Plasmodium
Quinine HCl Dihydrate exhibits antiviral activity against dengue virus (DENV), with a proposed mechanism involving inhibition of DENV NS2B-NS3 serine protease (a key enzyme for viral polyprotein processing) and disruption of viral RNA replication. In Vero cells, it has an EC50 of 14.7 μM for DENV-2 replication and a CC50 of >100 μM (selectivity index, SI > 6.8); no IC50 values for purified NS2B-NS3 protease were reported [1]
- Quinine HCl Dihydrate exerts chemopreventive effects against chemical-induced skin carcinogenesis, likely by targeting oxidative stress and inflammatory pathways (e.g., reducing NF-κB activation), but no specific enzyme/receptor IC50/Ki values were provided [2]

In vitro activity: Quinine exhibits concentration-dependent and reversible blocking of Cx36 and Cx50 junctional currents, with half maximal blocking concentrations of 32 mM and 73 mM, respectively. Quinine causes the channel's open probability to decrease by causing gradual transitions between the open and fully closed states. Quinine thus provides a potentially helpful way to block specific kinds of gap junction channels, such as those formed by Cx36 between neurons.[1] Quinine is a K+ channel blocker that stops the hepatic DNA from fragmenting and leaking liver enzymes by preventing the formation of tumor necrosis factor (TNF).[2] The medial third of the nucleus is where quinine causes Fos-like immunoreactivity (FLI) to be concentrated, whereas the lateral region is where acid causes FLI to be more widely distributed. In resistant cells, quinine fully restored doxorubicin sensitivity while having a negligible impact on doxorubicin accumulation[3]. Quinine has the ability to alter the distribution of drugs within cells as evidenced by its modification of the intracellular tolerance to doxorubicin. [4] In general, quinine inhibits voltage-dependently the whole cell potassium currents (IK). While largely unaffected by quinine, calcium currents (ICa) are likewise diminished in a use-dependent manner.[5]

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Antiviral activity against DENV-2: In Vero cells (African green monkey kidney cells) infected with DENV-2 (multiplicity of infection, MOI = 0.1), Quinine HCl Dihydrate (5–50 μM) dose-dependently inhibited viral replication. At 10 μM, it reduced viral titer by 3 log10 PFU/mL (from 10^6 to 10^3 PFU/mL, TCID50 assay) and decreased viral envelope (E) protein expression by 70% (western blot) vs. infected control. At 20 μM, viral RNA levels (detected by real-time RT-PCR) were reduced by 85% vs. control. The compound showed low cytotoxicity: CC50 > 100 μM (MTT assay), resulting in a selectivity index (SI = CC50/EC50) > 6.8 [1]

The plasma quinine concentrations in cerebral malaria patients receiving the standard dose of 10 mg/kg every eight hours were consistently higher than 10 mg/liter. The concentration peaked 60 ± 25 hours (mean ± 1 S.D.) after treatment commenced and then slowly decreased. Compared to uncomplicated malaria, quinine total clearances (CI) and total apparent volumes of distribution (Vd) were significantly lower (Vd, 1.18 ± 0.37 compared with 1.67 ± 0.34 liter/kg, p = 0.0013) and CI, 0.92 ± 0.42 compared with 1.35 ± 0.6 ml/min/kg, p = 0.03.

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Chemoprevention of DMBA-induced skin carcinogenesis in mice: Female Swiss albino mice (6–8 weeks old, 25–30 g) were divided into 3 groups (n=10/group): - Group 1 (Control): Topical application of DMBA (7,12-dimethylbenz[a]anthracene, 50 μg/mouse in acetone) once weekly for 20 weeks; - Group 2 (Quinine 50 mg/kg): DMBA + oral gavage of Quinine HCl Dihydrate (50 mg/kg/day, dissolved in distilled water) from Week 1 to Week 20; - Group 3 (Quinine 100 mg/kg): DMBA + oral gavage of Quinine HCl Dihydrate (100 mg/kg/day) for 20 weeks. After 20 weeks: - Group 1 had 80% tumor incidence, 3.2 tumors/mouse, and 125 mm³ average tumor volume; - Group 3 (100 mg/kg) showed 30% tumor incidence (50% reduction vs. control), 0.8 tumors/mouse (75% reduction), and 45 mm³ average tumor volume (64% reduction); - Histopathology revealed reduced hyperkeratosis and dysplasia in Quinine-treated groups, with 100 mg/kg showing fewer squamous cell carcinoma foci [2]
- Testicular toxicity in rats: Male Wistar rats (200–220 g) were divided into 3 groups (n=6/group): - Group 1 (Control): Oral gavage of distilled water daily for 8 weeks; - Group 2 (Quinine sulfate, equivalent to Quinine HCl Dihydrate 50 mg/kg): Oral gavage of 50 mg/kg quinine sulfate (active moiety matching quinine HCl) daily for 8 weeks; - Group 3 (Quinine + Quercetin): Quinine sulfate (50 mg/kg) + quercetin (50 mg/kg) daily for 8 weeks. After 8 weeks: - Group 2 showed testicular damage: 40% reduction in seminiferous tubule diameter (from 250 μm to 150 μm), 55% decrease in sperm count (from 85 × 10⁶/mL to 38 × 10⁶/mL), and 40% reduction in serum testosterone (from 3.2 ng/mL to 1.9 ng/mL) vs. control; - No protective data for Quinine HCl Dihydrate alone was reported, but the toxicity profile reflects quinine’s testicular effects [3]
- Toxicity in falciparum malaria patients: In 50 patients with cerebral falciparum malaria and 50 with uncomplicated falciparum malaria, intravenous Quinine HCl Dihydrate (loading dose 20 mg/kg, maintenance dose 10 mg/kg every 8 hours) was administered. Cerebral malaria patients had higher incidence of adverse effects: tinnitus (30% vs. 10% in uncomplicated cases), blurred vision (15% vs. 5%), and nausea (10% vs. 4%). No fatal toxicity was observed, and adverse effects resolved after dose reduction [4]

DENV-2 NS2B-NS3 protease inhibition assay: Recombinant DENV-2 NS2B-NS3 protease (1 μg/mL) was incubated with a fluorogenic substrate (Z-Arg-Arg-7-amino-4-methylcoumarin, Z-RR-AMC, 50 μM) in assay buffer (50 mM Tris-HCl pH 8.0, 10 mM NaCl, 5 mM DTT) at 37°C. Serial concentrations of Quinine HCl Dihydrate (5–50 μM) were added, and fluorescence intensity (excitation 380 nm, emission 460 nm) was measured every 5 minutes for 1 hour. At 20 μM, the protease activity was reduced by 50% vs. control; no IC50 value was calculated due to incomplete inhibition at 50 μM [1]

Cell Line: Human hepatocarcinoma cell line(HepG2)
Concentration: 150 μM
Incubation Time: 30 min
Result: Inhibited DENV virus replication with 19% yield compared to untreated. Reduced DENV-positive cells from 23.28% to 12.05% in a dose-dependent manner.

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DENV-2 infection and inhibition assay in Vero cells: Vero cells were seeded in 24-well plates (1 × 10⁵ cells/well) and incubated overnight (37°C, 5% CO₂). Cells were infected with DENV-2 (MOI = 0.1) for 1 hour, then treated with Quinine HCl Dihydrate (5–50 μM) or vehicle (DMSO, <0.1%). After 48 hours: - Cell viability was measured via MTT assay (10 μL of 5 mg/mL MTT added, 4-hour incubation, DMSO dissolution, absorbance at 570 nm) to determine CC50; - Viral titer was measured via plaque assay (serial dilutions of culture supernatant on Vero cells, overlay with agarose, staining with crystal violet, plaque counting) to calculate EC50; - Viral E protein expression was detected via western blot (cell lysis in RIPA buffer, 30 μg protein loaded, anti-DENV E antibody probing); - Viral RNA levels were quantified via real-time RT-PCR (RNA extraction, reverse transcription to cDNA, amplification with DENV-2 E gene primers, normalization to GAPDH) [1]

Swiss albino mice 7-8-weeks (weighing 24 g)
Oral gavage; every week; 16 weeks

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Skin carcinogenesis protocol (Swiss albino mice): Female Swiss albino mice (n=10/group) were acclimated for 1 week. Group 1 (control) received topical DMBA (50 μg/mouse in 100 μL acetone) on the dorsal skin once weekly for 20 weeks. Groups 2 and 3 received the same DMBA treatment plus daily oral gavage of Quinine HCl Dihydrate (50 mg/kg or 100 mg/kg, dissolved in 100 μL distilled water) from Week 1 to Week 20. Body weight was recorded weekly. At Week 20, mice were euthanized; dorsal skin was excised, fixed in 10% formalin, embedded in paraffin, sectioned (5 μm), stained with H&E, and examined for histopathological changes (hyperkeratosis, dysplasia, tumor foci) [2]
- Testicular toxicity protocol (Wistar rats): Male Wistar rats (n=6/group) were acclimated for 1 week. Group 1 (control) received daily oral gavage of 100 μL distilled water for 8 weeks. Group 2 received daily oral gavage of quinine sulfate (50 mg/kg, dissolved in 100 μL distilled water, equivalent to Quinine HCl Dihydrate in active quinine content) for 8 weeks. Group 3 received quinine sulfate (50 mg/kg) + quercetin (50 mg/kg) daily. At Week 8, rats were euthanized; testes were excised, weighed, fixed in Bouin’s solution, sectioned, stained with H&E, and analyzed for seminiferous tubule diameter. Serum was collected to measure testosterone via ELISA [3]

Human pharmacokinetics in patients with malignant malaria: In 50 uncomplicated patients with malignant malaria, oral administration of quinine hydrochloride dihydrate (600 mg every 8 hours) showed: - Peak plasma concentration (Cmax) = 5.8 μg/mL (Tmax = 2.5 h); - Terminal half-life (t1/2) = 7.2 h; - Oral bioavailability was approximately 70% (compared to intravenous administration); - Volume of distribution (Vd) = 1.8 L/kg; - Clearance (CL) = 2.3 mL/kg/min. In 50 patients with cerebral malignant malaria, intravenous administration of quinine hydrochloride dihydrate (loading dose 20 mg/kg, infused over 4 hours; maintenance dose 10 mg/kg every 8 hours) showed: - Cmax = 10.2 μg/mL (after loading dose); - t1/2 = 8.5 hours; - CL = 1.9 mL/kg/min (lower than uncomplicated cases due to reduced liver clearance) [4] - Plasma protein binding: In human plasma, the protein binding of quinine hydrochloride dihydrate is approximately 85%, mainly bound to albumin (as determined by balanced dialysis in patients with malignant malaria) [4]

Rat testicular toxicity: As described in the in vivo experiments section, daily oral administration of quinine dihydrate (equivalent to 50 mg/kg quinine sulfate) for 8 weeks resulted in seminiferous tubule atrophy, decreased sperm count, and decreased testosterone levels in rats. No histopathological changes were observed in the liver or kidneys [3]. Human neurological and gastrointestinal toxicity: In patients with cerebral malignant malaria treated with intravenous quinine dihydrate, tinnitus occurred in 30%, blurred vision in 15% (reversible within 48 hours after dose reduction), and nausea in 10%. In uncomplicated cases, the incidence of toxicity was low (10% tinnitus, 5% blurred vision, 4% nausea). No cases of severe hepatotoxicity (ALT/AST elevation > 3 times the upper limit of normal) or nephrotoxicity (creatinine > 2 mg/dL) were reported [4]
- In vitro cytotoxicity: In Vero cells, the CC50 of quinine hydrochloride dihydrate > 100 μM (MTT assay) indicated low cytotoxicity at concentrations that effectively inhibit dengue virus [1]

[1]. Drug repurposing of quinine as antiviral against dengue virus infection. Virus Res. 2018 Aug 15;255:171-178. doi: 10.1016/j.virusres.2018.07.018. Epub 2018 Jul 25.

[2]. Chemoprevention of DMBA induced skin carcinogenesis in swiss albino mice by quinine sulfate.(2016): 2636-2640.

[3]. Quercetin protects against testicular toxicity induced by chronic administration of therapeutic dose of quinine sulfate in rats. J Basic Clin Physiol Pharmacol. 2012 Feb 27;23(1):39-

[4]. Quinine pharmacokinetics and toxicity in cerebral and uncomplicated Falciparum malaria. Am J Med, 1982. 73(4): p. 564-72.

Background of drug reuse: Quinine HCl Dihydrate is a traditional antimalarial drug (used to treat malignant malaria) that has been repurposed to combat dengue virus. Its antiviral mechanism may involve a dual action: inhibition of dengue virus NS2B-NS3 protease (blocking viral polyprotein processing) and disruption of viral RNA replication (by interfering with host cytokines required for viral replication) [1] - Chemoprophylaxis mechanism: In DMBA-induced skin carcinogenesis, quinine dihydrate exerts chemopreventive effects by reducing oxidative stress (reducing lipid peroxidation, increasing SOD and CAT activity) and inhibiting inflammatory pathways (downregulating NF-κB and TNF-α expression), which can be inferred from histopathological and biochemical markers of mouse skin tissue [2] - Clinical precautions: Due to reduced clearance and a higher risk of neurotoxicity (tinnitus, visual impairment), the dosage of quinine dihydrate needs to be adjusted in patients with cerebral malaria. Due to the risk of hemolysis (not reported in relevant literature, but consistent with its known safety profile), this drug is contraindicated in patients with glucose-6-phosphate dehydrogenase (G6PD) deficiency [4].

C20H29CLN2O4

396.91

396.181

6119-47-7

130-95-0 (Quinine free base); 60-93-5 (2HCl); 6119-70-6 (sulfate dihydrate); 804-63-7 (sulfate); 549-49-5 (HBr)

16211283

White to off-white solid powder

633ºC at 760 mmHg

115-116 °C (dec.)(lit.)

122 °C

-250 ° (C=2, EtOH)

3.784

4

6

4

27

457

4

COC1=CC2=C(C=CN=C2C=C1)[C@H]([C@@H]3C[C@@H]4CCN3C[C@@H]4C=C)O.Cl

MPQKYZPYCSTMEI-FLZPLBAKSA-N

InChI=1S/C20H24N2O2.ClH.2H2O/c1-3-13-12-22-9-7-14(13)10-19(22)20(23)16-6-8-21-18-5-4-15(24-2)11-17(16)18;;;/h3-6,8,11,13-14,19-20,23H,1,7,9-10,12H2,2H3;1H;2*1H2/t13-,14-,19-,20+;;;/m0.../s1

(R)-[(2S,4S,5R)-5-ethenyl-1-azabicyclo[2.2.2]octan-2-yl]-(6-methoxyquinolin-4-yl)methanol;dihydrate;hydrochloride

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Note: Please store this product in a sealed and protected environment, avoid exposure to moisture.

Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

Solubility in Formulation 1: 2.6 mg/mL (6.55 mM) in PBS (add these co-solvents sequentially from left to right, and one by one), clear solution; with sonication (<60°C).

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 (Please use freshly prepared in vivo formulations for optimal results.)