Activation of seven-transmembrane (7TM) receptors by agonists does not always lead to uniform activation of all signaling pathways mediated by a given receptor. Relative to other ligands, many agonists are "biased" toward producing subsets of receptor behaviors. A hallmark of such "functional selectivity" is cell type dependence; this poses a particular problem for the profiling of agonists in whole cell test systems removed from the therapeutic one(s). Such response-specific cell-based variability makes it difficult to guide medicinal chemistry efforts aimed at identifying and optimizing therapeutically meaningful agonist bias. For this reason, we present a scale, based on the Black and Leff operational model, that contains the key elements required to describe 7TM agonism, namely, affinity (K(A) (-1)) for the receptor and efficacy (τ) in activating a particular signaling pathway. Utilizing a "transduction coefficient" term, log(τ/K(A)), this scale can statistically evaluate selective agonist effects in a manner that can theoretically inform structure-activity studies and/or drug candidate selection matrices. The bias of four chemokines for CCR5-mediated inositol phosphate production versus internalization is quantified to illustrate the practical application of this method. The independence of this method with respect to receptor density and the calculation of statistical estimates of confidence of differences are specifically discussed.

Antibody-drug conjugate (ADC) which delivers cytotoxic drugs specifically into targeted cells through internalization and lysosomal trafficking has emerged as an effective cancer therapy. We show that a bivalent biparatopic antibody targeting two non-overlapping epitopes on HER2 can induce HER2 receptor clustering, which in turn promotes robust internalization, lysosomal trafficking, and degradation. When conjugated with a tubulysin-based microtubule inhibitor, the biparatopic ADC demonstrates superior anti-tumor activity over ado-trastuzumab emtansine (T-DM1) in tumor models representing various patient subpopulations, including T-DM1 eligible, T-DM1 ineligible, and T-DM1 relapsed/refractory. Our findings indicate that this biparatopic ADC has promising potential as an effective therapy for metastatic breast cancer and a broader patient population may benefit from this unique HER2-targeting ADC.

XPC DNA repair gene mutations result in the cancer-prone disorder xeroderma pigmentosum. The XPC gene spans 33 kb and has 16 exons (82-882 bp) and 15 introns (0.08-5.4 kb). A 1.6 kb intron was found within exon 5. Sensitive real- time quantitative reverse transcription-polymerase chain reaction methods were developed to measure full-length XPC mRNA (the predominant form) and isoforms that skipped exons 4, 7 or 12. Exon 7 was skipped in approximately 0.07% of XPC mRNAs, consistent with the high information content of the exon 7 splice acceptor and donor sites (12.3 and 10.4 bits). In contrast, exon 4 was skipped in approximately 0.7% of the XPC mRNAs, consistent with the low information content of the exon 4 splice acceptor (-0.1 bits). A new common C/A single nucleotide polymorphism in the XPC intron 11 splice acceptor site (58% C in 97 normals) decreased its information content from 7.5 to 5.1 bits. Fibroblasts homozygous for A/A had significantly higher levels (approximately 2.6-fold) of the XPC mRNA isoform that skipped exon 12 than those homozygous for C/C. This abnormally spliced XPC mRNA isoform has diminished DNA repair function and may contribute to cancer susceptibility.

Xeroderma pigmentosum group C (XP-C) is a rare autosomal recessive disorder. Patients with two mutant alleles of the XPC DNA repair gene have sun sensitivity and a 1000-fold increase in skin cancers. Clinically normal parents of XP-C patients have one mutant allele and one normal allele. As a step toward evaluating cancer risk in these XPC heterozygotes we characterized cells from 16 XP families. We identified 15 causative mutations (5 frameshift, 6 nonsense and 4 splicing) in the XPC gene in cells from 16 XP probands. All had premature termination codons (PTC) and absence of normal XPC protein on western blotting. The cell lines from 26 parents were heterozygous for the same mutations. We employed a real-time quantitative reverse transcriptase-PCR assay as a rapid and sensitive method to measure XPC mRNA levels. The mean XPC mRNA levels in the cell lines from the XP-C probands were 24% (P<10(-7)) of that in 10 normal controls. This reduced XPC mRNA level in cells from XP-C patients was caused by the PTC that induces nonsense-mediated mRNA decay. The mean XPC mRNA levels in cell lines from the heterozygous XP-C carriers were intermediate (59%, P=10(-4)) between the values for the XP patients and the normal controls. This study demonstrates reduced XPC mRNA levels in XP-C patients and heterozygotes. Thus, XPC mRNA levels may be evaluated as a marker of cancer susceptibility in carriers of mutations in the XPC gene.

No abstract

Six allosteric HIV-1 entry inhibitor modulators of the chemokine (C-C motif) receptor 5 (CCR5) receptor are compared for their potency as inhibitors of HIV-1 entry [infection of human osteosarcoma (HOS) cells and peripheral blood mononuclear cells (PBMC)] and antagonists of chemokine (C-C motif) ligand 3-like 1 [CCL3L1]-mediated internalization of CCR5. This latter activity has been identified as a beneficial action of CCL3L1 in prolonging survival after HIV-1 infection (Science 307: 1434 -1440, 2005). The allosteric nature of these modulators was further confirmed with the finding of a 58-fold (HOS cells) and 282-fold (PBMC) difference in relative potency for blockade of CCL3L1-mediated internalization versus HIV-1 entry. For the CCR5 modulators, statistically significant differences in this ratio were found for maraviroc, vicriviroc, aplaviroc, Sch-C, TAK652, and TAK779. For instance, although TAK652 is 13-fold more potent as an HIV-1 inhibitor (over blockade of CCL3L1-mediated CCR5 internalization), this ratio of potency is reversed for Sch-C (22-fold more potent for CCR5-mediated internalization over HIV-1 entry). Quantitative analyses of the insurmountable antagonism of CCR5 internalization by these ligands suggest that all of them reduce the efficacy of CCL3L1 for CCR5 internalization. The relatively small magnitude of dextral displacement accompanying the depression of maximal responses for aplaviroc, maraviroc and vicriviroc suggests that these modulators have minimal effects on CCL3L1 affinity, although possible receptor reserve effects obscure complete interpretation of this effect. These data are discussed in terms of the possible benefits of sparing natural CCR5 chemokine function in HIV-1 entry inhibition treatment for AIDS involving allosteric inhibitors.HIV-1 has been shown to use the chemokine C receptor CCR5 to gain entry into cells to cause infection (Alkhatib et al., 1996;Choe et al., 1996;Deng et al., 1996;Dragic et al., 1996); therefore, efforts have centered on the development of CCR5 HIV entry inhibitors for potential treatment of AIDS and AIDS prevention. Several molecules have been described previously (Kazmierski et al., 2003(Kazmierski et al., , 2007Schols, 2006); presently, one of them, maraviroc, has been approved for therapeutic use (Fä tkenheuer et al., 2005). Another CCR5 entry inhibitor, aplaviroc (Demarest et al., 2004; Article, publication date, and citation information can be found at

In the originally published version of this article, in Figure 2E the representative immunoblots of lysates from antibody-treated cells did not indicate spliced lines between lane 7 and lane 8. When preparing the figure for publication, these lanes had been spliced together from the same immunoblot, as indicated in the corrected Figure 2E shown here, to remove an irrelevant lane. The authors apologize for any confusion this may have caused.948 Cancer Cell 35, 948-949, June 10, 2019 ª 2019 Elsevier Inc.

The lariat branch point sequence (BPS) is crucial for splicing of human nuclear pre-mRNA yet BPS mutations have infrequently been reported to cause human disease. Using an inverse RT-PCR technique we mapped two BPS to the adenosine residues at positions -4 and -24 in intron 3 of the human XPC DNA repair gene. We identified homozygous mutations in each of these BPS in two newly diagnosed Turkish families with the autosomal recessive disorder xeroderma pigmentosum (XP). Cells from two severely affected children in family A harbor a homozygous point mutation in XPC intron 3 (-9 T to A), located within the downstream BPS. Using a real-time quantitative reverse transcriptase-polymerase chain reaction (QRT-PCR) assay, these cells expressed no detectable (<0.1%) normal XPC message. Instead they expressed an XPC mRNA isoform with deletion of exon 4 that has no DNA repair activity in a host cell reactivation (HCR) assay. In contrast, in cells from three mildly affected siblings in family B, the BPS adenosine located at the -24 position in XPC intron 3 is mutated to a G. Real-time QRT-PCR revealed 3-5% of normal XPC message. These cells from family B had a higher level of HCR than cells from the severely affected siblings in family A, who had multiple skin cancers. Mutations identified in two BPS of the XPC intron 3 resulted in alternative splicing that impaired DNA repair function, thus implicating both of these BPS as essential for normal pre-mRNA splicing. However, a small amount of normal XPC mRNA can provide partial protection against skin cancers.