Molecular characterization of the in vivo alkylating agent resistant murine EMT-6 mammary carcinoma tumors

Impact of CTLA-4 blockade in conjunction with metronomic chemotherapy on preclinical breast cancer growth

Background:

Although there are reports that metronomic cyclophosphamide (CTX) can be immune stimulating, the impact of its combination with anti-CTLA-4 immunotherapy for the treatment of cancer remains to be evaluated.

Methods:

Murine EMT-6/P breast cancer, or its cisplatin or CTX-resistant variants, or CT-26 colon, were implanted into Balb/c mice. Established tumours were monitored for relative growth following treatment with anti-CTLA-4 antibody alone or in combination with; (a) metronomic CTX (ldCTX; 20 mg kg⁻¹ day⁻¹), b) bolus (150 mg kg⁻¹) plus ldCTX, or (c) sequential treatment with gemcitabine (160 mg kg⁻¹ every 3 days).

Results:

EMT-6/P tumours responded to anti-CTLA-4 therapy, but this response was less effective when combined with bolus plus ldCTX. Anti-CTLA-4 could be effectively combined with either ldCTX (without a bolus), or with regimens of either sequential or concomitant gemcitabine, including in orthotopic EMT-6 tumours, and independently of the schedule of drug administration. Tumour responses were confirmed with CT-26 tumours but were less pronounced in drug-resistant EMT-6/CTX or EMT-6/DDP tumour models than in the parent tumour. A number of tumour bearing mice developed spontaneous metastases under continuous therapy. The majority of cured mice rejected tumour re-challenges.

Conclusions:

Metronomic CTX can be combined with anti-CTLA-4 therapy, but this therapy is impaired by concomitant bolus CTX. Sequential therapy of anti-CTLA-4 followed by gemcitabine is effective in chemotherapy-naive tumours, although tumour relapses can occur, in some cases accompanied by the development of spontaneous metastases.

Synergistic nanoparticulate drug combination overcomes multidrug resistance, increases efficacy, and reduces cardiotoxicity in a nonimmunocompromised breast tumor model

Anthracyclines, commonly employed for cancer chemotherapy, suffer from dose-limiting cardiotoxicity and poor efficacy due to multidrug resistance (MDR). We previously demonstrated that simultaneous delivery of the synergistic drugs doxorubicin (DOX) and mitomycin C (MMC) by polymer-lipid hybrid nanoparticles (PLN) circumvented MDR, increased efficacy, and reduced cardiotoxicity in immuncompromised mice superior to poly(ethylene glycol)-coated (PEGylated) lipososmal DOX (PLD). Herein it is shown that the DOX-MMC combination was also synergistic in MDR EMT6/AR1 murine breast cancer cells and that their nanoparticle formulations were able to overcome the MDR phenotype. In contrast PLD exhibited little or no effect on the MDR cells. For the first time, these differences in in vitro efficacy are shown to be strongly correlated with cellular uptake and intracellular distribution of DOX brought about by DOX formulations (e.g., free solution, PLN vs PLD). To take into consideration the role of an intact immune system and tumor stroma in the response of host and tumor to chemotherapy, use was made of nonimmunocomprised mouse models to study the dose tolerance, cardiotoxicity, and efficacy of DOX-MMC coloaded PLN (DMsPLN) compared to PLD. DMsPLN treatment at 50 mg/m(2) DOX and 17 mg/m(2) of MMC singly or once every 4 days for 4 cycles were well tolerated by the mice without elevated systemic toxicity blood markers or myocardial damage. In contrast, PLD was limited to a single treatment due to significant total weight loss. The DMsPLN treatment delayed tumor growth up to 312% and 28% in EMT6/WT and EMT6/AR1 models, respectively. This work supports the translational value of DMsPLN for the aggressive management of either naïve or anthracycline-resistant tumors.

Electrochemical activation of chemotherapeutic prodrugs that mimic P450-catalyzed oxidation: proof-of-concept for a focal approach to chemical cancer treatment

The electrochemical oxidation of substrates cyclophosphamide and acetaminophen at Ti/RuO2 or (preferably) graphite anodes parallels P450-catalyzed oxidation in that both mechanisms involve transfer of an oxygen atom to the substrate. The aim of this work was to use this parallel to provide proof-of-concept for a localized approach to tumor chemotherapy using electrochemical oxidation to activate chemotherapeutic prodrugs ex situ. Cyclophosphamide and acetaminophen were electroactivated in batch and flow electrolytic cells and the products were tested against EMT6 mouse mammary adenocarcinoma cells. Cell viability was determined using a tetrazolium dye assay that monitored NADPH concentrations; microscopic examination showed consistent morphological differences between viable and nonviable cells. No cytotoxicity was observed in nonelectrolyzed control samples. The electrolyzed prodrugs demonstrated cytotoxicity up to the IC99 level at 5 mmol L−1 initial prodrug concentrations but not at 1 mmol L−1. The long-term objective of the work is to develop an ex situ electrochemical system for activating prodrugs to cause lethal toxicity to the cells of solid tumors, many of which lack sufficient P450s to bioactivate the toxicant themselves.

In vivo/ex vivo and in situ assays used in cancer research: a brief review

Predicting whether a potential new anticancer agent will have a positive therapeutic index in patients remains a challenge. This brief review provides examples of preclinical in vivo/ex vivo and in situ assays used to assess the therapeutic potential of experimental anticancer therapeutics. Excision assays involving removal of tumor, bone marrow, and other tissues from the host after treatment to determine the effects of therapy in ex vivo assays are important preclinical tools. The survival of malignant cells from tumors treated in vivo and then excised is often determined by colony formation (CFU) in culture. When mice bearing in vivo alkylating agent-resistant tumors were treated with anticancer drugs such as cyclophosphamide, the survival pattern of bone marrow granulocyte-macrophage-colony forming units (CFU-GM) paralleled tumor cell survival. When TNP-470 and minocycline, an antiangiogenic combination, were added to treatment with cytotoxic anticancer therapies, tumor response markedly increased. TNP-470/minocycline-treated mice had higher tissue drug levels than did mice treated with the drug alone. Enzastaurin, an antiangiogenic protein kinase Cbeta inhibitor, treatment decreased intratumoral vessels to one half to one quarter of controls. Simultaneous and sequential treatment regimens with enzastaurin and BCNU delayed tumor growth and increased lifespan in mice bearing subcutaneous or intracranial human T98G glioblastoma multiforme. Both TNP-470 and enzastaurin have undergone clinical trials. Enzastaurin is currently in Phase III clinical trials.

Molecular Determinants of the Cytotoxicity of Platinum Compounds

Gene expression profiling of tumors allows the establishment of relationships between gene expression profiles and sensitivity to anticancer drugs. In an attempt to study the molecular determinants of the activity of platinum compounds, we explored the publicly available databases of the National Cancer Institute (NCI; http://dtp.nci.nih.gov), which allow access to the gene expression profiles of the 60 cell lines for which drug cytotoxicity patterns already existed. Using this database, we have conducted an in silico research to identify the genes the expression of which was positively or negatively correlated to the sensitivity to four platinum compounds (cisplatin, carboplatin, oxaliplatin and tetraplatin). Important similarities were noticed between cisplatin and carboplatin on one hand, and tetraplatin and oxaliplatin on the other hand. In the restricted panel of 1416 genes and molecular markers, we identified 204 markers, among which 120 corresponded to identified genes, that significantly correlated (P < 0.001) with the cytotoxicity of at least one platinum compound. For example, the functionality of the p53-activated pathway appeared positively correlated with the cytotoxicity of all platinum compounds. More specific are the positive correlations between RAS gene mutations and MYC expression and the cellular sensitivity to oxaliplatin. Among the parameters already known as related to the sensitivity to platinum compounds, we identified, in the complete set of 9400 genes, numerous significant relationships, such as the negative correlations between ERB-B2 and BCL-X(L) expressions and the cytotoxicity of the platinum compounds. Public databases mining, therefore, appears to be a valuable tool for the identification of determinants of anticancer drug activity in tumors.

Increased expression of dihydrodiol dehydrogenase induces resistance to cisplatin in human ovarian carcinoma cells

We employed cDNA microarrays to identify the differentially expressed genes in a cisplatin-sensitive parental (2008) human ovarian carcinoma cell line and its cisplatin-resistant variant (2008/C13*). Differential expression of five genes was found in the 2008/C13* cells, a result confirmed by semi-quantitative reverse transcription-PCR. The five genes were identified as fibroblast muscle-type tropomyosin and skeletal muscle-type tropomyosin, dihydrodiol dehydrogenase, apolipoprotein J and glucose-6-phosphate dehydrogenase variant-A. Treatment of the 2008 cells with cisplatin (at its IC(50) concentration of 2 microm) induced expression of these genes, as determined by semi-quantitative reverse transcription-PCR analysis using gene-specific primers. In contrast, treatment of the drug-resistant 2008/C13* cells with cisplatin (at its IC(50) concentration of 20 microm) did not lead to the induction of any of the aforementioned genes. Most importantly, constitutive overexpression of dihydrodiol dehydrogenase (but not the other genes) in the 2008 cells led to induction of cisplatin resistance, clearly indicating its role in the development of the resistance phenotype in the 2008/C13* cells. The development of cisplatin resistance in the transfected cells was associated with an increase in the dihydrodiol dehydrogenase enzyme activity. Although at present it is not clear how dihydrodiol dehydrogenase is involved in cisplatin resistance, the identification of this gene as a causal factor suggests the existence of a hitherto undefined pathway resulting in cisplatin resistance.

Using mRNA expression profiling to determine anticancer drug efficacy

Pharmacogenomics is a fast-growing field of investigations that aims to further elucidate the inherited nature of interindividual differences in drug disposition and effects, with the ultimate goal of providing a stronger scientific basis for selecting the optimal drug therapy. Providing the right drug for the right patient is an important problem in the treatment of cancer. This is mainly due to the lack of information about the sensitivity of the tumor for a specific treatment modality, such as either chemotherapy or radiation treatment. This presentation highlights two approaches to identify responsiveness to treatment. Both approaches are based on the identification of expression profiles. The first approach concentrates on drug resistance and the second on the signaling pathways leading up to the death of the cell. Both approaches provide expression profiles; however, the more dynamic expression profiling as used to determine the signaling in damage cells promises to be a better determinant for the pharmacogenomic changes in expression profiles and, consequently, a potential better determinant for drug efficacy.

Identification of genes differentially expressed in association with acquired cisplatin resistance

The goal of this study was to identify genes whose mRNA levels are differentially expressed in human cells with acquired cisplatin (cDDP) resistance. Using the parental UMSCC10b head and neck carcinoma cell line and the 5.9-fold cDDP-resistant subline, UMSCC10b/Pt-S15, two suppressive subtraction hybridization (SSH) cDNA libraries were prepared. One library represented mRNAs whose levels were increased in the cDDP resistant variant (the UP library), the other one represented mRNAs whose levels were decreased in the resistant cells (the DOWN library). Arrays constructed with inserts recovered from these libraries were hybridized with SSH products to identify truly differentially expressed elements. A total of 51 cDNA fragments present in the UP library and 16 in the DOWN library met the criteria established for differential expression. The sequences of 87% of these cDNA fragments were identified in Genbank. Among the mRNAs in the UP library that were frequently isolated and that showed high levels of differential expression were cytochrome oxidase I, ribosomal protein 28S, elongation factor 1alpha, alpha-enolase, stathmin, and HSP70. The approach taken in this study permitted identification of many genes never before linked to the cDDP-resistant phenotype.

Reversal of in vivo drug resistance by the transforming growth factor-beta inhibitor decorin

Transforming growth factor-beta (TGF-beta) has been implicated in the in vivo resistance of the EMT-6/CTX and EMT-6/ CDDP murine mammary tumors. Both of these tumors have a higher number of intratumoral vessels than the EMT-6/ parent tumor. Animals bearing the resistant tumors have higher plasma levels of TGF-beta than animals bearing the parent tumors; however, upon treatment with cytotoxic therapies there is a greater rise in plasma TGF-beta levels in animals bearing the parent tumor than in animals bearing the resistant tumors. In situ hybridization for TGF-beta mRNA and immunohistochemical staining for TGF-beta protein showed that the resistant tumor levels of this growth factor are higher than those of the parent tumor prior to treatment; however, after cytotoxic therapy the increase in TGF-beta is greater in the parent tumor than in the resistant tumors. Treatment of tumor-bearing animals with the naturally occurring TGF-beta inhibitor decorin did not alter the sensitivity of the parent tumor to cyclophosphamide or to CDDP as determined by tumor cell survival assay. However, administration of decorin increased the sensitivity of the EMT-6/CTX tumor to cyclophosphamide and of the EMT-6/CDDP tumor to CDDP so that the drug resistance of these tumors was nearly ablated. A similar pattern was observed in the drug response of the bone marrow granulocyte-macrophage colony-stimulating factor of animals bearing each of the 3 tumors.

Dynamics of tumor oxygenation, CD31 staining and transforming growth factor-beta levels after treatment with radiation or cyclophosphamide in the rat 13762 mammary carcinoma

PURPOSE

Tumors are dynamic tissues that undergo marked molecular, biochemical, and physiologic changes in response to cytotoxic anticancer therapies. Understanding the changes in tumor oxygenation and transforming growth factor-beta expression may allow improved treatment regimens to be developed.

METHODS AND MATERIALS

The effects of a single dose of radiation therapy (20 Gy) or a single dose of chemotherapy (cyclophosphamide, 250 mg/kg) on several molecular and physiologic parameters of the rat 13762 mammary carcinoma growing subcutaneously in female Fischer 344 rats were explored.

RESULTS

Treatment of the tumor-bearing animals with 20 Gy of radiation killed about two logs (99%) of the 13762 tumor cells, and treatment with cyclophosphamide (250 mg/kg) killed about 1.5 logs (95%) of the 13762 tumor cells. Hypoxia, as determined by a pO2 electrode, initially decreased in the tumors of treated animals until 6 h. posttreatment and then increased, so that 24 h. after administration of the radiation therapy or the chemotherapy the number of intratumoral vessels as determined by CD31 staining increased until about 24 h after cytotoxic therapy. Transforming growth factor-beta1, measured by radioimmunoassay, peaked in the serum between 6 h and 18 h and again between 72 h and 96 h after radiation therapy and peaked in the tumor at 24 h and again at 72 h after radiation therapy. The first serum peak after cyclophosphamide was 3 h after drug injection, with second peaks at 36 h and 48 h after drug administration. In the tumor, transforming growth factor-beta1 peaked between 6 h and 8 h after drug administration and again 36 h and 72 h after drug. Apoptosis was maximal 6 h after 20 Gy and 24 h after cyclophosphamide. Vascular endothelial growth factor was also increased in tumors after cytotoxic therapy.

CONCLUSIONS

These changes in the tumor physiologic status are sufficient to protect the tumor from a second cytotoxic insult administered days afterwards and to result in a restructuring of the tissue.

Potentiation of cytotoxic therapies by TNP-470 and minocycline in mice bearing EMT-6 mammary carcinoma

The ability of the antiangiogenic agents TNP-470 and minocycline, singly or in combination, to potentiate the antitumor effects of several cytotoxic therapies was assessed in the murine EMT-6 mammary carcinoma as well as in two drug resistant sublines of that tumor designated EMT-6/CTX and EMT-6/CDDP. The antiangiogenic agents alone or in combination did not alter the growth of the tumors. However, their administration along with cyclophosphamide, CDDP, or thiotepa substantially increased the tumor growth delay produced by these cytotoxic therapies in tumors responsive to the drugs--the increase was about 2-fold for TNP-470 and minocycline together. In drug resistant tumors, treatment with the antiangiogenic agents did not reverse drug resistance but did increase the effect of the cytotoxic drugs. Treatment with TNP-470/minocycline also increased the oxygenation of each of the three tumors. Thus, TNP-470/minocycline administration increased the efficacy of fractionated radiation therapy, especially when used along with a perflubron emulsion oxygen delivery agent/carbogen. These results indicate that treatment regimens including therapies directed toward the proliferating normal cells within a tumor mass as well as therapies directed toward the malignant cells can produce improved outcomes.