Cell Counting Kit-8 (CCK8) was used to evaluate the in vitro anti-tumor activity and selectivity of Sal-A6 cell viability inhibitory effect of Sal, A6, compound E, and Sal-A6 was assessed in both CD44+ SKOV3 and CD44? A2780 cells. The results showed that peptide A6 exhibited no significant inhibitory effect on any tumor cells, in line with literature reports. Conversely, Sal and compound E significantly inhibited tumor cells proliferation while Sal-A6 conjugate exhibited the ability to suppress the cell viability of CD44+ SKOV3, demonstrating superior activity compared to Sal. However, it showed no significant inhibitory effect on CD44? A2780 cells, exerting only a moderate effect under high concentration conditions, possibly due to the target-mediated cellular entry of Sal-A6. To further validate whether the cytotoxicity of Sal-A6 is related to targeting via CD44, CD44+ SKOV3 cells co-incubated with A6 peptide and Sal-A6 at concentrations of 100 μM and 10 μM, respectively. Peptide A6 partially alleviated the cytotoxicity of Sal-A6, especially at saturated concentration (100 μM), leading to a significant reduction in the in vitro activity of Sal-A6 at both low (10 μM) and high (100 μM) concentrations. These results suggest that cells with low CD44 expression or treated with peptide A6 can mitigate the cellular inhibitory effects of Sal-A6. The onset of action of Sal-A6 was slower than that of Sal, which may be due to the fact that Sal-A6 exerts its efficacy through receptor-mediated entry into the cell and has a slower onset of action than the highly fat-soluble Sal. Overall, the competitive binding of cells with low CD44 expression and peptide A6 confirms that the in vitro activity of Sal-A6 is related to CD44 expression.

Cell Counting Kit-8 (CCK8) was used to evaluate the in vitro anti-tumor activity and selectivity of Sal-A6 cell viability inhibitory effect of Sal, A6, compound E, and Sal-A6 was assessed in both CD44+ SKOV3 and CD44? A2780 cells. The results showed that peptide A6 exhibited no significant inhibitory effect on any tumor cells, in line with literature reports. Conversely, Sal and compound E significantly inhibited tumor cells proliferation while Sal-A6 conjugate exhibited the ability to suppress the cell viability of CD44+ SKOV3, demonstrating superior activity compared to Sal. However, it showed no significant inhibitory effect on CD44? A2780 cells, exerting only a moderate effect under high concentration conditions, possibly due to the target-mediated cellular entry of Sal-A6. To further validate whether the cytotoxicity of Sal-A6 is related to targeting via CD44, CD44+ SKOV3 cells co-incubated with A6 peptide and Sal-A6 at concentrations of 100 μM and 10 μM, respectively. Peptide A6 partially alleviated the cytotoxicity of Sal-A6, especially at saturated concentration (100 μM), leading to a significant reduction in the in vitro activity of Sal-A6 at both low (10 μM) and high (100 μM) concentrations. These results suggest that cells with low CD44 expression or treated with peptide A6 can mitigate the cellular inhibitory effects of Sal-A6. The onset of action of Sal-A6 was slower than that of Sal, which may be due to the fact that Sal-A6 exerts its efficacy through receptor-mediated entry into the cell and has a slower onset of action than the highly fat-soluble Sal. Overall, the competitive binding of cells with low CD44 expression and peptide A6 confirms that the in vitro activity of Sal-A6 is related to CD44 expression.

Antiproliferative activity of conjugates were evaluated using HER2-positive SK-BR-3 and NCI-N87 cells. As shown in Fig. 5A, Conjugate 1 reduced the cell viability by 23, 38, 47 and 66% at 0.156, 0.625, 2.5 and 10 μM. Its cytotoxicity is significantly more than Conjugate 2 at 0.625 μM and 10 μM. It showed comparable cytotoxicity with CPT at 10 μM. And Conjugate 3 showed little cytotoxicity at any concentrations other than 10 μM, which may be related to the structure of Conjugate 3 where CPT is conjugated on the peptide by non-breakable bond preventing CPT from acting as an anticancer agent. Cyclo-GCGPep1 exhibited no significant cytotoxicity at any concentrations indicating that peptide part of PDCs is inactive for inducing cancer cell death. Similar results can be seen on NCI-N87 cells. Conjugate 1 reduced significantly more cell viability than Conjugate 2 at 0.156 μM and 2.5 μM. And Conjugate 1 exhibited comparable antiproliferation activity as CPT at 2.5 μM and 10 μM. The cytotoxicity of Conjugate 3 is still weak at any concentrations. Cyclo-GCGPep1 is non-toxic to NCI-N87 cells as well. These results told us antiproliferative activity of conjugates is closely related to the ways drugs are conjugated. The cleavable disulfide bonds in Conjugate 1 and 2 could be broken and then Camptothecin derivatives can be released in cells, which is much related to anti-proliferative activity. In general, Conjugate 1 showed best antiproliferative activity and it was selected for further research.

Antiproliferative activity of conjugates were evaluated using HER2-positive SK-BR-3 and NCI-N87 cells. As shown in Fig. 5A, Conjugate 1 reduced the cell viability by 23, 38, 47 and 66% at 0.156, 0.625, 2.5 and 10 μM. Its cytotoxicity is significantly more than Conjugate 2 at 0.625 μM and 10 μM. It showed comparable cytotoxicity with CPT at 10 μM. And Conjugate 3 showed little cytotoxicity at any concentrations other than 10 μM, which may be related to the structure of Conjugate 3 where CPT is conjugated on the peptide by non-breakable bond preventing CPT from acting as an anticancer agent. Cyclo-GCGPep1 exhibited no significant cytotoxicity at any concentrations indicating that peptide part of PDCs is inactive for inducing cancer cell death. Similar results can be seen on NCI-N87 cells. Conjugate 1 reduced significantly more cell viability than Conjugate 2 at 0.156 μM and 2.5 μM. And Conjugate 1 exhibited comparable antiproliferation activity as CPT at 2.5 μM and 10 μM. The cytotoxicity of Conjugate 3 is still weak at any concentrations. Cyclo-GCGPep1 is non-toxic to NCI-N87 cells as well. These results told us antiproliferative activity of conjugates is closely related to the ways drugs are conjugated. The cleavable disulfide bonds in Conjugate 1 and 2 could be broken and then Camptothecin derivatives can be released in cells, which is much related to anti-proliferative activity. In general, Conjugate 1 showed best antiproliferative activity and it was selected for further research.

Antiproliferative activity of conjugates were evaluated using HER2-positive SK-BR-3 and NCI-N87 cells. As shown in Fig. 5A, Conjugate 1 reduced the cell viability by 23, 38, 47 and 66% at 0.156, 0.625, 2.5 and 10 μM. Its cytotoxicity is significantly more than Conjugate 2 at 0.625 μM and 10 μM. It showed comparable cytotoxicity with CPT at 10 μM. And Conjugate 3 showed little cytotoxicity at any concentrations other than 10 μM, which may be related to the structure of Conjugate 3 where CPT is conjugated on the peptide by non-breakable bond preventing CPT from acting as an anticancer agent. Cyclo-GCGPep1 exhibited no significant cytotoxicity at any concentrations indicating that peptide part of PDCs is inactive for inducing cancer cell death. Similar results can be seen on NCI-N87 cells. Conjugate 1 reduced significantly more cell viability than Conjugate 2 at 0.156 μM and 2.5 μM. And Conjugate 1 exhibited comparable antiproliferation activity as CPT at 2.5 μM and 10 μM. The cytotoxicity of Conjugate 3 is still weak at any concentrations. Cyclo-GCGPep1 is non-toxic to NCI-N87 cells as well. These results told us antiproliferative activity of conjugates is closely related to the ways drugs are conjugated. The cleavable disulfide bonds in Conjugate 1 and 2 could be broken and then Camptothecin derivatives can be released in cells, which is much related to anti-proliferative activity. In general, Conjugate 1 showed best antiproliferative activity and it was selected for further research.

Antiproliferative activity of conjugates were evaluated using HER2-positive SK-BR-3 and NCI-N87 cells. As shown in Fig. 5A, Conjugate 1 reduced the cell viability by 23, 38, 47 and 66% at 0.156, 0.625, 2.5 and 10 μM. Its cytotoxicity is significantly more than Conjugate 2 at 0.625 μM and 10 μM. It showed comparable cytotoxicity with CPT at 10 μM. And Conjugate 3 showed little cytotoxicity at any concentrations other than 10 μM, which may be related to the structure of Conjugate 3 where CPT is conjugated on the peptide by non-breakable bond preventing CPT from acting as an anticancer agent. Cyclo-GCGPep1 exhibited no significant cytotoxicity at any concentrations indicating that peptide part of PDCs is inactive for inducing cancer cell death. Similar results can be seen on NCI-N87 cells. Conjugate 1 reduced significantly more cell viability than Conjugate 2 at 0.156 μM and 2.5 μM. And Conjugate 1 exhibited comparable antiproliferation activity as CPT at 2.5 μM and 10 μM. The cytotoxicity of Conjugate 3 is still weak at any concentrations. Cyclo-GCGPep1 is non-toxic to NCI-N87 cells as well. These results told us antiproliferative activity of conjugates is closely related to the ways drugs are conjugated. The cleavable disulfide bonds in Conjugate 1 and 2 could be broken and then Camptothecin derivatives can be released in cells, which is much related to anti-proliferative activity. In general, Conjugate 1 showed best antiproliferative activity and it was selected for further research.

Antiproliferative activity of conjugates were evaluated using HER2-positive SK-BR-3 and NCI-N87 cells. As shown in Fig. 5A, Conjugate 1 reduced the cell viability by 23, 38, 47 and 66% at 0.156, 0.625, 2.5 and 10 μM. Its cytotoxicity is significantly more than Conjugate 2 at 0.625 μM and 10 μM. It showed comparable cytotoxicity with CPT at 10 μM. And Conjugate 3 showed little cytotoxicity at any concentrations other than 10 μM, which may be related to the structure of Conjugate 3 where CPT is conjugated on the peptide by non-breakable bond preventing CPT from acting as an anticancer agent. Cyclo-GCGPep1 exhibited no significant cytotoxicity at any concentrations indicating that peptide part of PDCs is inactive for inducing cancer cell death. Similar results can be seen on NCI-N87 cells. Conjugate 1 reduced significantly more cell viability than Conjugate 2 at 0.156 μM and 2.5 μM. And Conjugate 1 exhibited comparable antiproliferation activity as CPT at 2.5 μM and 10 μM. The cytotoxicity of Conjugate 3 is still weak at any concentrations. Cyclo-GCGPep1 is non-toxic to NCI-N87 cells as well. These results told us antiproliferative activity of conjugates is closely related to the ways drugs are conjugated. The cleavable disulfide bonds in Conjugate 1 and 2 could be broken and then Camptothecin derivatives can be released in cells, which is much related to anti-proliferative activity. In general, Conjugate 1 showed best antiproliferative activity and it was selected for further research.

Antiproliferative activity of conjugates were evaluated using HER2-positive SK-BR-3 and NCI-N87 cells. As shown in Fig. 5A, Conjugate 1 reduced the cell viability by 23, 38, 47 and 66% at 0.156, 0.625, 2.5 and 10 μM. Its cytotoxicity is significantly more than Conjugate 2 at 0.625 μM and 10 μM. It showed comparable cytotoxicity with CPT at 10 μM. And Conjugate 3 showed little cytotoxicity at any concentrations other than 10 μM, which may be related to the structure of Conjugate 3 where CPT is conjugated on the peptide by non-breakable bond preventing CPT from acting as an anticancer agent. Cyclo-GCGPep1 exhibited no significant cytotoxicity at any concentrations indicating that peptide part of PDCs is inactive for inducing cancer cell death. Similar results can be seen on NCI-N87 cells. Conjugate 1 reduced significantly more cell viability than Conjugate 2 at 0.156 μM and 2.5 μM. And Conjugate 1 exhibited comparable antiproliferation activity as CPT at 2.5 μM and 10 μM. The cytotoxicity of Conjugate 3 is still weak at any concentrations. Cyclo-GCGPep1 is non-toxic to NCI-N87 cells as well. These results told us antiproliferative activity of conjugates is closely related to the ways drugs are conjugated. The cleavable disulfide bonds in Conjugate 1 and 2 could be broken and then Camptothecin derivatives can be released in cells, which is much related to anti-proliferative activity. In general, Conjugate 1 showed best antiproliferative activity and it was selected for further research.

Antiproliferative activity of conjugates were evaluated using HER2-positive SK-BR-3 and NCI-N87 cells. As shown in Fig. 5A, Conjugate 1 reduced the cell viability by 23, 38, 47 and 66% at 0.156, 0.625, 2.5 and 10 μM. Its cytotoxicity is significantly more than Conjugate 2 at 0.625 μM and 10 μM. It showed comparable cytotoxicity with CPT at 10 μM. And Conjugate 3 showed little cytotoxicity at any concentrations other than 10 μM, which may be related to the structure of Conjugate 3 where CPT is conjugated on the peptide by non-breakable bond preventing CPT from acting as an anticancer agent. Cyclo-GCGPep1 exhibited no significant cytotoxicity at any concentrations indicating that peptide part of PDCs is inactive for inducing cancer cell death. Similar results can be seen on NCI-N87 cells. Conjugate 1 reduced significantly more cell viability than Conjugate 2 at 0.156 μM and 2.5 μM. And Conjugate 1 exhibited comparable antiproliferation activity as CPT at 2.5 μM and 10 μM. The cytotoxicity of Conjugate 3 is still weak at any concentrations. Cyclo-GCGPep1 is non-toxic to NCI-N87 cells as well. These results told us antiproliferative activity of conjugates is closely related to the ways drugs are conjugated. The cleavable disulfide bonds in Conjugate 1 and 2 could be broken and then Camptothecin derivatives can be released in cells, which is much related to anti-proliferative activity. In general, Conjugate 1 showed best antiproliferative activity and it was selected for further research.

Antiproliferative activity of conjugates were evaluated using HER2-positive SK-BR-3 and NCI-N87 cells. As shown in Fig. 5A, Conjugate 1 reduced the cell viability by 23, 38, 47 and 66% at 0.156, 0.625, 2.5 and 10 μM. Its cytotoxicity is significantly more than Conjugate 2 at 0.625 μM and 10 μM. It showed comparable cytotoxicity with CPT at 10 μM. And Conjugate 3 showed little cytotoxicity at any concentrations other than 10 μM, which may be related to the structure of Conjugate 3 where CPT is conjugated on the peptide by non-breakable bond preventing CPT from acting as an anticancer agent. Cyclo-GCGPep1 exhibited no significant cytotoxicity at any concentrations indicating that peptide part of PDCs is inactive for inducing cancer cell death. Similar results can be seen on NCI-N87 cells. Conjugate 1 reduced significantly more cell viability than Conjugate 2 at 0.156 μM and 2.5 μM. And Conjugate 1 exhibited comparable antiproliferation activity as CPT at 2.5 μM and 10 μM. The cytotoxicity of Conjugate 3 is still weak at any concentrations. Cyclo-GCGPep1 is non-toxic to NCI-N87 cells as well. These results told us antiproliferative activity of conjugates is closely related to the ways drugs are conjugated. The cleavable disulfide bonds in Conjugate 1 and 2 could be broken and then Camptothecin derivatives can be released in cells, which is much related to anti-proliferative activity. In general, Conjugate 1 showed best antiproliferative activity and it was selected for further research.