Structure-guided design fine-tunes pharmacokinetics, tolerability, and antitumor profile of multispecific frizzled antibodies.

Aberrant activation of Wnt/ß-catenin signaling occurs frequently in cancer. However, therapeutic targeting of this pathway is complicated by the role of Wnt in stem cell maintenance and tissue homeostasis. Here, we evaluated antibodies blocking 6 of the 10 human Wnt/Frizzled (FZD) receptors as potential therapeutics. Crystal structures revealed a common binding site for these monoclonal antibodies (mAbs) on FZD, blocking the interaction with the Wnt palmitoleic acid moiety. However, these mAbs displayed gastrointestinal toxicity or poor plasma exposure in vivo. Structure-guided engineering was used to refine the binding of each mAb for FZD receptors, resulting in antibody variants with improved in vivo tolerability and developability. Importantly, the lead variant mAb significantly inhibited tumor growth in the HPAF-II pancreatic tumor xenograft model. Taken together, our data demonstrate that anti-FZD cancer therapeutic antibodies with broad specificity can be fine-tuned to navigate in vivo exposure and tolerability while driving therapeutic efficacy.

Hemodynamic responses to a hemoglobin bis-tetramer and its polyethylene glycol conjugate.

BACKGROUND: The design of hemoglobin-based oxygen carriers (HBOCs) poses a significant challenge as clinical trials of many materials have reported adverse side effects that may come from the scavenging of the vasodilator nitric oxide (NO). A compensating reaction, reduction of endogenous nitrite by hemoglobin (Hb) and its derivatives, generates NO. Polyethylene glycol (PEG) conjugation of Hb enhances the rate of the reaction. STUDY DESIGN AND METHODS: Hemoglobin bis-tetramers (BT) and their PEGylated derivative (BT-PEG) bind oxygen with a degree of cooperativity and also have significantly enhanced nitrite reductase activity compared to the native protein. Circulatory evaluation will test if the properties of BT and BT-PEG are reflected in their effects in vivo. BT and BT-PEG were evaluated as infusions into healthy wild-type (WT) and diabetic (db/db) mouse models. The effects were compared to infusions of murine Hb. RESULTS: The materials were found not to cause significant increases in systemic blood pressure in either WT mice or db/db mice. The latter are highly sensitive to NO scavenging. Further hemodynamic measurements in WT mice indicate that while a slight increase in systemic vascular resistance (SVR) was observed after infusion of BT, the extent is not significant. No change in SVR from baseline was observed after infusion of BT-PEG. CONCLUSION: The enlarged Hb derivatives do not evoke unfavorable circulatory responses that have been noted to result from infusion of Hb derivatives. These results suggest that a compromise between the P(50) , n(50) , and nitrite reductase activity of a Hb derivative can serve as the basis for producing HBOCs that can be tested for vasoactivity.

Enhancing nitrite reductase activity of modified hemoglobin: bis-tetramers and their PEGylated derivatives.

The clinical evaluation of stabilized tetrameric hemoglobin as alternatives to red cells revealed that the materials caused significant increases in blood pressure and related problems and this was attributed to the scavenging of nitric oxide and extravasation. The search for materials with reduced vasoactivity led to the report that conjugates of hemoglobin tetramers and polyethylene glycol (PEG) chains did not elicit these pressor effects. However, this material does not deliver oxygen efficiently due to its lack of cooperativity and high oxygen affinity, making it unsuitable as an oxygen carrier. It has been recently reported that PEG-conjugated hemoglobin converts nitrite to nitric oxide at a faster rate than does the native protein, which may compensate for the scavenging of nitric oxide. It is therefore important to alter hemoglobin in order to enhance nitrite reductase activity while retaining its ability to deliver oxygen. If the beneficial effect of PEG is associated with the increased size reducing extravasation, this can also be achieved by coupling cross-linked tetramers to one another, giving materials with appropriate oxygen affinity and cooperativity for use as circulating oxygen carriers. In the present study it is shown that cross-linked bis-tetramers with good oxygen delivery potential have enhanced nitrite reductase activity with k(obs) = 0.70 M(-1) s(-1) (24 degrees C), compared to native protein and cross-linked tetramers, k(obs) = 0.25 M(-1) s(-1) and k(obs) = 0.52 M(-1) s(-1), respectively, but are less active in reduction of nitrite than Hb-PEG5K(2) (k(obs) = 2.5 M(-1) s(-1)). However, conjugation of four PEG chains to the bis-tetramer (at each beta-Cys-93) produces a material with greatly increased nitrite reductase activity (k(obs) = 1.8 M(-1) s(-1)) while retaining cooperativity (P(50) = 4.1, n(50) = 2.4). Thus, PEGylated bis-tetramers combine increased size and enhanced nitrite reductase activity expected for decreased vasoactivity with characteristics of an acceptable HBOC.

Polyethylene glycol conjugation enhances the nitrite reductase activity of native and cross-linked hemoglobin.

Although stabilized hemoglobins have been evaluated as oxygen-carrying replacements for red cells in transfusions, in vivo evaluations have noted that these materials are associated with vasoactivity, a serious complication. Scavenging of endogenous nitric oxide by the deoxyheme sites of the stabilized proteins is one likely source of vasoactivity. Recent reports indicate that modification of cell-free hemoglobin derivatives with multiple chains of polyethylene glycol (PEG) suppresses vasoactivity. Gladwin and co-workers observed that the nitrite reductase activity of hemoglobin serves as a major endogenous source of nitric oxide. If PEG conjugation leads to enhanced nitrite reductase activity, this could compensate for scavenged endogenous nitric oxide. To test this possibility, the rates of conversion of nitrite ion to nitric oxide by altered hemoglobins with and without PEG were measured at 25 degrees C. Fumaryl (alpha99-alpha99) cross-linked hemoglobin reacts with nitrite with a bimolecular rate constant of 0.52 M (-1) s (-1), which is comparable to that associated with native hemoglobin (0.25 M (-1) s (-1)). Addition of PEG chains to the cross-linked hemoglobin at beta-Cys93 (alphaalpha-Hb-PEG5K 2) results in a material that produces nitric oxide much more rapidly ( k = 1.41 M (-1) s (-1)). R-State-stabilized hemoglobins with multiple PEG chains (Hb-PEG5K 2 and Hb-PEG5K 6) react 10 times faster with nitrite to produce nitric oxide than does native hemoglobin ( k = 2.5 and 2.4 M (-1) s (-1), respectively). These results, showing enhanced production of nitric oxide resulting from an increased proportion of the protein residing in the R-state, are consistent with the decrease in vasoactivity associated with PEG conjugation.

Identification of a small molecule that increases hemoglobin oxygen affinity and reduces SS erythrocyte sickling.

Small molecules that increase the oxygen affinity of human hemoglobin may reduce sickling of red blood cells in patients with sickle cell disease. We screened 38,700 compounds using small molecule microarrays and identified 427 molecules that bind to hemoglobin. We developed a high-throughput assay for evaluating the ability of the 427 small molecules to modulate the oxygen affinity of hemoglobin. We identified a novel allosteric effector of hemoglobin, di(5-(2,3-dihydro-1,4-benzodioxin-2-yl)-4H-1,2,4-triazol-3-yl)disulfide (TD-1). TD-1 induced a greater increase in oxygen affinity of human hemoglobin in solution and in red blood cells than did 5-hydroxymethyl-2-furfural (5-HMF), N-ethylmaleimide (NEM), or diformamidine disulfide. The three-dimensional structure of hemoglobin complexed with TD-1 revealed that monomeric units of TD-1 bound covalently to ß-Cys93 and ß-Cys112, as well as noncovalently to the central water cavity of the hemoglobin tetramer. The binding of TD-1 to hemoglobin stabilized the relaxed state (R3-state) of hemoglobin. TD-1 increased the oxygen affinity of sickle hemoglobin and inhibited in vitro hypoxia-induced sickling of red blood cells in patients with sickle cell disease without causing hemolysis. Our study indicates that TD-1 represents a novel lead molecule for the treatment of patients with sickle cell disease.

Hemoglobin bis-tetramers via cooperative azide-alkyne coupling.

Cross-linked hemoglobin-azides react with a bis-alkyne to form a bis-tetramer through sequential "click" reactions where the second step is promoted by the first.