A novel Bayesian generative approach for estimating tumor dynamics from published studies.

Tumor growth inhibition (TGI) modeling attempts to describe the time course changes in tumor size for patients undergoing cancer therapy. TGI models present several advantages over traditional exposure-response models that are based explicitly on clinical end points and have become a popular tool in the pharmacometrics community. Unfortunately, the data required to fit TGI models, namely longitudinal tumor measurements, are sparse or often not available in literature or publicly accessible databases. On the contrary, common end points such as progression-free survival (PFS) and objective response rate (ORR) are directly derived from longitudinal tumor measurements and are routinely published. To this end, a Bayesian generative model relating underlying tumor dynamics to summary PFS and ORR data is introduced to learn TGI model parameters using only published summary data. The parameterized model can describe the tumor dynamics, quantify treatment effect, and account for differences in the study population. The utility of this model is shown by applying it to several published studies, and learned parameters are combined to simulate an in silico trial of a novel combination therapy in a novel setting.

Xaluritamig, a STEAP1 × CD3 XmAb 2+1 Immune Therapy for Metastatic Castration-Resistant Prostate Cancer: Results from Dose Exploration in a First-in-Human Study.

Xaluritamig (AMG 509) is a six-transmembrane epithelial antigen of the prostate 1 (STEAP1)-targeted T-cell engager designed to facilitate lysis of STEAP1-expressing cancer cells, such as those in advanced prostate cancer. This first-in-human study reports monotherapy dose exploration for patients with metastatic castration-resistant prostate cancer (mCRPC), primarily taxane pretreated. Ninety-seven patients received ≥1 intravenous dose ranging from 0.001 to 2.0 mg weekly or every 2 weeks. MTD was identified as 1.5 mg i.v. weekly via a 3-step dose. The most common treatment-related adverse events were cytokine release syndrome (CRS; 72%), fatigue (45%), and myalgia (34%). CRS occurred primarily during cycle 1 and improved with premedication and step dosing. Prostate-specific antigen (PSA) and RECIST responses across cohorts were encouraging [49% PSA50; 24% objective response rate (ORR)], with greater frequency at target doses ≥0.75 mg (59% PSA50; 41% ORR). Xaluritamig is a novel immunotherapy for prostate cancer that has shown encouraging results supporting further development. SIGNIFICANCE: Xaluritamig demonstrated encouraging responses (PSA and RECIST) compared with historical established treatments for patients with late-line mCRPC. This study provides proof of concept for T-cell engagers as a potential treatment for prostate cancer, validates STEAP1 as a target, and supports further clinical investigation of xaluritamig in prostate cancer. See related commentary by Hage Chehade et al., p. 20. See related article by Nolan-Stevaux et al., p. 90. This article is featured in Selected Articles from This Issue, p. 5.

A Mechanistic Physiologically-Based Pharmacokinetic Platform Model to Guide Adult and Pediatric Intravenous and Subcutaneous Dosing for Bispecific T Cell Engagers.

Bispecific T cell engagers (Bi-TCEs) have revolutionized the treatment of oncology indications across both liquid and solid tumors. Bi-TCEs are rapidly evolving from conventional intravenous (i.v.) to more convenient subcutaneous (s.c.) administrations and extending beyond adults to also benefit pediatric patients. Leveraging clinical development experience across three generations of Bi-TCE molecules across both liquid and solid tumor indications from i.v./s.c. dosing in adults and pediatric subjects, we developed a mechanistic-physiologically-based pharmacokinetic (PBPK) platform model for Bi-TCEs. The model utilizes a full PBPK model framework and was successfully validated for PK predictions following i.v. and s.c. dosing across both liquid and solid tumor space in adults for eight Bi-TCEs. After refinement to incorporate physiological ontogeny, the model was successfully validated to predict pediatric PKs in 1 month - < 2 years, 2-11 years, and 12-17 years old subjects following i.v. dosing. Following s.c. dosing in pediatric subjects, the model predicted similar bioavailability, however, a shorter time to maximum concentration (Tmax ) for the three age groups compared with adults. The model was also applied to guide the dosing strategy for first generation of Bi-TCEs for organ impairment, specifically renal impairment, and was able to accurately predict the impact of renal impairment on PK for these relatively small-size Bi-TCEs. This work highlights a novel mechanistic platform model for accurately predicting the PK in adult and pediatric patients across liquid and solid tumor indications from i.v./s.c. dosing and can be used to guide optimal dose and dosing regimen selection and accelerating the clinical development for Bi-TCEs.

Characterizing the exposure-response relationship of idecabtagene vicleucel in patients with relapsed/refractory multiple myeloma.

Idecabtagene vicleucel (ide-cel; bb2121) is a B-cell maturation antigen-directed chimeric antigen receptor (CAR) T cell therapy approved for treatment of patients with heavily pretreated relapsed and refractory multiple myeloma. This analysis evaluated exposure-response (ER) relationships of ide-cel with key efficacy end points and safety events. Ide-cel exposure data were available from 127 patients treated at target doses of 150, 300, or 450 × 106 CAR+ T cells from the phase II KarMMa study (NCT03361748). Key exposure metrics, including area under the curve of the transgene level from 0 to 28 days and maximum transgene level, were calculated using noncompartmental methods. Logistic regression models, using both linear and maximum response function of exposure on the logit scale, were evaluated to quantify observed ER trends, and modified by including statistically significant individual covariates in a stepwise regression analysis. There was wide overlap of exposures across the target doses. ER relationships were observed for the overall and complete response rates, with higher response rates associated with higher exposures. Model-based evaluations identified female sex and baseline serum monoclonal protein less than or equal to 10 g/L as predictive of a higher objective response rate and a higher complete response rate, respectively. ER relationships were observed for safety events of cytokine release syndrome requiring tocilizumab or corticosteroids. The established ER models were used to quantify the ide-cel dose-response, which showed a positive benefit-risk assessment for the range of ide-cel exposures associated with the target dose range of 150-450 × 106 CAR+ T cells.

CC-99677, a novel, oral, selective covalent MK2 inhibitor, sustainably reduces pro-inflammatory cytokine production.

BACKGROUND: Mitogen-activated protein kinase (MAPK)-activated protein kinase-2 (MK2) is activated downstream of p38 MAPK and regulates stability of mRNAs encoding inflammatory cytokines. CC-99677 is a novel, irreversible, covalent MK2 inhibitor under development for the treatment of ankylosing spondylitis (AS) and other inflammatory diseases. As part of a phase I clinical trial to assess safety and tolerability, we evaluated target engagement, pharmacokinetics, and pharmacodynamics of CC-99677. METHODS: The MK2 inhibitor CC-99677 was evaluated for its effect on cytokine expression in vitro in peripheral blood mononuclear cells (PBMCs) from healthy donors and patients with a definitive AS diagnosis. A novel in vitro model was developed to compare the potential for tachyphylaxis of CC-99677 and p38 inhibitors in THP-1 cells. The effect of CC-99677 on tristetraprolin (TTP) and cytokine mRNA was assessed in stimulated human monocyte-derived macrophages. In a first-in-human study, thirty-seven healthy volunteers were randomly assigned to daily oral doses of CC-99677 or placebo, and blood was collected at pre-specified time points before and after dosing. CC-99677 concentrations were assessed in the plasma, and CC-99677 binding to MK2 was evaluated in PBMCs. Ex vivo stimulation of the whole blood was conducted from participants in the first-in-human study to assess the pharmacodynamic effects. RESULTS: In vitro, CC-99677 inhibited tumor necrosis factor (TNF), interleukin (IL)-6, and IL-17 protein production in samples of monocytes and macrophages from AS patients and healthy volunteers via an mRNA-destabilization mechanism. In the in vitro model of tachyphylaxis, CC-99677 showed a differentiated pattern of sustained TNF protein inhibition compared with p38 inhibitors. CC-99677 reduced TTP phosphorylation and accelerated the decay of inflammatory cytokine mRNA in lipopolysaccharide-stimulated macrophages. Administration of CC-99677 to healthy volunteers was safe and well-tolerated, with linear pharmacokinetics and sustained reduction of ex vivo whole blood TNF, IL-6, and chemokine synthesis. CONCLUSIONS: CC-99677 inhibition of MK2 is a promising approach for the treatment of inflammatory diseases and may overcome the limitations of p38 MAPK inhibition. TRIAL REGISTRATION: ClinicalTrials.gov NCT03554993 .

Discovery of CC-99677, a selective targeted covalent MAPKAPK2 (MK2) inhibitor for autoimmune disorders.

As an anti-inflammatory strategy, MAPK-activated protein kinase-2 (MK2) inhibition can potentially avoid the clinical failures seen for direct p38 inhibitors, especially tachyphylaxis. CC-99677, a selective targeted covalent MK2 inhibitor, employs a rare chloropyrimidine that bonds to the sulfur of cysteine 140 in the ATP binding site via a nucleophilic aromatic substitutions (SNAr) mechanism. This irreversible mechanism translates biochemical potency to cells shown by potent inhibition of heat shock protein 27 (HSP27) phosphorylation in LPS-activated monocytic THP-1 cells. The cytokine inhibitory profile of CC-99677 differentiates it from known p38 inhibitors, potentially suppressing a p38 pathway inflammatory response while avoiding tachyphylaxis. Dosed orally, CC-99677 is efficacious in a rat model of ankylosing spondylitis. Single doses, 3 to 400 mg, in healthy human volunteers show linear pharmacokinetics and apparent sustained tumor necrosis factor-α inhibition, with a favorable safety profile. These results support further development of CC-99677 for autoimmune diseases like ankylosing spondylitis.

Idecabtagene Vicleucel in Relapsed and Refractory Multiple Myeloma.

BACKGROUND: Idecabtagene vicleucel (ide-cel, also called bb2121), a B-cell maturation antigen-directed chimeric antigen receptor (CAR) T-cell therapy, has shown clinical activity with expected CAR T-cell toxic effects in patients with relapsed and refractory multiple myeloma. METHODS: In this phase 2 study, we sought to confirm the efficacy and safety of ide-cel in patients with relapsed and refractory myeloma. Patients with disease after at least three previous regimens including a proteasome inhibitor, an immunomodulatory agent, and an anti-CD38 antibody were enrolled. Patients received ide-cel target doses of 150 × 106 to 450 × 106 CAR-positive (CAR+) T cells. The primary end point was an overall response (partial response or better); a key secondary end point was a complete response or better (comprising complete and stringent complete responses). RESULTS: Of 140 patients enrolled, 128 received ide-cel. At a median follow-up of 13.3 months, 94 of 128 patients (73%) had a response, and 42 of 128 (33%) had a complete response or better. Minimal residual disease (MRD)-negative status (<10-5 nucleated cells) was confirmed in 33 patients, representing 26% of all 128 patients who were treated and 79% of the 42 patients who had a complete response or better. The median progression-free survival was 8.8 months (95% confidence interval, 5.6 to 11.6). Common toxic effects among the 128 treated patients included neutropenia in 117 patients (91%), anemia in 89 (70%), and thrombocytopenia in 81 (63%). Cytokine release syndrome was reported in 107 patients (84%), including 7 (5%) who had events of grade 3 or higher. Neurotoxic effects developed in 23 patients (18%) and were of grade 3 in 4 patients (3%); no neurotoxic effects higher than grade 3 occurred. Cellular kinetic analysis confirmed CAR+ T cells in 29 of 49 patients (59%) at 6 months and 4 of 11 patients (36%) at 12 months after infusion. CONCLUSIONS: Ide-cel induced responses in a majority of heavily pretreated patients with refractory and relapsed myeloma; MRD-negative status was achieved in 26% of treated patients. Almost all patients had grade 3 or 4 toxic effects, most commonly hematologic toxic effects and cytokine release syndrome. (Funded by bluebird bio and Celgene, a Bristol-Myers Squibb company; KarMMa ClinicalTrials.gov number, NCT03361748.).

Phase Ib Study of the Histone Deacetylase 6 Inhibitor Citarinostat in Combination With Paclitaxel in Patients With Advanced Solid Tumors.

BACKGROUND: Citarinostat (CC-96241; previously ACY-241), an oral inhibitor of histone deacetylases (HDACs) with selectivity for HDAC6, has demonstrated synergistic anticancer activity with paclitaxel in multiple solid tumor models. Combination therapy using citarinostat with paclitaxel was evaluated in this phase Ib 3 + 3 dose-escalation study in patients with advanced solid tumors. METHODS: Patients with previously treated advanced solid tumors received citarinostat 180, 360, or 480 mg once daily on days 1 to 21 plus paclitaxel 80 mg/m2 on days 1, 8, and 15 of 28-day cycles until disease progression or unacceptable toxicity. The primary endpoint was determination of the maximum tolerated dose (MTD). Secondary endpoints included safety, antitumor activity, pharmacokinetics, and pharmacodynamics. RESULTS: Twenty patients were enrolled and received study treatment; 15 had received prior taxane therapy. No dose-limiting toxicities were reported at any dose; therefore, the MTD was not identified. Citarinostat 360 vs 480 mg was associated with reduced incidence and severity of neutropenia. Three patients experienced a confirmed partial response and 13 achieved stable disease. Pharmacokinetic parameters were linear up to citarinostat 360 mg, the dose at which the highest levels of histone and tubulin acetylation were observed in peripheral blood mononuclear cells. CONCLUSIONS: The combination of citarinostat plus paclitaxel showed an acceptable safety profile, with no unexpected or dose-limiting toxicities and potential evidence of antitumor activity in patients with heavily pretreated advanced solid tumors. Citarinostat 360 mg once daily is considered the recommended phase II dose for use in combination with paclitaxel 80 mg/m2 every 3 of 4 weeks. This trial is registered on ClinicalTrials.gov (NCT02551185).

Modeling and simulation of the endogenous CYP3A induction marker 4ß-hydroxycholesterol during enasidenib treatment.

BACKGROUND: Enasidenib (IDHIFA®, AG-221) is a first-in-class, targeted inhibitor of mutant IDH2 proteins for treatment of relapsed or refractory acute myeloid leukemia. This was a Phase I/II study evaluating safety, efficacy, and pharmacokinetics/pharmacodynamics (PK/PD) of orally administered enasidenib in subjects with advanced hematologic malignancies with an IDH2 mutation. METHODS: Blood samples for PK and PD assessment were collected. A semi-mechanistic nonlinear mixed effect PK/PD model was successfully developed to characterize enasidenib plasma PK and to assess enasidenib-induced CYP3A activity. RESULTS: The PK model showed that enasidenib plasma concentrations were adequately described by a one-compartment model with first-order absorption and elimination; the PD model showed a high capacity to induce CYP3A (Emax=7.36) and a high enasidenib plasma concentration to produce half of maximum CYP3A induction (EC50 =31,400 ng/mL). Monte Carlo simulations based on the final PK/PD model showed that at 100 mg once daily dose there was significant drug accumulation and a maximum of three-fold CYP3A induction after multiple doses. Although the EC50 value for CYP3A induction by enasidenib is high, CYP3A induction was observed due to significant drug accumulation. CONCLUSION: CYP3A induction following enasidenib dosing should be considered when prescribing concomitant medication metabolized via this pathway.

Sotatercept Safety and Effects on Hemoglobin, Bone, and Vascular Calcification.

INTRODUCTION: Patients with end-stage kidney disease (ESKD) exhibit anemia, chronic kidney disease‒mineral bone disorder (CKD-MBD), and cardiovascular disease. The REN-001 and REN-002 phase II, multicenter, randomized studies examined safety, tolerability, and effects of sotatercept, an ActRIIA-IgG1 fusion protein trap, on hemoglobin concentration; REN-001 also explored effects on bone mineral density (BMD) and abdominal aortic vascular calcification. METHODS: Forty-three patients were treated in REN-001 (dose range: sotatercept 0.3‒0.7 mg/kg or placebo subcutaneously [s.c.] for 200 days) and 50 in REN-002 (dose range: 0.1‒0.4 mg/kg i.v. and 0.13‒0.5 mg/kg s.c. for 99 days). RESULTS: In REN-001, frequency of achieving target hemoglobin response (>10 g/dl [6.21 mmol/l]) with sotatercept was dose-related and greater than placebo (0.3 mg/kg: 33.3%; 0.5 mg/kg: 62.5%; 0.7 mg/kg: 77.8%; 0.7 mg/kg [doses 1 and 2]/0.4 mg/kg [doses 3‒15]: 33.3%; placebo: 27.3%). REN-002 hemoglobin findings were similar (i.v.: 16.7%-57.1%; s.c.: 11.1%‒42.9%). Dose-related achievement of ≥2% increase in femoral neck cortical BMD was seen among only REN-001 patients receiving sotatercept (0.3‒0.7 mg/kg: 20.0%‒57.1%; placebo: 0.0%). Abdominal aortic vascular calcification was slowed in a dose-related manner, with a ≤15% increase in Agatston score achieved by more REN-001 sotatercept versus placebo patients (60%‒100% vs. 16.7%). The most common adverse events during treatment were hypertension, muscle spasm, headache, arteriovenous fistula site complication, and influenza observed in both treatment and placebo groups. CONCLUSION: In patients with ESKD, sotatercept exhibited a favorable safety profile and was associated with trends in dose-related slowing of vascular calcification. Less-consistent trends in improved hemoglobin concentration and BMD were observed.

Population Pharmacokinetics of Lenalidomide in Healthy Volunteers and Patients With Hematologic Malignancies.

A population pharmacokinetic (PopPK) model of lenalidomide was developed using data pooled from 13 clinical studies (dose range, 5-400 mg) in participants who were considered to have adequate capability for renal excretion of lenalidomide (creatinine clearance [CrCl] > 50 mL/min). The analysis population included 305 healthy volunteers and 83 patients with multiple myeloma or myelodysplastic syndromes. A 1-compartment model with linear absorption and elimination described well the observed data for both healthy volunteers and patients. Covariate analysis suggested lenalidomide apparent clearance was positively correlated with CrCl, and lenalidomide volume of distribution was positively correlated with body weight. Both pharmacokinetic parameters were reduced by 29% in patients, independent of the effect of CrCl or body weight. Despite their statistical significance, effects of study population and body weight are considered clinically unimportant in adult patients with CrCl > 50 mL. After accounting for the above effects, body weight had no significant effect on CL/F, whereas age, sex, race, and mild hepatic impairment had no significant effect on either lenalidomide parameter. The PopPK model should be useful for future modeling of lenalidomide pharmacokinetics in the pediatric population and for further comparison of pharmacokinetic properties among structurally similar immunomodulatory drugs.

Pharmacokinetics and Pharmacogenomics of Bupropion in Three Different Formulations with Different Release Kinetics in Healthy Human Volunteers.

The purpose of this pharmacokinetics (PK) study was to investigate whether different release kinetics from bupropion hydrochloride (HCl) immediate release (IR), sustained release (SR), and extended release (ER) formulations alter its metabolism and to test the hypothesis that the unsuccessful bioequivalence (BE) study of the higher strength (300 mg) of bupropion HCl ER tablets based on the successful BE study of the lower strength (150 mg) was due to metabolic saturation in the gastrointestinal (GI) lumen. A randomized six-way crossover study was conducted in healthy volunteers. During each period, subjects took a single dose of IR (75/100 mg), SR (100/150 mg), or ER (150/300 mg) formulations of bupropion HCl; plasma samples for PK analysis were collected from 0-96 h for all formulations. In addition, each subject's whole blood was collected for the genotyping of various single-nucleotide polymorphisms (SNPs) of bupropion's major metabolic enzymes. The data indicates that the relative bioavailability of the ER formulations was 72.3-78.8% compared with IR 75 mg. No differences were observed for ratio of the area under the curve (AUC) of metabolite to AUC of parent for the three major metabolites. The pharmacogenomics analysis suggested no statistically significant correlation between polymorphisms and PK parameters of the various formulations. Altogether, these data suggested that the different release kinetics of the formulations did not change metabolites-to-parent ratio. Therefore, the differing BE result between the 150 and 300 mg bupropion HCl ER tablets was unlikely due to the metabolic saturation in the GI lumen caused by different release patterns.

Identification of non-reported bupropion metabolites in human plasma.

Bupropion and its three active metabolites exhibit clinical efficacy in the treatment of major depression, seasonal depression and smoking cessation. The pharmacokinetics of bupropion in humans is highly variable. It is not known if there are any non-reported metabolites formed in humans in addition to the three known active metabolites. This paper reports newly identified and non-reported metabolites of bupropion in human plasma samples. Human subjects were dosed with a single oral dose of 75 mg of an immediate release bupropion HCl tablet. Plasma samples were collected and analysed by LC-MS/MS at 0, 6 and 24 h. Two non-reported metabolites (M1 and M3) were identified with mass-to-charge (m/z) ratios of 276 (M1, hydration of bupropion) and 258 (M3, hydroxylation of threo/erythrohydrobupropion) from human plasma in addition to the known hydroxybupropion, threo/erythrohydrobupropion and the glucuronidation products of the major metabolites (M2 and M4-M7). These new metabolites may provide new insight and broaden the understanding of bupropion's variability in clinical pharmacokinetics. © 2016 The Authors Biopharmaceutics & Drug Disposition Published by John Wiley & Sons Ltd.

Novel cancer stem cell targets during epithelial to mesenchymal transition in PTEN-deficient trastuzumab-resistant breast cancer.

Continued use of trastuzumab in PTEN-deficient HER2+ breast cancer induces the epithelial-to-mesenchymal transition (EMT), transforms HER2+ to triple negative breast cancer, and expands breast cancer stem cells (BCSCs). Using cancer cell lines with two distinct states, epithelial and mesenchymal, we identified novel targets during EMT in PTEN-deficient trastuzumab-resistant breast cancer. Differential gene expression and distinct responses to a small molecule in BT474 (HER2+ trastuzumab-sensitive) and the PTEN-deficient trastuzumab-resistant derivative (BT474-PTEN-LTT) provided the selection tools to identify targets during EMT. siRNA knockdown and small molecule inhibition confirmed MEOX1 as one of the critical molecular targets to regulate both BCSCs and mesenchymal-like cell proliferation. MEOX1 was associated with poor survival, lymph node metastasis, and stage of breast cancer patients. These findings suggest that MEOX1 is a clinically relevant novel target in BCSCs and mesenchymal-like cancer cells in PTEN-deficient trastuzumab resistant breast cancer and may serve as target for future drug development.

Trastuzumab resistance induces EMT to transform HER2(+) PTEN(-) to a triple negative breast cancer that requires unique treatment options.

Although trastuzumab is an effective treatment in early stage HER2(+) breast cancer the majority of advanced HER2(+) breast cancers develop trastuzumab resistance, especially in the 40% of breast cancers with loss of PTEN. However, HER2(+) breast cancer patients continue to receive trastuzumab regardless PTEN status and the consequence of therapy in these patients is unknown. We demonstrate that continued use of trastuzumab in HER2(+) cells with loss of PTEN induces the epithelial-mesenchymal transition (EMT) and transform HER2(+) to a triple negative breast cancer. These transformed cells exhibited mesenchymal morphology and gene expression markers, while parent HER2(+) cells showed epithelial morphology and markers. The transformed cells exhibited loss of dependence on ERBB family signaling (such as HER2, HER3, HER4, BTC, HRG, EGF) and reduced estrogen and progesterone receptors. Continued use of trastuzumab in HER2(+) PTEN(-) cells increased the frequency of cancer stem cells (CSCs) and metastasis potential. Strikingly, parental HER2(+) cells and transformed resistant cells respond to treatment differently. Transformed resistant cells were sensitive to chemical probe (sulforaphane) through inhibition of IL-6/STAT3/NF-κB positive feedback loop whereas parental HER2(+) cells did not respond. This data suggests that trastuzumab resistance in HER2(+) PTEN- breast cancer induces EMT and subtype switching, which requires unique treatment options.

Metabolism of bupropion by carbonyl reductases in liver and intestine.

Bupropion's metabolism and the formation of hydroxybupropion in the liver by cytochrome P450 2B6 (CYP2B6) has been extensively studied; however, the metabolism and formation of erythro/threohydrobupropion in the liver and intestine by carbonyl reductases (CR) has not been well characterized. The purpose of this investigation was to compare the relative contribution of the two metabolism pathways of bupropion (by CYP2B6 and CR) in the subcellular fractions of liver and intestine and to identify the CRs responsible for erythro/threohydrobupropion formation in the liver and the intestine. The results showed that the liver microsome generated the highest amount of hydroxybupropion (Vmax = 131 pmol/min per milligram, Km = 87 µM). In addition, liver microsome and S9 fractions formed similar levels of threohydrobupropion by CR (Vmax = 98-99 pmol/min per milligram and Km = 186-265 µM). Interestingly, the liver has similar capability to form hydroxybupropion (by CYP2B6) and threohydrobupropion (by CR). In contrast, none of the intestinal fractions generate hydroxybupropion, suggesting that the intestine does not have CYP2B6 available for metabolism of bupropion. However, intestinal S9 fraction formed threohydrobupropion to the extent of 25% of the amount of threohydrobupropion formed by liver S9 fraction. Enzyme inhibition and Western blots identified that 11ß-dehydrogenase isozyme 1 in the liver microsome fraction is mainly responsible for the formation of threohydrobupropion, and in the intestine AKR7 may be responsible for the same metabolite formation. These quantitative comparisons of bupropion metabolism by CR in the liver and intestine may provide new insight into its efficacy and side effects with respect to these metabolites.

The molecular chaperone Hsp70 activates protein phosphatase 5 (PP5) by binding the tetratricopeptide repeat (TPR) domain.

Protein phosphatase 5 (PP5) is auto-inhibited by intramolecular interactions with its tetratricopeptide repeat (TPR) domain. Hsp90 has been shown to bind PP5 to activate its phosphatase activity. However, the functional implications of binding Hsp70 to PP5 are not yet clear. In this study, we find that both Hsp90 and Hsp70 bind to PP5 using a luciferase fragment complementation assay. A fluorescence polarization assay shows that Hsp90 (MEEVD motif) binds to the TPR domain of PP5 almost 3-fold higher affinity than Hsp70 (IEEVD motif). However, Hsp70 binding to PP5 stimulates higher phosphatase activity of PP5 than the binding of Hsp90. We find that PP5 forms a stable 1:1 complex with Hsp70, but the interaction appears asymmetric with Hsp90, with one PP5 binding the dimer. Solution NMR studies reveal that Hsc70 and PP5 proteins are dynamically independent in complex, tethered by a disordered region that connects the Hsc70 core and the IEEVD-TPR contact area. This tethered binding is expected to allow PP5 to carry out multi-site dephosphorylation of Hsp70-bound clients with a range of sizes and shapes. Together, these results demonstrate that Hsp70 recruits PP5 and activates its phosphatase activity which suggests dual roles for PP5 that might link chaperone systems with signaling pathways in cancer and development.

Analogs of the Allosteric Heat Shock Protein 70 (Hsp70) Inhibitor, MKT-077, as Anti-Cancer Agents.

The rhodacyanine, MKT-077, has anti-proliferative activity against cancer cell lines through its ability to inhibit members of the heat shock protein 70 (Hsp70) family of molecular chaperones. However, MKT-077 is rapidly metabolized, which limits its use as either a chemical probe or potential therapeutic. We report the synthesis and characterization of MKT-077 analogs designed for greater stability. The most potent molecules, such as 30 (JG-98), were at least 3-fold more active than MKT-077 against the breast cancer cell lines MDA-MB-231 and MCF-7 (EC50 values of 0.4 ± 0.03 µM and 0.7 ± 0.2 µM, respectively). The analogs modestly destabilized the chaperone "clients", Akt1 and Raf1, and induced apoptosis in these cells. Further, the microsomal half-life of JG-98 was improved at least 7-fold (t1/2 = 37 min) compared to MKT-077 (t1/2 < 5 min). Finally, NMR titration experiments suggested that these analogs bind an allosteric site that is known to accommodate MKT-077. These studies advance MKT-077 analogs as chemical probes for studying Hsp70's roles in cancer.