No abstract

Druglike small molecules with photoswitchable bioactivity—photopharmaceuticals—allow biologists to perform studies with exquisitely precise and reversible, spatial and temporal control over critical biological systems inaccessible to genetic manipulation. The photoresponsive pharmacophores disclosed have been almost exclusively azobenzenes, which has limited the structural and substituent scope of photopharmacology. More detrimentally, for azobenzene reagents, it is not researchers’ needs for adapted experimental tools, but rather protein binding site sterics, that typically force whether the trans (dark) or cis (lit) isomer is the more bioactive. We now present the rational design of HOTubs, the first hemithioindigo‐based pharmacophores enabling photoswitchable control over endogenous biological activity in cellulo. HOTubs optically control microtubule depolymerisation and cell death in unmodified mammalian cells. Notably, we show how the asymmetry of hemithioindigos allows a priori design of either Z‐ or E‐ (dark‐ or lit)‐toxic antimitotics, whereas the corresponding azobenzenes are exclusively lit‐toxic. We thus demonstrate that hemithioindigos enable an important expansion of the substituent and design scope of photopharmacological interventions for biological systems.

Small molecule inhibitors are prime reagents for studies in microtubule cytoskeleton research, being applicable across a range of biological models and not requiring genetic engineering. However, traditional chemical inhibitors cannot be experimentally applied with spatiotemporal precision suiting the length and time scales inherent to microtubule-dependent cellular processes. We have synthesised photoswitchable paclitaxel-based microtubule stabilisers, whose binding is induced by photoisomerisation to their metastable state. Photoisomerising these reagents in living cells allows optical control over microtubule network integrity and dynamics, cell division and survival, with biological response on the timescale of seconds and spatial precision to the level of individual cells within a population. In primary neurons, they enable regulation of microtubule dynamics resolved to subcellular regions within individual neurites. These azobenzene-based microtubule stabilisers thus enable non-invasive, spatiotemporally precise modulation of the microtubule cytoskeleton in living cells, and promise new possibilities for studying intracellular transport, cell motility, and neuronal physiology.

<p>Specialised cellular networks of oxidoreductases coordinate the dithiol/disulfide-exchange reactions that control metabolism, protein regulation, and redox homeostasis. For probes to be selective for redox enzymes and effector proteins (nM to µM concentrations), they must also be able to resist nonspecific triggering by the ca. 50 mM background of non-catalytic cellular monothiols. However, no such selective reduction-sensing systems have yet been established. Here, we used rational structural design to independently vary thermodynamic and kinetic aspects of disulfide stability, creating a series of unusual disulfide reduction trigger units designed for stability to monothiols. We integrated the motifs into modular series of fluorogenic probes that release and activate an arbitrary chemical cargo upon reduction, and compared their performance to that of the literature-known disulfides. The probes were comprehensively screened for biological stability and selectivity against a range of redox effector proteins and enzymes. This design process delivered the first disulfide probes with excellent stability to monothiols, yet high selectivity for the key redox-active protein effector, thioredoxin. We anticipate that further applications of these novel disulfide triggers will deliver unique probes targeting cellular thioredoxins. We also anticipate that further tuning following this design paradigm will deliver redox probes for other important dithiol-manifold redox proteins, that will be useful in revealing the hitherto hidden dynamics of endogenous cellular redox systems.</p>

The transcription factor Sox2 has been shown to play essential roles during embryonic development as well as in cancer. To more precisely understand tumor biology and to identify potential therapeutical targets, we thoroughly investigated the expression and function of Sox2 in medulloblastoma, a malignant embryonic brain tumor that initiates in the posterior fossa and eventually spreads throughout the entire cerebrospinal axis. We examined a large series of tumor samples (n ¼ 188) to show that SOX2 is specifically expressed in Sonic hedgehog (SHH)-associated medulloblastoma with an interesting preponderance in adolescent and adult cases. We further show that cerebellar granule neuron precursors (CGNP), which are believed to serve as the cell of origin for this medulloblastoma subgroup, express Sox2 in early stages. Also, Shh-associated medulloblastoma can be initiated from such Sox2-positive CGNPs in mice. Independent of their endogenous Sox2 expression, constitutive activation of Shh signaling in CGNPs resulted in significantly enhanced proliferation and ectopic expression of Sox2 in vitro and Sox2-positive medulloblastoma in vivo. Genetic ablation of Sox2 from murine medulloblastoma did not affect survival, most likely due to a compensatory overexpression of Sox3. However, acute deletion of Sox2 from primary cultures of CGNPs with constitutive Shh signaling significantly decreased proliferation, whereas overexpression of Sox2 enhanced proliferation of murine medulloblastoma cells. We conclude that Sox2 is a marker for Shhdependent medulloblastomas where it is required and sufficient to drive tumor cell proliferation. Cancer Res; 73(12); 3796-807. Ó2013 AACR.