Class 1 Class 1 3 Class Unknown 3 Class

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A crystallographic route to understand drug solubility: the case of 4-

aminoquinoline antimalarials

leonardo.lopresti@unimi.it

06.09.2019, MISCA V, Naples, Italy Università degli

Studi di Milano

Leonardo Lo Presti, Silvia Rizzato

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Outline

(i) Motivation

(ii) Malaria

(iii) The case of piperaquine

(iv) Conclusions

06.09.2019, MISCA V, Naples, Italy

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Dunne et al., BMC Pharmacology & Toxicology 2013, 14. 1

06.09.2019, MISCA V, Naples, Italy

Drug development

What formulation?

API: Active

Pharmaceutical Ingredient

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06.09.2019, MISCA V, Naples, Italy

Salts

~ 50 % of commercialized API are salts

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06.09.2019, MISCA V, Naples, Italy

Equivalent / alternative drugs

Pharmaceutically equivalent drugs Pharmaceutically alternativedrugs Same active ingredient (API) Same active ingredient (API)

Possibly different inactive ingredients (excipients, stabilizers, dyes, flavouring agents…)

Same salt, ester, complex Different salt, ester, complex

Same dosage forms Different dosage forms

Same release rate Different release rate

Same solubility Different solubility

Therapeutically equivalent (same clinical effect and safety profile)

Biologically equivalent (same metabolic target, but generally different pharmacokinetics)

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Advantages of salts

Liquids are more difficult to purify and maintain in pure

form

Solids are easier to stock and

transport

Higher melting points often mean improved

milling and compactability

Control of dissolution rates

(and timing of API release)

Metoprolol

Succinate

Slow release rate, more lipophilic

Tartrate

Fast release rate, more hydrophilic

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Disadvantages of salts

06.09.2019, MISCA V, Naples, Italy

Careful salt selection

study needed

Gould, Int. J. Pharm. 1986, 33, 1-3, 2011-2017 Kumar et al., Pharm. Technol. 2008, 32, 128-146

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06.09.2019, MISCA V, Naples, Italy

Salt selection study

To Identify the salt form most suitable for further

development and clinical trials

Hygroscopicity Solubility (T, pH) Crystallinity

Stability (degradation and polymorphism)

Most critical

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06.09.2019, MISCA V, Naples, Italy

Salt selection study

Criteria for salt formers

Williams et al. Pharm. Rev. 2013, 65, 315-499

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Outline

(i) Motivation

(ii) Malaria

(iii) The case of piperaquine

(iv) Conclusions

06.09.2019, MISCA V, Naples, Italy

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Malaria diffusion

06.09.2019, MISCA V, Naples, Italy

Siraj et al. Science, 2014, 343, 1154 Rogers, Science, 2000, 289,1763

2050

Torelli, Map of malaria in Italy, 1882

Yellow: endemic Red: next diffusion

P. Falciparum Anopheles

mosquito

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Pagola et al. Nature, 2000, 404, 307

Heme detoxification

Parasite Digestive Vacuole (DV)

pH ~ 4.5-5.5

FePPIX(OH)H₂ 2 x

2 H₂O

Crystallization

Hemozoin (natural) β-Hematin (synthetic)

P1

‘Malaria pigment’

FePPIX(FePPIXH)H

06.09.2019, MISCA V, Naples, Italy

Dimerization

Aminoquinoline drugs

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BM26A & ID26, ESRF, Grenoble (FR)

Macetti, Loconte, Rizzato, Gatti, Lo Presti, Crystal Growth Des. 2016, 16, 6043-6054 Macetti, Rizzato, Beghi, Silvestrini, Lo Presti, Physica Scripta 2016, 91, 023001

Finocchio, Rizzato, Lo Presti, in preparation

EXAFS+DFT XAS

+ CuBr₂ Chloroquine

Heme

Model systems

X-ray crystallography

Metabolic target

UV-Vis

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Outline

(i) Motivation

(ii) Malaria

(iii) The case of piperaquine

(iv) Conclusions

06.09.2019, MISCA V, Naples, Italy

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pKa ~ 6.2-6.8

Piperaquine, PQ

Piperaquine

pKa ~ 5.4-5.7

Possibility to improve formulation?

No other PQ salts are known PQH₄⁴⁺(H₂PO₄^-)₄·4H₂O

Poorly soluble in water Reduced oral bioavailability

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Synthesis

Hydrogen phosphate

Triflate

Hydrogen sulphate Bromide Nitrate

Class1 Class1 Class3 Class3Unknown

Sacchi, Loconte, Macetti, Rizzato, Lo Presti, Crystal Growth Des.2019,19, 1399-1410

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Salts

Counterion Label Habit Disorder Water

content

Space group

None Neutral Prism No No P2₁/n

H₂PO₄^- PPT Needles Rotational (2 H₂PO₄^-) + water

>4 P2₁/n HSO₄^- PHS Needles Rotational (all HSO₄^-) +

water

~6.6 + 1 H₃O⁺ Cc CF₃SO₃^-

(triflate)

PTT Plates Rotational (1 CF₃SO₃^-) + water

3 C2/c

Br^- PBT Prisms No 3 + 1 H₃O⁺ P1

NO₃^- PN Prisms No No P1

Single crystal X-ray diffraction Max resolution: 0.77-0.71 Å Completeness: 99.3-100 % R_int = 0.019-0.033

120 K – RT

06.09.2019, MISCA V, Naples, Italy

Sacchi, Loconte, Macetti, Rizzato, Lo Presti, Crystal Growth Des.2019,19, 1399-1410

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Crystal packing

H₂PO₄^- HSO₄^- CF₃SO₃^-

Br^- NO₃^-

06.09.2019, MISCA V, Naples, Italy

Hirshfeld surface fingerprint plots NH⁺···O^-

CH···Cl π··· π

Br···Cl

NH⁺···Br^-

CH···O CH···π

Cl···Cl

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Solubility

H₂PO₄^- HSO₄^- CF₃SO₃^- Br^-

NO₃^-

H₂PO₄^- HSO₄^- CF₃SO₃^- Br^-

NO₃^-

349 nm

344 nm

+ 7 4 0 %

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Understanding Solubility

Solubility

Cohesive Lattice energies

The model lacks of:

• Solute-solvent interactions

• Entropic effects

( )

∑

=

∆

−

∆ +

−

=

n

i

i i

i

E E

E

1

BSSE, rel,

iso, bulk

coh

DFT M06

06.09.2019, MISCA V, Naples, Italy

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Estimating solvation energies

06.09.2019, MISCA V, Naples, Italy

∆ =– RTln ·

= ⁄ · ′

Crystalline molar volume

Experimental solubility

Strength of crystal cohesion

Solute-solvent interactions Skyner et al., PCCP 2015,

17, 6174

Sacchi, Loconte, Macetti, Rizzato, Lo Presti, Crystal Growth Des.2019,19, 1399-1410

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Crystal cohesion

06.09.2019, MISCA V, Naples, Italy

Sacchi, Loconte, Macetti, Rizzato, Lo Presti, Crystal Growth Des. 2019,19, 1399-1410

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Crystal cohesion

∆ = ∆ − ∆

06.09.2019, MISCA V, Naples, Italy

∆ = ∆ + ∆

Experiment

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Entropic term

06.09.2019, MISCA V, Naples, Italy

∆ ≅ ∆

Assumptions:

(1) ∆S crystal gas ≈ ∆S crystal solution (2) Ensemble of non–interacting species

∆ ≈ ∆ = 1 $⁄ ∆% − ∆

∆ = ∆ − &$'( )

&$

∆Hº_sub= –E_coh – 2·RT

From quantum simulations in

the solid state Conversion to standard p, T state

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Results

Quantities referred to 25 ºC H₂PO₄^-

HSO₄^- CF₃SO₃^-

Br^- NO₃^-

HSO₄^- CF₃SO₃^-

Br^-

NO₃^- H₂PO₄^-

Lowest cohesive energy But: low ∆S_solv and ∆G_hyd

Highest cohesive energy

(largest Coulomb interactions)

PQH₄⁴⁺: hard acid Most soluble

Softest anion High ∆S_solv

Hardest anion

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The behaviour of nitrate

NO₃^-

No water and no disorder

Highest entropy gain upon dissolution than any other salt The effect is more pronounced at higher T

06.09.2019, MISCA V, Naples, Italy

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Outline

(i) Motivation

(ii) Malaria

(iii) The case of piperaquine

(iv) Conclusions

06.09.2019, MISCA V, Naples, Italy

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Conclusions

Five salts of piperaquine (PQ) were synthesized and characterized

06.09.2019, MISCA V, Naples, Italy

π⋅⋅⋅π stacking modes, or the number and type of hydrogen bonds, have no direct effect on the observed solubilities

Solubility stems from cooperative effects. If the crystal cohesion is very large, it dominates; otherwise, the η of the anion plays a central role.

Fully ordered bromide and nitrate have solubilities that increase faster as T is raised

• Coupling of the drug with soft anions to increase solubility and improve bioavailability

• Low disorder to have salts more soluble at higher T

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Acknowledgements

Prof. Silvia Rizzato

Dr. Laura Loconte

Dr. Lucia Silvestrini

Funding:

Development Plan for 2016-2017 (project NOVAQ)

ISCRA C initiative (Project MODELPIP)

Pietro Sacchi

Former PhD students

Gers Tusha

Matteo

Frigerio

Giada Finocchio

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Italian Crystal Growth 2020

Chairs:

Linda Pastero Marco Bruno

Torino, 01-02 October 2020

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