Safety and activity of alectinib plus bevacizumab in patients with advanced ALK-rearranged non-small-cell lung cancer: a phase I/II study

Background

Alectinib, a second-generation anaplastic lymphoma kinase (ALK) tyrosine kinase inhibitor (TKI), is highly effective in advanced ALK-rearranged non-small-cell lung cancer and represents a standard first-line therapy. New strategies are needed, however, to delay resistance. We conducted a phase I/II study to assess the safety and efficacy of combining alectinib with bevacizumab, a monoclonal antibody against vascular endothelial growth factor.

Patients and methods

Patients with advanced ALK-rearranged non-squamous non-small-cell lung cancer were enrolled. The phase I portion employed a dose de-escalation strategy with alectinib and bevacizumab starting at the individual standard doses. The primary objective was to determine the recommended phase II dose (RP2D). In phase II, the primary objective was to evaluate the safety of the combination at the RP2D; the secondary objective was to determine extracranial and intracranial efficacy.

Results

Eleven patients were enrolled between September 2015 and February 2020. Most patients (82%) had baseline brain metastases. Six patients (55%) were treatment-naive; five (46%) had received prior ALK TKIs (crizotinib, n = 3; ceritinib, n = 1; crizotinib then brigatinib, n = 1). No dose-limiting toxicities occurred. RP2D was determined as alectinib 600 mg orally twice daily plus bevacizumab 15 mg/kg intravenously every 3 weeks. Three patients experienced grade 3 treatment-related adverse events: pneumonitis related to alectinib, proteinuria related to bevacizumab, and hypertension related to bevacizumab. Treatment-related intracranial hemorrhage was not observed. Six (100%) of six treatment-naive patients and three (60%) of five ALK TKI-pretreated patients had objective responses; median progression-free survival was not reached (95% confidence interval, 9.0 months-not reached) and 9.5 months (95% confidence interval, 4.3 months-not reached), respectively. Intracranial responses occurred in four (100%) of four treatment-naive and three (60%) of five TKI-pretreated patients with baseline brain metastases. The study was stopped prematurely because of slow accrual.

Conclusions

Alectinib plus bevacizumab was well tolerated without unanticipated toxicities or dose-limiting toxicities.

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Alectinib plus bevacizumab is safe in patients with advanced ALK-rearranged non-small-cell lung cancer.

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Bevacizumab combined with alectinib does not increase risk of intracranial hemorrhage in patients with brain metastases.

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Enrollment challenges with this trial highlight important considerations for future studies of ALK inhibitor combinations.

Activity of the Hsp90 inhibitor luminespib among non-small-cell lung cancers harboring EGFR exon 20 insertions

Background

There are currently no approved targeted therapies for non-small-cell lung cancer (NSCLC) patients with EGFR exon 20 insertions (ins20), a subgroup of EGFR mutations that are generally refractory to first/second generation EGFR inhibitors. We report the final results of a phase II trial evaluating the activity of the Hsp90 inhibitor luminespib (AUY922) in NSCLC patients with EGFR ins20.

Patients and methods

Twenty-nine patients with stage IV NSCLC with EGFR ins20 identified on local testing and at least one prior therapy were enrolled on the trial between August 2013 and October 2016. The primary end point was objective response rate (ORR), with a pre-determined target rate of effectiveness [defined as the rate of partial response (PR) plus stable disease (SD) lasting ≥3 months] of 20%. Secondary end points were PFS, overall survival (OS), safety and response by EGFR ins20 subtype.

Results

Among the 29 patients (18 females, median age 60 years) the ORR was 17%, median progression-free survival was 2.9 months (95% CI 1.4-5.6) and median OS (mOS) was 13 months (95% CI 4.9-19.5). The results exceeded the pre-determined target rate of effectiveness with 11/29 (38%) patients having a PR or an SD ≥3 months. The most common luminespib-related toxicities were diarrhea (83%), visual changes (76%) and fatigue (45%). All study treatment was stopped on 28 February 2017 due to dissolution of study drug availability; 3 patients were on treatment at study termination.

Conclusion

The study met its primary end point, suggesting that luminespib may be an active therapy for advanced NSCLC patients with EGFR ins20. Luminespib is generally well-tolerated, though reversible low-grade ocular toxicity is common. Further study of luminespib and other hsp90 inhibitors in this population is warranted.

Study registration (ClinicalTrials.gov)

NCT01854034.

A prospective study of total plasma cell-free DNA as a predictive biomarker for response to systemic therapy in patients with advanced non-small-cell lung cancers

BACKGROUND

While previous studies have reported on the prognostic value of total plasma cell-free deoxyribonucleic acid (cfDNA) in lung cancers, few have prospectively evaluated its predictive value for systemic therapy response.

PATIENTS AND METHODS

We conducted a prospective study to evaluate the association between changes in total cfDNA and radiologic response to systemic therapy in patients with stage IIIB/IV non-small-cell lung cancers (NSCLCs). Paired blood collections for cfDNA and computed tomography (CT) assessments by RECIST v1.0 were performed at baseline and 6-12 weeks after therapy initiation. Total cfDNA levels were measured in plasma using quantitative real-time polymerase chain reaction. Associations between changes in cfDNA and radiologic response, progression-free survival (PFS), and overall survival (OS) were measured using Kruskal-Wallis and Kaplan-Meier estimates.

RESULTS

A total of 103 patients completed paired cfDNA and CT response assessments. Systemic therapy administered included cytotoxic chemotherapy in 57% (59/103), molecularly targeted therapy in 17% (17/103), and combination therapy in 26% (27/103). Median change in cfDNA from baseline to response assessment did not significantly differ by radiologic response categories of progression of disease, stable disease and partial response (P = 0.10). However, using radiologic response as continuous variable, there was a weak positive correlation between change in radiologic response and change in cfDNA (Spearman's correlation coefficient 0.21, P = 0.03). Baseline cfDNA levels were not associated with PFS [hazard ratio (HR) = 1.06, 95% confidence interval (CI) 0.93-1.20, P = 0.41] or OS (HR = 1.04, 95% CI 0.93-1.17, P = 0.51), neither were changes in cfDNA.

CONCLUSIONS

In this large prospective study, changes in total cfDNA over time did not significantly predict radiologic response from systemic therapy in patients with advanced NSCLC. Pretreatment levels of total cfDNA were not prognostic of survival. Total cfDNA level is not a highly specific predictive biomarker and future investigations in cfDNA should focus on tumor-specific genomic alterations using expanded capabilities of next-generation sequencing.

Impact on disease-free survival of adjuvant erlotinib or gefitinib in patients with resected lung adenocarcinomas that harbor epidermal growth factor receptor (EGFR) mutations

7523

Background: Patients with stage IV adenocarcinoma whose tumors harbor EGFR mutations have high rates of response (∼ 75%) and prolonged progression free survival after EGFR tyrosine kinase inhibitor (TKI) treatment. Adjuvant cisplatin-based chemotherapy improves disease free survival (DFS) and overall survival (OS) in patients with resected stages IB-IIIA NSCLC. To see if adjuvant treatment with EGFR TKI (gefitinib or erlotinib) improves DFS in patients with EGFR mutation NSCLC, we conducted a retrospective review of patients with resected lung adenocarcinoma harboring EGFR mutations, some of whom received EGFR TKIs postoperatively. Methods: With Institutional Review Board approval, clinical information was obtained on all patients with stage I-III lung adenocarcinoma harboring EGFR exon 19 or 21 mutations that underwent resection at MSKCC between May 2002 and August 2008. Age, gender, type of surgery, histology, EGFR mutation status (exon 19 deletions and exon 21 L858R), stage, perioperative therapy and survival were recorded. Kaplan-Meier analysis and Cox regression analysis were performed. Results: We studied 150 patients (112 women, 38 men) with completely resected stage I-III lung adenocarcinoma whose resection specimens contained EGFR activating mutations in exon 19 or 21. Median age was 69. Forty two patients (28%) received cytotoxic chemotherapy. Forty eight (32%) received either erlotinib (n=26) or gefitinib (n=22) postoperatively. The median time on TKI was 16 months. The median DFS was 43 months in the group that received a TKI vs. 31 months for those that did not. After controlling for stage, individuals who received adjuvant gefitinib or erlotinib had a better DFS (HR=0.38, 95%CI: 0.16–0.90) than the non-TKI group (p=0.03). The median overall survival has not been reached. Conclusions: These data indicate that the adjuvant use of either gefitinib or erlotinib improves DFS in patients with completely resected stage I -III lung adenocarcinomas with mutations in EGFR exons 19 and 21. These data justify a randomized trial in similar patients.

[Table: see text]

Phase II study of induction and adjuvant bevacizumab in patients with stage IB-IIIA non-small cell lung cancer (NSCLC) receiving induction docetaxel and cisplatin

7531

Background: VEGF supports growth of NSCLC and is blocked by bevacizumab. Bevacizumab with chemotherapy is an established treatment for advanced NSCLC. We conducted this study to assess the efficacy and toxicity of induction bevacizumab (Bev) with cisplatin (C) and docetaxel (D) in patients with resectable NSCLC. Methods: All patients (pts) had resectable Stage IB-IIIA NSCLC and received up to 4 cycles of D 75 mg/m2 and C 75 mg/m2 followed by surgery. Pts with non-squamous NSCLC also received 3 cycles of Bev 15 mg/kg along with induction DC (Bev-DC). Bev was not given in pre-operative cycle 4. Pts with squamous or central tumors or hemoptysis received 4 cycles of DC only (DC). All resected pts were eligible for adjuvant Bev 15 mg/kg q3 weeks for 1 year. The primary endpoint was rate of downstaging from pre-operative clinical stage to pathologic stage. Results: From Aug 2005 - Nov 2008, 47 pts were enrolled: 27 women; median age 62; Stage 1B -15%, Stage II-17%, Stage IIIA-68%. Of 36 pts given Bev-DC, 15/30 (50%) who have completed surgery were downstaged. Of 11 pts given DC, 3/11 (27%) were downstaged. In Bev-DC group, 22/33 (67%) completed all 4 cycles of DC without a dose reduction and 28/33 pts (85%) completed all 3 planned cycles of Bev. Pts received <3 cycles due to: hemoptysis (n=3), consent withdrawal (n=1), hypertension (n=1), and sepsis (n=1). For DC, 6/11 pts (55%) completed all 4 cycles of DC without a dose reduction. 42/43 patients were resected. R0 resection rate: 29/31 for Bev-DC and 9/11 for DC. Grade 3/4 surgical complications were seen in 5/31 pts (16%) in Bev-DC and 1/11 (9%) in DC. Only 17/41 (41%) who completed surgery received adjuvant bev (median 6 cycles), and 7/41 (17%) completed all adjuvant Bev. Pts did not receive adjuvant Bev due to: POD prior to adjuvant Bev (n=9), POD during adjuvant Bev (n=6), toxicity (n=4), consent withdrawal (n=1), RT for unresectable disease (n=1), surgical complications (n=4), chemotherapy complications (n=4). No treatment related deaths. Conclusions: Induction chemotherapy with Bev-DC in NSCLC is feasible and is associated with an improved rate of downstaging compared with historical controls (33%). In patients treated with DC-Bev, grade 3/4 surgical complications were increased by 7%.

[Table: see text]

A randomized phase II trial comparing pulsed erlotinib before or after carboplatin and paclitaxel in patients with stage IIIB or IV non-small cell lung cancer

7619

Background: A randomized phase 3 trial failed to show any improvement in response rate (RR) or overall survival (OS) when erlotinib was added to carboplatin and paclitaxel (TRIBUTE). However, preclinical data suggested that administration of erlotinib before or after chemotherapy may improve efficacy of chemotherapy [Gumerlock et al ASCO 2003, Solit et al Clin Can Res 2005]. We designed this trial to test the hypothesis that administration of pulsed erlotinib prior to or following chemotherapy would improve the response rate in patients with advanced NSCLC. Methods: All patients had chemotherapy naive, stage IIIB or IV NSCLC and were former or current smokers. All patients received carboplatin (AUC 6) and paclitaxel (200 mg/m2). Patients were randomly assigned to one of three arms: erlotinib 150 mg days 1,2, and chemotherapy on day 3; erlotinib 1500 mg days 1, 2 and chemotherapy on day 3; or chemotherapy on day 1 and erlotinib 1500 mg on days 2,3. Patients received up to six 21-day cycles of treatment. The primary endpoint was overall RR (CR+PR) using RECIST. We planned to enroll 29 patients to each arm in a “pick the winner” design comparing arms to the chemotherapy alone arm of TRIBUTE (RR 19%) with a desirable RR of 50%. Results: Eighty-seven patients were randomized to 3 arms. Accrual is complete. The most common grade 3/4 toxicities were neutropenia (39%), fatigue (15%), and anemia (12%). Grade 3/4 rash or diarrhea were uncommon. Conclusions: Treatment with erlotinib before (150 mg on days 1 and 2 or 1500 mg on days 1 and 2) or after (1500 mg on days 2 and 3) administration of carboplatin and paclitaxel failed to improve response rates compared to TRIBUTE. The benefit of pulsatile administration of erlotinib predicted by preclinical models was not evident in this clinical trial. Supported by Genentech, Inc.

[Table: see text] [Table: see text]

Combined inhibition of mTOR and EGFR with everolimus (RAD001) and gefitinib in patients with non-small cell lung cancer who have smoked cigarettes: A phase II trial

7575

Background: Most non-small cell lung cancers (NSCLC) are primarily resistant to the EGFR tyrosine kinase inhibitor gefitinib. One strategy to overcome resistance is to block parallel or downstream effectors that maintain tumor growth and proliferation. Preclinical data supports this hypothesis as inhibition of the PIK3CA/Akt/mTOR pathway restores gefitinib sensitivity in resistant cells. In a phase I study, gefitinib (250 mg) and the mTOR inhibitor everolimus (5 mg) were safely administered orally once-a-day (Milton Proc ASCO 2005). This combination induced regressions in patients with NSCLC. To assess the efficacy of this regimen, we designed this phase II trial. Methods: Two cohorts of patients with measurable stage IIIB/IV NSCLC were entered: (1) untreated with chemotherapy and (2) previously treated with cisplatin or carboplatin and docetaxel. A Simon two-stage design proposed to enroll up to 31 patients in each cohort. Response was assessed after 1 month then every 2 months. Pretreatment tumor specimens were collected on all patients. Results: To date, 25 patients have entered, 11 untreated and 14 previously treated. The median age was 66 years and KPS 80%. 52% were women, 68% had adenocarcinoma, and all were current (n=1) or former smokers. Partial responses (RECIST) have been observed in 4 of 23 evaluable patients (17%, 95% CI 5 to 39%) One of these 4 tumors harbored a KRAS mutation and one an EGFR exon 19 deletion. Responses lasted 3, 4, 9+, and 16+ months. Responses were observed in 2 of 13 untreated and 2 of 10 previously treated individuals. Toxicities: Grade 2/3 diarrhea in 13%, Grade 2 pustular rash in 25%, and Grade 2 mucosal ulcerations in 38%. 8% had dose reductions. There were no Grade 4 toxicities or treatment-related deaths. Conclusions: The combination of everolimus and gefitinib produced a 17% partial response rate in smokers with NSCLC, a group less likely to benefit from gefitinib. Enough responses have been seen in both untreated and previously treated cohorts to complete enrollment according to the two stage design of this trial. We plan to correlate outcomes with the molecular profile of tumors. Supported by Novartis, USA

No significant financial relationships to disclose.

Phase I study of the antifolate pralatrexate given with vitamin B12 and folic acid supplementation in patients (pts) with advanced non-small cell lung cancer (NSCLC)

13006

Background: Pralatrexate is a novel antifolate that has shown promising activity in the treatment of pts with previously- treated NSCLC at doses of 135–150 mg/m2 IV every other week (q2w). [Krug, Clin Cancer Res 9(6), 2003; 6(9), 2000] The addition of vitamin B12 and folic acid supplementation may mitigate toxicity from pralatrexate and improve efficacy by allowing higher doses to be delivered. Methods: This study is designed to determine the maximum tolerated dose (MTD) of pralatrexate in combination with vitamin B12 and folic acid supplementation in pts with NSCLC. Key eligibility criteria include confirmed stage IIIB or IV NSCLC; at least 1 prior chemotherapy regimen; Karnofsky performance status (KPS) = 70%; and no other active concurrent malignancy. Using a rapid escalation design, pralatrexate was initially administered at a dose of 150 mg/m2 IV q2w, escalating by 40 mg/m2 increments in successive cohorts, with one patient per cohort if no dose limiting toxicity (DLT) is encountered. All pts receive vitamin B12 1 mg intramuscular q 8–10 weeks and folic acid 1 mg by mouth once a day beginning at least 7 days prior to pralatrexate. All patients undergo pharmacokinetic testing following their first and second dose of pralatrexate. Results: Between 1/05–12/06, a total of 9 pts have been treated at the following dose levels: 150 (n=1), 190 (n=1), 230 (n=1), and 270 (n=6). Patient characteristics include: 2 male/7 female; median age 63 (range 52–73); KPS 80–90%; all pts had stage 4 NSCLC; 5 pts received 1 prior regimen and 4 pts received 2 or more prior regimens. Grade 3 esophagitis was a DLT in one patient at the 270 mg/m2 dose. Three other patients experienced grade 1–2 mucositis at this dose level without limiting drug delivery. The trial is ongoing, and enrollment is planned at 310 mg/m2 q2w to determine the MTD. Conclusions: When given in combination with vitamin B12 and folic acid supplementation, pralatrexate has been well tolerated in this pt population, with an MTD at least twice as high as achieved in previous phase 1 testing without supplementation. We plan to conduct a phase 2 trial of pralatrexate with vitamin B12 and folic acid supplementation to see if a higher dose will improve efficacy.

No significant financial relationships to disclose.

Interim results of two prospective trials measuring plasma total DNA and methylated genes before and after surgery, or chemotherapy, in patients with non-small cell lung cancer (NSCLC)

7123

Background: Measuring DNA in plasma using quantitative RT-PCR is a promising method for surveillance of NSCLC. This strategy has the potential to assess response more accurately or quickly than radiologic tests, or to confirm the success of surgical resection and select patients for adjuvant therapy. Methylated genes may be more specific than total DNA for the presence of cancer. Methods: We are conducting two prospective trials measuring total DNA, and 10 commonly hypermethylated genes in the plasma of NSCLC patients before and after therapy. For patients undergoing surgery, plasma samples are collected before, and at three timepoints after surgery (3–8 d, 2–5 w, 2–4 m). For patients on chemotherapy, collections are before, and coincident with up to 3 radiologic response assessments. DNA is extracted from a fixed volume of plasma, and measured using quantitative PCR of the β-Actin gene. After treating DNA with sodium metabisulfite, methylation-specific RT-PCR is performed to amplify the promoter region of APC, p16, MGMT, GSTP1, DAPK, CDH1, RASSF1A, WIF-1, SOCS-3, METH-2, assuming the promoter is fully methylated. Gene levels are normalized to β-Actin in modified DNA. Results: To date, plasma analysis has been completed on 50 patients with advanced NSCLC undergoing chemotherapy (320 planned), and 60 patients with early-stage NSCLC undergoing surgery (400 planned). Pretreatment levels of total DNA are higher in metastatic NSCLC (median 9.2, range 2.2–1020 ng/ml) compared to early-stage (median 3.6, range 0–1280 ng/ml), p < 0.001 by Wilcoxon rank sum test. At least one methylated gene is detectable in pretreatment plasma in 36% of patients with metastatic NSCLC, and 20% of patients with early-stage NSCLC. Conclusions: Methylated genes are rarely found in the pre-treatment plasma of NSCLC patients in this experiment, despite testing a panel of 10 genes. Plasma total DNA levels correlate with NSCLC stage. Correlation of baseline levels of total DNA, and temporal trends during treatment, to overall survival and radiologic response are planned. Supported by R01-CA092315.

[Table: see text]

Chemotherapy for early stage non-small cell lung cancer

For patients with locally advanced non-small cell lung cancer (NSCLC) undergoing surgery, both induction and adjuvant chemotherapy improve survival and curability. Induction chemotherapy is also feasible for patients with early stage NSCLC. Randomized trials of induction treatment for early stage NSCLC, as well as induction and adjuvant treatment for Stage IIIA patients, are in progress. These trials should build on current successes, and add new approaches such as targeted therapies and vaccines, in an attempt to prevent metastases, recurrence, and second primary malignancies.

Cooperation of p53 loss of function and v-Ha-ras in transformation of mouse keratinocyte cell lines

We previously demonstrated that after transduction with the v-Ha-ras oncogene and grafting onto nude mouse hosts, primary epidermal keratinocytes with a null mutation in the p53 gene form tumors with increased growth rates and predisposition to malignant conversion relative to p53 wild-type keratinocytes (Weinberg WC, et al., Cancer Res 54:5584-5592, 1994). To further explore the cooperation between p53 loss of function and activation of the ras oncogene, cell lines were established from the normal epidermises of newborn and adult p53-null mice, and parallel subclones were reconstituted with the p53val135 temperature-sensitive mutant. Reconstituted lines C, G, N, and V demonstrated functional p53 transcriptional activator activity at the wild-type-permissive temperature of 32 degrees C, compared with the hygromycin-selected control line X and parental p53-null lines NHK4 and AK1b. Hygromycin-selected subclones, but not the parental lines, made normal skin in vivo; all cell lines made carcinomas after introduction of v-Ha-ras, independent of p53 status. These cell lines were compared in vitro at 32 degrees C to maximize the amount of p53val135 in the wild-type conformation. Expression of v-Ha-ras did not consistently alter p53-mediated transcriptional activity, suggesting tat ras acts downstream or independently of p53. No correlation was observed between p53-mediated transcriptional activity and in vitro growth rates, colony formation after exposure to ultraviolet light, or suppression by normal neighboring keratinocytes. However, keratinocyte cell lines devoid of p53 and expressing v-Ha-ras formed colonies in soft agar; this was blocked at 32 degrees C in all cell lines reconstituted with p53val135. These keratinocyte lines provide a model for exploring the role of p53 and the interaction of p53 and ras in keratinocyte transformation.

p53-mediated transcriptional activity increases in differentiating epidermal keratinocytes in association with decreased p53 protein

The regulation of p53 protein synthesis and p53-mediated gene transactivation were evaluated in cultured mouse keratinocytes maintained as basal cells or induced to differentiate by Ca2+ > 0.1 mM. p53 protein half-life, p53 protein synthesis and the level of p53 mRNA decreased during terminal differentiation, as detected by immunoprecipitation with a panel of p53-specific antibodies and Northern blotting. Thus differentiating keratinocytes have lower levels of p53 protein. This decline is not observed following growth arrest alone, or in papilloma cell lines which do not terminally differentiate in response to Ca2+. In contrast, the ability of endogenous p53 to transactivate transcription from the PG13 CAT plasmid increased during differentiation in vitro. This change in activity cannot be explained by changes in p53 conformation or nuclear localization. Consistent with these findings, mRNA for the p53-mediated genes WAF1 and mdm-2 increased with Ca(2+)-induced differentiation in a time dependent manner, suggesting activation of p53 contributes to the differentiated phenotype. However, p53-null mice exhibit histologically normal skin and epidermal keratinocytes from these mice express the appropriate markers of differentiation and suppression of DNA synthesis in vitro when the [Ca2+] is > 0.1 mM. The observation that proliferating cells have higher levels of p53 protein which is less active for its function than differentiated cell types could have a consequence for the selection of p53 gene mutations during carcinogenesis, depending upon the stage of differentiation of the tumor cell type.

p53 gene dosage modifies growth and malignant progression of keratinocytes expressing the v-rasHa oncogene

Epidermal keratinocyte cultures were established from newborn mice expressing a null mutation in the p53 gene to explore the contribution of p53 to epidermal growth regulation and neoplasia. Keratinocytes were initiated by transduction with a replication-defective retrovirus encoding the v-rasHa oncogene and grafted onto nude mouse hosts. Tumors arising from keratinocytes heterozygous or null for functional p53 in the presence of v-rasHa have growth rates approximately 5-fold higher than those derived from p53(+/+) controls and rapidly form carcinomas, in contrast to the benign phenotype observed in p53(+/+)/v-rasHa grafts. In vitro, p53-deficient keratinocytes with and without v-rasHa expression display decreased responsiveness to the negative growth regulators transforming growth factors beta 1 and beta 2. In combination with v-rasHa, p53-deficient keratinocytes also exhibit decreased responsiveness to elevated Ca2+. These differences between genotypes cannot be attributed to changes in transforming growth factor beta receptor types present or altered levels of epidermal growth factor receptor and are independent of c-myc transcript levels. mRNA expression for the p-53 inducible protein WAF1 correlates with p53 gene dosage, but low levels are still detectable in p53(-/-) keratinocytes. The altered responsiveness of p53 deficient keratinocytes to negative growth regulators may provide a growth advantage to such cells in vivo and render them more susceptible to genetic alterations and malignant conversion.

Identification of a human achaete-scute homolog highly expressed in neuroendocrine tumors

Basic helix-loop-helix transcription factors of the achaete-scute family are instrumental in Drosophila neurosensory development and are candidate regulators of development in the mammalian central nervous system and neural crest. We report the isolation and initial characterization of a human achaete-scute homolog that is highly expressed in two neuroendocrine cancers, medullary thyroid cancer (MTC) and small cell lung cancer (SCLC). The human gene, which we have termed human achaete-scute homology 1 (hASH1), was cloned from a human MTC cDNA library. It encodes a predicted protein of 238 aa that is 95% homologous to mammalian achaete-scute homolog (MASH) 1, a rodent basic helix-loop-helix factor. The 57-residue basic helix-loop-helix domain is identical to that in the rodent gene, and the basic and helical regions, excluding the loop, are 72-80% identical to Drosophila achaete-scute family members. The proximal coding region of the hASH1 cDNA contains a striking 14-copy repeat of the triplet CAG that exhibits polymorphism in human genomic DNA. Thus, hASH1 is a candidate locus for disease-causing mutations via triplet repeat amplification. Analysis of rodent-human somatic cell hybrids permitted assignment of hASH1 to human chromosome 12. Northern blots revealed hASH1 transcripts in RNA from a human MTC cell line, two fresh MTC tumors, fetal brain, and three lines of human SCLC. In contrast, cultured lines of non-SCLC lung cancers and a panel of normal adult human tissues showed no detectable hASH1 transcripts. Expression of hASH1 may provide a useful marker for cancers with neuroendocrine features and may contribute to the differentiation and growth regulation of these cells.