Drug-biomarker co-development in oncology - 20 years and counting.

Predictive biomarkers for oncology are necessary to accurately identify patients who will benefit from anticancer treatment. Recently approved oncology drugs target discrete molecular aberrations or pathways in tumor cells and consequently are active on a subset of patient population, yet clinical studies have shown that not all biomarker-positive patients respond. The advancement of predictive biomarkers needs to detect novel and evolving drug resistance mechanisms, not only to guide the selection of patient subsets for specific treatments, but to identify new therapeutic targets. Going beyond the "one marker, one drug" model to incorporate genomics, transcriptomics, and receptor status assessments during biomarker-drug co-development can aid in the successful application of molecular marker-based cancer therapy. This review provides the latest update of biomarker-based cancer therapeutics approved by the US Food and Drug Administration. We provide case studies of therapeutics selectively targeting HER2, EGFR, or PD-1/PD-L1 signaling pathways. We also discuss the challenges and promising future directions in the co-development of targeted cancer therapeutics and paired predictive biomarkers.

Differences in binding to the ILK complex determines kindlin isoform adhesion localization and integrin activation.

Kindlins are essential FERM-domain-containing focal adhesion (FA) proteins required for proper integrin activation and signaling. Despite the widely accepted importance of each of the three mammalian kindlins in cell adhesion, the molecular basis for their function has yet to be fully elucidated, and the functional differences between isoforms have generally not been examined. Here, we report functional differences between kindlin-2 and -3 (also known as FERMT2 and FERMT3, respectively); GFP-tagged kindlin-2 localizes to FAs whereas kindlin-3 does not, and kindlin-2, but not kindlin-3, can rescue α5ß1 integrin activation defects in kindlin-2-knockdown fibroblasts. Using chimeric kindlins, we show that the relatively uncharacterized kindlin-2 F2 subdomain drives FA targeting and integrin activation. We find that the integrin-linked kinase (ILK)-PINCH-parvin complex binds strongly to the kindlin-2 F2 subdomain but poorly to that of kindlin-3. Using a point-mutated kindlin-2, we establish that efficient kindlin-2-mediated integrin activation and FA targeting require binding to the ILK complex. Thus, ILK-complex binding is crucial for normal kindlin-2 function and differential ILK binding contributes to kindlin isoform specificity.

Integrin cytoplasmic tail interactions.

Integrins are heterodimeric cell surface adhesion receptors essential for multicellular life. They connect cells to the extracellular environment and transduce chemical and mechanical signals to and from the cell. Intracellular proteins that bind the integrin cytoplasmic tail regulate integrin engagement of extracellular ligands as well as integrin localization and trafficking. Cytoplasmic integrin-binding proteins also function downstream of integrins, mediating links to the cytoskeleton and to signaling cascades that impact cell motility, growth, and survival. Here, we review key integrin-interacting proteins and their roles in regulating integrin activity, localization, and signaling.

Kindlin binds migfilin tandem LIM domains and regulates migfilin focal adhesion localization and recruitment dynamics.

Focal adhesions (FAs), sites of tight adhesion to the extracellular matrix, are composed of clusters of transmembrane integrin adhesion receptors and intracellular proteins that link integrins to the actin cytoskeleton and signaling pathways. Two integrin-binding proteins present in FAs, kindlin-1 and kindlin-2, are important for integrin activation, FA formation, and signaling. Migfilin, originally identified in a yeast two-hybrid screen for kindlin-2-interacting proteins, is a LIM domain-containing adaptor protein found in FAs and implicated in control of cell adhesion, spreading, and migration. By binding filamin, migfilin provides a link between kindlin and the actin cytoskeleton. Here, using a combination of kindlin knockdown, biochemical pulldown assays, fluorescence microscopy, fluorescence resonance energy transfer (FRET), and fluorescence recovery after photobleaching (FRAP), we have established that the C-terminal LIM domains of migfilin dictate its FA localization, shown that these domains mediate an interaction with kindlin in vitro and in cells, and demonstrated that kindlin is important for normal migfilin dynamics in cells. We also show that when the C-terminal LIM domain region is deleted, then the N-terminal filamin-binding region of the protein, which is capable of targeting migfilin to actin-rich stress fibers, is the predominant driver of migfilin localization. Our work details a correlation between migfilin domains that drive kindlin binding and those that drive FA localization as well as a kindlin dependence on migfilin FA recruitment and mobility. We therefore suggest that the kindlin interaction with migfilin LIM domains drives migfilin FA recruitment, localization, and mobility.

Filamin A controls matrix metalloproteinase activity and regulates cell invasion in human fibrosarcoma cells.

Filamins are an important family of actin-binding proteins that, in addition to bundling actin filaments, link cell surface adhesion proteins, signaling receptors and channels to the actin cytoskeleton, and serve as scaffolds for an array of intracellular signaling proteins. Filamins are known to regulate the actin cytoskeleton, act as mechanosensors that modulate tissue responses to matrix density, control cell motility and inhibit activation of integrin adhesion receptors. In this study, we extend the repertoire of filamin activities to include control of extracellular matrix (ECM) degradation. We show that knockdown of filamin increases matrix metalloproteinase (MMP) activity and induces MMP2 activation, enhancing the ability of cells to remodel the ECM and increasing their invasive potential, without significantly altering two-dimensional random cell migration. We further show that within filamin A, the actin-binding domain is necessary, but not sufficient, to suppress the ECM degradation seen in filamin-A-knockdown cells and that dimerization and integrin binding are not required. Filamin mutations are associated with neuronal migration disorders and a range of congenital malformations characterized by skeletal dysplasia and various combinations of cardiac, craniofacial and intestinal anomalies. Furthermore, in breast cancers loss of filamin A has been correlated with increased metastatic potential. Our data suggest that effects on ECM remodeling and cell invasion should be considered when attempting to provide cellular explanations for the physiological and pathological effects of altered filamin expression or filamin mutations.

A conserved lipid-binding loop in the kindlin FERM F1 domain is required for kindlin-mediated αIIbß3 integrin coactivation.

The activation of heterodimeric integrin adhesion receptors from low to high affinity states occurs in response to intracellular signals that act on the short cytoplasmic tails of integrin ß subunits. Binding of the talin FERM (four-point-one, ezrin, radixin, moesin) domain to the integrin ß tail provides one key activation signal, but recent data indicate that the kindlin family of FERM domain proteins also play a central role. Kindlins directly bind integrin ß subunit cytoplasmic domains at a site distinct from the talin-binding site, and target to focal adhesions in adherent cells. However, the mechanisms by which kindlins impact integrin activation remain largely unknown. A notable feature of kindlins is their similarity to the integrin-binding and activating talin FERM domain. Drawing on this similarity, here we report the identification of an unstructured insert in the kindlin F1 FERM domain, and provide evidence that a highly conserved polylysine motif in this loop supports binding to negatively charged phospholipid head groups. We further show that the F1 loop and its membrane-binding motif are required for kindlin-1 targeting to focal adhesions, and for the cooperation between kindlin-1 and -2 and the talin head in αIIbß3 integrin activation, but not for kindlin binding to integrin ß tails. These studies highlight the structural and functional similarities between kindlins and the talin head and indicate that as for talin, FERM domain interactions with acidic membrane phospholipids as well ß-integrin tails contribute to the ability of kindlins to activate integrins.

Structural and functional characterization of the kindlin-1 pleckstrin homology domain.

Inside-out activation of integrins is mediated via the binding of talin and kindlin to integrin ß-subunit cytoplasmic tails. The kindlin FERM domain is interrupted by a pleckstrin homology (PH) domain within its F2 subdomain. Here, we present data confirming the importance of the kindlin-1 PH domain for integrin activation and its x-ray crystal structure at a resolution of 2.1 Å revealing a C-terminal second α-helix integral to the domain but found only in the kindlin protein family. An isoform-specific salt bridge occludes the canonical phosphoinositide binding site, but molecular dynamics simulations display transient switching to an alternative open conformer. Molecular docking reveals that the opening of the pocket would enable potential ligands to bind within it. Although lipid overlay assays suggested the PH domain binds inositol monophosphates, surface plasmon resonance demonstrated weak affinities for inositol 3,4,5-triphosphate (Ins(3,4,5)P(3); K(D) ∼100 µM) and no monophosphate binding. Removing the salt bridge by site-directed mutagenesis increases the PH domain affinity for Ins(3,4,5)P(3) as measured by surface plasmon resonance and enables it to bind PtdIns(3,5)P(2) on a dot-blot. Structural comparison with other PH domains suggests that the phosphate binding pocket in the kindlin-1 PH domain is more occluded than in kindlins-2 and -3 due to its salt bridge. In addition, the apparent affinity for Ins(3,4,5)P(3) is affected by the presence of PO(4) ions in the buffer. We suggest the physiological ligand of the kindlin-1 PH domain is most likely not an inositol phosphate but another phosphorylated species.

Safety outcomes when switching between biosimilars and reference biologics: A systematic review and meta-analysis.

Biosimilars are increasingly available for the treatment of many serious disorders, however some concerns persist about switching a patient to a biosimilar whose condition is stable while on the reference biologic. Randomized controlled studies and extension studies with a switch treatment period (STP) to or from a biosimilar and its reference biologic were identified from publicly available information maintained by the U.S. Food and Drug Administration (FDA). These findings were augmented with data from peer reviewed publications containing information not captured in FDA reviews. Forty-four STPs were identified from 31 unique studies for 21 different biosimilars. Data were extracted and synthesized following PRISMA guidelines. Meta-analysis was conducted to estimate the overall risk difference across studies. A total of 5,252 patients who were switched to or from a biosimilar and its reference biologic were identified. Safety data including deaths, serious adverse events, and treatment discontinuation showed an overall risk difference (95% CI) of -0.00 (-0.00, 0.00), 0.00 (-0.01, 0.01), -0.00 (-0.01, 0.00) across STPs, respectively. Immunogenicity data showed similar incidence of anti-drug antibodies and neutralizing antibodies in patients within a STP who were switched to or from a biosimilar to its reference biologic and patients who were not switched. Immune related adverse events such as anaphylaxis, hypersensitivity reactions, and injections site reactions were similar in switched and non-switched patients. This first systematic review using statistical methods to address the risk of switching patients between reference biologics and biosimilars finds no difference in the safety profiles or immunogenicity rates in patients who were switched and those who remained on a reference biologic or a biosimilar.

Cell adhesion: a FERM grasp of the tail sorts out integrins.

As well as modulating integrin activation, a conserved NPxY motif in integrin cytoplasmic tails that binds the FERM-domain-containing proteins kindlin and sorting nexin 17 plays pivotal roles in integrin recycling and degradation.