Aphidicolin decreases ex vivo resistance to cytosine arabinoside in childhood acute leukaemia.

In order to assess the effect of the DNA polymerase inhibitor aphidicolin on resistance to cytosine arabinoside, blast cells from 15 children with ALL and 9 with AML were exposed to a range of concentrations of ara-C +/- aphidicolin. Cell survival was measured using the MTT assay. Aphidicolin significantly increased sensitivity to ara-C in blast cells from both ALL (p=0.001) and AML (p<0.01). The median fold increase (sensitisation ratio) for ALL was 3.4 (range 1.2-13.6) compared to 12.4-fold (range 6.0-148) for AML blasts (p=0.005). There was a striking relationship between increasing ara-C resistance and increasing effect of aphidicolin in AML (p<0.001) but not ALL (p>0.05). These remarkable results suggest that aphidicolin should be considered for future clinical trials as a modulator of ara-C resistance, particularly in AML.

Ex vivo chemosensitivity to mitomycin C in bladder cancer and its relationship with P-glycoprotein and apoptotic factors.

BACKGROUND: Intravesical treatment with mitomycin C (MMC) leads to a complete response rate of around 40% in superficial bladder cancer (TCC). In order to determine in advance which patients will fail to respond, we describe a study assessing the feasibility of applying the ATP assay to test the chemosensitivity of samples from patients with this disease. MATERIALS AND METHODS: TURBT or biopsy samples were received from 27 patients, 23 of which were suitable for the ATP assay (16 primary tumours and 7 recurrences). RESULTS: The success rate of the assay was 91%. There was a marked variation in the effect of MMC between patients with a > 50-fold range in LC50 values (drug concentration required to kill 50% of cells) from 2.99- > 150 microM with a median value of 22.4 microM. We were unable to determine any overall correlation between chemosensitivity and tumour stage or grade or the treatment status of the patient in this small data set. P-glycoprotein status and caspase-3 levels were assessed on these samples using immunohistochemistry but there did not appear to be any relationship between either of these parameters and MMC resistance. Apoptotic counts and mitotic counts were also measured but, whilst these appeared to correlate with grade (p < 0.01), there was no overall significant relationship established with MMC chemosensitivity. CONCLUSION: This study suggests that it is possible to use the ATP assay for chemosensitivity testing in TCCs. Despite a lack of overall correlation between ex vivo MMC resistance and the conventional prognostic factors tested, further studies are warranted in a larger data set to test the ability of this technique to predict clinical outcome in this disease.

Assessment of the classical MDR phenotype in epithelial ovarian carcinoma using primary cultures: a feasibility study.

This in vitro feasibility study has assessed a number of techniques and their applicability when looking at the role of multidrug resistance (MDR) in solid tumours. Fresh tumour material was obtained from 34 patients, (11 previously treated, 23 untreated) with ovarian adenocarcinoma. Doxorubicin sensitivity was measured using the MTT assay +/- the cyclosporins, Pgp expression was assessed by immunocytochemistry with the MRK-16 MoAb and flow cytometry was used to assess intracellular drug accumulation +/- PSC 833. 85% of samples showed some evidence of modest chemosensitisation by the cyclosporins (median 1.74-fold). We saw a marked variation in the number of Pgp positive cells between patients (1-87%, median 31%). 63% of samples tested showed an enhancement of DNR accumulation in the presence of PSC 833, with a median increase of 7% (sample range 0-29%). The present study highlights some of the technical difficulties encountered when working with fresh tumour material ex vivo. We conclude that screening of patients for their suitability to enter clinical trials incorporating MDR modulating agents is technically demanding, but feasible.