Abstract PR03: Selective degradation of mutant PIK3CA promotes increased mutant specificity in a subset of PI3K ATP-competitive inhibitors

Activating mutations in PIK3CA are among the most significant oncogenic events across all cancers, making it an important target for drug development. Yet the application of PI3K inhibitors in the clinic has been limited by the difficulty of achieving an adequate therapeutic window, due to the critical role that PI3K signaling plays in normal physiologic processes, such as glucose homeostasis. In theory, the therapeutic window could be improved if it were possible to design mutant selective inhibitors, as has been demonstrated with other oncogenes such as EGFR. However, unlike EGFR, the most predominant PIK3CA activating mutations do not reside in the kinase active site, presenting a major challenge for rational structure-based design. Nevertheless, it was recently shown that the PI3K inhibitor taselisib is able to achieve modest levels of mutant selectivity both across cancer lines as well as in cell lines that were engineered to express mutant or wild-type PIK3CA. Taselisib was also shown to selectively induce degradation of mutant versus wild-type PIK3CA, leading to the speculation that this degradation may be responsible for the observed selectivity. In order to better understand the origins of mutant selectivity for taselisib and several other PIK3CA inhibitors, we assessed these inhibitors in a variety of biophysical and biochemical assays under conditions designed to mimic physiologic settings. In parallel, we also investigated the mechanistic basis of this selectivity in our engineered cell lines. Our results are consistent with the hypothesis that selective degradation of mutant PIK3CA is the predominant mechanism underlying mutant selectivity for this class of PIK3CA active site inhibitors.

This abstract is also being presented as Poster B03.

Citation Format: Lan Nguyen, Kyle Edgar, Kyung Song, Stephen Schmidt, Victorai Schutz, Noriko Ishisoko, Eric Torres, Akash Das, Divya Murali, Steve Sideris, Timothy Wendorff, Matt Saabye, Hans Purkey, Jawahar Sudhamsu, Steven Staben, Emily Hanan, Georgia Hatzivassiliou, Lori Friedman, Nicholas F. Endres. Selective degradation of mutant PIK3CA promotes increased mutant specificity in a subset of PI3K ATP-competitive inhibitors [abstract]. In: Proceedings of the AACR Special Conference on Targeting PI3K/mTOR Signaling; 2018 Nov 30-Dec 8; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Res 2020;18(10_Suppl):Abstract nr PR03.

Phosphorylation primes vinculin for activation

Vinculin phosphorylation has been implicated as a potential mechanism for focal adhesion growth and maturation. Four vinculin residues-Y100, S1033, S1045, and Y1065-are phosphorylated by kinases during focal adhesion maturation. In this study, phosphorylation at each of these residues is simulated using molecular dynamics models. The simulations demonstrate that once each phosphorylated vinculin structure is at equilibrium, significant local conformational changes result that may impact either vinculin activation or vinculin binding to actin and PIP2. Simulation of vinculin activation after phosphorylation shows that the added phosphoryl groups can prime vinculin for activation. It remains to be seen if vinculin can be phosphorylated at S1033 in vivo, but these simulations highlight that in the event of a S1033 phophorylation vinculin will likely be primed for activation.

Why Hofmeister effects of many salts favor protein folding but not DNA helix formation

The majority ( approximately 70%) of surface buried in protein folding is hydrocarbon, whereas in DNA helix formation, the majority ( approximately 65%) of surface buried is relatively polar nitrogen and oxygen. Our previous quantification of salt exclusion from hydrocarbon (C) accessible surface area (ASA) and accumulation at amide nitrogen (N) and oxygen (O) ASA leads to a prediction of very different Hofmeister effects on processes that bury mostly polar (N, O) surface compared to the range of effects commonly observed for processes that bury mainly nonpolar (C) surface, e.g., micelle formation and protein folding. Here we quantify the effects of salts on folding of the monomeric DNA binding domain (DBD) of lac repressor (lac DBD) and on formation of an oligomeric DNA duplex. In accord with this prediction, no salt investigated has a stabilizing Hofmeister effect on DNA helix formation. Our ASA-based analyses of model compound data and estimates of the surface area buried in protein folding and DNA helix formation allow us to predict Hofmeister effects on these processes. We observe semiquantitative to quantitative agreement between these predictions and the experimental values, obtained from a novel separation of coulombic and Hofmeister effects. Possible explanations of deviations, including salt-dependent unfolded ensembles and interactions with other types of surface, are discussed.

Interactions of the osmolyte glycine betaine with molecular surfaces in water: thermodynamics, structural interpretation, and prediction of m-values

Noncovalent self-assembly of biopolymers is driven by molecular interactions between functional groups on complementary biopolymer surfaces, replacing interactions with water. Since individually these interactions are comparable in strength to interactions with water, they have been difficult to quantify. Solutes (osmolytes, denaturants) exert often large effects on these self-assembly interactions, determined in sign and magnitude by how well the solute competes with water to interact with the relevant biopolymer surfaces. Here, an osmometric method and a water-accessible surface area (ASA) analysis are developed to quantify and interpret the interactions of the remarkable osmolyte glycine betaine (GB) with molecular surfaces in water. We find that GB, lacking hydrogen bond donors, is unable to compete with water to interact with anionic and amide oxygens; this explains its effectiveness as an osmolyte in the Escherichia coli cytoplasm. GB competes effectively with water to interact with amide and cationic nitrogens (hydrogen bonding) and especially with aromatic hydrocarbon (cation-pi). The large stabilizing effect of GB on lac repressor-lac operator binding is predicted quantitatively from ASA information and shown to result largely from dehydration of anionic DNA phosphate oxygens in the protein-DNA interface. The incorporation of these results into theoretical and computational analyses will likely improve the ability to accurately model intra- and interprotein interactions. Additionally, these results pave the way for development of solutes as kinetic/mechanistic and thermodynamic probes of conformational changes and formation/disruption of molecular interfaces that occur in the steps of biomolecular self-assembly processes.

[Locomotion and depression. Clinical and physiological aspects of gait alterations in Parkinson's disease and major depression]

BACKGROUND

Behavioral disturbances of patients with major depression manifest in various motor domains and are relevant for differential diagnosis, therapeutic interventions, as residual symptoms and possibly early manifestation of Parkinson's disease. Alterations of gait as the main component of locomotion are a clinically well-known motor phenomenon of depressed patients. Therefore, pathophysiology of gait disturbances, different methods to analyze gait and empirical findings in patients with major depression are summarized.

METHODS

The current literature was examined including information of manufacturers, Medline, PubMed, PsychLIT and Excerpta Medica. Findings in healthy subjects, in Parkinson's disease, and in major depression are discussed in detail regarding specificity and clinical relevance.

RESULTS

Kinematic analysis of gait regulation by videography, ultrasound, opto-electronic measures reveals information about disturbances in central nervous motor programming. Only few studies exist about quantitative data of gait alterations in patients with major depression. Results indicate disturbances in functions of the basal ganglia.

CONCLUSIONS

Analysis of gait using modern technology yields information about cortical and subcortical dysfunctions. Empirical findings in major depression need further investigation regarding their relevance as residual symptoms, as response predictors, and as risk factors for manifestation of Parkinson's disease.

Comorbid anxiety and affective disorder in alcohol-dependent patients seeking treatment: the first Multicentre Study in Germany

The goals of this study were to describe demographic variables, drinking history, and the 6-month prevalence of Axis I comorbidity among alcohol-dependent subjects in GERMANY: The variables: amount of alcohol consumption, age at onset of the first alcohol consumed, age at onset of daily alcohol consumption, age at onset of withdrawal symptoms and number of detoxifications were related to the different comorbid disorders and gender. In this study, 556 patients from 25 alcohol treatment centres were enrolled between 1 January 1999 and 30 April 1999. After a minimum of 10 days of sobriety patients who fulfilled ICD-10 and DSM-IV criteria of alcohol dependence were interviewed for data collection using the Mini-DIPS (German version of the Anxiety Disorders Interview Schedule) and a standardized psychosocial interview. The 6-month prevalence of comorbid Axis I disorders was 53.1%. Among the patients with comorbidity, affective and anxiety disorders were most frequent. Comorbid stress disorder was associated with an early start of drinking, an early beginning of withdrawal symptoms, highest number of detoxifications, and the highest amount of alcohol consumed. Female patients with anxiety disorder consumed more alcohol and started earlier than females without this comorbid disorder. The data do not answer the question of the pathogenesis of comorbid disorders and alcoholism, but indicate that stress disorders in alcoholic patients and anxiety disorders in female alcoholics influence the course and severity of alcoholism.

[Disordered behavioral control in psychiatric illnesses. Neurophysiological aspects of impulsive behavior]

OBJECTIVE

Dysfunction of behavioral control represents a central component of many psychiatric disorders and may be connected with self-mutilating and antisocial behavior. However, only a few studies have investigated objective assessment and quantification of impulsive behavior, which is relevant for psychiatric practice and research. Because new techniques enable objective assessment of behavior generation and execution, the current knowledge about neurophysiological aspects of behavioral control is summarized.

METHOD

The contemporary literature on neuronal mechanisms of initiation and execution of behavior and movements and new neurophysiological methods and findings are discussed in respect to their application in psychiatry.

RESULTS

Behavior, defined as movements of a body in time and space, is the result of cortical and subcortical processes. These consist of two general components: (1) perception and selection of a stimulus and (2) execution of a movement, including decision and planning phases. Planning and execution, modulated by cognition and emotions, are dependent on the balance of inhibitory and excitatory aspects of behavior control. Combined detection of electrical brain activity and kinematic analysis of peripheral movements enables the analysis of control mechanisms.

CONCLUSION

Impulsiveness and inhibition of behavior depend on neuronal control mechanisms which can be analyzed by neurophysiological methods. Objective assessment of impulsive behavior related to psychiatric disturbances including eating disorders, substance abuse, and personality disorders may clarify underlying neurobiological mechanisms and enable rational pharmaco- and psychotherapeutic interventions.

Spatiotemporal gait patterns during over ground locomotion in major depression compared with healthy controls

Alterations of locomotion are frequent, observable features of patients suffering from depression and have been investigated in these patients by actigraphy, cinematography and ground reaction forces. However, spatiotemporal parameters and neurophysiological mechanisms of gait have not yet been studied in depth in depression. The relationship between spatial and temporal parameters may yield insight into the pathophysiology of altered movements in depression. Therefore, gait patterns were quantitatively assessed and analysed in depressed subjects (n=16) and compared to matched healthy controls. Spatiotemporal gait parameters were measured during over ground walking at self-selected walking speed on a walkway previously validated in healthy subjects and used for orthopaedic and neurological patients. Compared to controls, depressed patients showed significantly lower gait velocity (p<0.001), reduced stride length (p<0.005), double limb support (p<0.005) and cycle duration (p<0.005). There was a significant correlation between cadence and gait velocity in depressed patients (r=0.51, p<0.05), but not in healthy controls (r=0.11, p>0.05). In patients with major depression, reduced gait velocity was associated with stride hypometria and increased cycle duration. Velocity was associated with cadence in depressed patients but not in healthy controls. The results may indicate possible deficiencies in the motor control system in depression. These first results about alterations of spatiotemporal gait patterns in depression warrant further longitudinal and experimental studies.