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Gemcitabine is a new deoxycytidine analog that exhibits significant cytotoxicity against a variety of cultured murine and human tumor cells. The cytotoxic action of gemcitabine appears to be due to the inhibition of DNA synthesis by inhibition of ribonucleotide reductase and by competition with dCTP for incorporation into DNA. We have previously shown that gemcitabine, but not cytosine arabinoside (ara-C), has a broad spectrum of antitumor activity against 7 different types of murine solid tumors. The activity of gemcitabine was schedule dependent. To further characterize its activity, gemcitabine was tested against 12 human carcinoma xenografts. When given on an every 3 day x 4 schedule, the following percent inhibitions (at maximally tolerated doses [MTD]; MTD/2) in tumor growth were seen: MX-1 mammary (93%; 80%), CX-1 colon (92%; 82%), HC-1 colon (96%; 92%), GC3 colon (98%; 94%), VRC5 colon (99%; 100%), LX-1 lung (76%; 61%), CALU-6 lung (75%; 38%), NCI-H460 lung (45%; 46%), HS766T pancreatic (73%; not tested), PaCa-2 pancreatic (69%; 40%), PANC-1 pancreatic (70%; 60%), and BxPC-3 pancreatic (9%; 19%). In contrast, only the LX-1 lung carcinoma xenograft was responsive to ara-C treatment, which inhibited tumor growth by a marginal 62 percent. Thus, like its activity against murine solid tumors, gemcitabine has excellent antitumor activity against a broad spectrum of human solid tumors.

The melanocortin receptors have been implicated as potential targets for a number of important therapeutic indications, including inflammation, sexual dysfunction, and obesity. We identified compound 1, an arylpiperazine attached to the dipeptide H-d-Tic-d-p-Cl-Phe-OH, as a novel melanocortin subtype-4 receptor (MC4R) agonist through iterative directed screening of nonpeptidyl G-protein-coupled receptor biased libraries. Structure-activity relationship (SAR) studies demonstrated that substitutions at the ortho position of the aryl ring improved binding and functional potency. For example, the o-isopropyl-substituted compound 29 (K(i) = 720 nM) possessed 9-fold better binding affinity compared to the unsubstituted aryl ring (K(i) = 6600 nM). Sulfonamide 39 (K(i) = 220 nM) fills this space with a polar substituent, resulting in a further 2-fold improvement in binding affinity. The most potent compounds such as the diethylamine 44 (K(i) = 60 nM) contain a basic group at this position. Basic heterocycles such as the imidazole 50 (K(i) = 110 nM) were similarly effective. We also demonstrated good oral bioavailability for sulfonamide 39.

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