Specificity of drug transport mediated by CaMDR1: a major facilitator of Candida albicans.

CaMDR1 encodes a major facilitator superfamily (MFS) protein in Candida albicans whose expression has been linked to azole resistance and which is frequently encountered in this human pathogenic yeast. In this report we have overexpressed CaMdr1p in Sf9 insect cells and demonstrated for the first time that it can mediate methotrexate (MTX) and fluconazole (FLC) transport. MTX appeared to be a better substrate for CaMdr1p among these two tested drugs. Due to severe toxicity of these drugs to insect cells, further characterization of CaMdr1p as a drug transporter could not be done with this system. Therefore, as an alternative, CaMdr1p and Cdr1p, which is an ABC protein (ATP binding cassette) also involved in azole resistance in C. albicans, were independently expressed in a common hypersensitive host JG436 of Saccharomyces cerevisiae. This allowed a better comparison between the functionality of the two export pumps. We observed that while both FLC and MTX are effluxed by CaMdr1p, MTX appeared to be a poor substrate for Cdr1p. JG436 cells expressing Cdr1p thus conferred resistance to other antifungal drugs but remained hypersensitive to MTX. Since MTX is preferentially transported by CaMdr1p, it can be used for studying the function of this MFS protein.

Uracil with ftorafur and low dose oral folinic acid in advanced colorectal cancer.

BACKGROUND: Low dose oral Folinic acid was used together with uracil with ftorafur (UFT) producing some response with low toxicity in advanced colorectal cancer. However, the 28 day regimen produced 20 per cent severe (grade III, IV) diarrhea. This study required 21 days' treatment to evaluate the response rate and toxicity in advanced colorectal cancer. METHOD: UFT 300 mg/m2/day together with oral Folinic acid 7.5 mg/dose for 21 days with 7 days rest were required to treat 28 cases of recurrent or metastatic colorectal cancer. RESULTS: Partial response was seen in 13.6 per cent of 22 evaluable cases and minimal response seen in 18.2 per cent. The majority (77%) of these patients had previously been treated with 5-fluorouracil (5-FU). These results are comparable to other studies. Toxicity was low with 3.3 per cent grade III, IV diarrhea. CONCLUSION: This regimen produced some activity in metastatic colorectal cancer with low toxicity.

Unique bioactivation of tiazofurin--studies with resistant cells.

Using resistant cells mechanism of action of new oncolytic nucleoside, tiazofurin (2-beta-D-ribofuranosyl thiazole-4 carboxamide, RTC) was studied in tissue cultured cells of Chinese Hamster Ovary cells (CHO-cells). Tiazofurin got converted in CHO-cells to tiazofurin-monophosphate and to NAD-analogue, a potent inhibitor of inosinate dehydrogenase. Resistant cells produced tiazofurin-5'-monophosphate in vitro but had a much reduced capacity to produce NAD-analogue, indicating absence of any effect of tiazofurin on incorporation of [14C]formate into guanine, inhibition of inosinate dehydrogenase as well as GTP levels in resistant cells. Using competition with various possible substrates it is found that the initial tiazofurin metabolism is catalysed by nicotinamide nucleoside kinase and NAD-analog formation is mediated by NAD-pyrophosphorylase. Decreased activity of the latter enzyme found in tiazofurin resistant cells not only inhibited the NAD analog formation from tiazofurin-5'-monophosphate but also the NAD-formation from nictotinamide-5'-monophosphate.