Abstract P5-04-05: Targeting the pH regulatory mechanisms of breast cancer cells

Background:

The abnormal regulation of H+ ions, leading to a reversed pH gradient in tumor cells in comparison to normal cells, is considered to be one of the hallmarks of cancer. This feature, however, has yet to be exploited as a therapeutic target. The aim of this study was to assess whether targeting proteins (CAIX, NHE1 and V-ATPase) that permit hypoxic cancer cell adaptation to acidosis in the tumor microenvironment can produce an effective therapeutic response in breast cancer, using 2D and 3D models.

Method:

Western blotting and gene expression analysis were performed on MCF-7, MDA-MB-231 and HBL-100 cancer cells to assess target protein expression in differing O2 conditions in 2D, while IHC was used to measure protein levels in 3D using multicellular tumor spheroids. Sulforhodamine B assays were executed to analyze the effects of inhibitors targeting CAIX, NHE1 and V-ATPase on breast cancer cell proliferation in 2D. 3D invasion assays were performed with MDA-MB-231 spheroids and explant tissue derived from human patients to see if CAIX inhibition had any effect on cancer cell invasion. An MDA-MB-231 xenograft model was used to investigate the effects of CAIX inhibition in vivo. Clonogenic assays were performed with MDA-MB-231 spheroids to evaluate whether any of the drugs combined effectively with irradiation.

Results:

2D and 3D expression analysis showed that CAIX levels were extremely responsive to changes in O2 conditions in each of the cell lines, with HBL100 cells exhibiting the largest changes in both mRNA (42-fold increase) and protein (78-fold increase) levels at low (0.5%) O2 concentrations. NHE1 and V-ATPase mRNA/protein levels were, however, much more consistently expressed across the cell lines in different O2 conditions. Drugs targeting CAIX, NHE1 and V-ATPase had anti-proliferative effects on the breast cancer cells in 2D. Normoxic cancer cells were the most sensitive to drug treatment, acute hypoxic cancer cells showed increased resistance to the anti-proliferative effects of these drugs, while chronic hypoxic cells had IC50 values more similar to the normoxic cells. The results for the CAIX inhibitor were unexpected, as we had predicted that the increased levels of CAIX in the acute hypoxic cells would make them more sensitive to treatment. CAIX inhibition did, however, significantly reduce the invasion of cancer cells from both MDA-MB-231 spheroids (p≤0.01) and explant tissue (p≤0.001). Targeting pH regulation was also shown to have an effect in vivo on MDA-MB-231 xenografts, with CAIX inhibition significantly reducing the growth (p≤0.05) and proliferation (p≤0.05) of tumors within mice. Finally, clonogenic assays showed that drugs targeting both CAIX and NHE1 led to a significant reduction in colony number when combined with radiation (p≤0.05), compared to either drug individually or radiation treatment alone.

Conclusions:

This study shows that drugs targeting pH regulation molecules have potential in the treatment of breast cancer. This is highlighted by their ability to affect the proliferation and invasion of breast cancer cells, along with their ability to be combined with radiation. Of the 3 pH regulatory molecules, CAIX represents the target with the most promise.

Citation Format: Meehan J, Ward C, Jarman E, Xintaropoulou C, Martinez-Perez C, Turnbull A, Supuran C, Dixon M, Kunkler I, Langdon SP. Targeting the pH regulatory mechanisms of breast cancer cells. [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 P5-04-05.

HOMA-S is associated with greater HbA1c reduction with a GLP-1 analogue in patients with type 2 diabetes

Exenatide, a glucagon-like peptide-1 (GLP-1) analogue, is an effective glucoregulator for treating overweight individuals, not at target HbA1 c. This prospective study aimed to determine whether estimates of beta cell function (HOMA-B) and insulin sensitivity (HOMA-S) predict response to Exenatide treatment.Prospective data on 43 type 2 diabetes patients were collected for up to 2.8 years in UK primary care. HOMA-B and HOMA-S were estimated prior to initiating Exenatide, with monitoring of cardio-metabolic risk factors.Mean (SD) age and BMI pre-treatment were 54.1±10.5 years and 35.7±7.5 kg/m2 respectively. HbA1c decreased (mean reduction 0.9%, p=0.04; p for trend=0.01) in 61% of patients. In univariate analyses, HOMA-S as a measure of insulin sensitivity was inversely (β=- 0.41, p 0.009) related to change in HbA1c, with no relation for HOMA-B.In a random effects regression model that included age at baseline, weight, LDL-C, HDL-C and triglycerides, change in HbA1c (β= - 0.14, p<0.001) and HDL-C (β= - 0.52, p=0.011) were independently associated with increasing insulin sensitivity (r2=0.52). Thus patients with greater measured insulin sensitivity achieved greater reduction in HbA1c independent of the factors described above.In logistic regression those in the highest tertile of log-HOMA-S were 45% more likely to have a fall in HbA1c with an odds ratio (OR) of 0.55 (95% CI 0.47-0.66) p<0.0001 (log likelihood ratio for the model χ2=71.6, p<0.0001).Patients with greater measured insulin sensitivity achieve greater reduction in HbA1c with Exenatide. Determination of insulin sensitivity may assist in guiding outcome expectation in overweight patients treated with GLP-1 analogues.

A dual action of saturated fatty acids on electrical activity in rat pancreatic β-cells. Role of volume-regulated anion channel and KATP channel currents

Free fatty acids (FFAs) exert complex actions on pancreatic β-cells. Typically, an initial potentiation of insulin release is followed by a gradual impairment of β-cell function, the latter effect being of possible relevance to hyperlipidaemia in type 2 diabetes mellitus. The molecular actions of FFAs are poorly understood. The present study investigated the acute effects of saturated FFAs on electrophysiological responses of rat pancreatic β-cells. Membrane potential and KATP channel activity were recorded using the perforated patch technique. Volume-regulated anion channel (VRAC) activity was assessed from conventional whole-cell recordings. Cell volume regulation was measured using a video-imaging technique. Addition of octanoate caused a transient potentiation of glucose-induced electrical activity, followed by a gradual hyper-polarisation and a prolonged inhibition of electrical activity. Octanoate caused an initial increase in VRAC activity followed by a secondary inhibition coinciding with increased KATP channel activity. Similar effects were observed with palmitate and 2-bromopalmitate whereas butyrate was virtually ineffective. Octanoate and palmitate also exerted a dual effect on electrical activity evoked by tolbutamide. Octanoate significantly attenuated cell volume regulation in hypotonic solutions, consistent with VRAC inhibition. It is concluded that medium and long chain FFAs have a dual action on glucose-induced electrical activity in rat pancreatic β-cells: an initial stimulatory effect followed by a secondary inhibition. These effects appear to be the result of reciprocal actions on VRAC and KATP channel currents, and could contribute towards the stimulatory and inhibitory actions of FFAs on pancreatic β-cell function.

Relationship between IFN-gamma and skin test responsiveness to Mycobacterium tuberculosis PPD in healthy, non-BCG-vaccinated young adults in Northern Malawi

SETTING

Rural northern Malawi, where vaccination with BCG Glaxo (1077) provides protection against leprosy but not against pulmonary tuberculosis.

OBJECTIVE

To evaluate the patterns of responsiveness to purified protein derivative of Mycobacterium tuberculosis (PPD) in terms of delayed type hypersensitivity (DTH) and interferon-gamma (IFN-gamma) production.

DESIGN

IFN-gamma was measured in 6 day whole blood cultures diluted 1 in 10, stimulated with PPD RT48, and the results compared to the DTH response to PPD RT23. A total of 633 individuals aged 12 to 28 years, without prior BCG vaccination, were recruited.

RESULTS

Overall, 63% of subjects made a positive IFN-gamma response (defined as >62 pg/ml), and 37% gave a DTH induration of >5 mm. A strong correlation between skin test and IFN-gamma responses was observed, although with interesting exceptions: 13/270 individuals with zero DTH showed IFN-gamma responses >500 pg/ml, and 7/53 individuals with >10 mm induration showed IFN-gamma responses < or = 62 pg/ml. The prevalence of skin test responsiveness increased with age, and was higher among older males than females; age-sex patterns were less clear for IFN-gamma production.

CONCLUSION

The 6 day IFN-gamma response to PPD correlates well with Mantoux skin test induration. The discordant individuals may represent important subsets in terms of protective immunity and risk of clinical tuberculosis.