Role of RLIP76 in lung cancer doxorubicin resistance: II. Doxorubicin transport in lung cancer by RLIP76

Haploinsufficiency Interactions between RALBP1 and p53 in ERBB2 and PyVT Models of Mouse Mammary Carcinogenesis

Simple Summary

Rlip knockout has been reported to prevent cancer in highly cancer-susceptible mice lacking p53, and Rlip knockdown kills many types of cancer cells. In humans, breast cancer shows diverse characteristics, including HER2-driven subtypes and viral-driven subtypes. HER2 can be targeted; however, escape of the cancer from targeted therapies remains a problem. In this work we evaluated the capacity of Rlip knockout to prevent breast cancer in genetically engineered mouse models of HER2-driven breast cancer (Erbb2 model) and polyomavirus-driven breast cancer (PyVT model). We found that in Erbb2 mice, Rlip knockout significantly delayed oncogenesis and reduced the expression of genes associated with poor prognosis in patients. In PyVT mice, Rlip knockout did not delay oncogenesis or tumor growth, but Rlip knockdown reduced tumor metastasis to the lung. We conclude that Rlip inhibitors may significantly improve survival in HER2-positive patients, but are unlikely to offer benefits to patients with polyomavirus-associated tumors.

Abstract

We recently reported that loss of one or both alleles of Ralbp1, which encodes the stress-protective protein RLIP76 (Rlip), exerts a strong dominant negative effect on both the inherent cancer susceptibility and the chemically inducible cancer susceptibility of mice lacking one or both alleles of the tumor suppressor p53. In this paper, we examined whether congenital Rlip deficiency could prevent genetically-driven breast cancer in two transgenic mouse models: the MMTV-PyVT model, which expresses the polyomavirus middle T antigen (PyVT) under control of the mouse mammary tumor virus promoter (MMTV) and the MMTV-Erbb2 model which expresses MMTV-driven erythroblastic leukemia viral oncogene homolog 2 (Erbb2, HER2/Neu) and frequently acquires p53 mutations. We found that loss of either one or two Rlip alleles had a suppressive effect on carcinogenesis in Erbb2 over-expressing mice. Interestingly, Rlip deficiency did not affect tumor growth but significantly reduced the lung metastatic burden of breast cancer in the viral PyVT model, which does not depend on either Ras or loss of p53. Furthermore, spontaneous tumors of MMTV-PyVT/Rlip+/+ mice showed no regression following Rlip knockdown. Finally, mice lacking one or both Rlip alleles differentially expressed markers for apoptotic signaling, proliferation, angiogenesis, and cell cycling in PyVT and Erbb2 breast tumors. Our results support the efficacy of Rlip depletion in suppressing p53 inactivated cancers, and our findings may yield novel methods for prevention or treatment of cancer in patients with HER2 mutations or tumor HER2 expression.

Rlip Depletion Suppresses Growth of Breast Cancer

RLIP76 (RAL-binding protein-1, Rlip) is a stress-protective mercapturic-acid-pathway transporter protein that also plays a key role in regulating clathrin-dependent endocytosis as a Ral effector. Targeted inhibition or depletion of Rlip causes regression of xenografts of many cancers and is capable of abrogating tumor formation in p53-null mice. This is associated with the reversion of the abnormal methylomic profile of p53-null mice to wild-type. In a query of The Cancer Genome Atlas (TCGA) databases, we found that Rlip expression was associated with poor survival and with significant differences in the frequencies of PIK3CA mutation, MYC amplification, and CDKN2A/B deletion, which were the most commonly mutated, amplified, and deleted genes, respectively, among TCGA breast cancer patients. We conducted the present study to further examine the effects of Rlip inhibition and to evaluate the in vitro and in vivo efficacy in breast cancer. Using immunogold electron microscopy, we found that plasma-membrane Rlip was accessible to cell-surface antibodies in the MCF7 (ER+) breast cancer cell line. Rlip depletion resulted in decreased survival of MCF7 and MDA-MB-231 cells and increased terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) positivity and DNA laddering, indicating apoptotic cell death. Additionally, in vitro knockdown of Rlip inhibited EGF endocytosis and WNT/MAPK signaling. Xenograft studies in nude mice showed regression of breast cancer via antisense-mediated depletion of Rlip mRNA as well as by anti-Rlip antibody. Finally, knockdown of Rlip by antisense locked nucleic acid oligonucleotides increased markers for apoptotic signaling and decreased markers for proliferation, angiogenesis, and cell cycling in MCF7 and MDA-MB-231luc xenografts. Our findings validate Rlip as an attractive target in breast cancer.

Anticancer activity of 2'-hydroxyflavanone towards lung cancer

In previous studies, we found that 2'-hydroxyflavonone (2HF), a citrus flavonoid, inhibits the growth of renal cell carcinoma in a VHL-dependent manner. This was associated with the inhibition of glutathione S-transferases (GSTs), the first step enzyme of the mercapturic acid pathway that catalyzes formation of glutathione-electrophile conjugates (GS-E). We studied 2HF in small cell (SCLC) and non-small cell (NSCLC) lung cancer cell lines for sensitivity to 2HF antineoplastic activity and to determine the role of the GS-E transporter Rlip (Ral-interacting protein; RLIP76; RALBP1) in the mechanism of action of 2HF. Our results show that 2HF induced apoptosis in both histological types of lung cancer and inhibited proliferation and growth through suppression of CDK4, CCNB1, PIK3CA, AKT and RPS6KB1 (P70S6K) signaling. Increased E-cadherin and reduced fibronectin and vimentin indicated inhibition of epithelial-mesenchymal transition. Additionally, 2HF inhibited efflux of doxorubicin and increased its accumulation in the cells, but did not add to the transport inhibitory effect of anti-Rlip antibodies alone. Binding of Rlip to 2HF was evident from successful purification of Rlip by 2HF affinity chromatography. Consistent with increased drug accumulation, combined treatment with 1-chloro-2, 4-dinitrobenzene, reduced the GI50 of 2HF by an order of magnitude. Results of in-vivo nude mouse xenograft studies of SCLC and NSCLC, which showed that orally administered 2HF inhibited growth of both histological types of lung cancer, confirmed in-vitro study results. Our result suggest that Rlip inhibition is likely a mechanism of action. Our findings are basis of proposing 2HF as therapeutic or preventative drug for lung cancer.

Regression of Lung and Colon Cancer Xenografts by Depleting or Inhibiting RLIP76 (Ral-Binding Protein 1)

Ral-binding protein 1 (RALBP1) is a stress-responsive and stress-protective multispecific transporter of glutathione conjugates (GS-E) and xenobiotic toxins. It is frequently overexpressed in malignant cells and plays a prominent antiapoptotic role selectively in cancer cells through its ability to control cellular concentration of proapoptotic oxidized lipid byproducts. In the absence of chemotherapy, depletion or inhibition of RALBP1 causes regression of syngeneic mouse B16 melanoma. Because RALBP1 transports anthracycline and Vinca alkaloid drugs, as well as GS-E, and because it confers resistance to these drugs, we proposed that depletion or inhibition of RALBP1 should cause regression of human solid tumors that overexpress RALBP1 and augment chemotherapy efficacy. Non-small-cell lung cancer (NSCLC) H358 and H520 and colon SW480 cell lines were used. Cytotoxic synergy between anti-RALBP1 immunoglobulin G (IgG), cis-diammine-dichloroplatinum (II) [CDDP], and vinorelbine was examined in cell culture and xenografts of NSCLC cells. Effects of RALBP1 depletion by antisense were examined in xenografts of NSCLC H358, NSCLC H520, and colon SW480 cells. RALBP1 depletion by phosphorothioate antisense was confirmed and was associated with rapid, complete, and sustained remissions in established s.c. human lung and colon xenografts. RALBP1 inhibition by anti-RALBP1 IgG was equally as effective as antisense and enhanced CDDP-vinorelbine in lung cancer xenografts. These studies show that RALBP1 is a transporter that serves as a key effector function in cancer cell survival and is a valid target for cancer therapy, and confirm that inhibitory modulation of RALBP1 transport activity at the cell surface is sufficient for antitumor effects.

Regression of melanoma in a murine model by RLIP76 depletion

RLIP76/RALBP1 is a stress-responsive membrane protein implicated in the regulation of multiple cellular signaling pathways. It represents the predominant glutathione-conjugate transporter in cells, and our previous studies have shown that its inhibition by antibodies or depletion by short interfering RNA (siRNA) causes apoptosis in a number of cancer cell types. The present studies were done to explore the potential clinical applicability of our previous observations by comparing the relative expression of RLIP76 in cancer versus normal cell lines and to determine whether depletion of RLIP76 activity can exert cancer-specific apoptosis. RLIP76 expression was found to be significantly greater in malignant cells compared to nonmalignant cells. Inhibition of RLIP76, using antibodies towards a cell surface epitope, or depletion of RLIP76 using either siRNA or antisense phosphorothioate oligonucleotides preferentially caused apoptosis in malignant cells. More importantly, in vivo studies showed that administration of RLIP76 antibodies, siRNA, or antisense oligonucleotides to mice bearing syngeneic B16 mouse melanoma cells caused complete tumor regression within 10 days. These findings strongly suggest that RLIP76 depletion by genetic approaches or inhibition by antibodies may be a clinically viable antineoplastic therapy, particularly for melanoma.

RLIP76 Transports Vinorelbine and Mediates Drug Resistance in Non–Small Cell Lung Cancer

Vinorelbine (Navelbine), an amphiphilic semisynthetic Vinca alkaloid, has displayed superior activity and decreased resistance in the treatment of advanced non–small cell lung cancer (NSCLC) compared with other members of its class. Recently, vinorelbine and cisplatin combination chemotherapy has been shown for the first time to confer a significant survival advantage in early-stage lung cancer after surgical therapy. The biological mechanisms underlying the differential response of NSCLC to cytocidal activity of vinorelbine have yet to be elucidated. Our recent findings indicate a role of RLIP76, a non–ATP binding cassette transport protein, in catalyzing the ATP-dependent efflux of structurally and functionally unrelated chemotherapeutic agents such as doxorubicin and vinblastine in NSCLC. Present studies were conducted to assess whether RLIP76 mediates vinorelbine transport and resistance. Here we show that RLIP76 catalyzes the transport of vinorelbine in a saturable manner with respect to vinorelbine (Km 75 nmol/L) and ATP (Km = 3.4 mmol/L). Three-fold overexpression of RLIP76 in NSCLC and SCLC confers increased resistance to cytotoxicity. RLIP76 overexpression causes a sustained intracellular decrease in vinorelbine concentration because of increased efflux, and anti-RLIP76 antibodies sensitize lung cancer cells to vinorelbine by inhibiting its efflux. These studies for the first time show that RLIP76 mediates vinorelbine transport and is capable of conferring drug accumulation defect and resistance to lung cancer cells.