In vitro potency

Phosphonylmethoxyethyl)adenine [106941-25-7] (PMEA, 65) (173), synthesized in 1987 (174), is foremost among the acycHc nucleoside analogues proven to be effective inhibitors of HIV-1 repHcation. The in vitro potency and selectivity of PMEA is comparable to the antiHIV-1 potency and selectivity of 2, 3 -dideoxy-adenosine (175). Although less potent than AZT in vitro PMEA, CgH22N 04P, is markedly more potent than AZT as an in vivo inhibitor of retrovims repHcation (176). In fact, PMEA has proven efficacious in the treatment of murine, feline, and simian retrovims infections in mice, cats, and monkeys, respectively. 

Kassell (Takahashi et al., 1993) has described the activity of a novel tropolone U88999E in a rabbit model of cerebral vasosjrasm. U88999E inhibits lipid peroxidation and acts as a calcium antagonist. Kassell showed that the compound relaxed preconstricted arterial rings in vitro (potency slightly less than flunarizine or dil-tiazem) and that it reduced vasospasm of basilar arteries after rabbit subarachnoid haemorrhage (Takahashi etal., 1993). 

Fig. 3 The SAR by NMR approach. Example of a small bidentate molecule designed using this approach. The example shown is for the design of a potent inhibitors of the matrix metalloproteinase MMP3. (a) Docked structures of the identified fragment leads are shown with cyan carbons, whereas the linked compound is shown with green carbon atoms. All structures were experimentally determined by NMR. (b) Chemical structures (and in vitro potencies) of the fragment leads and subsequent high-affinity linked compounds. Adapted from [7]...

PMEA and its congeners are more effective in vivo than could be predicted from their in vitro potency. While less potent as an antiretrovirus agent than AZT in vitro, PMEA proved clearly superior to AZT when the two drugs were compared for their effectiveness in vivo, in mice infected with murine Moloney sarcoma virus [51,52]. PMEA was also shown to be effective against various other retrovirus infections, including Friend leukemia virus (FLV), Rauscher leukemia virus (RLV), and LP-BM5 (murine AIDS) virus infection in mice, feline leukemia virus (FeLV) or feline immunodeficiency virus (FIV) infection in cats, and SIV infection in macaque (rhesus) monkeys (for review, see Ref. 53). In the latter model [54], again PMEA proved far superior to AZT in suppressing several parameters of the disease. 

A series of 4,4-disubstituted quinazolin-2-ones derived from HTV nonnucleoside reverse transcriptase inhibitor leads have shown good in vitro potency and in vivo efficacy [28]. Using FLIPR assays on cell lines with different resting membrane potentials, TTA-Q3 (10) and TTA-Q6 (11)... 

Numerous y-secretase inhibitors featuring sulfonamide- and sulfone-based scaffolds have been disclosed. Bicyclononane thiophene sulfonamide 40 reduced brain Ap in transgenic mice by 50% after a dose of 100 mg/kg [100]. High potency (A p IC50 = 0.5 nM) and improved oral activity (ID50 = 17 mg/kg) was found in a series of related sulfamides represented by 41 [101]. Tetrahydroquinoline (42) and piperidine (43-44) sulfonamides have been developed [102-104]. Elaboration of the piperidine series with the cyclopropyl substituent present in 44 improved in vitro potency (Aft IC50 = 2.1 nM in membrane assay) and in vivo activity in transgenic mice (plasma Ap = 2% of control after oral dose of 30 mg/kg). Reductions of A p in the cortex were reported to be comparable to those observed in plasma. 

Among aliphatic substituents, the pentyl side chain was found to be optimal for both in vitro potency and efficacy. Derivative 5b (R5 = OH, R9 = M-pentyl) is a full agonist in the LMMP-GPI model (90% of the maximum efficacy of serotonin ... 

A similar strategy was employed to identify a DPP-IV inhibitor (6) with good in vivo potency in a mouse model of diabetes [44], Plasma protein binding, as assessed by shift assay (50% serum), was presented for all final compounds. The compound selected as having the best overall profile was active in vivo at 0.1 mg/kg. The activity at 1 h post-dose was consistent with the free drug principle - total plasma concentration 269 nM murine-free fraction 4% unbound plasma concentration 11 nM in vitro potency versus murine DPP-IV 6nM. 

Similarly, though plasma protein binding data were not ostensibly used in the identification of an oxytocin antagonist suitable for advancement to the clinic, such data were used to explain the differences between in vivo and in vitro potency [46]. 

Overall, trifluorophenyl analogue 1 was superior to all triazolopiperazine derivatives with respect to DPP-4 potency, off-target selectivity, pharmacokinetic profile and in vivo efficacy in preclinical species and was selected for further development. In vitro potency and selectivity of compound 1 (sitagliptin) are illustrated in Table 17.8. Sitagliptin is a very selective D P P-4 inhibitor, showing 2700-fold selectivity over D P P-8 and more than 5000-fold selectivity over other DASH proteins. Sitagliptin was further profiled in an extensive panel of over 170 enzymes, receptors and ion... 

Table 17.8 In vitro potency and selectivity of compound 1 (sitagliptin).

A number of substituted bisindole oxazolidinedione derivatives were prepared using the methods described above (Table VI) (79-81). When examined for their ability to induce a mitotic block in CHO cells, these compounds were active from 2 to 0.002 p.g/ml (Table VII), and compounds having the greatest degree of potency in this in vitro system were evaluated in several experimental tumor systems (Table VIII). The in vitro potency of these compounds appears to correlate with their in vivo potency as reflected by the minimum effective dose that could be administered without toxicity. Several of these compounds were evaluated for their antitumor efficacy when administered by the oral route (Table IX). Compounds 96 and 107 were shown to be exceptionally active in this regard. 

Fig. 2.10 Correlation of in vitro potency with plasma free drug concentration required for efficacy.

Fig. 2.12 Receptor occupancy based on PET scanning and in vitro potency combined with free plasma drug concentration. Log D74 values shown below compound names.

A similar example, also from endothelin antagonists, is the replacement of the amide group (Figure 3.7) in a series of amidothiophenesulfonamides with acetyl [11]. This move retained in vitro potency, but markedly improved oral bioavailability. 

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