Italian nivolumab Expanded Access Programme in melanoma adjuvant setting: patient outcomes and safety profile

INTRODUCTION

The CheckMate 238 randomised study demonstrated the relevant benefit in terms of recurrence-free survival (RFS) of nivolumab versus ipilimumab in resected stage IIIB-C or IV melanoma patients with a tolerable safety profile.

MATERIALS AND METHODS

From November 2018 to June 2019, 611 patients with stage III and IV resected melanoma were enroled to receive nivolumab as part of an Italian Expanded Access Programme (EAP). According to stages, 77% were stage III while 141 (23%) were stage IV with no evidence of disease (NED). Among stage III, 121 patients had IIIA (19.8%).

RESULTS

After a median follow-up of 23 months, the RFS in the Intention-to-Treat (ITT) population was 76.6% at 1 year and 59.6% at 2 years; 1- and 2-year distant metastasis-free survival were 83.7% and 71.2%, respectively. The overall survival rate in the ITT population was 93.8% at 1 year and 85.5% at 2 years. No significant differences in RFS were observed according to BRAF status. Treatment-related adverse events of grades 3-4 occurred in 11.5% of patients.

CONCLUSION

This paper reports the results of the Italian Nivolumab EAP in the adjuvant setting of stage III and IV NED melanoma patients. Our results confirm in a real-life setting the clinical activity and safety of nivolumab reported in the CheckMate238 registrative/pivotal. The enroled cohort of 611 patients highlights the relevant clinical need in this setting, also confirmed by the very short accrual time, representing one of the largest series reported as adjuvant EAP with the longest follow-up.

Abstract 5500: Patient-derived organotypic cultures (PDOCs) from melanoma metastases as a precision medicine test to improve patient management

INTRODUCTION Despite significant improvements in advanced melanoma therapy, there is still a pressing need for innovative therapies. Here, we optimized a method for testing the drug sensitivity of PDOCs and evaluated whether this preclinical model could be a valid tool for rapidly determining the patient’s tumor response profile to approved and alternative therapies.

METHODS PDOCs were generated from melanoma metastases (> 60 specimens) after mechanical or enzymatic dissociation. Tissue fragments (<70um) were harvested, embedded in 3D collagen beads (1.5 mg/mL type I collagen), and cultured in a 96-well plate for 6 days, maintaining tumor and stromal viability. More than 20 primary cell lines from the same samples were also stabilized. The melanoma cells or the PDOCs were left untreated or treated with the patient’s own therapy or with alternative drugs, and the efficacy of treatments was evaluated by MTT assay and flow cytometry. CD8+ T cell infiltration and cytokine secretion were also investigated.

RESULTS The first experiments were set up to validate PDOCs as predictive preclinical models of patient response to therapy. We tested approved melanoma therapies (i.e., the combination of BRAF and MEK inhibitors, or anti-PD-1 antibodies) on the same melanoma specimens at the IDI and IEO institutes. More than 10 different samples were compared, finding reproducible results between the two Institutions. Furthermore, drug response in PDOCs was comparable to the clinical response of matched patients undergoing the tested therapy, demonstrating PDOCs are reliable predictive tools. Then, we used primary cell lines to screen a pool of ten different targeted agents selected through functional screening of a bioactive library of 512 compounds on patient-derived xenografts, and based on known drug resistance mechanisms in melanoma. The three best-performing compounds were subsequently studied in PDOCs as single agents or in combination with immunotherapy. We found high heterogeneity of drug efficacy in different melanoma samples with no obvious correlation to BRAF or NRAS mutations, metastasis type, or patients’ prior therapies. Of note, in some cases, the combination with an anti-PD-1 inhibitor significantly improved the efficacy of one or more of the three drugs.

CONCLUSIONS We optimized and validated PDOCs as personalized preclinical models suitable for assessing the drug sensitivity/resistance profile of individual patient-derived melanomas. By retaining tumor stromal components and heterogeneity, PDOCs could be used to predict patients’ clinical response to currently approved agents, helping oncologists expedite decision-making when several treatment options are possible. Furthermore, the model could be used to evaluate the effectiveness of alternative treatments on tumors resistant to approved therapies, and to explore new drug combinations.

Citation Format: Antonella Bresin, Fiorenza Lotti, Lauretta Levati, Pier F. Ferrucci, Francesca Ricci, Francesco Scicchitano, Zorika C. Di Rocco, Giandomenico Russo, Luisa Lanfrancone. Patient-derived organotypic cultures (PDOCs) from melanoma metastases as a precision medicine test to improve patient management. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5500.

Dabrafenib plus trametinib is effective in the treatment of BRAF V600-mutated metastatic melanoma patients: analysis of patients from the dabrafenib plus trametinib Named Patient Program (DESCRIBE II)

In clinical trials, dabrafenib plus trametinib improved overall survival (OS) compared with single-agent BRAF inhibitors (BRAFi) in patients with BRAF V600-mutant unresectable or metastatic melanoma. We investigated dabrafenib plus trametinib therapy in a compassionate-use setting [Named Patient Program (NPP); DESCRIBE II]. A retrospective chart review of patients with BRAF V600-mutated unresectable stage III/IV melanoma receiving dabrafenib plus trametinib as compassionate use was conducted. Treatment patterns and duration, clinical outcomes, and tolerability were evaluated. Of 271 patients, 92.6% had stage IV melanoma, including 36.5% with brain metastases. Overall, 162 patients (59.8%) were BRAFi naive and 171 (63.1%) received first-line dabrafenib plus trametinib. Among BRAFi-naive patients, the overall response rate (ORR) was 67.3%, median OS (mOS) was 20.0 months, and median progression-free survival (mPFS) was 7.5 months. In BRAFi-naive patients with known brain metastases (n = 62), ORR was 61.3%, mOS was 15.5 months, and mPFS was 6.2 months. Eighty-four patients received BRAFi monotherapy for >30 days and switched to dabrafenib plus trametinib prior to progression. Of these 84 patients, 63 had known disease status at the time of switch, and 22 improved with the combination therapy. No new safety signals were identified, and dabrafenib plus trametinib was well tolerated. Dabrafenib plus trametinib showed substantial clinical activity in NPP patients with BRAF V600-mutated unresectable or metastatic melanoma. Analysis of treatment patterns demonstrated the effectiveness of the combination in patients with brain metastases and across lines of therapy with a well tolerated and manageable safety profile.

CheckMate 067: Long-term outcomes in patients with mucosal melanoma

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Background: Mucosal melanoma is a rare but aggressive malignancy with a poor prognosis. Here we report 5-y outcomes in a subgroup of patients with mucosal melanoma treated in CheckMate 067 with nivolumab plus ipilimumab (NIVO+IPI), NIVO alone, or IPI alone. Methods: Patients with previously untreated stage III or IV melanoma were randomized 1:1:1 to receive NIVO 1 mg/kg + IPI 3 mg/kg for 4 doses Q3W followed by NIVO 3 mg/kg Q2W, NIVO 3 mg/kg Q2W + placebo, or IPI 3 mg/kg Q3W for 4 doses + placebo until progression or unacceptable toxicity. Mucosal histology was not a stratification factor, and patients with mucosal melanoma were identified by local investigators in the study. Descriptive subgroup analyses were performed to evaluate efficacy (objective response rate [ORR], progression-free survival [PFS], overall survival [OS]), and safety. Results: A total of 79 patients with mucosal melanoma were treated. With a minimum follow-up of 60 mo, NIVO+IPI treatment was associated with the highest 5-y ORR (43% [vs 30% with NIVO and 7% with IPI]), PFS (29% [vs 14% and 0%, respectively]), and OS (36% [vs 17% and 7%, respectively]; Table), consistent with trends in the intent-to-treat (ITT) population; however, efficacy outcomes were generally less favorable overall relative to the ITT population. Complete response rates were higher with NIVO+IPI (14%) relative to monotherapy (NIVO, 4%; IPI, 0%) in patients with mucosal melanoma. Safety outcomes, including the grade 3/4 treatment-related adverse event rates of 54%, 26%, and 25%, respectively, were similar to the ITT population. Conclusions: This 5-y analysis showed that patients with mucosal melanoma in CheckMate 067 had similar safety outcomes but poorer long-term efficacy vs the ITT population. Patients with mucosal melanoma treated with NIVO+IPI appeared to have more favorable survival outcomes than those treated with NIVO or IPI alone. Novel therapies are needed to further improve long-term benefit in patients with mucosal melanoma. Clinical trial information: NCT01844505. [Table: see text]

Five-Year Survival with Combined Nivolumab and Ipilimumab in Advanced Melanoma

BACKGROUND

Nivolumab plus ipilimumab or nivolumab alone resulted in longer progression-free and overall survival than ipilimumab alone in a trial involving patients with advanced melanoma. We now report 5-year outcomes in the trial.

METHODS

We randomly assigned patients with previously untreated advanced melanoma to receive one of the following regimens: nivolumab (at a dose of 1 mg per kilogram of body weight) plus ipilimumab (3 mg per kilogram) every 3 weeks for four doses, followed by nivolumab (3 mg per kilogram every 2 weeks); nivolumab (3 mg per kilogram every 2 weeks) plus ipilimumab-matched placebo; or ipilimumab (3 mg per kilogram every 3 weeks for four doses) plus nivolumab-matched placebo. The two primary end points were progression-free survival and overall survival in the nivolumab-plus-ipilimumab group and in the nivolumab group, as compared with the ipilimumab group.

RESULTS

At a minimum follow-up of 60 months, the median overall survival was more than 60.0 months (median not reached) in the nivolumab-plus-ipilimumab group and 36.9 months in the nivolumab group, as compared with 19.9 months in the ipilimumab group (hazard ratio for death with nivolumab plus ipilimumab vs. ipilimumab, 0.52; hazard ratio for death with nivolumab vs. ipilimumab, 0.63). Overall survival at 5 years was 52% in the nivolumab-plus-ipilimumab group and 44% in the nivolumab group, as compared with 26% in the ipilimumab group. No sustained deterioration of health-related quality of life was observed during or after treatment with nivolumab plus ipilimumab or with nivolumab alone. No new late toxic effects were noted.

CONCLUSIONS

Among patients with advanced melanoma, sustained long-term overall survival at 5 years was observed in a greater percentage of patients who received nivolumab plus ipilimumab or nivolumab alone than in those who received ipilimumab alone, with no apparent loss of quality of life in the patients who received regimens containing nivolumab. (Funded by Bristol-Myers Squibb and others; CheckMate 067 ClinicalTrials.gov number, NCT01844505.).

The impact of patient characteristics and disease-specific factors on first-line treatment decisions for BRAF-mutated melanoma: results from a European expert panel study

Treatment decisions for advanced melanoma are increasingly complex and guidelines provide limited advice on how to choose between immunotherapy and targeted therapy for first-line treatment. A Delphi study was carried out to understand which patient characteristics and disease-related factors inform clinicians' choices of first-line treatment for BRAF-mutated melanoma. Twelve European melanoma specialists experienced in using immunotherapies and targeted agents participated in a double-blind two-phase Delphi study. In phase 1, participants completed a questionnaire developed after reviewing patient characteristics and disease-related factors reported in trials, clinical guidelines, and health technology assessments. Phase 2 was an expert panel meeting to explore outstanding issues from phase 1 and seek consensus, defined as 80% agreement. Twenty patient-related and disease-related characteristics were considered. There was consensus that tumor burden (83% of clinicians) and disease tempo (83%) are very or extremely important factors when selecting first-line treatment. Several components were deemed important when assessing tumor burden: brain metastases (82% of clinicians) and location of metastases (89%). There was consensus that disease tempo can be quantified in clinical practice, but not on a formal classification applicable to all patients. Lactate dehydrogenase level is a component of both tumor burden and disease tempo; all clinicians considered lactate dehydrogenase important when choosing first-line treatment. The majority (92%) did not routinely test programmed death ligand-1 status in patients with melanoma. Clinicians agreed that choosing a first-line treatment for advanced melanoma is a complex, multifactorial process and that clinical judgment remains the most important element of decision-making until research can provide clinicians with better scientific parameters and tools for first-line decision-making.

Overall Survival with Combined Nivolumab and Ipilimumab in Advanced Melanoma

BACKGROUND

Nivolumab combined with ipilimumab resulted in longer progression-free survival and a higher objective response rate than ipilimumab alone in a phase 3 trial involving patients with advanced melanoma. We now report 3-year overall survival outcomes in this trial.

METHODS

We randomly assigned, in a 1:1:1 ratio, patients with previously untreated advanced melanoma to receive nivolumab at a dose of 1 mg per kilogram of body weight plus ipilimumab at a dose of 3 mg per kilogram every 3 weeks for four doses, followed by nivolumab at a dose of 3 mg per kilogram every 2 weeks; nivolumab at a dose of 3 mg per kilogram every 2 weeks plus placebo; or ipilimumab at a dose of 3 mg per kilogram every 3 weeks for four doses plus placebo, until progression, the occurrence of unacceptable toxic effects, or withdrawal of consent. Randomization was stratified according to programmed death ligand 1 (PD-L1) status, BRAF mutation status, and metastasis stage. The two primary end points were progression-free survival and overall survival in the nivolumab-plus-ipilimumab group and in the nivolumab group versus the ipilimumab group.

RESULTS

At a minimum follow-up of 36 months, the median overall survival had not been reached in the nivolumab-plus-ipilimumab group and was 37.6 months in the nivolumab group, as compared with 19.9 months in the ipilimumab group (hazard ratio for death with nivolumab plus ipilimumab vs. ipilimumab, 0.55 [P<0.001]; hazard ratio for death with nivolumab vs. ipilimumab, 0.65 [P<0.001]). The overall survival rate at 3 years was 58% in the nivolumab-plus-ipilimumab group and 52% in the nivolumab group, as compared with 34% in the ipilimumab group. The safety profile was unchanged from the initial report. Treatment-related adverse events of grade 3 or 4 occurred in 59% of the patients in the nivolumab-plus-ipilimumab group, in 21% of those in the nivolumab group, and in 28% of those in the ipilimumab group.

CONCLUSIONS

Among patients with advanced melanoma, significantly longer overall survival occurred with combination therapy with nivolumab plus ipilimumab or with nivolumab alone than with ipilimumab alone. (Funded by Bristol-Myers Squibb and others; CheckMate 067 ClinicalTrials.gov number, NCT01844505 .).

Risk of second primary malignancies among 1537 melanoma patients and risk of second primary melanoma among 52 354 cancer patients in Northern Italy

BACKGROUND

The number of melanoma survivors has been increasing for decades due to early diagnosis and improved survival. These patients have an increased risk of developing a second primary cancer (SPC); also, melanoma is frequently diagnosed among patients firstly diagnosed with an extracutaneous malignancy.

OBJECTIVE

We evaluated the risk of developing a SPC among 1537 melanoma patients, and the risk of second primary melanoma (SPM) in 52 354 extracutaneous cancer patients, who were treated at the European Institute of Oncology in Milan, Italy, during 2000-2010.

MATERIAL AND METHODS

We calculated standardized incidence ratios (SIR) by applying gender-, age-, year- and region-specific reference rates to the follow-up time accrued between the diagnosis of the first and the second primary malignancies.

RESULTS

Seventy-six SPC were diagnosed during a median follow-up of 4 years, of which 49 (64%) during the first 2 years upon melanoma diagnosis. The SIR was increased for cancer of breast (4.10, 95% CI 2.79-6.03), thyroid (4.67, 95% CI 1.94-11.22), brain (6.13, 95% CI 2.30-16.33) and for non-Hodgkin lymphoma (3.12, 95% CI 1.30-7.50). During a median follow-up of 4 years, 127 SPM were diagnosed: thick lesions were less frequent than for melanoma diagnosed as first cancer. The SIR was increased for cancer of breast (5.13, 95%CI 3.91-6.73), thyroid (16.2, 95%CI: 5.22-50.2), head and neck (5.62, 95%CI 1.41-22.50), soft tissue (8.68, 95%CI 2.17-34.70), cervix (12.5, 95% CI 3.14-50.20), kidney (3.19, 95%CI 1.52-6.68), prostate (4.36, 95%CI 2.63-7.24) and acute myeloid leukaemia (6.44, 95%CI 2.42-17.20).

CONCLUSIONS

The most likely causes of these associations are the clustering of lifestyle risk factors in the same subgroups of population, mainly on a sociocultural basis and surveillance bias. This raises important questions about how to best follow cancer survivors by avoiding an inefficient use of resources and an excessive medicalization of these patients' lives.

Dabrafenib in metastatic melanoma: a monocentric 'real life' experience

Dabrafenib is a potent BRAF-kinase inhibitor. Its activity was evaluated on 40 consecutive metastatic melanoma patients (pts) harboring the V600BRAF mutations. Dabrafenib was administered orally at the dosage of 150 mg b.i.d. daily. ORR was 82%, with 7% CR, 62% PR, 13% SD and 18% PD. The median PFS and OS were seven and 17 months, respectively (median follow-up: 8.5 months). Increased risk of progression was found in pts with elevated LDH, ECOG PS >1 and more than two metastatic sites. Grade 3–4 adverse events were recorded in 4 pts. In this retrospective analysis, Dabrafenib confirmed its role as the standard clinical option in metastatic melanoma pts.

Ipilimumab retreatment in patients with pretreated advanced melanoma: the expanded access programme in Italy

BACKGROUND

Retreatment with ipilimumab has been shown to re-establish disease control in some patients with disease progression. Here, we report the efficacy and safety of retreatment with ipilimumab 3 mg kg(-1) among patients participating in an expanded access programme in Italy.

METHODS

Patients who achieved disease control during induction therapy were retreated with ipilimumab upon progression (3 mg kg(-1) every 3 weeks for up to four doses), providing they had not experienced toxicity that precluded further dosing. Tumour assessments were conducted after retreatment, and patients were monitored throughout for adverse events.

RESULTS

Of 855 patients treated with ipilimumab, 51 were retreated upon disease progression. Of these, 28 (55%) regained disease control upon retreatment and 42% were alive 2 years after the first induction dose of ipilimumab; median overall survival was 21 months. Eleven patients (22%) had a treatment-related adverse event of any grade during retreatment. These were generally mild-to-moderate and resolved within a median of 4 days. No new types of toxicity were reported.

CONCLUSIONS

For patients who meet predefined criteria, retreatment with ipilimumab is generally well tolerated and can translate into clinical benefit. This strategy should be compared with other therapeutic options in randomised controlled trials.

Newly identified tumor antigens as promising cancer vaccine targets for malignant melanoma treatment

Immunogenicity of tumour cells, immunomodulation and direct targeting of signalling pathways are promising avenues and matter of dated and innovative research in melanoma. Unfortunately, tumour cells are considered to be antigenic, but not immunogenic, either due to presentation of weakly recognized antigens or to the inability of the immune system to recognize them. However, spontaneous complete remission can be rarely observed in patients affected by melanoma, which are mainly attributed to the immune response against the tumour. Also, an elevated frequency of spontaneous humoral immune responses against tumour antigens was occasionally found in patients. These data confirm the existence of an interaction of the immune system with the tumour which can be used as a promising pathway for intervention and incorporates all portions of the immune system. The cancer immunotherapy approach is based on artificial activation of the immune system against the tumour and groups several types of treatments including immunization/vaccination but also modulation of immunity by cytokines or antibodies. Immunization approaches could either be based on undefined tumour antigens (e.g. whole tumour cells, tumour cell lysates, or tumour-antigen enriched fractions) or aimed at eliciting T-cell responses against specific tumour antigens. Novel and contemporary antigen-targeted therapy strategies, mainly directed to Cancer Testis and Heat Shock Proteins, leading to a possible active immunization against melanoma through T-cell specific activation, are discussed in this review.

Oncophage: step to the future for vaccine therapy in melanoma

Heat-shock proteins (HSPs) are a group of proteins whose expression is increased when the cells are exposed to elevated temperatures or other stressful conditions. This increase in expression is transcriptionally regulated. The function of HSPs is similar in virtually all living organisms, from bacteria to humans. Their expression also occur under non-stressful conditions, simply 'monitoring' the cell's proteins, i.e., they carry old proteins to the cell's 'recycling bin' and they help newly synthesized proteins fold properly. These activities are part of a cell's own repair system. HSPs are molecular chaperones for protein molecules. They are usually cytoplasmic proteins and they perform functions in various intracellular processes. Tumour-derived HSP-peptide complexes (HSPPCs) can be used for vaccination against malignancies. In particular, HSPPC-96 complex, called Vitespen (formerly Oncophage) is a HSPs-based vaccine made from individual patients' tumours with a promising role in cancer management. This vaccine has been extensively studied in Phase I and II clinical trials, showing activity on different malignancies, including gastric cancer, colorectal cancer, pancreatic cancer, non-Hodgkin's lymphoma and chronic myelogenous leukaemia. The vaccine has also been studied in Phase III clinical trials in melanoma and kidney cancer, showing an excellent safety profile with essentially no toxicity. Thus, HSP-based vaccines are a novel therapeutic approach with a promising role in cancer management.

Anti-CTLA4 monoclonal antibody Ipilimumab in the treatment of metastatic melanoma: recent findings

Use of monoclonal anti-CTLA4 antibodies represents a new promising strategy to block the activation of immunosuppressive CTLA-4 and thus induce tumour regression. This review is mainly focused on the report of existing data on the clinical use of Ipilimumab (formerly MDX-010) in the treatment of metastatic melanoma. Several phase I and II trials have been conducted to evaluate safety and efficacy of this form of immunotherapy either alone or in combination with vaccines or chemotherapy in patients with stage III or stage IV melanoma. Results from these studies are presented, patented and discussed. The mechanism of ipilimumab action may take time to induce an anti-tumour immune response and thus it is recommended that ipilimumab therapy should be carried out for at least 12 weeks, even in the presence of early progressive disease. Objective response of around 15% has been reported in patients treated with ipilimumab. However, ipilimumab-mediated objective response and stable disease tend to be durable. The therapy with ipilimumab is associated with different side effects classified as immune-related adverse events (IRAEs). The most common IRAEs are enterocolitis and dermatitis. Majority of IRAEs disappear with the discontinuation of ipilimumab anti-CTLA-4 therapy. Several phase II/III trials are ongoing to evaluate ipilimumab alone or in combination with other therapeutic modalities. Results from these trials are awaited.

Efficacy of 90Y ibritumomab-tiuxetan treatment in a case of resistant gastric MALT non-Hodgkin's lymphoma

Treatment modalities for resistant/relapsing gastric mucosa associated lymphoid tissue (MALT) non-Hodgkin's lymphoma (NHL) are not yet well standardized. In the past, most patients were treated surgically with a gastrectomy, while, more recently, radiotherapy and systemic approaches (chemotherapy and immunotherapy) have been used with improving results.Here, we report the case of a patient affected by MALT NHL resistant to antibiotics, chemotherapy and immunotherapy, who achieved a durable complete remission after radio-immunotherapy treatment with Zevalin ((90)Y ibritumomab-tiuxetan), administered in a single-standard dose. This observation must be confirmed on a larger series but suggests that radio-immunotherapy may be a valid approach in treating relapsing MALT NHL patients, or those resistant to conventional therapies, so avoiding more aggressive and toxic approaches.

A new comprehensive gene expression panel to study tumor micrometastasis in patients with high-risk breast cancer

The incidence and prognostic relevance of bone marrow (BM) and leukapheresis (PBPC) tumor cell contamination (TCC) in breast cancer patients is still to be circumstantiated. We developed a new comprehensive gene expression panel to study cytokeratins (CK), maspin (MAS) and mammaglobin (MAM) as possible predictors of prognosis. Forty-eight patients undergoing high dose chemotherapy (HDCT) and PBPC support were enrolled and analyzed for TCC on 116 PBPC apheresis and 96 BM obtained at basal conditions. All of the patients were evaluated by reverse transcriptase nested PCR (RT-PCR) for MAM and MAS gene expression and by immunocytochemistry (ICC) and nested RT-PCR to evaluate CK expression. PBPC and BM frequency of CK-positive (+) cells was 12-13% by ICC and 71-73% by RT-PCR respectively. Sixty-seven percent of CK ICC+ samples were MAM RT-PCR+ and 89% of them were MAS RT-PCR+. PBPC and BM frequency of MAM+ cells was 21% and 31% respectively, while for MAS+ cells it was 48% and 52% respectively by RT-PCR. After 71 mo median FU, 16 patients (33%) relapsed and 14 (88%) had BM/PBPC TCC. No marker had an impact on overall survival (OS) but MAS expression on BM and MAM expression on PBPC correlated with a statistically significant improved (p=0.05) and worsened RFS (p=0.06) respectively. These data confirm the activity of MAM as a negative prognostic factor and show for the first time that MAS could work as a tumor suppressor gene even in a clinical setting, since it protects from recurrence.

ACOD, a modified CHOP regimen for elderly patients with aggressive non-Hodgkin's lymphoma

The aim of this study is to verify the feasibility and the clinical activity of a new CHOP-like schedule (ACOD) with a fractionated days 1 and 8 administration in elderly patients. This regimen was chosen in the attempt to allow a sufficient dose intensity (DI) of each drug with better compliance. Fifty-two patients, (74 years, median age), with diffuse large B cell non-Hodgkin's lymphoma were retrospectively evaluated. Patients received ADM 25 mg/sqm, CTX 500 mg/sqm, VCR 1.2 mg/sqm (max 2 mg intravenously) days 1 and 8 and PDN 50 mg orally, days 1-8. Results showed that 54% of patients reached a complete remission, 21% a partial remission with an overall response rate of 75%. Two-thirds of the patients received at least 70% of the planned dose of cyclophosphamide and doxorubicin and 50% of vincristine and prednisone. The median duration of follow up was 12.6 months (range 0.7-61.4). The estimated median OS was 15.2 months (95%CI = [11.6, not estimable]); the estimated median PFS was 5.7 months (95%CI = [5.12, not estimable]). After 2 years, the proportion of patients alive was 47% (95%CI = 34-64%) and the proportion of patients free from progression was 39% (95%CI = 27-57%). Grade 3-4 leukopenia was observed in 61% of patients with 11% of febrile neutropenia. In conclusion, the ACOD chemotherapy regimen seems safe and feasible in elderly patients. This schedule allowed a sufficient DI of chemotherapic agents with clinical results very similar to those recorded with the standard CHOP regimen in young adults.

Thalidomide in multiple myeloma, myelodysplastic syndromes and histiocytosis. Analysis of clinical results and of surrogate angiogenesis markers

BACKGROUND

Thalidomide, as a single agent, has been recently found to induce a clinical response in one third of refractory or relapsed myeloma patients. Although it has been reported that thalidomide significantly inhibits angiogenesis. it is still unclear whether its clinical effect is mediated, at least in part, by its anti-angiogenic properties.

PATIENTS AND METHODS

We evaluated thalidomide as a single agent in myeloma, myelodysplastic syndromes (MDS) and histiocytosis, i.e. hematological diseases characterized by increased angiogenesis, and measured prospectively a number of surrogate angiogenesis markers.

RESULTS

Clinical responses were observed in 7 of 17 myeloma and 2 of 5 MDS patients. The histiocytosis patient had a partial response. At the time of the best clinical response, plasma levels of angiogenic growth factors, vascular endothelial growth factor (VEGF) and basic-fibroblast growth factor (b-FGF), were significantly decreased, and flow cytometry indicated a decrease of activated endothelial cells in the bone marrow of responding MDS patients.

CONCLUSIONS

These observations confirm thalidomide efficacy in myeloma, suggest a possible use in MDS and histiocytosis and may contribute to the prediction of clinical response and to understanding the mechanism of thalidomide's action.

Endostatin, an antiangiogenic drug, induces tumor stabilization after chemotherapy or anti-CD20 therapy in a NOD/SCID mouse model of human high-grade non-Hodgkin lymphoma

Both chemotherapy and chimeric anti-CD20 monoclonal antibodies are effective agents against B-cell non-Hodgkin lymphoma (NHL). However, patients achieving remission are at risk of relapse. To evaluate the effect of the antiangiogenic drug endostatin used alone and after the administration of cyclophosphamide (CTX) or the anti-CD20 antibody rituximab, we generated a new model of human NHL by transplanting Namalwa cells intraperitoneally into nonobese diabetic/severe combined immunodeficient (NOD/SCID) mice. First, we determined the most effective treatment schedule for the drugs assessed. When administered alone, CTX (3 courses of 75 mg/kg of body weight given intraperitoneally), rituximab (3 courses of 25 mg/kg given intraperitoneally), and endostatin (5 courses of 50 microg given subcutaneously) delayed tumor growth, and CTX was the most effective in controlling bulky disease. When given after chemotherapy or immunotherapy, endostatin effectively induced tumor stabilization. When mice given CTX or rituximab on days 3, 5, and 7 after transplantation were randomly assigned to receive endostatin or phosphate-buffered saline on days 15 to 19, tumor growth was prevented in endostatin-treated mice as long as the drug was administered. Furthermore, administration of endostatin on days 25 to 29 after tumor regrowth still induced significant tumor regression, whereas CTX and rituximab were not effective. The specific antiangiogenic action of endostatin was confirmed by in vitro and in vivo studies indicating that the drug inhibited proliferation and induced apoptosis of endothelial (but not of NHL) cells. In conclusion, sequential administration of chemotherapy and endostatin seems promising for treating bulky NHL, and the less toxic sequential administration of rituximab and endostatin is promising for treating limited disease. (

Idarubicinol myelotoxicity: a comparison of in vitro data with clinical outcome in patients treated with high-dose idarubicin

We evaluated in vitro the toxicity of idarubicin and its active metabolite idarubicinol on haematopoietic progenitors, using human umbilical cord blood and peripheral blood progenitors to obtain dose-response curves. We treated 16 patients with poor prognosis lymphoma in a phase I-II trial of high-dose idarubicin and melphalan and investigated if idarubicinol persisting in patients' plasma at the time of transplantation (day 0), on day +1 and +2 could result in an inhibition of infused progenitors. Colony inhibition was correlated with pharmacokinetic data and with the time of patients' engraftment. Plasma samples obtained before idarubicin treatment demonstrated a colony-stimulating effect, increasing the cloning efficiency by 72%. The inhibitory activity on colony forming unit granulocyte-macrophage (CFU-GM) of patients' plasma collected on the day of transplantation was lower than expected from dose-response curves (21% measured vs 70% expected). The time to patients' WBC and PLT recovery correlated with the amount of CD34+ cells reinfused and, to a lesser extent, with the colony-inhibiting effect of patients' plasma. The correlation between idarubicinol concentration and CFU-GM inhibition was not significant. These data suggest that plasma drug concentration on the day of stem cell reinfusion may overestimate the toxicity of residual anthracyclines to the transplanted cells.

Evaluation of acute toxicities associated with autologous peripheral blood progenitor cell reinfusion in patients undergoing high-dose chemotherapy

Peripheral blood progenitor cell reinfusion (PBPC) in patients undergoing high-dose chemotherapy (HDC) for poor prognosis malignancies, has been described as causing possible acute gastrointestinal (nausea, vomiting), allergic (oedema, bronchospasm, anaphyl- axis), renal (proteinuria, haematuria) and/or cardiovascular (hypotension, arrhythmia, conduction disturbances, transient ischaemic phenomena) toxicities. To establish the clinical relevance of these observations and the possible relationship with different HDC regimens used, we performed a clinical and instrumental evaluation on 33 patients with advanced breast cancer, non-Hodgkin's lymphoma, Hodgkin's disease, relapsed ovarian cancer, Ewing's sarcoma, extragonadal germinal tumour and small cell lung cancer. They underwent at least one reinfusion each for a total of 51 studied procedures. No patient had a previous history of cardiovascular disease or significant intercurrent illness such as diabetes or liver, renal or neurologic impairment. All patients had totally implanted central venous catheters, through which the transplants had been collected and reinfused without technical consequences. To evaluate cardiovascular function, we continuously monitored 12-lead ECGs, with arterial pressure (AP) measurements every 5 min from the beginning of the procedure to 15 min after the reinfusion ended. We did not observe any significant differences between basal and subsequent steps in AP, heart rate, PQ and QTc time, P wave and QRS complex duration or P wave and QRS electrical axes. No patient showed any ST-T tract pathological abnormality, but one patient developed a transient ectopic atrial rhythm, without any haemodynamic disfunction and with spontaneous reversion to sinus rhythm. No patient complained of symptoms of haemodynamic failure. Gastrointestinal side-effects appeared to be strictly related to speed of reinfusion and to the number of packs reinfused, probably reflecting on the amount of dimethylsulphoxide infused. In one patient a tonic-clonic seizure occurred during a vomiting episode, but no patient developed allergic or renal toxicities. We conclude that PBPC reinfusion, if managed according to the procedure we propose in patients without organic impairment, is a safe procedure not associated either with increased risk of acute arrhythmias or ischaemic or significant systemic acute toxicities. Bone Marrow Transplantation (2000) 25, 173-177.

Angiogenesis in myelodysplastic syndromes

It is now well established that solid tumour growth depends on angiogenesis. However, less is known about the generation of new vessels in haematological malignancies and, in particular, in preleukaemic-myelodysplastic syndromes (MDS). In this study, bone marrow microvessel density (MVD) was assessed by immunohistochemistry and compared in trephine biopsies from 14 controls, five infectious disease (ID), 82 MDS, 15 acute myeloid leukaemia (AML) and 14 myeloproliferative disorder (MPD) patients. Statistical analysis (P < 0.001) demonstrated that MDS MVD was higher than in controls and ID (21 +/- 9 vs 6 +/- 2 and 10 +/- 8 respectively) but lower than AML (30 +/- 12) and MPD (40 +/- 12). Among MDS-FAB subtypes, MVD was significantly higher in RAEB-t, CMML and fibrosis subsets compared to RA, RARS and RAEB subsets (P= 0.008). To further investigate angiogenesis machinery, the expression of vascular endothelial growth factor (VEGF) was evaluated by means of immunohistochemistry in control, MDS, AML and MPD biopsies. Even though VEGF mRNA expression was reported in the past in AML cell cultures and cell lines, in our samples VEGF expression was found to be particularly strong in most of the megakaryocytes but significantly less prominent in other cell populations including blasts. Since our findings suggest a correlation between angiogenesis and progression to leukaemia, additional work is now warranted to determine what regulates the generation of new vessels in MDS and leukaemia.

Angiogenic growth factors and endostatin in non-Hodgkin's lymphoma

A number of clinical studies have demonstrated the prognostic significance of angiogenesis and angiogenic growth factors in solid tumours; however, very little is known about the relevance of these parameters in haematological malignancies. We evaluated circulating levels of angiogenic growth factors and endostatin in 36 non-Hodgkin's lymphoma (NHL) patients. Baseline vascular endothelial growth factor (VEGF) levels of patients in complete remission (CR) after a median follow-up of 21 months were significantly lower than those of patients with progressive disease (P = 0.016). Event-free survival (EFS) rate was significantly higher in patients who had baseline VEGF and basic-fibroblast growth factor (b.FGF) levels below the median values of 147 and 19.5 pg/ml (P = 0.018 and 0.039 by log-rank test, respectively). Conversely, the levels of endostatin, angiogenin and leptin were not different in CR patients compared to relapsed patients and did not correlate with EFS. Our data suggest that b-FGF and, particularly, VEGF might be considered prognostic factors in NHL staging and management.

Totally implantable central venous access ports for high-dose chemotherapy administration and autologous stem cell transplantation: analysis of overall and septic complications in 68 cases using a single type of device

Sixty-eight patients suffering from breast cancer, ovarian cancer, lymphoma or multiple myeloma were treated with high-dose chemotherapy and autologous stem cell transplantation. They underwent placement of a central venous port via the subclavian vein for delivery of chemotherapy and reinfusion of stem cells. All patients were followed prospectively for device-related and overall complications, comprising a total of 18,213 days in situ (median: 267 days, range: 90-480). One patient experienced a pneumothorax (1.4%) spontaneously resolved, as an acute toxicity. Two patients (2.8%, 0.1 episodes/1000 days of use) were forced to have the port removed due to infection, caused by Streptococcus mitis in one case, while the causative agent was not identified by laboratory tests in the second. The other 66 patients completed the therapeutic programme, including peripheral stem cell reinfusions and supportive care, such as i.v. antibiotics, antiemetics or fluid administration and blood sample collection, without additional complications. In conclusion, the use of totally implantable central venous access ports has resulted in good long-term access to central veins, in spite of the severe neutropenia and increased septic risk of this category of oncology patients.

Caspases mediate retinoic acid-induced degradation of the acute promyelocytic leukemia PML/RARalpha fusion protein

All-trans-retinoic acid (RA) treatment induces morphological remission in acute promyelocytic leukemia (APL) patients carrying the t(15;17) and expressing the PML/RARalpha product by inducing terminal differentiation of the leukemic clone. RA treatment induces downregulation of PML/RARalpha and reorganization of the PML-nuclear bodies. These events have been proposed to be essential for the induction of APL cell differentiation by RA. Here, we show that in the APL-derived NB4 cell line as well as in myeloid precursor U937 cells expressing the PML/RARalpha (U937/PR9) and in blasts from APL patients, the PML/RARalpha fusion protein is cleaved by a caspase 3-like activity induced by RA treatment. In fact, a caspase 3-like activity is detectable in PML/RARalpha expressing cells after RA treatment, and selective caspase inhibitor peptides are able to prevent the RA-induced degradation of the fusion protein in vivo and in vitro. Using recombinant caspases and PML/RARalpha deletion mutants we mapped a caspase 3 cleavage site (Asp 522) within the alpha-helix region of the PML component of the fusion protein. The extent of PML/RARalpha cleavage directly correlates with the ability of RA to restore the normal PML nuclear bodies (NBs) pattern. However, RA-induced differentiation is not prevented by the persistence of the fusion product and occurs in the absence of normally structured PML NBs. These results indicate that PML/RARalpha is directly involved in conferring RA sensitivity of APL cells and that the RA-induced reassembly of PML NBs is the consequence of the disappearance of PML/RARalpha.

In vitro response to all-trans retinoic acid of acute promyelocytic leukemias with nonreciprocal PML/RARA or RARA/PML fusion genes

Acute promyelocytic leukemia (APL) is characterized by the t(15;17) cytogenetic abnormality leading to the expression of two fusion genes, PML/RARA and RARA/PML, and by its sensitivity to all-trans retinoic acid (ATRA) differentiating treatment. Rare APL cases lacking the t(15;17) have been described. We have previously reported two cases presenting with submicroscopic insertions of RARA or PML into chromosome 15 or 17, respectively. These insertions lead to the formation of potentially functional, nonreciprocal, PML/RARA or RARA/PML fusion genes, providing the unique opportunity to investigate in a human noncell-line model the respective role of PML/RARA or RARA/PML in retinoid signaling. Here, we report the in vitro response to ATRA of these two cases as well as of a third case presenting with submicroscopic insertion (15;17) and expressing exclusively PML/RARA, by morphological, functional, and immunological assays. The two cases expressing PML/RARA presented with an immunostaining pattern typical of APL and a positive response to ATRA, whereas the APL case expressing only a RARA/PML fusion transcript exhibited an immunostaining pattern typical of non-APL cells, and was resistant to ATRA. Our results confirm that sensitivity to ATRA requires expression of PML/RARA and strongly correlates with immunostaining, and demonstrate that expression of RARA/PML alone is sufficient for a cytological APL phenotype, but does not confer sensitivity to ATRA.

Cooperation between the RING + B1-B2 and coiled-coil domains of PML is necessary for its effects on cell survival

PML/RARalpha is the abnormal protein product of the Acute Promyelocytic Leukemia-specific 15;17 translocation. Both the PML and RARalpha components are required for the PML/RARalpha biological activities, namely its capacity to block differentiation and to increase survival of haematopoietic precursors. The physiological role of PML and its contribution to the function of the fusion protein are unknown. PML localizes to the cytoplasm and within specific nuclear bodies (NBs). In vitro, overexpression of PML correlates with suppression of cell transformation. The PML aminoterminal portion retained within the PML/RARalpha protein contains the RING finger, two newly defined cystein/histidine-rich motifs called B-boxes (B1 and B2) and a coiled-coil region. We report here that PML has a growth suppressive activity in all the cell lines tested, regardless of their transformed phenotype, and that the cellular basis for the PML growth suppression is induction of apoptotic cell death. Analysis of various nuclear and cytoplasmic PML isoforms showed that the PML growth suppressive activity correlates with its nuclear localization. Analysis of the localization and growth suppressive activity demonstrated that: (i) the Ring + B1-B2 and coiled-coil regions are both indispensable and sufficient to target PML to the NBs; (ii) individual deletions of the various PML domains have no effect on its growth suppressor activity; (iii) the Ring + B1-B2 region exerts a partial growth suppressor activity but its fusion with the coiled-coil region is sufficient to recapitulate the suppressive function of wild type PML. These results indicate that PML is involved in cell survival regulation and that the PML component of the fusion protein (Ring + B1-B2 and coiled-coil regions) retains intact biological activity, thereby suggesting that the effects of PML/RARalpha on survival derive from the activation of the incorporated PML sequence.

Cell death induction by the acute promyelocytic leukemia-specific PML/RARalpha fusion protein

PML/RARalpha is the abnormal protein product generated by the acute promyelocytic leukemia-specific t(15;17). Expression of PML/RARalpha in hematopoietic precursor cell lines induces block of differentiation and promotes survival. We report here that PML/RARalpha has a potent growth inhibitory effect on all nonhematopoietic cell lines and on the majority of the hematopoietic cell lines tested. Inducible expression of PML/RARalpha in fibroblasts demonstrated that the basis for the growth suppression is induction of cell death. Deletion of relevant promyelocytic leukemia (PML) and retinoic acid receptor (RARalpha) domains within the fusion protein revealed that its growth inhibitory effect depends on the integrity of the PML aminoterminal region (RING, B1, B2, and coiled coil regions) and the RARalpha DNA binding region. Analysis of the nuclear localization of the same PML/RARalpha deletion mutants by immunofluorescence and cell fractionation revealed that the biological activity of the fusion protein correlates with its microspeckled localization and its association to the nuclear matrix. The PML aminoterminal region, but not the RARalpha zinc fingers, is required for the proper nuclear localization of PML/RARalpha. We propose that the matrix-associated microspeckles are the active sites of PML/RARalpha and that targeting of RARalpha sequences to this specific nuclear subdomain through PML sequences is crucial to the activity of the fusion protein on survival regulation.

Opposite effects of the acute promyelocytic leukemia PML-retinoic acid receptor alpha (RAR alpha) and PLZF-RAR alpha fusion proteins on retinoic acid signalling

Fusion proteins involving the retinoic acid receptor alpha (RAR alpha) and the PML or PLZF nuclear protein are the genetic markers of acute promyelocytic leukemias (APLs). APLs with the PML-RAR alpha or the PLZF-RAR alpha fusion protein are phenotypically indistinguishable except that they differ in their sensitivity to retinoic acid (RA)-induced differentiation: PML-RAR alpha blasts are sensitive to RA and patients enter disease remission after RA treatment, while patients with PLZF-RAR alpha do not. We here report that (i) like PML-RAR alpha expression, PLZF-RAR alpha expression blocks terminal differentiation of hematopoietic precursor cell lines (U937 and HL-60) in response to different stimuli (vitamin D3, transforming growth factor beta1, and dimethyl sulfoxide); (ii) PML-RAR alpha, but not PLZF-RAR alpha, increases RA sensitivity of hematopoietic precursor cells and restores RA sensitivity of RA-resistant hematopoietic cells; (iii) PML-RAR alpha and PLZF-RAR alpha have similar RA binding affinities; and (iv) PML-RAR alpha enhances the RA response of RA target genes (those for RAR beta, RAR gamma, and transglutaminase type II [TGase]) in vivo, while PLZF-RAR alpha expression has either no effect (RAR beta) or an inhibitory activity (RAR gamma and type II TGase). These data demonstrate that PML-RAR alpha and PLZF-RAR alpha have similar (inhibitory) effects on RA-independent differentiation and opposite (stimulatory or inhibitory) effects on RA-dependent differentiation and that they behave in vivo as RA-dependent enhancers or inhibitors of RA-responsive genes, respectively. Their different activities on the RA signalling pathway might underlie the different responses of PML-RAR alpha and PLZF-RAR alpha APLs to RA treatment. The PLZF-RAR alpha fusion protein contains an approximately 120-amino-acid N-terminal motif (called the POZ domain), which is also found in a variety of zinc finger proteins and a group of poxvirus proteins and which mediates protein-protein interactions. Deletion of the PLZF POZ domain partially abrogated the inhibitory effect of PLZF-RAR alpha on RA-induced differentiation and on RA-mediated type II TGase up-regulation, suggesting that POZ-mediated protein interactions might be responsible for the inhibitory transcriptional activities of PLZF-RAR alpha.

Effects on differentiation by the promyelocytic leukemia PML/RARalpha protein depend on the fusion of the PML protein dimerization and RARalpha DNA binding domains

The block of terminal differentiation is a prominent feature of acute promyelocytic leukemia (APL) and its release by retinoic acid correlates with disease remission. Expression of the APL-specific PML/RARalpha fusion protein in hematopoietic precursor cell lines blocks terminal differentiation, suggesting that PML/ RARalpha may have the same activity in APL blasts. We expressed different PML/RARalpha mutants in U937 and TF-1 cells and demonstrated that the integrity of the PML protein dimerization and RARalpha DNA binding domains is crucial for the differentiation block induced by PML/RARalpha, and that these domains exert their functions only within the context of the fusion protein. Analysis of the in vivo dimerization and cell localization properties of the PML/RARalpha mutants revealed that PML/RARalpha--PML and PML/RARalpha--RXR heterodimers are not necessary for PML/RARalpha activity on differentiation. We propose that a crucial mechanism underlying PML/RARalpha oncogenic activity is the deregulation of a transcription factor, RARalpha, through its fusion with the dimerization interface of another nuclear protein, PML.

Characterization of a new monoclonal antibody (PG-M3) directed against the aminoterminal portion of the PML gene product: immunocytochemical evidence for high expression of PML proteins on activated macrophages, endothelial cells, and epithelia

PG-M3 is a new monoclonal antibody (MoAb) specifically directed against a peptide sequence located in the aminoterminal region of the human PML protein. PML gene fuses with the retinoic acid receptor alpha (RAR alpha) gene during the t(15; 17) chromosomal translocation of acute promyelocytic leukemia (APL). The epitope recognized by PG-M3 is species-specific and fixative-resistant and is shared by most PML isoforms and PML/RAR alpha fusion proteins. PML is consistently located within the nucleus, although a minority of cells (about 20%), both in vitro and in vivo, show positivity for PML also in the cytoplasm. The nuclear staining pattern of PG-M3 varies from speckled (cells other than APL) to micropunctate (APL cells). Although two physiologically expressed PML isoforms are detectable by immunocytochemistry only or predominantly in the cytoplasm of transfected cells, the cytoplasmic localization of PML is a property also shared by the PML isoforms that predominantly localize to the nuclei. Immunohistologic analysis of normal human tissues with the PG-M3 MoAb showed variable PML expression, with the highest levels of the protein in postmitotic, differentiated cell types, such as endothelial cells, epithelia, and tissue macrophages, especially activated ones. In keeping with this in vivo finding, PML appears strongly upregulated in the U937 promonocyte cell line after exposure to agents that induce monocyte/macrophage activation (interferon gamma) or maturation (vitamin D3 and transforming growth factor beta 1).

PML/RAR alpha+ U937 mutant and NB4 cell lines: retinoic acid restores the monocytic differentiation response to vitamin D3

We have analyzed the differentiation program of a U937 promonocytic leukemia clone transduced with the acute promyelocytic leukemia specific PML/RAR alpha fusion gene, the expression of which is under the control of the inducible metallothionine (MT) I promoter (MTPR9 clone). MTPR9 cells treated with Zn2+ hence exhibit levels of PML-RAR alpha protein as high as fresh acute promyelocytic leukemia blasts. In the absence of Zn2+, i.e., upon low level PML/RAR alpha expression, 1,25-dihydroxyvitamin D3 (D3) and particularly D3 plus transforming growth factor beta 1 (TGF-beta 1) induced terminal differentiation of MTPR9 cells (as observed in "wild-type" U937 cells), on the basis of morphology, membrane antigen pattern, and functional criteria. Conversely, in the presence of Zn2+, D3 and D3 plus TGF-beta 1 failed to induce terminal differentiation, as evaluated by the above parameters. Interestingly, retinoic acid (RA) treatment suppresses the differentiation blockade induced by high level PML-RAR alpha protein; indeed, Zn(2+)-treated MTPR9 cells incubated with RA plus D3 exhibited significant terminal monocytic maturation, comparable to that of cells treated with D3 alone or combined with RA in absence of Zn2+. Similar observations were made in NB4, a PML-RAR+ human acute leukemic line. As expected RA treatment of NB4 cells causes granulocytic differentiation. Interestingly, the cell line is only scarcely induced to mature monocytic cells by D3 or D3 plus TGF-beta 1 treatment, whereas it is effectively induced to monocytic maturation by combined treatment with D3 and RA. Accordingly, the rate of NB4 cell proliferation is only slightly affected by D3 or D3 plus TGF-beta 1 treatment, mildly inhibited by RA, and markedly decreased by D3 plus RA. These results indicate that in both U937 and NB4 cells high level PML/RAR alpha expression inhibits the monocytic terminal differentiation program triggered by D3 or D3 plus TGF-beta 1, whereas RA treatment effectively antagonizes this inhibitory PML-RAR alpha action and restores the D3 differentiative effect.

Effect of the acute promyelocytic leukemia PML/RAR alpha protein on differentiation and survival of myeloid precursors

Acute promyelocytic leukaemia is characterized by an expansion of haematopoietic precursors arrested at the promyelocytic stage (1). The differentiation block can be reversed by retinoic acid, which induces blast differentiation both in vitro (2) and in vivo (3-4). Acute promyelocytic leukaemia is also characterized by a 15;17 chromosome translocation (5) with breakpoints within the retinoic acid alpha receptor (RAR alpha) gene on 17 and within the PML gene, that encodes a putative transcription factor of unknown function (6-7), on 15 (8-10). As a consequence of the translocation a PML/RAR alpha gene is formed. It is transcriptionally active and encodes a PML/RAR alpha fusion protein detectable in all APL cases (11-14). We expressed the PML/RAR alpha protein in U937 myeloid precursor cell line and show that they: 1) lose the capacity to differentiate under the action of different stimuli (vitamin D3, transforming growth factor beta 1); ii) acquire enhanced sensitivity to retinoic acid; iii) exhibit a higher growth rate that is due to a reduction in apoptotic cell death. These results provide the first evidence of biological activity of PML/RAR alpha and recapitulate critical features of the promyelocytic leukemia phenotype.

The acute promyelocytic leukemia-specific PML-RAR alpha fusion protein inhibits differentiation and promotes survival of myeloid precursor cells

Acute promyelocytic leukemia is a clonal expansion of hematopoietic precursors blocked at the promyelocytic stage. The differentiation block can be reversed by retinoic acid, which induces blast maturation both in vitro and in vivo. Acute promyelocytic leukemia is characterized by a 15;17 chromosome translocation with breakpoints within the retinoic acid alpha receptor (RAR alpha) gene on 17 and the PML gene, which encodes a putative transcription factor, on 15. A PML-RAR alpha fusion protein is formed as a consequence of the translocation. We expressed the PML-RAR alpha protein in U937 myeloid precursor cells and showed that they lost the capacity to differentiate under the action of different stimuli (vitamin D3 and transforming growth factor beta 1), acquired enhanced sensitivity to retinoic acid, and exhibited a higher growth rate consequent to diminished apoptotic cell death. These results provide evidence of biological activity of PML-RAR alpha and recapitulate critical features of the promyelocytic leukemia phenotype.

The molecular genetics of acute promyelocytic leukemia

The chromosome breakpoints of the acute promyelocytic leukemia (APL)-specific 15;17 translocation have recently been isolated. They are localized on a previously unknown gene, PML, on chromosome 15 and in the gene that encodes the alpha retinoic acid receptor (RAR alpha) on 17. The translocation, which is balanced and reciprocal, leads to the formation of two fusion genes, PML/RAR alpha and RAR alpha/PML. Both are expressed in APL. The PML/RAR alpha gene codes for two abnormal proteins: the PML/RAR alpha fusion protein and an abnormal PML protein, the RAR alpha/PML gene encodes the RAR alpha/PML fusion protein. Experiments to investigate the biological activity of the abnormal translocation products are in progress. Preliminary results suggest that the PML/RAR alpha fusion protein is responsible for two important properties of the APL phenotype: the differentiation block characteristic of the leukemic blasts and the high sensitivity of the blasts to the differentiative action of retinoic acid (RA) both in vivo and in vitro. The mechanism through which PML/RAR alpha exerts its biological function remains unknown. However, there is accumulating evidence that it acts by interfering with normal endogenous pathways of both RAR alpha and PML. The RAR alpha receptor is implicated in regulating the myeloid differentiation induced by RA. Although the physiological function of PML is not known, it is probably a transcription factor. Definition of the molecular architecture of the t(15;17) has furnished further tools for: (1) molecular diagnosis of APL and (2) highly sensitive evaluation of the neoplastic clone during antileukaemic therapy. The molecular identification of residual APL disease after anti-leukaemia therapy allows patients at risk of relapse to be identified.