Discovery of novel cMET-targeting antibody Fab drug conjugates as potential treatment for solid tumors with highly expressed cMET.

BACKGROUND: Solid tumors are becoming prevalent affecting both old and young populations. Numerous solid tumors are associated with high cMET expression. The complexity of solid tumors combined with the highly interconnected nature of the cMET/HGF pathway with other cellular pathways make the pursuit of finding an effective treatment extremely challenging. The current standard of care for these malignancies is mostly small molecule-based chemotherapy. Antibody-based therapeutics as well as antibody drug conjugates are promising emerging classes against cMET-overexpressing solid tumors. RESEARCH DESIGN AND METHODS: In this study, we described the design, synthesis, in vitro and in vivo characterization of cMET-targeting Fab drug conjugates (FDCs) as an alternative therapeutic strategy. The format is comprised of a Fab conjugated to a potent cytotoxic drug via a cleavable linker employing lysine-based and cysteine-based conjugation chemistries. RESULTS: We found that the FDCs have potent anti-tumor efficacies in cancer cells with elevated overexpression of cMET. Moreover, they demonstrated a remarkable anti-tumor effect in a human gastric xenograft mouse model. CONCLUSIONS: The FDC format has the potential to overcome some of the challenges presented by the other classes of therapeutics. This study highlights the promise of antibody fragment-based drug conjugate formats for the treatment of solid tumors.

Author Correction: Chemically triggered drug release from an antibody-drug conjugate leads to potent antitumour activity in mice.

The original version of this Article omitted the following from the Acknowledgements: 'This work was supported by the Office of the Assistant Secretary of Defense for Health Affairs, through the Breast Cancer Research Program under Award No. W81XWH-15-1-0692. Opinions, interpretations, conclusions and recommendations are those of the author and are not necessarily endorsed by the Department of Defense'. This error has now been corrected in the PDF and HTML versions of the Article.

Chemically triggered drug release from an antibody-drug conjugate leads to potent antitumour activity in mice.

Current antibody-drug conjugates (ADCs) target internalising receptors on cancer cells leading to intracellular drug release. Typically, only a subset of patients with solid tumours has sufficient expression of such a receptor, while there are suitable non-internalising receptors and stroma targets. Here, we demonstrate potent therapy in murine tumour models using a non-internalising ADC that releases its drugs upon a click reaction with a chemical activator, which is administered in a second step. This was enabled by the development of a diabody-based ADC with a high tumour uptake and very low retention in healthy tissues, allowing systemic administration of the activator 2 days later, leading to efficient and selective activation throughout the tumour. In contrast, the analogous ADC comprising the protease-cleavable linker used in the FDA approved ADC Adcetris is not effective in these tumour models. This first-in-class ADC holds promise for a broader applicability of ADCs across patient populations.

High turnover of tissue factor enables efficient intracellular delivery of antibody-drug conjugates.

Antibody-drug conjugates (ADC) are emerging as powerful cancer treatments that combine antibody-mediated tumor targeting with the potent cytotoxic activity of toxins. We recently reported the development of a novel ADC that delivers the cytotoxic payload monomethyl auristatin E (MMAE) to tumor cells expressing tissue factor (TF). By carefully selecting a TF-specific antibody that interferes with TF:FVIIa-dependent intracellular signaling, but not with the procoagulant activity of TF, an ADC was developed (TF-011-MMAE/HuMax-TF-ADC) that efficiently kills tumor cells, with an acceptable toxicology profile. To gain more insight in the efficacy of TF-directed ADC treatment, we compared the internalization characteristics and intracellular routing of TF with the EGFR and HER2. Both in absence and presence of antibody, TF demonstrated more efficient internalization, lysosomal targeting, and degradation than EGFR and HER2. By conjugating TF, EGFR, and HER2-specific antibodies with duostatin-3, a toxin that induces potent cytotoxicity upon antibody-mediated internalization but lacks the ability to induce bystander killing, we were able to compare cytotoxicity of ADCs with different tumor specificities. TF-ADC demonstrated effective killing against tumor cell lines with variable levels of target expression. In xenograft models, TF-ADC was relatively potent in reducing tumor growth compared with EGFR- and HER2-ADCs. We hypothesize that the constant turnover of TF on tumor cells makes this protein specifically suitable for an ADC approach.

Heterobiaryl human immunodeficiency virus entry inhibitors.

Previously disclosed HIV (human immunodeficiency virus) attachment inhibitors, exemplified by BMS 806 (formally BMS378806, 1), are characterized by a substituted indole or azaindole ring linked to a benzoylpiperazine via a ketoamide or sulfonamide group. In the present report, we describe the discovery of a novel series of potent HIV entry inhibitors in which the indole or azaindole ring of previous inhibitors is replaced by a heterobiaryl group. Several of these analogues exhibited IC(50) values of less than 5 nM in a pseudotyped antiviral assay, and compound 13k was demonstrated to exhibit potency and selectivity similar to those of 1 against a panel of clinical viral isolates. Moreover, current structure-activity relationship studies of these novel biaryl gp120 inhibitors revealed that around the biaryl, a fine crevice might exist in the gp120 binding site. Taken in sum, these data reveal a hitherto unsuspected flexibility in the structure-activity relationships for these inhibitors and suggest new avenues for exploration and gp120 inhibitor design.

Design and synthesis of human immunodeficiency virus entry inhibitors: sulfonamide as an isostere for the alpha-ketoamide group.

The crystal structures of many tertiary alpha-ketoamides reveal an orthogonal arrangement of the two carbonyl groups. Based on the hypothesis that the alpha-ketoamide HIV attachment inhibitor BMS 806 (formally BMS378806, 26) might bind to its gp120 target via a similar conformation, we designed and synthesized a series of analogs in which the ketoamide group is replaced by an isosteric sulfonamide group. The most potent of these analogs, 14i, demonstrated antiviral potency comparable to 26 in the M33 pseudotyped antiviral assay. Flexible overlay calculations of a ketoamide inhibitor with a sulfonamide inhibitor revealed a single conformation of each that gave significantly better overlap of key pharmacophore features than other conformations and thus suggest a possible binding conformation for each class.

Novel asymmetric approach to proline-derived spiro-beta-lactams.

We describe a novel asymmetric approach using Staudinger chemistry to proline-derived spiro-beta-lactams. A chiral group at C-4 of the acid chloride of proline directs the stereoselectivity of Staudinger chemistry and later is sacrificed to obtain optically active 5.4-spiro-beta-lactams. The scope, limitations, and mechanistic rationale for the observed results of Staudinger Chemistry of the acid chloride of 4-alkyl(aryl)sulfonyloxy-l-proline with imines are also discussed.

Role of pyridine hydrogen-bonding sites in recognition of basic amino acid side chains.

A series of three, new artificial receptors for guanidinium and ammonium guests has been synthesized. All three receptors have highly preorganized clefts bearing two carboxylate groups. They differ in the number of nitrogen atoms contained in their clefts, as follows: four N atoms in receptor 3, three N atoms in 4, and two nitrogens in 5. Crystallographic studies have produced the solid-state structures of the following guanidinium complexes of each receptor: 3.2CH(3)CH(2)NHC(NH(2))(2)(+), 4.2CH(3)NHC(NH(2))(2)(+), and 5.2C(NH(2))(3)(+). The conformations of the receptor molecules in all three complexes are very similar. N-Alkylguanidinium guests are bound in the clefts of 3 and 4 in similar manners, despite the loss of one hydrogen-bond acceptor nitrogen in 4 and the possible hindrance of the cavity by a CH group. In the guanidinium complex of 5, neither guest enters the cavity containing two CH groups. Complexation studies were conducted in methanol by (1)H NMR titration for several guanidinium and ammonium guests, including derivatives of the amino acids arginine and lysine. Receptor 5 binds all such guests weakly (K(s) < 4000), while 3 binds most guests very strongly (K(s) > 100 000). Receptor 3 is selective for arginine versus lysine, while 4 binds lysine better than does 3. The results generally underscore the importance of receptor preorganization and hydrogen-bonding complementarity in the design of receptors that can serve as probes for biomolecules.

Circular dichroism readout of sugar recognition in the cleft of a fused-pyridine receptor.

Dicarboxamide host 2 forms 1:1 complexes with n-octyl pyranosides derived from D-glucose, D-mannose, D-galactose, D-fucose, D-lyxose, and D-arabinose. Association constants (K(a)) in the range of 77-940 M(-1) were measured in chloroform by means of induced circular dichroism and fluorescence spectroscopy. Variations in K(a) values correspond qualitatively to expected differences in hydrogen-bonding abilities of guest hydroxyl groups. Induced circular dichroism effects for complexes of saccharides bearing equatorial 3-OH, 4-OH, and 6-OH groups show that the host chromophore is twisted in a P-helical conformation. A structural model is proposed that is also consistent with the results of previous studies involving complexation of dicarboxylic acid 1 with cationic saccharides in methanol.