Abstract P4-03-09: Chromosomal instability predicts taxane sensitivity in breast cancer

Taxanes remain among the most effective agents for the treatment of breast cancer. However, ˜50% of patients who receive this therapy do not have a clinical response. Previously, we identified the mechanistic effects of taxane therapy by sampling primary human breast tumors 20 hours after infusion (Sci Trans Med 26:229ra43, 2014). We determined that paclitaxel caused cells to transit mitosis on multipolar spindles, resulting in increased chromosome gains and losses. Preclinical models suggest that tumors have enhanced sensitivity if they have baseline chromosome gains/losses, known as chromosome instability (CIN). The aim of this study was to compare CIN against other predictive biomarkers in a retrospective cohort of advanced breast cancer patients who receive single-agent taxane therapy.

Methods: We identified 36 subjects with metastatic breast cancer and measurable disease who received taxane therapy and had available archived tissue. Responses were determined by RECIST 1.1 criteria. We evaluated chromosome number on a cell-by-cell basis using 6 centromeric FISH probes. Additionally we measured rates of proliferation by phospho-histone H3 (p-HH3) and Ki67, previously reported biomarkers, β-tubulin III, P-gp1 and MAD1 by quantitative immunofluorescence. CIN was estimated as the fraction of cells with non-modal chromosome numbers across chromosomes 3, 4, 7, 9, 10, and 17.

Results: Of the 36 subjects, 19 had ER/PR+HER2- disease (53%), 9 had HER2-positive disease (25%), and 8 TNBC (22%). Single-agent chemotherapy was used for all including paclitaxel in 16, nab-paclitaxel in 17, and docetaxel in 3 (HER2+ patients received concurrent trastuzumab). RECIST responses ranged from disease progression (8%, n=3), stable disease (50%, n=18), and partial response (42%, n=15). No complete responses were observed. Time on therapy ranged from 1.4 months to 28 months. No statistically significant correlations were found between tumor type or prior chemotherapy and response to taxanes. Archived metastatic samples were available for 21 subjects. Analysis showed large variations in Ki67, pHH3, β-tubulin III, P-gp1, MAD1, and CIN amongst samples. The strongest correlation was found between tumor response and high levels of CIN, with a Spearman's correlation coefficient of 0.38 (p=0.04). Surprisingly, there was an inverse correlation between Ki67 and taxane response, although this did not reach statistical significance.

Biomarkers correlated with response to taxaneN=21Ki67 (%)pHH3 (H)βtub3 (H)P-gp1 (H)MAD1 (H)CIN (%)min0.850.000.673.002.8324.2max45.14.8915129923165.8Spearman rho-0.3650.242-0.1650.232-0.08960.382p (1-tailed)0.05190.1400.2370.1550.3500.0425H = H-score; CIN is estimated as % of cells with non-modal chromosomes

Conclusions: Chromosomal instability is a promising biomarker for predicting sensitivity to taxane therapies. Additional studies will be necessary to validate CIN as a biomarker and to determine whether 6-chromosome FISH can be supplanted by low-pass single-cell DNA sequencing.

Citation Format: Esbona K, Jin N, Correia-Staudt KL, Lager AM, Heidke T, Laffin J, Weaver BA, Burkard ME. Chromosomal instability predicts taxane sensitivity in breast cancer [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P4-03-09.

Abstract P3-07-53: Chromosomal instability as a predictor of sensitivity to paclitaxel

Background: Paclitaxel is one of the most effective therapies for breast cancer, although many patients do not benefit. Our goal is to identify those who will benefit, by understanding how this drug contributes to chromosomal instability (CIN). CIN is the gradual gain/loss of whole chromosomes that can occur with mitotic errors as tumors proliferate. Some breast cancers inherently have CIN whereas others lack CIN. Previous work suggests low rates of CIN can promote tumor growth by creating genetic diversity. By contrast, high rates of CIN are lethal, apparently due to a high incidence of deleterious karyotypes. We hypothesize that paclitaxel operates by increasing CIN, and that this has preferential anticancer effects in tumors with preexisting low CIN.

Methods: To assess rates of underlying CIN in human breast cancer, we performed 6-chromosome FISH on 354 human breast cancers and correlated with outcomes on a cohort with median 8.4 year follow-up. We measured the physiologic levels of paclitaxel that occur in human breast tumors. To do this, we treated 5 women with neoadjuvant paclitaxel 175mg/m2, performed tumor biopsy at 20 hours, performed LC to quantify intratumoral levels and analyzed mitotic spindles by IHC. Additionally, we performed timelapse videomicroscopy to analyze mitosis in fluorescently-labeled breast cancer cells in the laboratory after exposure to these levels. To evaluate whether CIN controls paclitaxel sensitivity we artificially introduced low levels of CIN into breast cancer cell lines by doxycycline-inducible expression of GFP-Mad1, a protein involved in the mitotic checkpoint, and tested whether this enhanced sensitivity to physiologic doses of paclitaxel.

Results: A total of 77% (270/349) of breast cancer have detectable underlying CIN, (average percentage of non-modal chromosomes averaged for 6 chromosomes) greater than the normals (n=11). CIN is higher in HER2+ and TNBC subtypes compared to HR+. CIN does not correlate with the proliferation marker, Ki67 (r2 = 0.04), which does not support the idea of a growth advantage. CIN greater than median levels correlated with worse breast cancer-specific survival (p=0.022 log rank), but no difference in OS or RFS. Paclitaxel in human breast cancer reaches a level mimicked by 5-50nM exposure in laboratory experiments. In the laboratory, breast cancer cells exposed to these levels exhibit multipolar divisions, and similar abnormal mitoses can be found in patient tumors. In breast cancer cells lacking CIN, chromosome analysis demonstrates that it can be artificially induced by conditionally expressing GFP-Mad1. Inducing GFP-Mad1 expression increases sensitivity to paclitaxel, demonstrating that CIN enhances taxane sensitivity.

Conclusions: These data support the idea that excessively high levels of CIN can be lethal to cancer cells and that paclitaxel enhances CIN. We predict that the anticancer effects of paclitaxel are marked in tumors with intrinsic CIN, as the enhanced levels are lethal. Thus CIN may be an effective biomarker to predict which women will benefit from taxane therapy. Ultimately, this could be applied in the clinic to substantially improve patient care by decreasing primary resistance or by reducing side effects associated with paclitaxel use.

Citation Format: Cavalcante LL, Denu R, Zasadil L, Weaver BA, Burkard M. Chromosomal instability as a predictor of sensitivity to paclitaxel. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P3-07-53.

Inhibition of follicle-stimulating hormone-induced preovulatory follicles in rats treated with a nonsteroidal negative allosteric modulator of follicle-stimulating hormone receptor

We previously described a negative allosteric modulator (NAM) of FSHR (ADX61623) that blocked FSH-induced cAMP and progesterone production but did not block estradiol production. That FSHR NAM did not affect FSH-induced preovulatory follicle development as evidenced by the lack of an effect on the number of FSH-dependent oocytes found in the ampullae following ovulation with hCG. A goal is the development of a nonsteroidal contraceptive. Toward this end, a high-throughput screen using human FSHR identified an additional nonsteroidal small molecule (ADX68692). Although ADX68692 behaved like ADX61623 in inhibiting production of cAMP and progesterone, it also inhibited FSH-induced estradiol in an in vitro rat granulosa primary cell culture bioassay. When immature, noncycling female rats were injected subcutaneously or by oral dosing prior to exogenous FSH administration, it was found that ADX68692 decreased the number of oocytes recovered from the ampullae. The estrous cycles of mature female rats were disrupted by administration by oral gavage of 25 mg/kg and 10 mg/kg ADX68692. In the highest dose tested (25 mg/kg), 55% of animals cohabited with mature males had implantation sites compared to 33% in the 10 mg/kg group and 77% in the control group. A surprising finding was that a structural analog ADX68693, while effectively blocking progesterone production with similar efficacy as ADX68692, did not block estrogen production and despite better oral availability did not decrease the number of oocytes found in the ampullae even when used at 100 mg/kg. These data demonstrate that because of biased antagonism of the FSHR, nonsteroidal contraception requires that both arms of the FSHR steroidogenic pathway must be effectively blocked, particularly estrogen biosynthesis. Thus, a corollary to these findings is that it seems reasonable to propose that the estrogen-dependent diseases such as endometriosis may benefit from inhibition of FSH action at the ovary using the FSHR NAM approach.

A negative allosteric modulator demonstrates biased antagonism of the follicle stimulating hormone receptor

High quality gamete production in males and females requires the pituitary gonadotropin follicle stimulating hormone (FSH). In this report a novel chemical class of small molecule inhibitors of FSH receptor (FSHR) is described. ADX61623, a negative allosteric modulator (NAM), increased the affinity of interaction between (125)I-hFSH and human FSHR (hFSHR) five fold. This form of FSHR occupied simultaneously by FSH and ADX61623 was inactive for cAMP and progesterone production in primary cultures of rat granulosa cells. In contrast, ADX61623 did not block estrogen production. This demonstrates for the first time, biased antagonism at the FSHR. To determine if ADX61623 blocked FSH induction of follicle development in vivo, a bioassay to measure follicular development and oocyte production in immature female rats was validated. ADX61623 was not completely effective in blocking FSH induced follicular development in vivo at doses up to 100mg/kg as oocyte production and ovarian weight gain were only moderately reduced. These data illustrate that FSHR couples to multiple signaling pathways in vivo. Suppression of one pool of FSHR uncouples Gαs and cAMP production, and decreases progesterone production. Occupancy of another pool of FSHR sensitizes granulosa cells to FSH induced estradiol production. Therefore, ADX61623 is a useful tool to investigate further the mechanism of the FSHR signaling dichotomy. This may lead to a greater understanding of the signaling infrastructure which enables estrogen biosynthesis and may prove useful in treating estrogen dependent disease.

Serotonin 5-HT(2C) receptor homodimerization is not regulated by agonist or inverse agonist treatment

Serotonin 5-HT(2C) receptors represent targets for therapeutics aimed at treating anxiety, depression, schizophrenia, and obesity. Previously, we demonstrated that 5-HT(2C) receptors function as homodimers. Herein, we investigated the effect of agonist and inverse agonist treatment on the homodimer status of two naturally occurring 5-HT(2C) receptor isoforms, one without basal activity (VGV) and one with constitutive activity (INI) with respect to Galpha(q) signaling. Cyan- and yellow-fluorescent proteins were used to monitor VGV and INI homodimer formation by western blot, and in living cells using bioluminescence and fluorescence resonance energy transfer (BRET and FRET). Western blots of solubilized membrane proteins revealed equal proportions of homodimeric receptor species from HEK293 cells transfected with either the VGV or INI isoform in the absence and presence of 5-HT. BRET ratios measured in HEK293 cells transfected with the VGV or INI isoform were the same and were not modulated by 5-HT. Similarly, FRET efficiencies were the same regardless of whether measured in cells expressing the VGV or INI isoform in the absence or presence of 5-HT or clozapine. The results indicate that serotonin 5-HT(2C) receptors form homodimers regardless of whether they are in an inactive or active conformation and are not regulated by drug treatment.

Serotonin 5-HT2C receptor homodimer biogenesis in the endoplasmic reticulum: real-time visualization with confocal fluorescence resonance energy transfer

Dimerization is a common property of G-protein-coupled receptors (GPCR). While the formation of GPCR dimers/oligomers has been reported to play important roles in regulating receptor expression, ligand binding, and second messenger activation, less is known about how and where GPCR dimerization occurs. The present study was performed to identify the precise cellular compartment in which class A GPCR dimer/oligomer biogenesis occurs. We addressed this issue using confocal microscopy and fluorescence resonance energy transfer (FRET) to monitor GPCR proximity within discrete intracellular compartments of intact living cells. Time-lapse confocal imaging was used to follow CFP- and YFP-tagged serotonin 5-HT2C receptors during biosynthesis in the endoplasmic reticulum (ER), trafficking through the Golgi apparatus and subsequent expression on the plasma membrane. Real-time monitoring of FRET between CFP- and YFP-tagged 5-HT2C receptors was performed by acceptor photobleaching within discrete regions of the ER, Golgi, and plasma membrane. The FRET signal was dependent on the ratio of CFP- to YFP-tagged 5-HT2C receptors expressed in each region and was independent of receptor expression level, as predicted for proteins in a non-random, clustered distribution. FRET efficiencies measured in the ER, Golgi, and plasma membrane were similar. These experiments provide direct evidence for homodimerization/oligomerization of class A GPCR in the ER and Golgi of intact living cells, and suggest that dimer/oligomer formation is a naturally occurring step in 5-HT2C receptor maturation and processing.

Tyrosine phosphorylation and regulation of swine carotid artery contraction

Regulation of [Ca2+]i and modulation of the [Ca2+]i sensitivity of myosin phosphorylation in smooth muscles may involve phosphorylation of one or more proteins on tyrosine residues. We tested this hypothesis by measuring tyrosine phosphorylation of proteins extracted from swine carotid artery and separated by SDS gel electrophoresis. Tyrosine phosphorylation was estimated by the binding of antiphosphotyrosine antibodies to proteins in SDS gels. We found four bands with approximate molecular weights of 120, 110, 85 and 75 kD in which tyrosine phosphorylation increased 1 min after histamine stimulation. After washout of histamine, dephosphorylation of the proteins in these four bands occurred at a slower rate than relaxation. Tyrosine phosphorylation of these four protein bands did not correlate with the [Ca2+]i sensitivity of myosin phosphorylation following agonist or high [K+]o stimulation. Phorbol dibutyrate stimulation also induced tyrosine phosphorylation of these four protein bands. These data suggest that tyrosine phosphorylation of the proteins in these four bands may be involved in the initial phase of swine carotid artery contraction. However, there was, at most, only a minor involvement of tyrosine phosphorylation of these four protein bands in the sustained phase of contraction or in the regulation of [Ca2+]i sensitivity of myosin phosphorylation in the swine carotid artery. These data do not rule out a role for other, less abundant tyrosine phosphoproteins in the regulation of sustained contraction or the [Ca2+]i sensitivity of myosin phosphorylation.

Myosin light chain kinase phosphorylation in swine carotid artery contraction and relaxation

We investigated the role of myosin light chain kinase (MLCK) phosphorylation in regulating the sensitivity of vascular smooth muscle myosin light chain (MLC) phosphorylation to intracellular Ca2+ concentration ([Ca2+]i). 32PO4-loaded swine carotid arteries were stimulated with histamine or high K+, MLCK was isolated, and the relative phosphorylation of tryptic peptides was measured. In nonlabeled tissues, we measured [Ca2+]i with aequorin, MLCK activity ratio, MLC phosphorylation, and force. A comparison of MLCK phosphorylation on peptide A (mol P in site A/mol MLCK) and MLCK activity ratio showed an inverse relation, suggesting that MLCK site A phosphorylation can regulate the Ca2+ sensitivity of MLCK. MLCK site A phosphorylation and MLCK activity ratio depended on [Ca2+]i. Histamine stimulation yielded greater MLC phosphorylation than high K+ stimulation over a range of [Ca2+]i; however, there were no apparent stimulus-dependent differences in MLCK phosphorylation, suggesting that stimulus-dependent differences in the Ca2+ sensitivity of MLC phosphorylation are not based on differences in MLCK phosphorylation. We also determined whether MLCK phosphorylation was involved in adenosine 3',5'-cyclic monophosphate-mediated relaxation. In histamine-contracted tissues, forskolin decreased [Ca2+]i, MLC phosphorylation, and force. MLCK phosphorylation decreased to an extent consistent with the decrease in [Ca2+]i. In KCl-stimulated tissues, forskolin did not alter [Ca2+]i or increase MLCK phosphorylation but forskolin did decrease MLC phosphorylation. Thus, in swine carotid artery, MLCK phosphorylation appears to be regulated exclusively by Ca2+ and plays little role in stimulus-dependent differences in Ca2+ sensitivity of MLC phosphorylation or in mediating forskolin-induced relaxation.

Depolarization decreases the [Ca2+]i sensitivity of myosin light-chain kinase in arterial smooth muscle: comparison of aequorin and fura 2 [Ca2+]i estimates

Histamine stimulation of swine arterial smooth muscle is associated with a high [Ca2+]i sensitivity for increases in myosin light-chain phosphorylation. In contrast, KCl depolarization produces a relatively lower [Ca2+]i sensitivity (i.e., similar increases in [Ca2+]i induce less myosin phosphorylation). We evaluated whether 1) artifacts in the methodology for measuring [Ca2+]i or 2) true alterations in the [Ca2+]i sensitivity of myosin light-chain kinase were responsible for these apparent changes in the [Ca2+]i sensitivity of phosphorylation. The [Ca2+]i sensitivity of phosphorylation was higher with histamine stimulation regardless of whether the [Ca2+]i indicator was aequorin (which was loaded intracellularly by reversible hyperpermeabilization) or Fura 2 (which was loaded intracellularly by incubation of the tissues in Fura 2 AM). Aequorin and Fura 2 appeared to detect qualitatively similar stimulus-induced changes in [Ca2+]i with the exception that the initial response to histamine stimulation was different (histamine initially induced a large aequorin light transient and a relatively smaller increase in Fura 2 fluorescence). The [Ca2+]i sensitivity of myosin light-chain kinase extracted from KCl depolarized tissues was lower than the [Ca2+]i sensitivity of myosin light-chain kinase extracted from unstimulated or histamine stimulated tissues. These results suggest that depolarization specifically modifies myosin light-chain kinase to decrease its [Ca2+]i sensitivity. Changes in the [Ca2+]i sensitivity of myosin light-chain phosphorylation are not an artifact of the [Ca2+]i measurement technique.

Adenosine triphosphate induces a low [Ca2+]i sensitivity of phosphorylation and an unusual form of receptor desensitization in smooth muscle

The contractile sensitivity of smooth muscle to changes in myoplasmic [Ca2+] is dependent on the form of stimulation. Both myosin phosphorylation and force are less sensitive to increases in [Ca2+]i derived from Ca2+ entry through L-type Ca2+ channels than to increases in [Ca2+] induced by agents which release internal Ca2+ stores. We hypothesized that activation of receptor-operated channels should produce a [Ca2+]i sensitivity similar to that induced by opening L channels. Aequorin-estimated myoplasmic [Ca2+] and myosin light chain phosphorylation were measured in swine carotid media tissues stimulated with ATP, an activator of the only known receptor-operated cation channel in smooth muscle. ATP, via activation of a P2x purinergic receptor, induced large, transient increases in [Ca2+]i, yet only small transient elevations in phosphorylation or force. Rapid desensitization to ATP was partially, but not completely, caused by hydrolysis of ATP into adenosine since 1) alpha-beta-methylene ATP (a poorly hydrolyzable analog of ATP) produced larger, yet still transient increases in [Ca2+]i, phosphorylation, and force; 2) BW A1433U, a P1 (adenosine) receptor antagonist, enhanced ATP-induced contractions; and 3) ATP, but not alpha-beta-methylene ATP increased bath [adenosine]. The [Ca2+]i sensitivity of phosphorylation during P2x receptor activation was similar to that observed with KCl-depolarization-induced opening of L channels, supporting the hypothesis that transplasmalemmal Ca2+ influx produces less phosphorylation and force than mobilization of intracellular Ca2+ stores. Cumulative additions of higher alpha-beta-methylene ATP concentrations induced repeated transient contractions, indicative of an unusual form of receptor desensitization which could be explained if the affinity of the P2x receptor for ATP, but not the receptor number were rapidly reduced.

[Ca2+], not diacylglycerol, is the primary regulator of sustained swine arterial smooth muscle contraction

Sustained smooth muscle contraction has been proposed to be regulated by either 1) sustained increases in intracellular Ca2+ concentration [(Ca2+]i)-dependent myosin phosphorylation or 2) diacylglycerol-dependent protein kinase C activation. We measured diacylglycerol mass with the diacylglycerol kinase assay and myoplasmic [Ca2+] with aequorin in swine carotid medial smooth muscle. Sustained and significant increases in [Ca2+], myosin light chain phosphorylation, and isometric stress were observed with histamine or endothelin stimulation. Neither stimuli, however, induced significant increases in diacylglycerol mass. Relaxation of histamine-stimulated tissues was induced by removal of histamine or removal of extracellular CaCl2 in the continued presence of histamine. The rate of decline of both [Ca2+] and force was similar in both protocols, suggesting that removal of Ca2+ (without removing the stimulus) was equivalent to removal of the stimulus. These data suggest that [Ca2+]i is the primary regulator of sustained swine arterial smooth muscle contraction, whereas diacylglycerol has, at most, only a minor role.

Enalapril maleate versus captopril. A comparison of the hormonal and antihypertensive effects

24 hypertensive patients were randomised into 2 groups to compare the antihypertensive effects of enalapril and captopril over a 10-week period. In the hydrochlorothiazide run-in period, blood pressure was reduced from 171 +/- 4/109 +/- 1mm Hg to 160 +/- 4/103 +/- 1mm Hg (p less than 0.05). Angiotensin-converting enzyme (ACE) inhibition decreased blood pressure to 132 +/- 3/87 +/- 2mm Hg. Captopril decreased diastolic blood pressure significantly more after 3 hours than enalapril (-24 versus -17mm Hg, p less than 0.05). After 10 weeks of therapy, this antihypertensive response was maintained at 134 +/- 3/83 +/- 1mm Hg. There was no difference between the captopril and enalapril treated groups. Acute and chronic responses of plasma renin activity, plasma aldosterone and ACE were determined. There was an acute positive correlation between the rise in plasma renin activity and the fall in blood pressures with captopril but not with enalapril. With chronic treatment there was no difference in the ability of either of the 2 drugs to reduce blood pressure, inhibit ACE, reduce aldosterone or stimulate plasma renin activity.