Optimal timing and dosage of chemotherapy as a combined treatment with androgen withdrawal in the human prostate LNCaP tumour model

Abstract

Although numerous chemotherapeutic agents have been evaluated for patients with advanced prostate cancer, none have demonstrated improved survival benefits. Here, in order to determine whether the efficacy of chemotherapy can be enhanced by changing the regimen, we evaluated the effect of the varied timing and dosage of chemotherapy in combination with androgen withdrawal on time to androgen-independent (AI) progression in the human androgen-dependent LNCaP tumour model. We first demonstrated the synergistic effect of mitoxantrone on induction of apoptosis in LNCaP cells maintained in the steroid hormone-depleted charcoal-stripped media (CSM) compared to those in the standard media. In addition, this synergy was most remarkable during the simultaneous treatment of LNCaP cells with mitoxantrone and CSM compared to the pre- or post-use of mitoxantrone with CSM. LNCaP tumour growth in athymic nude mice and their increase in serum PSA levels were significantly inhibited by the simultaneous injection of mitoxantrone with castration, compared to the administration of mitoxantrone 2 weeks before or after castration. The TUNEL staining revealed that apoptotic cell death was extensively induced in LNCaP tumours treated with simultaneous castration and mitoxantrone compared to tumours treated with the other schedules. Furthermore, nude mice bearing LNCaP tumours were injected with a total of 0.5 mg mitoxantrone divided into 2, 5 and 10 days, with the most significant therapeutic effect and delayed AI progression observed in mice given injection of mitoxantrone for 2 days. These findings suggest that this might be the optimal way to perform cytotoxic chemotherapy and androgen withdrawal simultaneously in patients with advanced prostate cancer and to administer chemotherapeutic agents at high dosage within short intervals.