SYNTHESIS, CONTROLLED-RELEASE PROPERTIES AND ANTITUMOR-ACTIVITY OF ALGINATE-CIS-ACONITYL-DAUNOMYCIN CONJUGATES

Covalent conjugates of alginate and the antitumour agent daunomycin (DNM) were synthesized to be stable in the circulation and allow release of the drug in the acidic milieu of the endosomal and lysosomal compartments of tumour cells or the slightly acidic extracellular fluid of some solid tumours. Alginates containing primary amine groups were first prepared by reacting alginate with excess ethylenediamine. DNM was first reacted with cis-aconitic anhydride to produce N-cis-aconityl-DNM and then subsequently bound to the amino-modified alginate using the water-soluble carbodiimide 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC). High (M(w) = 250000) and low (M(w) = 61000) molecular weight alginate-DNM conjugates were prepared. In vitro release studies showed that DMN was released from the conjugates (approx. 22-60%/48 h) under acidic conditions (pH 5 and 6) with minimal release occurring at neutral pH (approx. 2-4%/48 h). Reverse-phase HPLC confirmed that DNM was the only product released from high molecular weight alginate-DNM conjugate (22% released/48 h at pH 5), but the low molecular weight alginate-DNM liberated in addition a DNM derivative (approx. 60% released (total)/48 h at pH 5). Ina preliminary experiment to investigate the antitumour activity of alginate-DNM conjugate in vivo, administration of a single intraperitoneal injection of low molecular weight alginate-DNM (equivalent to 5 mg/kg DNM) to mice bearing B16 subcutaneous tumours resulted in a small, but significant delay in the growth of the tumour.