Modulation of chemotherapy resistance in regional therapy: a novel therapeutic approach to advanced extremity melanoma using intra-arterial temozolomide in combination with systemic O6-benzylguanine

Novel Imidazotetrazine Evades Known Resistance Mechanisms and Is Effective against Temozolomide-Resistant Brain Cancer in Cell Culture

Glioblastoma (GBM) is the most lethal primary brain tumor. Currently, frontline treatment for primary GBM includes the DNA-methylating drug temozolomide (TMZ, of the imidazotetrazine class), while the optimal treatment for recurrent GBM remains under investigation. Despite its widespread use, a majority of GBM patients do not respond to TMZ therapy; expression of the O⁶-methylguanine DNA methyltransferase (MGMT) enzyme and loss of mismatch repair (MMR) function as the principal clinical modes of resistance to TMZ. Here, we describe a novel imidazotetrazine designed to evade resistance by MGMT while retaining suitable hydrolytic stability, allowing for effective prodrug activation and biodistribution. This dual-substituted compound, called CPZ, exhibits activity against cancer cells irrespective of MGMT expression and MMR status. CPZ has greater blood-brain barrier penetrance and comparable hematological toxicity relative to TMZ, while also matching its maximum tolerated dose in mice when dosed once-per-day over five days. The activity of CPZ is independent of the two principal mechanisms suppressing the effectiveness of TMZ, making it a promising new candidate for the treatment of GBM, especially those that are TMZ-resistant.

p38 MAPK-dependent Nrf2 induction enhances the resistance of glioma cells against TMZ

Temozolomide (TMZ) is an effective agent for clinical glioma treatment, but the innate and acquired resistance of glioma always limits its application. Although some advances have been achieved to elucidate the molecular mechanism underlying TMZ resistance, the role of Nrf2 (a principle regulator of cellular defense against drugs and oxidative stress) has not been well established in the acquisition of this phenotype. Our data showed that TMZ treatment induces the activation of Nrf2 and p38 MAPK signaling in glioma cells, while p38 inhibition abolished the effect of TMZ on Nrf2. Further study revealed that Nrf2 silencing was able to enhance the response of glioma cells to TMZ. Additionally, Nrf2 overexpression overrides the effect of p38 MAPK activation on Temozolomide resistance. In conclusions, we identified a p38 MAPK/Nrf2 signaling as a key molecular network contributing to TMZ resistance of glioma, and provided evidence that suppressing this signaling may be a promising strategy to improve TMZ's therapeutic efficiency.

Regional therapies for in-transit disease

In-transit melanoma is an uncommon pattern of recurrence, but presents unique management challenges and opportunities for treatment. The clinical presentation usually involves from 1 to more than 100 small subcutaneous or cutaneous nodules, ranging from submillimeter to multiple centimeters in diameter. Regional chemotherapy techniques are a mainstay of treatment of patients without systemic disease spread. Future applications of regional therapy are likely to involve combination therapy with cytotoxic agents and novel immune modulators. Regional therapy provides distinct opportunities for the treatment of unresectable disease, and offers a unique platform for investigation of novel therapeutics in early-stage clinical trials.

Tamoxifen in combination with temozolomide induce a synergistic inhibition of PKC-pan in GBM cell lines

BACKGROUND

Glioblastoma (GBM) is a highly proliferative, angiogenic grade IV astrocytoma that develops resistance to the alkylating agents used in chemotherapy, such as temozolomide (TMZ), which is considered the gold standard. The mean survival time for GBM patients is approximately 12 months, increasing to 14.6 months after TMZ treatment. The resistance of GBM to chemotherapy seems to be associated to genetic alterations and to the constitutive activation of several signaling pathways. Therefore, the combination of different drugs with different mechanisms of action may contribute to circumvent the chemoresistance of glioma cells. Here we describe the potential synergistic behavior of the therapeutic combination of tamoxifen (TMX), a known inhibitor of PKC, and TMZ in GBM.

METHODS

We used two GBM cell lines incubated in absence and presence of TMX and/or TMZ and measured cell viability, proliferation, apoptosis, cell cycle, migration ability, cytoskeletal organization and the phosphorylated amount of the p-PKC-pan.

RESULTS

The combination of low doses of TMX with increasing doses of TMZ shows an increased antiproliferative and apoptotic effect compared to the effect with TMX alone.

CONCLUSIONS

The combination of TMX and TMZ seems to potentiate the effect of each other. These alterations seem to be associated to a decrease in the phosphorylation status of PKC.

GENERAL SIGNIFICANCE

We emphasize that TMX is an inhibitor of the p-PKC-pan and that these combination is more effective in the reduction of proliferation and in the increase of apoptosis than each drug alone, which presents a new therapeutic strategy in GBM treatment.

Cool-1-mediated inhibition of c-Cbl modulates multiple critical properties of glioblastomas, including the ability to generate tumors in vivo

We discovered that glioblastoma (GBM) cells use Cool-1/β-pix to inhibit normal activation of the c-Cbl ubiquitin ligase via the redox/Fyn/c-Cbl pathway and that c-Cbl inhibition is critical for GBM cell function. Restoring normal c-Cbl activity by Cool-1 knockdown in vitro reduced GBM cell division, almost eliminated generation of adhesion-independent spheroids, reduced the representation of cells expressing antigens thought to identify tumor initiating cells (TICs), reduced levels of several proteins of critical importance in TIC function (such as Notch-1 and Sox2), and increased sensitivity to BCNU (carmustine) and temozolomide (TMZ). In vivo, Cool-1 knockdown greatly suppressed the ability of GBM cells to generate tumors, an outcome that was c-Cbl dependent. In contrast, Cool-1 knockdown did not reduce division or increase BCNU or TMZ sensitivity in primary glial progenitor cells and Cool-1/c-Cbl complexes were not found in normal brain tissue. Our studies provide the first evidence that Cool-1 may be critical in the biology of human tumors, that suppression of c-Cbl by Cool-1 may be critical for generation of at least a subset of GBMs and offer a novel target that appears to be selectively necessary for TIC function and modulates chemoresistance in GBM cells. Targeting such proteins that inhibit c-Cbl offers potentially attractive opportunities for therapeutic development.

A multicenter phase I dose escalation trial to evaluate safety and tolerability of intra-arterial temozolomide for patients with advanced extremity melanoma using normothermic isolated limb infusion

BACKGROUND

L-phenylalanine mustard (LPAM) has been the standard for use in regional chemotherapy (RC) for unresectable in-transit melanoma. Preclinical data demonstrated that regional temozolomide (TMZ) may be more effective.

METHODS

Patients with AJCC Stage IIIB or IIIC extremity melanoma who failed previous LPAM-based RC were treated with TMZ via isolated limb infusion (ILI) according to a modified accelerated titration design. Drug pharmacokinetic (PK) analysis, tumor gene expression, methylation status of the O6-methylguanine methyltransferase (MGMT) promoter, and MGMT expression were evaluated. Primary objectives were to (1) determine dose-limiting toxicities (DLTs) and maximum tolerated dose (MTD) of TMZ via ILI and (2) explore biomarker correlates of response.

RESULTS

28 patients completed treatment over 2.5 years at 3 institutions. 19 patients were treated at the MTD defined as 3,200 mg/m(2) [multiplied by 0.09 (arm), 0.18 (leg)]. Two of five patients had DLTs at the 3,600 mg/m(2) level while only grade 1 (n = 15) and grade 2 (n = 4) clinical toxicities occurred at the MTD. At 3-month post-ILI, 10.5 % (2/19) had CR, 5.3 % (1/19) had PR, 15.8 % (3/19) had SD, and 68.4 % (13/19) had PD. Neither PK parameters of TMZ nor MGMT levels were associated with response or toxicity.

CONCLUSION

In this first ever use of intra-arterial TMZ in ILI for melanoma, the MTD was determined. While we could not define a marker for TMZ response, the minimal toxicity of TMZ ILI may allow for repeated treatments to increase the response rate as well as clarify the role of MGMT expression.

A patient-specific therapeutic approach for tumour cell population extinction and drug toxicity reduction using control systems-based dose-profile design

BACKGROUND

When anti-tumour therapy is administered to a tumour-host environment, an asymptotic tapering extremity of the tumour cell distribution is noticed. This extremity harbors a small number of residual tumour cells that later lead to secondary malignances. Thus, a method is needed that would enable the malignant population to be completely eliminated within a desired time-frame, negating the possibility of recurrence and drug-induced toxicity.

METHODS

In this study, we delineate a computational procedure using the inverse input-reconstruction approach to calculate the unknown drug stimulus input, when one desires a known output tissue-response (full tumour cell elimination, no excess toxicity). The asymptotic extremity is taken care of using a bias shift of tumour-cell distribution and guided control of drug administration, with toxicity limits enforced, during mutually-synchronized chemotherapy (as Temozolomide) and immunotherapy (Interleukin-2 and Cytotoxic T-lymphocyte).

RESULTS

Quantitative modeling is done using representative characteristics of rapidly and slowly-growing tumours. Both were fully eliminated within 2 months with checks for recurrence and toxicity over a two-year time-line. The dose-time profile of the therapeutic agents has similar features across tumours: biphasic (lymphocytes), monophasic (chemotherapy) and stationary (interleukin), with terminal pulses of the three agents together ensuring elimination of all malignant cells. The model is then justified with clinical case studies and animal models of different neurooncological tumours like glioma, meningioma and glioblastoma.

CONCLUSION

The conflicting oncological objectives of tumour-cell extinction and host protection can be simultaneously accommodated using the techniques of drug input reconstruction by enforcing a bias shift and guided control over the drug dose-time profile. For translational applicability, the procedure can be adapted to accommodate varying patient parameters, and for corrective clinical monitoring, to implement full tumour extinction, while maintaining the health profile of the patient.

SRC family kinase inhibition as a novel strategy to augment melphalan-based regional chemotherapy of advanced extremity melanoma

BACKGROUND

Src kinase inhibition has been shown to augment the efficacy of chemotherapy. Dasatinib, a dual Src/Abl kinase inhibitor approved for the treatment of CML, is under investigation as monotherapy for tumors with abnormal Src signaling, such as melanoma. The goal of this study was to determine if Src kinase inhibition using dasatinib could enhance the efficacy of regionally administered melphalan in advanced extremity melanoma.

METHODS

The mutational status of c-kit and patterns of gene expression predictive of dysregulated Src kinase signaling were evaluated in a panel of 26 human melanoma cell lines. The effectiveness of dasatinib was measured by quantifying protein expression and activation of Src kinase, focal adhesion kinase, and Crk-associated substrate (p130(CAS)), in conjunction with in vitro cell viability assays using seven melanoma cell lines. Utilizing a rat model of regional chemotherapy, we evaluated the effectiveness of systemic dasatinib in conjunction with regional melphalan against the human melanoma cell line, DM443, grown as a xenograft.

RESULTS

Only the WM3211 cell line harbored a c-kit mutation. Significant correlation was observed between Src-predicted dysregulation by gene expression and sensitivity to dasatinib in vitro. Tumor doubling time for DM443 xenografts treated with systemic dasatinib in combination with regional melphalan (44.8 days) was significantly longer (p = 0.007) than either dasatinib (21.3 days) or melphalan alone (24.7 days).

CONCLUSIONS

Systemic dasatinib prior to melphalan-based regional chemotherapy markedly improves the efficacy of this alkylating agent in this melanoma xenograft model. Validation of this concept should be considered in the context of a regional therapy clinical trial.

Isolated limb infusion as a model to test new agents to treat metastatic melanoma

The limb model of in-transit disease can expand our understanding of treating melanoma because of the ease of obtaining tissue biopsies for correlative studies and the availability of preclinical animal models that allow validation of novel therapeutic strategies. This review will focus on regional therapy for in-transit melanoma as a platform to investigate novel therapeutic approaches to improve regional disease control, and help us develop insights to more rationally design systemic therapy trials.

Resveratrol abrogates the temozolomide-induced G2 arrest leading to mitotic catastrophe and reinforces the temozolomide-induced senescence in glioma cells

Background

Temozolomide (TMZ) is the most widely used drug to treat glioblastoma (GBM), which is the most common and aggressive primary tumor of the Central Nervous System and one of the hardest challenges in oncotherapy. TMZ is an alkylating agent that induces autophagy, apoptosis and senescence in GBM cells. However, therapy with TMZ increases survival after diagnosis only from 12 to 14.4 months, making the development of combined therapies to treat GBM fundamental. One candidate for GBM therapy is Resveratrol (Rsv), which has additive toxicity with TMZ in several glioma cells in vitro and in vivo. However, the mechanism of Rsv and TMZ additive toxicity, which is the aim of the present work, is not clear, especially concerning cell cycle dynamics and long term effects.

Methods

Glioma cell lines were treated with Rsv and TMZ, alone or in combinations, and the induction and the role of autophagy, apoptosis, cell cycle dynamics, protein expression and phosphorylation status were measured. We further evaluated the long term senescence induction and clonogenic capacity.

Results

As expected, temozolomide caused a G2 cell cycle arrest and extensive DNA damage response. Rsv did not reduced this response, even increasing pATM, pChk2 and gammaH2Ax levels, but abrogated the temozolomide-induced G2 arrest, increasing levels of cyclin B and pRb(S807/811) and reducing levels of pWee1(S642) and pCdk1(Y15). This suggests a cellular state of forced passage through G2 checkpoint despite large DNA damage, a scenario that may produce mitotic catastrophe. Indeed, the proportion of cells with high nuclear irregularity increased from 6 to 26% in 48 h after cotreatment. At a long term, a reduction in clonogenic capacity was observed, accompanied by a large induction of senescence.

Conclusion

The presence of Rsv forces cells treated with TMZ through mitosis leading to mitotic catastrophe and senescence, reducing the clonogenic capacity of glioma cells and increasing the chronic effects of temozolomide.

Influence of DNA repair on nonlinear dose-responses for mutation

Recent evidence has challenged the default assumption that all DNA-reactive alkylating agents exhibit a linear dose-response. Emerging evidence suggests that the model alkylating agents methyl- and ethylmethanesulfonate and methylnitrosourea (MNU) and ethylnitrosourea observe a nonlinear dose-response with a no observed genotoxic effect level (NOGEL). Follow-up mechanistic studies are essential to understand the mechanism of cellular tolerance and biological relevance of such NOGELs. MNU is one of the most mutagenic simple alkylators. Therefore, understanding the mechanism of mutation induction, following low-dose MNU treatment, sets precedence for weaker mutagenic alkylating agents. Here, we tested MNU at 10-fold lower concentrations than a previous study and report a NOGEL of 0.0075 µg/ml (72.8nM) in human lymphoblastoid cells, quantified through the hypoxanthine (guanine) phosphoribosyltransferase assay (OECD 476). Mechanistic studies reveal that the NOGEL is dependent upon repair of O⁶-methylguanine (O⁶MeG) by the suicide enzyme O⁶MeG-DNA methyltransferase (MGMT). Inactivation of MGMT sensitizes cells to MNU-induced mutagenesis and shifts the NOGEL to the left on the dose axis.

Regional treatment strategies for in-transit melanoma metastasis

For in-transit melanoma confined to the extremities, regional chemotherapy in the form of hyperthermic isolated limb perfusion and isolated limb infusion are effective treatment modalities carrying superior response rates to current standard systemic therapy. Despite high response rates, most patients will eventually recur, supporting the role for novel research aimed at improving durable responses and minimizing toxicity. Although the standard cytotoxic agent for regional chemotherapy is melphalan, alternative agents such as temozolomide are currently being tested, with promising preliminary results. Current strategies for improving chemosensitivity to regional chemotherapy are aimed at overcoming classic resistance mechanisms such as drug metabolism and DNA repair, increasing drug delivery, inhibiting tumor-specific angiogenesis, and decreasing the apoptotic threshold of melanoma cells. Concurrent with development and testing of these agents, genomic profiling and biomolecular analysis of acquired tumor tissue may define patterns of tumor resistance and sensitivity from which personalized treatment may be tailored to optimize efficacy. In this article rational strategies for treatment of in-transit melanoma are outlined, with special emphasis on current translational and clinical research efforts.

Targeting O⁶-methylguanine-DNA methyltransferase with specific inhibitors as a strategy in cancer therapy

O (6)-methylguanine-DNA methyltransferase (MGMT) repairs the cancer chemotherapy-relevant DNA adducts, O (6)-methylguanine and O (6)-chloroethylguanine, induced by methylating and chloroethylating anticancer drugs, respectively. These adducts are cytotoxic, and given the overwhelming evidence that MGMT is a key factor in resistance, strategies for inactivating MGMT have been pursued. A number of drugs have been shown to inactivate MGMT in cells, human tumour models and cancer patients, and O (6)-benzylguanine and O (6)-[4-bromothenyl]guanine have been used in clinical trials. While these agents show no side effects per se, they also inactivate MGMT in normal tissues and hence exacerbate the toxic side effects of the alkylating drugs, requiring dose reduction. This might explain why, in any of the reported trials, the outcome has not been improved by their inclusion. It is, however, anticipated that, with the availability of tumour targeting strategies and hematopoetic stem cell protection, MGMT inactivators hold promise for enhancing the effectiveness of alkylating agent chemotherapy.

Sorafenib, a multikinase inhibitor, enhances the response of melanoma to regional chemotherapy

Melanoma responds poorly to standard chemotherapy due to its intrinsic chemoresistance. Multiple genetic and molecular defects, including an activating mutation in the BRaf kinase gene, are associated with melanoma, and the resulting alterations in signal transduction pathways regulating proliferation and apoptosis are thought to contribute to its chemoresistance. Sorafenib, a multikinase inhibitor that targets BRaf kinase, is Food and Drug Administration approved for use in advanced renal cell and hepatocellular carcinomas. Although sorafenib has shown little promise as a single agent in melanoma patients, recent clinical trials suggest that, when combined with chemotherapy, it may have more benefit. We evaluated the ability of sorafenib to augment the cytotoxic effects of melphalan, a regional chemotherapeutic agent, and temozolomide, used in systemic and regional treatment of melanoma, on a panel of 24 human melanoma-derived cell lines and in an animal model of melanoma. Marked differences in response to 10 micromol/L sorafenib alone were observed in vitro across cell lines. Response to sorafenib significantly correlated with extracellular signal-regulated kinase (ERK) downregulation and loss of Mcl-1 expression (P < 0.05). Experiments with the mitogen-activated protein kinase/ERK kinase inhibitor U0126 suggest a unique role for ERK downregulation in the observed effects. Sorafenib in combination with melphalan or temozolomide led to significantly improved responses in vitro (P < 0.05). In the animal model of melanoma, sorafenib in combination with regional melphalan or regional temozolomide was more effective than either treatment alone in slowing tumor growth. These results show that sorafenib in combination with chemotherapy provides a novel approach to enhance chemotherapeutic efficacy in the regional treatment of in-transit melanoma.

Optimizing regional infusion treatment strategies for melanoma of the extremities

The incidence of malignant melanoma is increasing faster than any other cancer. In cases of recurrent melanoma confined to the extremities, hyperthermic isolated limb perfusion and isolated limb infusion provide a way to isolate the extremity and deliver a dose of chemotherapy several orders of magnitude higher than would be tolerated systemically. Although complete response rates of up to 80% for hyperthermic isolated limb perfusion and 44% for isolated limb infusion have been observed, there is still room for improvement and standardization in these two procedures in an attempt to optimize response while minimizing toxicity. Currently, new chemotherapy agents and small-molecule inhibitors are being investigated as a means of overcoming chemoresistance and improving response rates. In patients with advanced cutaneous disease confined to the extremities, evaluation of these new therapies can be very informative, as tissue acquisition at multiple treatment time points is easy owing to the superficial and multifocal nature of the disease. Through studying the biomolecular and genetic alterations in tumor tissue in response to these new therapies, genetically customized treatment regimens in which tumor resistance and sensitivity is predicted and treatment strategy is optimized before treatment begins may soon be available. Progress in regional therapy will prove not only beneficial for patients with disease confined to an extremity, but may also provide insight into developing novel treatment strategies for patients with systemic disease for whom current disease management options are poor.

Inhibition of poly(ADP-ribose) polymerase enhances the effect of chemotherapy in an animal model of regional therapy for the treatment of advanced extremity malignant melanoma

BACKGROUND

Poly(ADP-ribose) polymerase (PARP) is an important regulator of programmed cell death in response to alkylating agents such as temozolomide (TMZ). The goal of this study was to determine if a systemically administered PARP-inhibitor (INO-1001) could augment the efficacy of TMZ in a rat model of extremity malignant melanoma.

MATERIALS AND METHODS

PARP activity was measured in vitro across a panel of 5 human malignant melanoma-derived cell lines. To evaluate tumor response to PARP inhibition in combination with regional isolated limb infusion (ILI) therapy with TMZ, two TMZ-resistant malignant melanoma cell lines were grown as xenografts in the hind limb of rats. INO-1001 (400 mg/kg) was injected intraperitoneally 7 times every 8 hours prior to ILI. Tumor volume was measured for up to 40 days.

RESULTS

In vitro inhibition of PARP activity by INO-1001 ranged from 25.5% to 65.6%. In a mismatch repair (MMR)-deficient xenograft, treatment with INO-1001 prior to ILI significantly (P < .04) increased the efficacy of TMZ. The increase in tumor volume at day 40 following TMZ-ILI with INO-1001 was only 22.6% compared with 322.8% with TMZ-ILI alone. In a xenograft that was MMR-proficient and had high levels of O(6)-methylguanine-DNA methyltransferase (MGMT) activity, there was little improvement in TMZ efficacy with INO-1001 treatment.

CONCLUSION

The PARP-inhibitor, INO-1001, can enhance the response of TMZ-resistant, MMR-deficient, malignant melanoma xenografts to intra-arterially administered TMZ in a regional treatment model of advanced extremity malignant melanoma.

Isolated limb infusion: a review

Isolated limb perfusion is the preferred treatment option for locally advanced melanoma and sarcoma confined to a limb. This treatment results in high response rates with a satisfying duration of response in both tumours. A drawback of isolated limb perfusion, however, is the invasive and complex character of the procedure.Isolated limb infusion has been designed as a minimally invasive alternative to isolated limb perfusion. Treatment results of this simple technique, reported by various centres worldwide, show comparable response rates for melanoma and sarcoma. Therefore isolated limb infusion may replace isolated limb perfusion in the future as the preferred treatment option for these locally advanced limb tumours.

Genomic and molecular profiling predicts response to temozolomide in melanoma

PURPOSE

Despite objective response rates of only approximately 13%, temozolomide remains one of the most effective single chemotherapy agents against metastatic melanoma, second only to dacarbazine, the current standard of care for systemic treatment of melanoma. The goal of this study was to identify molecular and/or genetic markers that correlate with, and could be used to predict, response to temozolomide-based treatment regimens and that reflect the intrinsic properties of a patient's tumor.

EXPERIMENTAL DESIGN

Using a panel of 26 human melanoma-derived cell lines, we determined in vitro temozolomide sensitivity, O(6)-methylguanine-DNA methyltransferase (MGMT) activity, MGMT protein expression and promoter methylation status, and mismatch repair proficiency, as well as the expression profile of 38,000 genes using an oligonucleotide-based microarray platform.

RESULTS

The results showed a broad spectrum of temozolomide sensitivity across the panel of cell lines, with IC(50) values ranging from 100 micromol/L to 1 mmol/L. There was a significant correlation between measured temozolomide sensitivity and a gene expression signature-derived prediction of temozolomide sensitivity (P < 0.005). Notably, MGMT alone showed a significant correlation with temozolomide sensitivity (MGMT activity, P < 0.0001; MGMT expression, P <or= 0.0001). The promoter methylation status of the MGMT gene, however, was not consistent with MGMT gene expression or temozolomide sensitivity.

CONCLUSIONS

These results show that melanoma resistance to temozolomide is conferred predominantly by MGMT activity and suggest that MGMT expression could potentially be a useful tool for predicting the response of melanoma patients to temozolomide therapy.

Pharmacokinetics & drug resistance of melphalan in regional chemotherapy: ILP versus ILI

Two forms of regional chemotherapy for the treatment of advanced melanoma or sarcoma of the extremity are isolated limb perfusion (ILP) and the more recently described isolated limb infusion (ILI). Melphalan is the most commonly employed agent in both ILP and ILI, although it is often used in conjunction with other cytotoxic and/or biologic therapies. While ILP and ILI are far more effective for the treatment of extremity disease than is systemic therapy, there is still significant room for improvement in outcomes, from the standpoint of both response rate and toxicity. An understanding of the pharmacokinetics of regional chemotherapy would allow for the prediction of tumor response and toxicity and therefore patient outcomes. In addition, elucidating the mechanisms of drug resistance would lead to opportunities to develop effective chemo-modulators that enhance the effectiveness of ILP and ILI. This paper reviews progress in these two key areas of active investigation.

Targeting N-cadherin enhances antitumor activity of cytotoxic therapies in melanoma treatment

Malignant transformation in melanoma is characterized by a phenotype "switch" from E- to N-cadherin, which is associated with increased motility and invasiveness of the tumor and altered signaling, leading to decreased apoptosis. We hypothesized that the novel pentapeptide (ADH-1), which disrupts N-cadherin adhesion, could sensitize melanoma tumors to the cytotoxic effects of chemotherapy. N-cadherin-expressing human melanoma-derived cell lines were used to generate xenografts in animal models to study isolated limb infusion with melphalan and systemic chemotherapy with temozolomide. We report here that melphalan in combination with ADH-1 significantly reduced tumor growth up to 30-fold over melphalan alone. ADH-1 enhancement of response to melphalan was associated with increased formation of DNA adducts, increased apoptosis, and intracellular signaling changes associated with focal adhesions and fibroblast growth factor receptors. Targeted therapy using an N-cadherin antagonist can dramatically augment the antitumor effects of chemotherapy and is a novel approach to optimizing treatment for melanoma.

Defining regional infusion treatment strategies for extremity melanoma: comparative analysis of melphalan and temozolomide as regional chemotherapeutic agents

Five different human melanoma xenografts were used in a xenograft model of extremity melanoma to evaluate the variability of tumor response to regionally administered melphalan or temozolomide and to determine if various components of pertinent drug resistance pathways for melphalan [glutathione S-transferase (GST)/glutathione] and temozolomide [O(6)-alkylguanine DNA alkyltranferase (AGT)/mismatch repair (MMR)] could be predictive of tumor response. Xenograft-bearing rats underwent regional isolated limb infusion with either melphalan (90 mg/kg) or temozolomide (2,000 mg/kg). The levels of AGT activity, GST activity, glutathione level, and GST/AGT expression were examined in this group of xenografts and found to be quite heterogeneous. No correlation was identified between melphalan sensitivity and the GST/glutathione cellular detoxification pathway. In contrast, a strong correlation between the levels of AGT activity and percentage increase in tumor volume on day 30 (r = 0.88) was noted for tumors treated with temozolomide. Regional therapy with temozolomide was more effective when compared with melphalan for the xenograft with the lowest AGT activity, whereas melphalan was more effective than temozolomide in another xenograft that had the highest AGT activity. In three other xenografts, there was no significant difference in response between the two chemotherapy agents. This study shows that AGT activity may be useful in predicting the utility of temozolomide-based regional therapy for advanced extremity melanoma tumors. Our observations also point out the limited ability of analysis of the GST/glutathione pathway to predict response to chemotherapies like melphalan whose resistance is primarily mediated through a complex mechanism of detoxification.