Impairment of the DNA repair and growth arrest pathways by p53R2 silencing enhances DNA damage-induced apoptosis in a p53-dependent manner in prostate cancer cells.

p53R2 is a p53-inducible ribonucleotide reductase that contributes to DNA repair by supplying deoxynucleotide triphosphate pools in response to DNA damage. In this study, we found that p53R2 was overexpressed in prostate tumor cell lines compared with immortalized prostatic epithelial cells and that the protein was induced upon DNA damage. We investigated the effects of p53R2 silencing on DNA damage in LNCaP cells (wild-type p53). Silencing p53R2 potentiated the apoptotic effects of ionizing radiation and doxorubicin treatment as shown by increased sub-G(1) content and decreased colony formation. This sensitizing effect was specific to DNA-damaging agents. Comet assay and gamma-H2AX phosphorylation status showed that the decreased p53R2 levels inhibited DNA repair. Silencing p53R2 also reduced the levels of p21(WAF1/CIP1) at the posttranscriptional level, suggesting links between the p53-dependent DNA repair and cell cycle arrest pathways. Using LNCaP sublines stably expressing dominant-negative mutant p53, we found that the sensitizing effect of p53R2 silencing is mediated by p53-dependent apoptosis pathways. In the LNCaP sublines (R273H, R248W, and G245S) that have defects in inducing p53-dependent apoptosis, p53R2 silencing did not potentiate DNA damage-induced apoptosis, whereas p53R2 silencing was effective in a LNCaP subline (P151S) which retains the ability to induce p53-dependent apoptosis. This study shows that p53R2 is a potential therapeutic target that could be used to enhance the effectiveness of ionizing radiation or DNA-damaging chemotherapy in a subset of patients with prostate cancer.

Schedule-dependent apoptosis in K-ras mutant non-small-cell lung cancer cell lines treated with docetaxel and erlotinib: rationale for pharmacodynamic separation.

BACKGROUND: Epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs) given concurrently with chemotherapy in 4 large randomized clinical trials did not improve patient outcomes compared with chemotherapy alone in advanced non-small-cell lung cancer (NSCLC). We hypothesized that the lack of benefit resulted from a negative interaction between chemotherapy and EGFR TKIs. MATERIALS AND METHODS: Herein, we report the cell cycle and apoptotic effects of treatment with erlotinib and docetaxel in the NSCLC cell lines A549 and Calu-1, both of which are mutant for K-ras and wild-type for EGFR. RESULTS: Treatment with erlotinib resulted in accumulation of cells in G(1) phase in A549 cells, with no evidence of apoptosis. Docetaxel treatment led to apoptosis as assessed by increased sub-G1 DNA content and cleavage of caspase 3 and poly (ADP-ribose) polymerase. The sequence of docetaxel followed by erlotinib resulted in significantly enhanced apoptosis compared with single-agent docetaxel in both cell lines. However, in the reverse sequence of erlotinib followed by docetaxel, a reduction of apoptosis was observed. We hypothesize that cell cycle arrest induced by erlotinib accounts for these findings in the presence of wild-type EGFR and that pharmacodynamic separation of the 2 drug classes will ameliorate these effects. CONCLUSION: These studies provide a rationale for intermittent dosing of EGFR TKIs with chemotherapy in order to enhance cytotoxicity.

A randomized phase II trial of the matrix metalloproteinase inhibitor BMS-275291 in hormone-refractory prostate cancer patients with bone metastases.

BACKGROUND: BMS-275291 is a selective matrix metalloproteinase inhibitor (MMPI) that does not inhibit sheddases implicated in the dose-limiting arthritis of older MMPIs. We conducted a randomized phase II trial of two doses of BMS-275291 (1,200 versus 2,400 mg) in hormone-refractory prostate cancer (HRPC) patients with bone metastases to probe for a dose-response relationship and to assess differential toxicities. Serial serum and urine specimens were collected to assess for markers of bone metabolism. METHODS: The primary end point was 4-month progression-free survival (PFS). Eligibility criteria included documentation of androgen-independent disease (including anti-androgen withdrawal), skeletal metastasis, adequate end-organ function and performance status, and no more than one prior chemotherapy regimen. Patients were randomized to 1,200 mg orally once daily (arm A) or 1,200 mg orally twice daily (arm B). Response was assessed every 56 days. RESULTS: Eighty patients were enrolled: 39 in arm A and 41 in arm B. There were no responders by prostate-specific antigen or measurable disease to treatment. Stable disease was noted at 8 weeks in 39% of patients in arm A and in 17% of patients in arm B. Progression of disease at 8 weeks was seen in 61% of patients in arm A versus 83% of patients in arm B. Median survival time was 21.6 months (95% confidence interval, 17.5; not reached), whereas median PFS time was 1.8 months (95% confidence interval 1.74; 2) for all patients. Patients in arm A had a median survival time that was not reached, whereas patients on arm B has a median survival time of 21 months (P = 0.2). PFS at 4 months favored arm A: 22% versus 10% (log-rank, P = 0.008). Grade 3 toxicities occurred in 5 (13%) patients in arm A and in 9 (22%) patients in arm B. Grade 4 toxicities were uncommon (only 4% of patients): one each of thrombosis, fatigue, and motor neuropathy was seen in the arm B. Bone marker studies showed that baseline serum levels of N-telopeptide, osteocalcin, procollagen I NH2-terminal propeptide, and PICP had prognostic significance for PFS and/or overall survival. CONCLUSIONS: Regardless of dose schedule, BMS-275291 was well tolerated in HRPC patients and had no dose-limiting arthritis. Toxicities differed modestly according to the dose schedule employed. As overall survival and PFS favored the once daily schedule, this dose schedule is recommended for future studies. Baseline markers of bone metabolism may have prognostic value in HRPC patients with bone metastases.

Pharmacodynamic separation of epidermal growth factor receptor tyrosine kinase inhibitors and chemotherapy in non-small-cell lung cancer.

Epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs) given concurrently with chemotherapy do not improve patient outcomes compared with chemotherapy alone in advanced-stage non-small-cell lung cancer (NSCLC). One potential explanation for this lack of benefit is a negative interaction or antagonism between chemotherapy and EGFR TKIs when delivered concomitantly. Support for this line of reasoning is provided by preclinical data demonstrating that EGFR TKIs induce primarily a cytostatic effect resulting from a G1 cell cycle arrest in cell lines with wild-type EGFR, reducing cell cycle phase-dependent activity of chemotherapy, whereas they induce apoptotic cell death in tumors with EGFR-activating mutations. Because the great majority of NSCLC tumors consist of wild-type EGFR, sequence-specific interactions of EGFR TKI/chemotherapy combinations might negatively influence the efficacy of these regimens in patients with NSCLC. Further evidence is provided by EGFR mutational analysis in patient tumor specimens from the TRIBUTE study. Herein we provide the preclinical and clinical rationale for studies examining the concept of pharmacodynamic separation as a means for overcoming hypothesized antagonism of EGFR TKIs and chemotherapy.

The cyclin-dependent kinase inhibitor UCN-01 plus cisplatin in advanced solid tumors: a California cancer consortium phase I pharmacokinetic and molecular correlative trial.

BACKGROUND: UCN-01 (7-hydroxy-staurosporine) is a novel antineoplastic agent targeting cyclin-dependent kinases, which shows potent in vitro and in vivo activity against a broad range of tumor types. Our group has previously shown that UCN-01 potentiates the apoptotic response of agents such as cisplatin in vitro by preventing sequence-specific abrogation of G2 arrest caused by DNA-damaging chemotherapies. PATIENTS AND METHODS: This National Cancer Institute-sponsored phase I trial was designed to determine the safety, maximum tolerated dose, and pharmacokinetics of escalating doses of cisplatin in combination with UCN-01 in patients with advanced malignant solid tumors, as well as to do molecular correlative studies on tumor specimens. Cisplatin was infused over 1 hour before UCN-01 (45 mg/m2/d) given as a 72-hour continuous infusion. Escalation of cisplatin was planned through five dose levels at 20, 30, 45, 60, and 75 mg/m2. RESULTS: Ten patients were accrued. Accrual was halted at dose level 2 (cisplatin, 30 mg/m2) due to dose-limiting toxicities consisting of grade 5 sepsis with respiratory failure associated with grade 3 creatinine (one patient) and grade 3 atrial fibrillation (one patient). Plasma and salivary pharmacokinetics of UCN-01 were unaffected by cisplatin. Pretreatment and posttreatment tumor biopsies showed that UCN-01 was active against a key molecular target, the checkpoint kinase Chk1. CONCLUSIONS: This phase I trial failed to achieve targeted therapeutic dose levels of cisplatin when combined with prolonged infusion UCN-01. However, because preclinical data indicate that UCN-01 potentiates response to platinum, further studies with alternative dose schedules of the combination, or with other platinum analogues, are warranted.

Functional p53 increases prostate cancer cell survival after exposure to fractionated doses of ionizing radiation.

External beam radiation therapy is an effective therapy for localized prostate cancer, although failures occur at high rates. One variable that may affect the radiosensitivity of prostate tumor cells is their p53 status because this gene controls radiation-induced cell cycle arrest, apoptosis, and the repair of DNA damage. Using a system in which p53 function was conditionally restored to p53-null PC3 prostate cancer cells by stable transfection with a human temperature-sensitive p53 mutant allele, we tested the hypothesis that functional p53 increases cell cycle arrest and contributes to increased clonogenic survival after ionizing radiation (IR) of prostate carcinoma cells. Cell cycle arrest and clonogenic survival in response to single and multiple daily exposures to clinically relevant 2-Gy doses of IR were examined. Whereas the temperature-sensitive p53 protein was activated by phosphorylation after IR exposure at both the restrictive and permissive temperatures, Cdkn1/p21 was only induced by functional p53 (at the permissive temperature). In the presence of functional p53, the maintenance of G(2) arrest was significantly longer (P < 0.01), and a small increase in cell survival measured by clonogenic assay was seen after exposure to a single 2-Gy dose of IR. However, functional p53 significantly increased clonogenic survival (P < 0.01) after exposure to daily doses of 2 Gy of IR and contributed to a more sustained G(2) arrest and increased G(1) arrest in response to the multifraction regimen. These studies implicate the presence of wild-type p53 with increased survival of prostate carcinoma cells after fractionated exposure to radiation. Additionally, the data provide evidence that wild-type p53 in prostate tumor cells may reduce the effectiveness of radiation therapy.

A phase II study of flavopiridol in patients with advanced renal cell carcinoma: results of Southwest Oncology Group Trial 0109.

PURPOSE: Flavopiridol is a cyclin-dependent kinase inhibitor that prevents cell cycle progression and tumor growth. In initial phase I studies, encouraging responses were seen in advanced renal cell cancer (RCC). In a phase II study of flavopiridol given as a 72-h continuous infusion every 2 weeks in RCC, a response rate of 6% was seen but with considerable grade 3 or 4 asthenia, diarrhea, and thrombosis. Subsequently, an alternative 1-h bolus schedule was reported to have enhanced tolerability in a phase I trial. We therefore conducted a phase II study of this bolus regimen. METHODS: A total of 38 patients with advanced RCC were entered into this multi-institutional phase II study. Flavopiridol (50 mg/m(2) per day) was administered by bolus intravenous injection daily for three consecutive days, repeated every 3 weeks. RESULTS: Out of 34 eligible patients, one complete response and three partial responses were observed, for an overall response rate of 12% (95% CI 3-27%). Of the 34 patients, 14 (41%) had stable disease (SD). The probability of not failing treatment by 6 months was 21% (95% CI 9-35%). Median overall survival time was 9 months (95% CI 8-18 months). The most common grade 3 or 4 toxicities were diarrhea (35%) and tumor pain (12%) along with anemia, dyspnea, and fatigue (9% each). CONCLUSIONS: Flavopiridol at this dose and schedule is feasible with an acceptable toxicity profile. Flavopiridol has some modest biologic activity against advanced RCC, as evidenced by its single-agent objective response and SD rates.

Bortezomib-based combinations in the treatment of non-small-cell lung cancer.

Lung cancer is the most common cause of cancer-related death among men and women in the United States. Current trials are focusing on the integration of novel therapeutic agents into current non-small-cell lung cancer (NSCLC) treatment paradigms. Bortezomib, a small-molecule proteasome inhibitor, has single-agent activity in NSCLC and in combination with agents commonly used in NSCLC. This article will review the rationale and preclinical data supporting bortezomib combinations and the clinical trials with bortezomib alone and in combination in NSCLC to date.

Proteasome inhibition in small-cell lung cancer: preclinical rationale and clinical applications.

Small-cell lung cancer (SCLC) is a tobacco-related malignancy that usually presents in an extensive and therefore incurable stage. Although initially sensitive to platinum agent-based therapy, SCLC rapidly becomes refractory to chemotherapy, leading to disease recurrence and ultimately patient death. Treatment options following failure of first-line platinum agent-based therapy are limited. Small-cell lung cancer is characterized by molecular aberrancies such as overexpression of the antiapoptotic protein Bcl-2, which is regulated in part by the inhibitory IkappaB, a target of the ubiquitin-proteasome degradative pathway. Bortezomib is a proteasome inhibitor that can decrease Bcl-2 expression through diminished IkappaB degradation. Efforts to promote apoptosis in SCLC through the integration of bortezomib into therapy are under way.

Therapeutic strategies for combined-modality therapy of locally advanced non-small-cell lung cancer: rationale for consolidation docetaxel therapy.

Currently, there is no accepted standard of care for locally advanced and surgically unresectable non-small-cell lung cancer. Typically, treatment for patients with good performance status consists of a combination of chemotherapy and thoracic radiation therapy (RT), but the integration of these modalities and the respective dose schedules vary considerably. Herein, we review the rationale for a treatment paradigm employing consolidation docetaxel therapy after concurrent chemotherapy/RT and the results of recent clinical trials using this approach.

Bronchioloalveolar carcinoma: a model for investigating the biology of epidermal growth factor receptor inhibition.

Bronchioloalveolar carcinoma (BAC) is a previously uncommon subset of non-small cell lung cancer (NSCLC) with unique epidemiology, pathology, clinical features, radiographic presentation, and natural history compared with other NSCLC subtypes. Recent data suggest that the incidence of BAC is increasing, notably in younger nonsmoking women. Despite reports of prolonged survival after repeated surgical resection of multifocal lesions and slow growth kinetics, advanced bilateral or recurrent diffuse BAC remains incurable, with the vast majority of patients dying of respiratory failure or intercurrent pneumonia within 5 years. Limited data suggest that chemotherapy may yield poor results in BAC. However, anecdotal reports of prolonged complete response to tyrosine kinase inhibitors of the epidermal growth factor receptor (EGFR), a member of the human epidermal growth factor receptor (erbB) family, have raised considerable interest in studying this NSCLC subset. Here we present clinical data and preliminary results of correlative science studies analyzing human epidermal growth factor receptor pathways from the following two prospective Southwest Oncology Group clinical trials performed in advanced stage BAC: S9714 testing a 96-h continuous infusion of paclitaxel (Taxol) and S0126 evaluating the small molecule EGFR inhibitor gefitinib (ZD1839 or Iressa). These studies provide a biological rationale for investigating BAC as a model of predictive markers of EGFR inhibition.

Tirapazamine plus carboplatin and paclitaxel in advanced malignant solid tumors: a california cancer consortium phase I and molecular correlative study.

PURPOSE: Tumor hypoxia confers chemotherapy resistance. Tirapazamine is a cytotoxin that selectively targets hypoxic cells and has supra-additive toxicity with platinums and taxanes in preclinical studies. We conducted a Phase I study of tirapazamine, carboplatin, and paclitaxel and assessed potential plasma markers of hypoxia as surrogates for response. EXPERIMENTAL DESIGN: Forty-two patients with advanced solid tumors were treated at four dose levels; parallel dose escalations were carried out in chemotherapy-naive and previously treated subjects. Pre and post-therapy plasma levels of the hypoxia-induced proteins plasminogen activator inhibitor-1 and vascular endothelial growth factor were measured. RESULTS: Three of four chemotherapy-naïve patients developed dose-limiting toxicities at dose level 4 (grade 3 stomatitis/infection, grade 3 emesis, and grade 4 febrile neutropenia). Four of seven previously treated patients developed dose-limiting toxicities at dose level 3, including one death [grade 3 myalgia, grade 3 infection/grade 4 neutropenia, grade 3 infection/grade 4 neutropenia, and grade 5 infection (death)/grade 4 neutropenia]. Of 38 patients assessable for response, 3 had a complete response, 1 a partial response, 1 an unconfirmed partial response, and 23 had stable disease in at least one evaluation; 10 quickly progressed. One complete responder had normalization of vascular endothelial growth factor and plasminogen activator inhibitor-1 levels. CONCLUSION: Dose levels 3 (carboplatin AUC of 6, 225 mg/m(2) paclitaxel, and 330 mg/m(2) tirapazamine) and 2 (carboplatin AUC 6, 225 mg/m(2) paclitaxel, and 260 mg/m(2) tirapazamine) are the maximum tolerated doses for chemotherapy naive and patients treated previously, respectively. Dose level 3 is the experimental arm of a Phase III Southwest Oncology Group trial (S0003) in advanced non-small cell lung cancer. Potential markers of tumor hypoxia may be useful correlates in studies of hypoxic cytotoxins and are being prospectively investigated in S0003.

SU5416 plus interferon alpha in advanced renal cell carcinoma: a phase II California Cancer Consortium Study with biological and imaging correlates of angiogenesis inhibition.

PURPOSE: Vascular endothelial growth factor (VEGF) is expressed in up to 70% of renal cell carcinomas (RCCs) and is a rational therapeutic target. SU5416 is a small molecule inhibitor of VEGF-mediated signaling through Flk-1, a transmembrane tyrosine kinase. IFN-alpha also possesses dose- and schedule-dependent antiangiogenic effects at doses lower than those used for RCC therapy. We hypothesized that SU5416 plus low dose IFN-alpha 2B (Intron-A) would result in a 1-year event-free survival (EFS), exceeding 20% in patients with metastatic RCC using the results of a randomized immunotherapy trial as historical control. Efficacy was correlated with serial plasma VEGF and plasminogen activator inhibitor-1 levels and with positron emission tomography scans. EXPERIMENTAL DESIGN: Thirty patients were treated with SU5416 145 mg/m(2) i.v. twice weekly plus Intron-A 1 million units s.c. twice daily, cycled every 6 weeks. RESULTS: Fifteen patients (50%) had stable disease (SD) at 12 weeks, including 1 minor response and 8 with progressive disease (27%). Median survival time was 10 months, and 1-year EFS was 6% (95% confidence interval, 1-35). The most common grade 3 or 4 toxicities included fatigue and lymphopenia, among others. There were 3 on-study deaths, 2 of which were infection-related. Significant declines in median plasma levels of VEGF pre- and posttherapy were observed. In 5 patients with paired FDG and O-15 positron emission tomography scans, tumor metabolism and perfusion were unchanged in 3 patients with SD, increased in 1 patient with progression, and decreased in 1 patient with SD. CONCLUSIONS: Although SU5146 plus low-dose IFN exhibits biological activity in RCC as evidenced by significant declines in serial VEGF and plasminogen activator inhibitor-1 plasma levels, the 1-year EFS of 6% and adverse toxicity profile diminishes enthusiasm for additional studies with this combination in advanced RCC.

Low ERCC1 expression correlates with prolonged survival after cisplatin plus gemcitabine chemotherapy in non-small cell lung cancer.

PURPOSE: Overexpression of the excision repair cross-complementing 1 (ERCC1) gene, which is crucial in the repair of cisplatin (CDDP)-DNA adducts, is reported to negatively influence the effectiveness of CDDP-based therapy for gastric and ovarian cancers. Recent evidence indicates that Gemcitabine (Gem) may modulate ERCC1 nucleotide excision repair activity, and down-regulation of DNA repair activity by ERCC1 antisense RNA reportedly inhibits synergism of CDDP/Gem. We investigated whether ERCC1 mRNA expression levels were associated with clinical outcomes after treatment with a combination Gem/CDDP regimen for patients with advanced stage non-small cell lung cancer (NSCLC). EXPERIMENTAL DESIGN: Response and survival were correlated with the level of ERCC1 expression in 56 patients with advanced (stage IIIb or IV) NSCLC treated as part of a multicenter randomized trial with Gem 1250 mg/m(2) days 1 and 8 plus CDDP 100 mg/m(2) on day 1 every 3 weeks. mRNA was isolated from paraffin-embedded pretreatment primary tumor specimens, and relative expression levels of ERCC1/beta-actin were measured using a quantitative reverse transcription-PCR (Taqman) system. RESULTS: ERCC1 expression was detectable in all tumors. There were no significant differences in ERCC1 levels by gender, age, performance status, weight loss, or tumor stage. The overall response rate was 44.7%. There were no significant associations between ERCC1 expression and response. Median overall survival was significantly longer in patients with low ERCC1 expression tumors (61.6 weeks; 95% confidence interval, 42.4-80.7 weeks) compared to patients with high expression tumors (20.4 weeks, 95% confidence interval, 6.9-33.9 weeks). ERCC1 expression, Eastern Cooperative Oncology Group performance status, and presence of weight loss were significant prognostic factors for survival in a Cox proportional hazards multivariable analysis. CONCLUSIONS: These data suggest that ERCC1 expression is a predictive factor for survival after CDDP/Gem therapy in advanced NSCLC. Although there was a trend toward decreased response with high ERCC1 mRNA levels, this difference failed to reach statistical significance. This result may reflect the impact of Gem and the requirement for ERCC1 expression for CDDP/Gem synergism or may be attributable to the relatively small patient sample size in this study. Prospective studies of ERCC1 as a predictive marker for activity of CDDP-based regimens in NSCLC are warranted.

Glycogen synthesis correlates with androgen-dependent growth arrest in prostate cancer.

BACKGROUND: Androgen withdrawal in normal prostate or androgen-dependent prostate cancer is associated with the downregulation of several glycolytic enzymes and with reduced glucose uptake. Although glycogen metabolism is known to regulate the intracellular glucose level its involvement in androgen response has not been studied. METHODS: We investigated the effects of androgen on glycogen phosphorylase (GP), glycogen synthase (GS) and on glycogen accumulation in the androgen-receptor (AR) reconstituted PC3 cell line containing either an empty vector (PC3-AR-V) or vector with HPV-E7 (PC3-AR-E7) and the LNCaP cell line. RESULTS: Androgen addition in PC3 cells expressing the AR mimics androgen ablation in androgen-dependent prostate cells. Incubation of PC3-AR-V or PC3-AR-E7 cells with the androgen R1881 induced G1 cell cycle arrest within 24 hours and resulted in a gradual cell number reduction over 5 days thereafter, which was accompanied by a 2 to 5 fold increase in glycogen content. 24 hours after androgen-treatment the level of Glucose-6-P (G-6-P) had increased threefold and after 48 hours the GS and GP activities increased twofold. Under this condition inhibition of glycogenolysis with the selective GP inhibitor CP-91149 enhanced the increase in glycogen content and further reduced the cell number. The androgen-dependent LNCaP cells that endogenously express AR responded to androgen withdrawal with growth arrest and increased glycogen content. CP-91149 further increased glycogen content and caused a reduction of cell number. CONCLUSION: Increased glycogenesis is part of the androgen receptor-mediated cellular response and blockage of glycogenolysis by the GP inhibitor CP-91149 further increased glycogenesis. The combined use of a GP inhibitor with hormone therapy may increase the efficacy of hormone treatment by decreasing the survival of prostate cancer cells and thereby reducing the chance of cancer recurrence.

Current strategies in the management of hormone refractory prostate cancer.

Prostate cancer is the most common cancer diagnosed in American males, and is the second leading cause of cancer-related deaths. Most patients who develop metastatic disease will initially respond to androgen deprivation, but response is invariably temporary. Most patients will develop androgen-independent ("hormone-refractory") disease that results in progressive clinical deterioration and ultimately death. This progression to androgen independence is accompanied by increasingly evident DNA instability and alterations in genes and gene expression, including mutations in p53, over-expression of Bcl2, and mutations in the androgen receptor gene, among others. Treatment options for hormone refractory disease include intensive supportive care, radiotherapy, bisphosphonates, second-line hormonal manipulations, cytotoxic chemotherapy and investigational agents. A post-treatment reduction in the level of prostate specific antigen (PSA) by 50% has been shown to correlate with survival and has been accepted by consensus as a valid endpoint in clinical trials. Chemotherapeutic agents such as mitoxantrone, estramustine, and the taxanes have yielded improved response rates and palliative benefit, but not improved survival. Therefore, current efforts must be focused on enrolling patients onto clinical trials of investigational agents with novel mechanisms of action, and on using survival, time to progression, and quality of life as end points in routine clinical practice.

Proteasome inhibition with PS-341 (bortezomib) in lung cancer therapy.

PS-341 (bortezomib) represents a new class of therapeutics that targets the ubiquitin-proteasome pathway. It has broad-spectrum single-agent anticancer activity and can potentiate chemotherapy and radiation in preclinical models. Early phase clinical studies have shown tolerability and activity in multiple myeloma, lymphoma, prostate cancer, and lung cancers. By its mechanism of inhibiting protein degradation, PS-341 targets a wide range of pathways relevant to tumor progression and therapy resistance and can directly modulate expression of cyclins, p27(Kip1), p53, nuclear factor-kappaB, Bcl-2, and Bax. PS-341 is currently in phase I/II clinical development in both non-small cell lung cancer and small cell lung cancer. This article will review the preclinical and clinical experience with PS-341 as it relates to lung cancer.

Tirapazamine: prototype for a novel class of therapeutic agents targeting tumor hypoxia.

Preclinical models in vitro and in vivo have shown that tumor hypoxia alters the malignant cell phenotype, selecting for p53 mutations, stimulating angiogenesis and metastasis, and markedly reducing the efficacy of both radiotherapy and chemotherapy. Similarly, clinical studies measuring pretreatment tumor oxygen status confirm that the presence of hypoxia confers a negative impact on local control, disease-free survival, and overall survival. Despite these data and extensive past research efforts, the promise of developing selective hypoxic-cell sensitizers has been largely unfulfilled. In contrast, tirapazamine is the rationally designed prototype for a new class of therapeutic agents targeting tumor hypoxia: hypoxic cytotoxins. Tirapazamine is bioreductively activated in hypoxic cells and has been shown to potentiate the cytotoxicity of radiation and a number of chemotherapeutic drug classes, in particular platinum compounds and taxanes. This article reviews the preclinical and clinical development of tirapazamine, as well as current trials in non-small cell lung cancer designed to provide proof of principle for this new category of cancer therapeutics.

Survival and cell cycle kinetics of human prostate cancer cell lines after single- and multifraction exposures to ionizing radiation.

PURPOSE: Fractionated radiation therapy is frequently used to treat prostate cancer with an underlying assumption that each daily dose of ionizing radiation (IR) results in equal cell killing. We used three human prostate cancer cell lines to evaluate how survival after a single 2-Gy dose may predict responses after daily repeated 2-Gy exposures. METHODS AND MATERIALS: LNCaP, CWR22R, and PC3 cells were used in these studies. Survival after IR exposures was assessed using clonogenic assays and cell cycle responses were determined by flow cytometry. RESULTS: The experimentally determined multifraction survival differed significantly from that predicted from their single-dose SF2. LNCaP and CWR22R cells showed lower than predicted survivals; PC3 cells exhibited greater than predicted survival. Daily IR exposures resulted in changes in the cell cycle distributions beyond those caused by a single exposure to IR. CONCLUSIONS: Our results show that in these prostate cancer cells: (1) survival after a clinically relevant dose of IR does not predict survival after multifraction IR, (2) cell cycle responses after a single 2 Gy dose can differ from those that occur when cells receive daily 2 Gy doses, and (3) some cell cycle changes that result from fractionated IR may predict their ultimate survival responses from such treatment.

Integration of the proteasome inhibitor PS-341 (Velcade) into the therapeutic approach to lung cancer.

PS-341, a potent and selective proteasome inhibitor, is the prototype for a new class of therapeutics that targets the ubiquitin-proteasome pathway. It is active as a single agent and potentiates chemotherapy and radiation in pre-clinical models. Early phase clinical studies have demonstrated tolerability and activity in multiple myeloma, lymphoma, prostate cancer and lung cancer. By its mechanism of inhibiting protein degradation, PS-341 targets a wide-range of pathways that are relevant to tumor progression and therapy resistance, and can directly modulate expression of cyclins, p27(Kip1), p53, NF-kappaB, Bcl-2 and Bax. PS-341 is currently in phase I/II clinical development in lung cancer. This paper will review the pre-clinical and clinical experience with PS-341 as it relates to lung cancer.