This commentary addresses data quality in equilibrium solubility measurement in aqueous solution. Broadly discussed is the “gold standard” shake-flask (SF) method used to measure equilibrium solubility of ionizable drug-like molecules as a function of pH. Many factors affecting the quality of the measurement are recognized. Case studies illustrating the analysis of both solution and solid state aspects of solubility measurement are presented. Coverage includes drug aggregation in solution (sub-micellar, micellar, complexation), use of mass spectrometry to assess aggregation in saturated solutions, solid state characterization (salts, polymorphs, cocrystals, polymorph creation by potentiometric method), solubility type (water, buffer, intrinsic), temperature, ionic strength, pH measurement, buffer issues, critical knowledge of the pKa, equilibration time (stirring and sedimentation), separating solid from saturated solution, solution handling and adsorption to untreated surfaces, solubility units, and tabulation/graphic presentation of reported data. The goal is to present cohesive recommendations that could lead to better assay design, to result in improved quality of measurements, and to impart a deeper understanding of the underlying solution chemistry in suspensions of drug solids.

Schistosomiasis is a serious disease currently estimated to affect more that 207 million people worldwide. Due to the intensive use of praziquantel, there is increasing concern about the development of drug-resistant strains. Therefore, it is necessary to search for and investigate new potential schistosomicidal compounds. This work reports the in vivo effect of the alkaloid epiisopiloturine (EPI) against adults and juvenile worms of Schistosoma mansoni. EPI was first purified its thermal behavior and theoretical solubility parameters charaterised. In the experiment, mice were treated with EPI over the 21 days post-infection with the doses of 40 and 200 mg/kg, and 45 days post-infection with single doses of 40, 100 and 300 mg/kg. The treatment with EPI at 40 mg/kg was more effective in adult worms when compared with doses of 100 and 300 mg/kg. The treatment with 40 mg/kg in adult worms reduced parasite burden significantly, lead to reduction in hepatosplenomegaly, reduced the egg burden in faeces, and decreased granuloma diameter. Scanning electron microscopy revealed morphological changes to the parasite tegument after treatment, including the loss of important features. Additionally, the in vivo treatment against juvenile with 40 mg/kg showed a reduction of the total worm burden of 50.2%. Histopathological studies were performed on liver, spleen, lung, kidney and brain and EPI was shown to have a DL50 of 8000 mg/kg. Therefore EPI shows potential to be used in schistosomiasis treatment. This is the first time that schistosomicidal in vivo activity of EPI has been reported. Schistosomiasis, a disease caused by worms from the genus Schistosoma, is one of the most widespread neglected tropical diseases in the world. Due to the intensive use of praziquantel, some reports of drug resistance have emerged. Thus it is important to search for new chemotherapeutic agents for the treatment disease. This research showed that epiisopiloturine, an imidazole alkaloid extracted from the leaves of Pilocarpus microphylus, has activity against S. mansoni in vivo. This material is produced as a by-product of an existing commercial process, and thus can be produced in large quantities at relatively low cost. The low toxicity and high drug tolerance in mammals shows the potential of epiisopiloturine as a new candidate schistosomicidal compound.

A new Zn(II)-based potential chemotherapeutic agent was synthesized from the ligand 2-quinolinecarboxaldehyde selenosemicarbazone (Hqasesc). Single crystal X-ray diffraction analysis showed that the Zn(II) complex consists of a cation [Zn(Hqasesc)₂]²⁺, two perchlorate anions and one ethanol solvent molecule. The interaction of calf thymus (CT) DNA and human serum albumin (HSA) with the Zn(II) complex was explored using absorption and emission spectral methods, and also has been supported by molecular docking studies. The complex has more affinity to minor DNA groove than major, with no significant intercalation. The HSA interaction studies of the complex revealed the quenching of the intrinsic fluorescence of the HSA through a static quenching mechanism. The antitumor activity of the ligand and the complex against pancreatic adenocarcinoma cell line (AsPC-1) and acute monocytic leukemia (THP-1) cells was evaluated. Both compounds are strong concentration-dependent apoptosis inducers in THP-1 cells. While Hqasesc in AsPC-1 cells induces apoptosis only at the highest concentration, treatment with the Zn complex shows a concentration-dependent apoptotic response, where the treated cells are arrested in the G1-to-S phase accompanied with extensive activation of caspase-8 and -9. These results indicate that the ligand and Zn(II) complex display cell phenotype specific activity.

Although solubility-pH data for desipramine hydrochloride (DsHCl) have been reported previously, the aim of the present study was to critically examine the aqueous solubility-pH behavior of DsHCl in buffer-free and buffered solutions, in the presence of physiologically-relevant chloride concentration, using experimental practices recommended in the recently-published "white paper" (Avdeef et al., 2016). The computer program pDISOL-X was used to design the structured experiments (pH-RSF method), to process the data, and to refine the equilibrium constants. Low-to-high and high-to-low pH assays (using HCl, H3PO4, or NaOH to adjust pH) were performed on phosphate-buffered (0.12‑0.15 M) saturated solutions of DsHCl in the pH 1.3-11.6 range. After equilibration (stirring 6 h, followed by 18 h stir-free sedimentation), filtration or centrifugation was used for phase separation. Concentration was measured using HPLC with UV/VIS detection. The 2:1 drug-phosphate solubility product (Ksp2:1 = [DsH+]2[HPO42-]) was determined from data in the pH 4-9 region. The free base of desipramine was prepared and used to determine the Ksp1:1 ([DsH+][H2PO4-]) in chloride-free acidified suspension. In addition, phosphate-free titrations were conducted to determine the intrinsic solubility, S0, and the 1:1 drug-chloride solubility product, KspDsHCl = [DsH+][Cl-]. Under the assay conditions, only the phosphate-free solutions showed some supersaturation near pHmax 8.0. In phosphate-containing solutions, pHmax was indicated at higher pH (8.8-9.6). Oils mixed with solids were observed to form in alkaline solutions (pH > 11). Notably, soluble drug-phosphate complexes appeared to form below pH 3.9 and above pHmax in saturated phosphate‑containing saline solutions. This was indicated by the systematic pH shift to higher values in the log S-pH curve in alkaline solution than expected from the Henderson-Hasselbalch equation. For pH < 3.9, saturated phosphate-containing saline solutions exhibited elevated solubility, with drug-hydrochloride as the sole precipitate. Salt solubility products, intrinsic solubility, and complexation constants, which rationalized the data, were determined. Elemental, thermogravimetric (TGA), differential scanning calorimetric (DSC), and powder X-ray diffraction (PXRD) analyses were used to characterize the precipitates isolated from suspensions at different pH.