Quantitative assessment of minimal effective concentration of erythropoiesis-stimulating agents

The Influence of Precursor Depletion and dose Regimens on Resistance to Erythropoiesis-Stimulating Agents: Insights from Simulations with Instantaneous Dose-Adaptation Algorithm

Erythropoiesis-stimulating agents (ESAs) have been a common treatment for anemia associated with chronic kidney disease (CKD), while 10-20 % of patients continue to suffer from persistent anemia despite receiving ESA treatments. Our previous findings suggested that intensive ESA usage can cause resistance by depleting the erythroid precursor cells. Here, we used a mechanism-based pharmacokinetic/pharmacodynamic (PK/PD) model of ESAs and conducted simulations to evaluate the influence of dose regimens and other factors (such as administration route, individual PK/PD parameters, types of ESAs, and disease status) on ESA resistance with instantaneous dose adaptations in healthy populations and anemic patients. The simulated results show that instantaneous dose-adaptation can reduce ESA resistance, but up to 30 % of subjects still ended up developing ESA resistance in healthy populations. The Smax is markedly higher in hypo-responders than in normal-responders, while hypo-responders possess fewer precursors and experience a faster decline compared to normal-responders. There is a ceiling effect of increasing ESA dosage to improve HGB responses and reduce ESA resistance, and the limit is lower in anemic patients compared to healthy populations. Subcutaneous administrations and ESAs with longer half-lives lead to stronger HGB responses and less resistance at equivalent doses. Taken together, this study indicates that precursor depletion contributes to ESA resistance and dose regimens can greatly influence the occurrence of ESA resistance. Furthermore, ESA treatment for patients showing ESA resistance should avoid continuously increasing doses and instead consider stimulating the renewal of precursors.

Dynamics of Erythroferrone Response to Erythropoietin in Rats

Background: Erythroferrone (ERFE) is a hormone identified recently as a master regulator connecting iron homeostasis and erythropoiesis. Serum ERFE concentrations significantly increase in animals and humans with normal or impaired kidney function after receiving exogenous erythropoiesis-stimulating agents (ESAs), which suggests it might be a predictive factor for erythropoiesis. To evaluate whether ERFE is an early, sensitive biomarker for long-term erythropoietic effects of ESAs, we investigated the relationship between ERFE dynamics and time courses of major erythropoietic responses to ESA treatment. Methods: Healthy rats received single dose and multiple doses (thrice a week for 2 weeks) of recombinant human erythropoietin (rHuEPO) at three dose levels (100, 450, and 1350 IU/kg) intravenously. The rHuEPO and ERFE concentrations in plasma were determined at a series of time points after dosing. Erythropoietic effects including red blood cell count and hemoglobin concentrations were continuously monitored for 24 days (single dose) or 60 days (multiple doses). The expansion of erythroblasts in bone marrow was quantified by flow cytometry analysis. Results: ERFE significantly increased within a few hours and return to baseline at 24 h after rHuEPO treatment. The ERFE response was enhanced after repeated treatment, which was consistent with the observed expansion of erythroblasts in the bone marrow. In addition, the dynamics of ERFE showed double peaks at approximately 2 and 10 h after rHuEPO stimulation, and the ERFE baseline displayed a significant circadian rhythm. There was a strong positive correlation between peak values of short-term ERFE responses and the long-term hemoglobin responses. Conclusion: The stimulated release of ERFE is a rapid process within 24 h. The second peak in the ERFE response to rHuEPO suggests the presence of a feedback mechanism counterregulating the ESA stimulation. The early increase of ERFE at 2 h appears to be a predictor of the hemoglobin response at 14 days after single dose of rHuEPO. Under multiple-dose regimen, the enhanced ERFE responses still correlate with the peak hemoglobin responses. The ERFE baseline also exhibits a circadian rhythm.

Proof-of-concept study on improved efficacy of rHuEPO administered as a long-term infusion in rats

Background

Human recombinant erythropoietin (rHuEPO) is often used in the treatment of diseases associated with a decreased production of red blood cells (RBC), such as chronic renal failure. rHuEPO is typically administered as an intravenous or subcutaneous (SC) injection every few days. The low minimum effective concentration (MEC) of rHuEPO, compared to the concentrations observed after standard doses, suggests that a low dose of the drug administered as a long-term infusion should be efficacious. This study aimed to compare the efficacy observed after a single subcutaneous administration of rHuEPO with that observed after a long-term infusion of rHuEPO via implanted osmotic pumps at a similar or lower dose.

Materials and methods

In this study three rats received rHuEPO as a single SC injection at a dose of 1350 IU/kg, nine via osmotic pumps at a rate of 0.25, 0.5 and 1 IU/kg and at a total dose of 333 IU/kg, 667 IU/kg, 1333 IU/kg. Three rats served as a control group. The erythropoietin concentrations, RBC count and hemoglobin were measured.

Results

An increase in RBC count and hemoglobin was observed after SC infusion of rHuEPO. The baseline corrected area under the effect curve for hemoglobin and RBC count was more than 10-times higher for the SC infusion than for a single SC administration with a comparable dose.

Conclusions

This study demonstrates that administration of rHuEPO as a long-term infusion at a rate ensuring MEC allows to achieve a high efficacy of therapy using relatively small doses of the drug.

Application of Pharmacokinetic-Pharmacodynamic Modeling in Drug Delivery: Development and Challenges

With the advancement of technology, drug delivery systems and molecules with more complex architecture are developed. As a result, the drug absorption and disposition processes after administration of these drug delivery systems and engineered molecules become exceedingly complex. As the pharmacokinetic and pharmacodynamic (PK-PD) modeling allows for the separation of the drug-, carrier- and pharmacological system-specific parameters, it has been widely used to improve understanding of the in vivo behavior of these complex delivery systems and help their development. In this review, we summarized the basic PK-PD modeling theory in drug delivery and demonstrated how it had been applied to help the development of new delivery systems and modified large molecules. The linkage between PK and PD was highlighted. In particular, we exemplified the application of PK-PD modeling in the development of extended-release formulations, liposomal drugs, modified proteins, and antibody-drug conjugates. Furthermore, the model-based simulation using primary PD models for direct and indirect PD responses was conducted to explain the assertion of hypothetical minimal effective concentration or threshold in the exposure-response relationship of many drugs and its misconception. The limitations and challenges of the mechanism-based PK-PD model were also discussed.

Pharmacodynamic and Pharmacokinetic Equivalences of Epoetin Hospira and Epogen(®) After Multiple Subcutaneous Doses to Healthy Male Subjects

PURPOSE

The purpose of this study was to evaluate the pharmacodynamic (PD) and pharmacokinetic (PK) equivalences of multiple doses of the proposed biosimilar Epoetin Hospira to the reference product Epogen(⁎), when each is administered three times per week over 28 days to healthy male subjects

METHODS

This single center, open-label, randomized, parallel group study was conducted in 129 healthy male subjects. Subjects were randomized to receive 100 U/kg Epoetin Hospira or 100 U/kg Epogen, each administered subcutaneously 3 times per week over 28 days. Blood was collected for determination of hemoglobin (Hb) concentrations for PD properties and for determination of epoetin concentrations for PK properties. The primary PD end point was the geometric mean ratio (GMR) of the 2 treatments for area under the effect curve for Hb from day 1 through 48 hours after the final dose of study drug administration on day 26, and the primary PK end point was the GMR of the 2 treatments for AUC0-48 and Cmax for epoetin after the final dose of study drug on day 26.

FINDINGS

The GMR (Epoetin Hospira/Epogen) for the area under the effect curve for Hb from day 1 through 48 hours after the final dose of study drug administration on day 26 was 1.006 with a 95% CI of 0.996 to 1.016, which was contained within the prespecified equivalence margin of 0.965 to 1.035. The GMRs (Epoetin Hospira/Epogen) for the epoetin-derived PK parameters were 0.974 for AUC0-48 with a 90% CI of 0.896 to 1.059, and 0.938 for Cmax with a 90% CI of 0.839 to 1.049, with both 90% CIs contained within the prespecified equivalence margin of 0.80 to 1.25. The incidence (21.2% and 23.8% for Epoetin Hospira and Epogen, respectively) and severity of adverse events were similar between the 2 groups. One subject in each treatment group had a positive recombinant human erythropoietin antibody result by radioimmunoprecipitation assay before dosing and throughout study conduct with negative immunoglobulin M and neutralizing antibodies and with no evidence of clinical deterioration or of impact on PD, PK, or safety profile.

IMPLICATIONS

The results of this study established PD and PK equivalences of multiple subcutaneous doses of the proposed biosimilar Epoetin Hospira to the reference product Epogen in healthy male subjects, and supported the overall demonstration of biosimilarity of Epoetin Hospira and Epogen.

Expression of platelet-derived growth factor BB, erythropoietin and erythropoietin receptor in canine and feline osteosarcoma

The discovery of expression of the erythropoietin receptor (EPO-R) on neoplastic cells has led to concerns about the safety of treating anaemic cancer patients with EPO. In addition to its endocrine function, the receptor may play a role in tumour progression through an autocrine mechanism. In this study, the expression of EPO, EPO-R and platelet-derived growth factor BB (PDGF-BB) was analysed in five feline and 13 canine osteosarcomas using immunohistochemistry (IHC) and reverse transcription polymerase chain reaction (RT-PCR).

EPO expression was positive in all tumours by IHC, but EPO mRNA was only detected in 38% of the canine and 40% of the feline samples. EPO-R was expressed in all samples by quantitative RT-PCR (RT-qPCR) and IHC. EPO-R mRNA was expressed at higher levels in all feline tumours, tumour cell lines, and kidney when compared to canine tissues. PDGF-BB expression was variable by IHC, but mRNA was detected in all samples. To assess the functionality of the EPO-R on tumour cells, the proliferation of canine and feline osteosarcoma cell lines was evaluated after EPO administration using an alamarBlue assay and Ki67 immunostaining. All primary cell lines responded to EPO treatment in at least one of the performed assays, but the effect on proliferation was very low indicating only a weak responsiveness of EPO-R. In conclusion, since EPO and its receptor are expressed by canine and feline osteosarcomas, an autocrine or paracrine tumour progression mechanism cannot be excluded, although in vitro data suggest a minimal role of EPO-R in osteosarcoma cell proliferation.