[The expression of mRNA and SDS-PAGE of L1210 cell strains and its cloned cells].

OBJECTIVE: To examine the expression difference of mRNA of L1210 cell strains and its cloned cells and discuss the methods for quality control of cell strains. METHODS: We used SDS-PAGE to observe the difference of protein and performed in situ hybridization to examine the expression of mRNA with the use of 6 cDNA probes that were marked by biotin. RESULTS: The number of protein bands of L1210 from Beijing Cancer Institute was 32. The number of protein bands of the two cloned cells L3E11 and L3F9 was 31. The 6 cDNA probes (p16, c-fos, c-jun, c-myc, p21, and p53 mRNA) were found to be existing in Beijing Cancer Institute L1210 and two different cloned cell strains. Expression of c-myc, c-fos, p53 mRNA could distinguish L3E11 and L3F9 cloned cells.

Characterization of a human alternatively spliced truncated reduced folate carrier increasing folate accumulation in parental leukemia cells.

Human CEM-7A cells established by gradual deprivation of leucovorin from the growth medium, display 100-fold overexpression of methotrexate transport activity. We found that this was associated with 10-fold reduced folate carrier gene amplification and 50-fold overexpression of both the principal 3 kb reduced folate carrier transcript and, surprisingly, a novel truncated 2 kb reduced folate carrier mRNA poorly expressed in parental CEM cells. The molecular basis for the generation of this truncated reduced folate carrier transcript and its potential functional role in folate accumulation were studied. Reduced folate carrier genomic and cDNA sequencing revealed that the truncated transcript had an internal deletion of 987 nucleotides which was a result of an alternative splicing utilizing a cryptic acceptor splice site within exon 6. This deletion consisted of the 3'-most 480 nucleotides of the reduced folate carrier ORF and the following 507 nucleotides of the 3'-UTR. These resulted in a truncated reduced folate carrier protein, which lacks the C-terminal 160 amino acids, but instead contains 58 new C-terminal amino acids obtained from reading through the 3'-UTR. Consequently, a truncated reduced folate carrier protein is generated that lacks the 12th transmembrane domain and contains a new and much shorter C-terminus predicted to reside at the extracellular face. Western analysis with plasma-membrane fraction from CEM-7A cells revealed marked overexpression of both a broadly migrating approximately 65-90 kDa native reduced folate carrier and a approximately 40-45 kDa truncated reduced folate carrier, the core molecular masses of which were confirmed by in vitro translation. However, unlike the native reduced folate carrier, the truncated reduced folate carrier protein failed to bind the affinity labels NHS-[3H]MTX and NHS-[3H]folic acid. Stable transfection of the truncated reduced folate carrier cDNA into mouse L1210 leukemia cells: increased folate accumulation, decreased their leucovorin and folic acid growth requirements, and increased their sensitivity to methotrexate. This constitutes the first documentation of an expressed alternatively spliced truncated reduced folate carrier that, when coexpressed along with the native carrier, augments folate accumulation and consequently decreases the cellular folate growth requirement. The possible mechanisms by which the truncated reduced folate carrier may increase folate accumulation and/or metabolism in cells coexpressing the truncated and native reduced folate carrier are discussed.

Synthesis, physical properties, and antitumor activity of tetraplatin and related tetrachloroplatinum(IV) stereoisomers of 1,2-diaminocyclohexane.

The synthesis, physical properties, and antitumor activity of the cis-, d,l-trans-, d-trans-, and l-trans- stereoisomers of 1,2-diaminocyclohexane tetrachloroplatinum(IV) are described. The objective of the study was to produce a platinum complex with activity against cisplatin-resistant tumor cells and with suitable pharmaceutical properties for formulation development. The isomers had the following solubilities in saline: cis-, 2 mg/ml; d,l-trans-, 6.5 mg/ml; and d-trans- and l-trans-, 15-16 mg/ml. The four complexes showed slightly better activity than cisplatin against the ip implanted murine L1210 leukemia. In contrast to cisplatin, all complexes produced significant increases in life span against L1210/cisplatin, a subline of L1210 with acquired resistance to cisplatin. However, the cis- isomer was less active against L1210/cisplatin. The d,l-trans- isomer (tetraplatin) was selected for further studies based on greater ease for large-scale synthesis. It showed superior activity to cisplatin against P388/cisplatin and like cisplatin showed significant and reproducible activity against the ip implanted B16 melanoma, ip implanted M5076 sarcoma, ip implanted P388 leukemia, and MX-1 human breast xenograft implanted under the renal capsule. Purity and stability (greater than 24 hours in saline) were evaluated by high-performance liquid chromatography and found to be suitable for development of a parenteral dosage form. Preliminary studies in a rat model (to be reported elsewhere) showed it to be less nephrotoxic than cisplatin on a molar basis and worthy of further study.

Drug resistance induction and cross-resistance studies with Pt-complexes.

In vitro drug resistance was induced against cis-diamminedichloroplatinum(II) (cis-DDP), 1,2-diaminocyclohexaneplatinum-(II)citrate (PEX) and 1,2-diaminocyclohexaneplatinum(II)glucarate (PTU) in L1210 leukemia cell line. Using the resistant sublines cross-resistance was found between cis-DDP and cis-diamminecyclobutane-1,1-dicarboxylatoplatinum(II) (CBDCA) and between the three 1,2-diaminocyclohexane (DACH) derivatives tested. No (or low degree) cross-resistance was found between cis-DDP and DACH derivatives.