Phase I study of gemcitabine given weekly as a short infusion for non-small cell lung cancer: results and possible immune system-related mechanisms.

PURPOSE: To define the maximum tolerated dose (MTD) and the nature of the toxicities associated with gemcitabine given as a short infusion to patients with non-small cell lung cancer (NSCLC). Secondary objectives were to monitor immunologic response, clinical response, and survival. PATIENTS AND METHODS: Thirty-two patients diagnosed with advanced inoperable NSCLC and performance status of 0 or 1 participated in this study. Patients consisted of 22 males and 10 females whose median age was 62 years (range 32-79). Gemcitabine was administered as a 30 min infusion once weekly for 3 weeks followed by 1 week of rest. Patients were enrolled at six gemcitabine dose levels ranging from 1000 to 3500 mg/m2. Patients completed a median of four cycles (range 1-17). Responses were evaluated after every two cycles. RESULTS: Toxicity was evaluated in all 32 patients. The MTD was not reached as gemcitabine was well tolerated at all dose levels. Grade 4 toxicity occurred in three (9%) patients: pulmonary and lymphocytopenia in one patient each, and both neurocortical and cardiac in one patient. Grade 3 toxicity was found in a total of 20 (63%) patients: pulmonary in 10 (31%) patients; pain in 6 (19%) patients; liver toxicity in 6 (19%) patients; leukopenia and lymphocytopenia in 5 (16%) patients each; anemia, nausea, and cardiac toxicity in 3 (9%) patients each; proteinuria and infection in 2 (6%) patients each; and hemorrhage in 1 (3%) patient. Of the 29 patients evaluable for response, seven objective responses were achieved: six at the 2200 mg/m2 dose level and one at the 2800 mg/m2 dose level. The distribution of responses differed significantly by dose (P = 0.0124 by the exact chi-square test for independence). The overall response rate was 24.1% (95% CI, 10.3-43.5%). At 6 h post-infusion, there was a significant increase in spontaneous tumor necrosis factor (TNF) release and stimulated interleukin (IL)-2 production, and significant decreases in total white blood cell and lymphocyte counts (CD3+, CD8+, and CD16+ lymphocytes) and resting and stimulated superoxide production by formyl-methionyl-leucyl-phenylalanine (fMLP), phorbol myristate acetate, and opsonized zymosan (OPS-Z). At 24 h post-infusion, there were significant decreases in total lymphocyte count, lymphocyte subsets (CD3+, CD4-, CD8+, CD56+, CD19+), and in resting and stimulated superoxide production by fMLP and OPS-Z. There also appeared to be an association between the levels of spontaneous TNF release and the severity of both gastrointestinal (GI) and pulmonary toxicities. CONCLUSION: Gemcitabine given as a short infusion was well tolerated at the dose levels of 1000-3500 mg/m2. The MTD was not reached. Toxicities appeared to be cumulative with multiple cycles. Gemcitabine appears to have activity against NSCLC. Although there was a differential dose-response rate among dose levels, increasing the gemcitabine dose beyond 2200mg/m2 did not show increased clinical response. Gemcitabine appears to modulate the immune response, which may in turn mediate both response and toxicity, although no statistically significant correlation between immune and clinical response was detected.

The generation of human dendritic and NK cells from hemopoietic progenitors induced by interleukin-15.

Interleukin-15 (IL-15) is a pleiotropic cytokine that induces the generation and differentiation of lymphoid cells and shares many biological activities with IL-2. We have shown here the development of dendritic cells (DC) from human CD34+ hemopoietic precursor cells cultured for 2-4 weeks with IL-15 alone. DC generated with IL-15 have typical morphological, immunocytochemical, phenotypic, and functional characteristics of mature DC. Dual flow cytometry analysis performed weekly demonstrated increasing co-expression of CD1a or CD83 with HLA-DR, CD80, CD86, IL-2R alpha, beta, and gamma. Two populations of cells were distinguished among CD34+ progeny. Small and medium-size cells were mainly natural killer (NK) cells (72.6-85.2% CD56+) and low numbers of DC (9.1-21.3% CD1a+). Large cells were mostly DC (75.4-95.4% CD1a+). Isolated CD34+ cells did not express IL-2R subunits but after 2-3 days in culture with IL-15, they were found to express IL-2Rgamma. Induced expression of IL-2Rgamma on CD34+ cells may explain the primary mechanism of IL-15-regulated differentiation of hemopoietic precursor cells. Thus, our data suggest that IL-15 stimulates CD34+ cells to differentiate into NK and DC and may represent a new growth and survival factor for lymphoid DC.

Enhancement of chemosensitivity and programmed cell death by tyrosine kinase inhibitors correlates with EGFR expression in non-small cell lung cancer cells.

Epidermal growth factor receptor (EGFR) is a 170 kD transmembrane glycoprotein with tyrosine kinase activity. Overexpression of the EGFR has been detected in many human cancers, including non-small cell lung cancer (NSCLC), and is correlated with poor prognosis and chemoresistance. We investigated the effects of tyrosine kinase inhibitors on chemosensitivity and chemotherapeutic drug-induced programmed cell death in NSCLC cell lines that express different levels of EGFR. NCI-H596 cells, which strongly express EGFR, were more resistant to the growth inhibitory effects of cisplatin, doxorubicin and etoposide than were NCI-H358 cells, which only weakly express EGFR. Both genistein, a general tyrosine kinase inhibitor, and tyrphostin AG 1478, a tyrosine kinase inhibitor specific for EGFR, inhibited phosphorylation of EGFR in NCI-H596. Combinations of genistein or tyrphostin AG 1478 with cisplatin, doxorubicin, or etoposide enhanced the antiproliferative effects and induced programmed cell death in NCI-H596 cells, whereas no such additive effects were observed in NCI-H358 cells. The programmed cell death induced by these agents involved CPP32 mediated PARP cleavage and DNA fragmentation. These results indicate that tyrosine kinase inhibitors in combination with chemotherapeutic drugs may prove to be a viable therapeutic strategy for the treatment of those types of NSCLC that demonstrate strong expression of EGFR.

Antisense bcl-2 treatment increases programmed cell death in non-small cell lung cancer cell lines.

Programmed cell death (PCD) is a genetically regulated pathway that is altered in many cancers. This process is, in part, regulated by the ratio of PCD inducers (Bax) or inhibitors (Bcl-2). An abnormally high ratio of Bcl-2 to Bax prevents PCD, thus contributing to resistance to chemotherapeutic agents, many of which are capable of inducing PCD. Non-small cell lung cancer (NSCLC) cells demonstrate resistance to these PCD-inducing agents. If Bcl-2 prevents NSCLC cells from entering the PCD pathway, then reducing the amount of endogenous Bcl-2 product may allow these cells to spontaneously enter the PCD pathway. Our purpose was to determine the effects of bcl-2 antisense treatment on the levels of programmed cell death in NSCLC cells. First, we determined whether bcl-2 and bax mRNA were expressed in three morphologically distinct NSCLC cell lines: NCI-H226 (squamous), NCI-H358 (adenocarcinoma), and NCI-H596 (adenosquamous). Cells were then exposed to synthetic antisense bcl-2 oligonucleotide treatment, after which programmed cell death was determined, as evidenced by DNA fragmentation. Bcl-2 protein expression was detected immunohistochemically. All three NSCLC cell lines expressed both bcl-2 and bax mRNA and had functional PCD pathways. Synthetic antisense bcl-2 oligonucleotide treatment resulted in decreased Bcl-2 levels, reduced cell proliferation, decreased cell viability, and increased levels of spontaneous PCD. This represents the first evidence that decreasing Bcl-2 in three morphologically distinct NSCLC cell lines allows the cells to spontaneously enter a PCD pathway. It also indicates the potential therapeutic use of antisense bcl-2 in the treatment of NSCLC.

Interaction of tissue transglutaminase with nuclear transport protein importin-alpha3.

Tissue transglutaminase is a multifunctional enzyme which has been involved in the regulation of cell growth, differentiation, and apoptosis. Recently, nuclear localization of tTG has been reported indicating the potential of active nuclear transport. In this study we use the yeast two-hybrid assay and co-immunoprecipitation to show that tTG interacts with the nuclear transport protein importin-alpha3. Using electron microscopy we demonstrate that nuclear expression of tTG in a non-small cell lung cancer cell line is induced by retinoic acid (RA). These data suggest that importin-alpha3 could mediate active nuclear transport of tTG which may be important for the regulation of critical cellular processes.

Mechanisms of growth stimulation by suramin in non-small-cell lung cancer cell lines.

PURPOSE: Suramin, a polysulfonated naphthylurea, has been shown to be effective in the treatment of several cancers. We have reported that suramin, at dose concentrations higher than 140 microM, exerts growth-stimulatory effects in several non-small-cell lung cancer (NSCLC) cell lines. The purpose of this study was to examine the mechanisms by which suramin exerts this growth-stimulatory effect in NSCLC cells. METHODS: NCI-H596 cells were treated with agarose-immobilized suramin, directly or by addition on cell culture inserts, after which growth was determined by [3H]thymidine incorporation. PPADS, a specific purinergic receptor antagonist, was used to determine whether suramin acts via purinergic receptors. The effect of suramin on epidermal growth factor receptor (EGFR) was determined by analyzing receptor phosphorylation and dimerization. XAMR 0721, a suramin analogue containing only one of the two polysulfonated arms, was also analyzed for its effects on growth and EGFR activation. RESULTS: Agarose-immobilized suramin stimulated NCI-H596 cell growth, but only when added directly to the cells. When the suramin-conjugated beads were added to the cells on cell culture inserts, which preclude an interaction with the cell surface but allow interaction with the culture medium, there was no effect on proliferation. PPADS had no effect on the growth stimulation by suramin; however suramin treatment resulted in rapid phosphorylation and dimerization of EGFR. Treatment with XAMR 0721 did not affect growth or tyrosine phosphorylation and dimerization of EGFR. CONCLUSIONS: Suramin need not enter NCI-H596 cells to exert its growth-stimulatory effect, nor is this effect mediated by an interaction with soluble growth factors. Rather, it appears that suramin acts via an interaction with EGFR, but not with purinergic receptors.

Induction of multiple programmed cell death pathways by IFN-beta in human non-small-cell lung cancer cell lines.

Tissue transglutaminase (tTG) and keratinocyte transglutaminase (kTG), as well as the cross-linked envelopes (CLE) that they form, have been associated with squamous differentiation and programmed cell death in epithelial cells. When interferon-beta (IFN-beta) was used to stimulate differentiation and programmed cell death in the human lung cancer cell lines NCI-H596 and NCI-H226, the cells underwent a decrease in cellular density. In NCI-H596 IFN-beta caused an increase in kTG activity and DNA fragmentation in the lower density cells, which were significantly slower growing than control cells. However, in the higher density cells, which were only slightly slower growing than control cells, IFN-beta caused an increase in tTG activity and CLE competence. Dual-parameter flow cytometry demonstrated that IFN-beta-induced squamous differentiation preceded programmed cell death. Treatment of NCI-H596 cells with monodansylcadaverine, a transglutaminase inhibitor, prevented the increase in CLE competence, but did not inhibit DNA fragmentation. These results suggest that IFN-beta can induce NCI-H596 cells to enter multiple cell death pathways and that these pathways are not only differentiation related, but may also be growth driven.

Tyrosine kinase inhibitors in preclinical development.

Due to the limited efficacy of cytotoxic chemotherapy in the treatment of advanced malignancy and its excessive toxicity precluding its use in chemoprevention, new therapeutic and preventive strategies have been sought. One of the most interesting of these new approaches is the manipulation of signal transduction pathways. Among the approaches being considered to eventuate such a strategy is the inhibition of autophosphorylation, a critical first step in the signal transduction pathways of many cell surface receptor tyrosine kinases, as well as of non-receptor tyrosine kinases. This article is intended to review those tyrosine kinase inhibitors that are currently in preclinical development, for which there are data to support consideration for their use in chemoprevention or cancer treatment. We will focus upon those agents that have received attention in the past several years.

Early effects of retinoic acid on proliferation, differentiation and apoptosis in non-small cell lung cancer cell lines.

BACKGROUND: Retinoids represent a potentially useful class of drugs in the chemoprevention and treatment of cancer, due to their ability to regulate cell proliferation and differentiation. However, there is controversy in the literature about the effects of all-trans retinoic acid (ATRA) in non- small cell lung cancer (NSCLC). In this study we examined the effects of ATRA on apoptotic death in NSCLC. MATERIALS AND METHODS: Cell proliferation was determined by thymidine incorporation in cultured NSCLC cells. DNA fragmentation was measured in NSCLC cell lines as a marker of apoptosis. The expression of keratinocyte transglutaminase and cytokeratin 10 were measured as markers of squamous differentiation. RESULTS: ATRA inhibited cell proliferation, and induced markers of both apoptosis and squamous differentiation after 24-48 hrs of treatment. CONCLUSIONS: These results indicate the possibility of the early growth-inhibitory and apoptotic effects of ATRA in NSCLC which may result in selection of ATRA-resistant cells.

Differentiation and programmed cell death-related intermediate biomarkers for the development of non-small cell lung cancer: a pilot study.

Fifty samples of lung tissue from patients with non-small cell lung cancer were analyzed for the expression and localization of biomarkers related to squamous differentiation and programmed cell death. These markers include tissue transglutaminase (tTG), keratinocyte transglutaminase (kTG), involucrin, loricrin, and Bcl-2. We found that all of these markers are overexpressed in tumors as compared with histologically normal lung epithelium, where expression is minimal. Expression of the oncoprotein, Bcl-2, increased starting in squamous metaplasia and remained elevated in all lesions, including frank carcinoma. In contrast, expression of the other markers was elevated in the histologically abnormal noninvasive lesions but was decreased somewhat in invasive malignancy. In addition, we found that tTG, kTG, and Bcl-2, when expressed, were detected in mutually exclusive areas. These findings suggest that (1) these markers may prove useful, with more extensive testing and clinical correlation, in predicting risk for the development of lung cancer; and (2) pulmonary carcinogenesis may result from the failure of differentiation and programmed cell death mechanisms in the presence of oncogene overexpression rather than through oncogene/tumor suppressor gene abnormalities alone.

Interleukin-2-induces development of denditric cells from cord blood CD34+ cells.

Dendritic cells (DC) have been shown to develop along a myeloid or lymphoid lineage of differentiation propagated from bone marrow or early thymic precursor cells with hematopoietic cytokines. In our study, we have induced growth and differentiation of DC from cord blood CD34+ cells initiated in interleukin-2 (IL-2) alone or in IL-2 + stem cell factor (SCF) + tumor necrosis factor alpha (TNF-alpha)-supplemented medium and cultured with IL-2 or IL-2 + SCF for 28-35 days. Dendritic morphology and antigenic phenotype of DC grown with IL-2 were characteristic for DC cultured in the presence of granulocyte-macrophage colony-stimulating factor (GM-CSF). Growth and differentiation of DC was followed by an increase in expression of MHC II and co-stimulating molecules CD80 and CD86. We have also shown the expression of the IL-2 receptor (IL-2R) gamma-chain in CD34+ cells after 2-3 days of culture with IL-2 alone. The co-expression of the IL-2R alpha, beta, and gamma subunits in both DC cultured with IL-2- or GM-CSF-containing cocktail of cytokines was also shown. The time curve for induction of IL-2R demonstrated low levels of subunit expression at the beginning of culture. The number of CD1a cells co-expressing CD25, CD122, and CDgamma increased to about 24-68 and to 78-95% after 21 and 28-35 days, respectively. Development of natural killer cells was shown along with DC. The proportion of CD56+ cells and cytotoxicity increased in a time-dependent manner.

EGF-dependent and independent programmed cell death pathways in NCI-H596 nonsmall cell lung cancer cells.

EGF receptor (EGFR) is a transmembrane glycoprotein with trosine kinase activity that is overexpressed in many human cancers, including lung. In the present study, we evaluated the effect of EGF and genistein, a tyrosine kinase inhibitor, on cell proliferation, EGFR phosphorylation and its downstream signal MAP kinase activation and investigated the involvement of these processes in programmed cell death in a human pulmonary adenosquamous carcinoma cell line, NCI-H596. Treatment with EGF resulted in phosphorylation of EGFR, activation of MAP kinase, phosphorylation of ERK 2 (an isoform of MAP kinase), increased cell proliferation and induction of cross-linked envelope (CLE) competence. Genistein abolished the ability of EGF to induce EGFR phosphorylation, to activate MAP kinase and to increase cell proliferation. Genistein alone stimulated CLE competence, but apparently by a different mechanism than EGF since genistein prevented EGF-stimulated CLE competence. The genistein-stimulated CLE competence was accompanied by a decrease in cell proliferation and increased DNA fragmentation. These results demonstrate that genistein antagonizes growth stimulatory EGF signaling upstream of MAP kinase and may simultaneously stimulate an apoptotic pathway. Furthermore, EGF appears to stimulate an alternate, growth related programmed cell death pathway, not involving DNA fragmentation, but characterized by rapid proliferation and genistein-sensitive CLE competence.

Effect of suramin on squamous differentiation and apoptosis in three human non-small-cell lung cancer cell lines.

Non-small cell lung cancer (NSCLC) is fatal in approximately 90% of all cases due to the failure of systemic therapy, secondary to resistance to chemotherapy. In such malignancies new therapeutic paradigms are needed. One such approach takes advantage of normal physiologic growth regulatory mechanisms, such as terminal cellular differentiation or apoptosis. Suramin, as an antineoplastic drug, has shown efficacy in the treatment of prostate cancer and is capable of promoting differentiation in several human cancer cell lines. Little is known about the differentiating effects of suramin in lung cancer. In the present investigation we evaluated the ability of suramin to induce cross-linked envelope (CLE) formation, as a common marker for squamous differentiation and apoptosis, in three representative human non-small cell lung cancer cell lines: NCI-H226 (squamous), NCI-H358 (bronchoalveolar [adenocarcinoma]), and NCI-H596 (adenosquamous). Among agents that we have tested, suramin demonstrated the unique ability to induce spontaneous CLE formation in the two cell lines with squamous features, NCI-H226 and NCI-H596. Suramin induced CLE formation was accompanied by DNA fragmentation, a marker for apoptosis, in NCI-H596 and NCI-H358, but not in NCI-H226. Stimulation of CLE formation by suramin correlated with the rapid induction of both type II transglutaminase (TG) activity and involucrin expression. These parameters were protein synthesis independent, suggesting posttranslational mechanisms of suramin activity. Induction of differentiation/apoptosis markers by suramin did not correlate with its effect on growth. Modulation of signal transduction is a likely candidate mechanism for suramin activity in lung cancer. The relationship between growth, squamous differentiation, and apoptosis is considered.

Mechanism of interferon beta-induced squamous differentiation and programmed cell death in human non-small-cell lung cancer cell lines.

BACKGROUND: Non-small-cell lung cancer (NSCLC) is one of the leading causes of cancer-related mortality due largely to the failure of systemic chemotherapy. Thus, new therapeutic paradigms involving the manipulation of normal physiologic growth-regulatory mechanisms, such as terminal cellular differentiation or programmed cell death, are being explored. Interferons may function as antineoplastic agents, in part because of their effects on cell proliferation and differentiation. We have previously demonstrated the antiproliferative and differentiating effects of interferon beta (IFN beta). PURPOSE: The present investigation was designed to study the mechanism of IFN beta on squamous differentiation and/or programmed cell death in cultured NSCLC cells. METHODS: Cross-linked envelope competence and transglutaminase expression and activity were measured in three NSCLC cell lines (NCI-H226, NCI-H358, and NCI-H596) as common markers for squamous differentiation and programmed cell death. DNA fragmentation, as determined by gel electrophoretic analysis, served as a marker for programmed cell death. In addition, the expression of several regulatory and differentiation-related genes (measured by Northern blot analysis of messenger RNA levels) as well as protein kinase C activity was measured to begin to explore possible mechanisms of IFN beta activity. RESULTS: IFN beta-induced cross-linked envelope competence occurred in cell lines with squamous features (NCI-H226 and NCI-H596); conversely, DNA fragmentation occurred in cell lines with glandular features (NCI-H358 and NCI-H596). Stimulation of cross-linked envelope competence by IFN beta was associated with the induction of tissue transglutaminase activity. Both of these parameters were protein-synthesis independent. As previously observed for NCI-H596, IFN beta suppressed the growth of the other two cell lines. Total protein kinase C activity was not altered. Expression of a variety of possibly relevant oncogenes and other genes was variably altered by IFN beta. CONCLUSIONS: IFN beta induces programmed cell death in NSCLC cell lines in a phenotype-specific manner. The programmed cell death pathway represented by cross-linked envelope competence is dependent on the expression of the squamous phenotype and is protein-synthesis independent, suggesting post-translational mechanisms. In addition, squamous differentiation itself may be induced. Changes in gene expression, while not necessary for induction of cross-linked envelope competence, may be involved in other aspects of cellular homeostasis, such as growth suppression. IMPLICATIONS: By inducing terminal cellular differentiation or programmed cell death, IFN beta may be therapeutically useful in NSCLC. The post-translational nature of IFN beta-induced effects suggests that it will be best used in combination with other agents that can regulate these cellular pathways at the pretranslational level, increasing the proportion of cells capable of being driven to a terminal state by this biotherapeutic agent.

Concomitant administration of interleukin-2 plus tumor necrosis factor in advanced non-small cell lung cancer.

Based upon in vitro and clinical data suggesting antitumor activity of interleukin-2 (IL-2) plus tumor necrosis factor (TNF) in non-small cell lung cancer (NSCLC), we conducted two parallel pilot studies of the combination in patients with advanced disease. Eight patients at the University of Wisconsin received 6 x 10(6) international U/m2/day of IL-2 by continuous infusion on days 1-4, 8-11, and 15-18 with 50 micrograms/m2/day of TNF administered intramuscularly on the same days. Seven patients at the University of Pittsburgh received IL-2 as a continuous infusion for 5 days at a dose of 6 x 10(6) U/m2/day, every 14 days. TNF was administered intramuscularly on days 1 through 5, starting at a dose of 50 micrograms/m2. Patients with no evidence of grade 3 or 4 toxicity on the first cycle had their dose of TNF escalated from 50 to 100 and then to 150 micrograms/m2. No responses were observed. The therapy was not well tolerated, with 11 of 15 patients developing grade 3 or 4 toxicity at some point during their therapy. The most common grade 3 or 4 toxicities were pulmonary (6 episodes) or cardiac (4 episodes) events. Constitutional symptoms were common, but not dose-limiting. Despite the lack of observed responses, the median survival was 11 months, with one patient with metastatic disease alive over 30 months later. We conclude that IL-2 plus TNF was not effective in inducing responses in patients with advanced NSCLC, but the prolonged survival suggests a role for IL-2 in NSCLC, which needs to be further defined by means other than classic response criteria.

Cross-linked envelope-related markers for squamous differentiation in human lung cancer cell lines.

Lung carcinoma cell lines were analyzed in culture and in nude mouse xenograft for both morphological appearance and expression of specific proteins that participate in cross-linked envelope formation during normal squamous cell terminal differentiation. Cross-linked envelope formation, induced by artificial influx of millimolar Ca2+ into the cultured cells, was an exclusive trait of squamous, adenosquamous, and mucoepidermoid carcinomas. Small cell lung carcinoma and non-squamous non-small cell lung carcinoma lines, such as adenocarcinoma and large cell carcinoma, were uniformly negative for cross-linked envelope formation. Involucrin, which is incorporated into the cross-linked envelope by the enzyme transglutaminase, was expressed at highest levels in squamous tumors, but several of the non-squamous non-small cell lung carcinoma lines also expressed comparable amounts. On the other hand, transglutaminase activity was consistently higher in squamous as opposed to non-squamous lines, so that in cell culture, a clear contrast between the groups could be observed. A Mr 195,000 protein that is incorporated into cultured human epidermal cell cross-linked envelopes was also observed in some but not all of the squamous lines. Two forms of transglutaminase are expressed in cultured keratinocytes. One of them, tissue transglutaminase, was expressed in the majority of squamous cell lines even though it is not a normal product of squamous differentiation in vivo. Keratinocyte transglutaminase, which is distinct from the tissue form and is normally expressed during terminal differentiation in squamous epithelia. was measurably present in only one of the six squamous cell lines tested. In nude mouse xenografts, keratinocyte transglutaminase, localized immunohistochemically with a biotinylated mouse monoclonal antibody, was again present only in a minority of the squamous lines whereas involucrin was expressed in all. In contrast to involucrin, keratinocyte transglutaminase is not an obligatory component of squamous differentiation in the pulmonary carcinoma cell lines tested. Its expression may be of value in further refining their classification.

Radiation sensitivity of human lung cancer cell lines.

X-Ray survival curves were determined using a panel of 17 human lung cancer cell lines, with emphasis on non-small cell lung cancer (NSCLC). In contrast to classic small cell lung cancer (SCLC) cell lines, NSCLC cell lines were generally less sensitive to radiation as evidenced by higher radiation survival curve extrapolation numbers, surviving fraction values following a 2 Gy dose (SF2) and the mean inactivation dose values (D) values. The spectrum of in vitro radiation responses observed was similar to that expected in clinical practice, although mesothelioma was unexpectedly sensitive in vitro. Differences in radiosensitivity were best distinguished by comparison of SF2 values. Some NSCLC lines were relatively sensitive, and in view of this demonstrable variability in radiation sensitivity, the SF2 value may be useful for in vitro predictive assay testing of clinical specimens.

An outlier theory of cancer curability. Tumor cell differentiation as a therapeutic goal.

Combinations of cytotoxic agents that cure a substantial percentage of patients with several childhood and adult malignancies are much less efficacious for the majority of solid tumors. Standard approaches for curability that rely solely on the concept of cytotoxicity may not be applicable for most epithelial and mesenchymal solid malignancies. Differentiation may play a more important role in cancer cure than heretofore suspected. Clinical and experimental evidence supports further investigation into models of inducing tumor cell differentiation. The question of why such models could predict for curative modalities of treatment is discussed.