Effect of lonidamine on the cytotoxicity of four alkylating agents in vitro

Cu(I) and Cu(II) Complexes Based on Lonidamine-Conjugated Ligands Designed to Promote Synergistic Antitumor Effects

Bis(pyrazol-1-yl)- and bis(3,5-dimethylpyrazol-1-yl)-acetates were conjugated with the 2-hydroxyethylester and 2-aminoethylamide derivatives of the antineoplastic drug lonidamine to prepare Cu(I) and Cu(II) complexes that might act through synergistic mechanisms of action due to the presence of lonidamine and copper in the same chemical entity. Synchrotron radiation-based complementary techniques [X-ray photorlectron spectroscopy and near-edge X-ray absorption fine structure (NEXAFS)] were used to characterize the electronic and molecular structures of the complexes and the local structure around the copper ion (XAFS) in selected complexes. All complexes showed significant antitumor activity, proving to be more effective than the reference drug cisplatin in a panel of human tumor cell lines, and were able to overcome oxaliplatin and multidrug resistance. Noticeably, these Cu complexes appeared much more effective than cisplatin against 3D spheroids of pancreatic PSN-1 cancer cells; among these, PPh₃-containing Cu(I) complex 15 appeared to be the most promising derivative. Mechanistic studies revealed that 15 induced cancer cell death by means of an apoptosis-alternative cell death.

Recent advances in platinum-based chemotherapeutics that exhibit inhibitory and targeted mechanisms of action

Current platinum-based drugs used in chemotherapy, like cisplatin and its derivatives, are greatly limited due to side-effects and drug resistance. This has inspired the search for novel platinum-based drugs that deviate from the conventional mechanism of action seen with current chemotherapeutics. This review highlights recent advances in platinum(II) and platinum(IV)-based complexes that have been developed within the past six years. The platinum compounds explored within this review are those that display a more targeted approach by incorporating ligands that act on selected cellular targets within cancer cells. This includes mitochondria, overexpressed receptors or proteins and enzymes that contribute to cancer cell proliferation. These types of platinum compounds have shown significant improvements in anticancer activity and as such, this review highlights the importance of pursuing these new designed platinum drugs for cancer therapy, with the potential of undergoing clinical trials.

Combination of Epirubicin and Lonidamine for Treatment of Advanced Breast Cancer

Aims and background

In vitro and in vivo studies have shown that lonidamine potentiates the cytotoxic effect of anthracyclines in simultaneous and sequential combination. On the basis of such evidence, we evaluated the activity and toxicity of a combination of epirubicin plus lonidamine in advanced breast cancer.

Methods

Between January 1991 and November 1993, 33 patients with advanced breast cancer, age <75 years and PS <2, were treated with epirubicin (75 mg/m2 i.v. on day 1, every 3 weeks), plus lonidamine (450 mg/day orally from day 1 continuously until disease progression).

Results

Thirty patients were evaluable for response: 4 achieved complete response (13%) and 8 partial response (27%) (total response rate = 40%), 6 (20%) had stabilization of disease, and 12 (40%) progression of disease. The median duration of response was 10 months (range, 4-24+ months). This scheme was tolerated, with a mild additional toxicity related to lonidamine: only WHO grade III myalgia in 1 patient (3%) and epigastralgia in 3 patients (9%).

Conclusions

Although some patients seem to have benefited from the combination at the dose levels of the drug used in the study, the therapeutic advantages of addition of lonidamine remain unclear.

Lonidamine plus Cyclophosphamide in the Treatment of Adanced Non-Small Cell Lung Cancer in the Elderly: A Phase II Study

Aim and background

The aim of this Phase II trial was to verify the therapeutic activity and tolerability of chemotherapy with lonidamine (LND) plus cyclophosphamide (CTX) in advanced non-small cell lung cancer (NSCLC) in the elderly. The rationale of the combination is reported. CTX showed mild toxicity, with a 12% objective response (OR) in monochemotherapy; LND potentiated the in vitro antiproliferative activity of alkylating agents, mainly CTX, without increasing myelotoxicity, particularly important in the elderly.

Methods

The schedule consisted of CTX, 600 mg/m2/i.v. on day 1 every 21 days for 6 cycles; LND, 450 mg/die/p.o. from day 1 to progression.

Results

Between November 1990 and April 1991, 41 patients with stage III–IV NSCLC were enrolled; 35 were assessable for response. Median age was 73 years (range, 71–79 years); 13 patients (32%) presented stage III A, 20 (49%) stage III b, and 8 (19%) stage IV disease. Cardiovascular conditions and/or chronic respiratory failure contraindicated surgical treatment in stage III A patients. Of enrolled patients, 14.6% experienced PR, 48.8% SD and 14.6% dropped out of the study. Median time to progression was 4 months (range, 2–9 months) and median survival 9 months (range 3–45 months). No patient showed WHO grade IV LND-related toxicity. In 1 patient (2.5%), LND was discontinued after 5 therapy cycles due to WHO grade III myalgia; in 80% of patients, LND oral dosage was reduced to 300 mg/day due to WHO grade II myalgia, and 20% of patients completed treatment with the full dose.

Conclusions

CTX plus LND can be considered a well tolerated therapeutic approach in the elderly with NSCLC with good PS and good liver, renal and cardiac conditions, but 14.6% PR is a slightly better result as compared with 12% PR obtainable with CTX alone as reported in the literature, even though most patients presented with advanced disease and no specific toxic effect was observed. Therefore, a confirmatory randomized trial (CTX vs CTS plus LND) would hardly be useful.

Effective platinum(IV) prodrugs conjugated with lonidamine as a functional group working on the mitochondria

Platinum-based anticancer drugs are one of the most widely used anticancer chemotherapeutics in oncology. Lonidamine (LND) could increase the response of human tumor cells to platinum(II) drugs in preclinical studies by working on the mitochondria. Herein, five platinum(IV) prodrugs conjugated with their potentiator LND are prepared, and most of the target complexes achieve improved anticancer activities compared with their platinum(II) precursors. Notably, Pt(NH₃)₂(LND)Cl₃ (complex 1) derived from cisplatin achieve significantly improved anticancer activities against LNCaP cells and could trigger cancer cell death via an apoptotic pathway and the cell cycle arrest mainly at S phases. And the induction of apoptosis by complex 1 in LNCaP cells is closely associated with mitochondrial function disruption and reactive oxygen species (ROS) accumulation. Moreover, it is possessed of the ability to overcome cisplatin-resistance. Further research revealed that complex 1 could be easily reduced to release its platinum(II) precursor and axial ligand by ascorbic acid. All the results provid evidence to support the design strategy of conjugating platinum complexes with its potentiator to improve their anticancer effect.

Regulation of glycolysis in head and neck squamous cell carcinoma

Glycolysis is highly upregulated in head and neck squamous cell carcinoma (HNSCC). HNSCC glycolysis is an important contributor to disease progression and decreases sensitivity to radiation or chemotherapy. Despite therapeutic advances, the survival rates for HNSCC patients remain low. Understanding glycolysis regulation in HNSCC will facilitate the development of effective therapeutic strategies for this disease. In this review, we will evaluate the regulation of altered HNSCC glycolysis and possible therapeutic approaches by targeting glycolytic pathways.

Limitations of the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay when compared to three commonly used cell enumeration assays

Background

The tetrazolium-based MTT assay has long been regarded as the gold standard of cytotoxicity assays as it is highly sensitive and has been miniaturised for use as a high-throughput screening assay. However, various reports refer to interference by different test compounds, including the glycolysis inhibitor 3-bromopyruvate, with the conversion of the dye to coloured formazan crystals. This study assessed the linear range and reproducibility of three commonly used cell enumeration assays; the neutral red uptake (NRU), resazurin reduction (RES) and sulforhodamine B (SRB) assays, in comparison to the MTT assay. Interference between the MTT assay and three glycolysis inhibitors, 2-deoxyglucose, 3-bromopyruvate and lonidamine, was investigated.

Results

Data indicate that the NRU, RES and SRB assays showed the smallest variability across the linear range, while the largest variation was observed for the MTT assay. This implies that these assays would more accurately detect small changes in cell number than the MTT assay. The SRB assay provided the most reproducible results as indicated by the coefficient of determination after a limited number of experiments. The SRB assay also produced the lowest variance in the derived 50% inhibitory concentration (IC₅₀), while IC₅₀ concentrations of 3-bromopyruvate could not be detected using either the MTT or RES assays after 24 hours incubation. Interference in the MTT assay was observed for all three tested glycolysis inhibitors in a cell-free environment. No interferences were observed for the NRU, SRB or RES assays.

Conclusions

This study demonstrated that the MTT assay was not the best assay in a number of parameters that must be considered when a cell enumeration assay is selected: the MTT assay was less accurate in detecting changes in cell number as indicated by the variation observed in the linear range, had the highest variation when the IC₅₀ concentrations of the glycolysis inhibitors were determined, and interference between the MTT assay and all the glycolysis inhibitors tested were observed. The SRB assay performed best overall considering all of the parameters, suggesting that it is the most suitable assay for use in preclinical screening of novel therapeutic compounds with oxido-reductive potential.

Electronic supplementary material

The online version of this article (doi:10.1186/s13104-015-1000-8) contains supplementary material, which is available to authorized users.

GBM's multifaceted landscape: highlighting regional and microenvironmental heterogeneity

Gliomas are a heterogeneous group of tumors that show variable proliferative potential, invasiveness, aggressiveness, histological grading, and clinical behavior. In this review, we focus on glioblastoma multiforme (GBM), a grade IV glioma, which is the most common and malignant of primary adult brain tumors. Research over the past several decades has revealed the existence of extensive cellular, molecular, genetic, epigenetic, and metabolic heterogeneity among tumors of the same grade and even within individual tumors. Evaluation of different tumor types has shown that tumors with advanced grade and clinical aggressiveness also display enhanced molecular, cellular, and microenvironmental heterogeneity. From a therapeutic standpoint, this heterogeneity is a major clinical hurdle for devising effective therapeutic strategies for patients and challenges personalized medicine. In this review, we will highlight key aspects of GBM heterogeneity, directing special attention to regional heterogeneity, hypoxia, genomic heterogeneity, tumor-specific metabolic reprogramming, neovascularization or angiogenesis, and stromal immune cells. We will further discuss the clinical implications of GBM heterogeneity in the context of therapy.

Targeting glucose metabolism: an emerging concept for anticancer therapy

Mortality from locally advanced and metastatic cancer remains high despite advances in our understanding of the molecular basis of the disease and improved adjuvant therapies. Recently, there has been an increased interest in cancer metabolomics, and in particular, the potential for targeting glucose metabolism, for therapeutic gain. This interest stems from the fact that cancer cells metabolize glucose very differently from normal cells. Cancer cells preferentially switch to aerobic glycolysis rather than oxidative phosphorylation as their means of glucose metabolism. This metabolic switch is believed to enhance cancer cell survival. Several therapeutic agents that target tumor metabolism have shown significant cancer cell cytotoxicity in preclinical studies, and some have progressed to clinical trials. In this review, we discuss the alteration of carbohydrate metabolism seen in cancer cells, the underlying mechanisms, and opportunities for targeting cancer metabolism for therapeutic purposes.

Metabolic effects of signal transduction inhibition in cancer assessed by magnetic resonance spectroscopy

Despite huge efforts in development of drugs targeting oncogenic signalling, the number of such drugs entering clinical practice to date remains limited. Rational use of biomarkers for drug candidate selection and early monitoring of response to therapy may accelerate this process. Magnetic resonance spectroscopy (MRS) can be used to assess metabolic effects of drug treatment both in vivo and in vitro, and technological advances are continuously increasing the utility of this non-invasive method. In this review, we summarise the use of MRS for monitoring the effect of targeted anticancer drugs, and discuss the potential role of MRS in the context of personalised cancer treatment.

Altered metabolism in head and neck squamous cell carcinoma: an opportunity for identification of novel biomarkers and drug targets

Tumor cells were first shown to exhibit a distinct metabolic phenotype over 80 years ago. Since then, it has become clear that multiple oncogenic events contribute to the development of a metabolic phenotype that supports rapid proliferation. Because this phenotype represents an essential component of tumorigenesis and disease progression, it also represents a potential source of biomarkers associated with aggressive disease. In addition, the addiction of tumor cells to specific nutrients and the up-regulation of key metabolic enzymes provide unique opportunities for pharmacologic manipulation. Despite the use of multimodality treatment, survival rates for patients with advanced head and neck squamous cell carcinoma (HNSCC) remain low, partially attributed to the development of drug resistance. In this review, we evaluate the role of altered HNSCC metabolism as both a source of novel biomarkers and a means to bypass resistance mechanisms to conventional forms of therapy.

Sugar-free approaches to cancer cell killing

Tumors show an increased rate of glucose uptake and utilization. For this reason, glucose analogs are used to visualize tumors by the positron emission tomography technique, and inhibitors of glycolytic metabolism are being tested in clinical trials. Upregulation of glycolysis confers several advantages to tumor cells: it promotes tumor growth and has also been shown to interfere with cell death at multiple levels. Enforcement of glycolysis inhibits apoptosis induced by cytokine deprivation. Conversely, antiglycolytic agents enhance cell death induced by radio- and chemotherapy. Synergistic effects are likely due to regulation of the apoptotic machinery, as glucose regulates activation and levels of proapoptotic BH3-only proteins such as Bim, Bad, Puma and Noxa, as well as the antiapoptotic Bcl-2 family of proteins. Moreover, inhibition of glucose metabolism sensitizes cells to death ligands. Glucose deprivation and antiglycolytic drugs induce tumor cell death, which can proceed through necrosis or through mitochondrial or caspase-8-mediated apoptosis. We will discuss how oncogenic pathways involved in metabolic stress signaling, such as p53, AMPK (adenosine monophosphate-activated protein kinase) and Akt/mTOR (mammalian target of rapamycin), influence sensitivity to inhibition of glucose metabolism. Finally, we will analyze the rationale for the use of antiglycolytic inhibitors in the clinic, either as single agents or as a part of combination therapies.

Targeting metabolic transformation for cancer therapy

Cancer therapy has long relied on the rapid proliferation of tumour cells for effective treatment. However, the lack of specificity in this approach often leads to undesirable side effects. Many reports have described various 'metabolic transformation' events that enable cancer cells to survive, suggesting that metabolic pathways might be good targets. There are currently several drugs under development or in clinical trials that are based on specifically targeting the altered metabolic pathways of tumours. This Review highlights pathways against which there are already drugs in different stages of development and also discusses additional druggable targets.

Small mitochondria-targeting molecules as anti-cancer agents

Alterations in mitochondrial structure and functions have long been observed in cancer cells. Targeting mitochondria as a cancer therapeutic strategy has gained momentum in the recent years. The signaling pathways that govern mitochondrial function, apoptosis and molecules that affect mitochondrial integrity and cell viability have been important topics of the recent review in the literature. In this article, we first briefly summarize the rationale and biological basis for developing mitochondrial-targeted compounds as potential anti-cancer agents, and then provide key examples of small molecules that either directly impact mitochondria or functionally affect the metabolic alterations in cancer cells with mitochondrial dysfunction. The main focus is on the small molecular weight compounds with potential applications in cancer treatment. We also summarize information on the drug developmental stages of the key mitochondria-targeted compounds and their clinical trial status. The advantages and potential shortcomings of targeting the mitochondria for cancer treatment are also discussed.

Targeting of cancer energy metabolism

The main purpose of this review is to update and analyze the effect of several antineoplastic drugs (adriamycin, apoptodilin, casiopeinas, cisplatin, clotrimazole, cyclophosphamide, ditercalinium, NSAIDs, tamoxifen, taxol, 6-mercaptopurine, and alpha-tocopheryl succinate) and energy metabolism inhibitors (2-DOG, gossypol, delocalized lipophilic cations, and uncouplers) on tumor development and progression. The possibility that these antineoplastic drugs currently used in in vitro cancer models, in chemo-therapy, or under study in phase I to III clinical trials induce tumor cellular death by altering also metabolite concentration (i.e., ATP), enzyme activities, and/or energy metabolism fluxes is assessed. It is proposed that the use of energy metabolic therapy, as an alternative or complementary strategy, might be a promising novel approach in the treatment of cancer.

Glycosyl and polyalcoholic prodrugs of lonidamine

Polyhydric alcohol derivatives of the anticancer agent lonidamine (LND) have been synthesized. The increased water solubility showed by prodrugs 4, 7, and 25 together with their logP values (2.19, 2.55, and 2.54, respectively) and chemical stability might be beneficial for prodrugs absorption after oral administration. Moreover, the new prodrugs undergo enzymatic hydrolysis in plasma and release LND demonstrating that they are promising candidates for in vivo investigations.

The Warburg effect and its cancer therapeutic implications

Increased aerobic glycolysis in cancer, a phenomenon known as the Warburg effect, has been observed in various tumor cells and represents a major biochemical alteration associated with malignant transformation. Although the exact molecular mechanisms underlying this metabolic change remain to be elucidated, the profound biochemical alteration in cancer cell energy metabolism provides exciting opportunities for the development of therapeutic strategies to preferentially kill cancer cells by targeting the glycolytic pathway. Several small molecules capable of inhibiting glycolysis in experimental systems have been shown to have promising anticancer activity in vitro and in vivo. This review article provides a brief summary of our current understanding of the Warburg effect, the underlying mechanisms, and its influence on the development of therapeutic strategies for cancer treatment.

Glycolysis inhibition for anticancer treatment

Most cancer cells exhibit increased glycolysis and use this metabolic pathway for generation of ATP as a main source of their energy supply. This phenomenon is known as the Warburg effect and is considered as one of the most fundamental metabolic alterations during malignant transformation. In recent years, there are significant progresses in our understanding of the underlying mechanisms and the potential therapeutic implications. Biochemical and molecular studies suggest several possible mechanisms by which this metabolic alteration may evolve during cancer development. These mechanisms include mitochondrial defects and malfunction, adaptation to hypoxic tumor microenvironment, oncogenic signaling, and abnormal expression of metabolic enzymes. Importantly, the increased dependence of cancer cells on glycolytic pathway for ATP generation provides a biochemical basis for the design of therapeutic strategies to preferentially kill cancer cells by pharmacological inhibition of glycolysis. Several small molecules have emerged that exhibit promising anticancer activity in vitro and in vivo, as single agent or in combination with other therapeutic modalities. The glycolytic inhibitors are particularly effective against cancer cells with mitochondrial defects or under hypoxic conditions, which are frequently associated with cellular resistance to conventional anticancer drugs and radiation therapy. Because increased aerobic glycolysis is commonly seen in a wide spectrum of human cancers and hypoxia is present in most tumor microenvironment, development of novel glycolytic inhibitors as a new class of anticancer agents is likely to have broad therapeutic applications.

Time to progression in metastatic breast cancer patients treated with epirubicin is not improved by the addition of either cisplatin or lonidamine: final results of a phase III study with a factorial design

PURPOSE

To investigate the value of the addition of either cisplatin (CDDP) or lonidamine (LND) to epirubicin (EPI) in the first-line treatment of advanced breast cancer.

PATIENTS AND METHODS

Three hundred seventy-one metastatic breast cancer patients with no prior systemic chemotherapy for advanced disease were randomized to receive either EPI alone (60 mg/m(2) on days 1 and 2 every 21 days), EPI and CDDP (30 mg/m(2) on days 1 and 2 every 21 days), EPI and LND (450 mg orally daily, given continuously), or EPI, CDDP, and LND. Time to progression, response rates, side effects, and survival were compared according to the 2 x 2 factorial design of this study.

RESULTS

The groups were well balanced with respect to prognostic factors. Time to progression did not differ in the comparison between CDDP arms and non-CDDP arms (median, 10.9 months v 9.4 months, respectively; P =.10) or between that of LND arms and non-LND arms (median, 10.8 months v 9.9 months, respectively; P =.47), nor did overall survival. The response rate did not significantly differ in the comparison between LND arms and non-LND arms (62.9% v 54.0%, P =.08). No difference in treatment activity was observed between CDDP arms and non-CDDP arms. Toxicity was significantly higher in the CDDP arms, leading to CDDP dose adjustment in 40% of cases. The most frequent side effects were of a hematologic and gastrointestinal nature. The addition of LND produced more myalgias and fatigue.

CONCLUSION

Neither CDDP nor LND was able to significantly improve the time to progression obtained by EPI. CDDP, however, significantly worsened the drug's tolerability.

Lonidamine as a modulator of taxol activity in human ovarian cancer cells: effects on cell cycle and induction of apoptosis

The ability of lonidamine (LND), an energolytic derivative of indazole-carboxylic acid, to modulate the cytotoxicity of Taxol (TX) was investigated in the A2780 human ovarian cancer cell line. Different cytotoxicity results were obtained as a function of treatment schedule. Specifically, TX followed by LND produced synergistic effects. Conversely, antagonistic effects were recorded when drugs were given simultaneously or according to the opposite sequence. TX induced an oligonucleosomal DNA fragmentation typical of the apoptotic process. The extent and the kinetics of DNA cleavage in samples treated with the taxane alone were similar to those of samples treated with the TX-LND sequence. Activation of Yama protease and degradation of poly (ADP-ribose) polymerase were not observed after individual or combined treatment. LND did not appreciably modify the effect exerted by TX on proteins involved in cell cycle progression (i.e., inhibition of p34cdc2 expression) and apoptosis (i.e., upregulation of wt p53 and transactivation of p21waf1), and only caused a slight induction of the Bax protein. LND alone did not affect tubulin polymerization in A2780 cells and, when administered after a 24 hr TX exposure, did not appreciably alter the extent of tubulin polymerization induced by the taxane. Although additional studies are needed to define the molecular basis of the TX-LND interaction, our results suggest that LND can positively modulate the antitumor activity of TX in ovarian cancer cells and indicate that the energolytic is potentially useful in combination therapy including the taxane in ovarian cancer patients.

Enhancement of doxorubicin content by the antitumor drug lonidamine in resistant Ehrlich ascites tumor cells through modulation of energy metabolism

The effect of the antitumor drug lonidamine (LND) on respiration, aerobic glycolysis, adenylate pool, doxorubicin (DOX) uptake, and efflux in DOX-resistant and DOX-sensitive Ehrlich tumor cells was investigated. The results may be summarized as follows: 1) In both types of cells, LND inhibited both respiration and glycolysis in a dose-dependent manner and lowered the ATP concentration. The effect was more marked in cells incubated in glucose-free medium; 2) LND raised, to a remarkable extent, the intracellular content of DOX in resistant and sensitive cells respiring on endogenous substrates because of reduced ATP availability, whereas in glucose-supplemented medium, where both respiration and glycolysis contributed to ATP synthesis, the increase was lower; and 3) when LND was added to DOX-loaded cells, it failed to significantly inhibit DOX efflux because of time-dependent phenomena. These findings indicated that LND, a drug currently employed in tumor therapy, might also be useful in reducing or overcoming multidrug resistance (MDR) of those cells with a reduced ability to accumulate and retain antitumor drugs.

Modulating effect of lonidamine on response to doxorubicin in metastatic breast cancer patients: results from a multicenter prospective randomized trial

Previous results from our preclinical studies have shown that lonidamine (LND) can positively modulate the antiproliferative activity of doxorubicin (DOX) on breast cancer cell lines. To evaluate the effect of LND in a clinical setting, a multicenter randomized trial was carried out on patients with advanced breast cancer. From September 1991 to July 1993, 181 patients were enrolled in the trial and received an initial treatment of DOX at 75 mg/m2 for 3 cycles. The 137 patients who reached complete remission, partial remission, or stable disease were randomized to receive either DOX alone (75 mg/m2 day 1) (arm A) or DOX plus LND (600 mg orally/day) (arm B). The patients enrolled in the two arms were fairly homogeneous in terms of major clinical characteristics. Toxicity was similar in both arms except for myalgia: WHO grade > or=2 was observed in 57% of arm B patients. Overall response rate to DOX + LND was 50% and to DOX alone 38% in evaluable patients, and 48% vs 37% in all registered patients, as determined by an intention-to-treat analysis. The differences did not reach statistical significance. Conversely, in agreement with previous findings, we observed a significant difference in response rate in the subgroup of patients with liver metastases, regardless of the extent of hepatic involvement (DOX + LND 68% vs DOX 33%, p=0.03). This observation makes LND an important tool in association with anthracyclines in the treatment of this subgroup of patients.

Mechanism of action of lonidamine in the 9L brain tumor model involves inhibition of lactate efflux and intracellular acidification

Malignant gliomas have been associated with a high rate of glycolytic activity which is believed necessary to sustain cellular function and integrity. Since lonidamine (LND) is believed to reduce tumor glucose utilization by inhibition of the mitochondrially-bound glycolytic enzyme hexokinase (HK), 31P magnetic resonance spectroscopy (MRS) was used to noninvasively follow the effects of LND on both tumor pH and the high-energy phosphate metabolites: ATP, phosphocreatine (PCr) and inorganic phosphate (Pi) in subcutaneous rat 9L gliosarcomas. 31P tumor spectra acquired in 5 min intervals pre- and post LND administration of 50 and 100 mg/kg, i.p. revealed an acidotic pH shift of -0.25 and -0.45 pH units, respectively within 30 min post administration. The ATP/Pi ratio of 9L tumors decreased to 40% of control and Pi levels increased to 280% of control over a 3 hr period. LND exerted no effect on tumor blood flow and mean arterial blood pressure. Brain and muscle metabolite levels and pH were also unaffected by LND. In vitro measurements of cultured 9L tumor cell intra- and extracellular lactate, pentose phosphate pathway (PPP) and hexokinase (HK) activities suggest that the mode of action of LND involves inhibition of lactate efflux and intracellular acidification. The selective reduction of tumor energy metabolites and pH by LND may be exploitable for sensitizing gliomas to radiation, chemotherapy or hyperthermia.

Efficacy of platinum-based regimens in non-small cell lung cancer. A negative report from the Cuneo Lung Cancer Study Group

Combination chemotherapy with cytotoxic agents is the regular treatment for patients with advanced non-small cell lung cancer (NSCLC), good performance status, and no major clinical contraindications. Since the early 1980s, platinum-based chemotherapy is the cornerstone of this treatment, while combinations containing long-acting alkylating agents have been nearly abandoned, and represent a sort of historical treatment. Nevertheless, the real survival benefits of cisplatin are uncertain and still debated. To attempt an answer, the Cuneo Lung Cancer Study Group (CuLCaSG) carried out a clinical trial comparing a platinum (MVP) versus a non-platinum-based combination chemotherapy (MACC). The study comprised 156 patients with advanced NSCLC randomly assigned to the two treatment arms. MACC and MVP chemotherapies were given as originally described and continued until progression of disease, unacceptable toxicity, or refusal by the patient. For a medium of four cycles of MVP and three cycles of MACC, the median dose intensity (DI) reached was, respectively, 95% and 100% of the intended (P = 0.0132). In all, 27 objective responses (1 complete and 16 partial responses in patients allocated to MVP versus 10 partial responses of the MACC group) were observed. Median progression-free and global survivals were, respectively, 21 and 34 weeks for MVP and 20 and 31 weeks for MACC (non-significant differences). The treatment plan was found non-significant also multivariate analysis of survival. Toxicity was rather similar in the two arms, except for more severe neurological toxicity, anemia, thrombocytopenia, nausea, and vomiting in patients on MVP. Alopecia was more common after MACC. Subjective tolerance to treatment, and perception of physical and psychological well-being were rated similarly by patients of both groups. In conclusion, MVP was moderately more active than MACC, and showed a foreseeable and reversible toxicity, of a low-medium grade. However, this CuLCaSG study failed to substantiate any survival benefit from the use of platinum in combination with other cytotoxic agents.

Comparison of action of the anti-neoplastic drug lonidamine on drug-sensitive and drug-resistant human breast cancer cells: 31P and 13C nuclear magnetic resonance studies

Lonidamine (LND) is a relatively new anti-cancer drug, and several clinical trials have indicated that it may be effective in combinations with other therapeutic modalities. LND is classified within the metabolic inhibitor agents. Multidrug resistance (MDR) phenomenon is often associated with increased energy requirements, and enhanced glycolysis rate. These studies were performed to delineate the mechanism of action of LND on MDR human breast cancer cells, and to investigate whether LND as a single agent, or in combination with another anti-metabolism drug, 2-deoxyglucose (2-DG), may be useful against MDR tumors. The effects of LND on intact perfused drug-sensitive (WT) and 33-fold resistant to Adriamycin (Adr) MCF-7 cells, embedded in alginate micro capsules, were continuously monitored by 31P and 13C nuclear magnetic resonance (NMR) spectroscopy. 31P NMR studies showed that LND induced intracellular acidification and depletion of NTP in both WT and Adr cells. However, pH and NTP levels decreased less in the Adr cells than in the WT cells (p < 0.05 for both parameters). 13C NMR demonstrated that LND inhibited lactate transport, and lactate signals were elevated in both cell lines. However, the intracellular lactate levels increased to a greater extent in the WT than in the Adr cells (p < 0.05). There were major differences in the effects of LND on metabolism between sensitive and resistant cells. While LND enhanced glucose uptake in the WT cells, and its administration was followed by continuous increase of lactate signal, both processes were not affected by LND in the Adr cells. 2-DG is a glucose analogue that inhibits both cellular uptake and utilization of glucose, leading to cell starvation. Combined treatment with LND and 2-DG yielded at best additive, but not synergistic, cellular toxicity, and the metabolic effects of LND were attenuated by 2-DG. These results showed that the principal mechanism of action of LND is inhibition of lactate transport leading to intracellular lactate accumulation and acidification in both WT and Adr cells. The Adr cells were only 2-fold resistant to LND (compared to the WT cells), and since cellular uptake of alkaloid chemotherapy is improved in acidic environment, LND may have a role in the treatment protocols of MDR tumors, especially when given as the initial means for induction of intracellular acidification.

Modulation by lonidamine on the combined activity of cisplatin and epidoxorubicin in human breast cancer cells

The ability of lonidamine (LND), an energolytic derivative of indazole-carboxylic acid, to modulate the cytotoxic activity of cisplatin (CDDP) and epidoxorubicin (EPI), singly or in combination, was investigated in two human breast cancer cell lines (MCF7 and T47D). A 72-hr post-incubation with a non-cytotoxic concentration of LND (75 microM) increased the activity of a 1-hr CDDP treatment as well as that of a 1 to 16-hr EPI treatment. A different pattern of interaction among the drugs and modulator was observed as a function of the sequence of drug treatment. Specifically, supra-additive or additive effects of the combination were obtained in the two cell lines according to the different treatment schemes. In particular, the maximum potentiation was observed in MCF7 cells simultaneously exposed to CDDP, EPI and LND for 1 hr and then post-incubated with LND for 72 hr, and in T47 first exposed to EPI and LND, then to CDDP and LND, and finally post-incubated with LND. Flow cytometric analysis of MCF7 cell distribution in the different cycle phases showed that combined treatment with EPI/CDDP/LND was able to stabilize cell cycle perturbations (mainly G2M accumulation) induced by individual agents. The ability of LND to potentiate CDDP and EPI cytotoxicity, and the consideration that LND causes side effects different from those caused by alkylating agents and anthracyclines, make this compound an attractive candidate for multidrug combination therapy in breast cancer.

Cisplatin, epirubicin, and vindesine with or without lonidamine in the treatment of inoperable nonsmall cell lung carcinoma: a multicenter randomized clinical trial

BACKGROUND

Lonidamine (LND) is an indazol-carboxylic acid derivative that selectively inhibits the energy metabolism of neoplastic cells, and increases the permeability of cell membranes. In vitro studies have demonstrated that LND can potentiate the oncolytic activity of cytotoxic drugs and is able to reverse the acquired multidrug resistance of neoplastic cells. Some clinical trials have suggested a synergism of LND with alkylating agents, cisplatin, and anthracyclines in various solid tumors.

METHODS

From June 1990 to June 1993, 158 previously untreated patients with Stage IIIB and IV nonsmall cell lung cancer (NSCLC) were enrolled into a multicentric randomized trial to evaluate the addition of LND to a cisplatin-epirubicin-vindesine regimen. Eighty patients in the control arm (A) received cisplatin, 60 mg/m2 intravenously (i.v.); epirubicin, 60 mg/m2 i.v.; and vindesine, 3 mg/m2 i.v. (PEV), on Day 1 every 4 weeks, whereas 78 patients in the experimental arm (B) received the same regimen with the addition of LND from 75 mg orally three times on Day 1 to 150 mg orally three times on Day 7+ until tumor progression occurred.

RESULTS

The experimental treatment achieved a significantly higher proportion of major responses in comparison with the control regimen (43% vs. 24%; P=0.02). The addition of LND apparently potentiated the activity of this cytotoxic treatment, particularly in patients with metastatic disease (overall response rate, 39% vs. 17%). The median time to progression (5 vs. 8 months; P=0.0007) and the median survival time (7.6 vs. 11 months; P=0.0013) were also statistically improved in Arm B. The acute toxicity of the 2 treatments was low: only 6% of patients in Arm A and 4% of patients in Arm B had to withdraw from treatment due to Grade 4 World Health Organization toxicity. The main additional side effects related to the administration of LND were epigastralgia, myalgia, asthenia, and orchialgia. However, these symptoms were mild and controlled by the concomitant administration of low doses of steroids.

CONCLUSIONS

The mild acute toxicity of the PEV regimen and the acceptable and nonoverlapping additional side effects of LND render our experimental therapy worthy of consideration for the management of NSCLC patients with poor performance status or low tolerance to more aggressive therapeutic approaches.

An on-line semi-automated solid-phase extraction procedure for high-performance liquid chromatographic determination of lonidamine in serum

A semi-automated solid-phase extraction procedure on-line with gradient elution reversed-phase chromatography permits the determination of lonidamine and its metabolite in human serum. The average recovery from serum at the 2.5 micrograms ml-1 level was (92.8 +/- 3.4)%. The limit of quantitation for a 100 microliter sample size was 50 ng ml-1. The within-day (n = 5) and between-day (n = 5) relative standard deviations for lonidamine determination in serum samples spiked at the 2.5 micrograms ml-1 level were 2.7% and 4.5%, respectively.

Whole-body hyperthermia and lonidamine as adjuvant therapy to treatment with cisplatin with or without local radiation in mouse bearing the Lewis lung carcinoma

The Lewis lung carcinoma implanted subcutaneously in the hind leg of a C57BL mouse metastasizes avidly to the lungs of the host. This tumour model system thus allows assessment of both primary and metastatic disease to treatment. Lonidamine (50 mg/kg) administered once or twice daily produced approximately additive tumour growth delay with whole-body hyperthermia (60 min to 42 degrees C and 60 min at 42 degrees C). The addition of lonidamine to treatment with cisplatin (10 mg/kg) and whole-body hyperthermia continued to produce increased tumour growth delay of up to 14.7 days compared with 10.8 days for cisplatin/whole-body hyperthermia. The response of the metastatic disease paralleled that of the primary tumour with a reduction in the number and percent of large metastases (> 3 mm) on day 20 post-tumour implantation. The addition of local fractionated radiation therapy (3 Gy x 5) to the primary tumour produced a very effective treatment regimen resulting in 37.5 days of tumour growth delay along with twice daily lonidamine/cisplatin whole-body hyperthermia. With this treatment regimen there was also a reduction to 50% of control of the number of lung metastases as well as the percent of large metastases on day 20. Further investigation of these treatment combinations is warranted.

Effect of whole-body hyperthermia on the pharmacokinetics and toxicity of lonidamine in dogs

The pharmacokinetics and toxicity of intravenous lonidamine were investigated in dogs receiving four cycles of lonidamine (400 or 800 mg/m2) +/- whole-body hyperthermia (WBH). Clearance and volume of distribution in dogs receiving lonidamine during WBH increased 1.6-2.3 and 1.9-3.5-fold respectively, relative to dogs receiving lonidamine under euthermic conditions (p < 0.02). In dogs receiving lonidamine under euthermic conditions or 400 mg/m2 + WBH, the area under the lonidamine concentration versus time curve (AUC) measured during the fourth treatment was 21-58% lower than the first treatment AUC. However, in dogs receiving 800 mg/m2 + WBH, the fourth treatment AUC was four-fold higher than the first treatment AUC (p < 0.02). This suggests repeated exposure to 800 mg/m2 lonidamine and WBH impairs lonidamine metabolism. Weakness, hypoglycaemia, and elevations in amylase, alanine aminotransferase, alkaline phosphatase and bilirubin were more severe or occurred exclusively in dogs receiving 800 mg/m2 + WBH. Since these changes were attributable to marked AUC increases, which occurred secondary to repeated exposure to 800 mg/m2 lonidamine during WBH, 400 mg/m2 was identified as the maximum tolerable dose to be administered intravenously to dogs during WBH.

Biochemical modulation of tumor cell energy in vivo: II. A lower dose of adriamycin is required and a greater antitumor activity is induced when cellular energy is depressed

A quadruple drug combination--consisting of a triple-drug combination of N-(phosphonacetyl)-L-aspartate (PALA) + 6-methylmercaptopurine riboside (MMPR) + 6-amino-nicotinamide (6-AN), designed to primarily deplete cellular energy in tumor cells, + Adriamycin (Adria)--yielded significantly enhanced anticancer activity (i.e., tumor regressions) over that produced by either Adria alone at maximum tolerated dose (MTD) or by the triple-drug combination, against large, spontaneous, autochthonous murine breast tumors. The adenosine triphosphate (ATP)-depleting triple-drug combination administered prior to Adria resulted in a 100% tumor regression rate (12% complete regression; 88% partial regression) of spontaneous tumors. Histological examination of treated tumors demonstrated that the treatment-induced mechanism of cancer cell death was by apoptosis. The augmented therapeutic results (100% tumor regressions) were obtained with approximately one-half the MTD of Adria as a single agent and suggest the potential clinical benefit of longer, more effective, and safer treatment by low doses of Adria when combined with the triple-drug combination. Two likely mechanisms of action are discussed: (1) prevention of DNA repair; (2) complementary disruption of biochemical pathways by both the triple-drug combination and the biochemical cascade of apoptosis that is induced by a DNA-damaging anticancer agents such as Adria.

A randomised trial of MACC chemotherapy with or without lonidamine in advanced non-small cell lung cancer. Cuneo Lung Cancer Study Group (CuLCaSG)

Combination chemotherapy with anti-proliferative agents is the usual treatment for patients with advanced non-small cell lung cancer (NSCLC), good performance status and no major clinical contraindications. Lonidamine (LND), a new drug with an innovative mechanism of action, might potentiate anti-cancer activity of conventional cytotoxic drugs, with no increase of specific toxicity. Following a pilot study of feasibility, we now report the results of a randomised trial evaluating MACC chemotherapy, as originally described, versus the same regimen+LND. 151 patients with advanced NSCLC were assigned at random to the two treatment arms. LND 150 mg was given orally three times daily. Treatment was continued until progression of disease, unacceptable toxicity or refusal by the patient (median number of cycles of MACC, three for both arms; median duration of LND administration, 8 weeks in the arm concerned). Actual dose intensities (DI) of MACC and LND were, respectively, 100 and 83% of those intended (median values). There was a negative correlation between duration of chemotherapy and the DI of MACC reached in each patient, but no correlation between the duration of treatment with LND and its DI. DIs of LND and MACC were not correlated with each other. In all, 15 objective responses (one complete and four partial responses in the MACC group, 10 partial responses in patients on MACC+LND) were observed. Median progression-free survivals were 20 weeks (confidence interval, CI 14-22) for the group on LND and 17 weeks (CI 12-17) for the control group (non-significant difference). Median overall survivals were, respectively, 30 weeks (CI 23-40) and 27 weeks (CI 22-34), P = non-significant. Toxicity was as expected by the use of MACC, and similar in both arms, except for more severe anaemia and gastric toxicity in the group on MACC+LND. Other uncommon side-effects, seen only in this latter group, were mild to moderate and reversible and included myalgia, asthenia, testicle pain, headache, visual troubles, incubi and dizziness. Subjective tolerance to the treatment, and perception of physical and psychological well-being were rated similarly by patients of both groups. MACC plus LND is a moderately active regimen in advanced NSCLC, with a foreseeable and reversible toxicity of low-medium grade. Potential enhancements of anti-tumour efficacy of chemotherapy, and possible host survival benefits derived from the use of LND are not substantiated by the results of this trial.

Enhancement of hyperthermic toxicity by lonidamine in the Dunning R3327G rat prostatic adenocarcinoma

Hyperthermia alone or with radiation is used therapeutically for localized solid tumors. Clinical experience shows that sustained tumor temperature exceeding 45 degrees C damages normal tissue. Any agent that enhances the effects of hyperthermia at or below this temperature may have clinical relevance. Lonidamine and hyperthermia were tested on the Dunning R3327G rat prostatic adenocarcinoma. Using colony-formation assays, cytotoxic effects of each agent alone and in combination were quantified. Lonidamine to 100 micrograms/ml was not significantly toxic, but in combination, it enhanced cytotoxicity. Survival patterns after fractionated hyperthermia revealed a rapid development and decay of thermotolerance. Measurement of cell-cycle progression following a single dose of hyperthermia revealed a reduction of S-phase cells, and subsequent accumulation in G1 over 24 hours. Combination treatment of tumor-bearing rats significantly reduced tumor growth rate when compared with individual agents. These results suggest a potential use of lonidamine in hyperthermic therapy of prostate tumors.

In vitro effect of lonidamine on the cytotoxicity of mitomycin C and BCNU in human colon adenocarcinoma cells

The ability of lonidamine (LND), an energolytic derivative of indazole carboxylic acid, to modulate the cytotoxic activity of mitomycin C (MMC) and 1,3,bis(2-chloroethyl)-1-nitrosourea (BCNU) was investigated in two human adenocarcinoma cell lines (LoVo and HT29) expressing different sensitivity profiles to the drugs. After a 1-h treatment with MMC or BCNU, cells were postincubated for 24 h with 150-225 microM LND. In the LoVo cells, a synergistic interaction between LND and MMC or BCNU was observed at both LND concentrations. In HT29 cells, only additive effects of the drugs given in sequence were seen. Flow cytometric analysis indicated that LND was generally able to stabilise the cell cycle perturbations induced by MMC and BCNU in the two cell lines. The ability of LND to potentiate anticancer drug activity, and the consideration that LND causes side-effects different from those of conventional antitumour drugs, make this compound an attractive candidate for multidrug combination therapy in colon cancer.

Randomised phase II study of methotrexate (MTX) versus methotrexate plus lonidamine (MTX + LND) in recurrent and/or metastatic carcinoma of the head and neck

Between March 1990 and March 1992, 89 patients with recurrent and/or metastatic squamous cell cancer of the head and neck were randomised to receive either intravenous methotrexate (MTX) at a weekly dose of 40 mg/m2 plus lonidamine (LND) given orally at a starting dose of 75 mg three times daily for 3 days and then at a dose of 150 mg three times daily (arm MTX + LND) or methotrexate alone (arm MTX) at the same doses as arm MTX + LND. Complete remissions were observed in 10.5% of the patients in arm MTX + LND, and partial remissions in another 15.8%, yielding a 26.3% response rate. In arm MTX, only partial remissions were observed, yielding an overall response rate of 18.2%. Haematological toxicity was mild in both groups. Mild testicular pain (21%) and myalgias (31%) occurred only in patients treated with LND.

Addition of a topoisomerase I inhibitor to trimodality therapy [cis-diamminedichloroplatinum(II)/heat/radiation] in a murine tumor

The cytotoxicity of the topoisomerase I inhibitors, camptothecin and topotecan, toward exponentially growing EMT-6 murine mammary carcinoma cells under various conditions of oxygenation, pH and temperature was assessed. Under normal pH (pH 7.40) conditions both camptothecin and topotecan were more cytotoxic toward normally oxygenated cells. Both agents were more cytotoxic under acidic pH (pH 6.45) and the differential in cytotoxicity due to the cellular oxygenation level disappeared. Neither camptothecin nor topotecan was enhanced in cytotoxicity by hyperthermia (42 degrees C or 43 degrees C, 60 min) during drug exposure. Both camptothecin and topotecan killed increasing numbers of FSaIIC tumor cells with increasing dose of the drugs in vivo in a log/linear manner. Local hyperthermia (43 degrees C, 30 min) increased the tumor cell killing of the drugs but decreased the toxicity of these agents to the bone marrow granulocyte/macrophage-colony-forming units. Topotecan was a more effective modulator of cisplatin than was camptothecin, as determined by FSaIIC tumor cell survival assay and by FSaIIC tumor growth delay. Although both camptothecin and topotecan were effective additions to a treatment regimen including cisplatin and daily fractionated radiation (5 x 3Gy), neither of these topoisomerase I inhibitors increased the tumor growth delay produced by the trimodality regimen of cisplatin/hyperthermia/radiation.

Modulation of antitumor alkylating agents by novobiocin, topotecan, and lonidamine

Topoisomerase I and topoisomerase II allow a metabolically active cell to mobilize its supercoiled chromosomal DNA and undergo replication, transcription, recombination, and repair. Several topoisomerase inhibitors have recently been shown to be active in preclinical systems. Topotecan (SK&F 104,864), a water-soluble camptothecin analog, is an inhibitor of topoisomerase I. Novobiocin is an inhibitor of topoisomerase II. Lonidamine depletes cellular adenosine 5'-triphosphate (ATP) and may impede energy-dependent DNA repair, MCF-7 human breast-cancer cells were treated in vitro with topotecan, novobiocin, and lonidamine alone, in paired combinations, and in combination with CDDP and melphalan. The three enzyme inhibitors alone and in combination did not increase tumor cell sensitivity to CDDP. However, the combinations of topotecan/novobiocin and lonidamine/novobiocin did enhance the cytotoxicity of melphalan. Mice bearing the FSaII fibrosarcoma were treated in vivo with topotecan, novobiocin, and lonidamine alone, in paired combinations, and in combination with CDDP, melphalan, BCNU, and cyclophosphamide. The combination of topotecan/novobiocin had the greatest impact on tumor cell sensitivity to each cytotoxic agent tested in both tumor cell-survival and tumor growth-delay assays. This sensitization was greatest at the highest concentrations of the cytotoxic agent tested. Combinations of topoisomerase I and topoisomerase II inhibitors may be useful as modulators of antitumor alkylating agents.

Enhancement of cisplatin activity by lonidamine in human ovarian cancer cells

The ability of lonidamine, an energolytic derivative of indazole-carboxylic acid, to modulate the cytotoxicity of cisplatin was investigated in human ovarian-cancer cell lines sensitive (A2780) or with experimentally induced resistance (A2780/cp8) to the alkylating agent. A 24-hr post-incubation with 300 microM lonidamine significantly potentiated the activity of a 1-hr cisplatin treatment in both cell lines. In particular, the cisplatin IC50 value was reduced 4-fold in the sensitive line and 5-fold in the resistant line. Flow cytometric analysis showed that, in the resistant cell line, lonidamine alone did not affect cell kinetics, but when given after cisplatin it was able to transform the temporary G2 + M cell accumulation induced by the alkylating agent to a persistent block in S/G2 + M. In the A2780/cp8 cell line, lonidamine was also able to significantly enhance the accumulation of cisplatin-induced DNA interstrand cross-links. Our results suggest that lonidamine can positively modulate the anti-tumor activity of cisplatin in ovarian cancer cells and also indicate that the drug is potentially useful in combination therapy including the alkylating agent for ovarian cancer patients.

Enhancement of sensitivity to hyperthermia by lonidamine in human cancer cells

Human glioma (87MG) and squamous cell carcinoma of the head and neck UMSCC-1 were shown to be sensitized to hyperthermia by Lonidamine treatment before and during hyperthermia. The degree of thermal sensitization increased with increasing heating times and temperatures. In addition, the thermal sensitization by Lonidamine as well as cellular thermal sensitivity were dependent on pH and increased with the more acidic pH. Even though plateau phase cells were more thermally resistant than exponentially growing cells, Lonidamine treatment caused thermal sensitization under both conditions. These data show that Lonidamine may hold potential to enhance the effectiveness of hyperthermia in cancer treatment and that especially in tumours with low pH an enhanced therapeutic gain may be achieved.

Fluosol-DA/carbogen with lonidamine or pentoxifylline as modulators of alkylating agents in the FSaIIC fibrosarcoma

In an effort to increase the efficacy of several antineoplastic alkylating agents (CDDP, L-PAM, CTX, or BCNU), we examined the effect of the modulator Fluosol-DA/carbogen in combination with a second modulator, either lonidamine or pentoxifylline, on the survival of FSaIIC tumor cells and of bone marrow CFU-GM from tumor-bearing C3H mice. Fluosol-DA/carbogen increased the tumor-cell killing activity of each alkylating agent by about 10 times. In contrast, lonidamine alone did not significantly increase the cytocidal activity of any of the alkylating agents tested. However, in combination with Fluosol-DA/carbogen, the use of lonidamine produced about a 100-fold increase in the tumor cell kill achieved with CDDP as compared with CDDP alone. No increase in tumor cell kill over that produced with the single modulator Fluosol-DA/carbogen was seen following the addition of lonidamine to the combination treatment with L-PAM, CTX, or BCNU. Unfortunately, although neither lonidamine nor Fluosol-DA/carbogen alone significantly increased alkylator toxicity to bone marrow CFU-GM, the combination of modulators increased the toxicity of each alkylating agent to bone marrow by about 10 times. Pentoxifylline caused an increase in alkylator activity against the FSaIIC fibrosarcoma only when used with BCNU; this effect was further augmented by the addition of Fluosol-DA/carbogen. The combination of modulators pentoxifylline plus Fluosol-DA/carbogen was more effective than Fluosol-DA/carbogen alone only when the former was used with BCNU, whereas only minimal increases in tumor-cell killing activity were obtained with this modulator combination and CDDP, L-PAM, or CTX. Pentoxifylline increased the bone marrow CFU-GM toxicity of L-PAM by about 10 times. The bone marrow CFU-GM toxicity was further increased by Fluosol-DA/carbogen, as was the toxicity of each of the other alkylating agents. Lonidamine plus Fluosol-DA/carbogen may be useful in increasing the therapeutic efficacy of CDDP, and the combination of pentoxifylline plus Fluosol-DA/carbogen might improve the antitumor activity of BCNU.