Phase I dose-finding and pharmacokinetic study of paclitaxel and carboplatin with oral valspodar in patients with advanced solid tumors

A Phase I Trial of the ABCB1 Inhibitor, Oral Valspodar, in Combination With Paclitaxel in Patients With Advanced Solid Tumors

OBJECTIVES

Multidrug resistance mediated by P-glycoprotein is a potential obstacle to cancer treatment. This phase 1 trial determined the safety of paclitaxel with valspodar, a P-glycoprotein inhibitor, in patients with advanced solid tumors.

METHODS

Patients were treated with single-agent paclitaxel Q3W 175 mg/m 2 (or 135 mg/m 2 if heavily pretreated) as a 3-hour infusion. If their disease was stable (SD) or progressive (PD), paclitaxel at 30% (52.5 mg/m 2 ), 40% (70 mg/m 2 ), or 50% (87.5 mg/m 2 ) of 175 mg/m 2 (full dose) was administered with valspodar 5 mg/kg orally 4 times daily for 12 doses. Pharmacokinetic sampling (PK) for paclitaxel and valspodar was performed during single-agent and combination therapy.

RESULTS

Sixteen patients had SD/PD after one cycle of paclitaxel and then received paclitaxel at 30% (n=3), 40% (n=3), and 50% (n=10) with valspodar. Hematologic adverse events (AEs) including myelosuppression at paclitaxel 40% were comparable to those of full-dose paclitaxel. Non-hematologic AEs consisted of reversible hepatic (hyperbilirubinemia and transaminitis) and neurologic AEs (ataxia and paresthesias). Eleven patients experienced SD with a median of 12.7 weeks (range, 5.4 to 36.0), 4 patients progressed, and 1 was inevaluable. Reduced dose paclitaxel with valspodar resulted in lower plasma peak concentrations of paclitaxel; otherwise, concentrations were similar to single-agent paclitaxel.

CONCLUSION

Paclitaxel at 70 mg/m 2 was administered safely with valspodar. Limited efficacy in hematologic and solid tumors resulted in discontinuation of its clinical development and other transporter inhibitors. Recently, the development of ATP-binding cassette transporter inhibitors has been reconsidered to mitigate resistance to antibody-drug conjugates.

P-Glycoprotein Inhibition Exacerbates Paclitaxel Neurotoxicity in Neurons and Patients With Cancer

Paclitaxel-induced peripheral neuropathy (PIPN) is a common and dose-limiting adverse event. The role of P-glycoprotein (P-gp) in the neuronal efflux of paclitaxel was assessed using a translational approach. SH-SY5Y cells were differentiated to neurons and paclitaxel toxicity in the absence and presence of a P-gp inhibitor was determined. Paclitaxel caused marked dose-dependent toxicity in SH-SY5Y-derived neurons. Paclitaxel neurotoxicity was exacerbated with concomitant P-gp inhibition by valspodar and verapamil, consistent with increased intracellular accumulation of paclitaxel. Patients with cancer treated with paclitaxel and P-gp inhibitors had a 2.4-fold (95% confidence interval (CI) 1.3-4.3) increased risk of peripheral neuropathy-induced dose modification while a 4.7-fold (95% CI 1.9-11.9) increased risk for patients treated with strong P-gp inhibitors was observed, and a 7.0-fold (95% CI 2.3-21.5) increased risk in patients treated with atorvastatin. Atorvastatin also increased neurotoxicity by paclitaxel in SH-SY5Y-derived neurons. Clinicians should be aware that comedication with P-gp inhibitors may lead to increased risk of PIPN.

Exploring β-Tubulin Inhibitors from Plant Origin using Computational Approach

INTRODUCTION

β-Tubulin is an important target for the binding of anti-cancer drugs, in particular, paclitaxel (taxol), vinblastine and epothilone. However, mutations in β-tubulin structure give resistance to chemotherapeutic agents. Notably, mutations at R306C, F270 V, L217R, L228F, A185T and A248V positions in β-tubulin give high resistance for paclitaxel binding.

OBJECTIVE

To discover novel inhibitors of β-tubulin from natural sources, particularly alkaloids, using a virtual screening approach.

METHODOLOGY

A virtual screening approach was employed to find potent lead molecules from the Naturally-occurring Plant-based Anti-cancer Compound-activity Target (NPACT) database. Alkaloids have great potential to be anti-cancer agents. Therefore, we have screened all alkaloids from a total of 1574 molecules from the NPACT database for our study. Initially, Molinspiration and DataWarrior programs were utilised to calculate pharmacokinetics and toxicity risks of the alkaloids, respectively. Subsequently, AutoDock algorithm was employed to understand the binding efficiency of alkaloids against β-tubulin. The binding affinity of the docked complex was confirmed by means of an intermolecular interaction study. Moreover, oral toxicity was predicted by using ProTox program. Further, metabolising capacity of drugs was studied by using SmartCYP software. Additionally, scaffold analysis was done with the help of scaffold trees and dendrograms, providing knowledge about the building blocks for parent-compound synthesis.

RESULTS

Overall, the results of our computational analysis indicate that isostrychnine, obtained from Strychnosnux-vomica, satisfies pharmacokinetic and bioavailability properties, binds efficiently with β-tubulin. Thus, it could be a promising lead for the treatment of paclitaxel resistant cancer types.

CONCLUSION

This is the first observation of inhibitory activity of isostrychnine against β-tubulin and warrants further experimental investigation. Copyright © 2016 John Wiley & Sons, Ltd.

Specifications of a continual reassessment method design for phase I trials of combined drugs

In studies of combinations of agents in phase I oncology trials, the dose-toxicity relationship may not be monotone for all combinations, in which case the toxicity probabilities follow a partial order. The continual reassessment method for partial orders (PO-CRM) is a design for phase I trials of combinations that leans upon identifying possible complete orders associated with the partial order. This article addresses some practical design considerations not previously undertaken when describing the PO-CRM. We describe an approach in choosing a proper subset of possible orderings, formulated according to the known toxicity relationships within a matrix of combination therapies. Other design issues, such as working model selection and stopping rules, are also discussed. We demonstrate the practical ability of PO-CRM as a phase I design for combinations through its use in a recent trial designed at the University of Virginia Cancer Center.

A model of competing saturable kinetic processes with application to the pharmacokinetics of the anticancer drug paclitaxel

A saturable multi-compartment pharmacokinetic model for the anti-cancer drug paclitaxel is proposed based on a meta-analysis of pharmacokinetic data published over the last two decades. We present and classify the results of time series for the drug concentration in the body to uncover the underlying power laws. Two dominant fractional power law exponents were found to characterize the tails of paclitaxel concentration-time curves. Short infusion times led to a power exponent of -1.57 ± 0.14, while long infusion times resulted in tails with roughly twice the exponent. Curves following intermediate infusion times were characterized by two power laws. An initial segment with the larger slope was followed by a long-time tail characterized by the smaller exponent. The area under the curve and the maximum concentration exhibited a power law dependence on dose, both with compatible fractional power exponents. Computer simulations using the proposed model revealed that a two-compartment model with both saturable distribution and elimination can reproduce both the single and crossover power laws. Also, the nonlinear dose-dependence is correlated with the empirical power law tails. The longer the infusion time the better the drug delivery to the tumor compartment is a clinical recommendation we propose.

Continual reassessment method for partial ordering

Much of the statistical methodology underlying the experimental design of phase 1 trials in oncology is intended for studies involving a single cytotoxic agent. The goal of these studies is to estimate the maximally tolerated dose, the highest dose that can be administered with an acceptable level of toxicity. A fundamental assumption of these methods is monotonicity of the dose-toxicity curve. This is a reasonable assumption for single-agent trials in which the administration of greater doses of the agent can be expected to produce dose-limiting toxicities in increasing proportions of patients. When studying multiple agents, the assumption may not hold because the ordering of the toxicity probabilities could possibly be unknown for several of the available drug combinations. At the same time, some of the orderings are known and so we describe the whole situation as that of a partial ordering. In this article, we propose a new two-dimensional dose-finding method for multiple-agent trials that simplifies to the continual reassessment method (CRM), introduced by O'Quigley, Pepe, and Fisher (1990, Biometrics 46, 33-48), when the ordering is fully known. This design enables us to relax the assumption of a monotonic dose-toxicity curve. We compare our approach and some simulation results to a CRM design in which the ordering is known as well as to other suggestions for partial orders.

Extended model-based designs for more complex dose-finding studies

We discuss extensions of model-based designs, such as the continual reassessment method, for use in dose-finding studies. Rather than work with a single model to carry out the design and analysis of a dose-finding study we indicate how the use of several models can greatly increase flexibility. We can appeal to established results on Bayesian model choice and this device makes the inferential problem essentially straightforward. The greater flexibility enables us to take on board many different kinds of added complexity. Examples include extended models to deal with subject heterogeneity, extended models to take account of different treatment schedules and extended models to tackle the problem of partial ordering.

23-Hydroxybetulinic acid from Pulsatilla chinensis (Bunge) Regel synergizes the antitumor activities of doxorubicin in vitro and in vivo

ETHNOPHARMACOLOGICAL REVELANCE: Pulsatilla chinensis (Bunge)Regel has been used as adjuvant in chemotherapy in traditional Chinese medicine. 23-Hydroxybetulinic acid, an isolated pentacyclic triterpene, is the major active constituent of Pulsatilla chinensis (Bunge) Regel.

AIM OF THIS STUDY

To evaluate the combinational anticancer effect of 23-hydroxybetulinic acid and doxorubicin in vitro and in vivo.

MATERIALS AND METHODS

The effect of combination treatment with 23-hydroxybetulinic acid and doxorubicin was evaluated with a quantitative combination index method based on the median-effect analysis in various cancer cell lines. And in vivo efficacy of combination chemotherapy was also evaluated using ICR mice bearing sarcoma 180 carcinoma tumors.

RESULTS

23-Hydroxybetulinic acid showed a synergistic cytotoxic effect on multiple cancer cell lines by combined use with doxorubicin. In vivo studies further demonstrated that co-administration of 23-HBA significantly improved the sensitivity of the tumor to doxorubicin through increasing intra-tumor doxorubicin concentration and inhibiting doxorubicin-induced up-regulation of P-gp in tumor.

CONCLUSION

These results suggest that the combined therapy with 23-hydroxybetulinic acid and doxorubicin may be a new promising strategy to promote the clinical chemotherapy, which needs further verification.

Phase III study of valspodar (PSC 833) combined with paclitaxel and carboplatin compared with paclitaxel and carboplatin alone in patients with stage IV or suboptimally debulked stage III epithelial ovarian cancer or primary peritoneal cancer

PURPOSE

To compare the safety and efficacy of carboplatin and paclitaxel administered with or without the multidrug resistance modulator valspodar (PSC 833) in untreated patients with advanced ovarian or primary peritoneal cancer.

PATIENTS AND METHODS

Seven hundred sixty-two patients with stage IV or suboptimally debulked stage III ovarian or primary peritoneal cancer were randomly assigned to receive either valspodar 5 mg/kg every 6 hours for 12 doses, paclitaxel 80 mg/m(2), and carboplatin area under the curve (AUC) 6 (PC-PSC; n = 381) or paclitaxel 175 mg/m(2) and carboplatin AUC 6 (PC; n = 381). Time to disease progression (TTP) was the primary end point. Secondary end points were overall survival time (OS), response rate (RR), safety, and tolerability.

RESULTS

With a median follow-up of 736 days (range, 1 to 2,280 days), the median TTP was 13.2 and 13.5 months in the PC-PSC and PC groups, respectively (P = .67); the median OS was 32 and 28.9 months, respectively (P = .94). The overall RR was higher in the PC group (41.5% v 33.6%; P = .02). Central and peripheral nervous system and GI toxicities were more common in the PC-PSC group. Ataxia occurred in 53.5% and 3.2% of PC-PSC-and PC-treated patients, respectively. Febrile neutropenia occurred more frequently in the PC-PSC group. More PC-PSC-treated patients discontinued therapy because of adverse events (AEs), experienced serious AEs, and required paclitaxel dose reductions.

CONCLUSION

The addition of valspodar to PC did not improve TTP or OS and was more toxic compared with PC in untreated patients with advanced ovarian or primary peritoneal cancer.

Effect of valspodar on the pharmacokinetics of unbound paclitaxel

The aim of this multicenter study was to determine whether valspodar (Amdray; code designation, SDZ PSC 833), a potent P-glycoprotein (P-gp) inhibitor, affects the pharmacokinetics of unbound paclitaxel (Cu). Data were obtained from 31 patients with advanced breast cancer. Thirteen patients were treated with paclitaxel alone (3-h infusion at 175 mg/m2) and another 18 received paclitaxel (3-h infusion at 70 mg/m2) in combination with a 21-day cycle of oral valspodar (5 mg/kg given four times a day) starting 1 day before administration of paclitaxel. Serial blood samples were taken in the first course and Cu in plasma determined using equilibrium dialysis with a [G-3H]paclitaxel tracer. The apparent clearance of Cu was not significantly different between the two groups, with mean +/- standard deviation (+/- SD) values of 230 +/- 56.0 and 202 +/- 49.9 L/h/m2 in the absence and presence of valspodar, respectively (P = 0.17). The volume of Cu distribution was slightly larger in the presence of valspodar (1160 +/- 474 vs. 1620 +/- 552 L/m2; P = 0.025), which contributed to a minor difference in the terminal disposition half-life (6.12 +/- 3.42 vs. 8.50 +/- 2.06 h; P = 0.028). These data indicate that (i) valspodar lacks the significant interaction with paclitaxel observed previously with other P-gp modulators, (ii) the majority of the increased toxicity of the combination does not appear to be attributable to increased levels of Cu, and (iii) provide further evidence of the conjecture that the plasma concentration of paclitaxel may not be an appropriate measure to monitor the impact of P-gp inhibition.

Effect of efflux inhibition on brain uptake of itraconazole in mice infected with Cryptococcus neoformans

Itraconazole is a fungistatic agent that, although highly lipophilic, shows poor transport through the blood brain barrier that may be due to efflux proteins. The combined administration of an efflux inhibitor with itraconazole should increase cerebral itraconazole concentrations and therefore, improve the treatment of Cryptococcus neoformans meningitis with this antifungal agent. To test this hypothesis, we have studied the influence of murine cerebral infection with C. neoformans and the inhibition of efflux by intraperitoneal injection of a P-glycoprotein inhibitor, GF120918 [N-(4-[2-(1,2,3,4-tetrahydro-6,7-dimethoxy-2-isoquinolinyl)-ethyl]-phenyl)9,10-dihydro-5-methoxy-9-oxo-4-acridine carboxamide], on the pharmacokinetics of itraconazole in plasma and brain after a single intraperitoneal itraconazole injection. We also investigated the influence of efflux inhibition on the efficacy of repeated doses of itraconazole in this murine model. The results showed that in healthy and infected mice pretreated or not with GF120918, plasma itraconazole values of area under the curve (AUC) were similar. In contrast, cerebral values of AUC were higher in infected mice compared with healthy mice. Moreover, the pretreatment of infected mice with GF120918 significantly increased cerebral itraconazole values of area under the curve and decreased weight loss in the treatment with itraconazole of a cerebral infection with C. neoformans.

A Phase I study of infusional vinblastine in combination with the P-glycoprotein antagonist PSC 833 (valspodar)

BACKGROUND

PSC 833 is a second-generation P-glycoprotein (Pgp) antagonist developed to reverse multidrug resistance (MDR). The authors conducted a Phase I study of orally administered PSC 833 in combination with vinblastine administered as a 5-day continuous infusion.

METHODS

Seventy-nine patients with advanced malignant disease were enrolled in the trial and treated with escalating doses of PSC 833. Pharmacokinetic interactions between PSC 833 and vinblastine were anticipated. Accordingly, when dose limiting toxicities were observed, the dose of vinblastine was reduced as PSC 833 was escalated. Three schedules and two formulations of PSC 833 were used in the study.

RESULTS

The maximum tolerated doses of PSC 833 were 12.5 mg/kg orally every 12 hours for 8 days for the liquid formulation in combination with 0.9 mg/m(2) per day vinblastine as a continuous intravenous infusion (CIV) for 5 days; and 4 mg/kg orally every 6 hours for 8 days for the microemulsion formulation in combination with 0.6 mg/m(2) per day vinblastine CIV for 5 days. The principal toxicities for PSC 833 were ataxia and paresthesias and for the combination, constipation, fever. and neutropenia. Increased oral bioavailability and increased peak and trough concentrations were observed with the microemulsion formulation. Significant interpatient variability in pharmacokinetic parameters was observed. Ten patients studied at the MTD for PSC 833 (4 mg/kg orally every 6 hours for 8 days) had inhibition of rhodamine efflux from CD56 positive peripheral lymphocytes as a surrogate for Pgp antagonism. Among 43 evaluable patients with clear cell carcinoma of the kidney, 3 patients had complete responses, and 1 patient had a partial response.

CONCLUSIONS

PSC 833 in combination with vinblastine can be administered safely to patients provided the vinblastine dose is adjusted for pharmacokinetic interactions. The high interpatient variability is a significant confounding factor. Surrogate studies with CD56 positive cells suggest that Pgp inhibition in the clinical setting is achievable. Improved methods for predicting pharmacokinetic interactions should improve future studies.

Overcoming drug resistance in ovarian carcinoma

Advanced epithelial ovarian carcinoma is treated with cytoreductive surgery and combination chemotherapy with a platinum compound and paclitaxel. Despite this treatment strategy, most women eventually relapse and die of resistant disease. Preclinical studies have shown that alterations in drug accumulation, drug metabolism, DNA repair, cellular targets and/or cell survival pathways may cause this resistance. Clinical studies have employed modulators of resistance in combination with chemotherapy as a means to overcome drug resistance. The most extensively studied modulators, buthionine sulfoximine and valspodar, are involved in reversing resistance caused by glutathione and P-glycoprotein, respectively. A phase III study comparing paclitaxel and carboplatin with and without valspodar is ongoing. However, other approaches to overcoming drug resistance are necessary for the effective treatment of women with this disease.