Novel therapeutic strategies for lymphoma: In vitro, overexpression of the mdr-1 gene product, P-glycoprotein (Pgp), in tumor cells can confer high level resistance to natural product derived cytotoxics- anthracyclines, vinca alkaloids, epipodophyllotoxins and taxanes. Miller et al reported that Pgp was detectable by immuno- histochemistry in 1/49 (2%) of untreated but was detectable in 6/8 (75%) treated lymphomas, suggesting that Pgp conferred drug resistance (1). To test this hypothesis, we developed and tested a mdr-1 reversal strategy in relapsed lymphomas using EPOCH (doxorubicin/vincristine/ etoposide over 96-hours days 1-4, prednisone daily days 1-5, cyclophosphamide bolus day 5) and dexverapamil. Based on our results showing EPOCH to be effective and well tolerated, we began a phase II study of EPOCH in previously untreated patients with aggressive lymphomas. In this study, EPOCH doses are escalated within patients to the maximum tolerated dose (MTD). Endpoints are dose- intensity, efficacy, toxicity and molecular markers of drug resistance. Early results show a high complete response rate of 89% with an EFS of 77% at 2 years median follow-up. Accrual continues to this trial. We have recently developed and tested a ?second generation? EPOCH regimen (EPOCH II) to replace stem cell transplant for lymphomas requiring high dose intensity including poor prognosis untreated aggressive lymphomas, potentially curable relapsed lymphomas and low-grade lymphomas. This regimen is based on experimental/clinical observations which suggest infusion schedules may improve the therapeutic index of natural product-derived cytotoxics, and that high dose alkylator therapy can overcome drug resistance in lymphoma. An important component is the study of immune modulation with IL-2 and peripheral blood stem cells (PBSC) on the generation of natural killer (NK) and lymphokine activated killer cells (LAK), immune recovery, and eradication of microscopic disease post-therapy (collaboration with Drs. Gress and Hakim). This approach is based on several lines of evidence (2-5): 1. T cells are largely eradicated by intensive chemotherapy; 2. Clinically relevant immune compromise is associated with T cell depletion; 3. T cell repopulation is accomplished through the thymus if the mature T cell population has been exposed to chemotherapy (but only after prolonged periods of time in older patients); 4. T cell repopulation pathways can be studied utilizing selected cell surface determinants and; 5. T cell repopulation can be influenced by cytokines, including IL-2 and IL-6. Additionally, in animal models, mature T cell precursors present in the PBSC can promote return of immunocompetence and possibly anti-tumor effects. Preliminary results show EPOCH II to have a response rate of 90% with 66% complete. Patients were able to tolerate 100% of the planned dose-intensity. IL-2 treatment acutely increased the CD4 cells, all within the CD4RO subset, and increased NK and LAK cells. However, this effect was not sustained after discontinuation of IL-2, and when long term immuno- reconstitution is compared between the IL-2 and non-IL-2 groups, there was not difference. In HIV-associated lymphomas, we are testing the efficacy and toxicity of EPOCH chemotherapy followed by interleukin-12. IL-12 is a TH1 cytokine which can stimulate conversions of a TH2 to TH1 phenotype in vitro. Furthermore, it has antitumor activity in murine models. We are also investigating the effect of chemotherapy on HIV plasma viral load and CD4 counts. We have had a long standing interest in lymphomatoid Granulomatosis, a EBV lymphoproliferative disorder which has similarity to post-transplant EBV LPDs. We are currently investigating the efficacy of alpha-interferon and EPOCH chemotherapy and assessing the immunological deficiency associated with this disorder. Examination of tumor tissues to assess potential mechanisms of drug resistance is an on going effort in our group. We have demonstrated the association of clinical drug resistance with p53 mutation and low roliferation rate in relapsed lymphomas. Currently, we are studying other novel cycle cycle proteins such as p27 in lymphomas. Recently, we have been interested in testing novel protein kinase inhibitors in lymphomas. One such inhibitor, UCN-01, has shown marked synergy with fludarabine in a variety of human cell lines. To further assess this drug, we will soon begin a phase I study of UCN-01 and fludarabine in patients with relapsed and refractory indolent lymphomas.
