Peripheral Neuropathy Induced by Microtubule-Targeted Chemotherapies: Insights into Acute Injury and Long-term Recovery.

Chemotherapy-induced peripheral neuropathy (CIPN) is a major cause of disability in cancer survivors. CIPN investigations in preclinical model systems have focused on either behaviors or acute changes in nerve conduction velocity (NCV) and amplitude, but greater understanding of the underlying nature of axonal injury and its long-term processes is needed as cancer patients live longer. In this study, we used multiple independent endpoints to systematically characterize CIPN recovery in mice exposed to the antitubulin cancer drugs eribulin, ixabepilone, paclitaxel, or vinorelbine at MTDs. All of the drugs ablated intraepidermal nerve fibers and produced axonopathy, with a secondary disruption in myelin structure within 2 weeks of drug administration. In addition, all of the drugs reduced sensory NCV and amplitude, with greater deficits after paclitaxel and lesser deficits after ixabepilone. These effects correlated with degeneration in dorsal root ganglia (DRG) and sciatic nerve and abundance of Schwann cells. Although most injuries were fully reversible after 3-6 months after administration of eribulin, vinorelbine, and ixabepilone, we observed delayed recovery after paclitaxel that produced a more severe, pervasive, and prolonged neurotoxicity. Compared with other agents, paclitaxel also displayed a unique prolonged exposure in sciatic nerve and DRG. The most sensitive indicator of toxicity was axonopathy and secondary myelin changes accompanied by a reduction in intraepidermal nerve fiber density. Taken together, our findings suggest that intraepidermal nerve fiber density and changes in NCV and amplitude might provide measures of axonal injury to guide clinical practice.Significance: This detailed preclinical study of the long-term effects of widely used antitubulin cancer drugs on the peripheral nervous system may help guide clinical evaluations to improve personalized care in limiting neurotoxicity in cancer survivors. Cancer Res; 78(3); 817-29. ©2017 AACR.

Eribulin shows high concentration and long retention in xenograft tumor tissues.

PURPOSE: Eribulin, a synthetic analog of the natural product halichondrin B, is a microtubule dynamics inhibitor. In this study, we report the pharmacokinetic profiles of eribulin in mice, rats, and dogs following intravenous administrations with optimized and validated bio-analytical methods. METHODS: Eribulin was administered at 0.5 and 2 mg/kg in mice, 0.5 and 1 mg/kg in rats, and 0.08 mg/kg in dogs. Tumor and brain penetration of eribulin was also evaluated in LOX human melanoma xenograft models. Concentrations in plasma, tumor, and brain were measured by the LC-MS/MS method. RESULTS: The profiles of eribulin were characterized by extensive distribution, moderate clearance, and slow elimination in the three species. The pharmacokinetics are linear in mice and rats. In xenograft mice, the penetration into the brain was low, as expected, since eribulin is a P-glycoprotein substrate. In contrast to disposition in brain, the exposure of eribulin was approximately 20-30 times higher in tumor than that in plasma and half-lives were 17.8-35.9 h after both single and multiple dose regimens. CONCLUSIONS: Eribulin was distributed rapidly and eliminated slowly in mice, rats, and dogs. The exposure of eribulin was approximately 20-30 times higher in tumor than in plasma in xenograft mice. These results might be caused by eribulin's mechanism of action including increased perfusion in tumor by vascular remodeling effect.

Apratoxin A Shows Novel Pancreas-Targeting Activity through the Binding of Sec 61.

Apratoxin A is a natural product with potent antiproliferative activity against many human cancer cell lines. However, we and other investigators observed that it has a narrow therapeutic window in vivo Previous mechanistic studies have suggested its involvement in the secretory pathway as well as the process of chaperone-mediated autophagy. Still the link between the biologic activities of apratoxin A and its in vivo toxicity has remained largely unknown. A better understanding of this relationship is critically important for any further development of apratoxin A as an anticancer drug. Here, we describe a detailed pathologic analysis that revealed a specific pancreas-targeting activity of apratoxin A, such that severe pancreatic atrophy was observed in apratoxin A-treated animals. Follow-up tissue distribution studies further uncovered a unique drug distribution profile for apratoxin A, showing high drug exposure in pancreas and salivary gland. It has been shown previously that apratoxin A inhibits the protein secretory pathway by preventing cotranslational translocation. However, the molecule targeted by apratoxin A in this pathway has not been well defined. By using a (3)H-labeled apratoxin A probe and specific Sec 61α/ß antibodies, we identified that the Sec 61 complex is the molecular target of apratoxin A. We conclude that apratoxin A in vivo toxicity is likely caused by pancreas atrophy due to high apratoxin A exposure. Mol Cancer Ther; 15(6); 1208-16. ©2016 AACR.

Pharmacokinetic characterization of a natural product-inspired novel MEK1 inhibitor E6201 in preclinical species.

PURPOSE: E6201 is a natural product-inspired novel inhibitor of mitogen-activated protein kinase/extracellular signal-regulated kinase kinase-1 (MEK1) and other kinases and is currently under development as an anticancer (parenteral administration) and antipsoriasis agent (topical application). In vitro and in vivo preclinical studies were performed to characterize the pharmacokinetics of E6201. Allometric scaling was applied to predict human pharmacokinetics of E6201. METHODS: In vitro metabolism studies for CYP induction and CYP inhibition were conducted using human hepatocytes and microsomes, respectively. Metabolic stability using microsomes and protein-binding studies using pooled plasma were performed for mice, rats, dogs, and human. Pharmacokinetics of E6201 and its isomeric metabolite, ER-813010, in mice, rats, and dogs was determined following single IV administration of E6201 at three dose levels. Bioanalysis was performed using LC/MS/MS. Pharmacokinetic parameters were determined using non-compartmental analysis, and allometric scaling with a two-compartment model was used to predict E6201 pharmacokinetics in humans. RESULTS: E6201 showed high plasma protein binding (>95%), and metabolic stability half-life ranged from 36 to 89 min across species. In vitro CYP inhibition (CYP1A2, 2C9, 2C19, 2D6, 2E1, and 3A) and CYP induction (CYP1A, 3A, 2C9, and 2C19) suggested no inhibitory or induction effect on the tested human CYPs up to 10 µM of E6201. Pharmacokinetics of E6201 in mice, rats, and dogs was characterized by mean clearance ranging from 3.45 to 10.92 L/h/kg, distribution volume ranging from 0.63 to 13.09 L/kg, and elimination half-life ranging from 0.4 to 1.6 h. ER-813010 was detected in all species with metabolite to parent exposure ratio (AUC(R)) ranging from 3.1 to 33.4% and exhibited fast elimination (<3 h). The allometry predicted high clearance and large volume of distribution of E6201 in humans and was in general in good agreement with the observed first human subject pharmacokinetics. CONCLUSIONS: E6201 exhibited high clearance, high to moderate distribution, and fast elimination in preclinical species. In vitro results suggested that E6201 has low risk of drug-drug interactions due to CYP inhibition and induction in humans. In the first-in-man study, E6201 exhibited high clearance, which was well predicted by allometric scaling.

Novel second generation analogs of eribulin. Part III: Blood-brain barrier permeability and in vivo activity in a brain tumor model.

Novel second generation analogs of eribulin mesylate, a tubulin agent recently approved for the treatment of breast cancer, are reported. Our recent efforts have focused on expanding the target indications for this class of compounds to other tumor types. Herein, we describe the design, synthesis and evaluation of eribulin analogs active against brain tumor cell lines in vitro and corresponding brain tumor models in mice. Attenuation of basicity of the amino group(s) in the C32 side-chain region led to compounds with lower susceptibility to P-gp mediated drug efflux, allowing these compounds to permeate through the blood-brain barrier. In preclinical in vivo studies, these compounds showed significantly higher levels in the brain and cerebrospinal fluid as compared to eribulin. In addition, analogs within this series showed antitumor activity in an orthotopic murine model of human glioblastoma.

Novel second generation analogs of eribulin. Part II: Orally available and active against resistant tumors in vivo.

Eribulin mesylate is a newly approved treatment for locally advanced and metastatic breast cancer. We targeted oral bioavailability and efficacy against multidrug resistant (MDR) tumors for further work. The design, synthesis and evaluation of novel amine-containing analogs of eribulin mesylate are described in this part. Attenuation of basicity of the amino group(s) in the C32 side-chain region led to compounds with low susceptibility to PgP-mediated drug efflux. These compounds were active against MDR tumor cell lines in vitro and in xenograft models in vivo, in addition to being orally bioavailable.