Anti-NaPi2b antibody-drug conjugate lifastuzumab vedotin (DNIB0600A) compared with pegylated liposomal doxorubicin in patients with platinum-resistant ovarian cancer in a randomized, open-label, phase II study.

Background: Lifastuzumab vedotin (LIFA) is a humanized anti-NaPi2b monoclonal antibody conjugated to a potent antimitotic agent, monomethyl auristatin E, which inhibits cell division by blocking the polymerization of tubulin. This study is the first to compare an antibody-drug conjugate (ADC) to standard-of-care in ovarian cancer (OC) patients. Patients and methods: Platinum-resistant OC patients were randomized to receive LIFA [2.4 mg/kg, intravenously, every 3 weeks (Q3W)] or pegylated liposomal doxorubicin (PLD) (40 mg/m2, intravenously, Q4W). NaPi2b expression and serum CA-125 and HE4 levels were assessed. The primary end point was progression-free survival (PFS) in intent-to-treat (ITT) and NaPi2b-high patients. Results: Ninety-five patients were randomized (47 LIFA; 48 PLD). The stratified PFS hazard ratio was 0.78 [95% confidence interval (95% CI), 0.46-1.31; P = 0.34] with a median PFS of 5.3 versus 3.1 months (LIFA versus PLD arm, respectively) in the ITT population, and 0.71 (95% CI, 0.40-1.26; P = 0.24) with a median PFS of 5.3 months versus 3.4 months (LIFA versus PLD arm, respectively) in NaPi2b-high patients. The objective response rate was 34% (95% CI, 22% to 49%, LIFA) versus 15% (95% CI, 7% to 28%, PLD) in the ITT population (P = 0.03), and 36% (95% CI, 22% to 52%, LIFA) versus 14% (95% CI, 6% to 27%, PLD) in NaPi2b-high patients (P = 0.02). Toxicities included grade ≥3 adverse events (AEs) (46% LIFA; 51% PLD), serious AEs (30% both arms), and AEs leading to discontinuation of drug (9% LIFA; 8% PLD). Five (11%) LIFA versus 2 (4%) PLD patients had grade ≥2 neuropathy. Conclusion: LIFA Q3W was well tolerated and improved objective response rate with a modest, nonstatistically significant improvement of PFS compared with PLD in platinum-resistant OC. While the response rate for the monomethyl auristatin E-containing ADC was promising, response durations were relatively short, thereby highlighting the importance of evaluating both response rates and duration of response when evaluating ADCs in OC. Clinical trials.gov: NCT01991210.

Benzodiazepine peptidomimetics: potent inhibitors of Ras farnesylation in animal cells.

Oncogenic Ras proteins transform animal cells to a malignant phenotype only when modified by farnesyl residues attached to cysteines near their carboxyl termini. The farnesyltransferase that catalyzes this reaction recognizes tetrapeptides of the sequence CAAX, where C is cysteine, A is an aliphatic amino acid, and X is a carboxyl-terminal methionine or serine. Replacement of the two aliphatic residues with a benzodiazepine-based mimic of a peptide turn generated potent inhibitors of farnesyltransferase [50 percent inhibitory concentration (IC50) < 1 nM]. Unlike tetrapeptides, the benzodiazepine peptidomimetics enter cells and block attachment of farnesyl to Ras, nuclear lamins, and several other proteins. At micromolar concentrations, these inhibitors restored a normal growth pattern to Ras-transformed cells. The benzodiazepine peptidomimetics may be useful in the design of treatments for tumors in which oncogenic Ras proteins contribute to abnormal growth, such as that of the colon, lung, and pancreas.

Preclinical assessment of the absorption, distribution, metabolism and excretion of GDC-0449 (2-chloro-N-(4-chloro-3-(pyridin-2-yl)phenyl)-4-(methylsulfonyl)benzamide), an orally bioavailable systemic Hedgehog signalling pathway inhibitor.

GDC-0449 (2-chloro-N-(4-chloro-3-(pyridin-2-yl)phenyl)-4-(methylsulfonyl)benzamide) is a potent, selective Hedgehog (Hh) signalling pathway inhibitor being developed for the treatment of various cancers. The in vivo clearance of GDC-0449 was estimated to be 23.0, 4.65, 0.338, and 19.3 ml min(-1) kg(-1) in mouse, rat, dog and monkeys, respectively. The volume of distribution ranged from 0.490 in rats to 1.68 l kg(-1) in mice. Oral bioavailability ranged from 13% in monkeys to 53% in dogs. Predicted human clearance using allometry was 0.096-0.649 ml min(-1) kg(-1) and the predicted volume of distribution was 0.766 l kg(-1). Protein binding was extensive with an unbound fraction less than or equal to 6%, and the blood-to-plasma partition ratio ranged from 0.6 to 0.8 in all species tested. GDC-0449 was metabolically stable in mouse, rat, dog and human hepatocytes and had a more rapid turnover in monkey hepatocytes. Proposed metabolites from exploratory metabolite identification in vitro (rat, dog and human liver microsomes) and in vivo (dog and rat urine) include three primary oxidative metabolites (M1-M3) and three sequential glucuronides (M4-M6). Oxidative metabolites identified in microsomes M1 and M3 were formed primarily by P4503A4/5 (M1) and P4502C9 (M3). GDC-0449 was not a potent inhibitor of P4501A2, P4502B6, P4502D6, and P4503A4/5 with IC50 estimates greater than 20 microM. K(i)'s estimated for P4502C8, P4502C9 and P4502C19 and were 6.0, 5.4 and 24 microM, respectively. An evaluation with Simcyp suggests that GDC-0449 has a low potential of inhibiting P4502C8 and P4502C9. Furthermore, GDC-0449 (15 microM) was not a potent P-glycoprotein/ABCB1 inhibitor in MDR1-MDCK cells. Overall, GDC-0449 has an attractive preclinical profile and is currently in Phase II clinical trials.

Farnesyl transferase inhibitors: the successes and surprises of a new class of potential cancer chemotherapeutics.

Proteins that transmit abnormal growth signals offer enticing points of intervention for the treatment of cancer. The discovery that isoprenoid attachment is required for the aberrant biological activity of oncogenic Ras proteins has provided just such a target.

Synthetic chimeras of mouse growth factor-associated glandular kallikreins. I. Kinetic properties.

A series of six chimeric proteins, composed of fragments corresponding to either one or the other of the growth factor-associated mouse glandular kallikreins-epidermal growth factor binding protein (EGF-BP) and the gamma-subunit of nerve growth factor (gamma-NGF)--were expressed in Escherichia coli and isolated, and their kinetic properties were characterized. The assembly of these synthetic proteases involved the substitution of regions of the proteins containing four specific surface loops that have been postulated to influence both kinetic specificity and the formation of growth factor complexes. The substrates utilized in the kinetic characterization of these chimeric kallikreins were tripeptide nitroanilides representing carboxyl termini of both the EGF and beta-NGF mature hormones, putative processing sites for these kallikreins in the precursors. Characterization of these hybrid enzymes demonstrates that Km and kcat kinetic constants may be independently affected by the regions utilized in construction of these chimeric kallikreins. Specifically, loop 1, located in the amino terminal region (Bode, W., et al., J. Mol. Biol. 164, 237-282, 1983), in gamma-NGF enhanced the kcat for substrates containing threonine in the P2 position, as is the case during the processing of the carboxy terminus of the beta-NGF precursor. Also, the central regions of the kallikreins containing loop 2 and the kallikrein loop dictated the generally inverted Km and kcat kinetic constants observed between EGF-BP and gamma-NGF. Finally, in gamma-NGF the autolysis loop, found in the carboxyl terminal region, functions to lower the Km kinetic constant for a variety of substrates. The results allow previously characterized kinetic differences between EGF-BP and gamma-NGF to be interpreted in terms of specific regions of the proteins and identify a subset of amino acid positions responsible for these functional characteristics.

Synthesis of 3-Amino-l-CarboxymethyI-Benzodiazepine (BZA) Peptidomimetics.

Replacement of key structural or binding elements of a peptide lead with nonpeptide components can improve affinity and metabolic stability (1-5). Such a strategy was successfully applied to the generation of potent, cell-permeable inhibitors of Ras famesyltransferase (FTase) (6,7). The central pair of amino acids in the CAAX tetrapeptide was replaced with the nonpeptide scaffold 3-methylamino-1-carboxymethyl-2,3-dihydro-5-phenyl-1H-1,4-benzodiazepin-2-one, (N-Me)BZA, shown below.

Synthesis, hybridization properties and antiviral activity of lipid-oligodeoxynucleotide conjugates.

Triethylammonium 1,2-di-O-hexadecyl-rac-glycero-3-H-phosphonate (2) was coupled to the 5' terminus of oligodeoxynucleotides via hydrogen phosphonate solid support DNA synthesis methodology. Duplex DNA oligomers with a single 5'-phospholipid melted at lower temperatures than the corresponding unmodified duplex, but duplexes bearing lipids at each 5' end had higher Tms. In uptake experiments with L929 cells, 8-10 times more lipid-DNA became cell-associated than did unmodified DNA. Unmodified antisense diesters were inactive in a VSV antiviral assay in L929 cells (at up to 200 microM). Attachment of a lipid to the oligomer, however, led to a greater than 90% at 150 microM (greater than 80% at 100 microM) reduction in viral protein synthesis. The antiviral activity depended on the sequence of the oligodeoxynucleotide, but some compounds having little or no base complementarity to the viral target were also effective. Phosphorothioate derivatives reduced viral protein synthesis by 20-30% at 100 microM in the VSV assay. The lipid-DNA compounds were not toxic to the cells at up to 100 microM.

Use of a prenylation inhibitor as a novel antiviral agent.

No specific therapy exists for hepatitis delta virus (HDV), which can cause severe liver disease. Molecular genetic studies have implicated the prenylation site of large delta antigen as a critical determinant of HDV particle assembly. We have established a cell culture model which produces HDV-like particles, and we show that delta antigen prenylation can be pharmacologically inhibited by the prenylation inhibitor BZA-5B. Furthermore, BZA-5B specifically abolishes particle production in a dose-dependent manner. These results demonstrate that the use of such a prenylation inhibitor-based antiviral therapy may be feasible and identify a novel class of potential antiviral agents.

Picosecond geminate recombination of nitrosylmyoglobins.

The kinetics of NO geminate recombination to sperm whale and elephant myoglobins has been studied on the picosecond time scale using an amplified colliding-pulse mode-locked ring dye laser. The dynamics of ligand rebinding are shown to be affected by the distal structure of the protein surrounding the heme pocket.

Substrate specificities of growth factor associated kallikreins of the mouse submandibular gland.

The kinetic constants for the hydrolysis of a series of tripeptide p-nitroanilide substrates by mouse epidermal growth factor binding protein (EGF-BP), the gamma-subunit of mouse nerve growth factor (gamma-NGF), bovine pancreatic trypsin (BPT), and porcine pancreatic kallikrein (PPK) have been evaluated. These substrates correspond to the carboxyl-terminal three amino acids of the mature forms of epidermal growth factor (EGF) and beta-nerve growth factor (beta-NGF), as well as various substitutions in the penultimate and antepenultimate positions, and, as such, represent potential recognition sites for precursor processing. The mouse kallikreins (EGF-BP and gamma-NGF) preferentially hydrolyze the substrates with the sequences of their specifically associated growth factors; however, the constants derived from these reactions do not account for the association constants observed with the mature growth factors, and additional significant binding interactions between EGF-BP and EGF and between gamma-NGF and beta-NGF are predicted to exist outside of the catalytic binding site, i.e., the P3 to P1 positions. A comparison of the kinetic constants of BPT, PPK, and the mouse kallikreins indicates that EGF-BP and gamma-NGF display a hybrid catalytic character. A favorable substrate P1 arginine guanidinium group interaction exists for the mouse kallikreins, similar to that of BPT, but a preference for a hydrophobic side chain in the substrate P2 position makes the mouse kallikreins, especially EGF-BP, more closely resemble PPK than BPT. These findings have significant implications with regard to molecular modeling of the mouse kallikreins.

Tetrapeptide inhibitors of protein farnesyltransferase: amino-terminal substitution in phenylalanine-containing tetrapeptides restores farnesylation.

Protein farnesyltransferase from rat brain transfers farnesyl residues to cysteine residues in tetrapeptides that conform to the sequence CA1A2X, where C is cysteine, A1 and A2 are aliphatic amino acids, and X is methionine or serine. When the A2 residue is aromatic [e.g., phenylalanine as in Cys-Val-Phe-Met (CVFM)], the tetrapeptide continues to bind to the enzyme, but it can no longer accept a farnesyl group, and it becomes a pure inhibitor. The current studies show that this resistance to farnesylation also requires a positive charge on the cysteine amino group. Derivatization of this group with acetyl, octanoyl, or cholic acid residues or extension of the peptide with an additional amino acid restores the ability of phenylalanine-containing peptides to accept a farnesyl residue. The same result was obtained when the amino group of cysteine was deleted (mercaptopropionyl-VFM). These data suggest that the positive change on the cysteine amino group acts in concert with an aromatic residue in the A2 position to render peptides resistant to farnesylation by the rat brain enzyme.

Benzodiazepine peptidomimetic inhibitors of farnesyltransferase.

A structural survey of protein Zn2+ binding geometries was instigated based upon the functional requirement of Ras farnesyltransferase for Zn2+. The Cys-X-X-Cys motif found in Zn(2+)-binding proteins such as aspartate transcarbamylase was used as a template to devise a bidentate-coordination model for Cys-A1-A2-X peptide inhibitors. Accordingly, replacement of the central dipeptide with the hydrophobic scaffold 3-amino-1-carboxymethyl-2,3-dihydro-5- phenyl-1H-1,4-benzodiazepin-2-one (BZA) yielded a peptidomimetic inhibitor, Cys(BZA)Met, of moderate potency (IC50 = 400 nM). N-Methylation of the cysteine amide improved potency almost 100-fold (IC50 = 0.3-1 nM). The increased affinity presumably correlates with a preferred conformation of the inhibitor which maximizes a hydrophobic interaction between the scaffold and the enzyme, and the proper presentation of cysteine and methionine to allow bidentate coordination at Zn2+. These non-peptide inhibitors have been shown to block farnesylation of the Ras protein in intact cells and provide lead compounds for the development of new cancer therapeutic agents.

Generation of an LFA-1 antagonist by the transfer of the ICAM-1 immunoregulatory epitope to a small molecule.

The protein-protein interaction between leukocyte functional antigen-1 (LFA-1) and intercellular adhesion molecule-1 (ICAM-1) is critical to lymphocyte and immune system function. Here, we report on the transfer of the contiguous, nonlinear epitope of ICAM-1, responsible for its association with LFA-1, to a small-molecule framework. These LFA-1 antagonists bound LFA-1, blocked binding of ICAM-1, and inhibited a mixed lymphocyte reaction (MLR) with potency significantly greater than that of cyclosporine A. Furthermore, in comparison to an antibody to LFA-1, they exhibited significant anti-inflammatory effects in vivo. These results demonstrate the utility of small-molecule mimics of nonlinear protein epitopes and the protein epitopes themselves as leads in the identification of novel pharmaceutical agents.