Nanoparticulate delivery of irinotecan active metabolite (SN38) in murine colorectal carcinoma through conjugation to poly (2-ethyl 2-oxazoline)-b-poly (L-glutamic acid) double hydrophilic copolymer.

SN-38 is the active metabolite of irinotecan, an FDA-approved chemotherapeutic agent indicated for colorectal carcinoma, which would not be clinically applicable due to its very poorly soluble and hydrolytic degradation properties. To overcome these limitations, it was proposed to conjugate SN38 to residing carboxylic acid residues in poly (2-ethyl 2-oxazoline) block poly (L-glutamic acid), inducing nano-assembly in aqueous medium. Following a series of reactions including poly (2-ethyl oxazoline) macro-initiated ring opening polymerization of N-carboxyanhydride, deprotection of benzyl group and chemical conjugation of SN38 via biodegradable ester linkage, the as-synthesized product was characterized by dynamic light scattering, ζ potential and transmission electron microscopy. The resulting particles presented about 90% loading efficiency with a mean size of 90 nm. Upon incubation with colorectal carcinoma CT26 cell line, higher association of SN-38 fluorescence and significantly more specific cytotoxicity was noticed for the SN38 conjugated particles than free drug. Therapeutic applicability of the as-synthesized product was evaluated in CT26 allograft tumor model in BALB/c mice, showing superior efficiency of the SN38 conjugated particles particularly in tumors with sizes larger than 200 mm3 than parent irinotecan and reduced mortality rate by 2.5 times. Conclusively, the poly (2-ethyl 2-oxazoline) decorated nano-conjugates of poly (L-glutamic acid) and SN38 can be regarded as a novel and potentially efficient drug delivery system for advanced colorectal carcinoma.