human - Infection

o The infected female mosquito engages the human to retrieve a blood meal o The parasite, in the form of sporozoites, is injected with the saliva at relatively low doses

- Establishment o The parasite enters the liver, invades cells, & starts multiplying via asexual reproduction o Within the liver cell the offspring are merozites. They accumulate, eventually causing the

cell to burst and are released into the bloodstream. - Blood Cell Destruction

o The human RBCs are targeted by the merozites, which invade and begin to multiply o Following sufficient accumulation, the merozites burst the RBC and find new RBC

hosts - Differentiation into gametocytes

o Some merozites in the RBC develop into sexual forms (gametocytes) o In this case, the next mosquito comes and ingests the blood, effectively

changing hosts - Mosquito - GI Frisky

o In the mosquito GI, the gametocytes mature into female and male gametes o The gametes engage in sexual reproduction, fusing, and forming a zygote

- Development o Zygote matures into a mobile form – Ookinete. It migrates to the cell wall of

the mosquito’s gut and matures into an Oocyst o Within, Sporoids develop, which rupture the oocyst releasing sporozoites

- Lock n Load o The sporozoites wanted into the saliva glands, awaiting a new host

Onset of Malarial Symptoms - Sx: Severe headache, splenomegaly, fever, muscle fatigue and pain, chills and sweating, back pain

Targets of Malaria: Treatment occurs at various stages of the parasite’s lifecycle. These have been noted by the blue arrows. Malarial infection can be characterized by an (1) Acute form and a (2) Dormant form. We must target both! There are 3 major targets for malaria treatment, providing us 3 major groups of drugs for treatment.

- (1) Hypnozoites: The dormant parasite cells of the liver, often responsible for relapse, either for many weeks or lifelong. These are usually conferred by P. vivax or P. ovale. (falciparum & tropica don’t have dormant forms)

- (2,3) Schizonts: The active parasitic cells. Variably present in the liver and blood - (4) Gametocytes: The sex cells. Found in the blood

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4-Subsituted Quinolines: Quinine, Chloroquine, Mefloquine, Halofantrine [First-Line] - Target: Blood Schizonts – the reproducing active form of the parasite in RBC - MoA: In the RBC, plasmodium have a large food vacuole to which they use to digest hemoglobin and produce

AA for their own synthesis. A digestion product, Heme, is very toxic to the plasmodium cells and RBC. Polymerization of heme to hemozin is the method for heme detoxification by plasmodium.

o Heme Accumulation: The 4-sub-Quinolines block the polymerization process by binding to Hemozin (via aromatic pi bonds) and preventing further polymer extension. This will block heme detoxification, leading to heme accumulation thus killing the cell and plasmodium parasite.

o Ion Trapping: The non-protonated forms of our quinolone drugs are weak bases. The drugs are naturally drawn to the food vacuole due to pH drift. Since it is uncharged intracellularly, it may freely enter the food vacuole, in which the pH is 5.5, Once entered, it becomes charged and can no longer escape. It will accumulate

o Hemozoin is known as the ‘malaria pigment’, which is dark blue/black and is non-toxic. n Quinine: The first known anti-malaria drug, known to the natives as ‘quinquina,’ was used to treat malaria

o Stereochemistry: Quinine has 2 stereocenters, on C8 and C9. They have strong implications on efficacy, mainly because parasite strains may be resistant to one versus the other.

§ 8S 9R - Quinine = Yes has activity § 8R 9R - 8-epi-quinine = No activity § 8R 9S - Quinidine = Yes has activity (Reserved for 2nd line therapy, more severe cases) § 8S 9S - 8-epi-quinidine = No activity

o Essential Elements: C9-OH, C8-NR2 Without these elements, the drug is not active. § The Quinuclidine ring is the bicyclic structure that has the essential Nitrogen

n Chloroquine (CQ): A 4-[choline]amine - Our most important antimalarial o Structure: Chlorine EQG stabilizes the aromatic group o CQ Resistance: Spontaneous gene mutations in the pfcrt transport protein of P.

falciparum, which enhances drug efflux against the ion trapping mechanism of quinolines. Upregulated P450 metabolism

n Mefloquine: A 4-[choline]methanol o Structure: Small CF3 group imitates CH3, thereby blocking metabolic

hydroxylation and oxidation reactions. Stable group, BioavailabilityÝ n Halofantrine: A 4-[choline]methanol

o Structure: Contains chlorine-substituted ring that acts as EWG, deactivating the ring and conferring stability against metabolism

- WHAT IF ~*% The Chemical Modification Game %*~ IF WHAT ~Starring CQ

8-Substituted Quinolines: Primaquine

- Target: Non-specific – But effective against the Liver host cells and Blood Gametocides o Capable of targeting the Hypnozoites, of which arise from P. vivax + ovale in M tertiana

- MoA: The 8-Subs generate destructive reactive oxygen species via auto-oxidation of their 8-amino group. This forms ROS like hydrogen peroxide, superoxide, and hydroxyl radical leading to oxidative cell damage. This is particularly effective against the dormant Hypnozoites of the liver. The dormant hypnozoites are associated with infections by P. vivax and P. ovale, treating the dormant form is necessary as it helps prevent relapse.

Antifolates: Pyrimethamine - Target: As monotherapy, they are effective in treating the active replicating Blood Schizonts - MoA: Potent inhibitors of the DHFR, antifolates are antagonistic to folic acid

N-Dealkylation

Removal of an alkyl group will make the Amine more acidic, and less basic As a result, its ability to cross membranes into the food vacuole will be hindered, making the 4-sub less effective.

De-chlorination of the Arly

The chlorine is responsible for deactivating the ring via EWG effect, preventing metabolism. By removing it, the drug will be more vulnerable to metabolism and be less effective

Alkylation of the Aromatic System

The 4-sub mechanism of action involves the aryl system engaging in pi-stacking interactions with the porphyrin nucleus of the growing hemozoin chain. Alkylation will produce steric hindrance, blocking this interaction and reducing drug activity.

Chloroquine

- Combination Products: Pyrimethamine is often combined with additional drugs to strongly enhance the interruption of folic acid metabolism. Folic acid is an essential vitamin for single-celled organisms, without it, they will die

o Sulfadoxine: A sulfonamide that blocks Dihydrofolate synthesis. Synergy with Pyrimethamine o Quinine: This combination is effective at treating and preventing qc-resistant malaria

Artemisins: Artemisinin à Artemether… and Artesnute (investigational) - Target: The oxidative damage targets Blood Schizonts and Young Gametocytes - MoA: These compounds are sesquiterpene lactones, which are sensitive to condensation. Their

reactivity produces free radicals (endoperoxide) which inflicts oxidative damage to the parasite membrane.

- Lore: In 2015, Tu Youyou became the first female citizen of the People’s Republic of China to receive a Nobel Prize – for her discovery of Artemisinin from the Artemisia annua plant. Her name, given to her by her father, is derived from ‘呦呦鹿鸣, 食野之蒿’from a poem in the Chinese Book of Odes, effectively translating to ‘the deer cries youyou,while they are eating the wild Hao’. Quite a coincidence, Hao is the Artemisia annua plant.

Atovaquone/Proguanil: Malarone - Target: Multi-drug+Cq-resistant strains of P falciparum and P. vivax. Targets only the active blood form - MoA: Atovaquone is a Naphthalene derivative that acts as a ubiquinone reductase inhibitor. Its activity leads to

the collapse of the mitochondrial membrane potential. In addition, Proguanil - an antifolate, inhibits the enzyme Dihydrofolate reductase. This combination is effective against resistant strains

Guidelines for the Treatment of Malaria – CDC - Empiric Therapy: Therapy should be initiated against CQ-resistant P. falciparum empirically if:

o (1) If the diagnosis of malaria is suspected but cannot be confirmed o (2) Diagnosis of malaria is confirmed, but the species determination is not possible o *Failed Prophylaxis: If a malaria infection occurs despite preventative therapy, the failed drug should not

be a part of the treatment regimen. We assume that there is resistance - Drug Therapy UNID = unidentified

o UNID in area w/o CQ-resistance à CQ Phosphate, 600mg LD, 300mg at 6º, 24º, 48º o UNID in area with CQ-resistance àAtovaquone Proguanil.

§ There are additional options such as Artemether-luefantine, quinine + doxycycline o Identified P falciparum in area with CQ-Resistance o Identified P. malaria or P. knowlesi à Treat with CQ, they rarely have resistance o Identified P. vivax or P. ovale à Treat with CQ + Primaquine x2w ~gotta get the dormant ones! o Severe Malaria à PARENTERAL, quinidine gluconate x24h until parasitemia <1%, then PO quinine

§ If quinidine is unavailable, use the investigational new drug Artesunate o Pregnancy: CQ. We can only treat the acute form, the unborn baby cannot tolerate Primaquine.

Following birth, we can use primaquine. - Uncomplicated: Treat to avoid potential complications - Severe malaria: Severe cases should be considered to be related to P. falciparum infection. Sx include:

o Parasitemia ³5%, Unconscious, coma, renal failure, jaundice, convulsions, spontaneous bleeds. Respiratory distress

- Base/Salt Conversion: The active component of these compounds is the base. Make sure to convert when calculating the dosing for therapy. 600mg base = 1000mg salt

Preventative Malarial therapies on the next page.

Preventative Therapy for Malaria Long trips

- Chloroquine (Aralen): Use for 1-2 weeks before travel, and 4 weeks after travel. 300mg base once weekly o AE: Vision problems, irreversible retinal damage may occur with prolonged tx (see eye doctor)

- Mefloquine (Lariam): Use for 2-3 weeks before travel, and 4 weeks after travel. 228mg base once weekly o ContraX: Seizures, mental disorders, cardiac conduction issues, preggers AE: tingling feet n hands

Short trips - Doxycycline (Adoxa): Use for 1-2 days before travel, and 4 weeks after travel. 100mg Qdaily

o MoA: Impairs the reproduction of malaria-specific plastids, ~ abnormal cell division o ContraX: Children < 8yo, Preggers. AE: Sun exposure stuff, teeth

- No antimalarial drug is 100% effective, personal protective measures should be taken for optimal coverage o Insect repellant, long sleeves, long pants, sleeping in mosquito-free setting

- Considerations for Travel: Duration of trip, endemic areas, DDI. Visit CDC for more information Last minute

- Atovaquone/Proguanil (Malarone): Use 1-2 days prior to travel, 7 days after travel. 250mg/100mg Qdaily o ContraX: Pregnancy, Breastfeeding, Renal impairment

- Primaquine: Use 1-2 days prior to travel and 7 days after travel. 30mg Qdaily. o This is the most effective medication for preventing P. vivax so use it if going to area with >90% P. vivax o ContraX: G6PD deficiency (tests are available), Pregnancy, Breastfeeding

LIVER BLOOD Hypnozoites Schizonts Schizonts Gametocides 4-substituted quinolones (CQ) - - + - 8-substituted quinolones (Primaquin) + + - + DHFR-Inhibitors (antifolate) - - + - Artemisins - - + + Atovaquone/Proguanil - - + ?