Abstract 2417: Preclinical evaluation of potential novel synthetic saponin adjuvants with conjugate cancer vaccines

We have tested a variety of naturally isolated and synthetic carbohydrate and peptide cancer antigens conjugated to keyhole limpet hemocyanin (KLH) plus an immunological adjuvant in pre clinical studies and clinical trials. The strength of the IgM and IgG antibody response was in each case determined by the potency of the immunological adjuvant, and the saponin fraction QS-21 was consistently the optimal adjuvant. However, there are draw backs to the use of QS-21 including local and systemic toxicity at immunologically relevant doses and poor stability at room temperature. Recent achievements in complex carbohydrate synthesis have enabled us to chemically synthesize a variety of saponin analogues. The effect of several of these synthetic saponin analogues were evaluated in mice in combination with GD3 ganglioside conjugated to KLH (GD3-KLH). Mice were immunized weekly for three weeks with GD3-KLH containing 10μg of GD3 alone, mixed with synthetic QS-21 (SQS-21) as positive control, or with 10, 20 or 50μg of synthetic QS-21 analogues SQS-101, SQS-102 or SQS-103 designed for improved stability as a consequence of amide modification. Toxicity (loss of weight) was monitored at 0h, 24h, 48h and 72h after each injection. Mice were bled 7 days after the third weekly vaccination and after the fourth (booster) vaccination on week 8. The sera were tested for the presence of antibody against GD3 or KLH by ELISA and against a tumor cell-line expressing GD3 antigen by FACS. We demonstrate that: 1) After vaccination with GD3-KLH alone, no IgM or IgG antibodies against GD3 were detected and the median titer of anti-KLH antibodies was 1/3200. 2) After vaccination with GD3-KLH plus 10 μg SQS-101, SQS-102 or SQS-103, or with positive control SQS-21, the boost antibody responses were similar with median anti-GD3 IgM titers of varies from 1/320 to 640, and anti-KLH IgG titers of 1/409,600 to 1,638,400. 3) SQS-21, SQS-101, SQS-102 and SQS-103, at the 50μg dose were each toxic with weight loss greater than 10% detected in most mice, but this was most extreme with SQS-102. The 10μg and 20μg dose of SQS-101 and 103, however, were well tolerated with no mice losing more than 10% weight. The 10μg and 20μg dose of SQS-102 mice lost more than 10% weight. 4) As expected anti-GD3 antibodies in each group were shown to react strongly with the cell surface of GD3 positive cancer cell lines by FACS. 5) These novel, amide-modified, non-natural synthetic saponin adjuvants selected for improved stability demonstrated adjuvant effects in vivo that equaled or exceeded that of SQS-21 and had comparable toxicity when mixed with a GD3-KLH conjugate vaccine. Supported by grants from the NIH (PO1 CA 52477) and Mr. William H. and Mrs. Alice Goodwin and the Commonwealth Foundation for Cancer Research” and “The Experimental Therapeutics Center of Memorial Sloan-Kettering Cancer Center” and the Geoffrey Beene Cancer Research Center grant Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2417.