Antonio Tito Fojo

Expression of a multidrug resistance gene in human cancers

Chemotherapy has proven to be an effective treatment for the cure and palliation of some human cancers (Chabner, 1982). Some tumors, however, appear to be intrinsically resistant to chemotherapy. For cancers that can be treated with chemotherapy, based on the hypothesis that resistance to single agents occurs with high frequency, protocols involving multiple drugs with different intracellular targets have been designed. In many cases, such as acute lymphocytic leukemia and neuroblastoma (Simone et al., 1982), Hodgkin’s disease (De-Vita and Hellman, 1982), and germ cell cancers (Paulson et al., 1982), dramatic results have been achieved with such protocols. However, all too frequently relapse occurs after such therapy and the recurrent tumors are resistant to further chemotherapy. In effect, such tumors develop a multidrug resistance (MDR) phenotype that is very similar to the intrinsic resistance of some primary cancers.

Isolation and genetic characterization of human KB cell lines resistant to multiple drugs

Human KB cell lines resistant to high levels of colchicine were isolated by several successive single-step selections. Most of these selection steps resulted in cross-resistance to vincristine, vinblastine, adriamycin, actinomycin D, and puromycin; however, at the highest levels of colchicine resistance, increased cross-resistance to other drugs was not observed. There was no major change in protein synthesis or alteration in protein phosphorylation or [14C]glucosamine labeling patterns accompanying the development of multiple drug resistance as measured by analysis of metabolically labeled proteins on SDS gels. Cell-cell hybridization experiments showed that the colchicine-resistant and multiple drug-resistant phenotypes were incompletely dominant. In addition, colchicine resistance was found to segregate independently from resistance to other drugs in one somatic cell hybrid, suggesting that complex genetic loci are involved in the development of the multiple drug-resistant phenotype. These mutants should be useful for the study of the clinically important problem of multiple drug resistance in human cancer.

Paclitaxel in doxorubicin-refractory or mitoxantrone-refractory breast cancer: a phase I/II trial of 96-hour infusion.

PURPOSE A phase I study of paclitaxel infused over 96-hours was performed to determine toxicity, maximum-tolerated dose (MTD), and pharmacokinetics in patients with incurable lymphomas and solid tumors. A phase II study was performed at the MTD of paclitaxel in patients with doxorubicin/mitoxantrone-refractory metastatic breast cancer. PATIENTS AND METHODS In the phase I study, paclitaxel dose levels ranged from 120 to 160 mg/m2, administered on a 21-day cycle. Patients with metastatic breast cancer who had either no response or a partial response (PR) to doxorubicin or mitoxantrone and had measurable disease were eligible for the phase I and II studies. Expression of the multidrug resistance (mdr-1) gene was determined in tumor biopsies by mRNA quantitative polymerase chain reaction. RESULTS Twelve patients received a total of 73 cycles of paclitaxel on the phase I study. Dose-limiting mucositis and/or grade IV granulocytopenia was reached at 160 mg/m2, and 140 mg/m2 was selected as the phase II dose. Thirty-six consecutive patients with metastatic breast cancer were treated, of whom three were not assessable. The median age was 49 years, with disease in the liver and/or lung in 76%. Patients received a median of two prior regimens for metastatic disease, and 73% had no response to prior doxorubicin or mitoxantrone. Of 33 patients treated with paclitaxel, 16 patients (48%) achieved a PR and five (15%) achieved a minor response (MR). With a median potential follow-up duration of 60 weeks, the median progression-free and overall survival durations were 27 and 43 weeks, respectively. No correlation was found between extent of prior treatment or prior response to doxorubicin/mitoxantrone, and response to paclitaxel. Paclitaxel pharmacokinetics showed a correlation between both granulocyte and mucosal toxicity, and serum steady-state concentrations (Css) more than 0.07 mumol/L. Patients with liver metastases had significantly decreased paclitaxel clearance and higher paclitaxel Css. Levels of mdr-1 were uniformly low in all tumor biopsies studied. CONCLUSION The recommended phase II dose of paclitaxel is 140 mg/m2 in patients without liver metastases and 105 mg/m2 in patients with liver metastases. Ninety-six-hour infusions of paclitaxel were effective and well tolerated in patients with doxorubicin/mitoxantrone-refractory breast cancer. Prolonged infusion schedules may be more effective than shorter schedules and deserve further study.

EPOCH chemotherapy: toxicity and efficacy in relapsed and refractory non-Hodgkin's lymphoma.

PURPOSE Based on in vitro evidence that tumor cells are less resistant to prolonged exposure to low concentrations of the natural product class, compared with brief higher concentration exposure, we developed a chemotherapy regimen (etoposide, vincristine, doxorubicin, cyclophosphamide, and prednisone [EPOCH]) in which the natural products are administered as a continuous infusion. PATIENTS AND METHODS This is a phase II study of etoposide, vincristine, and doxorubicin, administered as a 96-hour continuous infusion, with intravenous (IV) bolus cyclophosphamide and oral prednisone (EPOCH) in 74 consecutive patients who relapsed from or failed to respond to most of the same drugs administered on a bolus schedule. Patients with aggressive lymphomas who achieved a good response after EPOCH were eligible to undergo bone marrow transplantation. RESULTS Patients with intermediate- or high-grade lymphoma comprised 76% of this series and 77% had stage IV disease. Seventy-one percent had previously received all of the drugs contained in the EPOCH regimen and 92% had received at least four of the drugs. Seventy patients were assessable for response, of whom 19 (27%) achieved a complete remission (CR) and 42 (60%) a partial remission (PR). Among 21 patients who had no response to prior chemotherapy, 15 (71%) responded, but only one achieved a CR. Patients who relapsed from an initial CR had a 100% response rate, with 76% CRs. With a median potential follow-up duration of 19 months, there was a 28% probability of being event-free at 1 year. Toxicity was primarily hematologic with neutropenia during 51% of cycles, but only a 17% incidence of febrile neutropenia. Gastrointestinal, neurologic, and cardiac toxicity were minimal. CONCLUSION EPOCH chemotherapy was well tolerated and highly effective in patients who were resistant to or relapsed from the same drugs administered on a bolus schedule, suggesting that continuous infusion of the natural drug component of this regimen is capable of partially reversing drug resistance and reducing toxicity. Dose-intensity (DI) was > or = that achieved in primary treatment regimens for aggressive lymphomas.

Intrinsic drug resistance in human kidney cancer is associated with expression of a human multidrug-resistance gene.

The cloning of the cDNA for the mdr1 gene, whose expression is associated with the development of multidrug-resistance in cultured cells, has made it possible to explore the mechanism of multidrug resistance in human tumors. We have found that normal human kidney, six of eight adenocarcinomas of the kidney, and four cell lines derived from kidney adenocarcinomas express high levels of mdr1 mRNA. Two criteria suggest that primary multidrug resistance in human adenocarcinomas of the kidney results, at least in part, from expression of the mdr1 gene: (1) mdr1 mRNA levels are elevated in four unselected kidney adenocarcinoma cell lines that show a multidrug-resistant phenotype; and (2) multidrug resistance in these kidney cancer cell lines is reversed by verapamil and quinidine, agents known to reverse mdr1-associated drug resistance in cell lines selected for multidrug resistance in vitro. These results suggest that appropriate pharmacological intervention to reverse multidrug resistance might make adenocarcinomas of the kidney more sensitive to chemotherapy with agents such as Adriamycin (Adria Laboratories, Columbus, OH) and the vinca alkaloids.

Redistribution, Hyperproliferation, Activation of Natural Killer Cells and CD8 T Cells, and Cytokine Production During First-in-Human Clinical Trial of Recombinant Human Interleukin-15 in Patients With Cancer

PURPOSE Interleukin-15 (IL-15) has significant potential in cancer immunotherapy as an activator of antitumor CD8 T and natural killer (NK) cells. The primary objectives of this trial were to determine safety, adverse event profile, dose-limiting toxicity, and maximum-tolerated dose of recombinant human IL-15 (rhIL-15) administered as a daily intravenous bolus infusion for 12 consecutive days in patients with metastatic malignancy. PATIENTS AND METHODS We performed a first in-human trial of Escherichia coli-produced rhIL-15. Bolus infusions of 3.0, 1.0, and 0.3 μg/kg per day of IL-15 were administered for 12 consecutive days to patients with metastatic malignant melanoma or metastatic renal cell cancer. RESULTS Flow cytometry of peripheral blood lymphocytes revealed dramatic efflux of NK and memory CD8 T cells from the circulating blood within minutes of IL-15 administration, followed by influx and hyperproliferation yielding 10-fold expansions of NK cells that ultimately returned to baseline. Up to 50-fold increases of serum levels of multiple inflammatory cytokines were observed. Dose-limiting toxicities observed in patients receiving 3.0 and 1.0 μg/kg per day were grade 3 hypotension, thrombocytopenia, and elevations of ALT and AST, resulting in 0.3 μg/kg per day being determined the maximum-tolerated dose. Indications of activity included clearance of lung lesions in two patients. CONCLUSION IL-15 could be safely administered to patients with metastatic malignancy. IL-15 administration markedly altered homeostasis of lymphocyte subsets in blood, with NK cells and γδ cells most dramatically affected, followed by CD8 memory T cells. To reduce toxicity and increase efficacy, alternative dosing strategies have been initiated, including continuous intravenous infusions and subcutaneous IL-15 administration.

Inhibitors Targeting Mitosis: Tales of How Great Drugs against a Promising Target Were Brought Down by a Flawed Rationale

Although they have been advocated with an understandable enthusiasm, mitosis-specific agents such as inhibitors of mitotic kinases and kinesin spindle protein have not been successful clinically. These drugs were developed as agents that would build on the success of microtubule-targeting agents while avoiding the neurotoxicity that encumbers drugs such as taxanes and vinca alkaloids. The rationale for using mitosis-specific agents was based on the thesis that the clinical efficacy of microtubule-targeting agents could be ascribed to the induction of mitotic arrest. However, the latter concept, which has long been accepted as dogma, is likely important only in cell culture and rapidly growing preclinical models, and irrelevant in patient tumors, where interference with intracellular trafficking on microtubules is likely the principal mechanism of action. Here we review the preclinical and clinical data for a diverse group of inhibitors that target mitosis and identify the reasons why these highly specific, myelosuppressive compounds have failed to deliver on their promise. Clin Cancer Res; 18(1); 51–63. ©2012 AACR.

Controlled trial of dexverapamil, a modulator of multidrug resistance, in lymphomas refractory to EPOCH chemotherapy.

PURPOSE Overexpression of the multidrug resistance gene (mdr-1) is present in up to 60% of relapsed lymphomas. To study its role in lymphomas, we conducted a controlled trial of dexverapamil, an inhibitor of the mdr-1 gene product, P-glycoprotein (Pgp), in lymphomas refractory to etoposide, prednisone, vincristine, cyclophosphamide, and doxorubicin (EPOCH) chemotherapy. PATIENTS AND METHODS Eligible patients had recurrent Hodgkins (HD) or non-Hodgkins lymphomas (NHL) and measurable disease. Patients initially received EPOCH alone and those with stable tumor over two cycles or progressive disease crossed over to receive dexverapamil and EPOCH on subsequent cycles. Dexverapamil was escalated eight dose levels, from 240 to 1,200 mg/m2/d. When possible, serial biopsies were obtained to measure mdr-1 expression by quantitative polymerase chain reaction (PCR). RESULTS Of 154 patients entered onto the trial, 109 had NHL and 45 had HD. The median age was 44 years, 67% had stage IV disease, and the median number of prior regimens was two (range, one to 12) in NHL and one (range, one to four) in HD. Sixty-four patients (42%) crossed over, of which eight were not assessable. The maximum-tolerated dose of dexverapamil was 900 mg/m2/d. Among 41 NHL patients (excluding mycosis fungoides), there were three complete responses (CRs) and two partial responses (PRs) (12%) and five minor responses (MRs); two of 10 HD patients achieved PRs. The mdr-1 level was measured in 44 biopsies from 19 patients. Pretherapy, mdr-1 was low (median, 2.5 U) but increased (median, 12.2 U) at crossover. Of six patients with mdr-1 levels greater than 15 U, three responded to dexverapamil, while only one of eight patients with mdr-1 levels less than 15 U responded. EPOCH and dexverapamil were well tolerated, but compared with EPOCH alone, produced more hematologic toxicity. CONCLUSION These results suggest that Pgp plays a role in clinical drug resistance of lymphomas. However, they also suggest that mechanisms other than Pgp are prominent in heavily pretreated patients and that, although Pgp inhibition may be necessary, it is probably insufficient. Earlier intervention with dexverapamil may be more effective and warrants further study.

Targeting MDR in breast and lung cancer: Discriminating its potential importance from the failure of drug resistance reversal studies

This special issue of Drug Resistance Updates is dedicated to multidrug resistance protein 1 (MDR-1), 35 years after its discovery. While enormous progress has been made and our understanding of drug resistance has become more sophisticated and nuanced, after 35 years the role of MDR-1 in clinical oncology remains a work in progress. Despite clear in vitro evidence that P-glycoprotein (Pgp), encoded by MDR-1, is able to dramatically reduce drug concentrations in cultured cells, and that drug accumulation can be increased by small molecule inhibitors, clinical trials testing this paradigm have mostly failed. Some have argued that it is no longer worthy of study. However, repeated analyses have demonstrated MDR-1 expression in a tumor is a poor prognostic indicator leading some to conclude MDR-1 is a marker of a more aggressive phenotype, rather than a mechanism of drug resistance. In this review we will re-evaluate the MDR-1 story in light of our new understanding of molecular targeted therapy, using breast and lung cancer as examples. In the end we will reconcile the data available and the knowledge gained in support of a thesis that we understand far more than we realize, and that we can use this knowledge to improve future therapies.

Expression of the multidrug resistance, MDR1, gene in neuroblastomas.

Metastatic neuroblastoma is a childhood malignancy that is frequently responsive to chemotherapy with doxorubicin, vincristine, and teniposide (VM26), among other drugs, but in the majority of treated patients, the tumor recurs during or after chemotherapy. In this work, we have examined the hypothesis that the development of resistance to chemotherapy in neuroblastoma might be related to the expression of the human MDR1 gene, which encodes a multidrug transporter that functions as an energy-dependent drug efflux pump. RNA samples from 49 neuroblastomas were analyzed, including 31 from untreated and 18 from treated patients. MDR1 RNA was detectable in the majority of treated and untreated tumors using a sensitive, semiquantitative slot blot assay. Of the samples from treated patients, five of 18 were found to have high MDR1 RNA levels, whereas only three of 31 from untreated patients had high MDR1 levels, a statistically significant difference (P less than .01). These results show that high levels of MDR1 RNA are often associated with resistance to chemotherapy in neuroblastoma and suggest that they may contribute to this resistance. Many of the neuroblastoma samples were also evaluated for N-myc amplification but there was no correlation between N-myc copy number and the level of MDR1 mRNA expression.