Clinical Reversal of Multidrug Resistance

Ultrasound: A Chemotherapy Sensitizer

Chemotherapy plays a very important role in cancer treatment. However, there are still some barriers in the successful use of such therapies, mainly because of the adverse side effects of the anticancer agents and due to the development of chemoresistance. This paper focuses on the use of ultrasound to enhance chemotherapy and to overcome drug resistance. The action of many anticancer agents can be improved with the use of ultrasonic exposure either in vitro or in vivo. Drug resistance can be circumvented using ultrasound alone. Furthermore, the reversal attributable to chemoresistance modifiers, such as verapamil and PSC 833, is augmented by ultrasound. Ultrasound-mediated chemosensitization is usually achieved via increasing intracellular drug accumulation, although other mechanisms are also involved. Ultrasound also can play a role in targeted chemotherapy, releasing anticancer chemicals directly and efficiently into the lesions. However, this promising modality has not been clinically adopted so far and the reasons are discussed.

The "survivin suppressants" NSC 80467 and YM155 induce a DNA damage response

PURPOSE

To establish whether NSC80467, a novel fused naphthquinone imidazolium, has a similar spectrum of activity to the well-characterized "survivin suppressant" YM155 and to extend mechanistic studies for this structural class of agent.

METHODS

NSC80467 and YM155 were analyzed in parallel using assays measuring viability, survivin suppression, inhibition of DNA/RNA/protein synthesis and the cellular response to DNA damage.

RESULTS

GI(50) values generated for both compounds in the NCI-60 screen yielded a correlation coefficient of 0.748, suggesting significant concordance. Both agents were also shown to inhibit protein expression of survivin [BIRC5]. COMPARE analysis identified DNA damaging agents chromomycin A3 and bisantrene HCl and one DNA-directed inhibitor of transcription, actinomycin D, as correlating with the activity of NSC80467 and YM155. Furthermore, both agents were shown to preferentially inhibit DNA, over RNA and protein synthesis. Thus, the ability of NSC80467 and YM155 to induce a DNA damage response was examined further. Treatment of PC3 cells with either agent resulted in dose-dependent induction of γH2AX and pKAP1, two markers of DNA damage. The concentrations of agent required to stimulate γH2AX were considerably lower than those required to inhibit survivin, implicating DNA damage as an initiating event. The DNA damage response was then confirmed in a panel of cell lines treated with NSC80467 or YM155, suggesting that γH2AX and pKAP1 have potential as response biomarkers.

CONCLUSIONS

These data provide the first evidence that NSC80467 and YM155 are DNA damaging agents where suppression of survivin is a secondary event, likely a consequence of transcriptional repression.

Microtubule targeting agents: basic mechanisms of multidrug resistance (MDR)

Multidrug resistance (MDR) results in the loss of activity of anticancer agents against cells possessing the MDR phenotype. In some cases, tumor cells are intrinsically resistant to chemotherapeutic drugs (intrinsic resistance), while in other instances cells become resistant after exposure to cytotoxic agents (acquired resistance). MDR has a significant impact on the management of patients with solid tumors, including those with breast cancer, where it has been previously correlated with a decreased response to treatment and a poor prognosis. Taxanes are among the most important components of chemotherapy regimens to treat recurrent breast cancer. In taxane-refractory cells, the two mechanisms most commonly associated with the development of MDR are the overexpression of members of the ATP-binding cassette family of transporters, of which P-glycoprotein is the best known, and alterations of tubulin, which is the cellular target of the taxanes. In vitro and in vivo models have been developed to study the development of MDR and to assess the potential clinical application of MDR modulators. However, despite promising advances using MDR modulators in preclinical models, clinical applications have met with limited success. Novel strategies are needed to circumvent the development of drug resistance. New cytotoxic agents capable of evading MDR offer hope for patients with breast cancer.

Tesmilifene may enhance breast cancer chemotherapy by killing a clone of aggressive, multi-drug resistant cells through its action on the p-glycoprotein pump

Tesmilifene is a novel potentiator of chemotherapy which, when added to doxorubicin, achieved an unexpected and very large survival advantage over doxorubicin alone in a randomized trial in advanced breast cancer. This trial was unusual in that the early endpoints (response rate and median progression-free survival) were equivalent in the two arms, despite the ultimate survival difference. These aspects, coupled with the absence of a coherent molecular mechanism of action, and a pending confirmatory trial, have led oncologists to hold judgement on this drug. This paper reacts to this in three ways: firstly, a forensic subgroup analysis is presented with an explanation as to why it strongly supports the veracity of the survival difference; secondly a novel cellular explanation is provided for the decoupling of the early and late (survival) endpoints; finally, a molecular mechanism of action is proposed, for the first time, which reconciles the peculiarities of the trial with the laboratory data and background literature. This hypothesis explains how tesmilifene could meld two of the apparent strengths of the cancer cell (drug resistance pumps, and hypoxia-adapted energetics) into a potent weapon of self-destruction. Tesmilifene is proposed to allow chemotherapy (e.g. anthracycline or taxane) to additionally kill a small but critical population (clone) of aggressive, multi-drug resistant cells, the benefits of which cannot be appreciated until a period of time (about 6-8 months) has elapsed. These cells, present in women with more rapidly relapsing disease, very likely carry an energy-dependent extrusion pump which is paradoxically activated by tesmilifene plus the chemotherapy. The result is that, despite the chemotherapy's remaining extracellular, the cell dies from reactive oxygen species leaking from the electron chain transport in the abnormal mitochondria which characterize cancer. These mitochondria are activated in response to the ATP cost of this pump activation, in these predominantly glycolytic cells.

The role of rituximab and chemotherapy in aggressive B-cell lymphoma: A preliminary report of dose-adjusted EPOCH-R

Accumulating evidence suggests that the ability to activate apoptotic pathways may be an important determinant of chemotherapy sensitivity and presents a potentially important new therapeutic strategy. Monoclonal antibodies against the CD20 antigen directly induce apoptosis and may serve to modulate the threshold for chemotherapy-induced apoptosis. Rituximab (Rituxan; Genentech, Inc, South San Francisco, CA, and IDEC Pharmaceuticals, San Diego, CA), a monoclonal antibody against CD20, was combined with dose-adjusted EPOCH (infusional etoposide/vincristine/doxorubicin/bolus cyclophosphamide/prednisone) chemotherapy and tested in 38 untreated or relapsed poor-prognosis aggressive lymphomas. Twenty-three patients were untreated. Of these patients, all had large B-cell histologies, a median age of 52 years, Eastern Cooperative Oncology Group performance status ≥ 2 in 30%, and high-intermediate or high International Prognostic Index scores in 61%. Fifteen patients had relapsed or refractory lymphomas. These patients had received a median of two (range, one to four) prior regimens, 67% had aggressive histologies, and 60% had high-intermediate or high International Prognostic Index scores. Complete remissions were achieved in 85% and 64% of untreated and previously treated patients, respectively; additionally 42% of patients with disease refractory before therapy achieved complete remission. At a median follow-up of 12 months, progression-free and overall survival in the previously untreated group was 85% and 79%, respectively, and no patient in complete remission has relapsed. These results suggest that rituximab may modulate the sensitivity of B-cell lymphomas to chemotherapy. Semin Oncol 29 (suppl 2):41-47. This is a US government work. There are no restrictions on its use.