Starting the fight in the tumor: expert recommendations for the development of human intratumoral immunotherapy (HIT-IT)

A European Society for Medical Oncology (ESMO)-sponsored expert meeting was held in Paris on 8 March 2018 which comprised 11 experts from academia, 11 experts from the pharmaceutical industry and 2 clinicians who were representatives of ESMO. The focus of the meeting was exclusively on the intratumoral injection/delivery of immunostimulatory agents with the aim of harmonizing the standard terms and methodologies used in the reporting of human intratumoral immunotherapy (HIT-IT) clinical trials to ensure quality assurance and avoid a blurring of the data reported from different studies. The goal was to provide a reference document, endorsed by the panel members that could provide guidance to clinical investigators, pharmaceutical companies, ethics committees, independent review boards, patient advocates and the regulatory authorities and promote an increase in the number and quality of HIT-IT clinical trials in the future. Particular emphasis was placed not only on the development of precise definitions to facilitate a better understanding between investigators but also on the importance of systematic serial biopsies as a driver for translational research and the need for the recording and reporting of data, to facilitate a better understanding of the key processes involved.

Acute toxicity and effectiveness of idarubicin in childhood acute lymphoblastic leukemia

Anthracyclines have become important components of multi-agent remission induction and continuation therapy of acute lymphoblastic leukemia (ALL). New anthracycline derivatives are being investigated in an attempt to shift the balance of side effects and antileukemic potency. To evaluate the toxicity and efficacy of idarubicin (IDA) in childhood ALL, a prospective multicenter phase-II study was performed. A total of 51 children with prognostically poor recurrences of ALL were enrolled, all of whom had been exposed to anthracyclines during front-line treatment. A single 48-h continuous infusion of IDA at 24 mg/m2 was started on the first day of salvage treatment without concomitant systemic cytostatic agents. The response was assessed by reduction of leukemic blasts in the bone marrow and other compartments 2 wk later. IDA monotherapy caused complete and partial remissions in 5 and 20 patients, respectively (49%). Delays of treatment with subsequent polychemotherapy courses were frequent and mainly caused by prolonged intervals of myelosuppression and high rates of systemic infection. Non-hematological toxicities including acute cardiac reactions were transient and moderate. Our findings suggest that IDA is an effective drug for remission induction in children with ALL, with acute hematological toxicity being dose-limiting.

In vitro resistance to cytosine arabinoside, not to daunorubicin, is associated with the risk of relapse in de novo acute myeloid leukaemia

The efficacy of chemotherapy in acute myeloid leukaemia (AML) is limited by clinical drug resistance. We determined in vitro resistance to cytosine arabinoside (ARAC), daunorubicin (DNR), mitoxantrone (MITOX), m-amsacrine (AMSA) and etoposide (VP16) in 49 adults with de novo AML using the MTT assay. Results showed that nonresponders to chemotherapy were, in vitro, 2.9-fold more resistant to DNR, but not more resistant to ARA-C, compared to complete responders. However, complete responders who were in vitro resistant to ARA-C had a 4-fold higher risk of relapse (95% CI 1.3-12.5-fold) compared to complete responders in vitro sensitive to ARA-C. With a mean follow-up of 12 months the probability of continuous complete remission (CCR) for patients in vitro sensitive to ARA-C was 61% at 34 months (95% CI 28-82%), whereas all patients in vitro resistant to ARA-C relapsed within 18 months from diagnosis. This difference appeared to be independent of other clinical features such as sex, age, white blood cell count, FAB classification, and CD34 expression. In vitro resistance to DNR was not related to the probability of CCR. We conclude that in vitro drug resistance assessed with the MTT assay appears to be associated with short- and long-term clinical outcome in AML. Confirmatory studies comprising a sufficient number of patients for multivariate analyses should prove whether in vitro resistance to ARA-C will appear to be an independent risk factor.

In vitro cellular drug resistance in children with relapsed/refractory acute lymphoblastic leukemia

Cellular drug resistance is thought to be an important cause of the poor prognosis for children with relapsed or refractory acute lymphoblastic leukemia (ALL), but it is unknown when, to which drugs, and to what extent resistance is present. We determined in vitro resistance to 13 drugs with the MTT assay. Compared with 141 children with initial ALL, cells from 137 children with relapsed ALL were significantly more resistant to glucocorticoids, L-asparaginase, anthracyclines, and thiopurines, but not to vinca-alkaloids, cytarabine, ifosfamide, and epipodophyllotoxins. Relapsed ALL cells expressed the highest level of resistance to glucocorticoids, with a median level 357- and >24-fold more resistant to prednisolone and dexamethasone, respectively, than initial ALL cells, whereas the resistance ratios for the other drugs differed from 0.8- to 1.9-fold, intraindividual comparisons between initial and relapsed samples from 16 children with ALL showed that both de novo and acquired drug resistance were involved. Specific in vitro drug-resistance profiles were associated with high-risk relapsed ALL groups. In vitro drug resistance was also related to the clinical response to chemotherapy in relapsed/refractory childhood ALL. We conclude that drug resistance may explain the poor prognosis for children with relapsed/refractory ALL. These day may be helpful to design alternative treatment regimens for relapsed childhood ALL.

In vitro chemosensitivity assessed with the MTT assay in childhood acute non-lymphoblastic leukemia

Cellular drug resistance is supposed to play a major role in chemotherapy failures which frequently occur in childhood acute non-lymphoblastic leukemia (ANLL). Therefore, we determined in vitro chemosensitivity to daunorubicin, doxorubicin, mitoxantrone, 6-thioguanine, etoposide, and cytosine arabinoside (Ara-C) in childhood ANLL using the colorimetric MTT assay. The 4-day MTT assay was successfully performed in 62/73 samples obtained from 53 children with ANLL. We obtained comparable results from bone marrow or peripheral blood samples, and from fresh or cryopreserved samples. In vitro chemosensitivity was not related to clinical features such as sex, age, white blood cell count, or FAB-types. The group of poor responders to chemotherapy was median 3-fold more resistant to Ara-C than the group of good responders, but identification of a threshold for Ara-C sensitivity predictive for individual responses was limited due to the great overlap of in vitro chemosensitivities between both groups. Children with relapsed ANLL were in vitro median 3-fold more resistant to Ara-C than the initial ANLL group. No significant differences for the other drugs were observed with respect to clinical response or disease status. These results suggest that in vitro resistance to Ara-C plays an important role in chemotherapy failures in childhood ANLL, but larger studies are necessary to establish the predictive value of Ara-C sensitivity assessed with the MTT assay.

Topoisomerase II alpha gene expression in childhood acute lymphoblastic leukemia

Previously, we showed that in vitro resistance to daunorubicin (DNR) at initial diagnosis was related to a poor long-term clinical outcome in childhood acute lymphoblastic leukemia (ALL), and that cells of relapsed ALL were in vitro more resistant to DNR than cells of untreated ALL. Topoisomerase II (Topo II) is an intracellular target for anthracyclines and epipodophyllotoxins. Decreased levels and/or activity of Topo II have been associated with multidrug resistance in cell lines. We investigated Topo II alpha gene expression in fresh leukemic samples from 19 children with untreated and 14 children with relapsed ALL using a sensitive RNase protection assay. The in vitro cytotoxicity of the Topo II inhibitors DNA and teniposide (VM26) was measured using the MTT assay, and the cell cycle distribution of leukemic samples was analyzed by DNA flow cytometry. Results showed that (1) relapsed ALL samples were more resistant to DNR, but not to VM26 compared to untreated samples; (2) large interpatient variations existed in both Topo II alpha gene expression and in vitro cytotoxicity results; (3) Topo II alpha gene expression was detectable in 29/33 childhood ALL samples with a median expression of 5% the level of a relatively chemosensitive human small cell lung cancer cell line; (4) Topo II alpha gene expression did not differ between untreated and relapsed ALL; (5) Topo II alpha gene expression was positively correlated with the percentage of ALL cells in S- and G2M-phase, but not with the in vitro cytotoxicity of the drugs tested. In conclusion, resistance to DNR in childhood ALL can not be explained by decreased levels of Topo II alpha gene expression, but additional Topo II activity studies in fresh leukemia samples may need further exploration.

In vitro anthracycline cross-resistance pattern in childhood acute lymphoblastic leukaemia

Daunorubicin (DNR) is a major front-line drug in the treatment of childhood acute lymphoblastic leukaemia (ALL). Previously, we showed that in vitro resistance to DNR at diagnosis is related to a poor long-term clinical outcome in childhood ALL and that relapsed ALL samples are more resistant to DNR than untreated ALL samples. In cell line studies, idarubicin (IDR), aclarubicin (ACR) and mitoxantrone (MIT) showed a (partial) lack of cross-resistance to the conventional anthracyclines DNR and doxorubicin (DOX), but clinical studies in childhood ALL have been inconclusive about the suggested lack of cross-resistance. In the present study we determined the in vitro cross-resistance pattern between DNR, DOX, IDR, ACR and MIT in 48 untreated and 39 relapsed samples from children with ALL using the MTT assay. The relapsed ALL group was about twice as resistant to DNR, DOX, IDR, ACR and MTT as the untreated ALL group. Thus, resistance developed to all five drugs. We found a significant cross-resistance between DNR, DOX, IDR, ACR and MIT, although in some individual cases in vitro anthracycline cross-resistance was less pronounced. We conclude that IDR, ACR and MIT cannot circumvent in vitro resistance to DNR in childhood ALL. Clinical studies may still prove whether IDR, ACR or MIT has a more favourable toxicity profile than DNR.

Functional multidrug resistance phenotype associated with combined overexpression of Pgp/MDR1 and MRP together with 1-beta-D-arabinofuranosylcytosine sensitivity may predict clinical response in acute myeloid leukemia

Overexpression of P-glycoprotein (Pgp) or MDR1 mRNA has been shown to be a negative prognostic factor for clinical outcome in acute myeloid leukemia (AML). However, resistance to chemotherapy also occurs in the absence of Pgp overexpression. Therefore, besides Pgp expression, we have assessed the expression of MRP, a novel drug transporter gene, along with the functional multidrug-resistant (MDR) phenotype of leukemic cells. These MDR parameters are correlated with clinical outcome in individual patients. We found functional changes in fresh leukemic cells from de novo or relapsed patients similar to those reported for tumor cell lines with the MDR phenotype. These changes were reduced drug accumulation as assessed with radiolabeled doxorubicin (factor 1.6), daunomycin (factor 1.13), and vincristine (factor 1.6) in patients who were refractory to the combination treatment of 1-beta-D-arabinofuranosylcytosine (ara-C) and daunomycin or mitoxantrone as opposed to patients who had complete responses. Also, the intracellular distribution of doxorubicin fluorescence (nuclear/cytoplasmic ratio), as assessed with laser scan microscopy, was reduced 1.4-fold in blasts from refractory patients. Based on historically known clinical response to single-agent daunomycin or ara-C in the group of responding de novo AML patients, we have set a threshold level such that a defined part of the samples that had the highest drug accumulation or nuclear to cytoplasmic ratios were above this threshold value. This allowed discrimination between patients responding to daunomycin from those who were refractory to this drug. By using this threshold level, in the refractory group clinical resistance corresponded with high sensitivity with a resistant phenotype. A similar threshold was set for the data of the in vitro ara-C sensitivity test. By combining both assays for all individual patients, clinical refractoriness as well as sensitivity could be predicted with high accuracy. There appeared to be no stringent relationship between the functional MDR phenotype with expression of either Pgp (fluorescence-activated cell sorting analysis) or MRP mRNA (RNase protection). However, by combining both parameters the functional MDR phenotype correlated with the overexpression of either one or both of the parameters in 94% of the samples studied. It is concluded that this combined overexpression in conjunction with functional changes for MDR drugs and ara-C reveal a correlation of MDR phenotype with clinical resistance to combination chemotherapy in AML patients and hereby may adequately predict clinical MDR in individual AML patients.

Different cellular drug resistance profiles in childhood lymphoblastic and non-lymphoblastic leukemia: a preliminary report

The better prognosis of acute lymphoblastic leukemia (ALL) than of acute non-lymphoblastic leukemia (ANLL) in children, and the often observed better prognosis of myeloid-antigen (MyAg) negative ALL than of MyAg-positive ALL, may be related to differences in cellular drug resistance. We therefore compared the resistance to 12 drugs of 125 ALL and 28 ANLL samples with the MTT assay. ALL samples were median > 75-fold more sensitive to the glucocorticoids prednisolone and dexamethasone (p < 0.00001), and 2-fold more sensitive to vincristine (p = 0.05) than ANLL samples. Differences for the other drugs were not significant. MyAg-negative ALL samples were more sensitive to glucocorticoids than MyAg-positive ALL-samples (p < or = 0.04). Prednisolone, and dexamethasone if tested, had a stimulatory effect on leukemic cell survival in 36% of ANLL, but in only 2% of ALL samples (p < 0.0001). Vincristine, and vindesine if tested, had a similar effect in 11% of ANLL, and in 4% of ALL samples (p = 0.11). We conclude that the more favorable response of ALL against ANLL to combination chemotherapy in children may be explained by the higher antileukemic activity of glucocorticoids and of vincristine in ALL, while none of the drugs was more active in ANLL. Similarly, the better prognosis of MyAg-negative ALL than of MyAg-positive ALL may be explained by a relative sensitivity to glucocorticoids. Glucocorticoids and vinca-alkaloids induced leukemia cell proliferation in part of the samples, most frequently in ANLL. The findings may be useful in the design of new chemotherapeutic regimens for ALL and ANLL.

Glucocorticoid resistance in childhood leukemia

Glucocorticoids (GC) are being used in the treatment of childhood leukemia for several decades, most successfully in newly diagnosed acute lymphoblastic leukemia (ALL). However, GC resistance is seen in 10-30% of untreated ALL patients, and is much more frequent in relapsed ALL and in acute nonlymphoblastic leukemia (ANLL). Sensitivity or resistance to GC can be measured using a cell culture drug resistance assay. For this purpose, we use the colorimetric methyl-thiazol-tetrazolium (MTT) assay. We have shown that GC resistance in childhood leukemia is related to clinical and cell biological features, and to the clinical outcome after multi-drug chemotherapy. These results are summarized in this review. In addition, we describe the apoptotic 'cell-lysis pathway' by which GC exert their antileukemic activity. This description provides a model to discuss the mechanisms of GC resistance, and to summarize the relevant literature. Possible levels of resistance relate to the diffusion of GC through the cell membrane, binding to the GC receptor (GCR), activation of the GC-GCR complex, translocation of the complex into the nucleus, binding to DNA, endonuclease-mediated DNA fragmentation, and DNA repair. A low number of GCR has been shown to be the cause of resistance in some children with ALL. However, GC resistance is likely to be caused at the post-receptor level in most leukemias. Unfortunately, there is still a lack of knowledge relating to the clinical relevance of mechanisms of GC resistance at the post-receptor level. Studies on the mechanisms of GC resistance other than those directly related to the GCR should be initiated, especially if patient material is used, as the results might indicate ways to circumvent or modulate GC resistance. A further increase in our knowledge regarding the relation between GC resistance and patient and cell biological features, the clinical relevance of GC resistance, and the mechanisms of GC resistance in leukemia patients, may contribute to further improvement in the results of GC therapy in leukemia.

In vitro cytotoxicity of mitoxantrone, daunorubicin and doxorubicin in untreated childhood acute leukemia

Mitoxantrone (MIT) has not been studied as a single agent in children with untreated leukemia. The antileukemic activity of MIT in these patients and its activity in relation to clinical and cell biological features is unknown. We studied the in vitro cytotoxicity of MIT, daunorubicin (DNR) and doxorubicin (DOX) in untreated childhood acute lymphoblastic leukemia (ALL, n = 131) and acute nonlymphoblastic leukemia (ANLL, n = 20) samples, using the MTT assay. There were marked interindividual differences in resistance to all three drugs. A strong, significant cross-resistance was found in ALL between MIT, DNR and DOX. All samples of the T-lineage, a prognostically unfavorable immunophenotype, however, were significantly more resistant to DNR and DOX, but not to MIT, than common or pre-B ALL samples. ALL cells from children with a prognostically unfavorable age at diagnosis, especially those < 2 years, showed a relative resistance to all three drugs compared to the intermediate age-group. This was found within all patients, but also within the common or pre-B ALL cases only. Sex, white blood cell count, or FAB type was not related to in vitro drug resistance. None of the three drugs showed an overall preferential activity in ALL or ANLL. We conclude that the in vitro antileukemic activity of MIT, DNR and DOX is related to certain clinical and cell biological features. There were no major differences between the three drugs in antileukemic activity, except that T-ALL samples were more resistant than common or pre-B ALL samples to DNR and DOX, while MIT was equally active in these two immunophenotypes.

Clinical relevance of in vitro drug resistance testing in childhood acute lymphoblastic leukemia: the state of the art

Nowadays about two-thirds of children with acute lymphoblastic leukemia (ALL) can be cured with chemotherapy, but one-third die from the disease. The clinical response of leukemic cells to chemotherapy is roughly due to two factors: the effective drug levels reaching the cells and the resistance of these cells to the drugs. The clinical value of cellular drug resistance in children with ALL is not known. We developed an in vitro assay to study drug resistance in these children. In this article, the main results obtained with this MTT assay on samples from 137 children with ALL are summarized: (1) patients whose cells are resistant to several drugs at initial diagnosis have a poor prognosis; (2) relapsed leukemias show a considerable drug resistance which might partly explain the poor prognosis. Relapsed cases differ in their type and degree of resistance; (3) the poor outcome of high risk groups as defined by age and immunophenotype can partly be explained by specific patterns of drug resistance; (4) P-glycoprotein-mediated multidrug resistance is not an important cause of resistance in childhood ALL; and (5) no relation exists between the activities of the purine enzymes HGPRT, 5'NT, ADA, and PNP and drug resistance in childhood ALL. The conclusion is that in vitro drug resistance data have clinical relevance and can be used to develop more effective and less toxic treatment strategies in childhood ALL.

[The treatment of recurrence in children with acute lymphatic leukemia. Current results and various developments]

The results of current treatment of relapsed childhood acute lymphoblastic leukemia (ALL) are discussed, together with some recent developments which (might) influence such treatment. At present more than 95% of children with ALL will achieve a complete remission (CR), and +/- 70% will remain in CR. Nevertheless, 20-30% of the patients suffer a relapse, which implies a less favorable prognosis. However, after intensive treatment a part of these patients will have a prolonged second complete remission: 30-50% of children with a late relapse and 0-20% of children with an early relapse. It is important to prevent the occurrence of a relapse. The identification at diagnosis of patients at high risk for a relapse, and a subsequent more specific and more intensive treatment of these patients might contribute to that goal. Well-known risk factors are briefly mentioned, factors of which the prognostic significances is therapy-dependent. In addition, the treatment of relapsed ALL needs further improvement. Some alternatives to achieve this goal are discussed, including the role of in vitro cytostatic drug resistance testing.