Abstract 4419: BAL101553: A highly soluble prodrug of the potent microtubule destabilizer BAL27862
Authors: Pohlmann Jens , Bachmann Felix , Schmitt-Hoffmann Anne , Biringer Gérard , Burger Karin , Bucher Christian , Schlaefle Caroline , Pruschy Martin , Lane Heidi 
Published: February 2011

Abstract
Background: BAL27862 is a synthetic small molecule, inducing apoptosis in cancer cells through a unique, destabilizing effect on microtubules (MT). BAL27862 can be administered intravenously (i.v.) and orally, and exhibits broad antitumor activity against a range of human tumor histotypes, including models refractory to conventional agents such as taxanes and vinca alkaloids. To improve water solubility, allowing a well tolerated formulation, a novel prodrug (BAL101553) has been developed.
Materials and Methods: Solubility was determined by HPLC-quantitation of compound concentration in saturated solutions after filtration and appropriate dilution. Antiproliferative activity in vitro was analyzed by Crystal Violet assay. Effects on MTs were assessed by immunoblotting (IB) or immunofluorescence (IF) for α-tubulin. For pharmacokinetic (PK) studies, colon carcinoma SW480 xenografted mice were treated i.v. with BAL27862 or BAL101553 weekly for 4 weeks. Compound levels were determined in plasma, brain and tumors. Efficacy was assessed in a NSCLC A549 mouse xenograft model using weekly MTD doses.
Results: BAL27862 is insoluble in water (&lt;0.001 mg/mL), whereas the hydrochloride salt of BAL101553 has a solubility &gt;100 mg/mL. Using tumor lines in vitro, BAL101553 elicited antiproliferative IC50s approx. double those of the parent drug (e.g. A549: 34.5 nM and 18.5 nM, respectively), consistent with its conversion to active drug in cell culture. Importantly, BAL101553's antiproliferative activity was associated with efficient MT depolymerization, characterized by the formation of multiple, tiny MT asters in dividing cells. The latter is a phenomenon unique to BAL27862 and is not observed with conventional MT-targeted agents like taxanes and vinca alkaloids. In vivo, BAL101553 was converted to active BAL27862. In mice, after i.v. administration of BAL27862 or BAL101553, brain and tumor concentrations equal to plasma levels were detected 5 min and 30 min post-administration, respectively. There was no brain or tumor accumulation over time, as drug concentrations paralleled those in plasma. Notably, a higher maximum tolerated dose was reached with BAL101553 as compared to BAL27862. In terms of exposure, this translated to a 20% lower Cmax and a 10% higher AUC of active drug with BAL101553. When administered i.v. to A549 xenograft-bearing mice, the prodrug was well tolerated, eliciting significant antitumor effects (p≤0.05), equivalent to the parent drug (final %T/C: 44% BAL27862 [10 mg/kg], 40% BAL101553 [28 mg/kg]).
Conclusions: BAL101553 is a prodrug of BAL27862 with high water solubility, allowing i.v. administration in the absence of solubilizing excipients known to be associated with adverse side-effects. The in vitro profile, favorable PK characteristics and efficacy in animal tumor models support further evaluation of BAL101553 for the treatment of human cancers.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4419.