Resistance to cytotoxic therapy: a speculative overview

The role of pH dynamics and the Na+/H+ antiporter in the etiopathogenesis and treatment of cancer. Two faces of the same coin--one single nature

Looked at from the genetic point-of-view cancer represents a daunting and, frankly, confusing multiplicity of diseases (at least 100) that require an equally large variety of therapeutic strategies and substances designed to treat the particular tumor. However, when analyzed phenotypically cancer is a relatively uniform disease of very conserved 'hallmark' behaviors across the entire spectrum of tissue and genetic differences [D. Hanahan, R.A. Weinberg, Hallmarks of cancer, Cell 100 (2000) 57-70]. This suggests that cancers do, indeed, share common biochemical and physiological characteristics that are independent of the varied genetic backgrounds, and that there may be a common mechanism underlying both the neoplastic transformation/progression side and the antineoplastic/therapy side of oncology. The challenge of modern oncology is to integrate all the diverse experimental data to create a physiological/metabolic/energetic paradigm that can unite our thinking in order to understand how both neoplastic progression and therapies function. This reductionist view gives the hope that, as in chemistry and physics, it will possible to identify common underlying driving forces that define a tumor and will permit, for the first time, the actual calculated manipulation of their state. That is, a rational therapeutic design. In the present review, we present evidence, obtained from a great number of studies, for a fundamental, underlying mechanism involved in the initiation and evolution of the neoplastic process. There is an ever growing body of evidence that all the important neoplastic phenotypes are driven by an alkalization of the transformed cell, a process which seems specific for transformed cells since the same alkalinization has no effect in cells that have not been transformed. Seen in that light, different fields of cancer research, from etiopathogenesis, cancer cell metabolism and neovascularization, to multiple drug resistance (MDR), selective apoptosis, modern cancer chemotherapy and the spontaneous regression of cancer (SRC) all appear to have in common a pivotal characteristic, the aberrant regulation of hydrogen ion dynamics [S. Harguindey, J.L. Pedraz, R. García Cañero, J. Pérez de Diego, E.J. Cragoe Jr., Hydrogen ion-dependent oncogenesis and parallel new avenues to cancer prevention and treatment using a H+-mediated unifying approach: pH-related and pH-unrelated mechanisms, Crit. Rev. Oncog. 6 (1) (1995) 1-33]. Cancer cells have an acid-base disturbance that is completely different than observed in normal tissues and that increases in correspondence with increasing neoplastic state: an interstitial acid microenvironment linked to an intracellular alkalosis.

Integrating fields of cancer research through pivotal mechanisms and synthetic final pathways: a unifying and creative overview

From cancer etiopathogenesis to selective apoptosis, from multiple drug resistance to oncogen activation and from the phenomena of spontaneous regression of cancer to certain aspects of cancer chemotherapy, all these subfields of biology and oncology research share some deep-seated, both basic and clinical, essential features and characteristics. Certain apoptosis-inducing agents of unrelated families, ranging from ether lipids to Na(+)/H(+)-antiporter inhibitors to Delta(9)-tetrahydrocannabinol all have been reported to induce selective cancer-cell death. Behind a wide array of intermediary factors and mechanisms involved in their activity, they seem to share common pivotal and/or final pathways in inducing cell death mediated by a 'pathological' accumulation of intracellular hydrogen ions as a mechanism underlying core changes in intracellular signaling pathways. An H(+)-concentration initial perspective indicates that from pathogenesis to apoptosis and multiple drug resistance, as well as oncogen activity, tumor progression and even the phenomenon of spontaneous regression, all can be interpreted from their deep (H(+))-related basic and clinical essential characteristics. This speculative review discusses the potential integration of these previously disparate subfields of cancer research, through a model which also seems to lead toward improving understanding of the fundamental nature of malignant processes. It is concluded that this synthetic and universal approach allows advancement toward a combining of different areas of oncology into deeper and more comprehensive forms of rational understanding, with the hope of paving the way towards more selective, effective and all-encompassing forms of treatment.

Nursing implications of mylotarg: a novel antibody-targeted chemotherapy for CD33+ acute myeloid leukemia in first relapse

PURPOSE/OBJECTIVES

To review the nursing implications of gemtuzumab ozogamicin (Mylotarg(r), CMA-676, Wyeth Pharmaceuticals, Philadelphia, PA), a novel monoclonal antibody-targeted chemotherapy agent for relapsed acute myeloid leukemia (AML).

DATA SOURCES

Published articles, abstracts, book chapters, manufacturer information, unpublished clinical trial data, and personal experiences with gemtuzumab ozogamicin.

DATA SYNTHESIS

Conventional chemotherapy for AML is associated with toxicities that often limit treatment options when AML relapses. Gemtuzumab ozogamicin is a humanized recombinant anti-CD33 monoclonal antibody linked to calicheamicin, a potent cytotoxic agent. The antibody targets the CD33 antigen found on the surface of leukemic blast cells and myeloid precursors. This targeting effect reduces the toxicity of gemtuzumab ozogamicin. The efficacy and tolerability of gemtuzumab ozogamicin have been documented in relapsed AML, particularly in patients 60 years of age or older, who often have no other treatment options. As with other monoclonal antibody therapies, an "infusion syndrome" (i.e., fever and chills) may occur but can be managed effectively when administration guidelines are used.

CONCLUSIONS

Gemtuzumab ozogamicin is the first of a new class of targeted therapies for the treatment of relapsed AML. A number of implications for nurses exist.

IMPLICATIONS FOR NURSING

Nurses must be knowledgeable about gemtuzumab ozogamicin preparation and administration, patient selection and monitoring, and intervention procedures. This knowledge is necessary to accurately inform patients and their families of the possible course of treatment and potential side effects.

Hexahydrocolupulone and its antitumor cell proliferation activity in vitro

The purpose of this study was to evaluate the ability of hexahydrocolupulone (HHC) to inhibit the growth of tumor cells in vitro and to investigate the potential mechanism(s) involved. HHC was demonstrated to have a wide spectrum of activity against a number of established human tumor cell lines, including some exhibiting drug resistance. Culturing human breast adenocarcinoma (MCF-7) cells in the presence of HHC for 18 hr resulted in a significant decrease in the incorporation of [3H]uridine and [3H]leucine into RNA and protein, respectively. MCF-7 cells cultured in the presence of 1.5 microM HHC for 48 hr demonstrated an increase in the amount of cells detected in G0/G1 and a decrease in the amount of cells detected in S phase. In contrast, treatment with 25 microM HHC decreased the amount of cells detected in G0/G1 and increased the amount of cells detected in S phase. HHC did not cause single-stranded or double-stranded DNA breaks, interfere with topoisomerase function, or generate free radicals. Mice injected intraperitoneally for 5 consecutive days with HHC to a final in vivo blood concentration of 200 microM survived and showed no obvious signs of toxicity. Mass spectroscopy analysis, crystal generation, and structure elucidation confirmed HHC purity. Consequently, all activity observed can be attributed to HHC, a metabolite, and/or a combination thereof. These data suggest that HHC inhibits tumor cell proliferation in vitro via a mechanism(s) that may involve effects on macromolecular synthesis, precursor metabolism/transport, and/or the cell cycle or cell cycle-dependent pathway(s).

Reflections on the development of resistance during therapy for advanced breast cancer. Implications of high levels of activity of docetaxel in anthracycline-resistant breast cancer patients

Anthracyclines play a central role in the treatment of breast cancer. They are perhaps the most active single agents available for the treatment of this disease. For patients with primary breast cancer for whom chemotherapy would be appropriate, anthracyclines are often incorporated in adjuvant regimens. For patients with endocrine-therapy-resistant metastatic disease, anthracyclines are nearly always included in the first or second-line therapeutic regimes. Unfortunately, despite the fact that anthracyclines and anthracycline-containing regimens can achieve impressive objective response rates, this impressive activity has not translated into a great improvement in disease-free survival for patients with early stage breast cancer or overall survival for patients with metastatic disease. The addition of anthracyclines to adjuvant therapy regimens in general only modestly improves their efficacy and the use of anthracyclines in metastatic disease does not cure these patients. The clinical utility of anthracyclines would be greatly improved if we could predict which patients would be anthracycline resistant, interfere with the development or expression of anthracycline resistance and predict which anticancer agents would be non-cross-resistant with anthracyclines. Some progress is being made in all these areas. Preclinical studies have identified several intracellular processes that are perturbed by anthracyclines, or that may modulate anthracycline sensitivity of cells. These processes include topoisomerase II activity, drug and toxin transmembrane pumps, intracellular detoxification systems (such as that related to gluatathione), stress-related proteins and apoptotic mechanisms. Although measurement of the components of these systems has not yet shown clinical utility in breast cancer, some preclinical work and exploratory studies with small numbers of patients suggest that we may in the future be able to predict which patients will respond or be resistant to anthracyclines. An important avenue of work is the identification of anticancer agents that are non-cross-resistant with anthracyclines in breast cancer patients. These agents would be particularly valuable in patients with metastatic disease who had progressed while on anthracyclines. In general, such patients have a very poor prognosis with a median survival of less than 1 year. Also of importance in non-cross-resistant agents is that they might be used in combination with anthracyclines in regimens with very high response rates. Recently completed work suggests that taxoids might be such agents. This finding opens up exciting possibilities in the treatment of metastatic disease and, even more importantly, in the adjuvant arena. The identification of agents that clinically are non-cross-resistant with anthracyclines depends on the careful interpretation of clinical trial data. Unfortunately, a number of definitions of anthracycline resistance have been used in the medical literature. These range from very weak definitions, which include many patients with only prior anthracycline exposure (for example, in an adjuvant regimen), to more biologically and clinically appropriate definitions, such as documented progression while receiving an anthracycline. This distinction is very important because it is clear that many patients who have relapsed after an anthracycline-based adjuvant therapy will respond to anthracyclines for metastatic disease and are, therefore, not truly anthracycline resistant. In this regard, the recently completed trials with docetaxel in patients with rigorously defined anthracycline resistance are particularly provocative. These trials show that docetaxel maintains much of its excellent first-line levels of efficacy in patients with anthracycline-resistant breast cancer. Agents with this type of maintenance of efficacy in anthracycline-resistant tumours may find immediate utility in this clinical scenario as single agents but, more importantly, have gr