The conjugation of Vectocell peptides to cytotoxic molecules can modify the in vivo distribution of the therapeutic molecules, improving pharmacokinetic properties and/or reducing systemic toxicity by driving tissue and intracellular delivery.2,5 In addition, conjugation of Vectocell peptides to small molecules/drugs may also provide a means of inhibiting the extracellular export of the therapeutic agents by proteins involved in multidrug resistance (MDR). Multidrug resistance can seriously limit cancer chemotherapy treatment, for example, through the overexpression of membrane transporters that mediate unidirectional energy-dependent drug efflux, thus reducing intracellular drug levels. These membrane transporters are normally expressed in high levels within cells involved in detoxification, such as the liver, kidney, and colon. Tumors arising from these cells are often resistant to chemotherapy treatment from their onset, while other tumors can acquire resistance through the induction of MDR transport proteins during treatment. Many inhibitors of MDR transporters have been identified. However, these inhibitors also interfere with the clearance of the cytotoxic drug, resulting in elevated plasma concentrations of the cytotoxic agent and associated toxicity. An alternative approach is to circumvent rather than to directly inhibit MDR mechanisms, by developing anticancer therapies that are not substrates for extracellular export. Doxorubicin, an anthracycline antibiotic, remains among the most widely used cytotoxic agents for the treatment of a broad spectrum of cancers, including breast, stomach, non-Hodgkin's lymphoma, and bladder cancer. As with many cytotoxic drugs, doxorubicin has severe short- and long-term side effects, in this case mostly associated with bone marrow and myocardial cell toxicity. Cardiotoxicity limits the cumulative dosage of doxorubicin to 500-600 mg/m², which may be a dose at which tumor is still responding to treatment but for which no further doxorubicin treatment can be given. Another drawback of doxorubicin is the emergence of drug resistance that results in the reduction of the intracellular concentration of doxorubicin. The present study aimed to generate novel peptidic-doxorubicin conjugates by use of three Vectocell peptides that differ in terms of their charge, size, and intracellular delivery characteristics and to assess their ability to enhance the therapeutic potential of doxorubicin and to prevent the appearance of MDR. Different conjugation sites and linkers of different stabilities were used to generate Vectocell-doxorubicin conjugates in order to evaluate their effect on efficacy. Chemical routes were developed to allow the conjugation of doxorubicin to Vectocell peptides through ester, thioether, and amide chemical linkers. The ester and thioether involved carbon 14 of doxorubicin, and the amide carbon 3. In vitro and in vivo characterization has defined the optimal conjugate-linker combination that significantly increases efficacy above unconjugated doxorubicin in both doxorubicin-sensitive and -resistant models. The data presented therefore provide in vivo proof of concept for the use of Vectocell peptides to improve the therapeutic index of doxorubicin, and potentially many other cytotoxic or small molecule anticancer drugs.

The conjugation of Vectocell peptides to cytotoxic molecules can modify the in vivo distribution of the therapeutic molecules, improving pharmacokinetic properties and/or reducing systemic toxicity by driving tissue and intracellular delivery.2,5 In addition, conjugation of Vectocell peptides to small molecules/drugs may also provide a means of inhibiting the extracellular export of the therapeutic agents by proteins involved in multidrug resistance (MDR). Multidrug resistance can seriously limit cancer chemotherapy treatment, for example, through the overexpression of membrane transporters that mediate unidirectional energy-dependent drug efflux, thus reducing intracellular drug levels. These membrane transporters are normally expressed in high levels within cells involved in detoxification, such as the liver, kidney, and colon. Tumors arising from these cells are often resistant to chemotherapy treatment from their onset, while other tumors can acquire resistance through the induction of MDR transport proteins during treatment. Many inhibitors of MDR transporters have been identified. However, these inhibitors also interfere with the clearance of the cytotoxic drug, resulting in elevated plasma concentrations of the cytotoxic agent and associated toxicity. An alternative approach is to circumvent rather than to directly inhibit MDR mechanisms, by developing anticancer therapies that are not substrates for extracellular export. Doxorubicin, an anthracycline antibiotic, remains among the most widely used cytotoxic agents for the treatment of a broad spectrum of cancers, including breast, stomach, non-Hodgkin's lymphoma, and bladder cancer. As with many cytotoxic drugs, doxorubicin has severe short- and long-term side effects, in this case mostly associated with bone marrow and myocardial cell toxicity. Cardiotoxicity limits the cumulative dosage of doxorubicin to 500-600 mg/m², which may be a dose at which tumor is still responding to treatment but for which no further doxorubicin treatment can be given. Another drawback of doxorubicin is the emergence of drug resistance that results in the reduction of the intracellular concentration of doxorubicin. The present study aimed to generate novel peptidic-doxorubicin conjugates by use of three Vectocell peptides that differ in terms of their charge, size, and intracellular delivery characteristics and to assess their ability to enhance the therapeutic potential of doxorubicin and to prevent the appearance of MDR. Different conjugation sites and linkers of different stabilities were used to generate Vectocell-doxorubicin conjugates in order to evaluate their effect on efficacy. Chemical routes were developed to allow the conjugation of doxorubicin to Vectocell peptides through ester, thioether, and amide chemical linkers. The ester and thioether involved carbon 14 of doxorubicin, and the amide carbon 3. In vitro and in vivo characterization has defined the optimal conjugate-linker combination that significantly increases efficacy above unconjugated doxorubicin in both doxorubicin-sensitive and -resistant models. The data presented therefore provide in vivo proof of concept for the use of Vectocell peptides to improve the therapeutic index of doxorubicin, and potentially many other cytotoxic or small molecule anticancer drugs.

The conjugation of Vectocell peptides to cytotoxic molecules can modify the in vivo distribution of the therapeutic molecules, improving pharmacokinetic properties and/or reducing systemic toxicity by driving tissue and intracellular delivery.2,5 In addition, conjugation of Vectocell peptides to small molecules/drugs may also provide a means of inhibiting the extracellular export of the therapeutic agents by proteins involved in multidrug resistance (MDR). Multidrug resistance can seriously limit cancer chemotherapy treatment, for example, through the overexpression of membrane transporters that mediate unidirectional energy-dependent drug efflux, thus reducing intracellular drug levels. These membrane transporters are normally expressed in high levels within cells involved in detoxification, such as the liver, kidney, and colon. Tumors arising from these cells are often resistant to chemotherapy treatment from their onset, while other tumors can acquire resistance through the induction of MDR transport proteins during treatment. Many inhibitors of MDR transporters have been identified. However, these inhibitors also interfere with the clearance of the cytotoxic drug, resulting in elevated plasma concentrations of the cytotoxic agent and associated toxicity. An alternative approach is to circumvent rather than to directly inhibit MDR mechanisms, by developing anticancer therapies that are not substrates for extracellular export. Doxorubicin, an anthracycline antibiotic, remains among the most widely used cytotoxic agents for the treatment of a broad spectrum of cancers, including breast, stomach, non-Hodgkin's lymphoma, and bladder cancer. As with many cytotoxic drugs, doxorubicin has severe short- and long-term side effects, in this case mostly associated with bone marrow and myocardial cell toxicity. Cardiotoxicity limits the cumulative dosage of doxorubicin to 500-600 mg/m², which may be a dose at which tumor is still responding to treatment but for which no further doxorubicin treatment can be given. Another drawback of doxorubicin is the emergence of drug resistance that results in the reduction of the intracellular concentration of doxorubicin. The present study aimed to generate novel peptidic-doxorubicin conjugates by use of three Vectocell peptides that differ in terms of their charge, size, and intracellular delivery characteristics and to assess their ability to enhance the therapeutic potential of doxorubicin and to prevent the appearance of MDR. Different conjugation sites and linkers of different stabilities were used to generate Vectocell-doxorubicin conjugates in order to evaluate their effect on efficacy. Chemical routes were developed to allow the conjugation of doxorubicin to Vectocell peptides through ester, thioether, and amide chemical linkers. The ester and thioether involved carbon 14 of doxorubicin, and the amide carbon 3. In vitro and in vivo characterization has defined the optimal conjugate-linker combination that significantly increases efficacy above unconjugated doxorubicin in both doxorubicin-sensitive and -resistant models. The data presented therefore provide in vivo proof of concept for the use of Vectocell peptides to improve the therapeutic index of doxorubicin, and potentially many other cytotoxic or small molecule anticancer drugs.

The conjugation of Vectocell peptides to cytotoxic molecules can modify the in vivo distribution of the therapeutic molecules, improving pharmacokinetic properties and/or reducing systemic toxicity by driving tissue and intracellular delivery.2,5 In addition, conjugation of Vectocell peptides to small molecules/drugs may also provide a means of inhibiting the extracellular export of the therapeutic agents by proteins involved in multidrug resistance (MDR). Multidrug resistance can seriously limit cancer chemotherapy treatment, for example, through the overexpression of membrane transporters that mediate unidirectional energy-dependent drug efflux, thus reducing intracellular drug levels. These membrane transporters are normally expressed in high levels within cells involved in detoxification, such as the liver, kidney, and colon. Tumors arising from these cells are often resistant to chemotherapy treatment from their onset, while other tumors can acquire resistance through the induction of MDR transport proteins during treatment. Many inhibitors of MDR transporters have been identified. However, these inhibitors also interfere with the clearance of the cytotoxic drug, resulting in elevated plasma concentrations of the cytotoxic agent and associated toxicity. An alternative approach is to circumvent rather than to directly inhibit MDR mechanisms, by developing anticancer therapies that are not substrates for extracellular export. Doxorubicin, an anthracycline antibiotic, remains among the most widely used cytotoxic agents for the treatment of a broad spectrum of cancers, including breast, stomach, non-Hodgkin's lymphoma, and bladder cancer. As with many cytotoxic drugs, doxorubicin has severe short- and long-term side effects, in this case mostly associated with bone marrow and myocardial cell toxicity. Cardiotoxicity limits the cumulative dosage of doxorubicin to 500-600 mg/m², which may be a dose at which tumor is still responding to treatment but for which no further doxorubicin treatment can be given. Another drawback of doxorubicin is the emergence of drug resistance that results in the reduction of the intracellular concentration of doxorubicin. The present study aimed to generate novel peptidic-doxorubicin conjugates by use of three Vectocell peptides that differ in terms of their charge, size, and intracellular delivery characteristics and to assess their ability to enhance the therapeutic potential of doxorubicin and to prevent the appearance of MDR. Different conjugation sites and linkers of different stabilities were used to generate Vectocell-doxorubicin conjugates in order to evaluate their effect on efficacy. Chemical routes were developed to allow the conjugation of doxorubicin to Vectocell peptides through ester, thioether, and amide chemical linkers. The ester and thioether involved carbon 14 of doxorubicin, and the amide carbon 3. In vitro and in vivo characterization has defined the optimal conjugate-linker combination that significantly increases efficacy above unconjugated doxorubicin in both doxorubicin-sensitive and -resistant models. The data presented therefore provide in vivo proof of concept for the use of Vectocell peptides to improve the therapeutic index of doxorubicin, and potentially many other cytotoxic or small molecule anticancer drugs.

The conjugation of Vectocell peptides to cytotoxic molecules can modify the in vivo distribution of the therapeutic molecules, improving pharmacokinetic properties and/or reducing systemic toxicity by driving tissue and intracellular delivery.2,5 In addition, conjugation of Vectocell peptides to small molecules/drugs may also provide a means of inhibiting the extracellular export of the therapeutic agents by proteins involved in multidrug resistance (MDR). Multidrug resistance can seriously limit cancer chemotherapy treatment, for example, through the overexpression of membrane transporters that mediate unidirectional energy-dependent drug efflux, thus reducing intracellular drug levels. These membrane transporters are normally expressed in high levels within cells involved in detoxification, such as the liver, kidney, and colon. Tumors arising from these cells are often resistant to chemotherapy treatment from their onset, while other tumors can acquire resistance through the induction of MDR transport proteins during treatment. Many inhibitors of MDR transporters have been identified. However, these inhibitors also interfere with the clearance of the cytotoxic drug, resulting in elevated plasma concentrations of the cytotoxic agent and associated toxicity. An alternative approach is to circumvent rather than to directly inhibit MDR mechanisms, by developing anticancer therapies that are not substrates for extracellular export. Doxorubicin, an anthracycline antibiotic, remains among the most widely used cytotoxic agents for the treatment of a broad spectrum of cancers, including breast, stomach, non-Hodgkin's lymphoma, and bladder cancer. As with many cytotoxic drugs, doxorubicin has severe short- and long-term side effects, in this case mostly associated with bone marrow and myocardial cell toxicity. Cardiotoxicity limits the cumulative dosage of doxorubicin to 500-600 mg/m², which may be a dose at which tumor is still responding to treatment but for which no further doxorubicin treatment can be given. Another drawback of doxorubicin is the emergence of drug resistance that results in the reduction of the intracellular concentration of doxorubicin. The present study aimed to generate novel peptidic-doxorubicin conjugates by use of three Vectocell peptides that differ in terms of their charge, size, and intracellular delivery characteristics and to assess their ability to enhance the therapeutic potential of doxorubicin and to prevent the appearance of MDR. Different conjugation sites and linkers of different stabilities were used to generate Vectocell-doxorubicin conjugates in order to evaluate their effect on efficacy. Chemical routes were developed to allow the conjugation of doxorubicin to Vectocell peptides through ester, thioether, and amide chemical linkers. The ester and thioether involved carbon 14 of doxorubicin, and the amide carbon 3. In vitro and in vivo characterization has defined the optimal conjugate-linker combination that significantly increases efficacy above unconjugated doxorubicin in both doxorubicin-sensitive and -resistant models. The data presented therefore provide in vivo proof of concept for the use of Vectocell peptides to improve the therapeutic index of doxorubicin, and potentially many other cytotoxic or small molecule anticancer drugs.

The conjugation of Vectocell peptides to cytotoxic molecules can modify the in vivo distribution of the therapeutic molecules, improving pharmacokinetic properties and/or reducing systemic toxicity by driving tissue and intracellular delivery.2,5 In addition, conjugation of Vectocell peptides to small molecules/drugs may also provide a means of inhibiting the extracellular export of the therapeutic agents by proteins involved in multidrug resistance (MDR). Multidrug resistance can seriously limit cancer chemotherapy treatment, for example, through the overexpression of membrane transporters that mediate unidirectional energy-dependent drug efflux, thus reducing intracellular drug levels. These membrane transporters are normally expressed in high levels within cells involved in detoxification, such as the liver, kidney, and colon. Tumors arising from these cells are often resistant to chemotherapy treatment from their onset, while other tumors can acquire resistance through the induction of MDR transport proteins during treatment. Many inhibitors of MDR transporters have been identified. However, these inhibitors also interfere with the clearance of the cytotoxic drug, resulting in elevated plasma concentrations of the cytotoxic agent and associated toxicity. An alternative approach is to circumvent rather than to directly inhibit MDR mechanisms, by developing anticancer therapies that are not substrates for extracellular export. Doxorubicin, an anthracycline antibiotic, remains among the most widely used cytotoxic agents for the treatment of a broad spectrum of cancers, including breast, stomach, non-Hodgkin's lymphoma, and bladder cancer. As with many cytotoxic drugs, doxorubicin has severe short- and long-term side effects, in this case mostly associated with bone marrow and myocardial cell toxicity. Cardiotoxicity limits the cumulative dosage of doxorubicin to 500-600 mg/m², which may be a dose at which tumor is still responding to treatment but for which no further doxorubicin treatment can be given. Another drawback of doxorubicin is the emergence of drug resistance that results in the reduction of the intracellular concentration of doxorubicin. The present study aimed to generate novel peptidic-doxorubicin conjugates by use of three Vectocell peptides that differ in terms of their charge, size, and intracellular delivery characteristics and to assess their ability to enhance the therapeutic potential of doxorubicin and to prevent the appearance of MDR. Different conjugation sites and linkers of different stabilities were used to generate Vectocell-doxorubicin conjugates in order to evaluate their effect on efficacy. Chemical routes were developed to allow the conjugation of doxorubicin to Vectocell peptides through ester, thioether, and amide chemical linkers. The ester and thioether involved carbon 14 of doxorubicin, and the amide carbon 3. In vitro and in vivo characterization has defined the optimal conjugate-linker combination that significantly increases efficacy above unconjugated doxorubicin in both doxorubicin-sensitive and -resistant models. The data presented therefore provide in vivo proof of concept for the use of Vectocell peptides to improve the therapeutic index of doxorubicin, and potentially many other cytotoxic or small molecule anticancer drugs.

The conjugation of Vectocell peptides to cytotoxic molecules can modify the in vivo distribution of the therapeutic molecules, improving pharmacokinetic properties and/or reducing systemic toxicity by driving tissue and intracellular delivery.2,5 In addition, conjugation of Vectocell peptides to small molecules/drugs may also provide a means of inhibiting the extracellular export of the therapeutic agents by proteins involved in multidrug resistance (MDR). Multidrug resistance can seriously limit cancer chemotherapy treatment, for example, through the overexpression of membrane transporters that mediate unidirectional energy-dependent drug efflux, thus reducing intracellular drug levels. These membrane transporters are normally expressed in high levels within cells involved in detoxification, such as the liver, kidney, and colon. Tumors arising from these cells are often resistant to chemotherapy treatment from their onset, while other tumors can acquire resistance through the induction of MDR transport proteins during treatment. Many inhibitors of MDR transporters have been identified. However, these inhibitors also interfere with the clearance of the cytotoxic drug, resulting in elevated plasma concentrations of the cytotoxic agent and associated toxicity. An alternative approach is to circumvent rather than to directly inhibit MDR mechanisms, by developing anticancer therapies that are not substrates for extracellular export. Doxorubicin, an anthracycline antibiotic, remains among the most widely used cytotoxic agents for the treatment of a broad spectrum of cancers, including breast, stomach, non-Hodgkin's lymphoma, and bladder cancer. As with many cytotoxic drugs, doxorubicin has severe short- and long-term side effects, in this case mostly associated with bone marrow and myocardial cell toxicity. Cardiotoxicity limits the cumulative dosage of doxorubicin to 500-600 mg/m², which may be a dose at which tumor is still responding to treatment but for which no further doxorubicin treatment can be given. Another drawback of doxorubicin is the emergence of drug resistance that results in the reduction of the intracellular concentration of doxorubicin. The present study aimed to generate novel peptidic-doxorubicin conjugates by use of three Vectocell peptides that differ in terms of their charge, size, and intracellular delivery characteristics and to assess their ability to enhance the therapeutic potential of doxorubicin and to prevent the appearance of MDR. Different conjugation sites and linkers of different stabilities were used to generate Vectocell-doxorubicin conjugates in order to evaluate their effect on efficacy. Chemical routes were developed to allow the conjugation of doxorubicin to Vectocell peptides through ester, thioether, and amide chemical linkers. The ester and thioether involved carbon 14 of doxorubicin, and the amide carbon 3. In vitro and in vivo characterization has defined the optimal conjugate-linker combination that significantly increases efficacy above unconjugated doxorubicin in both doxorubicin-sensitive and -resistant models. The data presented therefore provide in vivo proof of concept for the use of Vectocell peptides to improve the therapeutic index of doxorubicin, and potentially many other cytotoxic or small molecule anticancer drugs.

The conjugation of Vectocell peptides to cytotoxic molecules can modify the in vivo distribution of the therapeutic molecules, improving pharmacokinetic properties and/or reducing systemic toxicity by driving tissue and intracellular delivery.2,5 In addition, conjugation of Vectocell peptides to small molecules/drugs may also provide a means of inhibiting the extracellular export of the therapeutic agents by proteins involved in multidrug resistance (MDR). Multidrug resistance can seriously limit cancer chemotherapy treatment, for example, through the overexpression of membrane transporters that mediate unidirectional energy-dependent drug efflux, thus reducing intracellular drug levels. These membrane transporters are normally expressed in high levels within cells involved in detoxification, such as the liver, kidney, and colon. Tumors arising from these cells are often resistant to chemotherapy treatment from their onset, while other tumors can acquire resistance through the induction of MDR transport proteins during treatment. Many inhibitors of MDR transporters have been identified. However, these inhibitors also interfere with the clearance of the cytotoxic drug, resulting in elevated plasma concentrations of the cytotoxic agent and associated toxicity. An alternative approach is to circumvent rather than to directly inhibit MDR mechanisms, by developing anticancer therapies that are not substrates for extracellular export. Doxorubicin, an anthracycline antibiotic, remains among the most widely used cytotoxic agents for the treatment of a broad spectrum of cancers, including breast, stomach, non-Hodgkin's lymphoma, and bladder cancer. As with many cytotoxic drugs, doxorubicin has severe short- and long-term side effects, in this case mostly associated with bone marrow and myocardial cell toxicity. Cardiotoxicity limits the cumulative dosage of doxorubicin to 500-600 mg/m², which may be a dose at which tumor is still responding to treatment but for which no further doxorubicin treatment can be given. Another drawback of doxorubicin is the emergence of drug resistance that results in the reduction of the intracellular concentration of doxorubicin. The present study aimed to generate novel peptidic-doxorubicin conjugates by use of three Vectocell peptides that differ in terms of their charge, size, and intracellular delivery characteristics and to assess their ability to enhance the therapeutic potential of doxorubicin and to prevent the appearance of MDR. Different conjugation sites and linkers of different stabilities were used to generate Vectocell-doxorubicin conjugates in order to evaluate their effect on efficacy. Chemical routes were developed to allow the conjugation of doxorubicin to Vectocell peptides through ester, thioether, and amide chemical linkers. The ester and thioether involved carbon 14 of doxorubicin, and the amide carbon 3. In vitro and in vivo characterization has defined the optimal conjugate-linker combination that significantly increases efficacy above unconjugated doxorubicin in both doxorubicin-sensitive and -resistant models. The data presented therefore provide in vivo proof of concept for the use of Vectocell peptides to improve the therapeutic index of doxorubicin, and potentially many other cytotoxic or small molecule anticancer drugs.

The conjugation of Vectocell peptides to cytotoxic molecules can modify the in vivo distribution of the therapeutic molecules, improving pharmacokinetic properties and/or reducing systemic toxicity by driving tissue and intracellular delivery.2,5 In addition, conjugation of Vectocell peptides to small molecules/drugs may also provide a means of inhibiting the extracellular export of the therapeutic agents by proteins involved in multidrug resistance (MDR). Multidrug resistance can seriously limit cancer chemotherapy treatment, for example, through the overexpression of membrane transporters that mediate unidirectional energy-dependent drug efflux, thus reducing intracellular drug levels. These membrane transporters are normally expressed in high levels within cells involved in detoxification, such as the liver, kidney, and colon. Tumors arising from these cells are often resistant to chemotherapy treatment from their onset, while other tumors can acquire resistance through the induction of MDR transport proteins during treatment. Many inhibitors of MDR transporters have been identified. However, these inhibitors also interfere with the clearance of the cytotoxic drug, resulting in elevated plasma concentrations of the cytotoxic agent and associated toxicity. An alternative approach is to circumvent rather than to directly inhibit MDR mechanisms, by developing anticancer therapies that are not substrates for extracellular export. Doxorubicin, an anthracycline antibiotic, remains among the most widely used cytotoxic agents for the treatment of a broad spectrum of cancers, including breast, stomach, non-Hodgkin's lymphoma, and bladder cancer. As with many cytotoxic drugs, doxorubicin has severe short- and long-term side effects, in this case mostly associated with bone marrow and myocardial cell toxicity. Cardiotoxicity limits the cumulative dosage of doxorubicin to 500-600 mg/m², which may be a dose at which tumor is still responding to treatment but for which no further doxorubicin treatment can be given. Another drawback of doxorubicin is the emergence of drug resistance that results in the reduction of the intracellular concentration of doxorubicin. The present study aimed to generate novel peptidic-doxorubicin conjugates by use of three Vectocell peptides that differ in terms of their charge, size, and intracellular delivery characteristics and to assess their ability to enhance the therapeutic potential of doxorubicin and to prevent the appearance of MDR. Different conjugation sites and linkers of different stabilities were used to generate Vectocell-doxorubicin conjugates in order to evaluate their effect on efficacy. Chemical routes were developed to allow the conjugation of doxorubicin to Vectocell peptides through ester, thioether, and amide chemical linkers. The ester and thioether involved carbon 14 of doxorubicin, and the amide carbon 3. In vitro and in vivo characterization has defined the optimal conjugate-linker combination that significantly increases efficacy above unconjugated doxorubicin in both doxorubicin-sensitive and -resistant models. The data presented therefore provide in vivo proof of concept for the use of Vectocell peptides to improve the therapeutic index of doxorubicin, and potentially many other cytotoxic or small molecule anticancer drugs.

The conjugation of Vectocell peptides to cytotoxic molecules can modify the in vivo distribution of the therapeutic molecules, improving pharmacokinetic properties and/or reducing systemic toxicity by driving tissue and intracellular delivery.2,5 In addition, conjugation of Vectocell peptides to small molecules/drugs may also provide a means of inhibiting the extracellular export of the therapeutic agents by proteins involved in multidrug resistance (MDR). Multidrug resistance can seriously limit cancer chemotherapy treatment, for example, through the overexpression of membrane transporters that mediate unidirectional energy-dependent drug efflux, thus reducing intracellular drug levels. These membrane transporters are normally expressed in high levels within cells involved in detoxification, such as the liver, kidney, and colon. Tumors arising from these cells are often resistant to chemotherapy treatment from their onset, while other tumors can acquire resistance through the induction of MDR transport proteins during treatment. Many inhibitors of MDR transporters have been identified. However, these inhibitors also interfere with the clearance of the cytotoxic drug, resulting in elevated plasma concentrations of the cytotoxic agent and associated toxicity. An alternative approach is to circumvent rather than to directly inhibit MDR mechanisms, by developing anticancer therapies that are not substrates for extracellular export. Doxorubicin, an anthracycline antibiotic, remains among the most widely used cytotoxic agents for the treatment of a broad spectrum of cancers, including breast, stomach, non-Hodgkin's lymphoma, and bladder cancer. As with many cytotoxic drugs, doxorubicin has severe short- and long-term side effects, in this case mostly associated with bone marrow and myocardial cell toxicity. Cardiotoxicity limits the cumulative dosage of doxorubicin to 500-600 mg/m², which may be a dose at which tumor is still responding to treatment but for which no further doxorubicin treatment can be given. Another drawback of doxorubicin is the emergence of drug resistance that results in the reduction of the intracellular concentration of doxorubicin. The present study aimed to generate novel peptidic-doxorubicin conjugates by use of three Vectocell peptides that differ in terms of their charge, size, and intracellular delivery characteristics and to assess their ability to enhance the therapeutic potential of doxorubicin and to prevent the appearance of MDR. Different conjugation sites and linkers of different stabilities were used to generate Vectocell-doxorubicin conjugates in order to evaluate their effect on efficacy. Chemical routes were developed to allow the conjugation of doxorubicin to Vectocell peptides through ester, thioether, and amide chemical linkers. The ester and thioether involved carbon 14 of doxorubicin, and the amide carbon 3. In vitro and in vivo characterization has defined the optimal conjugate-linker combination that significantly increases efficacy above unconjugated doxorubicin in both doxorubicin-sensitive and -resistant models. The data presented therefore provide in vivo proof of concept for the use of Vectocell peptides to improve the therapeutic index of doxorubicin, and potentially many other cytotoxic or small molecule anticancer drugs.

The conjugation of Vectocell peptides to cytotoxic molecules can modify the in vivo distribution of the therapeutic molecules, improving pharmacokinetic properties and/or reducing systemic toxicity by driving tissue and intracellular delivery.2,5 In addition, conjugation of Vectocell peptides to small molecules/drugs may also provide a means of inhibiting the extracellular export of the therapeutic agents by proteins involved in multidrug resistance (MDR). Multidrug resistance can seriously limit cancer chemotherapy treatment, for example, through the overexpression of membrane transporters that mediate unidirectional energy-dependent drug efflux, thus reducing intracellular drug levels. These membrane transporters are normally expressed in high levels within cells involved in detoxification, such as the liver, kidney, and colon. Tumors arising from these cells are often resistant to chemotherapy treatment from their onset, while other tumors can acquire resistance through the induction of MDR transport proteins during treatment. Many inhibitors of MDR transporters have been identified. However, these inhibitors also interfere with the clearance of the cytotoxic drug, resulting in elevated plasma concentrations of the cytotoxic agent and associated toxicity. An alternative approach is to circumvent rather than to directly inhibit MDR mechanisms, by developing anticancer therapies that are not substrates for extracellular export. Doxorubicin, an anthracycline antibiotic, remains among the most widely used cytotoxic agents for the treatment of a broad spectrum of cancers, including breast, stomach, non-Hodgkin's lymphoma, and bladder cancer. As with many cytotoxic drugs, doxorubicin has severe short- and long-term side effects, in this case mostly associated with bone marrow and myocardial cell toxicity. Cardiotoxicity limits the cumulative dosage of doxorubicin to 500-600 mg/m², which may be a dose at which tumor is still responding to treatment but for which no further doxorubicin treatment can be given. Another drawback of doxorubicin is the emergence of drug resistance that results in the reduction of the intracellular concentration of doxorubicin. The present study aimed to generate novel peptidic-doxorubicin conjugates by use of three Vectocell peptides that differ in terms of their charge, size, and intracellular delivery characteristics and to assess their ability to enhance the therapeutic potential of doxorubicin and to prevent the appearance of MDR. Different conjugation sites and linkers of different stabilities were used to generate Vectocell-doxorubicin conjugates in order to evaluate their effect on efficacy. Chemical routes were developed to allow the conjugation of doxorubicin to Vectocell peptides through ester, thioether, and amide chemical linkers. The ester and thioether involved carbon 14 of doxorubicin, and the amide carbon 3. In vitro and in vivo characterization has defined the optimal conjugate-linker combination that significantly increases efficacy above unconjugated doxorubicin in both doxorubicin-sensitive and -resistant models. The data presented therefore provide in vivo proof of concept for the use of Vectocell peptides to improve the therapeutic index of doxorubicin, and potentially many other cytotoxic or small molecule anticancer drugs.

The conjugation of Vectocell peptides to cytotoxic molecules can modify the in vivo distribution of the therapeutic molecules, improving pharmacokinetic properties and/or reducing systemic toxicity by driving tissue and intracellular delivery.2,5 In addition, conjugation of Vectocell peptides to small molecules/drugs may also provide a means of inhibiting the extracellular export of the therapeutic agents by proteins involved in multidrug resistance (MDR). Multidrug resistance can seriously limit cancer chemotherapy treatment, for example, through the overexpression of membrane transporters that mediate unidirectional energy-dependent drug efflux, thus reducing intracellular drug levels. These membrane transporters are normally expressed in high levels within cells involved in detoxification, such as the liver, kidney, and colon. Tumors arising from these cells are often resistant to chemotherapy treatment from their onset, while other tumors can acquire resistance through the induction of MDR transport proteins during treatment. Many inhibitors of MDR transporters have been identified. However, these inhibitors also interfere with the clearance of the cytotoxic drug, resulting in elevated plasma concentrations of the cytotoxic agent and associated toxicity. An alternative approach is to circumvent rather than to directly inhibit MDR mechanisms, by developing anticancer therapies that are not substrates for extracellular export. Doxorubicin, an anthracycline antibiotic, remains among the most widely used cytotoxic agents for the treatment of a broad spectrum of cancers, including breast, stomach, non-Hodgkin's lymphoma, and bladder cancer. As with many cytotoxic drugs, doxorubicin has severe short- and long-term side effects, in this case mostly associated with bone marrow and myocardial cell toxicity. Cardiotoxicity limits the cumulative dosage of doxorubicin to 500-600 mg/m², which may be a dose at which tumor is still responding to treatment but for which no further doxorubicin treatment can be given. Another drawback of doxorubicin is the emergence of drug resistance that results in the reduction of the intracellular concentration of doxorubicin. The present study aimed to generate novel peptidic-doxorubicin conjugates by use of three Vectocell peptides that differ in terms of their charge, size, and intracellular delivery characteristics and to assess their ability to enhance the therapeutic potential of doxorubicin and to prevent the appearance of MDR. Different conjugation sites and linkers of different stabilities were used to generate Vectocell-doxorubicin conjugates in order to evaluate their effect on efficacy. Chemical routes were developed to allow the conjugation of doxorubicin to Vectocell peptides through ester, thioether, and amide chemical linkers. The ester and thioether involved carbon 14 of doxorubicin, and the amide carbon 3. In vitro and in vivo characterization has defined the optimal conjugate-linker combination that significantly increases efficacy above unconjugated doxorubicin in both doxorubicin-sensitive and -resistant models. The data presented therefore provide in vivo proof of concept for the use of Vectocell peptides to improve the therapeutic index of doxorubicin, and potentially many other cytotoxic or small molecule anticancer drugs.

The conjugation of Vectocell peptides to cytotoxic molecules can modify the in vivo distribution of the therapeutic molecules, improving pharmacokinetic properties and/or reducing systemic toxicity by driving tissue and intracellular delivery.2,5 In addition, conjugation of Vectocell peptides to small molecules/drugs may also provide a means of inhibiting the extracellular export of the therapeutic agents by proteins involved in multidrug resistance (MDR). Multidrug resistance can seriously limit cancer chemotherapy treatment, for example, through the overexpression of membrane transporters that mediate unidirectional energy-dependent drug efflux, thus reducing intracellular drug levels. These membrane transporters are normally expressed in high levels within cells involved in detoxification, such as the liver, kidney, and colon. Tumors arising from these cells are often resistant to chemotherapy treatment from their onset, while other tumors can acquire resistance through the induction of MDR transport proteins during treatment. Many inhibitors of MDR transporters have been identified. However, these inhibitors also interfere with the clearance of the cytotoxic drug, resulting in elevated plasma concentrations of the cytotoxic agent and associated toxicity. An alternative approach is to circumvent rather than to directly inhibit MDR mechanisms, by developing anticancer therapies that are not substrates for extracellular export. Doxorubicin, an anthracycline antibiotic, remains among the most widely used cytotoxic agents for the treatment of a broad spectrum of cancers, including breast, stomach, non-Hodgkin's lymphoma, and bladder cancer. As with many cytotoxic drugs, doxorubicin has severe short- and long-term side effects, in this case mostly associated with bone marrow and myocardial cell toxicity. Cardiotoxicity limits the cumulative dosage of doxorubicin to 500-600 mg/m², which may be a dose at which tumor is still responding to treatment but for which no further doxorubicin treatment can be given. Another drawback of doxorubicin is the emergence of drug resistance that results in the reduction of the intracellular concentration of doxorubicin. The present study aimed to generate novel peptidic-doxorubicin conjugates by use of three Vectocell peptides that differ in terms of their charge, size, and intracellular delivery characteristics and to assess their ability to enhance the therapeutic potential of doxorubicin and to prevent the appearance of MDR. Different conjugation sites and linkers of different stabilities were used to generate Vectocell-doxorubicin conjugates in order to evaluate their effect on efficacy. Chemical routes were developed to allow the conjugation of doxorubicin to Vectocell peptides through ester, thioether, and amide chemical linkers. The ester and thioether involved carbon 14 of doxorubicin, and the amide carbon 3. In vitro and in vivo characterization has defined the optimal conjugate-linker combination that significantly increases efficacy above unconjugated doxorubicin in both doxorubicin-sensitive and -resistant models. The data presented therefore provide in vivo proof of concept for the use of Vectocell peptides to improve the therapeutic index of doxorubicin, and potentially many other cytotoxic or small molecule anticancer drugs.

The conjugation of Vectocell peptides to cytotoxic molecules can modify the in vivo distribution of the therapeutic molecules, improving pharmacokinetic properties and/or reducing systemic toxicity by driving tissue and intracellular delivery.2,5 In addition, conjugation of Vectocell peptides to small molecules/drugs may also provide a means of inhibiting the extracellular export of the therapeutic agents by proteins involved in multidrug resistance (MDR). Multidrug resistance can seriously limit cancer chemotherapy treatment, for example, through the overexpression of membrane transporters that mediate unidirectional energy-dependent drug efflux, thus reducing intracellular drug levels. These membrane transporters are normally expressed in high levels within cells involved in detoxification, such as the liver, kidney, and colon. Tumors arising from these cells are often resistant to chemotherapy treatment from their onset, while other tumors can acquire resistance through the induction of MDR transport proteins during treatment. Many inhibitors of MDR transporters have been identified. However, these inhibitors also interfere with the clearance of the cytotoxic drug, resulting in elevated plasma concentrations of the cytotoxic agent and associated toxicity. An alternative approach is to circumvent rather than to directly inhibit MDR mechanisms, by developing anticancer therapies that are not substrates for extracellular export. Doxorubicin, an anthracycline antibiotic, remains among the most widely used cytotoxic agents for the treatment of a broad spectrum of cancers, including breast, stomach, non-Hodgkin's lymphoma, and bladder cancer. As with many cytotoxic drugs, doxorubicin has severe short- and long-term side effects, in this case mostly associated with bone marrow and myocardial cell toxicity. Cardiotoxicity limits the cumulative dosage of doxorubicin to 500-600 mg/m², which may be a dose at which tumor is still responding to treatment but for which no further doxorubicin treatment can be given. Another drawback of doxorubicin is the emergence of drug resistance that results in the reduction of the intracellular concentration of doxorubicin. The present study aimed to generate novel peptidic-doxorubicin conjugates by use of three Vectocell peptides that differ in terms of their charge, size, and intracellular delivery characteristics and to assess their ability to enhance the therapeutic potential of doxorubicin and to prevent the appearance of MDR. Different conjugation sites and linkers of different stabilities were used to generate Vectocell-doxorubicin conjugates in order to evaluate their effect on efficacy. Chemical routes were developed to allow the conjugation of doxorubicin to Vectocell peptides through ester, thioether, and amide chemical linkers. The ester and thioether involved carbon 14 of doxorubicin, and the amide carbon 3. In vitro and in vivo characterization has defined the optimal conjugate-linker combination that significantly increases efficacy above unconjugated doxorubicin in both doxorubicin-sensitive and -resistant models. The data presented therefore provide in vivo proof of concept for the use of Vectocell peptides to improve the therapeutic index of doxorubicin, and potentially many other cytotoxic or small molecule anticancer drugs.

The conjugation of Vectocell peptides to cytotoxic molecules can modify the in vivo distribution of the therapeutic molecules, improving pharmacokinetic properties and/or reducing systemic toxicity by driving tissue and intracellular delivery.2,5 In addition, conjugation of Vectocell peptides to small molecules/drugs may also provide a means of inhibiting the extracellular export of the therapeutic agents by proteins involved in multidrug resistance (MDR). Multidrug resistance can seriously limit cancer chemotherapy treatment, for example, through the overexpression of membrane transporters that mediate unidirectional energy-dependent drug efflux, thus reducing intracellular drug levels. These membrane transporters are normally expressed in high levels within cells involved in detoxification, such as the liver, kidney, and colon. Tumors arising from these cells are often resistant to chemotherapy treatment from their onset, while other tumors can acquire resistance through the induction of MDR transport proteins during treatment. Many inhibitors of MDR transporters have been identified. However, these inhibitors also interfere with the clearance of the cytotoxic drug, resulting in elevated plasma concentrations of the cytotoxic agent and associated toxicity. An alternative approach is to circumvent rather than to directly inhibit MDR mechanisms, by developing anticancer therapies that are not substrates for extracellular export. Doxorubicin, an anthracycline antibiotic, remains among the most widely used cytotoxic agents for the treatment of a broad spectrum of cancers, including breast, stomach, non-Hodgkin's lymphoma, and bladder cancer. As with many cytotoxic drugs, doxorubicin has severe short- and long-term side effects, in this case mostly associated with bone marrow and myocardial cell toxicity. Cardiotoxicity limits the cumulative dosage of doxorubicin to 500-600 mg/m², which may be a dose at which tumor is still responding to treatment but for which no further doxorubicin treatment can be given. Another drawback of doxorubicin is the emergence of drug resistance that results in the reduction of the intracellular concentration of doxorubicin. The present study aimed to generate novel peptidic-doxorubicin conjugates by use of three Vectocell peptides that differ in terms of their charge, size, and intracellular delivery characteristics and to assess their ability to enhance the therapeutic potential of doxorubicin and to prevent the appearance of MDR. Different conjugation sites and linkers of different stabilities were used to generate Vectocell-doxorubicin conjugates in order to evaluate their effect on efficacy. Chemical routes were developed to allow the conjugation of doxorubicin to Vectocell peptides through ester, thioether, and amide chemical linkers. The ester and thioether involved carbon 14 of doxorubicin, and the amide carbon 3. In vitro and in vivo characterization has defined the optimal conjugate-linker combination that significantly increases efficacy above unconjugated doxorubicin in both doxorubicin-sensitive and -resistant models. The data presented therefore provide in vivo proof of concept for the use of Vectocell peptides to improve the therapeutic index of doxorubicin, and potentially many other cytotoxic or small molecule anticancer drugs.