Overcoming Drug Resistance through the Development of Selective Inhibitors of UDP-Glucuronosyltransferase Enzymes

Drug resistance is a major cause of cancer-related mortality. Glucuronidation of drugs via elevation of UDP-glucuronosyltransferases (UGT1As) correlates with clinical resistance. The nine UGT1A family members have broad substrate specificities attributed to their variable N-terminal domains and share a common C-terminal domain. Development of UGT1As as pharmacological targets has been hampered by toxicity of pan-UGT inhibitors and by difficulty in isolating pure N-terminal domains or full-length proteins. Here, we developed a strategy to target selected UGT1As which exploited the biochemical tractability of the C-domain and its ability to allosterically communicate with the catalytic site. By combining NMR fragment screening with in vitro glucuronidation assays, we identified inhibitors selective for UGT1A4. Significantly, these compounds selectively restored sensitivity in resistant cancer cells only for substrates of the targeted UGT1A. This strategy represents a crucial first step toward developing compounds to overcome unwanted glucuronidation thereby reversing resistance in patients.     

Pharmacogenetic testing: proofs of principle and pharmacoeconomic implications

Several proofs of principle have established that pharmacogenetic testing for mutations altering expression and functions of genes associated with drug disposition and response can decrease the "trial-and-error" dosing and reduce the risk of adverse drug reactions. These proofs of principle include thiopurine methyltransferase and thiopurine therapy, dihydropyrimidine dehydrogenase/thymidylate synthase and 5-fluorouracil therapy, folate enzyme MTHFR and methotrexate therapy, UGT1A1 and irinotecan therapy and CYP450 2C9 and S-warfarin therapy. These evidences advocate for the prospective identification of mutations associated with drug response, serious adverse reactions and treatment failure. More recent evidence with the HLA basis of hypersensitivity to the retroviral agent abacavir demonstrates the potential of pharmacogenetic testing and its pharmacoeconomic implications. With the convergence of rising drug costs and evidence supporting the clinical benefits of pharmacogenetic testing, it will be important to demonstrate the improved net health outcomes attributed to the additional costs for this testing.     

Genetic analysis of chemoresistance in primary murine lymphomas

Understanding the basis of chemoresistance is a principal goal of molecular oncology. We have exploited a murine lymphoma model and retroviral gene transfer to rapidly generate a series of spontaneous tumors differing only in a gene of interest, and subsequently studied the impact of the test gene on the treatment sensitivity of tumors at their natural site. We demonstrate that the Bcl-2 oncoprotein produces multi-drug resistance when assessed in primary lymphomas in vivo. In contrast, this effect was dramatically reduced when the primary lymphomas were subjected to long-term culture, and completely missed in the standard clonogenic survival assay. This model highlights the importance of physiological test systems to address the complexity of clinical drug resistance and provides a novel strategy to evaluate compounds targeting specific genetic lesions.     

Recent Efforts in Identification of Privileged Scaffolds as Antiviral Agents

Viral infections are the most important health concern nowadays to mankind, which is unexpectedly increasing the health complications and fatality rate worldwide. The recent viral infection outbreak developed a pressing need for small molecules that can be quickly deployed for the control/treatment of re-emerging or new emerging viral infections. Numerous viruses, including the human immunodeficiency virus (HIV), hepatitis, influenza, SARS-CoV-1, SARS-CoV-2, and others, are still challenging due to emerging resistance to known drugs. Therefore, there is always a need to search for new antiviral small molecules that can combat viral infection with new modes of action. This review highlighted recent progress in developing new antiviral molecules based on natural product-inspired scaffolds. Herein, the structure-activity relationship of the FDA-approved drugs along with the molecular docking studies of selected compounds have been discussed against several target proteins. The findings of new small molecules as neuraminidase inhibitors, other than known drug scaffolds, Anti-HIV and SARS-CoV are incorporated in this review paper.     

Evolution of a major drug metabolizing enzyme defect in the domestic cat and other felidae: phylogenetic timing and the role of hypercarnivory

The domestic cat (Felis catus) shows remarkable sensitivity to the adverse effects of phenolic drugs, including acetaminophen and aspirin, as well as structurally-related toxicants found in the diet and environment. This idiosyncrasy results from pseudogenization of the gene encoding UDP-glucuronosyltransferase (UGT) 1A6, the major species-conserved phenol detoxification enzyme. Here, we established the phylogenetic timing of disruptive UGT1A6 mutations and explored the hypothesis that gene inactivation in cats was enabled by minimal exposure to plant-derived toxicants. Fixation of the UGT1A6 pseudogene was estimated to have occurred between 35 and 11 million years ago with all extant Felidae having dysfunctional UGT1A6. Out of 22 additional taxa sampled, representative of most Carnivora families, only brown hyena (Parahyaena brunnea) and northern elephant seal (Mirounga angustirostris) showed inactivating UGT1A6 mutations. A comprehensive literature review of the natural diet of the sampled taxa indicated that all species with defective UGT1A6 were hypercarnivores (>70% dietary animal matter). Furthermore those species with UGT1A6 defects showed evidence for reduced amino acid constraint (increased dN/dS ratios approaching the neutral selection value of 1.0) as compared with species with intact UGT1A6. In contrast, there was no evidence for reduced amino acid constraint for these same species within UGT1A1, the gene encoding the enzyme responsible for detoxification of endogenously generated bilirubin. Our results provide the first evidence suggesting that diet may have played a permissive role in the devolution of a mammalian drug metabolizing enzyme. Further work is needed to establish whether these preliminary findings can be generalized to all Carnivora.     

Anti-Cancer Drugs Elicit Re-Expression of UDP-Glucuronosyltransferases in Melanoma Cells

The UDP-glucuronosyltransferase (UGT) family of enzymes plays a vital role in the detoxification of carcinogens as well as clearance of anti-cancer drugs. In humans, 19 UGT family members have been identified and are expressed in a tissue specific manner throughout the body. However, the UGTs have not been previously characterized in melanocytes or melanoma. In the present study, UGT2B7, UGT2B10, and UGT2B15 were identified as being normally expressed in human melanocytes. The same three UGT family members were also expressed in the primary melanoma cell line WM115. No UGT expression was detected in another primary melanoma cell line, WM3211, or in any metastatic melanoma cell line examined. These results suggest that UGT expression is lost during melanoma progression. Treatment of WM3211 or metastatic melanoma cell lines with anti-cancer agents (including vemurafenib) induced expression of UGT2B7, UGT2B10 and UGT2B15 demonstrating that melanoma cells retain the ability to re-express these same three UGTs. The corresponding increase in glucuronidation activity in melanoma cells following anti-cancer treatment was also observed. Furthermore, knockdown of UGT2B7 in WM115 cells sensitized these cells to treatment by adriamycin and epirubicin indicating that UGT2B7 is involved in resistance to these drugs. However, knockdown of UGT2B7 had no effect on temozolomide toxicity. Taken together, these results clearly demonstrate a role for UGTs in melanoma etiology. Since the UGTs are drug metabolism enzymes, we propose that re-expression of the UGTs constitutes a previously unsuspected mechanism for intratumoral drug resistance in melanoma.     

Identification of residues that confer sugar selectivity to UDP-glycosyltransferase 3A (UGT3A) enzymes

Recent studies in this laboratory characterized the UGT3A family enzymes, UGT3A1 and UGT3A2, and showed that neither uses the traditional UDP-glycosyltransferase UGT co-substrate UDP-glucuronic acid. Rather, UGT3A1 uses GlcNAc as preferred sugar donor and UGT3A2 uses UDP-Glc. The enzymatic characterization of UGT3A mutants, structural modeling, and multispecies gene analysis have now been employed to identify a residue within the active site of these enzymes that confers their unique sugar preferences. An asparagine (Asn-391) in the UGT signature sequence of UGT3A1 is necessary for utilization of UDP-GlcNAc. Conversely, a phenylalanine (Phe-391) in UGT3A2 favors UDP-Glc use. Mutation of Asn-391 to Phe in UGT3A1 enhances its ability to utilize UDP-Glc and completely inhibits its ability to use UDP-GlcNAc. An analysis of homology models docked with UDP-sugar donors indicates that Asn-391 in UGT3A1 is able to accommodate the N-acetyl group on C2 of UDP-GlcNAc so that the anomeric carbon atom (C1) is optimally situated for catalysis involving His-35. Replacement of Asn with Phe at position 391 disrupts this catalytically productive orientation of UDP-GlcNAc but allows a more optimal alignment of UDP-Glc for sugar donation. Multispecies sequence analysis reveals that only primates possess UGT3A sequences containing Asn-391, suggesting that other mammals may not have the capacity to N-acetylglucosaminidate small molecules. In support of this hypothesis, Asn-391-containing UGT3A forms from two non-human primates were found to use UDP-GlcNAc, whereas UGT3A isoforms from non-primates could not use this sugar donor. This work gives new insight into the residues that confer sugar specificity to UGT family members and suggests a primate-specific innovation in glycosidation of small molecules.     

Genetic diversity in cytokines associated with immune variation and resistance to multiple pathogens in a natural rodent population

Pathogens are believed to drive genetic diversity at host loci involved in immunity to infectious disease. To date, studies exploring the genetic basis of pathogen resistance in the wild have focussed almost exclusively on genes of the Major Histocompatibility Complex (MHC); the role of genetic variation elsewhere in the genome as a basis for variation in pathogen resistance has rarely been explored in natural populations. Cytokines are signalling molecules with a role in many immunological and physiological processes. Here we use a natural population of field voles (Microtus agrestis) to examine how genetic diversity at a suite of cytokine and other immune loci impacts the immune response phenotype and resistance to several endemic pathogen species. By using linear models to first control for a range of non-genetic factors, we demonstrate strong effects of genetic variation at cytokine loci both on host immunological parameters and on resistance to multiple pathogens. These effects were primarily localized to three cytokine genes (Interleukin 1 beta (Il1b), Il2, and Il12b), rather than to other cytokines tested, or to membrane-bound, non-cytokine immune loci. The observed genetic effects were as great as for other intrinsic factors such as sex and body weight. Our results demonstrate that genetic diversity at cytokine loci is a novel and important source of individual variation in immune function and pathogen resistance in natural populations. The products of these loci are therefore likely to affect interactions between pathogens and help determine survival and reproductive success in natural populations. Our study also highlights the utility of wild rodents as a model of ecological immunology, to better understand the causes and consequences of variation in immune function in natural populations including humans.     

Steering Evolution with Sequential Therapy to Prevent the Emergence of Bacterial Antibiotic Resistance

The increasing rate of antibiotic resistance and slowing discovery of novel antibiotic treatments presents a growing threat to public health. Here, we consider a simple model of evolution in asexually reproducing populations which considers adaptation as a biased random walk on a fitness landscape. This model associates the global properties of the fitness landscape with the algebraic properties of a Markov chain transition matrix and allows us to derive general results on the non-commutativity and irreversibility of natural selection as well as antibiotic cycling strategies. Using this formalism, we analyze 15 empirical fitness landscapes of E. coli under selection by different β-lactam antibiotics and demonstrate that the emergence of resistance to a given antibiotic can be either hindered or promoted by different sequences of drug application. Specifically, we demonstrate that the majority, approximately 70%, of sequential drug treatments with 2–4 drugs promote resistance to the final antibiotic. Further, we derive optimal drug application sequences with which we can probabilistically ‘steer’ the population through genotype space to avoid the emergence of resistance. This suggests a new strategy in the war against antibiotic–resistant organisms: drug sequencing to shepherd evolution through genotype space to states from which resistance cannot emerge and by which to maximize the chance of successful therapy.     

Early Sorafenib-Induced Toxicity Is Associated with Drug Exposure and UGTIA9 Genetic Polymorphism in Patients with Solid Tumors: A Preliminary Study

Background

Identifying predictive biomarkers of drug response is of key importance to improve therapy management and drug selection in cancer therapy. To date, the influence of drug exposure and pharmacogenetic variants on sorafenib-induced toxicity remains poorly documented. The aim of this pharmacokinetic/pharmacodynamic (PK/PD) study was to investigate the relationship between early toxicity and drug exposure or pharmacogenetic variants in unselected adult outpatients treated with single-agent sorafenib for advanced solid tumors.

Methods

Toxicity was recorded in 54 patients on days 15 and 30 after treatment initiation and sorafenib exposure was assessed in 51 patients. The influence of polymorphisms in CYP3A5, UGT1A9, ABCB1 and ABCG2 was examined in relation to sorafenib exposure and toxicity. Clinical characteristics, drug exposure and pharmacogenetic variants were tested univariately for association with toxicities. Candidate variables with p<0.1 were analyzed in a multivariate analysis.

Results

Gender was the sole parameter independently associated with sorafenib exposure (p = 0.0008). Multivariate analysis showed that increased cumulated sorafenib (AUC_cum) was independently associated with any grade ≥3 toxicity (p = 0.037); UGT1A9 polymorphism (rs17868320) with grade ≥2 diarrhea (p = 0.015) and female gender with grade ≥2 hand-foot skin reaction (p = 0.018). Using ROC curve, the threshold AUC_cum value of 3,161 mg/L.h was associated with the highest risk to develop any grade ≥3 toxicity (p = 0.018).

Conclusion

In this preliminary study, increased cumulated drug exposure and UGT1A9 polymorphism (rs17868320) identified patients at high risk for early sorafenib-induced severe toxicity. Further PK/PD studies on larger population are warranted to confirm these preliminary results.     

Label-enhanced surface plasmon resonance applied to label-free interaction analysis of small molecules and fragments

Surface plasmon resonance (SPR) is a well-established method for studying interactions between small molecules and biomolecules. In particular, SPR is being increasingly applied within fragment-based drug discovery; however, within this application area, the limited sensitivity of SPR may constitute a problem. This problem can be circumvented by the use of label-enhanced SPR that shows a 100-fold higher sensitivity as compared with conventional SPR. Truly label-free interaction data for small molecules can be obtained by applying label-enhanced SPR in a surface competition assay format. The enhanced sensitivity is accompanied by an increased specificity and inertness toward disturbances (e.g., bulk refractive index disturbances). Label-enhanced SPR can be used for fragment screening in a competitive assay format; the competitive format has the added advantage of confirming the specificity of the molecular interaction. In addition, label-enhanced SPR extends the accessible kinetic regime of SPR to the analysis of very fast fragment binding kinetics. In this article, we demonstrate the working principles and benchmark the performance of label-enhanced SPR in a model system—the interaction between carbonic anhydrase II and a number of small-molecule sulfonamide-based inhibitors.     

The Arabidopsis glucosyltransferase UGT76B1 conjugates isoleucic acid and modulates plant defense and senescence

Plants coordinate and tightly regulate pathogen defense by the mostly antagonistic salicylate (SA)- and jasmonate (JA)-mediated signaling pathways. Here, we show that the previously uncharacterized glucosyltransferase UGT76B1 is a novel player in this SA-JA signaling crosstalk. UGT76B1 was selected as the top stress-induced isoform among all 122 members of the Arabidopsis thaliana UGT family. Loss of UGT76B1 function leads to enhanced resistance to the biotrophic pathogen Pseudomonas syringae and accelerated senescence but increased susceptibility toward necrotrophic Alternaria brassicicola. This is accompanied by constitutively elevated SA levels and SA-related marker gene expression, whereas JA-dependent markers are repressed. Conversely, UGT76B1 overexpression has the opposite effect. Thus, UGT76B1 attenuates SA-dependent plant defense in the absence of infection, promotes the JA response, and delays senescence. The ugt76b1 phenotypes were SA dependent, whereas UGT76B1 overexpression indicated that this gene possibly also has a direct effect on the JA pathway. Nontargeted metabolomic analysis of UGT76B1 knockout and overexpression lines using ultra-high-resolution mass spectrometry and activity assays with the recombinant enzyme led to the ab initio identification of isoleucic acid (2-hydroxy-3-methyl-pentanoic acid) as a substrate of UGT76B1. Exogenously applied isoleucic acid increased resistance against P. syringae infection. These findings indicate a novel link between amino acid-related molecules and plant defense that is mediated by small-molecule glucosylation.     

Three most common nonsynonymous UGT1A6*2 polymorphisms (Thr181Ala,Arg184Serand Ser7Ala) and therapeutic response to deferiprone in β-thalassemia major patients

Deferiprone is used as a chelation agent in chronic iron overload in β-thalassemia patients. Patients on deferiprone therapy show variable response to this drug in terms of reduction in iron overload as well as adverse drug reactions (ADRs). The pharmacogenetic studies on deferiprone have not carried out in patients with blood disorders in India. Therefore, the present study was carried out to evaluate the three most common nonsynonymous UGT1A6 polymorphisms Thr181Ala (541 A/G), Arg184Ser (552 A/C) and Ser7Ala (19 T/G) and therapeutic response to deferiprone in β-thalassemia major patients. Two hundred and eighty six (286) β-thalassemia major patients were involved in the study. Serum ferritin levels were estimated periodically to assess the status of the iron overload and the patients were grouped into responders and non-responders depending on the ferritin levels. The UGT1A6*2 polymorphisms were detected by PCR-RFLP methods. The association between the genotypes and outcome as well as ADRs was evaluated by Open EPI software. A significant difference was observed in the genotypic distribution of UGT1A6*2 Thr181Ala polymorphism in responders and non-responders. However, there was no difference in the genotypic distribution between patients with and without ADRs. As far as the UGT1A6*2 Arg184Ser polymorphism is concerned, no significant difference was observed between responders and non-responders. Further, evaluating the association of UGT1A6*2 Ser7Ala polymorphism with drug response, there was no significant difference in the genotypic distribution between responders and non-responders. However, there was a significant difference between responders with and without ADRs and non-responders with and without ADRs. In addition to this haplotype analysis was also carried out. However, we did not find any specific haplotype to be significantly associated with the deferiprone response in β-thalassemia major patients.     

Molecular Genetics External Quality Assessment Pilot Scheme for Irinotecan-Related UGT1A1 Genotyping in China

Irinotecan is widely used in the treatment of solid tumors, especially in colorectal cancer and lung cancer. Molecular testing for UGT1A1 genotyping is increasingly required in China for optimum irinotecan administration. In order to determine the performance of laboratories with regard to the whole testing process for UGT1A1 to ensure the consistency and accuracy of the test results, the National Center for Clinical Laboratories conducted an external quality assessment program for UGT1A1*28 genotyping in 2015. The panel, which comprised of four known mutational samples and six wild-type samples, was distributed to 45 laboratories that test for the presence of UGT1A1*28 polymorphisms. Participating laboratories were allowed to perform polymorphism analysis by using their routine methods. The accuracy of the genotyping and reporting of results was analyzed. Other information from the individual laboratories, including the number of samples tested each month, accreditation/certification status, and test methodology, was reviewed. Forty-four of the 45 participants reported the correct results for all samples. There was only one genotyping error, with a corresponding analytical sensitivity of 99.44% (179/180 challenges; 95% confidence interval: 96.94−99.99%) and an analytical specificity of 100% (270/270 challenges; 95% confidence interval: 98.64−100%). Both commercial kits and laboratory development tests were commonly used by the laboratories, and pyrosequencing was the main methodology used (n = 26, 57.8%). The style of the written reports showed large variation, and many reports showed a shortage of information. In summary, the first UGT1A1 genotyping external quality assessment result demonstrated that UGT1A1 genotype analysis of good quality was performed in the majority of pharmacogenetic testing centers that were investigated. However, greater education on the reporting of UGT1A1 genetic testing results is needed.     

Compensatory effects in the PI3K/PTEN/AKT signaling network following receptor tyrosine kinase inhibition

Overcoming de novo and acquired resistance to anticancer drugs that target signaling networks is a formidable challenge for drug design and effective cancer therapy. Understanding the mechanisms by which this resistance arises may offer a route to addressing the insensitivity of signaling networks to drug intervention and restore the efficacy of anticancer therapy. Extending our recent work identifying PTEN as a key regulator of Herceptin sensitivity, we present an integrated theoretical and experimental approach to study the compensatory mechanisms within the PI3K/PTEN/AKT signaling network that afford resistance to receptor tyrosine kinase (RTK) inhibition by anti-HER2 monoclonal antibodies. In a computational model representing the dynamics of the signaling network, we define a single control parameter that encapsulates the balance of activities of the enzymes involved in the PI3K/PTEN/AKT cycle. By varying this control parameter we are able to demonstrate both distinct dynamic regimes of behavior of the signaling network and the transitions between those regimes. We demonstrate resistance, sensitivity, and suppression of RTK signals by the signaling network. Through model analysis we link the sensitivity-to-resistance transition to specific compensatory mechanisms within the signaling network. We study this transition in detail theoretically by variation of activities of PTEN, PI3K, AKT enzymes, and use the results to inform experiments that perturb the signaling network using combinatorial inhibition of RTK, PTEN, and PI3K enzymes in human ovarian carcinoma cell lines. We find good alignment between theoretical predictions and experimental results. We discuss the application of the results to the challenges of hypersensitivity of the signaling network to RTK signals, suppression of drug resistance, and efficacy of drug combinations in anticancer therapy.     

UGT76B1, a promiscuous hub of small molecule-based immune signaling,glucosylates N-hydroxypipecolic acid,and balances plant immunity

Glucosylation modulates the biological activity of small molecules and frequently leads to their inactivation. The Arabidopsis thaliana glucosyltransferase UGT76B1 is involved in conjugating the stress hormone salicylic acid (SA) as well as isoleucic acid (ILA). Here, we show that UGT76B1 also glucosylates N-hydroxypipecolic acid (NHP), which is synthesized by FLAVIN-DEPENDENT MONOOXYGENASE 1 (FMO1) and activates systemic acquired resistance (SAR). Upon pathogen attack, Arabidopsis leaves generate two distinct NHP hexose conjugates, NHP-O-β-glucoside and NHP glucose ester, whereupon only NHP-O-β-glucoside formation requires a functional SA pathway. The ugt76b1 mutants specifically fail to generate the NHP-O-β-glucoside, and recombinant UGT76B1 synthesizes NHP-O-β-glucoside in vitro in competition with SA and ILA. The loss of UGT76B1 elevates the endogenous levels of NHP, SA, and ILA and establishes a constitutive SAR-like immune status. Introgression of the fmo1 mutant lacking NHP biosynthesis into the ugt76b1 background abolishes this SAR-like resistance. Moreover, overexpression of UGT76B1 in Arabidopsis shifts the NHP and SA pools toward O-β-glucoside formation and abrogates pathogen-induced SAR. Our results further indicate that NHP-triggered immunity is SA-dependent and relies on UGT76B1 as a common metabolic hub. Thereby, UGT76B1-mediated glucosylation controls the levels of active NHP, SA, and ILA in concert to balance the plant immune status.