Design and development of microemulsion systems of a new antineoplaston A10 analog for enhanced intravenous antitumor activity: In vitro characterization, molecular docking, I-radiolabeling and in vivo biodistribution studies.

A10, (3-phenylacetylamino-2,6-piperidinedione), is a natural peptide with broad antineoplastic activity. Recently, in vitro antitumor effect of a new A10 analog [3-(4-methoxybenzoylamino)-2,6-piperidinedione] (MPD) has been verified. However, poor aqueous solubility represents an obstacle towards intravenous formulation of MPD and impedes successful in vivo antitumor activity. To surmount such limitation, MPD microemulsion (MPDME) was developed. A 32 full factorial design using Design-Expert® software was adopted to study the influence of different parameters and select the optimum formulation (MPDME1). Transmission electron microscopy (TEM) displayed spherical droplets of MPDME1. The cytotoxicity of MPDME1 in Michigan Cancer Foundation 7 (MCF-7) breast cancer cell line exceeded that of MPD solution (MPDS) and tamoxifen. Compatibility with injectable diluents, in vitro hemolytic studies and in vivo histopathological examination confirmed the safety of parenteral application of MPDME1. Molecular docking results showed almost same binding affinity of A10, MPD and I-MPD with histone deacetylase 8 (HDAC8) receptor. Accordingly, radioiodination of MPDME1 and MPDS was done via direct electrophilic substitution reaction. Biodistribution of I-MPDME1 and I-MPDS in normal and tumor (ascites and solid) bearing mice showed high accumulation of I-MPDME1 in tumor tissues. Overall, the results proved that MPDME represents promising parenteral delivery system capable of improving antineoplastic activity of MPD.