M. Schott 1 M. Reincke 1 D. Ortmann 2 S. R. Bornstein 1
Immunotherapy: New Strategies for the Treatment of Adrenocortical Carcinoma
Adrenocortical carcinoma (ACC) is a rare malignancy associated with a dismal prognosis. As stated at the 2002 National Institute of Science Consensus Conference, the likelihood of having a malig- nant adrenal tumor is clearly related to the size of an adrenal mass - 6% of tumors greater than 4 cm are malignant, whereas as many as 25% of masses greater than 6 cm present as ACC. At the time of diagnosis, approximately 40-70% of tumors have al- ready undergone metastatic spread [1]. ACC has a very poor prognosis with an overall 5-year survival of less than 10-25% [1,2]. The treatment options for metastatic ACC are limited. Al- though ACC is potentially curable in early stages with surgical re- section, only 30% of tumors have been reported as confined to the adrenal gland at the time of initial presentation [3]. Mitotane (o,p’DDD), an analogue of DDT insecticide, has been used in the treatment of ACC either alone or in combination with other agents. Although early studies in the era before modern imaging modalities reported high response rates, it now is clear that mi- totane has a response rate in about a quarter of all patients at best. Moreover, these tumors also fail to respond to conventional therapy, including chemotherapy, with agents such as doxorubi- cin, vincristine or etoposide, or with radiation [4]. Other thera- pies such as image-guided percutaneous radiofrequency abla- tion may help to treat local metastases; however, this does not have any influence on clinical outcome in these patients [5].
The ineffectiveness of these modalities coupled with the poten- tially harmful effects of such treatments emphasize the need to search for novel tumor therapies. This includes alternative strat- egies such as gene therapy using adenoviral and retroviral vec- tors, immunotherapy with DNA vaccination, antigen-presenting dendritic cells (DCs), or a combination of these regimens. A
gene therapy-based approach using transcomplementing adeno- viral vectors resulted in a greater tumor volume reduction in an ACC mouse model [6]. A comparable in vitro study with various adenoviral deletion mutants induced an impairment of adreno- cortical steroidogenesis [7]. Finally, active immunotherapy with autologous DCs pulsed with tumor antigens may serve as a pro- mising adjuvant therapy in the treatment of ACC. DCs are anti- gen-presenting cells involved in the induction of primary im- mune responses. Several protocols have been generated for the purpose of obtaining large numbers of activated human DCs from either CD34+ bone-marrow cells or peripheral blood mono- cytes by culturing in media supplemented with GM-CSF and IL-4, followed by stimulation with TNF-« or monocyte-conditioned medium [8-10]. The unique ability of DCs to activate naive and memory CD4- and CD8-positive T-cells suggested that they could be used for the induction of specific anti-tumor immunity. Within the past few years, many in vitro and in vivo studies in ro- dents and humans have demonstrated that immunization with these cells pulsed with tumor antigens results in protective im- munity and rejection of established tumors in various malignan- cies. Important data were reported in diverse carcinomas with as yet identified tumor-specific antigens or shared antigens such as malignant melanoma [11,12], B-cell lymphoma [13], prostate cancer [14] and other malignancies. Because of the lack of specif- ic tumor antigens in endocrine cancers such as in ACC, there are two alternatives for DC vaccination: first, preparations of autolo- gous tumor cells could be used for antigen delivery within DC therapy. This approach was applied in our own pilot studies in neuroendocrine pancreas carcinoma and parathyroid carcinoma patients in advanced disease stages resulting in tumor lysate (TL)-specific anti-tumor immunity [15,16]. Second, cell-specific
Affiliation
1 Department of Endocrinology, Heinrich-Heine-University Duesseldorf, Duesseldorf, Germany
2 Department of Internal Medicine 2, Divison of Endocrinology, Albert-Ludwigs-University of Freiburg, Hugstetter Str. 55, 79106 Freiburg, Germany
Correspondence
M. Schott . Department of Endocrinology . Heinrich-Heine-University Duesseldorf . Moorenstr. 5 . 40225 Duesseldorf . Germany . E-Mail: schottmt@uni-duesseldorf.de
Received 5 March 2003 . Accepted after revision 27 March 2003
Horm Metab Res 2003; 35: 451-453 @ Georg Thieme Verlag Stuttgart . New York . ISSN 0018-5043
antigens, such as specific proteins involved in the synthesis of hormones or hormones themselves, might be used for inducing a cytotoxic T-cell response against ACC. This approach has al- ready been reported successful in inducing a Th1-dominated cel- lular immune and clinical responses in metastasized medullary thyroid carcinomas [17,18].
Based on these results, a multitude of adrenocortical enzymes such as 11ß-hydroxylase (P450c11), 21-hydroxylase (P450c21) and P450scc (side chain cleavage enzyme) as well as regulatory proteins such as steroidogenic acute regulatory protein (StAR) and DAX-1 may serve as specific targets for cytotoxic immune re- sponse in ACC. Recently, we have shown that 21-hydroxylase, which represents a key enzyme essential for normal zona glo- merulosa and fasciculata function, is expressed in cortisol-pro- ducing (but not aldosterone-producing) carcinomas [19]. Similar data were demonstrated for the P450 side chain cleavage en- zyme with some expression in non-functional adrenal carcino- mas [20]. Steroidogenic acute regulatory protein (StAR) may prove to be an interesting and complementary target for anti-tu- mor immune response; this protein is responsible for the trans- port of cholesterol through the outer to the inner mitochondrial membrane during the process of steroid biosynthesis. StAR ex- pression has not only been demonstrated in adrenocortical ade- nomas but also in carcinomas [21], and can therefore be used within an immunotherapy approach. DAX-1, which is essential for normal fetal development of the adrenal cortex, has been re- ported to act as a transcriptional repressor of steroidogenic StAR, suppressing steroidogenesis. Since DAX-1 is expressed in an in- termediate fashion in non-aldosterone-producing adrenal carci- nomas, it may also serve as a potent target within the adrenal gland [22]. As proof of principal, we investigated StAR as a poten- tial target for an immune based therapy in a syngen mouse tu- mor model using DNA vaccination [23]. BALB/c mice were vacci- nated three times within 3 weeks with cDNA expression vectors encoding for StAR or a control peptide followed by vaccine virus boosting. At four weeks, mice were subcutaneously inoculated with SP-2.0 myeloma tumor cells stably expressing StAR or con- trol proteins. This vaccination strategy induced a specific cyto- toxic T-cell response as measured by ELISPOT. Compared to con- trol experiments vaccination against StAR protein resulted in a highly efficient protection against SP-2.0 tumor formation. No side effects on normal adrenocortical function were observed. These results demonstrate that tissue specific antigens such as StAR may serve as a potential target for immune therapy-based treatment strategies.
The key question besides the choice of target protein to be used is, however, how to present these antigens to the immune sys- tem in order to induce an efficient anti-tumor response. Trans- fection of autologous DCs with antigen-specific plasmid-DNA or RNA, respectively, promises to be a very elegant method since it has been successfully demonstrated in prostate cancer [14]. This approach would then use the advantage of efficient antigen transfection together with the highly effective antigen-present- ing capability of DCs. Alternatively, these potent antigens could also be delivered by retroviral or adenoviral vectors coding for these targets by subcutaneous injections or gene-gun delivery. As mentioned, we have shown that adenoviral vectors them- selves can also impair adrenocortical steroidogenesis [7]. There-
fore, this approach would even help to ameliorate the hormonal effects in patients with ACC suffering from Cushing’s syndrome or virilization in cases of ineffective anti-tumor response. Finally, both approaches could also be used in combination. In animals, DCs transduced with adenoviruses or retroviruses coding for an- tigens were successfully used to induce protective and therapeu- tic anti-tumor response against various tumor types [24,25].
In summary, tissue-specific enzymes or regulatory proteins might be used in the future as targets to induce an immune re- sponse associated with the elimination of endocrine carcinoma cells in spite of the lack of defined tumor antigens in ACC. DCs, which might be pulsed with proteins or transfected with adeno- viruses, should than represent an elegant vehicle to present these antigens to the immune system in order to induce a strong immune response.
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