Membrane transport proteins in human melanoma: associations with tumour aggressiveness and metastasis.

BACKGROUND: Malignant melanoma, generally described as incurable, is notoriously refractory to chemotherapy. The mechanisms contributing to this have not yet been defined and the contributions of drug efflux pumps, implicated in chemo-resistance of many other cancer types, have not been extensively investigated in melanoma. METHODS: In this study, expression of multi-drug resistant (MDR1/P-gp and MRP-1) proteins was examined, by immunohistochemistry, in archival specimens from 134 melanoma patients. This included 92 primary tumours and 42 metastases. RESULTS: On assessing all specimens, MRP-1 and MDR1/P-gp expression was found to be common, with the majority (81%) of melanomas expressing at least one of these efflux pumps. Although there is significant association between expression of these pumps (P=0.007), MRP-1 was found to be the predominant (67% of cases) form detected. chi(2) analysis showed significant associations between expression of MRP-1 and/or MDR1/P-gp and the aggressive nature of this disease specifically increased Breslow's depth, Clark's level and spread to lymph nodes. This association with aggressiveness and spread is further supported by the observation that a significantly higher percentage of metastases, than primary tumours, express MRP-1 (91% vs 57%; P<0.0001) and MDR1/P-gp (74% vs 50%; P=0.010). CONCLUSION: The predominant expression of these pumps and, in particular, MRP-1 suggests that they may be important contributors to the inherent aggressive and resistant nature of malignant melanoma.

Methods for generation of monoclonal antibodies to the very small drug hapten, 5-benzimidazolecarboxylic acid.

Drug-specific monoclonal antibodies (MAbs) were produced against the very small drug hapten (162.15 Da), 5-benzimidazolecarboxylic acid, an analogue of 2-(4-Thiazolyl)benzimidazole (TBZ) but lacking the thiol group. TBZ is widely used as a broad-spectrum anthelmintic in various animal species and humans and also as a food preservative and agricultural fungicide. The anti-5-benzimidazolecarboxylic acid antibodies produced have potential use for extraction and/or detection of protein-bound residue forms of TBZ. Three in vivo immunisation regimes (with combinations of two related small drug haptens and two different adjuvants/carrier molecules) and an in vitro immunisation procedure using a combination of three related unconjugated small drug haptens were investigated. Specificity for the hapten immunogen/s was initially determined using two different ELISA procedures. BIACORE analysis, in conjunction with drug binding inhibition studies, was used to confirm the specificity of a small number of selected clones. In vivo immunisation with a drug molecule conjugated to a lipopeptide/T-cell epitope, which acts both as a carrier molecule and an adjuvant was the most useful of the methods tested for the production of specific MAbs to a typically very small hapten with low immunogenic properties.

MDR1 expression is associated with adverse survival in melanoma of the uveal tract.

Metastatic uveal melanoma is profoundly chemoresistant and has a very poor outcome. We have previously shown that the MDR1 gene and its gene product P-glycoprotein (P-gp), which are known to cause drug resistance in cancer cells, are expressed in ocular melanoma. Overexpression of MDR1 has been associated with a poor survival in some tumor types treated by chemotherapy and in some untreated tumours. To assess whether MDR1 expression is of prognostic value in uveal melanoma, we evaluated the expression of MDR1 by immunohistochemistry in 108 cases. Three semiquantitative grades were used to evaluate positive staining. We detected MDR1 expression in 80% of cases; 28% showed grade I staining; 30%, grade II staining; and 22%, grade III staining. There was a statistically significant association (P=.004) between MDR1 expression by tumor cells and shorter survival times (n=96), which was most striking at grade III levels of expression. Multivariate analysis showed that MDR1 expression is an independent prognostic indicator of poor survival. We conclude that (1) MDR1 may be involved in chemoresistance and tumor propagation in primary uveal melanoma, and (2) increasing levels of expression are prognostically significant and may prove a useful marker of tumor invasiveness, independent of established prognostic factors.

Co-expression of MDR-associated markers, including P-170, MRP and LRP and cytoskeletal proteins, in three resistant variants of the human ovarian carcinoma cell line, OAW42.

Variants of the human ovarian carcinoma cell line, OAW42, exhibiting low-level intrinsic resistance (OAW42-SR) and drug-induced higher-level resistance (OAW42-A1 & OAW42-A), were studied along with a sensitive clonal population (OAW42-S) which was isolated from OAW42-SR. Expression of the MDR-associated protein P-170, the more recently discovered LRP (lung resistance-related protein) and MRP (multidrug resistance-associated protein), topoisomerase II alpha and beta, GST pi and the cytoskeletal proteins, cytokeratin 8 and vimentin, were studied (using immunocytochemistry and Western blotting techniques) in conjunction with drug (doxorubicin) accumulation and subcellular distribution. Expression of mRNA for P-170, MRP, topoisomerase 11 alpha and beta and GST pi was studied using RT-PCR (reverse transcriptase polymerase chain reaction). Results indicate differential co-expression of four MDR-associated parameters (P-170, MRP, LRP and reduced topoisomerase II alpha and beta) in the OAW42-SR and OAW42-A1 variants, whereas resistance in the OAW42-A variant appeared to be mainly P-170 mediated. Comparable amounts of MRP and greater amounts of LRP were detected in the OAW42-S cells compared to the OAW42-SR variant (which showed increased resistance compared to the OAW42-S cells), but all cell lines expressed similar low-level amounts of MRP mRNA (by RT-PCR). GST pi levels did not differ markedly between variants. Increased levels of the cytoskeletal proteins were observed with increasing levels of resistance. The relative resistance of the variants, OAW42-SR and OAW42-A1, compared with OAW42-S was seen to change during increased serial passaging of the cells. There was greater drug accumulation by the sensitive OAW42-S cell line compared with that of the resistant variants, particularly the most highly resistant OAW42-A cells. Both verapamil and cyclosporin A effectively restored the accumulation defects seen in the resistant variants, cyclosporin A being the more effective of the two. Sub-cellular location of drug was predominantly in the nucleus with maximum levels seen in the sensitive OAW42-S variant and minimum levels in the most resistant OAW42-A clone.