Learned associations between effects of abused drugs and the drug administration environment play important roles in drug addiction. Histochemical and electrophysiological studies suggest that these associations are encoded in sparsely distributed nucleus accumbens neurons that are selectively activated by drugs and drug-associated cues. Although correlations between accumbens neuronal activity and responsivity to drugs and drug cues have been observed, no technique exists for selectively manipulating these activated neurons and establishing their causal role in behavioral effects of drugs and drug cues. Here we describe a novel method, termed ‘Daun02-inactivation method’, that selectively inactivates a minority of neurons activated by cocaine in an environment repeatedly paired with cocaine to demonstrate a causal role for these activated neurons in context-specific cocaine-induced psychomotor sensitization in rats. This method provides a new tool to study causal roles of selectively activated neurons in behavioral effects of drugs and drug cues and in other learned behaviors.

Numerous human tumor types, including ovarian cancer, display a significant expression of the CD44 family of cell surface proteoglycans. To develop tumor-targeted drugs, we have initially evaluated whether the CD44 ligand hyaluronic acid (HA) could serve as a backbone for paclitaxel (TXL) prodrugs. HA-TXL was prepared by modification of previous techniques. The in vitro cytotoxicity of HA-TXL against the CD44(+) human ovarian carcinoma cell lines SKOV-3ip and NMP-1 could be significantly blocked by preincubation with a molar excess of free HA. Female nude mice bearing intraperitoneal implants of NMP-1 cells were treated intraperitoneally with a single sub-maximum tolerated dose dose of HA-TXL or with multiple-dose regimens of paclitaxel (Taxol; Mead Johnson, Princeton, NJ) to determine the effects of these regimens on host survival and intraperitoneal tumor burden, with the latter being assessed by magnetic resonance imaging. NMP-1 xenografts were highly resistant to Taxol regimens, as host survival was only nominally improved compared to controls (T//C approximately 120), whereas single-dose HA-TXL treatment significantly improved survival in this model (T//C approximately 140; P = .004). In both NMP-1 and SKOV-3ip models, MR images of abdomens of HA-TXL-treated mice obtained shortly before controls required humane sacrifice revealed markedly reduced tumor burdens compared to control mice. This study is among the first to demonstrate that HA-based prodrugs administered locoregionally have antitumor activity in vivo.

The bis[(pivaloyloxy)methyl] [PIV2] derivative of 2'-deoxy-5- fluorouridine 5'-monophosphate (FdUMP) was synthesized as a potential membrane-permeable prodrug of FdUMP. The compound was designed to enter cells by passive diffusion and to revert to FdUMP after removal of the PIV groups by hydrolytic enzymes. The most convenient preparation of PIV2FdUMP was by condensation of 2'-deoxy-5-fluorouridine (FUdR) with PIV2 phosphate in the presence of triphenylphosphine and diethyl azodicarboxylate (the Mitsunobo reagent). PIV2FdUMP was stable in the pH range 1.0-4.0 (t1/2 > 100 h). It was also fairly stable at pH 7.4 (t1/2 = 40.2 h). In 0.05 M NaOH solution, however, it was rapidly degraded (t1/2 < 2 min). In the presence of hog liver carboxylate esterases, PIV2FdUMP was converted quantitatively to the mono-[(pivaloyloxy)methyl] [PIV1] analogue PIV1FdUMP. After a 24 h incubation, only trace amounts of FdUMP (1-3%) were observed, indicating that PIV1FdUMP is a poor substrate for carboxylate esterases. In mouse plasma, PIV2FdUMP was rapidly metabolized, first to PIV1FdUMP and then to FdUMP. With continued incubation, FUdR was formed, presumably due to further catabolism of FdUMP by plasma phosphatases or 5'-nucleotidases. Since PIV1FdUMP is a poor substrate for carboxylate esterase, the cleavage of the second PIV group is most likely mediated by plasma phosphodiesterases. The rate of degradation of PIV2FdUMP in the presence of acid and alkaline phosphatase, 5'-nucleotidase, or spleen phosphodiesterase was the same as that in buffer controls, indicating that the compound is not a substrate for these nucleotide catabolizing enzymes. The concentration of PIV2FdUMP and its 3'-O-acetyl ester (PIV2 3'-O-Ac-FdUMP) required to inhibit the growth of Chinese hamster ovary (CHO) cells in vitro to less than 50 cells per colony was 5 x 10(-6) M, the same as that required for 5-fluorouracil (FU). Both nucleotide prodrugs showed the same growth-inhibitory potency against a mutant CHO cell line that was 20-fold resistant to FU (CHO/FU). Administered intraperitoneally at optimal dosage for 5 consecutive days, PIV2FdUMP and PIV2 3'-O-Ac-FdUMP were as effective as FU at prolonging the life spans of mice bearing intraperitoneally implanted P388 leukemia. Both prodrugs retained full therapeutic activity against a P388 subline resistant to FU. Collectively, these data indicate that PIV2FdUMP and PIV2 3'-O-Ac-FdUMP are effective membrane-permeable prodrugs of FdUMP.

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We previously reported the synthesis of a series of doxorubicin analogue prodrugs that give rise to intensely cytotoxic metabolites in the presence of carboxylate esterases. We now report studies on structurally related beta-glucuronide prodrugs that are converted to similar potent metabolites in the presence of beta-glucuronidases. These prodrugs were prepared by reductive condensation of daunomycin or doxorubicin with methyl 1-O-[(1'RS)-1'-ethoxy-4'-oxobutyl]-2,3,4-tri-O-acetyl-beta-D- glucopyranosyluronate in the presence of sodium cyanoborohydride followed by base-mediated cleavage of the glucuronate protective groups. The doxorubicin derivatives were isolated in very low yield, most likely because of the inherent base lability of the parent aglycone. By contrast, fairly good yields of the more base-stable daunomycin analogues were obtained. The target daunomycin glucuronide, N-[(4"RS)-4"-ethoxy-4"-(sodium 1"'-O-beta-D-glucopyranuronate)butyl]daunorubicin (6a), had a half-life of 30 h when incubated at a concentration of 12 microM in aqueous 0.05 M phosphate buffer, pH 7.4, at 37 degrees C. Under identical conditions in the presence of 197 units/mumol of Escherichia coli beta-glucuronidase, 6a was hydrolyzed with a half-life of 1.7 h. The single metabolite observed was chromatographically identical with that formed from the hydrolysis of N-(4,4-diacetoxybut-1-yl)daunomycin by carboxylate esterases. 6a was approximately 10,000-fold more toxic to human A375 melanoma cells in the presence of E. coli beta-glucuronidase than in the absence of the enzyme. These findings indicate the therapeutic potential of anthracycline glucuronide prodrugs as independent entities or four use in conjunction with enzyme tissue-targeting strategies such as antibody-directed enzyme prodrug therapy (ADEPT) or gene-directed enzyme prodrug therapy (GDEPT).

Paclitaxel (Taxol) has demonstrated clinical activity in non-small-cell lung cancer (NSCLC), but its use has not led to marked improvements in survival. This ineffectiveness can in part be attributed to inadequate delivery of effective drug levels to the lung via systemic administration and to drug resistance mechanisms. Locoregional drug administration and the use of drug copolymers are possible approaches to address these issues. In this study, we evaluated the activity of a poly(L-glutamic acid)-paclitaxel (PGA-TXL) formulation administered by intratracheal injection to mice bearing orthotopic human NSCLC tumors (H460, H358). H460 cells were found to be sensitive to paclitaxel and PGA-TXL in vitro, in a time-and concentration-dependent manner. In preliminary acute toxicity studies, PGA-TXL administered by intratracheal injection was found to be much less toxic than paclitaxel, as anticipated. Mice into which H460 cells had been implanted by intratracheal injection were given single-dose intratracheal treatments with paclitaxel (1.2 or 2.4 mg/kg) or with PGA-TXL (15 mg/kg, paclitaxel equivalents) 1 week later. When the mice were sacrificed at up to 65 days after tumor implantation, they were evaluated grossly for tumor at bronchial, neck, and lung sites. Control mice had tumors in 60% of all three sites, and all of the control mice had tumors in at least one site. The low-and high-dose Taxol groups had fewer incidences at these three sites (27-33%) and 60 -80% of these mice had tumors in at least one site. The PGA-TXL mice displayed a low (13%) incidence at these sites, and only 40% had detectable tumors. In a subsequent survival study with the intratracheal H358 model, control mice had a mean life span of 95 days, whereas both the intratracheal Taxol (2.5 mg/kg, every 7th day for three doses) and the intratracheal PGA-TXL (20 mg/kg, paclitaxel equivalents, every 7th day for three doses) groups had improved survival (mean life spans: 133.5 and 136.5 days, respectively). In pilot studies intended to compare the feasibility of the development of paclitaxel aerosols suitable for clinical application, based either on Cremophor solutions or on PGA backbones, only the latter gave acceptable particle size distributions and flow rates. These results encourage the development and application of Cremophor-free copolymer formulations of paclitaxel for locoregional treatment (e.g., as aerosol) of endobronchial malignant diseases.

Bis(pivaloyloxymethyl) azidothymidine 5'-monophosphate (piv 2-AZTMP) was designed as a cell membrane-permeable precursor of AZTMP. We have reported previously that when incubated with CEM cells deficient in thymidine kinase, piv 2-AZTMP gives rise to intracellular AZTMP and the corresponding diphosphate (AZTDP) and triphosphate (AZTTP). Under similar conditions, no intracellular nucleotides were formed with AZT. However, the mechanism bỹ ich piv 2-AZTMP is converted to AZTMP has not been established. To address this question, we have used the recently developed 'on-line ISRP-cleaning' HPLC technique to investigate the stability and metabolic fate of piv 2-AZTMP (1) in RPMI 1640 medium, (2) in RPMI containing 10% heat-inactivated fetal calf serum, and (3) in CEM cell extracts. Similar studies were conducted starting with mono(pivaloyloxymethyl) azidothymidine 5'-monophosphate (piv 1-AZTMP).From the kinetics of these reactions, it appears that piv 2-AZTMP is slowly hydrolyzed to piv 1-AZTMP in RPMI and that the metabolic sequence in cell extract and in tissue culture medium is clearly: piv 2-AZTMP~piv1-AZTMP~AZTMP~AZT. The rate constants are quite different in these three media. Although it is evident that the first step in the metabolism of piv 2-AZTMP is catalysed by carboxy-. *For correspondence. Tel. +67545873; Fax. +67 0420 29. late esterase, the enzyme(s) responsible for the second step, piv1-AZTMP~AZTMP, is less apparent, as carboxylate esterases and/or phosphodiesterases can be taken in account. However, analysis of the kinetic data strongly suggests that carboxylate esterase does not playa significant role and that this second step is mediated by phosphodiesterases. Collectively, these studies demonstrate, that piv 2-AZTMP is an effective prodrug of AZTMP. They also establish that piv1-AZTMP is an intermediate in this process, and define the sequence of the overall metabolic reaction. With this increased understanding of the metabolism of piv 2-AZTMP, it should be possible rationally to design analogues with optimal structural and pharmacological properties for use in vivo.

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