Clinical benefit of continuing ALK inhibition with crizotinib beyond initial disease progression in patients with advanced ALK-positive NSCLC.

BACKGROUND: Crizotinib is approved to treat advanced ALK-positive non-small-cell lung cancer (NSCLC), but most patients ultimately develop progressive disease (PD). We investigated whether continuing ALK inhibition with crizotinib beyond PD (CBPD) is clinically beneficial and attempted to identify clinicopathologic characteristics associated with patients who experience clinical benefit. PATIENTS AND METHODS: Patients with advanced ALK-positive NSCLC enrolled in two ongoing multicenter, single-arm trials who developed RECIST-defined PD were allowed to continue crizotinib if they were deriving ongoing clinical benefit. In the present retrospective analysis, continuation of CBPD was defined as >3 weeks of crizotinib treatment after PD documentation. Patients who had PD as best response to initial crizotinib treatment were excluded. Baseline and post-progression characteristics, sites of PD, and overall survival (OS) were compared in patients who continued CBPD versus those who did not. The impact of continuing CBPD on OS after adjusting for potential confounding factors was assessed. RESULTS: Among 194 crizotinib-treated patients with RECIST-defined PD, 120 (62%) continued CBPD. A significantly higher proportion of patients who continued CBPD than patients who did not had an ECOG performance status (PS) of 0/1 at PD (96% versus 82%; P=0.02). CBPD patients had significantly longer OS from the time of PD [median 16.4 versus 3.9 months; hazards ratio (HR) 0.27, 95% confidence interval (CI): 0.17-0.42; P<0.0001] and from the time of initial crizotinib treatment (median 29.6 versus 10.8 months; HR 0.30, 95% CI: 0.19-0.46; P<0.0001). The multiple-covariate Cox regression analysis revealed that CBPD remained significantly associated with improved OS after adjusting for relevant factors. CONCLUSIONS: Patients who continued CBPD were more likely to have good ECOG PS (0/1) at the time of PD. Continuing ALK inhibition with crizotinib after PD may provide survival benefit to patients with advanced ALK-positive NSCLC.

A single-arm, multicenter, phase II trial of osimertinib in patients with epidermal growth factor receptor exon 18 G719X, exon 20 S768I, or exon 21 L861Q mutations.

BACKGROUND: For patients with stage IV non-small-cell lung cancer with epidermal growth factor receptor (EGFR) exon 19 deletions and exon 21 L858R mutations, osimertinib is the standard of care. Investigating the activity and safety of osimertinib in patients with EGFR exon 18 G719X, exon 20 S768I, or exon 21 L861Q mutations is of clinical interest. PATIENTS AND METHODS: Patients with stage IV non-small-cell lung cancer with confirmed EGFR exon 18 G719X, exon 20 S768I, or exon 21 L861Q mutations were eligible. Patients were required to have measurable disease, an Eastern Cooperative Oncology Group performance status of 0 or 1, and adequate organ function. Patients were required to be EGFR tyrosine kinase inhibitor-naive. The primary objective was objective response rate, and secondary objectives were progression-free survival, safety, and overall survival. The study used a two-stage design with a plan to enroll 17 patients in the first stage, and the study was terminated after the first stage due to slow accrual. RESULTS: Between May 2018 and March 2020, 17 patients were enrolled and received study therapy. The median age of patients was 70 years (interquartile range 62-76), the majority were female (n = 11), had a performance status of 1 (n = 10), and five patients had brain metastases at baseline. The objective response rate was 47% [95% confidence interval (CI) 23% to 72%], and the radiographic responses observed were partial response (n = 8), stable disease (n = 8), and progressive disease (n = 1). The median progression-free survival was 10.5 months (95% CI 5.0-15.2 months), and the median OS was 13.8 months (95% CI 7.3-29.2 months). The median duration on treatment was 6.1 months (range 3.6-11.9 months), and the most common adverse events (regardless of attribution) were diarrhea, fatigue, anorexia, weight loss, and dyspnea. CONCLUSIONS: This trial suggests osimertinib has activity in patients with these uncommon EGFR mutations.

A phase I, open-label dose-escalation study of continuous treatment with BIBF 1120 in combination with paclitaxel and carboplatin as first-line treatment in patients with advanced non-small-cell lung cancer.

BACKGROUND: BIBF 1120 is an oral potent inhibitor of vascular endothelial growth factor receptor, fibroblast growth factor receptor and platelet-derived growth factor receptor, the three key receptor families involved in angiogenesis. This phase I, open-label dose-escalation study investigated BIBF 1120 combined with paclitaxel (Taxol) and carboplatin in first-line patients with advanced (IIIB/IV) non-small-cell lung cancer. PATIENTS AND METHODS: Patients received BIBF 1120 (starting dose 50 mg b.i.d.) on days 2-21 and paclitaxel (200 mg/m2) and carboplatin [area under curve (AUC)=6 mg/ml/min] on day 1 of each 21-day cycle. Primary end points were safety and BIBF 1120 maximum tolerated dose (MTD) in this combination. Pharmacokinetics (PK) profiles were evaluated. RESULTS: Twenty-six patients were treated (BIBF 1120 50-250 mg b.i.d.). BIBF 1120 MTD was 200 mg b.i.d. in combination with paclitaxel and carboplatin. Six dose-limiting toxicity events occurred during treatment cycle 1 (liver enzyme elevations, thrombocytopenia, abdominal pain, and rash). Best responses included 7 confirmed partial responses (26.9%); 10 patients had stable disease. BIBF 1120 200 mg b.i.d. had no clinically relevant influence on the PK of paclitaxel 200 mg/m2 and carboplatin AUC 6 mg/ml/min and vice versa. CONCLUSIONS: BIBF 1120 MTD was 200 mg b.i.d when given with paclitaxel and carboplatin; this combination demonstrated an acceptable safety profile. No relevant changes in PK parameters of the backbone chemotherapeutic agents or BIBF 1120 were observed.

An epigenetic mechanism for capecitabine resistance in mesothelioma.

Mesothelioma is an uncommon malignancy whose global incidence continues to rise. The therapeutic standard for advanced disease is intravenous pemetrexed and cisplatin. The anti-folate capecitabine is significantly less effective than pemetrexed. The balance between thymidylate synthase (TS), dihydropyrimidine dehydrogenase (DPD), and thymidine phosphorylase (TP) is critical to the efficacy of capecitabine. DNA from mesothelioma cell lines was bisulfite treated and examined by MS-PCR, RNA was obtained for real-time PCR analysis, and protein lysates were obtained for Western immunoblot analysis. Cytotoxicity was assessed by MTT assay, comparing 5-aza-CdR pretreated or untreated cells with 5'-deoxy-5-fluorouridine (DFUR), 5-FU, and pemetrexed. Finally bisulfite sequencing of the extracellular growth factor-1 (ECGF-1) gene was performed on 4 mesothelioma samples and pericardial tissue. One of the four cell lines tested (H290) was methylated for ECGF-1. This corresponded to a lack of TP expression by real-time PCR and Western immunoblot. Treatment with 1muM 5-aza-CdR increased TP mRNA and protein expression in H290. DFUR, the substrate for TP, showed increased cytotoxicity when delivered after 5-aza-CdR exposure in the methylated cell line. There was no difference in any of the unmethylated cell lines when cells were exposed to 5-FU or pemetrexed with or without 5-aza-CdR. Patient tumor samples revealed an increased number of methylated CpG sites in ECGF-1 compared to normal pericardium. Methylation of ECGF-1, leads to transcriptional silencing of TP and may explain the lack of any effect of capecitabine, especially when compared to pemetrexed.

Noncytotoxic suramin as a chemosensitizer in patients with advanced non-small-cell lung cancer: a phase II study.

BACKGROUND: The purpose of this study was to evaluate the potential of noncytotoxic doses of suramin to reverse chemotherapy resistance in advanced chemonaive and chemoresistant non-small-cell lung cancer patients. PATIENTS AND METHODS: Patients received paclitaxel (Taxol) (200 mg/m(2)) and carboplatin (area under the concentration-time curve 6 mg/ml/min) every 3 weeks. The total suramin per cycle dose was calculated using a nomogram derived from the preceding phase I trial to obtain the desirable plasma concentration range of 10-50 microM. RESULTS: Thirty-nine response-assessable chemonaive patients (arm A) received 213 cycles. Thirty-eight cycles were administered to 15 patients with demonstrated resistance to paclitaxel and carboplatin (arm B). The pattern/frequency of toxic effects was similar to those expected for paclitaxel/carboplatin, and pharmacokinetic analyses (199 cycles) showed suramin plasma concentrations maintained between 10 and 50 microM in 94% of cycles. In arm A, response evaluation criteria in solid tumors (RECIST) response rate was 36% (95% confidence interval 22% to 54%; two complete, 12 partial); 15 patients (38%) had disease stabilization for > or =4 months; median progression-free survival (intention to treat) was 6.4 months; median overall survival (OS) 10.4 months and 1-year survival rate 38%. In arm B, no RECIST responses occurred; four patients had disease stabilization for > or =4 months; median OS was 132 days and 1-year survival rate 7%. Plasma basic fibroblast growth factor levels were higher in chemopretreated/refractory patients compared with chemonaive patients (P = 0.05). Sequence analysis of the EGFR tyrosine kinase domain in a long-term disease-free survivor revealed an ATP-binding pocket mutation (T790M). CONCLUSIONS: Noncytotoxic suramin did not increase paclitaxel/carboplatin's toxicity and the suramin dose was predicted from clinical parameters. No clinically significant reversal of primary resistance was documented, but a modulatory effect in chemotherapy-naive patients cannot be excluded. Controlled randomization is planned for further evaluation of this treatment strategy.

MicroRNA-126 inhibits invasion in non-small cell lung carcinoma cell lines.

Crk is a member of a family of adaptor proteins that are involved in intracellular signal pathways altering cell adhesion, proliferation, and migration. Increased expression of Crk has been described in lung cancer and associated with increased tumor invasiveness. MicroRNAs (miRNAs) are a family of small non-coding RNAs (approximately 21-25 nt long) that are capable of targeting genes for either degradation of mRNA or inhibition of translation. Crk is a predicted putative target gene for miR-126. Over-expression of miR126 in a lung cancer cell line resulted in a decrease in Crk protein without any alteration in the associated mRNA. These lung cancer cells exhibit a decrease in adhesion, migration, and invasion. Decreased cancer cell invasion was also evident following targeted knockdown of Crk. MiR-126 alters lung cancer cell phenotype by inhibiting adhesion, migration, and invasion and the effects on invasion may be partially mediated through Crk regulation.

The N-terminal domain of c-Myc associates with alpha-tubulin and microtubules in vivo and in vitro.

The polymerization of alpha- and beta-tubulin into microtubules results in a complex network of microfibrils that have important structural and functional roles in all eukaryotic cells. In addition, microtubules can interact with a diverse family of polypeptides which are believed to directly promote the assembly of microtubules and to modulate their functional activity. We have demonstrated that the c-Myc oncoprotein interacts in vivo and in vitro with alpha-tubulin and with polymerized microtubules and have defined the binding site to the N-terminal region within the transactivation domain of c-Myc. In addition, we have shown that c-Myc colocalizes with microtubules and remains tightly bound to the microtubule network after detergent extraction of intact cells. These findings suggest a potential role for Myc-tubulin interaction in vivo.

Differential specificity for binding of retinoblastoma binding protein 2 to RB, p107, and TATA-binding protein.

The growth suppressor activities of the RB and p107 products are believed to be mediated by the reversible binding of a heterogeneous family of cellular proteins to a conserved T/E1A pocket domain that is present within both proteins. To study the functional role of these interactions, we examined the properties of cellular retinoblastoma binding protein 2 (RBP2) binding to RB, p107, and the related TATA-binding protein (TBP) product. We observed that although RBP2 bound exclusively to the T/E1A pocket of p107, it could interact with RB through independent T/E1A and non-T/E1A domains and with TBP only through the non-T/E1A domain. Consistent with this observation, we found that a mutation within the Leu-X-Cys-X-Glu motif of RBP2 resulted in loss of ability to precipitate p107, while RB- and TBP-binding activities were retained. We located the non-T/E1A binding site of RBP2 on a 15-kDa fragment that is independent from the Leu-X-Cys-X-Glu motif and encodes binding activity for RB and TBP but does not interact with p107. Despite the presence of a non-T/E1A binding site, however, recombinant RBP2 retained the ability to preferentially precipitate active hypophosphorylated RB from whole-cell lysates. In addition, we found that cotransfection of RBP2 can reverse in vivo RB-mediated suppression of E2F activity. These findings confirm the differential binding specificities of the related RB, p107, and TBP proteins and support the presence of multifunctional domains on the nuclear RBP2 product which may allow complex interactions with the cellular transcription machinery.

Protein expression and functional analysis of the FHIT gene in human tumor cells.

BACKGROUND: The fragile histidine triad (FHIT) gene at chromosome 3p14.2 has been proposed to be a candidate tumor suppressor gene in human cancers. To test whether FHIT exhibits the functional properties of a tumor suppressor gene, we studied the expression of its protein (pFHIT) in human carcinoma cells and examined the ability of FHIT to inhibit the neoplastic phenotype of cancer cells. METHODS: Subcellular localization and patterns of protein expression in tumor cells were determined by immunohistochemical analysis and immunoblotting with the use of polyclonal anti-pFHIT antisera. In tumor cells with undetectable pFHIT, we examined the effect of recombinant pFHIT expression on morphology, growth rate, colony formation, and in vivo tumor formation. RESULTS: We demonstrated that pFHIT is a cytoplasmic 17-kd polypeptide whose expression could not be detected in 30 of 52 human carcinoma cell lines tested. We observed, however, that the stable overexpression of pFHIT did not alter cell morphology, inhibit colony formation, or inhibit cell proliferation in vitro. Furthermore, overexpression of pFHIT did not lead to altered cell cycle kinetics in dividing cells. The in vivo tumorigenicity of a tumor cell line that expressed high levels of recombinant pFHIT was equivalent to that of control transfectants and of parental cells. CONCLUSIONS: These results suggest that the replacement of pFHIT in human carcinoma cells does not suppress tumor cell growth and that this protein may be involved in tumorigenesis in ways that are distinct from the "classic" tumor suppressor paradigm.

Immunohistochemical analysis of the p16INK4 cyclin-dependent kinase inhibitor in malignant mesothelioma.

BACKGROUND: The identification in 1994 of the CDKN2 gene as a target for mutations in a wide range of human cancers, including malignant mesothelioma, has been controversial because subsequent studies have detected a lower frequency of CDKN2 gene mutations in primary tumors than in cultured cell lines. These reports raised the hypothesis that another gene, distinct from CDKN2, might be the target of the chromosome 9p21 deletions frequently observed in these tumors. PURPOSE: To address whether inactivation of CDKN2 function is an essential event in the etiology of malignant mesothelioma, we examined p16INK4 protein expression in primary thoracic mesotheliomas, in nonmalignant pleural tissues, and in independent mesothelioma cell lines. We also studied the growth rate of tumor cell lines following stable transfection of CDKN2 gene. METHODS: Retinoblastoma (Rb) and p16INK4 protein expression was determined by immunohistochemical analysis from archival paraffin specimens of 12 primary thoracic mesotheliomas and a nonmalignant pleural biopsy specimen. In addition, protein immunoblot analysis for Rb and p16INK4 expression was conducted on 15 independent mesothelioma cell lines, and the ability of a transfected CDKN2 gene to suppress the growth of the mesothelioma cell lines H2373 and H2461 in vitro was examined. RESULTS: We demonstrated abnormal p16INK4 expression in 12 of 12 primary mesothelioma specimens and in 15 of 15 mesothelioma cell lines. All tumor specimens and the tumor cell lines showed expression of wild-type Rb protein. In addition, we have confirmed the ability of a transfected CDKN2 gene to suppress growth of two independent mesothelioma cell lines. CONCLUSIONS: Immunohistochemical analysis of the p16INK4 gene product is feasible in archival biopsy samples. With this analysis, CDKN2 gene inactivation can be determined in tumors that are contaminated with nonmalignant cells. Furthermore, since loss of p16INK4 protein expression can result from both genetic (gene mutations) and epigenetic (abnormal DNA hypermethylation) mechanisms, as we and others have shown recently, examination of protein expression is a highly sensitive method for analyzing the CDKN2 status in large numbers of tumor samples. IMPLICATIONS: This study suggests that inactivation of the CDKN2 gene is an essential step in the etiology of malignant mesotheliomas. Defining the role of the p16INK4:Rb tumor suppressor pathway and its immediate downstream substrates will be an important goal in designing future therapeutic strategies.

DNA methyltransferase inhibition enhances apoptosis induced by histone deacetylase inhibitors.

Histone acetylation has long been associated with transcriptional activation, whereas conversely, deacetylation of histones is associated with gene silencing and transcriptional repression. Here we report that inhibitors of histone deacetylase (HDAC), depsipeptide and trichostatin A, induce apoptotic cell death in human lung cancer cells as demonstrated by DNA flow cytometry and Western immunoblot to detect cleavage of poly(ADP-ribose) polymerase. This HDAC inhibitorinduced apoptosis is greatly enhanced in the presence of the DNA methyltransferase inhibitor, 5-aza-2'-deoxycytidine (DAC). The HDAC inhibitor-induced apoptosis appears to be p53 independent, because no change in apoptotic cell death was observed in H1299 cells that expressed exogenous wild-type p53 (H1299 cells express no endogenous p53 protein). To further investigate the mechanism of DAC-enhanced, HDAC inhibitor-induced apoptosis, we analyzed histone H3 and H4 acetylation by Western immunoblotting. Results showed that depsipeptide induced a dose-dependent acetylation of histones H3 and H4, which was greatly increased in DAC-pretreated cells. By analyzing the acetylation of specific lysine residues at the amino terminus of histone H4 (Ac-5, Ac-8, Ac-12, and Ac-16), we found that the enhancement of HDAC inhibitor-induced acetylation of histones in the DAC-pretreated cells was not lysine site specific. These results demonstrate that DNA methylation status is an important determinant of apoptotic susceptibility to HDAC inhibitors.

Alternative splicing of the RBP1 gene clusters in an internal exon that encodes potential phosphorylation sites.

We have isolated cDNA and genomic clones for the human retinoblastoma binding protein 1 (RBP1) gene, and have identified alternative splicing of RBP1 clustered within a 207-nucleotide internal exon. Three of the predicted RPB1 peptides share amino-terminal and carboxy-terminal domains, while a fourth species encodes a distinct carboxy-terminal domain. Functional analysis of these peptides demonstrated that they are capable of precipitating retinoblastoma (RB) protein in vitro from K562 cell lysates, but cannot bind to mutant RB protein. However, each of the RBP1 peptides differed within an internal exon that contains potential casein kinase II and p34cdc2 phosphorylation sites. Immunoblot analysis using polyclonal alpha-RBP1 antiserum revealed that the RBP1 protein is expressed in a wide range of cell lines of differing histologic type and migrates on sodium dodecyl sulfate-polyacrylamide gel electrophoresis predominantly as a 200-kDa protein. Immunohistochemical analysis using the alpha-RBP1 antiserum demonstrated a distinct nuclear staining pattern that was eliminated when the antiserum was preabsorbed with RBP1 peptide. The RBP1 gene encodes a widely expressed 200-kDa nuclear protein and undergoes alternative splicing that predicts a family of RB-binding peptides.

CDKN2 gene silencing in lung cancer by DNA hypermethylation and kinetics of p16INK4 protein induction by 5-aza 2'deoxycytidine.

Absent expression of the cyclin dependent kinase-inhibitor, p16INK4, is observed in a wide range of primary human cancers. Although homozygous deletions and point mutations have been reported in a subset of these tumors, the molecular basis for absent p16INK4 in other samples is unknown. We have examined 33 tumor cell lines and have shown that hypermethylation of a G:C-rich region within exon 1 of the CDKN2 gene was present in 100% of samples with wildtype RB expression and no detectable CDKN2 mutations. Treatment for at least 4 hours with the demethylating agent 5-aza 2'deoxycytidine, but not 5-azacytidine or 6-azacytidine, induces the prolonged expression of p16INK4 protein in each of these samples following a discrete 24-48 hour lag period. Consistent with the hypothesis that hypermethylation of the CDKN2 gene is a tumor-specific mechanism for gene inactivation, we observed hypomethylation at the exon 1 site exclusively in tumor lines that expressed p16INK4 or that had sustained inactivating point mutations within the CDKN2 open reading frame. These findings demonstrate a link between DNA methylation and the p16INK4:RB tumor suppressor pathway.

Absence of p16INK4 protein is restricted to the subset of lung cancer lines that retains wildtype RB.

Cell cycle dependent phosphorylation of the RB tumor suppressor protein is mediated by a family of G1 cyclin dependent kinases (cdks) and cyclins including the activated cdk4:cyclin D complex. The identification of a cdk4 inhibitor, p16INK4, as a target for mutations in cultured tumor lines and primary tumors suggested that RB activity may be affected in these cells. We have examined 88 lung cancer lines for p16INK4 protein expression and have observed a striking inverse correlation between the presence of p16INK4 and wildtype RB. We demonstrated that only 6/55 (11%) of small cell lung cancer (SCLC) samples had absent p16INK4 protein, and all 6 belonged to the rare subset of SCLC with wildtype RB expression. Conversely of 48 SCLC samples with absent or mutant RB, all showed detectable levels of p16INK4 protein. In contrast, we observed that 23/33 (70%) of non-SCLC samples had loss of p16INK4. Twenty-two of 26 non-SCLC lines with wildtype RB had absent p16INK4 while 6 of 7 non-SCLC lines with absent or mutant RB had detectable p16INK4. The inverse correlation of RB and p16INK4 expression and the absence of p16INK4 inactivation in RB (-/-) SCLC lines (0/48) confirms a common p16INK4/RB growth suppressor pathway in human cancers and provides evidence that p16INK4, and not an adjacent gene on chromosome 9p, is a specific target for mutational events.

RET cooperates with RB/p53 inactivation in a somatic multi-step model for murine thyroid cancer.

Mice bred to carry germline Rb and p53 null alleles are associated with a tumor spectrum that overlaps with the inherited multiple endocrine neoplasia-1 (MEN1) and MEN2 syndromes in humans, including medullary thyroid cancer (MTC). To study the genetic basis for these tumors, we microdissected MTC specimens or obtained fresh MTC tissue from nine independent Rb(+/-) p53(+/-) mice, amplified the region of the Ret gene known to be mutated in human MTC, and detected acquired missense Ret mutations in four different mice. These mutations were localized to a group of tandem cysteines which are analogous to activating germline mutations observed in human MEN2A and familial MTC (FMTC). To determine whether the remaining wild type Rb allele was inactivated in these murine MTC samples, we subjected tumor tissue to immunohistochemical staining with an Rb antibody, and demonstrated the absence of RB staining in murine MTC, while normal tissue retained RB nuclear staining. These findings demonstrate the ability of the gene knockout model to recapitulate somatic multi-step tumorigenesis and suggest that the development of a murine neuroendocrine tumor requires mutational dysregulation within both receptor tyrosine kinase and nuclear tumor suppressor gene pathways.

Apoptosis is associated with cleavage of a 5 kDa fragment from RB which mimics dephosphorylation and modulates E2F binding.

Dephosphorylation of the RB protein has been reported to be associated with apoptosis. In contrast, we show that treatment of HL60 cells with etoposide or cytosine arabinoside or treatment of breast epithelial cells with alpha-FAS is associated with the cleavage of a 5 kDa fragment from the C-terminus of RB, resulting in a truncated product that we have designated as p100cl. This cleavage event coincides with the activation of cysteine proteases at the onset of apoptosis, is blocked by the addition of iodoacetamide to cells prior to the onset of apoptosis, and results in the expression of faster migrating protein species which can mimic dephosphorylated RB. The free 5 kDa fragment is detected only during apoptosis, predicts a cleavage site that we have mapped to a unique CPP32-like recognition sequence which is present at the C-terminus of all reported RB homologues, and results in a truncated RB protein with enhanced E2F binding affinity. While the causality for this cleavage event in the apoptotic process is still under investigation, our findings suggest distinct post-translational pathways for the RB product between cells examined during growth arrest (p105 hypophosphorylated RB) or apoptosis (p100cl).

RB protein status and clinical correlation from 171 cell lines representing lung cancer, extrapulmonary small cell carcinoma, and mesothelioma.

We have studied RB protein expression in 171 cell lines derived from patients with small cell lung cancer (SCLC), non-small cell lung cancer (NSCLC), pulmonary carcinoid, mesothelioma, and extrapulmonary small cell cancer (EPSC) and have correlated this data with clinical outcome. We detected absent or aberrant RB protein expression in 66/75 SCLC, 12/80 NSCLC, 1/6 carcinoid, 0/5 mesothelioma, and 4/5 EPSC samples. In addition, we observed integration of human papilloma virus (HPV) DNA in the single EPSC cell line that retained wildtype RB protein. We did not detect integration of HPV, SV40 or adenoviral DNA in other tumor samples with wildtype RB status. We also noted a stable, hypophosphorylated mutant RB in 12 SCLC and 3 NSCLC samples which might have been falsely interpreted as wildtype by current immunohistochemical techniques. Analysis of the matched clinical data showed no associations between RB status and age, sex, extent of disease, performance status, smoking history, and previous treatment. In addition, retrospective analyses showed no consistent correlation of RB protein expression with either best clinical response, overall survival, or in vitro chemotherapeutic drug sensitivity. The stable expression of RB after gene transfection into RB(-) SCLC cells, however, resulted in a trend toward increased in vitro resistance to etoposide, cisplatin and doxorubicin.

Partial inactivation of the RB product in a family with incomplete penetrance of familial retinoblastoma and benign retinal tumors.

While familial retinoblastoma has served as the paradigm for the two-hit theory of tumorigenesis and for the concept of the tumor suppressor gene, the etiology of incomplete penetrance of familial retinoblastoma is poorly understood. To address the molecular basis for this phenotype we have studied the functional properties of a mutant Rb gene identified in a kindred with incomplete penetrance of familial retinoblastoma and evidence for regressed retinal lesions (retinomas). In contrast to all previously isolated RB mutant proteins, we demonstrated that the mutant product from this kindred retained the wildtype properties of nuclear localization, the ability to undergo hyperphosphorylation in vivo, and the capacity to suppress growth of RB(-) cells. Protein binding ('pocket') activity, however, was defective defining a new class of RB mutant with partial inactivation. The presence of this unique RB mutant in the germline of obligate carriers with incomplete penetrance and regressed retinal lesions suggests a molecular basis for this phenotype and supports the hypothesis that a minimum 'RB threshold' level of protein binding activity is required to suppress tumorigenesis.

Increased expression of unmethylated CDKN2D by 5-aza-2'-deoxycytidine in human lung cancer cells.

DNA hypermethylation of CpG islands in the promoter region of genes is associated with transcriptional silencing. Treatment with hypo-methylating agents can lead to expression of these silenced genes. However, whether inhibition of DNA methylation influences the expression of unmethylated genes has not been extensively studied. We analysed the methylation status of CDKN2A and CDKN2D in human lung cancer cell lines and demonstrated that the CDKN2A CpG island is methylated, whereas CDKN2D is unmethylated. Treatment of cells with 5-aza-2'-deoxycytidine (5-Aza-CdR), an inhibitor of DNA methyltransferase 1, induced a dose and duration dependent increased expression of both p16(INK4a) and p19(INK4d), the products of CDKN2A and CDKN2D, respectively. These data indicate that global DNA demethylation not only influences the expression of methylated genes but also of unmethylated genes. Histone acetylation is linked to methylation induced transcriptional silencing. Depsipeptide, an inhibitor of histone deacetylase, acts synergistically with 5-Aza-CdR in inducing expression of p16(INK4a) and p19(INK4d). However, when cells were treated with higher concentrations of 5-Aza-CdR and depsipeptide, p16(INK4a) expression was decreased together with significant suppression of cell growth. Interestingly, p19(INK4d) expression was enhanced even more by the higher concentrations of 5-Aza-CdR and depsipeptide. Our data suggest that p19(INK4d) plays a distinct role from other INK4 family members in response to the cytotoxicity induced by inhibition of DNA methylation and histone deacetylation.

Phase I study of high-dose piroxantrone with granulocyte colony-stimulating factor.

PURPOSE: We performed a phase I trial of piroxantrone with and without granulocyte colony-stimulating factor (G-CSF) to determine whether the use of this cytokine would enable us to increase the dose-intensity of piroxantrone. PATIENTS AND METHODS: Thirty-eight patients received 121 courses of piroxantrone administered once every 21 days. Initial patient cohorts received piroxantrone alone starting at 150 mg/m2 and the dose was escalated in subsequent patients until dose-limiting toxicity (DLT) was reached. Patient cohorts then received escalating doses of piroxantrone starting at 185 mg/m2 administered with G-CSF beginning day 2. RESULTS: Dose-limiting neutropenia occurred in three of six patients treated with 185 mg/m2 piroxantrone; the maximum-tolerated dose (MTD) of piroxantrone alone was 150 mg/m2. Three of six patients treated with piroxantrone and G-CSF exhibited dose-limiting thrombocytopenia at 445 mg/m2; the MTD of piroxantrone with G-CSF was thus 355 mg/m2. Seven patients developed symptomatic congestive heart failure (CHF) at cumulative piroxantrone doses ranging from 855 to 2,475 mg/m2 and two have died of cardiotoxicity. Of these patients, six of seven had previously received doxorubicin. Other nonhematologic toxicity was mild. CONCLUSION: The use of G-CSF results in a more than twofold increase in the MTD of piroxantrone. However, symptomatic cardiotoxicity is prominent, especially in patients who have received prior treatment with anthracyclines.