Controlled release of therapeutic agents: slow delivery and cell encapsulation

Some of the most promising systems for the controlled release of bioactive agents, i.e., peptides or hormones, involve the encapsulation or entrapment of hormones or peptides in biocompatible polymeric devices that enable their continuous release over prolonged periods. In urology, two major pathologic conditions, androgen deficiency and prostate cancer, currently benefit from treatments based on controlled delivery. Leuprolide acetate depot (Lupron-depot) was one of the first controlled-delivery systems used for the treatment of prostate cancer. Clinical studies indicate that patients with prostate cancer who undergo therapy with leuprolide acetate depot can benefit from this treatment. Currently available androgen-replacement therapies include the oral administration of testosterone tablets or capsules, depot injections, sublingual treatment, and skin patches. However, side effects such as metabolic inactivation of testosterone on oral administration; fluctuations in levels of the hormone; and burning, rash, and skin necrosis during the use of skin patches may occur. These side effects may be avoided through the application of encapsulated Leydig cells, which produce testosterone. Studies in our laboratory have shown that Leydig cells encapsulated in alginate/poly-L-lysine/alginate microspheres are capable of secreting testosterone in culture and in vivo. Microencapsulated Leydig cells delivered intraperitoneally into castrated rats maintained a testosterone level of 0.51 ng/ml for more than 3 months without any human chorionic gonadotropin stimulation. Similar studies are also being conducted in our laboratory on encapsulation of ovarian cells for the secretion of progesterone and estrogen in culture and in vivo using microencapsulation techniques.