Enzymatic activation of double-targeted 5'-O-L-valyl-decitabine prodrug by biphenyl hydrolase-like protein and its molecular design basis

Tissue-Specific Proteomics Analysis of Anti-COVID-19 Nucleoside and Nucleotide Prodrug-Activating Enzymes Provides Insights into the Optimization of Prodrug Design and Pharmacotherapy Strategy

Nucleoside and nucleotide analogs are an essential class of antivirals for COVID-19 treatment. Several nucleoside/nucleotide analogs have shown promising effects against SARS-CoV-2 in vitro; however, their in vivo efficacy is limited. Nucleoside/nucleotide analogs are often formed as ester prodrugs to improve pharmacokinetics (PK) performance. After entering cells, the prodrugs undergo several enzymatic metabolism steps to form the active metabolite triphosphate nucleoside (TP-Nuc); prodrug activation is therefore associated with the abundance and catalytic activity of the corresponding activating enzymes. Having the activation of nucleoside/nucleotide prodrugs occur at the target site of action, such as the lung, is critical for anti-SARS-CoV-2 efficacy. Herein, we conducted an absolute quantitative proteomics study to determine the expression of relevant activating enzymes in human organs related to the PK and antiviral efficacy of nucleoside/nucleotide prodrugs, including the lung, liver, intestine, and kidney. The protein levels of prodrug-activating enzymes differed significantly among the tissues. Using catalytic activity values reported previously for individual enzymes, we calculated prodrug activation profiles in these tissues. The prodrugs evaluated in this study include nine McGuigan phosphoramidate prodrugs, two cyclic monophosphate prodrugs, two l-valyl ester prodrugs, and one octanoate prodrug. Our analysis showed that most orally administered nucleoside/nucleotide prodrugs were primarily activated in the liver, suggesting that parenteral delivery routes such as inhalation and intravenous infusion could be better options when these antiviral prodrugs are used to treat COVID-19. The results also indicated that the l-valyl ester prodrug design can plausibly improve drug bioavailability and enhance effects against SARS-CoV-2 intestinal infections. This study further revealed that an octanoate prodrug could provide a long-acting antiviral effect targeting SARS-CoV-2 infections in the lung. Finally, our molecular docking analysis suggested several prodrug forms of favipiravir and GS-441524 that are likely to exhibit favorable PK features over existing prodrug forms. In sum, this study revealed the activation mechanisms of various nucleoside/nucleotide prodrugs relevant to COVID-19 treatment in different organs and shed light on the development of more effective anti-COVID-19 prodrugs.

Apically targeted oral micelles exhibit highly efficient intestinal uptake and oral absorption

Introduction

Polymeric micelles (PMs) hold promise for improving solubility and oral absorption of poorly soluble drugs. Unfortunately, the oral absorption of PMs is also limited by intestinal epithelium. To improve the oral delivery efficiency of micelles, transporter-mediated micelles could enhance the transport efficiency across the epithelial barrier, and they have attracted more attention.

Methods

Peptide transporter 1 (PepT1)-mediated micelles (Val-PMs/Phe-PMs) were designed by grafting valine (or phenylalanine) onto the surface of curcumin (Cur)-loaded-D-α-tocopheryl polyethylene glycol 1000 succinate micelles (TP-PMs). The oral absorption mechanism and oral bioavailability were further investigated in vitro and in vivo.

Results

The cellular study showed that Val-PMs/Phe-PMs had a high PepT1 affinity, resulting in a higher drug uptake and transcellular transport than TP-PMs. In rats, Val-PMs/Phe-PMs exhibited higher intestinal accumulation in the apical side of the intestinal epithelium than TP-PMs, promoting drug diffusion across epithelial barrier. The oral bioavailability of Cur was significantly improved by Val-PMs/Phe-PMs, which was about 10.50- and 3.40-fold greater than that of Cur-Sol and TP-PMs, respectively.

Conclusion

PepT-1-mediated micelles, using PepT1 as a target on intestinal epithelium, have unique functions with intestine and prove promising for oral delivery of poorly water-soluble drugs.

Regulating the alky chain length of fatty acid-didanosine prodrugs and evaluating its role in albumin binding

Rational design of prodrugs for efficient albumin binding shows distinct advantages in drug delivery in terms of drug availability, systemic circulation, and potential targeting effect. And fatty acids are good candidates due to their high affinity to albumin. However, how the alkyl chain length of fatty acids affects the binding dynamics between prodrugs and albumin, despite its importance, is still unclear. In the present study, three prodrugs of didanosine (DDI) and fatty acids were designed and synthesized to evaluate the effect of the alkyl chain length on prodrug-albumin binding process, including capric acid-didanosine (CA-DDI), myristic acid-didanosine (MA-DDI), and stearic acid-didanosine (SA-DDI). The binding dynamics between these prodrugs with bovine serum albumin (BSA) were studied by fluorometry, circular dichroism (CD), UV analysis, and molecular docking. It turned out that DDI itself showed poor binding affinity to BSA. In contrast, CA-DDI, MA-DDI, and SA-DDI demonstrated significantly improved binding affinity. Interestingly, the binding affinity between DDI prodrugs and BSA was correlated with the alkyl chain length of fatty acids, and the binding constant significantly increased with the extension of alkyl chain length (K_CA-DDI = 5.86 × 103 M^-1, K_MA-DDI = 8.57 × 103 M^-1, and K_SA-DDI = 11.42 × 103 M^-1 at 298 K).

Effect of biphenyl hydrolase-like (BPHL) gene disruption on the intestinal stability, permeability and absorption of valacyclovir in wildtype and Bphl knockout mice

Biphenyl hydrolase-like protein (BPHL) is a novel human serine hydrolase that was originally cloned from a breast carcinoma cDNA library and shown to convert valacyclovir to acyclovir and valganciclovir to ganciclovir. However, the exclusivity of this process has not been determined and, indeed, it is possible that a number of esterases/proteases may mediate the hydrolysis of valacyclovir and similar prodrugs. The objectives of the present study were to evaluate the in situ intestinal permeability and stability of valacyclovir in wildtype (WT) and Bphl knockout (KO) mice, as well as the in vivo oral absorption and intravenous disposition of valacyclovir and acyclovir in the two mouse genotypes. We found that Bphl knockout mice had no obvious phenotype and that Bphl ablation did not alter the jejunal permeability of valacyclovir during in situ perfusions (i.e., 0.54 × 10^-4 in WT vs. 0.53 × 10^-4 cm/s in KO). Whereas no meaningful changes occurred between genotypes in the gene expression of proton-coupled oligopeptide transporters (i.e., PepT1, PepT2, PhT1, PhT2), enzymatic upregulation of Cyp3a11, Cyp3a16, Abhd14a and Abhd14b was observed in some tissues of Bphl knockout mice. Most importantly, we found that valacyclovir was rapidly and efficiently hydrolyzed to acyclovir in the absence of BPHL, and that hydrolysis was more extensive after the oral vs. intravenous route of administration (for both genotypes). Taken as a whole, BPHL is not obligatory for the conversion of valacyclovir to acyclovir either presystemically or systemically.

Cytosine arabinoside prodrug designed to bind plasma serum albumin for drug delivery

Rational design of anticancer prodrugs for efficient albumin binding can show distinct advantages in drug delivery in terms of high drug availability, long systemic circulation, potential targeting effect, and enhanced chemotherapy effect. In the present study, we reported a cytosine arabinoside (Ara-C) prodrug which could well formulate in solution and instantly transform into long-circulating nanocomplexes by hitchhiking blood-circulating albumin after i.v. administration. Specifically, Ara-C was conjugated with an albumin-binding maleimide derivative, the resulting Ara-C maleimide caproic acid conjugate (AM) was well formulated in aqueous solution, conferring high albumin-binding ability in vitro albumin-binding studies. Moreover, in vivo fluorescence images of sulfo-cyanine5 maleimide indirectly demonstrated that AM showed better accumulation in tumors, exhibiting superior tumor targeting ability and antitumor activity compared to Ara-C. Such a uniquely developed strategy, integrating high albumin-binding capability, has great potential to be applied in clinical cancer therapy.

Intestinal absorption and activation of decitabine amino acid ester prodrugs mediated by peptide transporter PEPT1 and enterocyte enzymes

Decitabine (DAC), a potent DNA methyltransferase (DNMT) inhibitor, has a limited oral bioavailability. Its 5'-amino acid ester prodrugs could improve its oral delivery but the specific absorption mechanism is not yet fully understood. The aim of this present study was to investigate the in vivo absorption and activation mechanism of these prodrugs using in situ intestinal perfusion and pharmacokinetics studies in rats. Although PEPT1 transporter is pH dependent, there appeared to be no proton cotransport in the perfusion experiment with a preferable transport at pH 7.4 rather than pH 6.5. This suggested that the transport was mostly dependent on the dissociated state of the prodrugs and the proton gradient might play only a limited role. In pH 7.4 HEPES buffer, an increase in P_eff was observed for L-val-DAC, D-val-DAC, L-phe-DAC and L-trp-DAC (2.89-fold, 1.2-fold, 2.73-fold, and 1.90-fold, respectively), compared with the parent drug. When co-perfusing the prodrug with Glysar, a known substrate of PEPT1, the permeabilities of the prodrugs were significantly inhibited compared with the control. To further investigate the absorption of the prodrugs, L-val-DAC was selected and found to be concentration-dependent and saturable, suggesting a carrier-mediated process (intrinsic K_m: 7.80 ± 2.61 mM) along with passive transport. Determination of drug in intestinal homogenate after perfusion further confirmed that the metabolic activation mainly involved an intestinal first-pass effect. In a pharmacokinetic evaluation, the oral bioavailability of L-val-DAC, L-phe-DAC and L-trp-DAC were nearly 1.74-fold, 1.69-fold and 1.49-fold greater than that of DAC. The differences in membrane permeability and oral bioavailability might be due to the different stability in the intestinal lumen and the distinct PEPT1 affinity which is mainly caused by the stereochemistry, hydrophobicity and steric hindrance of the side chains. In summary, the detailed investigation of the absorption mechanism by in vivo intestinal perfusion and pharmacokinetic studies showed that the prodrugs of DAC exhibited excellent permeability and oral bioavailability, which might be attributed to a hybrid (partly PEPT1-mediated and partly passive) transport mode and a rapid activation process in enterocytes.