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Clear cell renal cell carcinoma (CCRCC) evolves due to mutations in the Von Hippel-Lindau (VHL) tumor suppressor gene. Although the loss of VHL enables survival and proliferation of CCRCC cells, it is also expected to introduce vulnerabilities that may be exploited for therapeutics discovery. To this end, we developed a high-throughput screen to identify small molecules derived from plants, microorganisms, and marine organisms to which CCRCC cells are sensitive. Screening over 8,000 compounds using this approach, we report here the identification of the microbially derived compound carminomycin I (CA) as an effective inhibitor of VHL-defective (VHL(-/-)) CCRCC cell proliferation. CA also induced apoptosis in CCRCC cells by a mechanism independent of p53 or hypoxia-inducible factor 2. We found that P-glycoprotein (P-gp) sequestered CA within the Golgi complex. Interestingly, Golgi sequestration was critical for the antiproliferative effects of CA and P-gp inhibitors abrogated this activity. Furthermore, CA induced cleavage of the Golgi protein p115 and the translocation of its C-terminal fragment to the nucleus. Finally, examination of the activity of the VHL-interacting Golgi protein, endoplasmic reticulum-Golgi intermediate compartment, ERGIC-53 showed that VHL could mediate protection from CA in CCRCC cells. Our natural product-based screening approach has revealed the P-gp-mediated localization of anticancer compounds within the Golgi in CCRCC cells as a potential strategy of targeting VHL-deficient CCRCC cells., (© 2011 AACR.)

We previously reported that MX2, a new morpholino anthracycline, showed marked effects on pleiotropic drug-resistant sublines of murine P388 leukemia in vivo as well as in vitro. In this study we examine the in vitro cytotoxicity against pleiotropic drug-resistant sublines of human tumor cell lines. MX2 was effective against multidrug-resistant sublines of four human tumor cell lines; these cells, having a 4.8- to 200-fold cross-resistance to Adriamycin (ADM) showed only a 0.7- to 2.3-fold resistance to MX2 compared with the sensitive cells. To elucidate the mechanism by which MX2 overcomes multidrug resistance, the intracellular pharmacology of MX2 in human myelogenous leukemia K562 and its ADM-resistant subline (K562/ADM) was examined. Both K562 and K562/ADM cells accumulated MX2 more easily than ADM, and the intracellular accumulation of MX2 attained a steady state in both cell lines within 30 min of incubation at 37 degrees C. The amount of MX2 that accumulated in K562/ADM at a steady state was only 1.3 times lower than that in K562. However, ADM was accumulated slowly in both cell lines compared with MX2, and the intercellular concentration reached a steady state in K562/ADM after 90 min of incubation and in K562 after more than 120 min. K562/ADM cells accumulated a 3.3-fold lower concentration of ADM than K562 after 120 min of exposure. The steady-state concentration of ADM in K562/ADM was 8.3 times lower than that of MX2. In addition, greater than 70% of MX2 was retained in both cell lines after 150 min of incubation in the absence of this drug. Verapamil, a calcium antagonist, hardly augmented the cytotoxicity of MX2 against K562/ADM, and no distinct effect of this drug on both the time course and the maximal level of accumulation of MX2 was observed. Interestingly, MX2 effectively inhibited ATP/Mg2(+)-dependent [3H]vincristine binding to K562/ADM membrane preparations, indicating that MX2 could be transported outside the cell by an active efflux pump. The high intracellular accumulation and retention of MX2 in K562/ADM through the rapid influx of the drug into the cells may be one of the reasons why MX2 circumvents pleiotropic drug resistance.

The mechanism of action of 3'-deamino-3'-morpholino-13-deoxo-10-hydroxycarminomycin (MX2) was examined in a human leukemia cell line (K562) and its Adriamycin (ADM)-resistant subline (K562/ADM). ADM and MX2 showed an equivalent antitumor effect against K562. K562/ADM was highly resistant to ADM. In cellular pharmacokinetic studies, MX2 showed faster and greater influx than did ADM in both K562 and K562/ADM. The efflux of ADM was rapid in K562/ADM but not in K562. On the other hand, the efflux of MX2 was rapid in both cell lines. The formation of DNA single-strand breaks and double-strand breaks by ADM was significantly lower in K562/ADM than K562. On the other hand, formation of those breaks by MX2 was not decreased. Although some of the DNA breaks induced by MX2 were resealed, there was no difference in the degree of resealing in K562 and K562/ADM cells. On the other hand, most of the small number of DNA breaks in K562/ADM induced by ADM were resealed. The topoisomerase II activity in K562 and K562/ADM was not significantly different. It is concluded that MX2 conquers multidrug resistance by rapid influx following a higher frequency of formation of DNA single- and double-strand breaks in K562/ADM cells.

Carminomycin (CMN) was administered i.v. to 44 patients with a variety of nonhematological cancers every 4 weeks at doses of 15, 20, 22.5, and 25 mg/sq m. Granulocytopenia was the dose-limiting toxicity. The median granulocyte count for previously untreated patients receiving 22.5 mg/sq m was 0.962 cells/microliters, and for previously treated patients receiving 20 mg/sq m it was 0.420 cell/microliters. Moderate to severe phlebitis was associated with drug administration in 50% of cases. Nausea, vomiting, and alopecia were mild. Three of nine patients who received a total CMN dose of greater than or equal to 100 mg/sq m (mean, 132 mg/sq m) developed unexplained decreases in radionuclide cardiac ejection fraction, with one patient developing decreased QRS amplitude and congestive heart failure at a total dose of 160 mg/sq m. CMN is rapidly metabolized to carminomycinol. The elimination half-lives of CMN and carminomycinol are 6 to 10 and 50 hr, respectively. CMN was found to be a more potent inhibitor of human granulocyte-macrophage colony-forming units than was carminomycinol. Objective partial responses were seen in two of seven previously untreated patients with non-small cell lung cancer and one of three patients with squamous cell carcinoma of the head and neck previously untreated with chemotherapy.

The sensitivity of bone marrow granulocyte-macrophage colony-forming cells to 4 anthracyclines, carminomycin, marcellomycin, aclacinomycin A, and N,N-dibenzyldaunorubicin, was studied using the agar diffusion chamber technique which allows exposure of target cells to drug metabolized by the chamber-bearing host after i.v. injection. Colony-forming cells from mice, dogs, and humans were all found to have exponential dose-response curves for the agents studied, with variation of the slopes between species and agents. Species sensitivities as determined by the assay related well to the available toxicological and clinical data for specific drugs. The rank order of sensitivity of human marrow colony-forming cells to five anthracyclines tested in this and a previous study related very closely to doses producing moderate leukopenia in Phase I and II clinical studies. A dose of 200 mg/sq m of N,N-dibenzyldaunorubicin would be expected to produce moderate leukopenia in future clinical trials. This assay may be useful in predicting human bone marrow toxicity of new agents before actual clinical trial because of the ability to study the survival of human colony-forming cells directly.

Previous reports have claimed Adriamycin to be cytotoxic to cultured tumor cells when the drug is covalently immobilized on a solid support, thus suggesting a cell surface mechanism of action for the drug. Although these previous reports attempted to rule out released drug or endocytosis of drug-support particles as alternative explanations for the observed cytotoxicity, a more thorough analysis is necessary to substantiate fully the cell surface idea. In the present work, the stability of the drug-support linkage was increased by use of cross-linked polyvinyl alcohol as the support and cyanuric chloride or a diazonium salt for attachment of the drug. Different anthracycline orientations were tested by coupling Adriamycin at the amino sugar and carminomycin at the D-ring. The Adriamycin cross-linked polyvinyl alcohol and carminomycin cross-linked polyvinyl alcohol preparations had much lower drug release rates than did the earlier used carbamate-linked Adriamycin cross-linked agarose materials. All three immobilized drug preparations inhibited the growth of L1210 or S180 clones following 2- or 20-h incubation with cells at 37 degrees C. The results strongly support the concept that immobilized anthracyclines can be cytotoxic to cultured cells, for at least two different orientations of the drug on the support.

This study was designed to determine the effects of several antitimor anthracyclines, including Adriamycin and its analogs, carminomycin and marcellomycin, on the ultrastructure of nucleoli of Novikoff hepatoma cells. Adriamycin and carminomycin, which are structurally related, induce nucleolar segregation following the formation of conspicuous fibrillar centers. Marcellomycin did not induce formation of nucleolar fibrillar centers. Instead, numerous microspherules formed following treatment with marcellomycin; later complete nucleolar segregation developed. The microspherules were observed to be in various stages of extrusion from the nucleolar body. This microspherule "migration" appeared to be both time and drug concentration dependent. These results show that the rate and extent of nucleolar ultrastructural aberration may be related to structural differences of the various anthracyclines.

Male Sprague-Dawley rats were treated with carminomycin i.v. in doses ranging from 1 to 40 mg/kg. Within 1 hr after the administration of carminomycin, 20 mg/kg, nucleoli of cardiac and skeletal muscle cells were segregated, while nucleoli of liver parenchyma cells were unaffected. Three and one-half hr after drug administration, cardiac muscle nucleoli reverted to normal ultrastructure. However, some skeletal muscle cell nucleoli were still segregated. Following treatment with carminomycin, 10 mg/kg, no significant ultrastructural changes were observed. These results demonstrate that at sufficiently high doses carminomycin induces ultrastructural lesions in nucleoli of both cardiac and muscle cells. The dose of carminomycin required to produce nucleolar segregation in cardiac and skeletal muscle is 6 times greater than the dose of Adriamycin (3.5 mg/kg) required to induce equivalent alterations.