Despite breakthroughs achieved with cancer checkpoint blockade therapy (CBT), many patients do not respond to anti–programmed cell death-1 (PD-1) due to primary or acquired resistance. Human tumor profiling and preclinical studies in tumor models have recently uncovered transforming growth factor–β (TGFβ) signaling activity as a potential point of intervention to overcome primary resistance to CBT. However, the development of therapies targeting TGFβ signaling has been hindered by dose-limiting cardiotoxicities, possibly due to nonselective inhibition of multiple TGFβ isoforms. Analysis of mRNA expression data from The Cancer Genome Atlas revealed that TGFΒ1 is the most prevalent TGFβ isoform expressed in many types of human tumors, suggesting that TGFβ1 may be a key contributor to primary CBT resistance. To test whether selective TGFβ1 inhibition is sufficient to overcome CBT resistance, we generated a high-affinity, fully human antibody, SRK-181, that selectively binds to latent TGFβ1 and inhibits its activation. Coadministration of SRK-181-mIgG1 and an anti–PD-1 antibody in mice harboring syngeneic tumors refractory to anti–PD-1 treatment induced profound antitumor responses and survival benefit. Specific targeting of TGFβ1 was also effective in tumors expressing more than one TGFβ isoform. Combined SRK-181-mIgG1 and anti–PD-1 treatment resulted in increased intratumoral CD8+ T cells and decreased immunosuppressive myeloid cells. No cardiac valvulopathy was observed in a 4-week rat toxicology study with SRK-181, suggesting that selectively blocking TGFβ1 activation may avoid dose-limiting toxicities previously observed with pan-TGFβ inhibitors. These results establish a rationale for exploring selective TGFβ1 inhibition to overcome primary resistance to CBT.

The distribution of neuregulin transcripts in rat brains was studied by both RNA blotting and in situ hybridization. Our data demonstrate that multiple neuregulin transcripts are expressed in neurons of the basal forebrain, the hippocampus, the diencephalon, the cerebellum, the brainstem, and the spinal cord. Developmental changes in the distribution of neuregulin transcripts were observed only in the cerebellum and the hippocampus. The intense neuregulin hybridization signals in the brainstem motor and sensory nuclei and the spinal motor neurons are suggestive of a functional involvement of neuregulins in motor and sensory systems. The expression of neuregulins in other parts of the brain also indicates that these factors are involved in a variety of central nervous system functions.

The tenth human fibronectin type three domain ((10)Fn3) is a small (10 kDa), extremely stable and soluble protein with an immunoglobulin-like fold, but without cysteine residues. Selections from (10)Fn3-based libraries of proteins with randomized loops have yielded high-affinity, target-specific antibody mimics. However, little is known about the biophysical properties of such antibody mimics, which will determine their suitability for in vitro and medical applications. We characterized target binding and biophysical properties of two related (10)Fn3-based antibody mimics that bind vascular endothelial growth factor receptor two (VEGF-R2). The first antibody mimic, which has a dissociation constant (K(d)) of 13 nM, is highly stable [melting temperature (T(m))=62 degrees C] and soluble, whereas the second, which binds VEGF-R2 with 40 x higher affinity, is less stable (T(m) < 40 degrees C) and relatively insoluble. We used our understanding of these two (10)Fn3 derivatives and of wild-type (10)Fn3 structure to engineer the next generation of antibody mimics, which have an improved combination of high affinity (K(d)=0.59 nM), stability (T(m)=53 degrees C) and solubility. Our findings illustrate that (10)Fn3-based antibody mimics can be engineered for favorable biophysical properties even when 20% of the wild-type (10)Fn3 sequence is mutated in order to satisfy target-binding requirements.

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