Tirzepatide Immunogenicity on Pharmacokinetics, Efficacy, and Safety: Analysis of Data From Phase 3 Studies.

CONTEXT: Antidrug antibodies (ADA) can potentially affect drug pharmacokinetics, safety, and efficacy. OBJECTIVE: This work aimed to evaluate treatment-emergent (TE) ADA in tirzepatide (TZP)-treated participants across 7 phase 3 trials and their potential effect on pharmacokinetics, efficacy, and safety. METHODS: ADA were assessed at baseline and throughout the study until end point, defined as week 40 (SURPASS-1, -2, and -5) or week 52 (SURPASS-3, -4, Japan-Mono, and Japan-Combo). Samples for ADA characterization were collected at SURPASS trial sites. Participants included ADA-evaluable TZP-treated patients with type 2 diabetes (N = 5025). Interventions included TZP 5, 10, or 15 mg. ADA were detected and characterized for their ability to cross-react with native glucose-dependent insulinotropic polypeptide (nGIP) and glucagon-like peptide-1 (nGLP-1), neutralize tirzepatide activity on GIP and GLP-1 receptors, and neutralize nGIP and nGLP-1. RESULTS: TE ADA developed in 51.1% of tirzepatide-treated patients. Proportions were similar across dose groups. Maximum ADA titers ranged from 1:20 to 1: 81 920 among TE ADA+ patients. Neutralizing antibodies (NAb) against TZP activity on GIP and GLP-1 receptors were observed in 1.9% and 2.1% of patients, respectively. Less than 1.0% of patients had cross-reactive NAb against nGIP or nGLP-1. TE ADA status, ADA titer, and NAb status had no effect on the pharmacokinetics or efficacy of TZP. More TE ADA+ patients experienced hypersensitivity reactions or injection site reactions than TE ADA- patients. The majority of hypersensitivity and injection site reactions were nonserious and nonsevere, and most events occurred and/or resolved irrespective of TE ADA status or titer. CONCLUSION: Immunogenicity did not affect TZP pharmacokinetics or efficacy. The majority of hypersensitivity or injection site reactions experienced by TE ADA+ patients were mild to moderate in severity.

A systematic examination of anti-drug antibody titer estimation: Applied recommendations.

Biologic drugs (therapeutic proteins or peptides) have become one of the most important therapeutic modalities over the past few decades. Drug-induced immunogenicity is a significant concern as it may affect safety, tolerability, and efficacy. With more sensitive and drug-tolerant screening assays in use today, reliable estimation of anti-drug-antibody (ADA) titer has become more important for understanding clinically relevant ADA levels. Titer is commonly defined as the dilution factor resulting in an assay signal equal to a pre-specified cut point factor. Given its influence on the resulting titer precision, the choice of a titer cut point factor warrants careful consideration. In this paper, we discuss the theoretical dilution model, investigate how titer variability depends on the cut point factor and propose a standardized cut point factor to increase precision of titer estimates. Additionally, we demonstrate that non-linear regression-based titer estimation provides both improved precision and implementation efficiency relative to commonly used estimation approaches.

Anti-drug Antibody Sample Testing and Reporting Harmonization.

A clear scientific and operational need exists for harmonized bioanalytical immunogenicity study reporting to facilitate communication of immunogenicity findings and expedient review by industry and health authorities. To address these key bioanalytical reporting gaps and provide a report structure for documenting immunogenicity results, this cross-industry group was formed to establish harmonized recommendations and a develop a submission template to facilitate agency filings. Provided here are recommendations for reporting clinical anti-drug antibody (ADA) assay results using ligand-binding assay technologies. This publication describes the essential bioanalytical report (BAR) elements such as the method, critical reagents and equipment, study samples, results, and data analysis, and provides a template for a suggested structure for the ADA BAR. This publication focuses on the content and presentation of the bioanalytical ADA sample analysis report. The interpretation of immunogenicity data, including the evaluation of the impact of ADA on safety, exposure, and efficacy, is out of scope of this publication.

Architecture of the two metal-binding sites in prolactin.

Metal binding by members of the growth hormone (GH) family of hematopoietic cytokines has been a subject of considerable interest. However, beyond appreciation of its role in reversible packing of GH proteins in secretory granules, the molecular mechanisms of metal binding and granule formation remain poorly understood. Here, we investigate metal binding by a GH family member prolactin (PRL) using paramagnetic metal titration and chelation experiments. Cu2+-mediated paramagnetic relaxation enhancement measurements identified two partial metal-binding sites on the opposite faces of PRL composed of residues H30/H180 and E93/H97, respectively. Coordination of metal ions by these two sites causes formation of inter-molecular bridges between the PRL protomers and enables formation of reversible higher aggregates. These findings in vitro suggest a model for reversible packaging of PRL in secretory granules. The proposed mechanism of metal-promoted PRL aggregation lends insight and support to the previously suggested role of metal coordination in secretory granule formation by GH proteins.

Anti-drug Antibody Validation Testing and Reporting Harmonization.

Evolving immunogenicity assay performance expectations and a lack of harmonized anti-drug antibody validation testing and reporting tools have resulted in significant time spent by health authorities and sponsors on resolving filing queries. Following debate at the American Association of Pharmaceutical Sciences National Biotechnology Conference, a group was formed to address these gaps. Over the last 3 years, 44 members from 29 organizations (including 5 members from Europe and 10 members from FDA) discussed gaps in understanding immunogenicity assay requirements and have developed harmonization tools for use by industry scientists to facilitate filings to health authorities. Herein, this team provides testing and reporting strategies and tools for the following assessments: (1) pre-study validation cut point; (2) in-study cut points, including procedures for applying cut points to mixed populations; (3) system suitability control criteria for in-study plate acceptance; (4) assay sensitivity, including the selection of an appropriate low positive control; (5) specificity, including drug and target tolerance; (6) sample stability that reflects sample storage and handling conditions; (7) assay selectivity to matrix components, including hemolytic, lipemic, and disease state matrices; (8) domain specificity for multi-domain therapeutics; (9) and minimum required dilution and extraction-based sample processing for titer reporting.

Novel methodology comparing two assay formats for the assessment of immunogenicity from clinical trial samples.

Aim: We present a novel methodology to compare results between distinct immunogenicity assays, performed by two laboratories, for the same biotherapeutic. Materials & methods: Human serum pools from clinical trials were generated to provide representative immunogenicity titers. Pools were evaluated at two laboratories in a blinded fashion to assess the effect of assay format and laboratory change on clinical interpretation of immunogenicity results. Results: The laboratories validated two different assay formats and demonstrated comparable sensitivity and drug tolerance. Overall, the comparisons in assay format and laboratory ensured a comparable ability to detect treatment-emergent antidrug antibodies for a biotherapeutic. Conclusion: We have established an approach, using pooling of patient samples, that allows for the interlaboratory comparisons without creating duplicative results.

Lay abstract Measuring immunogenicity, an immune response to a drug, is important in understanding the benefits and risks associated with a drug. Immunogenicity is measured by specific tests within a laboratory; however, these tests and laboratories may change over time. This paper proposes a method to determine if a change in test and laboratory will impact the interpretation of immunogenicity for a drug. Blood samples from clinical trial patients were combined in order to provide representative samples for the immunogenicity tests. The samples were tested at two laboratories with two tests to measure if any interpretation of immunogenicity results would change due to the different tests and laboratories. Laboratories and tests demonstrated similar and reliable results of the samples. This study has established a method which allows for the comparison of immunogenicity results when tests and/or laboratories are changed.

The method history report: an adaptable tool for communicating immunogenicity assay development and validation.

Over the developmental lifetime of a therapeutic protein, the immunogenicity assay validation history can become substantial, frustrating review of clinical immunogenicity within the biologics license application. In our experience, this can lead to questions by regulators, resulting in numerous information requests during the review process. To address this, we propose a new document, the method history report (MHR), which can comprehensively present the history of the immunogenicity assay for regulators, including assay development and validation. The flexibility of the MHR allows for adaptation to the specific needs of each therapeutic program, while maintaining a consistent template. Here, we detail the rationale, general outline and template for the MHR and recommend others consider adopting it for their biologics license application-related activities.

Development and validation of a novel immunogenicity assay to detect anti-drug and anti-PEG antibodies simultaneously with high sensitivity.

Polyethylene glycol (PEG) represents an effective strategy to improve the pharmacokinetic profile of a molecule as it extends the biotherapeutic's half-life, masks immunogenic epitopes or modifies its distribution. The addition of one or multiple PEG moieties, in either linear or branched form, is known to carry the risk of potentially inducing an immunogenic response against PEG. The importance of accurately quantifying anti-PEG antibodies during a clinical study is well recognized and stems from the fact that anti-PEG antibodies have been shown to negatively impact the efficacy of the biotherapeutic that the PEG is coupled to. As a consequence, sponsors are encouraged to develop immunogenicity assays to assess appropriately the presence of anti-drug antibodies (ADA) against the protein component as well as the PEG. However, detection of anti-PEG antibodies is complicated by a number of technical challenges, including the availability of appropriate positive control material. In addition, the fact that some anti-PEG antibodies are known to circulate as low-affinity IgM, drives the need for an assay able to detect low affinity anti-PEG ADA even in the presence of high concentrations of the biotherapeutic. To address this need, we developed and validated an Affinity Capture Elution (ACE)-AGL assay to detect anti-drug and anti-PEG antibodies. In this assay, which we call ACE-AGL, ADA are captured by biotin-PEG-drug, acid eluted and re-captured on a second plate coated with protein AGL. ADA are then detected using Ruthenium-PEG-drug. The new assay format described is highly sensitive to both anti-drug and anti-PEG antibodies and very drug-tolerant. The ACE-AGL assay is easy to perform and has been successfully validated at two separate CROs. We propose the ACE-AGL format as a valid and effective alternative to the currently available assay methods.

High-Throughput Screening of a Functional Human CXCL12-CXCR4 Signaling Axis in a Genetically Modified S. cerevisiae: Discovery of a Novel Up-Regulator of CXCR4 Activity.

CXCL12 activates CXCR4 and is involved in embryogenesis, hematopoiesis, and angiogenesis. It has pathological roles in HIV-1, WHIM disease, cancer, and autoimmune diseases. An antagonist, AMD3100, is used for the release of CD34+ hematopoietic stem cells from the bone marrow for autologous transplantation for lymphoma or multiple myeloma patients. Adverse effects are tolerated due to its short-term treatment, but AMD3100 is cardiotoxic in clinical studies for HIV-1. In an effort to determine whether Saccharomyces cerevisiae expressing a functional human CXCR4 could be used as a platform for identifying a ligand from a library of less ∼1,000 compounds, a high-throughput screening was developed. We report that 2-carboxyphenyl phosphate (fosfosal) up-regulates CXCR4 activation only in the presence of CXCL12. This is the first identification of a compound that increases CXCR4 activity by any mechanism. We mapped the fosfosal binding site on CXCL12, described its mechanism of action, and studied its chemical components, salicylate and phosphate, to conclude that they synergize to achieve the functional effect.

Assessment of immunogenicity from galcanezumab phase 3 trials in patients with episodic or chronic migraine.

BACKGROUND: This analysis characterizes the immunogenicity profile of galcanezumab, a humanized monoclonal antibody that selectively binds calcitonin gene-related peptide and inhibits its activity, in phase 3 migraine trials. METHODS: Immunogenicity data were analyzed from baseline and double-blind, placebo-controlled phases of the 3-month chronic migraine study REGAIN, the 6-month episodic migraine studies EVOLVE-1 and EVOLVE-2, and from baseline and open-label phases of the 12-month chronic and episodic migraine Study CGAJ. The incidence of baseline antidrug antibodies, treatment-emergent antidrug antibodies, neutralizing antidrug antibodies, and the effect of antidrug antibody titer on pharmacokinetics and pharmacodynamics were assessed. The relationship between antidrug antibody status and efficacy was explored using average change in monthly migraine headache days. Safety analyses assessed the potential relationship between treatment-emergent antidrug antibodies and hypersensitivity events or adverse events related to injection sites. FINDINGS: Across studies, 5.9-11.2% of patients had baseline antidrug antibodies. The incidence of treatment-emergent antidrug antibodies was 2.6-12.4% in the galcanezumab group and 0.5-1.7% in the placebo group. The majority of treatment-emergent antidrug antibodies were detected approximately 3-6 months after first study drug dose. Overall, the observed antidrug antibody titer did not impact galcanezumab concentrations, calcitonin gene-related peptide concentrations, or galcanezumab efficacy. There was no evidence that hypersensitivity events or adverse events related to injection sites were mediated by treatment-emergent antidrug antibodies. INTERPRETATION: These data showed that immunogenicity did not impact galcanezumab concentrations, calcitonin gene-related peptide concentrations, or the efficacy and hypersensitivity profile of galcanezumab in patients with migraine.

Investigation of pre-existing reactivity to biotherapeutics can uncover potential immunogenic epitopes and predict immunogenicity risk.

Despite recent advances in the development of tools to predict immunogenicity risk of biotherapeutic molecules, the ability of a protein to elicit the formation of anti-drug antibodies (ADA) remains one of the most common causes for termination of clinical development programs. In this study, we use ADA assays to detect and measure pre-existing reactivity or the ability of a molecule to produce an ADA-like response in serum from treatment-naïve, healthy donors. We report herein that the magnitude of pre-existing reactivity evaluated pre-clinically and expressed as the 90th percentile of Tier 2 inhibition correlates with the subsequent rate of ADA emergence in the clinic. Furthermore, a multi-domain biotherapeutic (IgG-scFv bispecific antibody) showed the highest pre-existing reactivity and incidence of treatment-emergent ADA (TE-ADA) (57% and 93%, respectively). Using the components of the multidomain molecule in the Tier 2 step of the ADA assay, we were able to identify the scFv as the target of the serum pre-existing reactivity. Most importantly, the domain specificity of pre-existing ADA was the same as that of the TE-ADA from patients treated with the molecule. Based on these data, we propose the evaluation of the magnitude and of the domain specificity of pre-existing reactivity as a powerful tool to understand the immunogenic potential of novel biotherapeutics.

Safety of galcanezumab in patients with episodic migraine: A randomized placebo-controlled dose-ranging Phase 2b study.

Background Safety findings from a Phase 2b study of galcanezumab, a humanized monoclonal antibody against calcitonin gene-related peptide, for prevention of migraine (NCT02163993) are reported here. Methods Patients aged 18-65 years with episodic migraine were evaluated in this multicenter, double-blind, randomized study. After randomization, 410 patients were administered 5, 50, 120 or 300 mg of galcanezumab or placebo subcutaneously once every 4 weeks for 12 weeks, followed by a post-treatment off-drug period lasting 12 weeks. Results Treatment-emergent adverse events (TEAEs) were primarily rated as mild to moderate. Serious adverse events reported in galcanezumab dose groups were appendicitis, Crohn's disease, suicidal ideation, and congenital ankyloglossia in an infant of a paternal pregnancy; each of these were reported by one patient. Adverse events leading to discontinuation with galcanezumab treatment were abdominal pain, visual impairment, and upper limb fracture, each reported by one patient. Treatment-emergent injection-site reactions were reported significantly more frequently ( p = 0.013) with galcanezumab (13.9%) than with placebo (5.8%). Injection-site pain was the most common injection-site reaction (galcanezumab 11.4%; placebo 2.9%, p = 0.004). Upper respiratory tract infection (galcanezumab 10.0%; placebo 8.8%) and nasopharyngitis (galcanezumab 7.0%; placebo 2.2%) also occurred more frequently with galcanezumab treatment. Potential hypersensitivity events were reported at similar frequencies in galcanezumab (3.3%) and placebo (5.1%) groups. Incidence of treatment-emergent anti-drug antibodies in galcanezumab dose groups (4.6% of patients during treatment period) did not appear to have any meaningful effects on safety, the pharmacokinetics of galcanezumab, or its ability to bind to the target ligand. Conclusion The results from this 3-month Phase 2b study support the initiation of larger Phase 3 trials of longer duration.

Conformational dynamics of Ca2+-dependent responses in the polycystin-2 C-terminal tail.

PC2 (polycystin-2) forms a Ca(2+)-permeable channel in the cell membrane and its function is regulated by cytosolic Ca(2+) levels. Mutations in the C-terminal tail of human PC2 (HPC2 Cterm) lead to autosomal dominant polycystic kidney disease. The HPC2 Cterm protein contains a Ca(2+)-binding site responsible for channel gating and function. To provide the foundation for understanding how Ca(2+) regulates the channel through the HPC2 Cterm, we characterized Ca(2+) binding and its conformational and dynamic responses within the HPC2 Cterm. By examining hydrogen-deuterium (H-D) exchange profiles, we show that part of the coiled-coil domain in the HPC2 Cterm forms a stable helix bundle regardless of the presence of Ca(2+). The HPC2 L1EF construct contains the Ca(2+)-binding EF-hand and the N-terminal linker 1 region without the downstream coiled coil. We show that the linker stabilizes the Ca(2+)-bound conformation of the EF-hand, thus enhancing its Ca(2+)-binding affinity to the same level as the HPC2 Cterm. In comparison, the coiled coil is not required for the high-affinity binding. By comparing the conformational dynamics of the HPC2 Cterm and HPC2 L1EF with saturating Ca(2+), we show that the HPC2 Cterm and HPC2 L1EF share a similar increase in structural stability upon Ca(2+) binding. Nevertheless, they have different profiles of H-D exchange under non-saturating Ca(2+) conditions, implying their different conformational exchange between the Ca(2+)-bound and -unbound states. The present study, for the first time, provides a complete map of dynamic responses to Ca(2+)-binding within the full-length HPC2 Cterm. Our results suggest mechanisms for functional regulation of the PC2 channel and PC2's roles in the pathophysiology of polycystic kidney disease.

Oligomerization of the polycystin-2 C-terminal tail and effects on its Ca2+-binding properties.

Polycystin-2 (PC2) belongs to the transient receptor potential (TRP) family and forms a Ca(2+)-regulated channel. The C-terminal cytoplasmic tail of human PC2 (HPC2 Cterm) is important for PC2 channel assembly and regulation. In this study, we characterized the oligomeric states and Ca(2+)-binding profiles in the C-terminal tail using biophysical approaches. Specifically, we determined that HPC2 Cterm forms a trimer in solution with and without Ca(2+) bound, although TRP channels are believed to be tetramers. We found that there is only one Ca(2+)-binding site in the HPC2 Cterm, located within its EF-hand domain. However, the Ca(2+) binding affinity of the HPC2 Cterm trimer is greatly enhanced relative to the intrinsic binding affinity of the isolated EF-hand domain. We also employed the sea urchin PC2 (SUPC2) as a model for biophysical and structural characterization. The sea urchin C-terminal construct (SUPC2 Ccore) also forms trimers in solution, independent of Ca(2+) binding. In contrast to the human PC2, the SUPC2 Ccore contains two cooperative Ca(2+)-binding sites within its EF-hand domain. Consequently, trimerization does not further improve the affinity of Ca(2+) binding in the SUPC2 Ccore relative to the isolated EF-hand domain. Using NMR, we localized the Ca(2+)-binding sites in the SUPC2 Ccore and characterized the conformational changes in its EF-hand domain due to trimer formation. Our study provides a structural basis for understanding the Ca(2+)-dependent regulation of the PC2 channel by its cytosolic C-terminal domain. The improved methodology also serves as a good strategy to characterize other Ca(2+)-binding proteins.

Specific and nonspecific interactions in ultraweak protein-protein associations revealed by solvent paramagnetic relaxation enhancements.

Weak and transient protein-protein interactions underlie numerous biological processes. However, the location of the interaction sites of the specific complexes and the effect of transient, nonspecific protein-protein interactions often remain elusive. We have investigated the weak self-association of human growth hormone (hGH, KD = 0.90 ± 0.03 mM) at neutral pH by the paramagnetic relaxation enhancement (PRE) of the amide protons induced by the soluble paramagnetic relaxation agent, gadodiamide (Gd(DTPA-BMA)). Primarily, it was found that the PREs are in agreement with the general Hwang-Freed model for relaxation by translational diffusion (J. Chem. Phys. 1975, 63, 4017-4025), only if crowding effects on the diffusion in the protein solution are taken into account. Second, by measuring the PREs of the amide protons at increasing hGH concentrations and a constant concentration of the relaxation agent, it is shown that a distinction can be made between residues that are affected only by transient, nonspecific protein-protein interactions and residues that are involved in specific protein-protein associations. Thus, the PREs of the former residues increase linearly with the hGH concentration in the entire concentration range because of a reduction of the diffusion caused by the transient, nonspecific protein-protein interactions, while the PREs of the latter residues increase only at the lower hGH concentrations but decrease at the higher concentrations because of specific protein-protein associations that impede the access of gadodiamide to the residues of the interaction surface. Finally, it is found that the ultraweak aggregation of hGH involves several interaction sites that are located in patches covering a large part of the protein surface.

The number and location of EF hand motifs dictates the calcium dependence of polycystin-2 function.

Polycystin 2 (PC2) is a calcium-dependent calcium channel, and mutations to human PC2 (hPC2) are associated with polycystic kidney disease. The C-terminal tail of hPC2 contains 2 EF hand motifs, but only the second binds calcium. Here, we investigate whether these EF hand motifs serve as a calcium sensor responsible for the calcium dependence of PC2 function. Using NMR and bioinformatics, we show that the overall fold is highly conserved, but in evolutionarily earlier species, both EF hands bind calcium. To test whether the EF hand motif is truly a calcium sensor controlling PC2 channel function, we altered the number of calcium binding sites in hPC2. NMR studies confirmed that modified hPC2 binds an additional calcium ion. Single-channel recordings demonstrated a leftward shift in the calcium dependence, and imaging studies in cells showed that calcium transients were enhanced compared with wild-type hPC2. However, biophysics and functional studies showed that the first EF hand can only bind calcium and be functionally active if the second (native) calcium-binding EF hand is intact. These results suggest that the number and location of calcium-binding sites in the EF hand senses the concentration of calcium required for PC2 channel activity and cellular function.

An explicit formulation approach for the analysis of calcium binding to EF-hand proteins using isothermal titration calorimetry.

We present an improved and extended version of a recently proposed mathematical approach for modeling isotherms of ligand-to-macromolecule binding from isothermal titration calorimetry. Our approach uses ordinary differential equations, solved implicitly and numerically as initial value problems, to provide a quantitative description of the fraction bound of each competing member of a complex mixture of macromolecules from the basis of general binding polynomials. This approach greatly simplifies the formulation of complex binding models. In addition to our generalized, model-free approach, we have introduced a mathematical treatment for the case where ligand is present before the onset of the titration, essential for data analysis when complete removal of the binding partner may disrupt the structural and functional characteristics of the macromolecule. Demonstration programs playable on a freely available software platform are provided. Our method is experimentally validated with classic calcium (Ca(2+)) ion-selective potentiometry and isotherms of Ca(2+) binding to a mixture of chelators with and without residual ligand present in the reaction vessel. Finally, we simulate and compare experimental data fits for the binding isotherms of Ca(2+) binding to its canonical binding site (EF-hand domain) of polycystin 2, a Ca(2+)-dependent channel with relevance to polycystic kidney disease.

Rapid detection of carbapenemase activity through monitoring ertapenem hydrolysis in Enterobacteriaceae with LC-MS/MS.

BACKGROUND: Bacteria are increasingly resistant to antibiotics used to treat life-threatening infections in critically ill patients. The carbapenems represent the last line of defense against Gram-negative rods that are increasingly resistant to all other classes of ß-lactam antibiotics used to treat life-threatening infections in critically ill patients. Carbapenem resistance in Gram-negative rods is most commonly caused by expression of carbapenemases, enzymes that hydrolyze the ß-lactam ring of carbapenem antibiotics rendering them inactive. All of the available diagnostic tests rely on bacterial growth rendering them time consuming; therefore, rapid diagnostic tests are needed to identify multidrug (including carbapenem)-resistant bacteria. RESULTS: We report the development of a novel LC-MS/MS method that detects carbapenemase activity from bacterial isolates. Incubation of a bacterial suspension with physiological levels of ertapenem leads to carbapenemase-mediated drug hydrolysis that produces a specific metabolite with an 18 Da increase in m/z within 1 h. Using the ratio of metabolite:parent, detected by LC-MS/MS from the culture, the sensitivity, specificity and a threshold cutoff for carbapenemase production (interpretive criteria) have been determined. CONCLUSION: A 100% correlation of our LC-MS/MS assay with the modified Hodge test (functional test for carbapenemase production) and PCR emphasizes the robust nature of this assay. The assay requires minimal hands-on time and a straightforward protocol allowing convenient implementation into clinical laboratories. Inclusion of stable isotope-labeled standard will further increase the robustness of the assay. This assay offers several advantages over other similar assays that use MALDI-TOF MS analysis.

In silico investigation of pH-dependence of prolactin and human growth hormone binding to human prolactin receptor.

Experimental data shows that the binding of human prolactin (hPRL) to human prolactin receptor (hPRLr-ECD) is strongly pH-dependent, while the binding of the same receptor to human growth hormone (hGH) is pH-independent. Here we carry in silico analysis of the molecular effects causing such a difference and reveal the role of individual amino acids. It is shown that the computational modeling correctly predicts experimentally determined pKa's of histidine residues in an unbound state in the majority of the cases and the pH-dependence of the binding free energy. Structural analysis carried in conjunction with calculated pH-dependence of the binding revealed that the main reason for pH-dependence of the binding of hPRL-hPRLr-ECD is a number of salt- bridges across the interface of the complex, while no salt-bridges are formed in the hGH-hPRlr-ECD. Specifically, most of the salt-bridges involve histidine residues and this is the reason for the pH-dependence across a physiological range of pH. The analysis not only revealed the molecular mechanism of the pH-dependence of the hPRL-hPRLr-ECD, but also provided critical insight into the underlying physic-chemical mechanism.

Inhibition of paclitaxel-induced decreases in calcium signaling.

Peripheral neuropathy is one of the most severe and irreversible side effects caused by treatment from several chemotherapeutic drugs, including paclitaxel (Taxol®) and vincristine. Strategies are needed that inhibit this unwanted side effect without altering the chemotherapeutic action of these drugs. We previously identified two proteins in the cellular pathway that lead to Taxol-induced peripheral neuropathy, neuronal calcium sensor-1 (NCS-1) and calpain. Prolonged treatment with Taxol induces activation of calpain, degradation of NCS-1, and loss of intracellular calcium signaling. This paper has focused on understanding the molecular basis for prevention of peripheral neuropathy by testing the effects of addition of two candidate compounds to the existing chemotherapeutic drug regime: lithium and ibudilast. We found that the co-administration of either lithium or ibudilast to neuroblastoma cells that were treated with Taxol or vincristine inhibited activation of calpain and the reductions in NCS-1 levels and calcium signaling associated with these chemotherapeutic drugs. The ability of Taxol to alter microtubule formation was unchanged by the addition of either candidate compound. These results allow us to suggest that it is possible to prevent the unnecessary and irreversible damage caused by chemotherapeutic drugs while still maintaining therapeutic efficacy. Specifically, the addition of either lithium or ibudilast to existing chemotherapy treatment protocols has the potential to prevent chemotherapy-induced peripheral neuropathy.