High dose lansoprazole combined with metronomic chemotherapy: a phase I/II study in companion animals with spontaneously occurring tumors

Cancer initiation, invasion and dissemination are dynamic phenomena influenced by tumor microenvironment and host factors. Standard anticancer drugs were devised accordingly to Erlich’s magic bullet concept and rely on their capacity to directly kill malignant cells. In the attempt to maximize their efficacy, they are administered at a maximal tolerated dose (MTD), the highest amount of the drug associated with tolerable toxicity and manageable side effects [1],[2]. As a consequence of this approach, patients must go through long periods off therapy, allowing for their full recovery from the adverse effects of chemotherapy. These interruptions, however, also permit cancer cells to become resistant to chemotherapy and hence to promote a disease recurrence [3],[4]. As a consequence, despite the discovery of a significant number of these drugs and the huge number of clinical trials that have been undertaken to develop novel multi-drugs protocols, results has been modest in terms of cure or life extension of cancer patients, especially those with advanced-stage or metastatic disease [5]. A new therapeutic paradigm has recently been devised, consisting of the use of low-dose chemotherapeutics at short intervals (so-called, metronomic chemotherapy), in the absence of extended drug-free periods [6],[7]. Metronomic chemotherapy is not only almost devoid of toxic effects, but also exerts e direct citotoxicity combined with an antiangiogenic activity resulting in significant efficacy [8],[9]. Several studies in human and veterinary oncology have shown efficacy of low dose alkylating agents such as cyclophosphamide and chlorambucil to directly approach refractory cancers or as adjuvant therapy for highly metastatic or metastasizing tumor [10]-[17]. The other factor to be taken into account when planning a treatment procotol, is the response to chemotherapy by tumor cells. This depends on the concentration of cytostatics accumulated within the cells, phenomenon that is dependent on functional expression of efflux transporters, but also on the pH of extracellular microenvironment. In fact, the acidity of tumor microenvironment is a key factor in the low level of responsiveness of tumor cells to chemotherapeutics, and proton exchangers have a crucial impact in extracellular acidification of cancer cells [18],[19]. Tumor cells rely on H⁺ exchangers, in particular the vacuolar H⁺-ATPases (V-ATPases) to dispose of the dangerous protons byproduct of cancer metabolism [20]-[22]. The acidic tumor environment is a consequence of anaerobic glucose metabolism resulting in accumulation of acids such as lactates, leading to enhanced transmembrane pH regulation [22]. These proton pumps, together with other ion exchangers, play a crucial function in the establishment and maintenance of cancer microenvironment and their action results in the selection of more aggressive cell phenotypes able to survive in this highly hostile microenvironment, with a key role in the establishment and maintenance of chemoresistance [19]. There are several proposed mechanisms involved in this phenomenon, including decreased uptake or neutralization of weakly basic drugs by the acidic tumor microenvironment or the confinement of chemotherapy drugs within lysosomal vesicles [23]. An accelerated turnover of acidic vesicles may represent an additional tumor strategy of drug resistance based on counteracting current transportation [24]. Recently, a role of nanovesicles (exosomes) released by resistant cancer cells has been in elimination of tumor drug such as cisplatin, and extracellular acidity and exosomes release belong to a framework exerting a central role of malignant cancer unresponsiveness to chemotherapy [25]. Interestingly, the expression of proton pumps is increased in chemoresistant phenotypes and further increased by anticancer drugs as well [24]. Proton pump inhibitors have been shown to be highly effective in inhibiting V-ATPases in vitro and well tolerated and effective in murine models, improving response to chemotherapy and tumor control [24]. Moreover, in a previous study, our group showed that high dose of the proton pump inhibitor lansoprazole could reverse chemoresistance in a cohort of pets affected by spontaneous chemoresistant neoplasms, obtaining an high percentage of responders with minimal toxicities [26]. A recent clinical study in osteosarcoma patients has shown a clear effectiveness of PPI in increasing the effectiveness of standard chemotherapy, particularly in those patients that show low level of responsiveness to the standard protocols [27]. Thus, the ensemble of these studies, but also the evidence that a systemic buffering approach may represent a useful new strategy in both preventing [28] and in treating [29] cancer, suggested that a therapy combining different anti-acidic approaches, may represent a real new path in the war against cancer. Thus, the aim of this study was to investigate the feasibility, tolerability and efficacy of high dose proton pump inhibitor lansoprazole combined with water alkalization within a metronomic protocol in companion animals affected by advanced or highly metastatic neoplasms.

Twenty-four pets affected by different solid tumors were enrolled in the study (twenty-two dogs and two cats) over a 30 months period. There were 11 male dogs and 11 female dogs, most of whom where spayed while the two cats were both female. Age ranged from 6 to 13 years. Patients characteristics and response to therapy are shown in Table 4. Eight patient had previous surgery for their primary tumors (six of them had either regional metastases or local recurrence when referred for therapy) and one had three sessions of electrochemotherapy resulting in partial remission of the tumor. This last patient then switched to metronomic chemotherapy for financial reasons and further improved the tumor response. None of the patients with metastatic disease had metastasectomy performed prior to referral, having all the owners elected their pets to be pharmacologically treated. The only patients that has no evidence of disease at the time of referral were four patients with ruptured splenic hemangiosarcoma (two per each cohort) that have been enrolled in the survival study in consideration of the extremely high metastatic tendency of this neoplasm in the canine population. All the four patients begun their medical therapy two weeks after splenectomy. Survival time was calculated from the beginning of metronomic chemotherapy. The historical control group consisted with 10 dogs affected by different neoplasms whose characteristics are summarized in Table 5. In this group there were 6 females and 4 males who tolerated the metronomic therapy without side effects. The combination of metronomic chemotherapy and alkalizing treatment was overall well tolerated, one dog had mild diarrhea but continued the therapy albeit at a decreased lansoprazole dose (2 mg/kg in the three loading days). Two dogs had vomiting that resulted in lansoprazole reduction from 5 mg/kg to 3 mg/kg. Finally 8 dogs out of 22 experienced different degrees of flatulence that partially improved with the addition of probiotics to their diet. The overall responses rate was 75%, including 4 complete remissions, 10 partial responses, 4 no evidence of disease (adjuvant therapy group), 2 stable diseases and 4 progressive diseases. On the other hand, the overall response rate in the control group was 40% with two short lived NEDs in dogs with highly metastatic cancers, one PR in a dog with a ulnar OSA that recurred after partial ulnectomy and one long lasting CR in a dog with an inflammatory mammary carcinoma. In this cohort only one patient out of ten experienced a complete long lasting response, while all the other were non responders or short lived responders. Figure 1 shows two patients that successfully responded to the therapy while Figure 2 shows a stable disease in a dog with a large lung tumor. At the time of writing a total of 9 patients (8 dogs and 1 cat) are still alive and periodically monitored leading to a survival rate of 37.5% while only one control patient is still alive with a survival rate of 10%. The mean time to terminal event was 48 weeks in the experimental cohort and 18 weeks in the control group, median time to terminal event was 34 weeks versus 2. Figure 3 shows the Kaplan-Meier survavial curve for the two groups. In general, the owners of the experimental group reported increased activity level as well as food and water consumption and improved quality of life. Questioning the owners regarding their degree of satisfaction with the outcome of the therapy yielded a total of 90% of appreciation in the PPI group and a 40% in the control group. Appreciation was greatly influenced on the pets moving up in the karnofsky scale as a consequence of improved response and degree of side effects and ranged from “somewhat satisfied” to “enthusiastic”. Figure 4 summarizes the degree of satisfaction among the different groups of owners. While tumor control was the major issue in the control group, in the PPI cohort, as a consequence of a better clinical outcome, the major causes of complains were the gastrointestinal side effects (specifically the flatulence) experienced by some dogs rather than the degree of tumor response. The management of these complications through diet and integration with probiotics greatly improved the owners degree of satisfaction.

The proton pump inhibitor lansoprazole, administered at high dose and combined with a water alkalizer, has proven to enhance tumor response to metronomic chemotherapy, increasing the number of complete responders [4] and significantly delaying the onset of metastases in pets with highly metastasizing neoplasms. This is a very promising result, since a “flaw” of metronomic chemotherapy is the low number of patients experiencing complete responses as well as the difficulty to have a significant delay for the onset of metastatic disease in patients with advanced cancer [10]-[17]. The broad spectrum of solid tumors that responded to this clinical approach including two patients with metastasized anal sac carcinoma makes this combination extremely promising. Of course this study had some limitations due to the lack of tumor homogeneity in our two cohorts. This bias can’t be overcome, inasmuch pets with advanced cancer stage suitable to be included to this study presented tumors that very often varied in their histologies. Moreover, the owners of the pets affected with advanced cancer were particularly available in trying new approached being well aware of the disease in their companion animals and of their expected poor prognosis. Notably, although the level of cancer progression and the size of the cancer, we observed a clear improvement of the clinical response to the metronomic therapy when combined with an alkalinizing treatment, independently from the nature of cancer, suggesting that systemic alkalinisation might represent one of the most important new implementation in cancer therapy, inasmuch as tumor extracellular acidity is a feature common to all cancers. This is for sure a novelty in the clinical management of cancer patients that should be taken into careful account in the future anti-cancer strategies. Of course our study lacked a system to assess the in vivo pH changes as well; this was due to the absence of pH measurement methodology approved for the clinical use but also to the financial constrains to an observational setting. In order to improve the protocol and to identify prognostic factors, steps should be made to measure changes in tumor pH during the therapy in order to monitor progresses and also to have a parameter to be monitored in order to identify escape from medical control. Furthermore, a reliable and portable system to quantify variation in growth factors involved in tumor progression and angiogenesis should be devised [17]. The combination of water alkalinisation and high dosage proton pump inhibitors has been shown to effectiveness of metronomic therapy on tumour progression, but also to highly improve the quality of life of pets affected by spontaneous malignant tumors. In particular the animals did not show to refuse the alkalinized water, while occasional experience in human patients showed that sodium bicarbonate may not be administered for a long period of time, inasmuch as patients very often refused it. Notably, while this study allowed to try with a real experimental clinical approach against advanced cancer, it did not allow to quantify the exact contribution of PPIs and alkalized water to the increased efficacy of metronomic chemotherapy, while alkalinizing approaches using sodium bicarbonate suggest a potential efficacy of water alkalinisation in cancer treatment [33]. Further studies will be mandatory to evaluate the effects of single alkalinizing approaches as potential anti-cancer treatments . In our study the owners of the pet included in the experimental group provided the emotional component and a daily evaluation of the quality of life, providing a rough estimate of the patient toleration of the therapeutic regimen, allowing the investigators to work in a close approximation of the human clinical condition. Moreover, sodium bicarbonate is an unbalanced buffer with only sodium as an oligoelement, and this may raise cardiovascular problems in long term administrations. The inclusion of multiple drugs affecting tumor acidity is highly desirable in order to develop multidrug protocols to increase cancer control [33]. Finally, there is accumulating evidence also indicating that some metronomic regimens might be able to promote disease eradication by stimulating anticancer immune and selectively eliminating immunosuppressive cells [9],[15]. The increased anti-tumor immune response by proton pump inhibitors has been clearly shown [34],[35], and the overall response to the combination of proton pump inhibitors, alkalinized water and metronomic therapy, suggest that this approach may be highly helpful in the generalized response of the body against cancer. Further investigations are clearly warranted also in this perspective to assess the weight of the immune component in the long term control of tumors in patient undergoing alkalizing metronomic chemotherapy [35].