Mitotane enhances cytotoxicity of chemotherapy in cell lines expressing a multidrug resistance gene (mdr-1/P-glycoprotein) which is also expressed by adrenocortical carcinomas

Adrenal cortical carcinoma

Adrenal cortical carcinoma is a rare endocrine tumor for which complete surgical resection is the only potentially curative treatment. Accurate preoperative evaluation (biochemical and radiographic) of the patient who presents with an adrenal mass maximizes the opportunity for the patient to undergo a complete, margin-negative resection of the primary tumor, which is the most powerful prognostic variable for long-term survival. The response to chemotherapy or mitotane is modest in patients with advanced disease. Hopefully, an improved understanding of the molecular pathogenesis of this challenging tumor will lead to the development of more effective therapies in the future.

[Drug therapy of endocrine neoplasms. Part I: Thyroid neoplasms, adrenal neoplasms and parathyroid neoplasms]

BACKGROUND

The incidence of endocrine carcinomas is about 5.3 persons per 100,000 population. Most frequent are malignancies of the thyroid gland (about 89%).

THERAPY

Because of low incidences and missing prospective studies as well as radiotherapy and chemotherapy resistance, general accepted therapy guidelines for endocrine carcinomas are still missing. Surgery and radionucleotide treatment is generally the first-line therapy. Hormonal active carcinomas can be additionally treated with special substances such as octreotide and mitotane. Chemotherapy is frequently not effective. Widely used substances are cyclophosphamide, cisplatin, doxorubicine, dacarbazine, vincristine and etoposide. This first part of the review will present medical therapies of thyroid carcinomas, adrenal carcinomas and parathyroid carcinomas. The second part in one of the next issues will focus on less frequent endocrine carcinomas of the gastrointestinal tract.

Gene rearrangement: a novel mechanism for MDR-1 gene activation

Drug resistance, a major obstacle to cancer chemotherapy, can be mediated by MDR-1/P-glycoprotein. Deletion of the first 68 residues of MDR-1 in an adriamycin-selected cell line after a 4;7 translocation, t(4q;7q), resulted in a hybrid mRNA containing sequences from both MDR-1 and a novel chromosome 4 gene. Further selection resulted in amplification of a hybrid gene. Expression of the hybrid mRNA was controlled by the chromosome 4 gene, providing a model for overexpression of MDR-1. Additional hybrid mRNAs in other drug-selected cell lines and in patients with refractory leukemia, with MDR-1 juxtaposed 3' to an active gene, establishes random chromosomal rearrangements with overexpression of hybrid MDR-1 mRNAs as a mechanism of acquired drug resistance.

Steroid treatment, accumulation, and antagonism of P-glycoprotein in multidrug-resistant cells

According to multiple reports, progesterone is not transported by P-glycoprotein (Pgp), which mediates multidrug resistance through active drug efflux. However, progesterone has been shown to block Pgp- mediated efflux of other drugs. To extend these observations and to examine the effect of modulating Pgp phosphorylation, the accumulation of progesterone and 14 other steroids in untreated and calphostin C-treated multidrug-resistant human colon carcinoma SW620 Ad300 cells was compared to the accumulation in parental SW620 cells. However, the accumlation of more hydrophilic steroids was reduced by as much as 50%. Progesterone and progesterone-like compounds, however were potent inhibitors of Pgp-mediated vinblastine efflux; increased antagonism correlated with increased steroid hydrophobicity. Treatment with calphostin C, a PKC inhibitor which decreases Pgp phosphorylation, increased progesterone efflux, modulated Pgp antagonism by steroids, and inhibited photoaffinity labeling of Pgp by progesterone. These results extend previous observations that Pgp can mediate the transport of, and be antagonized by, a variety of steroids and that these properties vary with both steroid's hydrophobicity and the phosphorylated state of Pgp.

NCI series of cell lines: an historical perspective

The NCI series of cell lines represent a unique collection of permanent human tumor cell lines established by one laboratory over a period of approximately 16 years. More than 300 cell lines were established, mainly from human lung cancers (both small cell and non-small cell types). In addition, smaller numbers of lines were established from rare and unusual tumors such as cutaneous T cell lymphomas, myelomas and adrenal cortical carcinoma. The T cell lines played a pivotal role in the isolation of human retroviruses including HTLV-1 and HIV. The establishment of such a large panel of lines was aided by the development of defined media for culturing specific cell types. The lines are well characterized, and full clinical data are available for most of them. Many of the lines have been deposited with the American Type Culture Collection, Rockville, MD, where they are readily available for a modest handling fee. The lines have been widely distributed to investigators, and have had a major impact on biomedical research.

Expression of P-glycoprotein in relation to clinical manifestation, treatment and prognosis of adrenocortical cancer

The presence of P-glycoprotein, associated with multiple drug resistance and present in the normal adrenal cortex, was studied in 15 cases of adrenocortical carcinoma. P-glycoprotein was found in eight tumours; no correlation was found with clinical presentation, steroid production or histological index. 10 patients received mitotane. Remarkably, 3 patients with P-glycoprotein-positive tumours achieved complete remission. On the other hand, 2 patients with P-glycoprotein-negative tumours showed progression of the disease despite mitotane treatment. These findings suggest that the expression of P-glycoprotein in adrenocortical carcinoma is not related to clinical manifestations, steroid production, histological index or response to mitotane therapy.