Immunological and antitumor effects of IL-23 as a cancer vaccine adjuvant

The promising, but modest, clinical results of many human cancer vaccines indicate a need for vaccine adjuvants that can increase both the quantity and the quality of vaccine-induced, tumor-specific T cells. In this study we tested the immunological and antitumor effects of the proinflammatory cytokine, IL-23, in gp100 peptide vaccine therapy of established murine melanoma. Neither systemic nor local IL-23 alone had any impact on tumor growth or tumor-specific T cell numbers. Upon specific vaccination, however, systemic IL-23 greatly increased the relative and absolute numbers of vaccine-induced CD8(+) T cells and enhanced their effector function at the tumor site. Although IL-23 specifically increased IFN-gamma production by tumor-specific T cells, IFN-gamma itself was not a primary mediator of the vaccine adjuvant effect. The IL-23-induced antitumor effect and accompanying reversible weight loss were both partially mediated by TNF-alpha. In contrast, local expression of IL-23 at the tumor site maintained antitumor activity in the absence of weight loss. Under these conditions, it was also clear that enhanced effector function of vaccine-induced CD8(+) T cells, rather than increased T cell number, is a primary mechanism underlying the antitumor effect of IL-23. Collectively, these results suggest that IL-23 is a potent vaccine adjuvant for the induction of therapeutic, tumor-specific CD8(+) T cell responses.

Platinated DNA adducts enhance poisoning of DNA topoisomerase I by camptothecin

Camptothecins constitute a novel class of chemotherapeutics that selectively target DNA topoisomerase I (Top1) by reversibly stabilizing a covalent enzyme-DNA intermediate. This cytotoxic mechanism contrasts with that of platinum drugs, such as cisplatin, which induce inter- and intrastrand DNA adducts. In vitro combination studies using platinum drugs combined with Top1 poisons, such as topotecan, showed a schedule-dependent synergistic activity, with promising results in the clinic. However, whereas the molecular mechanism of these single agents may be relatively well understood, the mode of action of these chemotherapeutic agents in combination necessitates a more complete understanding. Indeed, we recently reported that a functional homologous recombination pathway is required for cisplatin and topotecan synergy yet represses the synergistic toxicity of 1-beta-D-arabinofuranosyl cytidine in combination with topotecan (van Waardenburg, R. C., de Jong, L. A., van Delft, F., van Eijndhoven, M. A., Bohlander, M., Bjornsti, M. A., Brouwer, J., and Schellens, J. H. (2004) Mol. Cancer Ther. 3, 393-402). Here we provide direct evidence for Pt-1,3-d(GTG) poisoning of Top1 in vitro and demonstrate that persistent Pt-DNA adducts correlate with increased covalent Top1-DNA complexes in vivo. This contrasts with a lack of persistent lesions induced by the alkylating agent bis[chloroethyl]nitrosourea, which exhibits only additive activity with topotecan in a range of cell lines. In human IGROV-1 ovarian cancer cells, the synergistic activity of cisplatin with topotecan requires processive DNA polymerization, whereas overexpression of Top1 enhances yeast cell sensitivity to cisplatin. These results indicate that the cytotoxic activity of cisplatin is due, in part, to poisoning of Top1, which is exacerbated in the presence of topotecan.

Homologous recombination is a highly conserved determinant of the synergistic cytotoxicity between cisplatin and DNA topoisomerase I poisons

Phase I and II clinical trails are currently investigating the antitumor activity of cisplatin and camptothecins (CPTs; DNA topoisomerase I poisons), based on the dramatic synergistic cytotoxicity of these agents in some preclinical models. However, the mechanistic basis for this synergism is poorly understood. By exploiting the evolutionary conservation of DNA repair pathways from genetically tractable organisms such as budding and fission yeasts to mammalian cells, we demonstrate that the synergism of CPT and cisplatin requires homologous recombination. In yeast and mammalian cell lines defective for RAD52 and XRCC2/3, respectively, the combination of these agents proved antagonistic, while greater than additive activity was evident in isogenic wild-type cells. Homologous recombination appears to mediate a similar interaction of X-rays and CPT, but antagonizes the synergism of cytarabine (Ara-C) with CPT. These findings suggest that homologous recombination comprises an evolutionarily conserved determinant of cellular sensitivity when CPTs are used in combination with other therapeutics.

Homologous recombination is a highly conserved determinant of the synergistic cytotoxicity between cisplatin and DNA topoisomerase I poisons

Phase I and II clinical trails are currently investigating the antitumor activity of cisplatin and camptothecins (CPTs; DNA topoisomerase I poisons), based on the dramatic synergistic cytotoxicity of these agents in some preclinical models. However, the mechanistic basis for this synergism is poorly understood. By exploiting the evolutionary conservation of DNA repair pathways from genetically tractable organisms such as budding and fission yeasts to mammalian cells, we demonstrate that the synergism of CPT and cisplatin requires homologous recombination. In yeast and mammalian cell lines defective for RAD52 and XRCC2/3, respectively, the combination of these agents proved antagonistic, while greater than additive activity was evident in isogenic wild-type cells. Homologous recombination appears to mediate a similar interaction of X-rays and CPT, but antagonizes the synergism of cytarabine (Ara-C) with CPT. These findings suggest that homologous recombination comprises an evolutionarily conserved determinant of cellular sensitivity when CPTs are used in combination with other therapeutics.

Tumor regression and autoimmunity after reversal of a functionally tolerant state of self-reactive CD8+ T cells

Many tumor-associated antigens are derived from nonmutated "self" proteins. T cells infiltrating tumor deposits recognize self-antigens presented by tumor cells and can be expanded in vivo with vaccination. These T cells exist in a functionally tolerant state, as they rarely result in tumor eradication. We found that tumor growth and lethality were unchanged in mice even after adoptive transfer of large numbers of T cells specific for an MHC class I-restricted epitope of the self/tumor antigen gp100. We sought to develop new strategies that would reverse the functionally tolerant state of self/tumor antigen-reactive T cells and enable the destruction of large (with products of perpendicular diameters of >50 mm2), subcutaneous, unmanipulated, poorly immunogenic B16 tumors that were established for up to 14 d before the start of treatment. We have defined three elements that are all strictly necessary to induce tumor regression in this model: (a) adoptive transfer of tumor-specific T cells; (b) T cell stimulation through antigen-specific vaccination with an altered peptide ligand, rather than the native self-peptide; and (c) coadministration of a T cell growth and activation factor. Cells, vaccination, or cyto-kine given alone or any two in combination were insufficient to induce tumor destruction. Autoimmune vitiligo was observed in mice cured of their disease. These findings illustrate that adoptive transfer of T cells and IL-2 can augment the function of a cancer vaccine. Furthermore, these data represent the first demonstration of complete cures of large, established, poorly immunogenic, unmanipulated solid tumors using T cells specific for a true self/tumor antigen and form the basis for a new approach to the treatment of patients with cancer.

Topoisomerase I levels in white blood cells of patients with ovarian cancer treated with paclitaxel-cisplatin-topotecan in a phase I study

Topotecan stabilizes the topoisomerase I (Topo I) cleavable complex. We measured Topo I levels in white blood cells of patients with ovarian cancer treated with topotecan. Topotecan was given i.v. daily x 5 q 3 weeks in combination with paclitaxel (1 day before topotecan) and cisplatin (just prior topotecan). Our aim was to correlate Topo I levels to pharmacokinetics and toxicity. Topo I levels were determined using Western blotting and were expressed relative to the Topo I level present in 10 microg cell lysate of the human IGROV1 ovarian cancer cell line. We found no correlation between Topo I levels and (non-)hematological toxicity. Topo I levels after the fifth topotecan infusion were significantly negatively correlated with the AUC of topotecan (R = -0.64, p = 0.026), in contrast with Topo I levels prior to (R = -0.25, p = 0.4) and after (R = -0.30, p = 0.3) the first topotecan infusion. Topo I levels after the fifth topotecan infusion (48 +/- 27%, mean +/- SD) were higher than Topo I levels prior to and after the first topotecan infusion (3.0 +/- 4.7 and 2.7 +/- 3.6%, respectively) (p = 0.001). In conclusion, we detected a significant inverse correlation between Topo I level and topotecan AUC at day 5, and we found increasing Topo I levels during a daily x 5 schedule of treatment with topotecan.