Co-occurring gain-of-function mutations in HER2 and HER3 modulate HER2/HER3 activation, oncogenesis, and HER2 inhibitor sensitivity

Activating mutations in HER2 (ERBB2) drive the growth of a subset of breast and other cancers and tend to co-occur with HER3 (ERBB3) missense mutations. The HER2 tyrosine kinase inhibitor neratinib has shown clinical activity against HER2-mutant tumors. To characterize the role of HER3 mutations in HER2-mutant tumors, we integrate computational structural modeling with biochemical and cell biological analyses. Computational modeling predicts that the frequent HER3E928G kinase domain mutation enhances the affinity of HER2/HER3 and reduces binding of HER2 to its inhibitor neratinib. Co-expression of mutant HER2/HER3 enhances HER2/HER3 co-immunoprecipitation and ligand-independent activation of HER2/HER3 and PI3K/AKT, resulting in enhanced growth, invasiveness, and resistance to HER2-targeted therapies, which can be reversed by combined treatment with PI3Kα inhibitors. Our results provide a mechanistic rationale for the evolutionary selection of co-occurring HER2/HER3 mutations and the recent clinical observations that HER3 mutations are associated with a poor response to neratinib in HER2-mutant cancers.

Emollient structure and chemical functionality effects on the biomechanical function of human stratum corneum

OBJECTIVE

Cosmetic emollients are widely used in skincare formulations due to their ability to 'soften' the skin and modulate formulation spreadability. Though emollients are commonly used, little is known about their effects on the biomechanical barrier properties of human stratum corneum (SC), which play a critical role in consumer perception of formulation efficacy. Accordingly, our objective was to provide new insights with a study involving fourteen cosmetic emollient molecules with widely varying structures, molecular weights, SC diffusivities, topological polar surface areas (TPSAs), viscosities and chemical functionalities.

METHODS

Mechanical stress in the SC was measured in vitro using a substrate curvature measurement technique. Stress development due to SC drying was measured before and after topical treatment with cosmetic emollients. Emollient diffusivity and alterations to lipid content in SC after treatment were measured via ATR-FTIR spectroscopy. The maximum penetration volume of emollient in SC was characterized to elucidate mechanisms underlying emollient effects on stress.

RESULTS

The application of all cosmetic emollients caused a reduction in SC mechanical stress under dehydrating conditions, and a linear correlation was discovered between emollient penetration volume and the degree of stress reduction. These molecules also induced increases in stress equilibration rate, signalling changes to SC transport kinetics. Stress equilibration rate increases linearly correlated with decreasing intensity of the νCH2 band, indicating a previously unknown interaction between cosmetic emollients and SC lipids. Stress and penetration volume results were rationalized in terms of a multi-parameter model including emollient molecular weight, diffusivity, TPSA and viscosity.

CONCLUSION

We provide a new rational basis for understanding the effects of cosmetic emollient choice on biomechanical properties affecting SC barrier function and consumer perception. We demonstrate for the first time that emollients very likely reduce SC mechanical stress through their ability to take up volume when penetrating the SC, and how molecular weight, SC diffusivity, TPSA and viscosity are predictive of this ability. As cosmetic formulations continue to evolve to meet the needs of customers, emollient molecules can be selected that not only contribute to formulation texture and/or spreadability but that also leverage this novel connection between emollient penetration and SC biomechanics.

Abstract GS6-04: Co-occurring gain-of-function mutations in HER2 and HER3 modulate HER2/HER3 activation, breast cancer progression, and HER2 inhibitor sensitivity

Activating mutations in HER2 (ERBB2) drive the growth of a subset of breast cancers. The HER2 tyrosine kinase inhibitor (TKI) neratinib has shown clinical activity against cancers harboring HER2 activating mutations. Co-occurring HER2 and HER3 (ERBB3) mutations have been reported to co-occur in patients with breast cancer, suggesting the possibility of cooperativity of both oncogenes.

Interrogation of the Project GENIE database revealed that gain-of-function missense mutations in HER2 and HER3 exhibit statistically significant co-occurence [q value=0.006 (breast cancer); q=1.01x10−26 (all cancer types)]. On the other hand, HER3 mutations were nearly absent in cancers harboring HER2 in-frame insertions and cancers with HER2 amplification. In breast cancer, co-occurring HER3 mutations were mutually exclusive with PIK3CA mutations, suggestive of potential functional redundancy.

Sixty-eight unique breast cancers from cBioPortal, GENIE, and Foundation Medicine were found to harbor co-occurring mutations in HER2 and HER3, the most common of which were L755S, V777L, L869R/Q, and S310F, each with HER3E928G. Computational structural modeling suggested that the E928G substitution in HER3 enhances the interface energy between HER2 and HER3 kinase domains. This was confirmed by co-immunoprecipitation assays in HEK293 cells transfected with wild-type (WT) or mutant HER2 and HER3. This binding was further enhanced between HER3E928G and HER2 missense mutants. Further, structural modeling of L755S, V777L, and L869R/Q in HER2 revealed that each of these mutations increase HER2 kinase activation. Accordingly, each of these HER2 mutants, as well has HER2S310F in the extracellular domain, increased ligand-independent P-HER2 and P-HER3 in HEK293 cells. P-HER3 levels were the highest HEK293 in cells co-expressing HER2 and HER3 mutations. Similar results were observed in MCF10A breast epithelial cells stably expressing mutant HER2 and mutant HER3. Enhanced activation of the PI3K pathway (P-AKT and P-S6) was observed in cells expressing both mutations compared to cells expressing mutant HER2 with HER3WT or vice-versa.

MCF10A HER2WT/HER3E982G cells did not form colonies in ligand-free 3D Matrigel assays, whereas cells expressing HER2L755S/HER3WT formed organized acini. In contrast, HER2L755S/HER3E928G acini were highly invasive. Addition of the HER3 ligand neuregulin (NRG) to HER2L755S/HER3WT cells phenocopied the effect of HER3E928G. Interestingly, MCF10A cells expressing the HER2Y772_A775 (YVMA) insertion together with HER3WT also formed invasive acini in the absence of NRG, suggesting that this HER2 insertion mutation is more transforming than HER2 missense mutations. Similar results were obtained with invasion assays using Matrigel-coated chambers.

Finally, we examined the effects of HER2/HER3 co-mutations on sensitivity to HER2 inhibitors. Structural analysis was performed of the HER3/HER2 kinase domain complex docked with neratinib. HER3E928G, when bound to HER2, is located close to the neratinib-binding pocket of HER2 and was predicted to reduce HER2/neratinib binding affinity. Similarly, co-expression of HER3E928G reduced the ability of neratinib to inhibit P-HER3, P-AKT, P-S6, and growth of MCF10A cells expressing HER2/HER3 co-mutations. The PI3Kα inhibitor alpelisib restored neratinib sensitivity.

Conclusions: Co-expression of mutant HER2 and mutant HER3 promotes ligand-independent HER2/HER association, HER3 phosphorylation, and cancer cell invasion via enhanced activation of the PI3K pathway; this enhanced signaling output is incompletely blocked by neratinib. Therefore, breast cancers expressing co-occurring HER2 and HER3 mutations may require the addition of a PI3Kα inhibitor to a HER2 TKI.

Citation Format: Ariella B. Hanker, Harikrishna Sekar Jayanthan, Dan Ye, Chang-Ching Lin, Hiroaki Akamatsu, Jonathan H. Sheehan, James P. Koch, Dhivya R. Sudhan, Monica Red Brewer, Alberto Servetto, Jie He, Vincent A. Miller, Alshad S. Lalani, Jens Meiler, Carlos L. Arteaga. Co-occurring gain-of-function mutations in HER2 and HER3 modulate HER2/HER3 activation, breast cancer progression, and HER2 inhibitor sensitivity [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr GS6-04.

Abstract PD3-05: Co-occurring gain-of-function mutations in HER2 and HER3 cooperate to enhance HER2/HER3 binding, HER-dependent signaling, and breast cancer growth

ERBB2, the gene encoding HER2, is mutated in 2-4% of breast cancers. The HER2 tyrosine kinase inhibitor neratinib has shown clinical activity against breast cancers harboring HER2 activating mutations, suggesting these tumors depend on HER2 signaling. Co-occurring HER2 and HER3 (ERBB3) mutations have been reported in patients who respond to neratinib (Hanker et al., Cancer Discov. 2017) suggesting the possibility of cooperativity of both oncogenes. Co-expression of the mutant intracellular domains of HER2 and HER3 in HEK293 cells enhanced phosphorylation of HER3 and ERK compared to expression of either mutant alone, which was blocked by 100 nM neratinib. Interrogation of TCGA, METABRIC, Project GENIE, and Foundation Medicine datasets revealed that gain-of-function mutations in ERBB2 and ERBB3 co-occur with a statistically significant frequency. For example, in GENIE, ERBB2 mutations co-occur with mutations in ERBB3 (8.3% of ERBB2-mutant vs 2.3% of ERBB2 WT; q=1.37x10-10).

We hypothesized that co-occurring mutations in HER2 and HER3 cooperate to enhance HER2 signaling and dependence and breast cancer progression.

Thirty-four unique breast cancers were found to harbor co-occurring mutations in HER2 and HER3, the most common of which were ERBB2L755S/ERBB3E928G (n=10), ERBB2V777L/ERBB3E928G(n=6), and ERBB2L869R/Q/ERBB3E928G (n=4). Using co-immunoprecipitation assays with HER2 and HER3 antibodies in transfected HEK293 cells, we found that co-expression of HER3E928G with wild type (WT) HER2, or co-expression of HER2L755S or HER2L869R with HER3WT, slightly increased HER2-HER3 dimerization. However, binding was strongest between double mutants. This was accompanied by the highest levels of Y1289 p-HER3 in cells expressing both HER3E928G and each HER2L755S, HER2V777L, or HER2L869R compared to cells expressing each HER2 or HER3 mutant with a respective WT heterodimer partner. Structural modeling of the HER2L869R/HER3E928G double-mutant predicted that the HER3 mutation, located at the dimer interface, may enhance heterodimerization of the kinase domains through decreased bulk and electrostatic repulsion. We also noted that the HER2L755S mutation is predicted to be in close proximity to HER3E928G (<4 Å) and may impact binding affinity. Investigation of the structural basis for the enhanced binding of other double mutants is in progress.

MCF7 “knock-in” cells incorporating HER2L755S, HER2V777L, or HER2L869R (or HER2WT) were stably transduced with HER3E928G or HER3WT. Co-expression of double mutants strongly enhanced estrogen-independent growth in 3D Matrigel over cells expressing either mutant alone. We are currently testing inhibitors of HER2/HER3 signaling, including neratinib ± trastuzumab, trastuzumab + pertuzumab, and the ERBB1-3 antibody mixture Sym013, to determine therapeutic strategies to block the cooperative growth induced by co-occurring HER2 and HER2 mutations.

Conclusions: Co-expression of mutant HER2 and mutant HER3 promotes HER2/HER binding, HER3 phosphorylation, and breast tumor cell proliferation. We aim to identify therapeutic vulnerabilities for patients with co-occurring HER2 and HER3 mutations.

Citation Format: Hanker AB, Koch JP, Ye D, Sliwoski G, Sheehan J, Kinch LN, Red Brewer M, He J, Miller VA, Lalani AS, Cutler, Jr. RE, Croessmann S, Zabransky DJ, Meiler J, Arteaga CL. Co-occurring gain-of-function mutations in HER2 and HER3 cooperate to enhance HER2/HER3 binding, HER-dependent signaling, and breast cancer growth [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr PD3-05.

Extracellular Matrix/Integrin Signaling Promotes Resistance to Combined Inhibition of HER2 and PI3K in HER2+ Breast Cancer

PIK3CA mutations are associated with resistance to HER2-targeted therapies. We previously showed that HER2⁺/PIK3CA^H1047R transgenic mammary tumors are resistant to the HER2 antibodies trastuzumab and pertuzumab but respond to PI3K inhibitor buparlisib (TPB). In this study, we identified mechanisms of resistance to combined inhibition of HER2 and PI3K. TPB-resistant tumors were generated by treating HER2⁺/PIK3CA^H1047R tumor-bearing mice long term with the drug combination. RNA sequencing of TPB-resistant tumors revealed that extracellular matrix and cell adhesion genes, including collagen II (Col2a1), were markedly upregulated, accompanied by activation of integrin β1/Src. Cells derived from drug-resistant tumors were sensitive to TBP when grown in vitro, but exhibited resistance when plated on collagen or when reintroduced into mice. Drug resistance was partially reversed by the collagen synthesis inhibitor ethyl-3,4-dihydroxybenzoate. Inhibition of integrin β1/Src blocked collagen-induced resistance to TPB and inhibited growth of drug-resistant tumors. High collagen II expression was associated with significantly lower clinical response to neoadjuvant anti-HER2 therapy in HER2⁺ breast cancer patients. Overall, these data suggest that upregulation of collagen/integrin/Src signaling contributes to resistance to combinatorial HER2 and PI3K inhibition. Cancer Res; 77(12); 3280-92. ©2017 AACR.

HER2-Overexpressing Breast Cancers Amplify FGFR Signaling upon Acquisition of Resistance to Dual Therapeutic Blockade of HER2

Purpose: Dual blockade of HER2 with trastuzumab and lapatinib or pertuzumab has been shown to be superior to single-agent trastuzumab. However, a significant fraction of HER2-overexpressing (HER2⁺) breast cancers escape from these drug combinations. In this study, we sought to discover the mechanisms of acquired resistance to the combination of lapatinib + trastuzumab.Experimental Design: HER2⁺ BT474 xenografts were treated with lapatinib + trastuzumab long-term until resistance developed. Potential mechanisms of acquired resistance were evaluated in lapatinib + trastuzumab-resistant (LTR) tumors by targeted capture next-generation sequencing. In vitro experiments were performed to corroborate these findings, and a novel drug combination was tested against LTR xenografts. Gene expression and copy-number analyses were performed to corroborate our findings in clinical samples.Results: LTR tumors exhibited an increase in FGF3/4/19 copy number, together with an increase in FGFR phosphorylation, marked stromal changes in the tumor microenvironment, and reduced tumor uptake of lapatinib. Stimulation of BT474 cells with FGF4 promoted resistance to lapatinib + trastuzumab in vitro Treatment with FGFR tyrosine kinase inhibitors reversed these changes and overcame resistance to lapatinib + trastuzumab. High expression of FGFR1 correlated with a statistically shorter progression-free survival in patients with HER2⁺ early breast cancer treated with adjuvant trastuzumab. Finally, FGFR1 and/or FGF3 gene amplification correlated with a lower pathologic complete response in patients with HER2⁺ early breast cancer treated with neoadjuvant anti-HER2 therapy.Conclusions: Amplification of FGFR signaling promotes resistance to HER2 inhibition, which can be diminished by the combination of HER2 and FGFR inhibitors. Clin Cancer Res; 23(15); 4323-34. ©2017 AACR.

An Acquired HER2T798I Gatekeeper Mutation Induces Resistance to Neratinib in a Patient with HER2 Mutant-Driven Breast Cancer

We report a HER2^T798I gatekeeper mutation in a patient with HER2^L869R-mutant breast cancer with acquired resistance to neratinib. Laboratory studies suggested that HER2^L869R is a neratinib-sensitive, gain-of-function mutation that upon dimerization with mutant HER3^E928G, also present in the breast cancer, amplifies HER2 signaling. The patient was treated with neratinib and exhibited a sustained partial response. Upon clinical progression, HER2^T798I was detected in plasma tumor cell-free DNA. Structural modeling of this acquired mutation suggested that the increased bulk of isoleucine in HER2^T798I reduces neratinib binding. Neratinib blocked HER2-mediated signaling and growth in cells expressing HER2^L869R but not HER2^L869R/T798I In contrast, afatinib and the osimertinib metabolite AZ5104 strongly suppressed HER2^L869R/T798I-induced signaling and cell growth. Acquisition of HER2^T798I upon development of resistance to neratinib in a breast cancer with an initial activating HER2 mutation suggests HER2^L869R is a driver mutation. HER2^T798I-mediated neratinib resistance may be overcome by other irreversible HER2 inhibitors like afatinib.Significance: We found an acquired HER2 gatekeeper mutation in a patient with HER2-mutant breast cancer upon clinical progression on neratinib. We speculate that HER2^T798I may arise as a secondary mutation following response to effective HER2 tyrosine kinase inhibitors (TKI) in other cancers with HER2-activating mutations. This resistance may be overcome by other irreversible HER2 TKIs, such as afatinib. Cancer Discov; 7(6); 575-85. ©2017 AACR.This article is highlighted in the In This Issue feature, p. 539.

Abstract P3-03-03: An acquired HER2 T798I gatekeeper mutation induces resistance to neratinib in a patient with HER2 mutant-driven breast cancer

ERBB2, the gene encoding HER2, is mutated in 2-4% of breast cancers. The HER2 irreversible tyrosine kinase inhibitor (TKI) neratinib has shown clinical activity against breast cancer cells harboring HER2 activating mutations. Here, we report for the first time an acquired gatekeeper HER2T798I mutation in a patient with HER2-mutant breast cancer after an initial exceptional response to neratinib.

A patient with ER+/PR+/HER2-negative invasive lobular breast cancer progressing on standard therapy was found to harbor a L869R kinase domain mutation in HER2. HER2L869R is homologous to the known activating mutation EGFRL861R/Q. MCF10A breast epithelial cells expressing HER2L869R displayed enhanced HER2-mediated signaling and were resistant to lapatinib and trastuzumab but sensitive to neratinib. The patient was enrolled in the phase II SUMMIT trial (NCT01953926) and treated with neratinib, achieving a partial response lasting 16 months before developing progression. Next gen sequencing of DNA from both a new skin metastasis and plasma cell-free DNA (cfDNA) identified HER2L869R (8.7% cfDNA), whereas a novel HER2T798I mutation was detected only in plasma at 1.3%. Deep sequencing of pre-therapy tumor tissue and plasma did not detect HER2T798I, suggesting that this mutation arose upon resistance. HER2T798I has not been reported in TCGA, COSMIC, or among plasma samples from 17,345 cancer patients subjected to digital DNA sequencing using the Guardant360 assay.

HER2T798I is homologous to the EGFRT790M, KITT670I and BCR-ABLT315I gatekeeper mutations known to mediate resistance to erlotinib/gefitinib and imatinib. To examine if HER2T798I mediates resistance to neratinib, we employed biochemical and biological assays and molecular modeling of wild-type (WT) HER2 and HER2T798I. Structural modeling showed the increased bulk of the isoleucine at position 798 would result in a steric clash with neratinib, thus reducing drug binding. We stably expressed HER2WT, HER2T798I, HER2L869R and HER2L869R/T798I in MCF10A cells and NR6 mouse fibroblasts. Neratinib (10-100 nM) blocked HER2-mediated signaling in cells expressing HER2WT or HER2L869R but did not in cells expressing HER2T798I. The EGFR irreversible TKI osimertinib (100 nM), which isselective for mutant EGFR (including EGFRT790M) and approved for treatment of NSCLC expressing EGFRT790M, failed to inhibit HER2WT, HER2L869R or HER2T798I. In contrast, either the EGFR/HER2 irreversible TKI afatinib or AZ5104, a metabolite of osimertinib, strongly blocked signaling induced by HER2WT, HER2L869R or HER2T798I. Cells expressing HER2T798M displayed a significantly higher IC50 to neratinib than cells expressing HER2WT, whereas afatinib or AZ5014 were very active against all cells (IC50<10 nM).

Conclusions: The acquisition of a T798I gatekeeper mutation in HER2 upon development of clinical resistance to neratinib in a breast cancer with an initial activating mutation in HER2 strongly suggests that HER2L869R is a driver mutation. We speculate that HER2T798I may arise as a secondary mutation following response to effective HER2 TKIs in other cancers with HER2 activating mutations. Certain irreversible EGFR inhibitors may be effective in patients with HER2-driven breast cancer resistant to neratinib.

Citation Format: Hanker AB, Red Brewer M, Sheehan JH, Koch JP, Lanman R, Hyman DM, Cutler, Jr. RE, Lalani AS, Cross D, Lovly CM, Meiler J, Arteaga CL. An acquired HER2 T798I gatekeeper mutation induces resistance to neratinib in a patient with HER2 mutant-driven breast cancer [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P3-03-03.

Treatment of Triple-Negative Breast Cancer with TORC1/2 Inhibitors Sustains a Drug-Resistant and Notch-Dependent Cancer Stem Cell Population

Approximately 30% of triple-negative breast cancers (TNBC) harbor molecular alterations in PI3K/mTOR signaling, but therapeutic inhibition of this pathway has not been effective. We hypothesized that intrinsic resistance to TORC1/2 inhibition is driven by cancer stem cell (CSC)-like populations that could be targeted to enhance the antitumor action of these drugs. Therefore, we investigated the molecular mechanisms by which PI3K/mTOR inhibitors affect the stem-like properties of TNBC cells. Treatment of established TNBC cell lines with a PI3K/mTOR inhibitor or a TORC1/2 inhibitor increased the expression of CSC markers and mammosphere formation. A CSC-specific PCR array revealed that inhibition of TORC1/2 increased FGF1 and Notch1 expression. Notch1 activity was also induced in TNBC cells treated with TORC1/2 inhibitors and associated with increased mitochondrial metabolism and FGFR1 signaling. Notably, genetic and pharmacologic blockade of Notch1 abrogated the increase in CSC markers, mammosphere formation, and in vivo tumor-initiating capacity induced by TORC1/2 inhibition. These results suggest that targeting the FGFR-mitochondrial metabolism-Notch1 axis prevents resistance to TORC1/2 inhibitors by eradicating drug-resistant CSCs in TNBC, and may thus represent an attractive therapeutic strategy to improve drug responsiveness and efficacy.

Abstract LB-012: Inhibition of PI3K induces paracrine factors, which promote growth and survival of human breast cancer cells

Phosphoinositide 3-kinase (PI3K) is aberrantly activated in many human cancers. To blunt the mitogenic action of this oncogenic pathway, PI3K inhibitors are currently in clinical development. However, inhibition of PI3K results in feedback activation of receptor tyrosine kinases (RTKs) and cap-independent translation of pro-survival proteins, thus diminishing the net antitumor effect of PI3K inhibitors. Therefore, characterization of pathways potentially activated by PI3K inhibitors is necessary in order to identify drug combinations which will better eradicate tumors. We demonstrate herein that inhibition of PI3K in breast cancer cells resulted in the increased expression of EGFR ligands and activation of EGFR/ERK signaling. FoxO transcription factors are repressed by PI3K and previous studies have shown that inhibition of PI3K results in nuclear localization of FoxO and activation of FoxO-mediated transcription of RTKs and IGF-I/II. However, RNAi-mediated knockdown of FoxO3A only partially attenuated the activation of EGFR induced by PI3K inhibition. Using a panel of transcription factor luciferase reporters, we identified 10 transcription factors (including FoxO) which are activated upon PI3K inhibition in three breast cancer cell lines from different intrinsic subtypes (MCF7, BT20 and SUM159). In addition, the serum-free media conditioned by MCF7 or BT20 cells in the presence of the pan-PI3K inhibitor BKM120 induced the survival and proliferation of recipient cancer cells which otherwise undergo apoptosis in serum-free conditions. Thus, we hypothesized that inhibition of PI3K results in

activation of paracrine factors, including EGFR ligands, which may promote the survival of a heterogeneous tumor cell population. Indeed, evaluation of media conditioned by MCF7 and BT20 cells with cytokine/growth factor antibody arrays demonstrated over 100 proteins to be induced by PI3K inhibition, including ligands for receptors in the EGF, FGF, cytokine, chemokine and TGFβ families. We are currently performing SILAC-based mass spectrometry profiling of media conditioned by breast cancer cells ± PI3K inhibitors to determine modulation of secreted factors upon inhibition of PI3K. We are also

determining whether inhibition of PI3K results in increased ADAM protease activity, inducing the shedding of EGFR ligands from the cell membrane. The results of these experiments will identify extracellular factors activated by the inhibition of PI3K and suggest which pathways need to be simultaneously inhibited to maximize the clinical activity of PI3K inhibitors. Further, these secreted proteins may serve as circulating pharmacodynamics biomarkers indicative of effective blockade of PI3K in patients.

Citation Format: Christian D. Young, James P. Koch, Rebecca S. Cook, Carlos L. Arteaga. Inhibition of PI3K induces paracrine factors, which promote growth and survival of human breast cancer cells. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr LB-012. doi:10.1158/1538-7445.AM2015-LB-012

The disulfonic stilbene DIDS and the marine poison maitotoxin activate the same two types of endogenous cation conductance in the cell membrane of Xenopus laevis oocytes

In the present experiments we exposed the intra- or extracellular surface of excised giant membrane patches of Xenopus laevis oocytes bathed in 140 mmol/l Na-aspartate solution to the anion transport inhibitor 4,4'-diisothiocyanatostilbene-2,2'-disulfonate (DIDS, 250 micromol/l). We observed that DIDS activated at least two cation conductances: (1) a non-selective cation (NSC) conductance that was mediated by channels of approximately 27 pS and resembled the stretch-activated cation conductance that has been observed in the oocyte cell membrane previously, and (2) a Na+-selective conductance, the single-channel events of which could not be resolved and which resembled the depolarization-induced Na+ conductance that has also been observed in the oocyte cell membrane previously. Both conductances were blocked by 1 mmol/l amiloride from the intra- and extracellular surfaces but inhibition of the NSC conductance by extracellular amiloride was less pronounced. Both conductances activated only slowly with a delay of 15-60 s after application of DIDS and remained active even after DIDS was washed off. This suggests that DIDS caused the exocytosis of preformed channels and this interpretation was supported by our additional observation that extracellular application of maitotoxin (MTX) mimicked the effects of DIDS. MTX is a marine toxin that has recently been reported to induce exocytosis in Xenopus laevis oocytes. The fact that DIDS and MTX each carry two sulfonyl groups suggests that they act on the same positively charged binding sites of an exocytosis-inducing protein. Our observations demonstrate that using DIDS to inhibit heterologously expressed anion transporters in the cell membrane of Xenopus laevis oocytes may compromise proper determination of the transporter currents. This effect can be prevented if the DIDS-activated endogenous cation conductances are suppressed by application of amiloride to the cytoplasmic surface of the cell membrane.

Mechanism of shrinkage activation of nonselective cation channels in M-1 mouse cortical collecting duct cells

It has previously been shown that osmotic cell shrinkage activates a nonselective cation (NSC) channel in M-1 mouse cortical collecting duct cells [54] and in a variety of other cell types [20]. In the present study we further characterized the shrinkage-activated NSC channel in M-1 cells and its mechanism of activation using whole-cell current recordings. Osmotic cell shrinkage induced by addition of 100 mm sucrose to the bath solution caused a 20-fold increase in whole-cell inward currents from -10.8 +/- 1.5 pA to -211 +/- 10.2 pA (n = 103). A similar response was observed when cell shrinkage was elicited using a hypo-osmotic pipette solution. This indicates that cell shrinkage and not extracellular osmolarity per se is the signal for current activation. Cation substitution experiments revealed that the activated channels discriminate poorly between monovalent cations with a selectivity sequence NH(4) (1.2) > or = Na(+) (1) approximately K(+) (0.9) approximately Li(+) (0.9). In contrast there was no measurable permeability for Ca(2+) or Ba(2+) and the cation-to-anion permeability ratio was about 14. The DPC-derivatives flufenamic acid, 4-methyl-DPC and DCDPC were the most effective blockers followed by LOE 908, while amiloride and bumetanide were ineffective. The putative channel activator maitotoxin had no effect. Current activation was dependent upon the presence of intracellular ATP and Mg(2+) and was inhibited by staurosporine (1 microm) and calphostin C (1 microm). Moreover, cytochalasin D (10 microm) and taxol (2 microm) reduced the current response to cell shrinkage. These findings suggest that the activation mechanism of the shrinkage-activated NSC channel involves protein kinase mediated phosphorylation steps and cytoskeletal elements.

Validation of a high-performance liquid chromatography assay for quantification of caffeine and paraxanthine in human serum in the context of CYP1A2 phenotyping

In this study the validation of a reversed-phase high-performance liquid chromatography (HPLC) method, with UV-detection, for both caffeine and paraxanthine in human serum is described. This method is feasible for cytochrome P450 1A2 (CYP1A2) phenotyping, according to the results of a pilot study. With this HPLC method caffeine and paraxanthine can be determined selectively and specifically. In the expected concentration range, caffeine recoveries were 98-108% (within-run variation 4.0-6.4%, between-run variation 6.4-8.8%), paraxanthine recoveries were 96.6-97.5% (within-run variation 5.0-7.2%, between-run variation 7.2-10.8%). The limits of detection for caffeine and paraxanthine using this HPLC system were 0.3 and 0.1 mg/L, respectively. Linear calibration curves for both caffeine and paraxanthine were obtained in the concentration range 0.5-30 mg/L (r > 0.9999. Serum samples were stable for a week, when stored at -20 and +4 degrees C.

Determinants of low systemic vascular resistance during cardiopulmonary bypass

Although low systemic vascular resistance occurs during normothermic and hypothermic cardiopulmonary bypass, the determinants of depressed systemic vascular resistance and its effect on outcomes are unknown. To assess the predictors and clinical effects of low systemic vascular resistance, 555 patients undergoing isolated coronary artery bypass grafting were evaluated prospectively. The extent of low systemic vascular resistance during bypass was estimated by the amount of the vasoconstrictor phenylephrine administered: group 1, 0 to 160 micrograms; group 2, 161 to 800 micrograms; group 3, more than 800 micrograms. Multivariate analysis identified bypass temperature, bypass time, and ventricular function as determinants of low systemic vascular resistance. Patients on normothermic bypass accounted for 65% of the patients in group 3 and only 34% of the patients in group 1 (p < 0.0001). The bypass time was longer in the patients in group 3 (97 +/- 28 minutes) than in the patients in group 1 (89 +/- 24 minutes; p < 0.006). Patients with a preoperative left ventricular ejection fraction of 0.40 or less required less phenylephrine during cardiopulmonary bypass (498 +/- 68 micrograms) than did patients with a fraction exceeding 0.40 (1,087 +/- 88 micrograms; p < 0.001). By multivariate analysis, advanced age and the presence of peripheral vascular disease were found to decrease the likelihood of low systemic vascular resistance during normothermic bypass. Diabetes, the left ventricular ejection fraction, the bypass time, and the total cardioplegia infused were found to influence the likelihood of low systemic vascular resistance during hypothermic bypass. Patients in group 3 had a higher cardiac index and lower-mean arterial pressure and systemic vascular resistance postoperatively. In those patients who received a left internal mammary artery graft, the incidences of the low-output syndrome (group 1, 4.9%; group 3, 2.7%; p = not significant) and myocardial infarction (group 1, 1.4%; group 3, 1.8%; p = not significant) were not influenced by the amount of phenylephrine infused during cardiopulmonary bypass. In those patients who were at high risk of suffering a stroke preoperatively, the hypotension induced by the low systemic vascular resistance and its treatment with phenylephrine was not associated with an increased incidence of stroke (group 1, 5.8%; group 3, 2.8%; p = not significant).

A randomized study of the systemic effects of warm heart surgery

The technique of warm heart surgery is defined as continuous warm blood cardioplegia and normothermic cardiopulmonary bypass. Although the systemic effects of traditional myocardial protection are well known, the effects of warm heart surgery are not. In a prospective trial, 204 patients undergoing coronary artery bypass grafting were randomized to the warm heart surgery technique (normothermic group) or traditional intermittent cold blood cardioplegia and cardiopulmonary bypass (hypothermic group). The groups had similar heparin sodium requirement, activated clotting times, urine output, hematocrit, and blood product utilization. There were no differences in hemodynamics immediately after cardiopulmonary bypass. The normothermic patients had a higher incidence of spontaneous defibrillation at cross-clamp removal (84%) than the hypothermic patients (33%) (p less than 0.01). An increase in the flow rate of low K+ cardioplegia was necessary to eradicate electrical activity during aortic occlusion more often in the normothermic patients (20%) than in the hypothermic patients (3%) (p less than 0.01). When low K+ cardioplegia was ineffective, high K+ cardioplegia was necessary to eradicate electrical activity in 31% of the normothermic patients compared with 10% of the hypothermic patients (p less than 0.05). The total cardioplegia volume delivered to the normothermic group (4.7 +/- 1.9 L) was higher than that delivered to the hypothermic group (2.6 +/- 0.8 L) (p less than 0.01). Although urine output was similar in both groups, the serum K+ levels were higher in the normothermic group (5.7 +/- 0.8 mmol/L) than in the hypothermic group (5.3 +/- 0.8 mmol/L) (p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

The safety of awake tracheal intubation in cervical spine injury

As a referral centre for cervical spine injuries, we have routinely performed awake tracheal intubation when intubation was indicated. A retrospective case control study was undertaken to review the frequency of neurological deterioration and aspiration associated with our approach. Neurological deterioration was assessed by a change in level of injury or neurological grade at admission and discharge. Four hundred and fifty-four patients with critical cervical spine and/or cord injuries were reviewed over an eight-year period. A case group of 165 patients underwent tracheal intubation awake within two months of injury. A control group of 289 remained unintubated during the same period. A comparison of spinal neurological status between admission and discharge revealed no statistically significant difference in neurological deterioration between the two groups. This occurred despite a greater injury severity score in the case group. No evidence of aspiration during intubation was documented. We conclude that awake tracheal intubation is a safe method of airway management in patients with cervical spine injuries.

Anaesthetic management of acute blunt thoracic trauma

Sunnybrook Health Science Centre is an adult regional trauma unit serving metropolitan Toronto and environs. We undertook a two-year retrospective review of patients admitted to our institution with blunt thoracic trauma. Three hundred and thirty-three patients with blunt trauma and an injury severity score (ISS) greater than 17 required emergency surgery. Of these, 208 had blunt thoracic injuries while 125 did not have chest injuries. Both groups were similar with respect to age but patients with thoracic trauma had a greater ISS. (P less than 0.05) and greater intraoperative mortality (P less than 0.01). The aetiology of the intraoperative deaths with one exception was exsanguination. Emergency thoracotomy or sternotomy indicated a poor prognosis with a mortality rate of 80%. The most common intraoperative problem was an elevated airway pressure. Awake intubation was undertaken in 77.5% of patients requiring anaesthesia and surgery because of the potentially compromised airways and difficult intubations due to the nature of the associated injuries. Finally, 74% of patients undergoing urgent surgery required mechanical postoperative ventilation. The presence of blunt chest trauma should be considered a marker of the severity of injury sustained by the patient.

The use of halothane in the treatment of status asthmaticus

The case is presented of a 39-year-old male in status asthmaticus who failed to respond to conventional therapy, including positive pressure ventilation, and who required halothane anesthesia. The urgent need to reduce his elevated airway pressure and his risk of barotrauma prompted this action. The patient's response was prompt with marked reductions in airway pressure. Discontinuing halothane resulted in rises in airway pressure, necessitating reinstitution of halothane on several occasions. The mechanism of the bronchodilating action of halothane, as well as potential interactions with other pharmacotherapy and precautions for its use, are described.

The Prentif contraceptive cervical cap: acceptability aspects and their implications for future cap design

Patients in a private gynecological practice were offered the Prentif contraceptive cervical cap. The first 413 acceptors were sent a questionnaire covering in detail many of the aspects of their experience. The 371 responses contained a wealth of information concerned with safety, effectiveness and acceptability. Safety and effectiveness are dealt with in the companion article preceding, while the less serious risk factors that reduce the acceptability of the Prentif cap are presented and discussed herein. In order of descending frequency, these factors include: odor; difficulty removing; discomfort to partner; difficulty inserting; dislike of spermicide; discomfort to self; urinary discomforts; vaginal infections; vaginal discharge; and vaginal itching. The most attractive features of the cap, as compared with the diaphragm, were: increased convenience; greater safety; less interference with spontaneity; increased frequency of intercourse; and increased libido. Despite multiple problems with Prentif caps, 67.4% of the cap recipients were still using their caps after one year. However, this was among a select group of highly motivated women of above-average intelligence. The causes of cap acceptability problems are discussed along with probable future improvements in cap design that may solve them.

The Prentif contraceptive cervical cap: a contemporary study of its clinical safety and effectiveness

Because they seemed to be an overlooked, underutilized, and underdeveloped means of contraception, cervical caps were offered to patients in a private gynecological practice and the first 413 acceptors were sent a detailed questionnaire about their experiences. The 371 who responded provided generous amounts of information helpful in assessing not only cap safety and effectiveness, which are dealt with herein, but also in assessing acceptability which is dealt with in the companion article that follows. With regard to safety considerations, "cervical erosion" was not found to contraindicate cap use and no other significant safety hazards were encountered, although two concerns were suggested for further evaluation. The failure rate was 8.4 per 100 women per year by the life table method. Of 25 failures, 11 were labeled method failures and 14 were labeled human failures by the respondents themselves. The role of cap dislodgement as a cause of method failures is analyzed. It is concluded that caps are as safe and effective as diaphragms and that for many women they are the most suitable form of contraception available. It is reasonable to expect that they will soon be able to be approved for general use.

Changes in peripheral vascular and cardiac sympathetic activity before and after coronary artery bypass surgery: interrelationships with hemodynamic alterations

The plasma catecholamine levels obtained simultaneously from radial artery (A), pulmonary artery (MV), brachial vein (PV), and coronary sinus (CS) were measured concurrent with hemodynamic determinations during coronary artery bypass graft (CABG) operations. Arterial catecholamine levels decreased after induction of anesthesia and increased after sternotomy; changes in veno-arterial norepinephrine (NE) differences ([PV-A]ne, [MV-A]ne, and [CS-A]ne) were of the same magnitude and direction, suggesting that NE release from various organs was of the same extent. After operation, arterial NE increased further, but the veno-arterial NE differences were in striking contrast; [PV-A]ne became markedly positive, whereas [CS-A]ne became markedly negative, indicating that NE release from extremity peripheral vasculature increased markedly while cardiac NE release decreased. These differential changes in regional sympathetic activity appear to be related to postoperative hypertension (HT) and low cardiac output (CO). There were close relationships of changes in [MV-A]ne to mean arterial pressure (r = 0.78, p less than 0.001) and systemic vascular resistance (r = 0.62, p less than 0.010, suggesting that the sympathetic nervous system plays an important role in CABG perioperative hemodynamic alterations.

Results of operation for obstructive hypertrophic cardiomyopathy in the elderly. Septal myotomy and myectomy in 20 patients 65 years of age or older

The results of operative treatment in 20 patients with hypertrophic cardiomyopathy 65 years of age or older are described. All 20 patients were severely symptomatic before operation. Seventeen of the 20 patients had marked left ventricular outflow tract obstruction under basal conditions (average pressure gradient 107 mm Hg); the other three patients had outflow gradients of more than 50 mm Hg only with provocation. One patient died at operation, and one died 4 years after operation of circumstances unrelated to hypertrophic cardiomyopathy. Sixteen of the 18 long-term survivors have had persistent and significant functional improvement for up to 6 years after operation, including 7 patients who are now asymptomatic. Two patients experienced symptomatic deterioration after manifesting initial symptomatic improvement for 3 and 4 years, respectively, after operation. Operation resulted in a marked decrease or abolition of the left ventricular outflow gradient in each of the 17 patients studied with postoperative cardiac catheterization. These data show that gratifying symptomatic and hemodynamic improvement may be obtained by septal myotomy and myectomy in the elderly patient with hypertrophic cardiomyopathy. Accordingly, advanced age in itself is not a contraindication to operative intervention in such patients.

Left ventricular myotomy and myectomy in patients with obstructive hypertrophic cardiomyopathy and previous cardiac arrest

Left ventricle myotomy and myectomy was carried out in nine patients with obstructive hypertrophic cardiomyopathy solely because of a previously documented episode of cardiac arrest. Before cardiac arrest, each patient had either no or only minimal functional limitation and therefore would not have met the usual criteria for operation, namely, severe symptoms unresponsive to medical therapy. Of the nine patients, one died in the perioperative period, and one died suddenly and unexpectedly 9 months postoperatively. The remaining seven patients have survived 9 months to 5.5 years after operation; six of the seven are asymptomatic and one has only mild symptoms. Operation resulted in a marked decrease or abolition of the left ventricular outflow gradient under basal conditions in seven of the eight patients studied postoperatively. Significant residual outflow obstruction was demonstrated after operation in the patient who later died. Sudden death in patients with obstructive hypertrophic cardiomyopathy appears usually to result from ventricular arrhythmia, and prevention of recurrent fatal arrhythmia is the goal of treatment in patients who have had cardiac arrest and have been resuscitated. Such patients should be treated indefinitely with antiarrhythmic drugs. In addition, when severe outflow obstruction is present, we postulate that effective operative relief of obstruction and consequent reduction of left ventricular systolic pressure will provide additional protection.

Growth stasis by accumulated L-alpha-glycerophosphate in Escherichia coli

Cozzarelli, N. R. (Harvard Medical School, Boston, Mass.), J. P. Koch, S. Hayashi, and E. C. C. Lin. Growth stasis by accumulated l-alpha-glycerophosphate in Escherichia coli. J. Bacteriol. 90:1325-1329.1965.-Cells of Escherichia coli K-12 can grow on either glycerol or l-alpha-glycerophosphate as the sole source of carbon and energy. The first step in the dissimilation of glycerol requires a kinase, and the initial process of utilization of l-alpha-glycerophosphate involves an active transport system. In either case, intracellular l-alpha-glycerophosphate is an intermediate whose further metabolism depends upon a dehydrogenase. When this enzyme is lost by mutation, the cells not only fail to grow on glycerol or l-alpha-glycerophosphate, but are subject to growth inhibition in the presence of either compound. Resistance to inhibition by glycerol can be achieved by the loss of glycerol kinase. Such cells are still susceptible to growth inhibition by l-alpha-glycerophosphate. Similarly, in dehydrogenase-deficient cells, immunity to exogenous l-alpha-glycerophosphate can be achieved by genetic blocking of the active transport system. Such cells are still sensitive to free glycerol in the growth medium. Reversal of inhibition by glycerol or l-alpha-glycerophosphate in cells lacking the dehydrogenase can also be brought about by the addition of glucose. Glucose achieves this effect without recourse to catabolite repression. Our results suggest that growth stasis associated with the over-accumulation of l-alpha-glycerophosphate is due to interference with other cellular processes by competition with physiological substrates rather than to depletion of cellular stores of adenosine triphosphate or inorganic phosphate.