Discovery and Optimization of HKT288, a Cadherin-6-Targeting ADC for the Treatment of Ovarian and Renal Cancers.

Despite an improving therapeutic landscape, significant challenges remain in treating the majority of patients with advanced ovarian or renal cancer. We identified the cell-cell adhesion molecule cadherin-6 (CDH6) as a lineage gene having significant differential expression in ovarian and kidney cancers. HKT288 is an optimized CDH6-targeting DM4-based antibody-drug conjugate (ADC) developed for the treatment of these diseases. Our study provides mechanistic evidence supporting the importance of linker choice for optimal antitumor activity and highlights CDH6 as an antigen for biotherapeutic development. To more robustly predict patient benefit of targeting CDH6, we incorporate a population-based patient-derived xenograft (PDX) clinical trial (PCT) to capture the heterogeneity of response across an unselected cohort of 30 models-a novel preclinical approach in ADC development. HKT288 induces durable tumor regressions of ovarian and renal cancer models in vivo, including 40% of models on the PCT, and features a preclinical safety profile supportive of progression toward clinical evaluation.Significance: We identify CDH6 as a target for biotherapeutics development and demonstrate how an integrated pharmacology strategy that incorporates mechanistic pharmacodynamics and toxicology studies provides a rich dataset for optimizing the therapeutic format. We highlight how a population-based PDX clinical trial and retrospective biomarker analysis can provide correlates of activity and response to guide initial patient selection for first-in-human trials of HKT288. Cancer Discov; 7(9); 1030-45. ©2017 AACR.This article is highlighted in the In This Issue feature, p. 920.

Heterogeneity of toxicant response: sources of human variability.

While risk assessment models attempt to predict human risk to toxicant exposure, in many cases these models cannot account for the wide variety of human responses. This review addresses several primary sources of heterogeneity that may affect individual responses to drug or toxicant exposure. Consideration was given to genetic polymorphisms, age-related factors during development and senescence, gender differences associated with hormonal function, and preexisting diseases influenced by toxicant exposure. These selected examples demonstrate the need for additional steps in risk assessment that are needed to more accurately predict human responses to toxicants and drugs.

Synthesis and in vitro antioxidant properties of manganese(III) beta-octabromo-meso-tetrakis(4-carboxyphenyl)porphyrin.

Manganese(III) meso-tetrakis(4-carboxypheny)porphyrin (MnTBAP) is a readily available and widely used agent to scavenge reactive oxygen species. A major limitation of MnTBAP is its relatively weak potency due to its low metal centered redox potential. The goal of these studies was to prepare a more potent analog of MnTBAP by increasing its redox potential through beta-substitution on the porphyrin ring by bromination. Manganese(III) beta-octabromo-meso-tetrakis(4-carboxyphenyl)porphyrin (MnBr(8)TBAP) was prepared in three steps starting from the methyl ester of the free ligand meso-tetrakis(4-carboxyphenyl)porphyrin, with an overall yield of 50%. The superoxide dismutase (SOD)-like activity of MnBr(8)TBAP (IC(50)=0.7 microM) was the same as manganese(III) meso-tetrakis(N-methylpyridinium-4-yl)porphyrin (MnTM-4-PyP(5+)), while the metal-centered redox potential of the first was considerably higher than the second (E(1/2)=+128 and 0 mV vs. normal hydrogen electrode, respectively). However, a number of these cationic Mn-porphyrins (such as MnTM-4-PyP(5+)) redox-cycle with cytochrome P450 reductase in the presence of oxygen and NADPH whereas MnTBAP and its halogenated analog, MnBr(8)TBAP do not. The enhanced ability of MnBr(8)TBAP to inhibit paraquat- and hypoxia-induced injuries in vitro is also reported. In these in vitro models, in which cationic Mn-porphyrins exhibit very low activity, MnBr(8)TBAP appears to be at least eightfold more active than the non-brominated analog MnTBAP.

Nonclinical evaluation of GMA161--an antihuman CD16 (FcγRIII) monoclonal antibody for treatment of autoimmune disorders in CD16 transgenic mice.

Fc receptors are a critical component of the innate immune system responsible for the recognition of cross-linked antibodies and the subsequent clearance of pathogens. However, in autoimmune diseases, these receptors play a role in the deleterious action of self-directed antibodies and as such are candidate targets for treatment. GMA161 is an aglycosyl, humanized version of the murine antibody 3G8 that targets the human low-affinity Fcγ receptor III (CD16). As CD16 expression and sequence have high species specificity, preclinical assessments were conducted in mice transgenic for both isoforms of human CD16, CD16A, and CD16B. This transgenic mouse model was useful in transitioning into phase I clinical trials, as it generated positive efficacy data in a relevant disease model and an acceptable single-dose safety profile. However, when GMA161 or its murine parent 3G8 were dosed repeatedly in transgenic mice having both human CD16 isoforms, severe reactions were observed that were not associated with significant cytokine release, nor were they alleviated by antihistamine administration. Prophylactic dosing with an inhibitor of platelet-activating factor (PAF), however, completely eliminated all signs of hypersensitivity. These findings suggest that (1) GMA161 elicits a reaction that is target dependent, (2) immunogenicity and similar adverse reactions were observed with a murine version of the antibody, and (3) the reaction is driven by the atypical hypersensitivity pathway mediated by PAF.

An investigation of hemopexin redox properties by spectroelectrochemistry: biological relevance for heme uptake.

Hemopexin (HPX) has two principal roles: it sequesters free heme in vivo for the purpose of preventing the toxic effects of this moiety, which is largely due to heme's ability to catalyze free radical formation, and it transports heme intracellularly thus limiting its availability as an iron source for pathogens. Spectroelectrochemistry was used to determine the redox potential for heme and meso-heme (mH) when bound by HPX. At pH 7.2, the heme-HPX assembly exhibits E (1/2) values in the range 45-90 mV and the mH-HPX assembly in the range 5-55 mV, depending on environmental electrolyte identity. The E (1/2) value exhibits a 100 mV positive shift with a change in pH from 7.2 to 5.5 for mH-HPX, suggesting a single proton dependent equilibrium. The E (1/2) values for heme-HPX are more positive in the presence of NaCl than KCl indicating that Na(+), as well as low pH (5.5) stabilizes ferro-heme-HPX. Furthermore, comparing KCl with K(2)HPO(4), the chloride salt containing system has a lower potential, indicating that heme-HPX is easier to oxidize. These physical properties related to ferri-/ferro-heme reduction are both structurally and biologically relevant for heme release from HPX for transport and regulation of heme oxygenase expression. Consistent with this, when the acidification of endosomes is prevented by bafilomycin then heme oxygenase-1 induction by heme-HPX no longer occurs.