1. ¹British Columbia Cancer Agency, Vancouver, BC, Canada V5Z 1L3
2. ²Tumor Biology Group, Australian National University Medical School and The Canberra Hospital, Woden, ACT 2603, Australia

Correspondence: Dr M Korbelik, E-mail: mkorbelik@bccrc.ca

Revised 3 November 2006; Accepted 6 November 2006; Published online 5 December 2006.

Abstract

Host response elicited by photodynamic therapy (PDT) of cancerous lesions is a critical contributor to the clinical outcome, and complement system has emerged as its important element. Amplification of complement action was shown to improve tumour PDT response. In search of a clinically relevant complement activator for use as a PDT adjuvant, this study focused on -inulin and examined its effects on PDT response of mouse tumours. Intralesional -inulin (0.1 mg mouse^-1) delivered immediately after PDT rivaled zymosan (potent classical complement activator) in delaying the recurrence of B16BL6 melanomas. This effect of -inulin was further enhanced by IFN- pretreatment. Tumour C3 protein levels, already elevated after individual PDT or -inulin treatments, increased much higher after their combination. With fibrosarcomas MCA205 and FsaR, adjuvant -inulin proved highly effective in reducing recurrence rates following PDT using four different photosensitisers (BPD, ce6, Photofrin, and mTHPC). At 3 days after PDT plus -inulin treatment, over 50% of cells found at the tumour site were CTLs engaged in killing specific targets via perforin–granzyme pathway. This study demonstrates that -inulin is highly effective PDT adjuvant and suggests that by amplifying the activation of complement system, this agent potentiates the development of CTL-mediated immunity against PDT-treated tumours.