Engineering of thermoresponsive gels as a fake metastatic niche

Chemoattraction through the CXCR4-CXCL12 axis has been shown to be an important mechanism to direct circulating tumor cells toward distant sites. The objective of this work was to prepare a fake metastatic niche made up of a gel loaded with CXCL12. The gel is designed to create a steep concentration gradient of the chemokine in the proximity of the site of administration/injection, aimed to divert and capture circulating CXCR4⁺ tumor cells. To this aim, different thermoresponsive gels based on methylcellulose (MC) or poloxamers, loaded with CXCL12, with or without hyaluronic acid (HA) were designed and their mechanical properties correlated with the ability to attract and capture in vitro CXCR4⁺ cells. Results of in vitro cell studies showed that all prepared gels induced CEM tumor cell migration whereas only gels based on MC embedded with CXCL12 are able to capture them.

Abstract 1656: CXCR4 antagonist-expressing liposomes reduce lung metastases and deliver drugs to CXCR4 expressing cells: a new drug-targeting device

Introduction. CXCR4 is overexpressed in multiple tumors regulating metastatic dissemination. A new class of cyclic peptides antagonist for CXCR4 receptors was recently developed1. To improve peptide efficacy and increase its delivery delivery to target cancer cells the most active antagonist, Pep R, was coupled to PEGylated liposomes (PL).

Experimental Procedures. PL conjugated to the liposomes (Lip-PepR) were prepared starting by athiolated derivative of antiCXCR4 peptides coupled to the pre-formed PL. Doxorubicin (DOX) was then encapsulated by remote loading method. Lip-PepR was evaluated through migration assay in A498 human renal cancer cell line in vitro and in an experimental animal model of pulmonary metastasis development in vivo (C57/BL mice injected with B16-CXCR4 cells and treated with 0.1 mg/kg Lipo-PepR and lipo-unconjucated i.v. twice a week for two weeks). DOX-encapsulating Lipo-PepR was evaluated in CXCR4 positive cells A498 and HT29 (human renal and colon cancer cell lines, respectivally) versus negative CXCR4 expressing cells FB-1(human anaplastic thyroid cell line), as mean cellular fluorescence. Finally, the cytotoxic effect of the lipo-DOX-PepR was examined, in A498, and HT29 cells.

Results. To evaluate the antagonistic CXCR4 function of Lipo-PepR, migration assays were conducted in A498, CXCR4 expressing cells. A498 cells were treated with the PepR or with liposome preparation (Lipo-PepR) and induced to migrate toward the CXCR4 ligand CXCL12. PepR alone inhibited cell migration such as the CXCR4 antagonist, AMD3100 while the functionalized peptide, Lipo-PepR (10µM) more efficiently inhibited migration CXCL12-induced compared. To validate the Lipo-PepR efficacy in vivo, metastases development assays were conducted. C57/BL mice were injected with murine B16-hCXCR4 melanoma cells and treated twice a week iv with Lipo-PepR versus Peptide R alone. A significant reduction in lung metastases was detected in mice treated with Lipo-Pep R even with lower dose of the Lipo-PepR (0.1mg/kg) compared to the usually used (2mg/kg). Moreover, to allow a target selective drug delivery, Lipo-PepR liposomes were loaded with doxorubicin (DOX). A CXCR4 dependent higher DOX accumulation was registered in CXCR4 positive cells, A498 and HT29 resulting in a specific higher cytotoxicity.

Conclusions. Liposomes conjugated- rationally designed CXCR4 antagonist were more efficient in inhibiting CXCR4 in vitro and in vivo. Moreover Lip-PepR loaded with a chemotherapeutic drug, such as DOX, demonstrated an enhanced drug accumulation into CXCR4 overexpressing cells.

1. Portella L et al. PLoS One. 2013 Sep 13;8(9):e74548

Citation Format: Caterina Ierano, Sara Lusa, Crescenzo D'Alterio, Giuseppina Salzano, Maria Napolitano, Maria Buoncervello, Massimo Spada, Daniele Macchia, Antonio Barbieri, Antonio Luciano, Lucia Gabriele, Giuseppe De Rosa, Stefania Scala. CXCR4 antagonist-expressing liposomes reduce lung metastases and deliver drugs to CXCR4 expressing cells: a new drug-targeting device. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1656. doi:10.1158/1538-7445.AM2014-1656

Loss of the proteins Bak and Bax prevents apoptosis mediated by histone deacetylase inhibitors

Burkitt lymphoma is characterized by deregulation of c-myc, and therapies targeting c-myc are under investigation as treatments. Histone deacetylase inhibitors are known to abrogate c-myc expression, leading us to examine their effect in a series of Burkitt lymphoma cell lines. While treatment with romidepsin, panobinostat, vorinostat, or belinostat for 48 h resulted in complete cell death in the Ramos and ST486 lines, CA46 and DG75 cells were resistant. In parallel studies, CA46 and DG75 cells were also insensitive to 48 h treatment with the Aurora kinase inhibitors (AKIs) MLN8237 (alisertib), VX-680 (tozasertib), or ZM447439. Bax knockdown is known to lead to HDI resistance, and we found that loss of Bax or both Bak and Bax correlated with resistance to both AKIs and HDIs in the Burkitt cell lines. As proof-of-concept to evaluate the contribution of Bax and Bak to HDI-mediated apoptosis, we found that apoptosis was unaffected in HCT-116 colon carcinoma cells lacking Bak, blunted in cells lacking Bax, and nearly completely abrogated in cells lacking both Bak and Bax compared with wild-type cells. To explore potential clinical variations in Bak and Bax expression, a series of samples from 16 patients diagnosed with Burkitt lymphoma was examined. While the majority of samples were positive for both Bak and Bax, some (3/16) expressed low levels of both proteins. We thus conclude that HDI-mediated and AKI-mediated apoptosis requires mitochondrial engagement, and that baseline Bax and Bak expression may serve as biomarkers for patients with Burkitt lymphoma likely to respond to HDI treatment.

Histone deacetylase inhibitors induce CXCR4 mRNA but antagonize CXCR4 migration

The stromal cell-derived factor-1α SDF-1α (CXCL12)/CXCR4 axis has been linked to poor prognosis in some cancers. As histone deacetylase inhibitors (HDIs) exert antitumor effects by targeting proteins affecting cell migration, we sought to evaluate the effects of the HDIs apicidin, vorinostat, entinostat (MS-275) and romidepsin on the expression and function of CXCR4 in human cancer cell lines. After treatment with romidepsin, CXCR4 mRNA expression increased 12-fold in UOK121 renal cancer cells, 16-fold in H460 non-small cell cancer cells and 4-fold in SF295 glioma cells; treatment with other HDIs yielded similar effects. CXCR4 induction was not observed in MCF7 breast cancer cells or SW620 colon cancer cells. To evaluate the corresponding functional increase, the effect of CXCR4 ligand, CXCL12, on ERK1/2, STAT3 and c-SRC activation and cell migration was examined in UOK121, SF295 and H460 cells. Alone, the HDIs increased pERK1/2, while reducing pSTAT-3 and pSRC. Following CXCL12 exposure, pERK1/2 induction was maintained, but STAT3 and SRC phosphorylation was impaired. These findings resulted in reduced basal and CXCL12-mediated cell migration. In conclusion, HDIs upregulated CXCR4 mRNA expression but impaired CXCL12-dependent signaling cascades through STAT3 and c-SRC, suggesting a potential role for HDIs in delaying or preventing metastatic processes in solid tumors.

Histone deacetylase inhibitors influence chemotherapy transport by modulating expression and trafficking of a common polymorphic variant of the ABCG2 efflux transporter

Histone deacetylase inhibitors (HDI) have exhibited some efficacy in clinical trials, but it is clear that their most effective applications have yet to be fully determined. In this study, we show that HDIs influence the expression of a common polymorphic variant of the chemotherapy drug efflux transporter ABCG2, which contributes to normal tissue protection. As one of the most frequent variants in human ABCG2, the polymorphism Q141K impairs expression, localization, and function, thereby reducing drug clearance and increasing chemotherapy toxicity. Mechanistic investigations revealed that the ABCG2 Q141K variant was fully processed but retained in the aggresome, a perinuclear structure, where misfolded proteins aggregate. In screening for compounds that could correct its expression, localization, and function, we found that the microtubule-disrupting agent colchicine could induce relocalization of the variant from the aggresome to the cell surface. More strikingly, we found that HDIs could produce a similar effect but also restore protein expression to wild-type levels, yielding a restoration of ABCG2-mediated specific drug efflux activity. Notably, HDIs did not modify aggresome structures but instead rescued newly synthesized protein and prevented aggresome targeting, suggesting that HDIs disturbed trafficking along microtubules by eliciting changes in motor protein expression. Together, these results showed how HDIs are able to restore wild-type functions of the common Q141K polymorphic isoform of ABCG2. More broadly, our findings expand the potential uses of HDIs in the clinic.

The challenge of exploiting ABCG2 in the clinic

ABCG2, or breast cancer resistance protein (BCRP), is an ATP-binding cassette half transporter that has been shown to transport a wide range of substrates including chemotherapeutics, antivirals, antibiotics and flavonoids. Given its wide range of substrates, much work has been dedicated to developing ABCG2 as a clinical target. But where can we intervene clinically and how can we avoid the mistakes made in past clinical trials targeting P-glycoprotein? This review will summarize the normal tissue distribution, cancer tissue expression, substrates and inhibitors of ABCG2, and highlight the challenges presented in exploiting ABCG2 in the clinic. We discuss the possibility of inhibiting ABCG2, so as to increase oral bioavailability or increase drug penetration into sanctuary sites, especially the central nervous system; and at the other end of the spectrum, the possibility of improving ABCG2 function, in the case of gout caused by a single nucleotide polymphism. Together, these aspects of ABCG2/BCRP make the protein a target of continuing interest for oncologists, biologists, and pharmacologists.

Abstract 2610: Histone deacetylase inhibitors mediate pharmacological rescue of the ABCG2 Q141K variant: Potential for therapeutics in cancer and gout

ABCG2 is an ATP-binding cassette half-transporter that has garnered interest in pharmacogenomics as a modulator of oral drug absorption, drug excretion, and drug distribution through expression at the blood-brain barrier and the maternal-fetal barrier. A single nucleotide polymorphism (SNP) C421A in ABCG2, resulting in a glutamic acid to lysine mutation at amino acid 141 (Q141K), confers impaired protein expression and function. Pharmacogenomic studies have linked the SNP to increased exposure to substrate drugs including irinotecan, topotecan, sunitinib and gefitinib. Moreover, it has been shown that 10 % of gout cases can be attributed to the Q141K variant.

We have studied the biology underlying altered expression and function of the ABCG2 variant. Q141K protein was resistant to degradation by Endo H, suggesting that it was fully processed and folded. Q141K ABCG2 expression was increased by the lysosome inhibitor bafilomycin, indicating that some of the protein reached the cell surface, although at reduced levels. But the largest fraction of the Q141K variant was retained in an intracellular compartment where a part was eliminated through the proteasomal pathway while the undegraded ABCG2 accumulated in the aggresomes, as shown by colocalization of the transporter with the centrosome marker, γ-tubulin. The ability of several agents to impact ABCG2 trafficking to the cell surface was evaluated. Mitoxantrone, an ABCG2 substrate previously noted to act as a pharmacological chaperone, induced a 2-fold increase in Q141K ABCG2 expression at the cell surface but only slightly enhanced ABCG2-related efflux. Romidepsin and other histone deacetylase inhibitors (HDIs), known to increase levels of ABCG2 mRNA, were also assayed. A significant increase in total protein, surface expression, and function was seen in Q141K ABCG2 variant when exposed to various HDIs. Immunofluorescence analysis by confocal microscopy showed a dramatic shift to the plasma membrane following exposure to the HDIs, whereas the localization of α-tubulin, HDAC6 and vimentin, involved in aggresome formation and structure, were unchanged. These results support the notion that Q141K ABCG2 variant is trapped in the aggresome and that HDIs aid localization to the surface. Some supplementary experiments showed that the Q141K ABCG2 states of phosphorylation, acetylation and dimerization were unmodified after HDIs treatment, and that the chaperones BiP, Hsp70 or Hsp90 were not involved in rescue. Investigations into the HDI-mediated mechanisms are underway.

In addition to non-oncologic indications, the restoration of ABCG2 function has potential applications in oncology, in improving normal tissue protection and drug elimination, as well as in cancer prevention since several carcinogens are substrates for ABCG2.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2610. doi:10.1158/1538-7445.AM2011-2610

Abstract 2633: Histone deacetylase inhibitors induce CXCR4 mRNA but antagonize CXCR4 migration

The stromal cell-derived factor-1α SDF-1α (CXCL12)/CXCR4 axis has a critical role, particularly in renal cancer where CXCR4 expression has been linked to poor prognosis. Histone deacetylase inhibitors (HDIs) exert antitumor effects by targeting both histone and nonhistone proteins affecting cell migration, apoptosis, cell proliferation and angiogenesis. Thus, the aim of the present work was to evaluate the effects of the HDIs apicidin, vorinostat, MS-275 and romidepsin on the expression and function of CXCR4 in human cancer cell lines including renal, non-small cell lung, breast, colon and glioma cell lines. After treatment with romidepsin or apicidin, CXCR4 mRNA expression increased 12-fold in UOK121 and 2.5-fold in UOK143 renal cancer cell lines; treatment with vorinostat or MS-275 yielded similar effects. CXCR4 induction was also observed in H460 non-small cell lung cancer cells, and SF-295 glioblastoma cells, but not in MCF-7 breast cancer cells or SW620 colon cancer cells. To evaluate the corresponding CXCR4 functional increase, CXCL12-induced ERK1/2, STAT-3, and c-SRC activation and cell migration were examined in UOK121, SF295 and H460 cells. In general, the HDIs increased pERK1/2, while reducing pSTAT-3 and pSRC. Following CXCL12 pERK1/2 induction was maintained but STAT3 and SRC phosphorylation was impaired. These findings resulted in reduced basal and CXCL12-mediated cell migration. In conclusion, HDIs up-regulated CXCR4 mRNA expression but impaired signalling cascades CXCL12-dependent on STAT3 and c-SRC, suggesting a role for HDI in delaying or preventing metastatic process in solid tumors.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2633. doi:10.1158/1538-7445.AM2011-2633

Abstract 3528: Mutational analysis of threonine 402 adjacent to the GXXXG dimerization motif in TM1 of ABCG2

ABCG2 is an ATP-binding cassette half-transporter important in normal tissue protection, drug distribution and excretion. ABCG2 requires homodimerization for function, though the mechanism for dimerization has not been worked out. We carried out mutational analysis of threonine 402, three residues away from the GXXXG motif in TM1, to study its potential role in ABCG2 dimerization (TXXXGXXXG). Single mutations to leucine (T402L) or arginine (T402R) did not have significant impact on the ABCG2 protein. On the other hand, combining the T402 mutations with the GXXXG glycine to leucine mutations (T402L/G406L/G410L and T402R/G406L/G410L) resulted in substantially reduced expression, altered glycosylation, degradation by a proteosome independent pathway and partial retention in the endoplasmic reticulum as suggested by immunostaining, Endoglycosidase H sensitivity and MG132 and bafilomycin failed effect. The T402L/G406L/G410L mutant when incubated with the ABCG2-substrate mitoxantrone showed a shift on immunoblot analysis to the band representing the fully matured glycoprotein. The T402R/G406L/G410L mutant carrying the more drastic substitution failed to shift to the surface with mitoxantrone. The same set of mutations also displayed impaired dimerization in the TOXCAT assay for TM1 compared to the wild type. Homology modeling of ABCG2 places the TXXXGXXXG motif at the dimer interface. These studies are consistent with a role for the extended TXXXGXXXG motif in ABCG2 folding, processing, and/or dimerization.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3528.

Mutational analysis of threonine 402 adjacent to the GXXXG dimerization motif in transmembrane segment 1 of ABCG2

ABCG2 is an ATP-binding cassette half-transporter important in normal tissue protection, drug distribution, and excretion. ABCG2 requires homodimerization for function, though the mechanism for dimerization has not been elucidated. We conducted mutational analysis of threonine 402, three residues from the GXXXG motif in TM1, to study its potential role in ABCG2 dimerization (TXXXGXXXG). Single mutations to leucine (T402L) or arginine (T402R) did not have a significant impact on the ABCG2 protein. On the other hand, combining the T402 mutations with the GXXXG glycine to leucine mutations (T402L/G406L/G410L and T402R/G406L/G410L) resulted in a substantially reduced level of expression, altered glycosylation, degradation by a proteosome-independent pathway, and partial retention in the endoplasmic reticulum as suggested by immunostaining, Endo H sensitivity, and MG132 and bafilomycin failed effect. The T402L/G406L/G410L mutant when incubated with the ABCG2 substrate MX showed a shift on immunoblot analysis to the band representing the fully mature glycoprotein. The T402R/G406L/G410L mutant carrying the more drastic substitution was found to primarily localize intracellularly. The same set of mutations also displayed impaired dimerization in the TOXCAT assay for TM1 compared to that of the wild type. Homology modeling of ABCG2 places the TXXXGXXXG motif at the dimer interface. These studies are consistent with a role for the extended TXXXGXXXG motif in ABCG2 folding, processing, and/or dimerization.

"CXCR4-CXCL12 and VEGF correlate to uveal melanoma progression"

Despite improvements in early diagnosis of uveal melanoma, prognosis is still poor due to metastases development. Neoangiogenesis and migration are requisites to metastasis promotion. Cross-talking between CXCR4-CXCL12 axis and the VEGF pathway was shown to favours tumour progression. CXCR4-CXCL12-VEGF expression was evaluated by immunohistochemistry in 53 selected cases of primary uveal melanoma and in liver melanoma metastases. CXCR4 protein was detected in 41.4 per cent cases, CXCL12 in 43.4 per cent cases and VEGF expression in 39.6 per cent cases. A significant correlation was found between CXCR4 and VEGF expression (p=0.011), CXCL12 and both tumour dimension and (p=0.006) and epithelioid-mixed cytotype (p=0.012). The two cases of uveal melanoma liver metastases in our series showed CXCR4 expression, weak immunoreactivity for CXCL12 and absent VEGF immunostaining. These data indicate that CXCR4-CXCL12 axis and its cross-talking with VEGF plays a role in uveal melanoma metastases and may be new prognostic markers in UMM. Moreover, these results suggest that targeted inhibition of CXCR4 could be introduced to control metastasis development in UMM.

A point mutation (G574A) in the chemokine receptor CXCR4 detected in human cancer cells enhances migration

The chemokine receptor CXCR4 is widely expressed in human cancers and regulates cell invasion, proliferation and survival. Because mutations in the CXCR4 gene could regulate its function we sequenced the coding region of the CXCR4 gene in 18 human melanoma and 3 human colon carcinoma cell lines. The same somatic point mutation (G574A; V160I) in the fourth transmembrane region of CXCR4 was detected in one colon cancer cell line (PD) and one melanoma cell line (LB). CXCR4 was expressed and functional in both PD and LB cells, PD and LB cells migrated specifically toward the receptor ligand, CXCL12 and P-Erk was specifically induced by CXCL12. To give insight into the function of the mutant CXCR4 receptor, human A431, epidermoid carcinoma cells, were stably transfected with both mutant and wild type CXCR4. In vitro, A431 cells harboring CXCR4(G574A) migrated specifically toward CXCL12 and CXCL12 induced ERK phosphorylation. Interestingly, in vivo studies showed that the growth of A431 tumors harboring CXCR4(G574A) was delayed compared to those harboring WT CXCR4. As expected, treatment with AMD3100, a specific CXCR4 inhibitor, reduced the in vivo growth of CXCR4(G574A) tumor b(G574A) but surprisingly, increased the growth of CXCR4(G574A) A431 cells. This is the first report of a spontaneously occurring, functionally active CXCR4 mutation in human cancer cells. While the mutation impairs cell growth in vivo, the CXCR4 inhibitor, AMD3100, stimulated the growth of cells harboring CXCR4(G574A).